JP7795877B2 - Salt, acid generator, resist composition and method for producing resist pattern - Google Patents

Description

The present invention relates to a salt, an acid generator, a resist composition, and a method for producing a resist pattern.

Patent Document 1 describes a resist composition containing a salt represented by the following formula as an acid generator.
Patent Document 2 describes a resist composition containing a salt represented by the following formula as an acid generator.
Patent Document 3 describes a salt represented by the following formula and a resist composition containing the salt as an acid generator.

JP 2011-006399 A JP 2011-186248 A Japanese Patent Application Laid-Open No. 2020-015713

An object of the present invention is to provide a salt that forms a resist pattern with better resolution than a resist pattern formed from a resist composition containing the above salt.

The present invention includes the following inventions.
[1] A salt represented by formula (I).
[In formula (I),
R ¹ , R ² and R ³ each independently represent -O-R ¹⁰ , -O-CO-R ¹⁰ , -O-CO-O-R ¹⁰ or -OL ¹ -CO-O-R ¹⁰ .
R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ and R ⁹ each independently represent a halogen atom, a hydroxy group, a fluorinated alkyl group having 1 to 12 carbon atoms or a hydrocarbon group having 1 to 18 carbon atoms, the hydrocarbon group may have a substituent, and -CH ₂ - contained in the hydrocarbon group may be replaced by -O-, -S-, -CO- or -SO ₂ -.
^L1 represents an alkanediyl group having 1 to 6 carbon atoms.
R ¹⁰ represents an alicyclic hydrocarbon group having one or more —OR ¹¹ groups.
R ¹¹ represents a hydrogen atom or an acid labile group.
X ¹ , X ² and X ³ each independently represent an oxygen atom or a sulfur atom.
m1 represents an integer of 0 to 5, and when m1 is 2 or more, the groups in the parentheses may be the same or different.
m2 represents an integer of 0 to 4, and when m2 is 2 or more, the groups in the parentheses may be the same or different.
m3 represents an integer of 0 to 4, and when m3 is 2 or more, the groups in the parentheses may be the same or different.
m4 represents an integer of 0 to 4, and when m4 is 2 or greater, multiple R ^4s may be the same or different.
m5 represents an integer of 0 to 4, and when m5 is 2 or more, the multiple ^R5s may be the same or different.
m6 represents an integer of 0 to 4, and when m6 is 2 or greater, multiple R ^6s may be the same or different.
m7 represents an integer of 0 to 5, and when m7 is 2 or greater, the multiple ^R7s may be the same or different.
m8 represents an integer of 0 to 4, and when m8 is 2 or greater, multiple R ^8s may be the same or different.
m9 represents an integer of 0 to 4, and when m9 is 2 or more, the multiple R ^9s may be the same or different.
However, 0≦m1+m7≦5, 0≦m2+m8≦4, 0≦m3+m9≦4, and at least one of m1, m2, and m3 represents an integer of 1 or more.
X ⁴ represents a single bond, —CH ₂ —, —O—, —S—, —CO—, —SO— or —SO ₂ —.
AI ⁻ represents an organic anion.
[2] The salt according to [1], wherein X ¹ , X ² and X ³ are oxygen atoms.
[3] The salt according to [1] or [2], wherein R ¹ , R ² and R ³ are —O—CO—O—R ¹⁰ — or —OL ¹ —CO—O—R ¹⁰ .
[4] The salt according to any one of [1] to [3], wherein R ¹⁰ is an adamantyl group having an —OR ¹¹ group (R ¹¹ represents a hydrogen atom or an acid labile group).
[5] The salt according to any one of [1] to [4], wherein R ¹¹ is an acid labile group, and the acid labile group of R ¹¹ is a group represented by formula (1a) or a group represented by formula (2a).
[In formula (1a), R ^aa1 , R ^aa2 and R ^aa3 each independently represent an alkyl group of 1 to 8 carbon atoms which may have a substituent, an alkenyl group of 2 to 8 carbon atoms which may have a substituent, an alicyclic hydrocarbon group of 3 to 20 carbon atoms which may have a substituent, or an aromatic hydrocarbon group of 6 to 18 carbon atoms which may have a substituent, or R ^aa1 and R ^aa2 are bonded to each other to form an alicyclic hydrocarbon group of 3 to 20 carbon atoms together with the carbon atom to which they are bonded.]
naa represents 0 or 1.
* represents a bond.
[In formula (2a), R ^aa1′ and R ^aa2′ each independently represent a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms; R ^aa3′ represents a hydrocarbon group having 1 to 20 carbon atoms; or R ^aa2′ and R ^aa3′ are bonded to each other to form, together with —C-X ^a — to which they are bonded, a heterocyclic group having 3 to 20 carbon atoms; and —CH ₂ — contained in the hydrocarbon group and the heterocyclic group may be replaced by —O— or —S—.]
^Xa represents an oxygen atom or a sulfur atom.
* represents a bond.
[6] The salt according to any one of [1] to [4], wherein R ¹¹ is a hydrogen atom.
[7] The salt according to any one of [1] to [6], wherein m1 is an integer of 0 to 2, and when m1 is 1 or 2, m2 and m3 are each 0 or 1, and when m1 is 0, m2 and m3 are each 1.
[8] The salt according to any one of [1] to [7], wherein AI ⁻ is a sulfonate anion, a sulfonylimide anion, a sulfonylmethide anion, or a carboxylate anion.
[9] The salt according to any one of [1] to [8], wherein AI ⁻ is a sulfonate anion, and the sulfonate anion is an anion represented by formula (IA):
[In formula (IA),
Q ¹ and Q ² each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms.
^L1 represents a saturated hydrocarbon group having 1 to 24 carbon atoms, in which —CH ₂ — contained in the saturated hydrocarbon group may be replaced by —O— or —CO—, and in which a hydrogen atom contained in the saturated hydrocarbon group may be replaced by a fluorine atom or a hydroxy group.
^Y1 represents an optionally substituted methyl group or an optionally substituted alicyclic hydrocarbon group having 3 to 24 carbon atoms, and one —CH ₂ — contained in the alicyclic hydrocarbon group may be replaced by —O—, —SO ₂ — or —CO—.]
[10] An acid generator containing the salt according to any one of [1] to [9].
[11] A resist composition comprising the acid generator according to [10] and a resin having an acid labile group.
[12] The resist composition according to [11], wherein the resin having an acid labile group comprises at least one selected from the group consisting of a structural unit represented by formula (a1-1) and a structural unit represented by formula (a1-2):
[In formula (a1-1) and formula (a1-2),
L ^a1 and L ^a2 each independently represent —O— or *-O—(CH ₂ ) _k1 —CO—O—, where k1 represents an integer of 1 to 7, and * represents a bond to —CO—.
R ^a4 and R ^a5 each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom.
R ^a6 and R ^a7 each independently represent an alkyl group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, or a combination thereof.
m1 represents an integer of 0 to 14.
n1 represents an integer of 0 to 10.
n1′ represents an integer of 0 to 3.
[13] The resist composition according to [11] or [12], wherein the resin having an acid labile group contains a structural unit represented by formula (a2-A):
[In formula (a2-A),
R ^a50 represents a hydrogen atom, a halogen atom or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom.
R ^a51 represents a halogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkoxyalkyl group having 2 to 12 carbon atoms, an alkoxyalkoxy group having 2 to 12 carbon atoms, an alkylcarbonyl group having 2 to 4 carbon atoms, an alkylcarbonyloxy group having 2 to 4 carbon atoms, an acryloyloxy group, or a methacryloyloxy group.
A ^a50 represents a single bond or ^* -X ^a51 -(A ^a52 -X ^a52 ) _nb -, where * represents a bond to the carbon atom to which -R ^a50 is bonded.
A ^a52 represents an alkanediyl group having 1 to 6 carbon atoms.
X ^a51 and X ^a52 each independently represent —O—, —CO—O—, or —O—CO—.
nb represents 0 or 1.
mb represents an integer of 0 to 4. When mb is an integer of 2 or more, multiple R ^a51 may be the same or different.]
[14] The resist composition according to any one of [11] to [13], further comprising a salt that generates an acid that is weaker in acidity than the acid generated from the acid generator.
[15] (1) A step of applying the resist composition according to any one of [11] to [14] onto a substrate;
(2) a step of drying the applied composition to form a composition layer;
(3) exposing the composition layer to light;
(4) a step of heating the composition layer after exposure; and (5) a step of developing the composition layer after heating.

By using a resist composition containing the salt of the present invention, it is possible to produce resist patterns with good resolution.

In this specification, "(meth)acrylic monomer" means "at least one of an acrylic monomer and a methacrylic monomer." The terms "(meth)acrylate" and "(meth)acrylic acid" have the same meaning. Regarding groups described in this specification, those that can have both a linear structure and a branched structure are acceptable. When -CH ₂ - contained in a hydrocarbon group or the like is replaced with -O-, -S-, -CO-, or -SO ₂ -, the same examples apply to each group. A "combined group" refers to a group in which two or more of the exemplified groups are bonded together, and the valence of these groups may vary appropriately depending on the bonding form. "Derived from" or "derived from" refers to a polymerizable C═C bond contained in the molecule becoming a -C-C- group by polymerization. When stereoisomers exist, all stereoisomers are included.

[Salt represented by formula (I)]
The present invention relates to a salt represented by formula (I) (hereinafter, may be referred to as "salt (I)").
In the salt (I), the negatively charged side is sometimes referred to as the "anion (I)" and the positively charged side is sometimes referred to as the "cation (I)".
[In the formula, all symbols have the same meanings as defined above.]

In formula (I), examples of the alkanediyl group in L ¹ contained in R ¹ , R ² , and R ³ include linear alkanediyl groups such as methylene, ethylene, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, and hexane-1,6-diyl groups; and branched alkanediyl groups such as ethane-1,1-diyl, propane-1,1-diyl, propane-1,2-diyl, propane-2,2-diyl, pentane-2,4-diyl, 2-methylpropane-1,3-diyl, 2-methylpropane-1,2-diyl, pentane-1,4-diyl, and 2-methylbutane-1,4-diyl groups.
^L1 is preferably an alkanediyl group having 1 to 3 carbon atoms, and more preferably a methylene group.

Examples of the alicyclic hydrocarbon group of ^R10 included in ^R1 , ^R2 , and ^R3 include the groups shown below. The bonding site can be any position. Specifically, the alicyclic hydrocarbon group may be either monocyclic or polycyclic. Examples of monocyclic alicyclic hydrocarbon groups include cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and cyclodecyl. Examples of polycyclic alicyclic hydrocarbon groups include decahydronaphthyl, adamantyl, and norbornyl. The number of carbon atoms in the alicyclic hydrocarbon group is preferably 3 to 18, more preferably 3 to 16, and even more preferably 3 to 12.
The alicyclic hydrocarbon group for R ¹⁰ is preferably an adamantyl group.

The acid labile group for R ¹¹ means a group that, when contacted with an acid (for example, trifluoromethanesulfonic acid), the group represented by R ¹¹ is eliminated to form a hydroxy group.
As the acid labile group, a group represented by formula (1a) (hereinafter sometimes referred to as "acid labile group (1a)") or a group represented by formula (2a) (hereinafter sometimes referred to as "acid labile group (2a)") is preferred.
[In formula (1a), R ^aa1 , R ^aa2 and R ^aa3 each independently represent an alkyl group of 1 to 8 carbon atoms which may have a substituent, an alkenyl group of 2 to 8 carbon atoms which may have a substituent, an alicyclic hydrocarbon group of 3 to 20 carbon atoms which may have a substituent, or an aromatic hydrocarbon group of 6 to 18 carbon atoms which may have a substituent, or R ^aa1 and R ^aa2 are bonded to each other to form an alicyclic hydrocarbon group of 3 to 20 carbon atoms together with the carbon atom to which they are bonded.]
naa represents 0 or 1.
* represents a bond.
[In formula (2a), R ^aa1′ and R ^aa2′ each independently represent a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms; R ^aa3′ represents a hydrocarbon group having 1 to 20 carbon atoms; or R ^aa2′ and R ^aa3′ are bonded to each other to form, together with —C-X ^a — to which they are bonded, a heterocyclic group having 3 to 20 carbon atoms; and —CH ₂ — contained in the hydrocarbon group and the heterocyclic group may be replaced by —O— or —S—.]
^Xa represents an oxygen atom or a sulfur atom.
* represents a bond.

Examples of the alkyl group of R ^aa1 , R ^aa2 and R ^aa3 include a methyl group, an ethyl group, a propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, etc. The number of carbon atoms in the alkyl groups of ^{R aa1} , R ^aa2 and R ^aa3 is preferably 1 to 6, and more preferably 1 to 3.
Examples of the alkenyl group for R ^aa1 , R ^aa2 and R ^aa3 include an ethenyl group, a propenyl group, an isopropenyl group, a butenyl group, an isobutenyl group, a tert-butenyl group, a pentenyl group, a hexenyl group, a heptenyl group, an octenyl group, an isooctenyl group and a nonenyl group.
The alicyclic hydrocarbon groups of R ^aa1 , R ^aa2 and R ^aa3 may be either monocyclic or polycyclic. Examples of monocyclic alicyclic hydrocarbon groups include cycloalkyl groups such as a cyclopentyl group, a cyclohexyl group, a cycloheptyl group and a cyclooctyl group. Examples of polycyclic alicyclic hydrocarbon groups include a decahydronaphthyl group, an adamantyl group, a norbornyl group and the following groups (* represents a bond): The alicyclic hydrocarbon groups of R ^aa1 , R ^aa2 and R ^aa3 preferably have 3 to 16 carbon atoms, more preferably 3 to 12 carbon atoms.
Examples of the aromatic hydrocarbon group of R ^aa1 , R ^aa2 and R ^aa3 include aryl groups such as a phenyl group, a naphthyl group, an anthryl group, a biphenyl group, a phenanthryl group, etc. The aromatic hydrocarbon group of R ^aa1 , R ^aa2 and R ^aa3 preferably has 6 to 14 carbon atoms, and more preferably 6 to 10 carbon atoms.

Examples of the substituent for the alkyl group having 1 to 8 carbon atoms, which may have a substituent, include an alkenyl group having 2 to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to 20 carbon atoms, and an aromatic hydrocarbon group having 6 to 18 carbon atoms. Examples of the substituent for the alkenyl group having 2 to 8 carbon atoms, which may have a substituent, include an alkyl group having 1 to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to 20 carbon atoms, and an aromatic hydrocarbon group having 6 to 18 carbon atoms. Examples of the substituent for the alicyclic hydrocarbon group having 3 to 20 carbon atoms, which may have a substituent, include an alkyl group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, and an aromatic hydrocarbon group having 6 to 18 carbon atoms. Examples of the substituent for the aromatic hydrocarbon group having 6 to 18 carbon atoms, which may have a substituent, include an alkyl group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, and an alicyclic hydrocarbon group having 3 to 20 carbon atoms. More specific examples include groups in which the above-mentioned alkyl group and alicyclic hydrocarbon group are combined (for example, alkylcycloalkyl groups or cycloalkylalkyl groups such as methylcyclohexyl group, dimethylcyclohexyl group, methylnorbornyl group, cyclohexylmethyl group, adamantylmethyl group, adamantyldimethyl group, and norbornylethyl group), aralkyl groups such as benzyl group, aromatic hydrocarbon groups having an alkyl group (p-methylphenyl group, p-tert-butylphenyl group, tolyl group, xylyl group, cumenyl group, mesityl group, 2,6-diethylphenyl group, 2-methyl-6-ethylphenyl group, etc.), aromatic hydrocarbon groups having an alicyclic hydrocarbon group (p-cyclohexylphenyl group, p-adamantylphenyl group, etc.), and phenylcyclohexyl group.
naa is preferably 1.

When R ^aa1 and R ^aa2 bond to each other to form an alicyclic hydrocarbon group together with the carbon atom to which they are bonded, examples of -C(R ^aa1 )(R ^aa2 )(R ^aa3 ) include the following groups. The alicyclic hydrocarbon group preferably has 3 to 16 carbon atoms, more preferably 3 to 12 carbon atoms. * represents a bond to -O-.

Examples of the group represented by formula (1a) include a 1,1-dialkylalkoxycarbonyl group (a group in which R ^aa1 , R ^aa2 and R ^aa3 are alkyl groups in formula (1a), preferably a tert-butoxycarbonyl group), a 2-alkyladamantan-2-yloxycarbonyl group (a group in formula (1a) where R ^aa1 , R ^aa2 and the carbon atoms to which they are bonded form an adamantyl group, and R ^aa3 is an alkyl group), and a 1-(adamantan-1-yl)-1-alkylalkoxycarbonyl group (a group in formula (1a) where R ^aa1 and R ^aa2 are alkyl groups and R ^aa3 is an adamantyl group).

Examples of the hydrocarbon group of R ^aa1′ , R ^aa2′ and R ^aa3′ include an alkyl group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group and a group formed by combining these groups.
Examples of the alkyl group and alicyclic hydrocarbon group include the same groups as those exemplified for R ^aa1 , R ^aa2 and R ^aa3 .
Examples of the aromatic hydrocarbon group include aryl groups such as a phenyl group, a naphthyl group, an anthryl group, a biphenyl group, and a phenanthryl group.
Examples of the combined group include a group in which the above-mentioned alkyl group is combined with an alicyclic hydrocarbon group (for example, a cycloalkylalkyl group or an alkylcycloalkyl group such as a methylcyclohexyl group, a dimethylcyclohexyl group, a methylnorbornyl group, a cyclohexylmethyl group, an adamantylmethyl group, an adamantyldimethyl group, or a norbornylethyl group), an aralkyl group such as a benzyl group, an aromatic hydrocarbon group having an alkyl group (for example, a p-methylphenyl group, a p-tert-butylphenyl group, a tolyl group, a xylyl group, a cumenyl group, a mesityl group, a 2,6-diethylphenyl group, or a 2-methyl-6-ethylphenyl group), an aromatic hydrocarbon group having an alicyclic hydrocarbon group (for example, a p-cyclohexylphenyl group or a p-adamantylphenyl group), and an aryl-cycloalkyl group such as a phenylcyclohexyl group.
When R ^aa2′ and R ^aa3′ are bonded to each other to form a heterocyclic group together with the carbon atom to which they are bonded and X ^a , examples of —C(R ^aa1′ )(R ^aa2′ )—X ^a —(R ^aa3′ ) include the following groups: * represents a bond.
At least one of R ^aa1′ and R ^aa2′ is preferably a hydrogen atom.

Specific examples of the acid labile group (1a) include the following groups: * represents a bond.

Specific examples of the acid labile group (2a) include the following groups: * represents a bond.
Among these, R ¹¹ is preferably a hydrogen atom or an acid labile group (1a).
R ¹ , R ² and R ³ are preferably —O—CO—R ¹⁰ , —O—CO—O—R ¹⁰ or —OL ¹ —CO—O—R ¹⁰ , and more preferably —OL ¹ —CO—O—R ¹⁰ .
The bonding positions of R ¹ , R ² and R ³ may be any of the o-position, m- ^position and p-position relative to the bonding positions of X ¹ , X 2 and X ³ , respectively. In particular, it is preferable that they are bonded to the p-position relative to the bonding positions of X ¹ , X ² and X ³ .

Examples of the halogen atom for R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ and R ⁹ include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.
The fluorinated alkyl group having 1 to 12 carbon atoms for R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ and R ⁹ represents an alkyl group having 1 to 12 carbon atoms and a fluorine atom, and examples thereof include perfluoroalkyl groups having 1 to 12 carbon atoms (trifluoromethyl group, pentafluoroethyl group, heptafluoropropyl group, nonafluorobutyl group), as well as 2,2,2-trifluoroethyl group, 3,3,3-trifluoropropyl group, 4,4,4-trifluorobutyl group, and 3,3,4,4,4-pentafluorobutyl group. The number of carbon atoms in the fluorinated alkyl group is preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 to 3.
Examples of the hydrocarbon group having 1 to 18 carbon atoms for R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ and R ⁹ include chain hydrocarbon groups such as alkyl groups, alicyclic hydrocarbon groups, aromatic hydrocarbon groups and groups formed by combining these.
Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, a 2-ethylhexyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, and a dodecyl group. The number of carbon atoms in the alkyl group is preferably 1 to 12, more preferably 1 to 9, even more preferably 1 to 6, and still more preferably 1 to 4.
The alicyclic hydrocarbon group may be either monocyclic or polycyclic, and examples include the groups shown below. The bonding site can be any position. Specific examples of the alicyclic hydrocarbon group include monocyclic alicyclic hydrocarbon groups such as cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and cyclodecyl. Examples of polycyclic alicyclic hydrocarbon groups include decahydronaphthyl, adamantyl, and norbornyl. The number of carbon atoms in the alicyclic hydrocarbon group is preferably 3 to 18, more preferably 3 to 16, and even more preferably 3 to 12.
Examples of the aromatic hydrocarbon group include a phenyl group, a naphthyl group, a biphenyl group, an anthryl group, a phenanthryl group, a binaphthyl group, etc. The aromatic hydrocarbon group preferably has 6 to 18 carbon atoms, more preferably 6 to 14 carbon atoms, and even more preferably 6 to 10 carbon atoms.
Groups formed by combination include groups formed by combining an aromatic hydrocarbon group with a chain hydrocarbon group (for example, aromatic hydrocarbon group-alkanediyl group-*, alkyl group-aromatic hydrocarbon group-*), groups formed by combining an alicyclic hydrocarbon group with a chain hydrocarbon group (for example, alicyclic hydrocarbon group-alkanediyl group-*, alkyl group-alicyclic hydrocarbon group-*), and groups formed by combining an aromatic hydrocarbon group with a alicyclic hydrocarbon group (for example, aromatic hydrocarbon group-alicyclic hydrocarbon group-*, alicyclic hydrocarbon group-aromatic hydrocarbon group-*). * represents a bonding site.
Examples of the aromatic hydrocarbon group -alkanediyl group-* include aralkyl groups such as benzyl and phenethyl.
Examples of the alkyl group-aromatic hydrocarbon group-* include a tolyl group, a xylyl group, and a cumenyl group.
Examples of the alicyclic hydrocarbon group -alkanediyl group-* include cycloalkylalkyl groups such as cyclohexylmethyl group, cyclohexylethyl group, 1-(adamantan-1-yl)methyl group, and 1-(adamantan-1-yl)-1-methylethyl group.
Examples of the alkyl group-alicyclic hydrocarbon group-* include cycloalkyl groups having an alkyl group such as a methylcyclohexyl group, a dimethylcyclohexyl group, and a 2-alkyladamantan-2-yl group.
Examples of the aromatic hydrocarbon group-alicyclic hydrocarbon group-* include a phenylcyclohexyl group.
Examples of the alicyclic hydrocarbon group-aromatic hydrocarbon group-* include a cyclohexylphenyl group.
In addition, two or more types of alicyclic hydrocarbon groups, aromatic hydrocarbon groups, and chain hydrocarbon groups may be combined. Furthermore, —CH ₂ — contained in the cyclic hydrocarbon group or chain hydrocarbon group (alkanediyl group, alkyl group) may be replaced with —O—, —S—, —CO—, or —SO ₂ —. Any of the combined groups may be bonded to the benzene ring.
Examples of groups in which —CH ₂ — in a hydrocarbon group is replaced by —O—, —S—, —CO— or —SO ₂ — include a hydroxy group (a group in which —CH ₂ — in a methyl group is replaced by —O—), a carboxy group (a group in which —CH _{2 —} in an ethyl group is replaced by —O—CO—), a thiol group (a group in which —CH ₂ — in a methyl group is replaced by —S—), an alkoxy group (a group in which —CH ₂ — at any position in an alkyl group is replaced by —O—), an alkylthio group (a group in which —CH ₂ — at any position in an alkyl group is replaced by —S—), an alkoxycarbonyl group (a group in which —CH ₂ —CH ₂ — at any position in an alkyl group is replaced by —O—CO—), and an alkylsulfonyl group (a group in which —CH ₂ — at any position in an alkyl group is replaced by —SO ₂ -substituted with -), alkylcarbonyl groups (groups in which -CH ₂ - at any position in an alkyl group is replaced with -CO-), alkylcarbonyloxy groups (groups in which -CH ₂ -CH ₂ - at any position in an alkyl group is replaced with -CO-O-), cycloalkoxy groups, cycloalkylalkoxy groups, alkoxycarbonyloxy groups, aromatic hydrocarbon group-carbonyloxy groups, and groups in which two or more of these groups are combined.
Examples of the alkoxy group include alkoxy groups having 1 to 17 carbon atoms, such as a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentyloxy group, a hexyloxy group, an octyloxy group, a 2-ethylhexyloxy group, a nonyloxy group, a decyloxy group, an undecyloxy group, etc. The number of carbon atoms in the alkoxy group is preferably 1 to 11, more preferably 1 to 6, and even more preferably 1 to 4.
The alkylthio group includes alkylthio groups having 1 to 17 carbon atoms, such as a methylthio group, an ethylthio group, a propylthio group, a butylthio group, etc. The number of carbon atoms in the alkylthio group is preferably 1 to 11, more preferably 1 to 6, and even more preferably 1 to 4.
The alkoxycarbonyl group, alkylcarbonyl group and alkylcarbonyloxy group represent groups in which a carbonyl group or carbonyloxy group is bonded to the above-mentioned alkyl group or alkoxy group.
Examples of alkoxycarbonyl groups include alkoxycarbonyl groups having 2 to 17 carbon atoms, such as methoxycarbonyl, ethoxycarbonyl, and butoxycarbonyl groups. Examples of alkylcarbonyl groups include alkylcarbonyl groups having 2 to 18 carbon atoms, such as acetyl, propionyl, and butyryl groups. Examples of alkylcarbonyloxy groups include alkylcarbonyloxy groups having 2 to 17 carbon atoms, such as acetyloxy, propionyloxy, and butyryloxy groups. The number of carbon atoms in the alkoxycarbonyl group is preferably 2 to 11, more preferably 2 to 6, and even more preferably 2 to 4. The number of carbon atoms in the alkylcarbonyl group is preferably 2 to 12, more preferably 2 to 6, and even more preferably 2 to 4. The number of carbon atoms in the alkylcarbonyloxy group is preferably 2 to 11, more preferably 2 to 6, and even more preferably 2 to 4.
The alkylsulfonyl group includes alkylsulfonyl groups having 1 to 17 carbon atoms, such as a methylsulfonyl group, an ethylsulfonyl group, a propylsulfonyl group, etc. The number of carbon atoms in the alkylsulfonyl group is preferably 1 to 11, more preferably 1 to 6, and even more preferably 1 to 4.
Examples of cycloalkoxy groups include cycloalkoxy groups having 3 to 17 carbon atoms, such as a cyclohexyloxy group. Examples of cycloalkylalkoxy groups include cycloalkylalkoxy groups having 4 to 17 carbon atoms, such as a cyclohexylmethoxy group. Examples of alkoxycarbonyloxy groups include alkoxycarbonyloxy groups having 2 to 16 carbon atoms, such as a butoxycarbonyloxy group. Examples of aromatic hydrocarbon group-carbonyloxy groups include aromatic hydrocarbon group-carbonyloxy groups having 7 to 17 carbon atoms, such as a benzoyloxy group.
Examples of groups in which —CH ₂ — contained in an alicyclic hydrocarbon group is replaced with —O— or —CO— include the groups shown below. The —O— or —CO— position shown below may be replaced with —S— or —SO ₂ —, respectively. The bonding site may be at any position.
When a —CH ₂ — contained in the hydrocarbon group is replaced with —O—, —CO—, —S—, or —SO ₂ —, the number of carbon atoms before the replacement is taken as the total number of carbon atoms in the hydrocarbon group. In addition, the number may be 1 or 2 or more.
Substituents that the hydrocarbon groups of R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ and R ⁹ may have include a halogen atom, a cyano group, and an alkyl group having 1 to 12 carbon atoms (-CH ₂ - contained in the alkyl group may be replaced with -O- or -CO-).
Examples of the halogen atom include the same groups as those mentioned above.
Examples of the alkyl group having 1 to 12 carbon atoms include the same groups as those mentioned above.
When —CH ₂ — contained in an alkyl group is replaced with —O— or —CO— as a substituent, the number of carbon atoms before the replacement is counted as the total number of carbon atoms in the alkyl group. Examples of the replaced group include a hydroxy group, a carboxy group, an alkoxy group, an alkoxycarbonyl group, an alkylcarbonyl group, and an alkylcarbonyloxy group.
Examples of the alkoxy group, alkoxycarbonyl group, alkylcarbonyl group and alkylcarbonyloxy group include the same groups as those described above.
The hydrocarbon group may have one or more substituents.

^X1 is preferably an oxygen atom.
^X2 is preferably an oxygen atom.
^X3 is preferably an oxygen atom.
The bonding positions of X ¹ , X ² and X ³ may be any of the o-position, m-position and p-position relative to the bonding position of S ⁺ . In particular, bonding to the p-position or m-position relative to the bonding position of S ⁺ is preferred, and bonding to the p-position is more preferred.
m1 is preferably 0, 1 or 2, more preferably 1 or 2, and even more preferably 1.
m2 is preferably 0 or 1.
m3 is preferably 0 or 1.
When m1 is 0, it is preferable that m2 and m3 are both 1.
m4 is preferably 0, 1, 2 or 4. When m4 is 1 or 2, the bonding position of at least one ^R4 is preferably in the o-position relative to the bonding position of ^X1 , and when m4 is 2, it is preferable that the bonding position of one ^R4 is in the o-position relative to the bonding position of ^X1 and the bonding position of the other ^R4 is in the m-position relative to the bonding position of ^X1 .
m5 is preferably 0, 1 or 2. When m5 is 1 or 2, it is preferable that the bonding position of at least one ^R5 is o-positioned relative to the bonding position of ^X2 , and when m5 is 2, it is preferable that the bonding position of one ^R5 is o-positioned relative to the bonding position of ^X2 and the bonding position of the other ^R5 is m-positioned relative to the bonding position of ^X2 .
m6 is preferably 0, 1 or 2. When m6 is 1 or 2, it is preferable that the bonding position of at least one ^R6 is o-positioned relative to the bonding position of ^X3 , and when m6 is 2, it is preferable that the bonding position of one ^R6 is o-positioned relative to the bonding position of ^X3 and the bonding position of the other ^R6 is m-positioned relative to the bonding position of ^X3 .
m7 is preferably 0, 1 or 2, and more preferably 0 or 1.
m8 is preferably 0 or 1.
m9 is preferably 0 or 1.
When m1+m2+m3 is 2 or more, the groups in the parentheses may be the same as or different from each other. In other words, when there are multiple X ¹ to X ³ , multiple R ¹ to R ³ , or multiple R ⁴ to R ⁶ , they may be the same as or different from each other.
R ⁴ , R ⁵ and R ⁶ are each independently preferably a halogen atom, a fluorinated alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 6 carbon atoms (wherein —CH ₂ — contained in the alkyl group may be replaced with —O— or —CO—), more preferably a halogen atom, a fluorinated alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms (wherein —CH ₂ — contained in the alkyl group may be replaced with —O— or —CO—), and even more preferably a fluorine atom, an iodine atom, a trifluoromethyl group or an alkyl group having 1 to 4 carbon atoms. R ⁷ , R ⁸ and R ⁹ are each independently preferably a halogen atom, a fluorinated alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 6 carbon atoms (wherein the —CH ₂ — contained in the alkyl group may be replaced with —O— or —CO—), more preferably a halogen atom, a fluorinated alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms (wherein the —CH ₂ — contained in the alkyl group may be replaced with —O— or —CO—), even more preferably a fluorine atom, an iodine atom, a perfluoroalkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms (wherein the —CH ₂ — contained in the alkyl group may be replaced with —O— or —CO—), and even more preferably a fluorine atom, an iodine atom, a trifluoromethyl group, a methyl group, a t-butyl group, a hydroxy group or a methoxy group.
The bonding positions of R ⁷ , R ⁸ and R ⁹ are not particularly limited. When m2 is 0, the bonding position of R ⁸ may be any of the o-position, m-position, and p-position relative to the bonding position of S ⁺ , and it is more preferable that R 8 be bonded to the p-position relative to the bonding position of S ⁺ . When m3 is 0, the bonding position of R ⁹ may be any of the o-position, m-position, and p-position relative to the bonding position of S +, and it is more preferable that R ⁹ be bonded to the p-position relative to the bonding position of S ⁺ .
X ⁴ is preferably a single bond, —CH ₂ —, —O— or —CO—, more preferably a single bond or —CH ₂ —, and even more preferably a single bond.

Examples of the cation of the salt (I) include cations represented by the following formulae (I-c-1) to (I-c-53).

Examples of the organic anion represented by AI ^- include a sulfonate anion, a sulfonylimide anion, a sulfonylmethide anion, a carboxylate anion, etc. The organic anions represented by ^{AI -} are each independently preferably a sulfonate anion, and more preferably each independently an anion represented by formula (IA).
[In formula (IA),
Q ¹ and Q ² each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms.
^L1 represents a saturated hydrocarbon group having 1 to 24 carbon atoms, in which —CH ₂ — contained in the saturated hydrocarbon group may be replaced by —O— or —CO—, and in which a hydrogen atom contained in the saturated hydrocarbon group may be replaced by a fluorine atom or a hydroxy group.
^Y1 represents an optionally substituted methyl group or an optionally substituted alicyclic hydrocarbon group having 3 to 24 carbon atoms, and one —CH ₂ — contained in the alicyclic hydrocarbon group may be replaced by —O—, —SO ₂ — or —CO—.]

In the anion represented by formula (IA), when —CH ₂ — in the saturated hydrocarbon group is replaced with —O— or —CO—, the number of carbon atoms in the saturated hydrocarbon group before the replacement is taken as the number of carbon atoms in the saturated hydrocarbon group. Also, when —CH ₂ — in the alicyclic hydrocarbon group is replaced with —O—, —SO ₂ —, or —CO—, the number of carbon atoms in the alicyclic hydrocarbon group before the replacement is taken as the number of carbon atoms in the alicyclic hydrocarbon group.

Examples of the perfluoroalkyl group having 1 to 6 carbon atoms for ^Q1 and ^Q2 include a trifluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluoroisopropyl group, a perfluorobutyl group, a perfluorosec-butyl group, a perfluorotert-butyl group, a perfluoropentyl group, and a perfluorohexyl group.
Q ¹ and Q ² are each preferably a fluorine atom or a trifluoromethyl group, and more preferably both are fluorine atoms.

Examples of the divalent saturated hydrocarbon group for ^L1 include a linear alkanediyl group, a branched alkanediyl group, and a monocyclic or polycyclic divalent alicyclic saturated hydrocarbon group, and may also be a group formed by combining two or more of these groups.
Specific examples thereof include linear alkanediyl groups such as a methylene group, an ethylene group, a propane-1,3-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diyl group, a heptane-1,7-diyl group, an octane-1,8-diyl group, a nonane-1,9-diyl group, a decane-1,10-diyl group, an undecane-1,11-diyl group, a dodecane-1,12-diyl group, a tridecane-1,13-diyl group, a tetradecane-1,14-diyl group, a pentadecane-1,15-diyl group, a hexadecane-1,16-diyl group, and a heptadecane-1,17-diyl group;
branched alkanediyl groups such as an ethane-1,1-diyl group, a propane-1,1-diyl group, a propane-1,2-diyl group, a propane-2,2-diyl group, a pentane-2,4-diyl group, a 2-methylpropane-1,3-diyl group, a 2-methylpropane-1,2-diyl group, a pentane-1,4-diyl group, and a 2-methylbutane-1,4-diyl group;
a monocyclic divalent alicyclic saturated hydrocarbon group such as a cycloalkanediyl group, such as a cyclobutane-1,3-diyl group, a cyclopentane-1,3-diyl group, a cyclohexane-1,4-diyl group, or a cyclooctane-1,5-diyl group;
Examples include polycyclic divalent alicyclic saturated hydrocarbon groups such as norbornane-1,4-diyl group, norbornane-2,5-diyl group, adamantane-1,5-diyl group, and adamantane-2,6-diyl group.

Examples of the divalent saturated hydrocarbon group represented by ^L1 in which one -CH ₂ - is replaced with -O- or -CO- include groups represented by any of formulas (b1-1) to (b1-3). In the groups represented by formulas (b1-1) to (b1-3) and specific examples thereof, groups represented by formulas (b1-4) to (b1-11), * and ** represent bonding sites, and * represents a bond to ^-Y1 .

[In formula (b1-1),
L ^b2 represents a single bond or a divalent saturated hydrocarbon group having 1 to 22 carbon atoms, and a hydrogen atom contained in the saturated hydrocarbon group may be substituted with a fluorine atom.
L ^b3 represents a single bond or a divalent saturated hydrocarbon group having 1 to 22 carbon atoms, and a hydrogen atom contained in the saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group, and a —CH ₂ — contained in the saturated hydrocarbon group may be substituted with —O— or —CO—.
However, the total number of carbon atoms in L ^b2 and L ^b3 is 22 or less.
In formula (b1-2),
L ^b4 represents a single bond or a divalent saturated hydrocarbon group having 1 to 22 carbon atoms, and a hydrogen atom contained in the saturated hydrocarbon group may be substituted with a fluorine atom.
L ^b5 represents a single bond or a divalent saturated hydrocarbon group having 1 to 22 carbon atoms, wherein a hydrogen atom contained in the saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group, and wherein a —CH ₂ — contained in the saturated hydrocarbon group may be substituted with —O— or —CO—.
However, the total number of carbon atoms in L ^b4 and L ^b5 is 22 or less.
In formula (b1-3),
L ^b6 represents a single bond or a divalent saturated hydrocarbon group having 1 to 23 carbon atoms, and a hydrogen atom contained in the saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group.
L ^b7 represents a single bond or a divalent saturated hydrocarbon group having 1 to 23 carbon atoms, wherein a hydrogen atom contained in the saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group, and wherein a —CH ₂ — contained in the saturated hydrocarbon group may be substituted with —O— or —CO—.
However, the total number of carbon atoms in L ^b6 and L ^b7 is 23 or less.]

In the groups represented by formulae (b1-1) to (b1-3), when —CH ₂ — contained in the saturated hydrocarbon group is replaced with —O— or —CO—, the number of carbon atoms before replacement is regarded as the number of carbon atoms of the saturated hydrocarbon group.
Examples of the divalent saturated hydrocarbon group include the same divalent saturated hydrocarbon groups as those for L ^b1 .
L ^b2 is preferably a single bond.
L ^b3 is preferably a divalent saturated hydrocarbon group having 1 to 4 carbon atoms.
L ^b4 is preferably a divalent saturated hydrocarbon group having 1 to 8 carbon atoms, and a hydrogen atom contained in the divalent saturated hydrocarbon group may be substituted with a fluorine atom.
L ^b5 is preferably a single bond or a divalent saturated hydrocarbon group having 1 to 8 carbon atoms.
L ^b6 is preferably a single bond or a divalent saturated hydrocarbon group having 1 to 4 carbon atoms, and a hydrogen atom contained in the saturated hydrocarbon group may be substituted with a fluorine atom.
L ^b7 is preferably a single bond or a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, in which a hydrogen atom contained in the saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group, and a —CH ₂ — contained in the divalent saturated hydrocarbon group may be substituted with —O— or —CO—.
The divalent saturated hydrocarbon group represented by L ¹ in which one —CH ₂ — group is replaced by —O— or —CO— is preferably a group represented by formula (b1-1) or formula (b1-3).

Examples of the group represented by formula (b1-1) include groups represented by formulas (b1-4) to (b1-8).
[In formula (b1-4),
L ^b8 represents a single bond or a divalent saturated hydrocarbon group having 1 to 22 carbon atoms, and a hydrogen atom contained in the saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group.
In formula (b1-5),
L ^b9 represents a divalent saturated hydrocarbon group having 1 to 20 carbon atoms, and one —CH ₂ — contained in the divalent saturated hydrocarbon group may be replaced by —O— or —CO—.
L ^b10 represents a single bond or a divalent saturated hydrocarbon group having 1 to 19 carbon atoms, and a hydrogen atom contained in the divalent saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group.
However, the total number of carbon atoms in L ^b9 and L ^b10 is 20 or less.
In formula (b1-6),
L ^b11 represents a divalent saturated hydrocarbon group having 1 to 21 carbon atoms.
L ^b12 represents a single bond or a divalent saturated hydrocarbon group having 1 to 20 carbon atoms, and a hydrogen atom contained in the divalent saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group.
However, the total number of carbon atoms in L ^b11 and L ^b12 is 21 or less.
In formula (b1-7),
L ^b13 represents a divalent saturated hydrocarbon group having 1 to 19 carbon atoms.
L ^b14 represents a single bond or a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, and one --CH ₂ -- contained in the divalent saturated hydrocarbon group may be replaced with --O-- or --CO--.
L ^b15 represents a single bond or a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, and a hydrogen atom contained in the divalent saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group.
However, the total number of carbon atoms of L ^b13 to L ^b15 is 19 or less.
In formula (b1-8),
L ^b16 represents a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, and one --CH ₂ -- contained in the divalent saturated hydrocarbon group may be replaced by --O-- or --CO--.
L ^b17 represents a divalent saturated hydrocarbon group having 1 to 18 carbon atoms.
L ^b18 represents a single bond or a divalent saturated hydrocarbon group having 1 to 17 carbon atoms, and a hydrogen atom contained in the divalent saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group.
However, the total number of carbon atoms of L ^b16 to L ^b18 is 19 or less.]

L ^b8 is preferably a divalent saturated hydrocarbon group having 1 to 4 carbon atoms.
L ^b9 is preferably a divalent saturated hydrocarbon group having 1 to 8 carbon atoms.
L ^b10 is preferably a single bond or a divalent saturated hydrocarbon group having 1 to 19 carbon atoms, and more preferably a single bond or a divalent saturated hydrocarbon group having 1 to 8 carbon atoms.
L ^b11 is preferably a divalent saturated hydrocarbon group having 1 to 8 carbon atoms.
L ^b12 is preferably a single bond or a divalent saturated hydrocarbon group having 1 to 8 carbon atoms.
L ^b13 is preferably a divalent saturated hydrocarbon group having 1 to 12 carbon atoms.
L ^b14 is preferably a single bond or a divalent saturated hydrocarbon group having 1 to 6 carbon atoms.
L ^b15 is preferably a single bond or a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, and more preferably a single bond or a divalent saturated hydrocarbon group having 1 to 8 carbon atoms.
L ^b16 is preferably a divalent saturated hydrocarbon group having 1 to 12 carbon atoms.
L ^b17 is preferably a divalent saturated hydrocarbon group having 1 to 6 carbon atoms.
L ^b18 is preferably a single bond or a divalent saturated hydrocarbon group having 1 to 17 carbon atoms, and more preferably a single bond or a divalent saturated hydrocarbon group having 1 to 4 carbon atoms.

Examples of the group represented by formula (b1-3) include groups represented by formulas (b1-9) to (b1-11).
In formula (b1-9),
L ^b19 represents a single bond or a divalent saturated hydrocarbon group having 1 to 23 carbon atoms, and a hydrogen atom contained in the saturated hydrocarbon group may be substituted with a fluorine atom.
L ^b20 represents a single bond or a divalent saturated hydrocarbon group having 1 to 23 carbon atoms, wherein a hydrogen atom contained in the saturated hydrocarbon group may be substituted with a fluorine atom, a hydroxy group, or an alkylcarbonyloxy group, wherein a —CH ₂ — contained in the alkylcarbonyloxy group may be replaced with —O— or —CO—, and a hydrogen atom contained in the alkylcarbonyloxy group may be substituted with a hydroxy group.
However, the total number of carbon atoms in L ^b19 and L ^b20 is 23 or less.
In formula (b1-10),
L ^b21 represents a single bond or a divalent saturated hydrocarbon group having 1 to 21 carbon atoms, and a hydrogen atom contained in the saturated hydrocarbon group may be substituted with a fluorine atom.
L ^b22 represents a single bond or a divalent saturated hydrocarbon group having 1 to 21 carbon atoms.
L ^b23 represents a single bond or a divalent saturated hydrocarbon group having 1 to 21 carbon atoms, and a hydrogen atom contained in the saturated hydrocarbon group may be substituted with a fluorine atom, a hydroxy group, or an alkylcarbonyloxy group. A —CH ₂ — contained in the alkylcarbonyloxy group may be replaced with —O— or —CO—, and a hydrogen atom contained in the alkylcarbonyloxy group may be substituted with a hydroxy group.
However, the total number of carbon atoms of L ^b21 , L ^b22 and L ^b23 is 21 or less.
In formula (b1-11),
L ^b24 represents a single bond or a divalent saturated hydrocarbon group having 1 to 20 carbon atoms, and a hydrogen atom contained in the saturated hydrocarbon group may be substituted with a fluorine atom.
L ^b25 represents a divalent saturated hydrocarbon group having 1 to 21 carbon atoms.
L ^b26 represents a single bond or a divalent saturated hydrocarbon group having 1 to 20 carbon atoms, and a hydrogen atom contained in the saturated hydrocarbon group may be substituted with a fluorine atom, a hydroxy group, or an alkylcarbonyloxy group. A —CH ₂ — contained in the alkylcarbonyloxy group may be replaced with —O— or —CO—, and a hydrogen atom contained in the alkylcarbonyloxy group may be substituted with a hydroxy group.
However, the total number of carbon atoms in L ^b24 , L ^b25 and L ^b26 is 21 or less.

In addition, in the groups represented by formulas (b1-9) to (b1-11), if a hydrogen atom contained in a saturated hydrocarbon group is substituted with an alkylcarbonyloxy group, the number of carbon atoms before substitution is regarded as the number of carbon atoms in the saturated hydrocarbon group.

Examples of alkylcarbonyloxy groups include acetyloxy groups, propionyloxy groups, butyryloxy groups, cyclohexylcarbonyloxy groups, and adamantylcarbonyloxy groups.

Examples of the group represented by formula (b1-4) include the following.

Examples of the group represented by formula (b1-5) include the following.

Examples of the group represented by formula (b1-6) include the following.

Examples of the group represented by formula (b1-7) include the following.

Examples of the group represented by formula (b1-8) include the following.

Examples of the group represented by formula (b1-2) include the following.

Examples of the group represented by formula (b1-9) include the following.

Examples of the group represented by formula (b1-10) include the following.

Examples of the group represented by formula (b1-11) include the following.

Examples of the alicyclic hydrocarbon group represented by ^Y1 include groups represented by formulae (Y1) to (Y11) and (Y36) to (Y38).
When a —CH ₂ — contained in the alicyclic hydrocarbon group represented by ^Y1 is replaced by —O—, —SO ₂ — or —CO—, the number may be 1 or 2 or more. Examples of such groups include groups represented by formulae (Y12) to (Y35) and formulae (Y39) to (Y43). * indicates the bonding position with ^L1 .

The alicyclic hydrocarbon group represented by ^Y1 is preferably a group represented by any one of formulas (Y1) to (Y20), (Y26), (Y27), (Y30), (Y31), and (Y39) to (Y43), more preferably a group represented by formula (Y11), (Y15), (Y16), (Y20), (Y26), (Y27), (Y30), (Y31), (Y39), (Y40), (Y42), or (Y43), and even more preferably a group represented by formula (Y11), (Y15), (Y20), (Y26), (Y27), (Y30), (Y31), (Y39), (Y40), (Y42), or (Y43).
When the alicyclic hydrocarbon group represented by ^Y1 is a spiro ring such as those of formulae (Y28) to (Y35), (Y39), (Y40), (Y42), and (Y43), the alkanediyl group between the two oxygen atoms preferably has one or more fluorine atoms. Furthermore, among the alkanediyl groups contained in the ketal structure, it is preferred that the methylene group adjacent to the oxygen atom is not substituted with a fluorine atom.

Examples of the substituent on the methyl group represented by ^Y1 include a halogen atom, a hydroxy group, an alicyclic hydrocarbon group having 3 to 16 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, a glycidyloxy group, a -(CH ₂ ) _ja -CO-O-R ^b1 group, or a -(CH ₂ ) _ja -O-CO-R ^b1 group (wherein R ^b1 represents an alkyl group having 1 to 16 carbon atoms, an alicyclic hydrocarbon group having 3 to 16 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, or a group formed by combining these; ja represents an integer of 0 to 4; -CH ₂ - contained in the alkyl group and the alicyclic hydrocarbon group may be replaced by -O-, -SO ₂ - or -CO-; and a hydrogen atom contained in the alkyl group, the alicyclic hydrocarbon group, and the aromatic hydrocarbon group may be replaced by a hydroxy group or a fluorine atom).
Substituents for the alicyclic hydrocarbon group represented by ^Y1 include a halogen atom, a hydroxy group, an alkyl group having 1 to 16 carbon atoms which may be substituted with a hydroxy group (wherein —CH ₂ — contained in the alkyl group may be replaced with —O— or —CO—), an alicyclic hydrocarbon group having 3 to 16 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, an aralkyl group having 7 to 21 carbon atoms, a glycidyloxy group, a —(CH ₂ ) _ja -CO-O-R ^b1 group, or a —(CH ₂ ) _ja -O-CO-R ^b1 group (wherein R ^b1 represents an alkyl group having 1 to 16 carbon atoms, an alicyclic hydrocarbon group having 3 to 16 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, or a group combining these; ja represents an integer of 0 to 4. The —CH ₂ — contained in the alkyl group and the alicyclic hydrocarbon group may be replaced with —O—, —SO ₂ - or -CO-, and a hydrogen atom contained in the alkyl group, the alicyclic hydrocarbon group, and the aromatic hydrocarbon group may be replaced by a hydroxy group or a fluorine atom.

Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.
Examples of the alicyclic hydrocarbon group include a cyclopentyl group, a cyclohexyl group, a methylcyclohexyl group, a dimethylcyclohexyl group, a cycloheptyl group, a cyclooctyl group, a norbornyl group, and an adamantyl group. The alicyclic hydrocarbon group may have a chain hydrocarbon group, such as a methylcyclohexyl group or a dimethylcyclohexyl group. The number of carbon atoms in the alicyclic hydrocarbon group is preferably 3 to 12, and more preferably 3 to 10.
Examples of aromatic hydrocarbon groups include aryl groups such as phenyl, naphthyl, anthryl, biphenyl, and phenanthryl. The aromatic hydrocarbon group may have a chain hydrocarbon group or an alicyclic hydrocarbon group. Examples of aromatic hydrocarbon groups having a chain hydrocarbon group include tolyl, xylyl, cumenyl, mesityl, p-ethylphenyl, p-tert-butylphenyl, 2,6-diethylphenyl, and 2-methyl-6-ethylphenyl. Examples of aromatic hydrocarbon groups having an alicyclic hydrocarbon group include p-cyclohexylphenyl and p-adamantylphenyl. The aromatic hydrocarbon group preferably has 6 to 14 carbon atoms, and more preferably 6 to 10 carbon atoms.
Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, a 2-ethylhexyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, etc. The number of carbon atoms in the alkyl group is preferably 1 to 12, more preferably 1 to 9, even more preferably 1 to 6, and still more preferably 1 to 4.
Examples of the alkyl group substituted with a hydroxy group include hydroxyalkyl groups such as a hydroxymethyl group and a hydroxyethyl group.
Examples of the aralkyl group include a benzyl group, a phenethyl group, a phenylpropyl group, a naphthylmethyl group, and a naphthylethyl group.
Examples of the alkyl group in which —CH ₂ — is replaced by —O—, —SO ₂ —, —CO— or the like include an alkoxy group, an alkylsulfonyl group, an alkoxycarbonyl group, an alkylcarbonyl group, an alkylcarbonyloxy group, or a combination thereof.
Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group, an octyloxy group, a decyloxy group, and a dodecyloxy group. The number of carbon atoms in the alkoxy group is preferably 1 to 12, more preferably 1 to 6, and even more preferably 1 to 4.
Examples of the alkylsulfonyl group include a methylsulfonyl group, an ethylsulfonyl group, a propylsulfonyl group, etc. The number of carbon atoms in the alkylsulfonyl group is preferably 1 to 12, more preferably 1 to 6, and even more preferably 1 to 4.
Examples of the alkoxycarbonyl group include a methoxycarbonyl group, an ethoxycarbonyl group, a butoxycarbonyl group, etc. The number of carbon atoms in the alkoxycarbonyl group is preferably 2 to 12, more preferably 2 to 6, and even more preferably 2 to 4.
Examples of the alkylcarbonyl group include an acetyl group, a propionyl group, and a butyryl group. The alkylcarbonyl group preferably has 2 to 12 carbon atoms, more preferably 2 to 6 carbon atoms, and even more preferably 2 to 4 carbon atoms.
Examples of the alkylcarbonyloxy group include an acetyloxy group, a propionyloxy group, a butyryloxy group, etc. The number of carbon atoms in the alkylcarbonyloxy group is preferably 2 to 12, more preferably 2 to 6, and even more preferably 2 to 4.
Examples of the combined group include a group combining an alkoxy group and an alkyl group, a group combining an alkoxy group and an alkoxy group, a group combining an alkoxy group and an alkylcarbonyl group, and a group combining an alkoxy group and an alkylcarbonyloxy group.
Examples of the group combining an alkoxy group and an alkyl group include alkoxyalkyl groups such as a methoxymethyl group, a methoxyethyl group, an ethoxyethyl group, an ethoxymethyl group, etc. The number of carbon atoms in the alkoxyalkyl group is preferably 2 to 12, more preferably 2 to 6, and even more preferably 2 to 4.
Examples of a group formed by combining an alkoxy group with another alkoxy group include alkoxyalkoxy groups such as a methoxymethoxy group, a methoxyethoxy group, an ethoxymethoxy group, and an ethoxyethoxy group. The number of carbon atoms in the alkoxyalkoxy group is preferably 2 to 12, more preferably 2 to 6, and even more preferably 2 to 4.
Examples of the group combining an alkoxy group and an alkylcarbonyl group include alkoxyalkylcarbonyl groups such as a methoxyacetyl group, a methoxypropionyl group, an ethoxyacetyl group, an ethoxypropionyl group, etc. The number of carbon atoms in the alkoxyalkylcarbonyl group is preferably 3 to 13, more preferably 3 to 7, and even more preferably 3 to 5.
Examples of a group combining an alkoxy group and an alkylcarbonyloxy group include alkoxyalkylcarbonyloxy groups such as a methoxyacetyloxy group, a methoxypropionyloxy group, an ethoxyacetyloxy group, an ethoxypropionyloxy group, etc. The number of carbon atoms in the alkoxyalkylcarbonyloxy group is preferably 3 to 13, more preferably 3 to 7, and even more preferably 3 to 5.
Examples of the alicyclic hydrocarbon group in which —CH ₂ — is replaced by —O—, —SO ₂ —, —CO— or the like include groups represented by formulae (Y12) to (Y35) and formulae (Y39) to (Y43).

Examples of ^Y1 include the following.

^Y1 is preferably an alicyclic hydrocarbon group of 3 to 24 carbon atoms which may have a substituent, more preferably an alicyclic hydrocarbon group of 3 to 20 carbon atoms which may have a substituent, even more preferably an alicyclic hydrocarbon group of 3 to 18 carbon atoms which may have a substituent, still more preferably an alicyclic hydrocarbon group substituted with a hydroxy group, and even more preferably an adamantyl group which may have a substituent, wherein —CH ₂ — constituting the alicyclic hydrocarbon group or the adamantyl group may be replaced by —CO—, —SO ₂ — or —CO—. Specifically, ^Y1 is preferably an adamantyl group, a hydroxyadamantyl group, an oxoadamantyl group, or a group represented by formula (Y42) or formula (Y100) to formula (Y114), and particularly preferably a hydroxyadamantyl group, an oxoadamantyl group, or a group containing these.

The anion represented by formula (I-A) is preferably an anion represented by formula (I-A-1) to formula (I-A-59) [hereinafter, these may be referred to as "anion (I-A-1)" or the like depending on the formula number.], and more preferably an anion represented by any of formulas (I-A-1) to (I-A-4), (I-A-9), (I-A-10), (I-A-24) to (I-A-33), (I-A-36) to (I-A-40), and (I-A-47) to (I-A-59).

Here, R ⁱ² to R ⁱ⁷ are each independently, for example, an alkyl group having 1 to 4 carbon atoms, preferably a methyl group or an ethyl group. ^{R i8} is, for example, an open-chain hydrocarbon group having 1 to 12 carbon atoms, preferably an alkyl group having 1 to 4 carbon atoms, an alicyclic hydrocarbon group having 5 to 12 carbon atoms, or a group formed by combining these, more preferably a methyl group, an ethyl group, a cyclohexyl group, or an adamantyl group. L ^A41 is a single bond or an alkanediyl group having 1 to 4 carbon atoms. ^{Q 1} and Q ² are as defined above.
Specific examples of the anion represented by formula (IA) include the anions described in JP-A-2010-204646.

The anion represented by formula (IA) preferably includes anions represented by formulas (Ia-1) to (Ia-38).

Among these, anions represented by any of formulas (I-a-1) to (I-a-3), (I-a-7) to (I-a-19), and (I-a-22) to (I-a-38) are preferred.

Examples of the sulfonylimide anion represented by ^AI- include the following.
Sulfonylmethide anions represented ^by AI include the following:
Examples of the carboxylate anion represented by ^AI- include the following.

Specific examples of the salt (I) include salts formed by any combination of the above-mentioned cations and anions. Specific examples of the salt (I) are shown in the table below.
In the table below, each symbol represents the symbol attached to the structure representing the above-mentioned anion or cation, and "to" indicates that the salt (I) corresponds to the anion (I). For example, salt (I-1) is a salt consisting of an anion represented by formula (I-a-1) and a cation represented by formula (I-c-1), salt (I-2) is a salt consisting of an anion represented by formula (I-a-2) and a cation represented by formula (I-c-1), and salt (I-39) is a salt consisting of an anion represented by formula (I-a-1) and a cation represented by formula (I-c-2).

Among these, salt (I) is preferably a salt combining an anion represented by any one of formulas (I-a-1) to (I-a-4), (I-a-7) to (I-a-11), (I-a-14) to (I-a-30), and (I-a-35) to (I-a-38) with a cation represented by any one of formulas (I-c-1) to (I-c-53), specifically salts (I-1) to (I-4), (I-7) to (I-11), (I-14) to (I-30), (I-35) to (I-38), (I-39) to (I-42), (I-45) to (I-49), and (I-52) to (I- 68), salt (I-73) to salt (I-76), salt (I-77) to salt (I-80), salt (I-83) to salt (I-87), salt (I-90) to salt (I-106), salt (I-111) to salt (I-114), salt (I-115) to salt (I-118), salt (I-121) to salt (I-125), salt (I-128 ) to salt (I-144), salt (I-149) to salt (I-152), salt (I-153) to salt (I-156), salt (I-159) to salt (I-163), salt (I-166) to salt (I-182), salt (I-187) to salt (I-190), salt (I-191) to salt (I-194), salt (I-197) to salt (I -201), salt (I-204) to salt (I-220), salt (I-225) to salt (I-228), salt (I-229) to salt (I-232), salt (I-235) to salt (I-239), salt (I-242) to salt (I-258), salt (I-263) to salt (I-266), salt (I-267) to salt (I-270) ), salt (I-273) to salt (I-277), salt (I-280) to salt (I-296), salt (I-301) to salt (I-304), salt (I-305) to salt (I-308), salt (I-311) to salt (I-315), salt (I-318) to salt (I-334), salt (I-339) to salt (I-342), salt ( Salt (I-343) to salt (I-346), salt (I-349) to salt (I-353), salt (I-356) to salt (I-372), salt (I-377) to salt (I-380), salt (I-381) to salt (I-384), salt (I-387) to salt (I-391), salt (I-394) to salt (I-410), salt (I-41 5) ~ Salt (I-418), Salt (I-419) ~ Salt (I-422), Salt (I-425) ~ Salt (I-429), Salt (I-432) ~ Salt (I-448), Salt (I-453) ~ Salt (I-456), Salt (I-457) ~ Salt (I-460), Salt (I-463) ~ Salt (I-467), Salt (I-470) ~ Salt ( I-486), salt (I-491) to salt (I-494), salt (I-495) to salt (I-498), salt (I-501) to salt (I-505), salt (I-508) to salt (I-524), salt (I-529) to salt (I-532), salt (I-533) to salt (I-536), salt (I-539) to salt (I-54) 3), Salt (I-546) to Salt (I-562), Salt (I-567) to Salt (I-570), Salt (I-571) to Salt (I-574), Salt (I-577) to Salt (I-581), Salt (I-584) to Salt (I-600), Salt (I-605) to Salt (I-608), Salt (I-609) to Salt (I-612), Salt (I-615) to salt (I-619), salt (I-622) to salt (I-638), salt (I-643) to salt (I-646), salt (I-647) to salt (I-650), salt (I-653) to salt (I-657), salt (I-660) to salt (I-676), salt (I-681) to salt (I-684), salt (I-6 85) ~ Salt (I-688), Salt (I-691) ~ Salt (I-695), Salt (I-698) ~ Salt (I-714), Salt (I-719) ~ Salt (I-722), Salt (I-723) ~ Salt (I-726), Salt (I-729) ~ Salt (I-733), Salt (I-736) ~ Salt (I-752), Salt (I-757) ~ Salt (I-760), salt (I-761) to salt (I-764), salt (I-767) to salt (I-771), salt (I-774) to salt (I-790), salt (I-795) to salt (I-798), salt (I-799) to salt (I-802), salt (I-805) to salt (I-809), salt (I-812) to salt (I-8 28), salt (I-833) to salt (I-836), salt (I-837) to salt (I-840), salt (I-843) to salt (I-847), salt (I-850) to salt (I-866), salt (I-871) to salt (I-874), salt (I-875) to salt (I-878), salt (I-881) to salt (I-885), Salt (I-888) to Salt (I-904), Salt (I-909) to Salt (I-912), Salt (I-913) to Salt (I-916), Salt (I-919) to Salt (I-923), Salt (I-926) to Salt (I-942), Salt (I-947) to Salt (I-950), Salt (I-951) to Salt (I-954), Salt (I- 957) to salt (I-961), salt (I-964) to salt (I-980), salt (I-985) to salt (I-988), salt (I-989) to salt (I-992), salt (I-995) to salt (I-999), salt (I-1002) to salt (I-1018), salt (I-1023) to salt (I-1026), salt (I-1 027) to salt (I-1030), salt (I-1033) to salt (I-1037), salt (I-1040) to salt (I-1056), salt (I-1061) to salt (I-1064), salt (I-1065) to salt (I-1068), salt (I-1071) to salt (I-1075), salt (I-1078) to salt (I-1 094), salt (I-1099) to salt (I-1102), salt (I-1103) to salt (I-1106), salt (I-1109) to salt (I-1113), salt (I-1116) to salt (I-1132), salt (I-1137) to salt (I-1140), salt (I-1141) to salt (I-1144), salt (I-1 147) to salt (I-1151), salt (I-1154) to salt (I-1170), salt (I-1175) to salt (I-1178), salt (I-1179) to salt (I-1182), salt (I-1185) to salt (I-1189), salt (I-1192) to salt (I-1208), salt (I-1213) to salt (I-1 216), salt (I-1217) to salt (I-1220), salt (I-1223) to salt (I-1227), salt (I-1230) to salt (I-1246), salt (I-1251) to salt (I-1254), salt (I-1255) to salt (I-1258), salt (I-1261) to salt (I-1265), salt (I-12 68) ~ Salt (I-1284), Salt (I-1289) ~ Salt (I-1292), Salt (I-1293) ~ Salt (I-1296), Salt (I-1299) ~ Salt (I-1303), Salt (I-1306) ~ Salt (I-1322), Salt (I-1327) ~ Salt (I-1330), Salt (I-1331) ~ Salt (I-13 34), salt (I-1337) to salt (I-1341), salt (I-1344) to salt (I-1360), salt (I-1365) to salt (I-1368), salt (I-1369) to salt (I-1372), salt (I-1375) to salt (I-1379), salt (I-1382) to salt (I-1398), salt (I-14 03) ~ Salt (I-1406), Salt (I-1407) ~ Salt (I-1410), Salt (I-1413) ~ Salt (I-1417), Salt (I-1420) ~ Salt (I-1436), Salt (I-1441) ~ Salt (I-1444), Salt (I-1445) ~ Salt (I-1448), Salt (I-1451) ~ Salt (I-14 55), Salt (I-1458) to Salt (I-1474), Salt (I-1479) to Salt (I-1482), Salt (I-1483) to Salt (I-1486), Salt (I-1489) to Salt (I-1493), Salt (I-1496) to Salt (I-1512), Salt (I-1517) to Salt (I-1520), Salt (I-152 1) ~ Salt (I-1524), Salt (I-1527) ~ Salt (I-1531), Salt (I-1534) ~ Salt (I-1550), Salt (I-1555) ~ Salt (I-1558), Salt (I-1559) ~ Salt (I-1562), Salt (I-1565) ~ Salt (I-1569), Salt (I-1572) ~ Salt (I-158 8), Salt (I-1593) to Salt (I-1596), Salt (I-1597) to Salt (I-1600), Salt (I-1603) to Salt (I-1607), Salt (I-1610) to Salt (I-1626), Salt (I-1631) to Salt (I-1634), Salt (I-1635) to Salt (I-1638), Salt (I-164 1) ~ Salt (I-1645), Salt (I-1648) ~ Salt (I-1664), Salt (I-1669) ~ Salt (I-1672), Salt (I-1673) ~ Salt (I-1676), Salt (I-1679) ~ Salt (I-1683), Salt (I-1686) ~ Salt (I-1702), Salt (I-1707) ~ Salt (I-171) 0), Salt (I-1711) to Salt (I-1714), Salt (I-1717) to Salt (I-1721), Salt (I-1724) to Salt (I-1740), Salt (I-1745) to Salt (I-1748), Salt (I-1749) to Salt (I-1752), Salt (I-1755 to Salt (I-1759), Salt (I-1762) ) ~ Salt (I-1778), Salt (I-1783) ~ Salt (I-1786), Salt (I-1787) ~ Salt (I-1790), Salt (I-1793) ~ Salt (I-1797), Salt (I-1800) ~ Salt (I-1816), Salt (I-1821) ~ Salt (I-1824), Salt (I-1825 ~ Salt (I-1828) ), Salt (I-1831) ~ Salt (I-1835), Salt (I-1838) ~ Salt (I-1854), Salt (I-1859) ~ Salt (I-1862), Salt (I-1863) ~ Salt (I-1866), Salt (I-1869) ~ Salt (I-1873), Salt (I-1876) ~ Salt (I-1892), Salt (I-1897) Salt (I-1900) to salt (I-1901) to salt (I-1904), salt (I-1907) to salt (I-1911), salt (I-1914) to salt (I-1930), salt (I-1935) to salt (I-1938), salt (I-1939) to salt (I-1942), salt (I-1945) to salt (I-1949), salt (I-1952) to salt (I-1968), salt (I-1973) to salt (I-1976), salt (I-1977) to salt (I-1980), salt (I-1983) to salt (I-1987), salt (I-1990) to salt (I-2006), and salt (I-2011) to salt (I-2014) are preferred.

<Method for producing salt (I)>
The salt (I) can be produced by reacting a salt represented by formula (Ia) with a salt represented by formula (Ib) in a solvent.
[In the formula, all symbols have the same meaning as defined above. R ^A , R ^B , and R ^C each independently represent a hydrocarbon group having 1 to 12 carbon atoms, or R ^A , R ^B , and R ^C may combine to form an aromatic ring. R ^D represents a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms.]
Examples of the solvent include chloroform, monochlorobenzene, acetonitrile, and water.
The reaction temperature is usually 15° C. to 80° C., and the reaction time is usually 0.5 to 24 hours.

Examples of the salt represented by formula (I-b) include salts represented by the following formula: These salts can be easily produced by the same method as that described in JP-A Nos. 2011-116747 and 2016-047815, or by known production methods.

The salt (I-a) in which R ¹ , R ² and R ³ are -OL ¹ -CO-O-R ¹⁰ (the salt represented by formula (I-a1)) can be produced by reacting the salt represented by formula (I-c) with the compound represented by formula (I-d) in a solvent in the presence of a base catalyst.
[In the formula, all symbols have the same meanings as defined above.]
Examples of the base include potassium carbonate, potassium iodide, pyridine, and triethylamine.
Examples of the solvent include chloroform, monochlorobenzene, dimethylformamide, acetonitrile, ethyl acetate, and water.
The reaction temperature is usually 15° C. to 80° C., and the reaction time is usually 0.5 to 24 hours.

Examples of compounds represented by formula (I-d) include the compounds represented by the following formulas, which are readily available on the market and can also be easily produced by known production methods.

The salt represented by formula (I-c) can be produced by reacting the salt represented by formula (I-e), a compound represented by formula (I-f1), a compound represented by formula (I-f2), and a compound represented by formula (I-f3) in a solvent in the presence of a catalyst.
[In the formula, all symbols have the same meanings as defined above.]
Examples of the catalyst include potassium carbonate and sodium hydride.
Examples of the solvent include chloroform, monochlorobenzene, acetonitrile, and water.
The reaction temperature is usually 15° C. to 100° C., and the reaction time is usually 0.5 to 24 hours.

Examples of the salt represented by formula (Ie) include salts represented by the following formula, which are readily available on the market.

Examples of the compound represented by formula (I-f1), the compound represented by formula (I-f2), and the compound represented by formula (I-f3) include the compounds represented below, which are easily available on the market.

The salt represented by formula (I-c) can also be produced by reacting the salt represented by formula (I-e), the compound represented by formula (I-f4), the compound represented by formula (I-f5), and the compound represented by formula (I-f6) in a solvent in the presence of potassium carbonate, followed by acid treatment.
wherein all symbols have the same meanings as defined above.
R ^ac represents an acid labile group.
Examples of the solvent include chloroform, monochlorobenzene, acetonitrile, and water.
The reaction temperature is usually 15° C. to 100° C., and the reaction time is usually 0.5 to 24 hours.
The acid includes p-toluenesulfonic acid, hydrochloric acid, and the like.

Examples of the compound represented by formula (I-f4), the compound represented by formula (I-f5), and the compound represented by formula (I-f6) include the compounds represented below, which are easily available on the market.

A salt (I-a) in which R ¹ , R ² and R ³ are —O—CO—R ¹⁰ (a salt represented by formula (I-a2)) can be produced by reacting a salt represented by formula (I-c) with a compound represented by formula (I-d2) in a solvent in the presence of a base catalyst.
[In the formula, all symbols have the same meanings as defined above.]
Examples of the base include potassium carbonate, potassium iodide, pyridine, and triethylamine.
Examples of the solvent include chloroform, monochlorobenzene, dimethylformamide, acetonitrile, ethyl acetate, and water.
The reaction temperature is usually 15° C. to 80° C., and the reaction time is usually 0.5 to 24 hours.

Examples of the compound represented by formula (I-d2) include the compounds represented by the following formulas, which are readily available on the market and can also be easily produced by known production methods.

A salt of salt (I-a) in which R ¹ , R ² and R ³ are —O—R ¹⁰ (a salt represented by formula (I-a3)) can be produced by reacting a salt of formula (I-c) with a compound of formula (I-d3) in a solvent in the presence of a base catalyst.
[In the formula, all symbols have the same meanings as defined above.]
Examples of the base include sodium hydroxide and potassium hydroxide.
Examples of the solvent include chloroform, monochlorobenzene, dimethylformamide, acetonitrile, ethyl acetate, and water.
The reaction temperature is usually 15° C. to 80° C., and the reaction time is usually 0.5 to 24 hours.

Examples of the compound represented by formula (I-d3) include the compounds represented by the following formulas, which are readily available on the market and can also be easily produced by known production methods.

A salt of salt (I-a) in which R ¹ , R ² and R ³ are —O—CO—O—R ¹⁰ (a salt represented by formula (I-a4)) can be produced by reacting a salt of formula (I-c) with a compound of formula (I-d3) in a solvent in the presence of carbonyldiimidazole.
[In the formula, all symbols have the same meanings as defined above.]
Examples of the solvent include chloroform, monochlorobenzene, dimethylformamide, acetonitrile, ethyl acetate, and water.
The reaction temperature is usually 15° C. to 80° C., and the reaction time is usually 0.5 to 24 hours.

[Acid Generator]
The acid generator of the present invention is an acid generator containing a salt (I). It may contain one kind of salt (I) or two or more kinds of salts (I).
The acid generator of the present invention may contain, in addition to the salt (I), an acid generator known in the resist field (hereinafter, sometimes referred to as "acid generator (B)"). The acid generator (B) may be used alone or in combination of two or more kinds.

The acid generator (B) may be either nonionic or ionic. Nonionic acid generators include sulfonate esters (e.g., 2-nitrobenzyl ester, aromatic sulfonate, oxime sulfonate, N-sulfonyloxyimide, sulfonyloxyketone, diazonaphthoquinone 4-sulfonate), sulfones (e.g., disulfone, ketosulfone, sulfonyldiazomethane), etc. Ionic acid generators include onium salts containing onium cations (e.g., diazonium salts, phosphonium salts, sulfonium salts, iodonium salts). Anions of onium salts include sulfonate anions, sulfonylimide anions, sulfonylmethide anions, etc.

The acid generator (B) may be a compound that generates an acid when exposed to radiation, as described in JP-A Nos. 63-26653, 55-164824, 62-69263, 63-146038, 63-163452, 62-153853, 63-146029, U.S. Pat. No. 3,779,778, 3,849,137, German Patent No. 3,914,407, or European Patent No. 126,712. Compounds produced by known methods may also be used. Two or more types of acid generator (B) may be used in combination.

The acid generator (B) is preferably a fluorine-containing acid generator, and more preferably a salt represented by formula (B1) (hereinafter, sometimes referred to as "acid generator (B1)", excluding salt (I)).
[In formula (B1),
Q ^b1 and Q ^b2 each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms.
L ^b1 represents a divalent saturated hydrocarbon group having 1 to 24 carbon atoms, in which —CH ₂ — contained in the divalent saturated hydrocarbon group may be replaced by —O— or —CO—, and in which a hydrogen atom contained in the divalent saturated hydrocarbon group may be substituted by a fluorine atom or a hydroxy group.
Y represents an optionally substituted methyl group or an optionally substituted alicyclic hydrocarbon group having 3 to 24 carbon atoms, and one —CH ₂ — contained in the alicyclic hydrocarbon group may be replaced by —O—, —SO ₂ — or —CO—.
Z1 ⁺ represents an organic cation.

Q ^b1 , Q ^b2 , L ^b1 and Y in formula (B1) are the same as Q ¹ , Q ² , L ¹ and Y ¹ in formula (IA) above, respectively.
Examples of the sulfonate anion in formula (B1) include the same anions as those represented by formula (IA).

Examples of the organic cation for Z1 ⁺ include organic onium cations, organic sulfonium cations, organic iodonium cations, organic ammonium cations, benzothiazolium cations, and organic phosphonium cations. Among these, organic sulfonium cations and organic iodonium cations are preferred, and arylsulfonium cations are more preferred. Specific examples include cations represented by any of formulas (b2-1) to (b2-4) (hereinafter, these may be referred to as "cation (b2-1)" or the like depending on the formula number).

In formulas (b2-1) to (b2-4),
R ^b4 to R ^b6 each independently represent a chain hydrocarbon group having 1 to 30 carbon atoms, an alicyclic hydrocarbon group having 3 to 36 carbon atoms, or an aromatic hydrocarbon group having 6 to 36 carbon atoms, a hydrogen atom contained in the chain hydrocarbon group may be substituted with a hydroxy group, an alkoxy group having 1 to 12 carbon atoms, an alicyclic hydrocarbon group having 3 to 12 carbon atoms, or an aromatic hydrocarbon group having 6 to 18 carbon atoms, a hydrogen atom contained in the alicyclic hydrocarbon group may be substituted with a halogen atom, an aliphatic hydrocarbon group having 1 to 18 carbon atoms, an alkylcarbonyl group having 2 to 4 carbon atoms, or a glycidyloxy group, and a hydrogen atom contained in the aromatic hydrocarbon group may be substituted with a halogen atom, a hydroxy group, an aliphatic hydrocarbon group having 1 to 18 carbon atoms, a fluorinated alkyl group having 1 to 12 carbon atoms, or an alkoxy group having 1 to 12 carbon atoms.
R ^b4 and R ^b5 may be bonded to each other to form a ring together with the sulfur atom to which they are bonded, and —CH ₂ — contained in the ring may be replaced by —O—, —S— or —CO—.
R ^b7 and R ^b8 each independently represent a halogen atom, a hydroxy group, an aliphatic hydrocarbon group having 1 to 12 carbon atoms, or an alkoxy group having 1 to 12 carbon atoms.
m2 and n2 each independently represent an integer of 0 to 5.
When m2 is 2 or more, multiple R ^b7s may be the same or different, and when n2 is 2 or more, multiple R ^b8s may be the same or different.
R ^b9 and R ^b10 each independently represent a chain hydrocarbon group having 1 to 36 carbon atoms or an alicyclic hydrocarbon group having 3 to 36 carbon atoms.
R ^b9 and R ^b10 may be bonded to each other to form a ring together with the sulfur atom to which they are bonded, and --CH ₂ -- contained in the ring may be replaced with --O--, --S-- or --CO--.
R ^b11 represents a hydrogen atom, a chain hydrocarbon group having 1 to 36 carbon atoms, an alicyclic hydrocarbon group having 3 to 36 carbon atoms, or an aromatic hydrocarbon group having 6 to 18 carbon atoms.
R ^b12 represents a chain hydrocarbon group having 1 to 12 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbon atoms, or an aromatic hydrocarbon group having 6 to 18 carbon atoms, and a hydrogen atom contained in the chain hydrocarbon group may be substituted with an aromatic hydrocarbon group having 6 to 18 carbon atoms, or a hydrogen atom contained in the aromatic hydrocarbon group may be substituted with an alkoxy group having 1 to 12 carbon atoms or an alkylcarbonyloxy group having 1 to 12 carbon atoms.
R ^b11 and R ^b12 may be bonded to each other to form a ring including the —CH—CO— to which they are bonded, and —CH ₂ — contained in the ring may be replaced by —O—, —S— or —CO—.
R ^b13 to R ^b18 each independently represent a halogen atom, a hydroxy group, an aliphatic hydrocarbon group having 1 to 12 carbon atoms, a fluorinated alkyl group having 1 to 12 carbon atoms, or an alkoxy group having 1 to 12 carbon atoms.
L ^b31 represents a sulfur atom or an oxygen atom.
o2, p2, s2, and t2 each independently represent an integer of 0 to 5.
q2 and r2 each independently represent an integer of 0 to 4.
u2 represents 0 or 1;
When o2 is 2 or more, multiple R ^b13s are the same or different; when p2 is 2 or more, multiple R ^b14s are the same or different; when q2 is 2 or more, multiple R ^b15s are the same or different; when r2 is 2 or more, multiple R ^b16s are the same or different; when s2 is 2 or more, multiple R ^b17s are the same or different; and when t2 is 2 or more, multiple R ^b18s are the same or different.
The aliphatic hydrocarbon group refers to a chain hydrocarbon group and an alicyclic hydrocarbon group.
Examples of the chain hydrocarbon group include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, pentyl, hexyl, octyl, and 2-ethylhexyl.
In particular, the chain hydrocarbon groups of R ^b9 to R ^b12 preferably have 1 to 12 carbon atoms.
The alicyclic hydrocarbon group may be either monocyclic or polycyclic, and examples of the monocyclic alicyclic hydrocarbon group include cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and cyclodecyl. Examples of the polycyclic alicyclic hydrocarbon group include decahydronaphthyl, adamantyl, and norbornyl groups, as well as the following groups:
In particular, the alicyclic hydrocarbon groups of R ^b9 to R ^b12 preferably have 3 to 18 carbon atoms, and more preferably have 4 to 12 carbon atoms.
Examples of the alicyclic hydrocarbon group in which a hydrogen atom is substituted with an aliphatic hydrocarbon group include a methylcyclohexyl group, a dimethylcyclohexyl group, a 2-methyladamantan-2-yl group, a 2-ethyladamantan-2-yl group, a 2-isopropyladamantan-2-yl group, a methylnorbornyl group, an isobornyl group, etc. In the alicyclic hydrocarbon group in which a hydrogen atom is substituted with an aliphatic hydrocarbon group, the total number of carbon atoms in the alicyclic hydrocarbon group and the aliphatic hydrocarbon group is preferably 20 or less.
The fluorinated alkyl group refers to an alkyl group having 1 to 12 carbon atoms and a fluorine atom, and examples thereof include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a perfluorobutyl group, etc. The number of carbon atoms in the fluorinated alkyl group is preferably 1 to 9, more preferably 1 to 6, and even more preferably 1 to 4.
Examples of aromatic hydrocarbon groups include aryl groups such as phenyl, biphenyl, naphthyl, and phenanthryl. The aromatic hydrocarbon group may have a chain hydrocarbon group or an alicyclic hydrocarbon group, and examples include aromatic hydrocarbon groups having a chain hydrocarbon group of 1 to 18 carbon atoms (such as tolyl, xylyl, cumenyl, mesityl, p-ethylphenyl, p-tert-butylphenyl, 2,6-diethylphenyl, and 2-methyl-6-ethylphenyl), and aromatic hydrocarbon groups having an alicyclic hydrocarbon group of 3 to 18 carbon atoms (such as p-cyclohexylphenyl and p-adamantylphenyl). When the aromatic hydrocarbon group has a chain hydrocarbon group or an alicyclic hydrocarbon group, chain hydrocarbon groups having 1 to 18 carbon atoms and alicyclic hydrocarbon groups having 3 to 18 carbon atoms are preferred.
Examples of aromatic hydrocarbon groups in which hydrogen atoms are substituted with alkoxy groups include p-methoxyphenyl groups.
Examples of the chain hydrocarbon group in which a hydrogen atom is substituted with an aromatic hydrocarbon group include aralkyl groups such as a benzyl group, a phenethyl group, a phenylpropyl group, a trityl group, a naphthylmethyl group, and a naphthylethyl group.
Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group, an octyloxy group, a decyloxy group, and a dodecyloxy group.
Examples of the alkylcarbonyl group include an acetyl group, a propionyl group, and a butyryl group.
Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.
Examples of the alkylcarbonyloxy group include a methylcarbonyloxy group, an ethylcarbonyloxy group, a propylcarbonyloxy group, an isopropylcarbonyloxy group, a butylcarbonyloxy group, a sec-butylcarbonyloxy group, a tert-butylcarbonyloxy group, a pentylcarbonyloxy group, a hexylcarbonyloxy group, an octylcarbonyloxy group, and a 2-ethylhexylcarbonyloxy group.
The ring formed by R ^b4 and R ^b5 bonding to each other and together with the sulfur atom to which they are bonded may be any of monocyclic, polycyclic, aromatic, non-aromatic, saturated and unsaturated rings. This ring may be a ring having 3 to 18 carbon atoms, preferably a ring having 4 to 18 carbon atoms. Furthermore, the ring containing a sulfur atom may be a 3- to 12-membered ring, preferably a 3- to 7-membered ring, and examples thereof include the rings shown below. * represents a bond.
The ring formed by R ^b9 and R ^b10 together may be any of monocyclic, polycyclic, aromatic, non-aromatic, saturated and unsaturated rings. This ring may be a 3- to 12-membered ring, preferably a 3- to 7-membered ring. Examples of this ring include a thiolan-1-ium ring (tetrahydrothiophenium ring), a thian-1-ium ring, and a 1,4-oxathian-4-ium ring.
The ring formed by R ^b11 and R ^b12 together may be any of monocyclic, polycyclic, aromatic, non-aromatic, saturated and unsaturated rings. This ring may be a 3- to 12-membered ring, preferably a 3- to 7-membered ring. Examples of the ring include an oxocycloheptane ring, an oxocyclohexane ring, an oxonorbornane ring, and an oxoadamantane ring.

Among the cations (b2-1) to (b2-4), the cation (b2-1) is preferred.
Examples of the cation (b2-1) include the following cations.

Examples of the cation (b2-2) include the following cations.

Examples of the cation (b2-3) include the following cations.

Examples of the cation (b2-4) include the following cations.

Acid generator (B) is a combination of the above-mentioned anions and the above-mentioned organic cations, and these can be combined in any desired manner. Acid generator (B) is preferably a combination of an anion represented by any of formulas (I-a-1) to (I-a-3), (I-a-7) to (I-a-16), (I-a-18), (I-a-19), and (I-a-22) to (I-a-38) with cation (b2-1), cation (b2-3), or cation (b2-4).

The acid generator (B) is preferably one represented by any of formulas (B1-1) to (B1-56). Of these, those containing an arylsulfonium cation are preferred, and those represented by formulas (B1-1) to (B1-3), (B1-5) to (B1-7), (B1-11) to (B1-14), (B1-20) to (B1-26), (B1-29), and (B1-31) to (B1-56) are particularly preferred.

When salt (I) and acid generator (B) are contained as acid generators, the ratio of the salt (I) to acid generator (B) (mass ratio; salt (I):acid generator (B)) is typically 1:99 to 99:1, preferably 2:98 to 98:2, more preferably 5:95 to 95:5, even more preferably 10:90 to 90:10, and particularly preferably 15:85 to 85:15.

[Resist Composition]
The resist composition of the present invention contains an acid generator containing a salt (I) and a resin having an acid labile group (hereinafter may be referred to as "resin (A)"). Here, the "acid labile group" refers to a group that has a leaving group and that is eliminated upon contact with an acid, converting the structural unit into a structural unit having a hydrophilic group (for example, a hydroxy group or a carboxy group).
The resist composition of the present invention preferably contains a quencher such as a salt that generates an acid that is weaker in acidity than the acid generated from the acid generator (hereinafter may be referred to as "quencher (C)"), and preferably contains a solvent (hereinafter may be referred to as "solvent (E)").

<Acid Generator>
In the resist composition of the present invention, the total content of the acid generators is preferably 1 part by mass or more and 45 parts by mass or less, more preferably 1 part by mass or more and 40 parts by mass or less, even more preferably 3 parts by mass or more and 40 parts by mass or less, still more preferably 3 parts by mass or more and 35 parts by mass or less, and particularly preferably 5 parts by mass or more and 35 parts by mass or less, relative to 100 parts by mass of the resin (A) described below.

<Resin (A)>
Resin (A) has a structural unit having an acid labile group (hereinafter may be referred to as "structural unit (a1)"). Resin (A) preferably further contains a structural unit other than the structural unit (a1). Examples of structural units other than the structural unit (a1) include a structural unit not having an acid labile group (hereinafter may be referred to as "structural unit (s)"), structural units other than the structural unit (a1) and the structural unit (s) (for example, a structural unit having a halogen atom (hereinafter may be referred to as "structural unit (a4)") described below, a structural unit having a non-leaving hydrocarbon group (hereinafter may be referred to as "structural unit (a5)") described below), and other structural units derived from monomers known in the art.

<Structural Unit (a1)>
The structural unit (a1) is derived from a monomer having an acid labile group (hereinafter, sometimes referred to as "monomer (a1)").
The acid labile group contained in the resin (A) is preferably a group represented by formula (1) (hereinafter also referred to as group (1)) and/or a group represented by formula (2) (hereinafter also referred to as group (2)).
[In formula (1), R ^a1 , R ^a2 and R ^a3 each independently represent an alkyl group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to 20 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, or a group combining these, or R ^a1 and R ^a2 bond to each other to form an alicyclic hydrocarbon group having 3 to 20 carbon atoms together with the carbon atom to which they are bonded.]
ma and na each independently represent 0 or 1, and at least one of ma and na represents 1.
* represents a bond.
[In formula (2), R ^a1' and R ^a2' each independently represent a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms; R ^a3' represents a hydrocarbon group having 1 to 20 carbon atoms; or R ^a2' and R ^a3' are bonded to each other to form, together with the carbon atom to which they are bonded and X, a heterocyclic group having 3 to 20 carbon atoms, and —CH ₂ — contained in the hydrocarbon group and the heterocyclic group may be replaced by —O— or —S—.]
X represents an oxygen atom or a sulfur atom.
na' represents 0 or 1.
* represents a bond.

Examples of the alkyl group for R ^a1 , R ^a2 and R ^a3 include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group and an octyl group.
Examples of the alkenyl group for R ^a1 , R ^a2 and R ^a3 include an ethenyl group, a propenyl group, an isopropenyl group, a butenyl group, an isobutenyl group, a tert-butenyl group, a pentenyl group, a hexenyl group, a heptenyl group, an octynyl group, an isooctynyl group and a nonenyl group.
The alicyclic hydrocarbon groups for R ^a1 , R ^a2 and R ^a3 may be either monocyclic or polycyclic. Examples of monocyclic alicyclic hydrocarbon groups include cycloalkyl groups such as a cyclopentyl group, a cyclohexyl group, a cycloheptyl group and a cyclooctyl group. Examples of polycyclic alicyclic hydrocarbon groups include a decahydronaphthyl group, an adamantyl group, a norbornyl group and the following groups (* represents a bond): The number of carbon atoms in the alicyclic hydrocarbon groups for ^{R a1} , R ^a2 and R ^a3 is preferably 3 to 16.
Examples of the aromatic hydrocarbon group for R ^a1 , R ^a2 and R ^a3 include aryl groups such as a phenyl group, a naphthyl group, an anthryl group, a biphenyl group and a phenanthryl group.
Examples of the combined group include a group in which the above-mentioned alkyl group and alicyclic hydrocarbon group are combined (for example, an alkylcycloalkyl group or a cycloalkylalkyl group), an aralkyl group such as a benzyl group, an aromatic hydrocarbon group having an alkyl group (for example, a p-methylphenyl group, a p-tert-butylphenyl group, a tolyl group, a xylyl group, a cumenyl group, a mesityl group, a 2,6-diethylphenyl group, a 2-methyl-6-ethylphenyl group), an aromatic hydrocarbon group having an alicyclic hydrocarbon group (for example, a p-cyclohexylphenyl group, a p-adamantylphenyl group), and an aryl-cycloalkyl group such as a phenylcyclohexyl group.
Preferably, ma is 0 and na is 1.
When R ^a1 and R ^a2 are bonded to each other to form an alicyclic hydrocarbon group, examples of -C(R ^a1 )(R ^a2 )(R ^a3 ) include the following groups. The alicyclic hydrocarbon group preferably has 3 to 12 carbon atoms. * represents a bond to -O-.

Examples of the hydrocarbon group for R ^a1′ , R ^a2′ and R ^a3′ include an alkyl group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group and a group formed by combining these groups.
Examples of the alkyl group and alicyclic hydrocarbon group include the same groups as those exemplified for R ^a1 , R ^a2 and R ^a3 .
Examples of the aromatic hydrocarbon group include aryl groups such as a phenyl group, a naphthyl group, an anthryl group, a biphenyl group, and a phenanthryl group.
Examples of the combined group include a group in which the above-mentioned alkyl group and alicyclic hydrocarbon group are combined (for example, an alkylcycloalkyl group or a cycloalkylalkyl group), an aralkyl group such as a benzyl group, an aromatic hydrocarbon group having an alkyl group (for example, a p-methylphenyl group, a p-tert-butylphenyl group, a tolyl group, a xylyl group, a cumenyl group, a mesityl group, a 2,6-diethylphenyl group, a 2-methyl-6-ethylphenyl group), an aromatic hydrocarbon group having an alicyclic hydrocarbon group (for example, a p-cyclohexylphenyl group, a p-adamantylphenyl group), and an aryl-cycloalkyl group such as a phenylcyclohexyl group.
When R ^a2′ and R ^a3′ are bonded to each other to form a heterocyclic group together with the carbon atom to which they are bonded and X, examples of —C(R ^a1′ )(R ^a2′ )—X—R ^a3′ include the following groups: * represents a bond.
At least one of R ^a1′ and R ^a2′ is preferably a hydrogen atom.
na' is preferably 0.

Examples of the group (1) include the following groups.
A group in which R ^a1 , R ^a2 and R ^a3 in formula (1) are alkyl groups, ma = 0 and na = 1. The group is preferably a tert-butoxycarbonyl group.
A group in which, in formula (1), R ^a1 and R ^a2 together with the carbon atom to which they are bonded form an adamantyl group, R ^a3 is an alkyl group, ma=0, and na=1.
A group represented by formula (1), in which R ^a1 and R ^a2 each independently represent an alkyl group, R ^a3 represents an adamantyl group, ma=0, and na=1.
Specific examples of the group (1) include the following: * represents a bond.

Specific examples of the group (2) include the following groups: * represents a bond.

Monomer (a1) is preferably a monomer having an acid labile group and an ethylenically unsaturated bond, more preferably a (meth)acrylic monomer having an acid labile group.

Among (meth)acrylic monomers having an acid labile group, those having an alicyclic hydrocarbon group having 5 to 20 carbon atoms are preferred. The use of a resin (A) having structural units derived from a monomer (a1) having a bulky structure such as an alicyclic hydrocarbon group in a resist composition can improve the resolution of the resist pattern.

The structural unit derived from a (meth)acrylic monomer having group (1) is preferably a structural unit represented by formula (a1-0) (hereinafter, may be referred to as structural unit (a1-0)), a structural unit represented by formula (a1-1) (hereinafter, may be referred to as structural unit (a1-1)), or a structural unit represented by formula (a1-2) (hereinafter, may be referred to as structural unit (a1-2)). More preferably, it is at least one structural unit selected from the group consisting of the structural unit (a1-1) and the structural unit (a1-2). These may be used alone or in combination of two or more.
[In formula (a1-0), formula (a1-1) and formula (a1-2),
L ^a01 , L ^a1 and L ^a2 each independently represent —O— or *-O—(CH ₂ ) _k1 —CO—O—, where k1 represents an integer of 1 to 7, and * represents a bond to —CO—.
R ^a01 , R ^a4 and R ^a5 each independently represent a hydrogen atom, a halogen atom or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom.
R ^a02 , R ^a03 and R ^a04 each independently represent an alkyl group having 1 to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms or a combination thereof.
R ^a6 and R ^a7 each independently represent an alkyl group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, or a group formed by combining these.
m1 represents an integer of 0 to 14.
n1 represents an integer of 0 to 10.
n1′ represents an integer of 0 to 3.]

R ^a01 , R ^a4 and R ^a5 are preferably a hydrogen atom or a methyl group, more preferably a methyl group.
L ^a01 , L ^a1 and L ^a2 are preferably an oxygen atom or *-O-(CH ₂ ) _k01 -CO-O- (wherein k01 is preferably an integer of 1 to 4, more preferably 1), and more preferably an oxygen atom.
Examples of the alkyl group, alicyclic hydrocarbon group, aromatic hydrocarbon group, and combinations thereof for R ^a02 , R ^a03 , and R ^a04 include the same groups as those exemplified for R ^a1 , R ^a2 , and R ^a3 in formula (1).
Examples of the alkyl group, alkenyl group, alicyclic hydrocarbon group, aromatic hydrocarbon group, and combinations thereof for R ^a6 and R ^a7 include the same groups as those exemplified for R ^a1 , R ^a2 , and R ^a3 in formula (1).
The alkyl group in R ^a02 , R ^a03 , and R ^a04 is preferably an alkyl group having 1 to 6 carbon atoms, more preferably a methyl group or an ethyl group, and even more preferably a methyl group.
The alkyl group in R ^a6 and R ^a7 is preferably an alkyl group having 1 to 6 carbon atoms, more preferably a methyl group, an ethyl group, an isopropyl group, or a t-butyl group, and even more preferably an ethyl group, an isopropyl group, or a t-butyl group.
The alicyclic hydrocarbon groups of R ^a02 , R ^a03 , R ^a04 , R ^a6 and R ^a7 preferably have 5 to 12 carbon atoms, and more preferably 5 to 10 carbon atoms.
The aromatic hydrocarbon groups of R ^a02 , R ^a03 , R ^a04 , R ^a6 and R ^a7 preferably have 6 to 12 carbon atoms, and more preferably 6 to 10 carbon atoms.
In the group in which an alkyl group and an alicyclic hydrocarbon group are combined, the total number of carbon atoms in the combination of the alkyl group and the alicyclic hydrocarbon group is preferably 18 or less.
In the group in which an alkyl group and an aromatic hydrocarbon group are combined, the total number of carbon atoms in the combination of the alkyl group and the aromatic hydrocarbon group is preferably 18 or less.
R ^a02 and R ^a03 are preferably alkyl groups having 1 to 6 carbon atoms, more preferably methyl groups or ethyl groups.
R ^a04 is preferably an alkyl group having 1 to 6 carbon atoms or an alicyclic hydrocarbon group having 5 to 12 carbon atoms, and more preferably a methyl group, an ethyl group, a cyclohexyl group or an adamantyl group.
R ^a6 and R ^a7 are preferably an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an aromatic hydrocarbon group having 6 to 12 carbon atoms, more preferably a methyl group, an ethyl group, an isopropyl group, a t-butyl group, an ethenyl group, a phenyl group, or a naphthyl group, and even more preferably an ethyl group, an isopropyl group, a t-butyl group, an ethenyl group, or a phenyl group.
m1 is preferably an integer of 0 to 3, and more preferably 0 or 1.
n1 is preferably an integer of 0 to 3, and more preferably 0 or 1.
n1' is preferably 0 or 1.

Examples of the structural unit (a1-0) include structural units represented by any one of formulas (a1-0-1) to (a1-0-18) and structural units in which the methyl group corresponding to R ^a01 in the structural unit (a1-0) has been replaced with a hydrogen atom, a halogen atom, a haloalkyl group, or another alkyl group, and structural units represented by any one of formulas (a1-0-1) to (a1-0-10), (a1-0-13), and (a1-0-14) are preferred.

Examples of the structural unit (a1-1) include structural units derived from monomers described in JP 2010-204646 A. Among these, structural units represented by any one of formulas (a1-1-1) to (a1-1-7) and structural units in which the methyl group corresponding to R ^a4 in the structural unit (a1-1) has been replaced with a hydrogen atom are preferred, and structural units represented by any one of formulas (a1-1-1) to (a1-1-4) are more preferred.

Examples of the structural unit (a1-2) include structural units represented by any one of formulas (a1-2-1) to (a1-2-14) and structural units in which the methyl group corresponding to R ^a5 in the structural unit (a1-2) has been replaced with a hydrogen atom, a halogen atom, a haloalkyl group, or another alkyl group, and structural units represented by any one of formulas (a1-2-2), (a1-2-5), (a1-2-6), and (a1-2-10) to (a1-2-14) are preferred.

When resin (A) contains structural unit (a1-0) and/or structural unit (a1-1) and/or structural unit (a1-2), the total content of these is typically 10 to 95 mol%, preferably 15 to 90 mol%, more preferably 20 to 85 mol%, even more preferably 25 to 70 mol%, and still more preferably 30 to 70 mol%, based on all structural units in resin (A).

The structural unit (a1) having the group (2) includes a structural unit represented by formula (a1-4) (hereinafter, sometimes referred to as "structural unit (a1-4)").
[In formula (a1-4),
R ^a32 represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom.
R ^a33 represents a halogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkoxyalkyl group having 2 to 12 carbon atoms, an alkoxyalkoxy group having 2 to 12 carbon atoms, an alkylcarbonyl group having 2 to 4 carbon atoms, an alkylcarbonyloxy group having 2 to 4 carbon atoms, an acryloyloxy group, or a methacryloyloxy group.
A ^a30 represents a single bond or ^* -X ^a31 -(A ^a32 -X ^a32 ) _nc -, where * represents the bonding site with the carbon atom to which -R ^a32 is bonded.
A ^a32 represents an alkanediyl group having 1 to 6 carbon atoms.
X ^a31 and X ^a32 each independently represent —O—, —CO—O—, or —O—CO—.
nc represents 0 or 1.
Ia represents an integer of 0 to 4. When Ia is an integer of 2 or more, multiple R ^a33s may be the same or different.
R ^a34 and R ^a35 each independently represent a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms, R ^a36 represents a hydrocarbon group having 1 to 20 carbon atoms, or R ^a35 and R ^a36 are bonded to each other to form a divalent hydrocarbon group having 2 to 20 carbon atoms together with the —C—O— to which they are bonded, and —CH ₂ — contained in the hydrocarbon group and the divalent hydrocarbon group may be replaced by —O— or —S—.]

Examples of the halogen atom in R ^a32 and R ^a33 include a fluorine atom, a chlorine atom, and a bromine atom.
Examples of the alkyl group having 1 to 6 carbon atoms which may have a halogen atom for R ^a32 include a trifluoromethyl group, a difluoromethyl group, a methyl group, a perfluoroethyl group, a 2,2,2-trifluoroethyl group, a 1,1,2,2-tetrafluoroethyl group, an ethyl group, a perfluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group, a propyl group, a perfluorobutyl group, a 1,1,2,2,3,3,4,4-octafluorobutyl group, a butyl group, a perfluoropentyl group, a 2,2,3,3,4,4,5,5,5-nonafluoropentyl group, a pentyl group, a hexyl group, and a perfluorohexyl group.
R ^a32 is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom, a methyl group or an ethyl group, and even more preferably a hydrogen atom or a methyl group.
Examples of the alkyl group for R ^a33 include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, and a hexyl group.
Examples of the alkoxy group for R ^a33 include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, a sec-butoxy group, a tert-butoxy group, a pentyloxy group, and a hexyloxy group. The alkoxy group is preferably an alkoxy group having 1 to 4 carbon atoms, more preferably a methoxy group or an ethoxy group, and even more preferably a methoxy group.
Examples of the alkoxyalkyl group for R ^a33 include a methoxymethyl group, an ethoxyethyl group, a propoxymethyl group, an isopropoxymethyl group, a butoxymethyl group, a sec-butoxymethyl group, and a tert-butoxymethyl group. The alkoxyalkyl group is preferably an alkoxyalkyl group having 2 to 8 carbon atoms, more preferably a methoxymethyl group or an ethoxyethyl group, and even more preferably a methoxymethyl group.
Examples of the alkoxyalkoxy group for R ^a33 include a methoxymethoxy group, a methoxyethoxy group, an ethoxymethoxy group, an ethoxyethoxy group, a propoxymethoxy group, an isopropoxymethoxy group, a butoxymethoxy group, a sec-butoxymethoxy group, and a tert-butoxymethoxy group. The alkoxyalkoxy group is preferably an alkoxyalkoxy group having 2 to 8 carbon atoms, and more preferably a methoxyethyl group or an ethoxyethyl group.
Examples of the alkylcarbonyl group for R ^a33 include an acetyl group, a propionyl group, a butyryl group, etc. The alkylcarbonyl group is preferably an alkylcarbonyl group having 2 to 3 carbon atoms, and more preferably an acetyl group.
Examples of the alkylcarbonyloxy group for R ^a33 include an acetyloxy group, a propionyloxy group, and a butyryloxy group. The alkylcarbonyloxy group is preferably an alkylcarbonyloxy group having 2 to 3 carbon atoms, and more preferably an acetyloxy group.
R ^a33 is preferably a halogen atom, a hydroxy group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an alkoxyalkoxy group having 2 to 8 carbon atoms, more preferably a fluorine atom, an iodine atom, a hydroxy group, a methyl group, a methoxy group, an ethoxy group, an ethoxyethoxy group, or an ethoxymethoxy group, and even more preferably a fluorine atom, an iodine atom, a hydroxy group, a methyl group, a methoxy group, or an ethoxyethoxy group.

Examples of *-X ^a31 -(A ^a32 -X ^a32 ) _nc - include *-O-, *-CO-O-, *-O-CO-, *-CO-O-A ^a32 -CO-O-, *-O-CO-A ^a32 -O-, *-O-A ^a32 -CO-O-, *-CO-O-A ^a32 -O-CO-, *-O-CO-A ^a32 -O-CO-. Of these, *-CO-O-, *-CO-O-A ^a32 -CO-O- or *-O-A ^a32 -CO-O- are preferred.

Examples of the alkanediyl group include a methylene group, an ethylene group, a propane-1,3-diyl group, a propane-1,2-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diyl group, a butane-1,3-diyl group, a 2-methylpropane-1,3-diyl group, a 2-methylpropane-1,2-diyl group, a pentane-1,4-diyl group, and a 2-methylbutane-1,4-diyl group.
A ^a32 is preferably a methylene group or an ethylene group.

A ^a30 is preferably a single bond, *-CO-O-, or *-CO-O-A ^a32 -CO-O-, more preferably a single bond, *-CO-O-, or *-CO-O-CH ₂ -CO-O-, and even more preferably a single bond or *-CO-O-.

Ia is preferably 0, 1 or 2, more preferably 0 or 1, and even more preferably 0.
Examples of the hydrocarbon group for R ^a34 , R ^a35 and R ^a36 include an alkyl group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group and a group formed by combining these groups.
Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, and an octyl group.
The alicyclic hydrocarbon group may be either monocyclic or polycyclic. Examples of monocyclic alicyclic hydrocarbon groups include cycloalkyl groups such as cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl. Examples of polycyclic alicyclic hydrocarbon groups include decahydronaphthyl, adamantyl, and norbornyl groups, as well as the following groups (* indicates a bonding site):
Examples of the aromatic hydrocarbon group include aryl groups such as a phenyl group, a naphthyl group, an anthryl group, a biphenyl group, and a phenanthryl group.
Examples of the combined group include a group combining the above-mentioned alkyl group and alicyclic hydrocarbon group (for example, a cycloalkylalkyl group), aralkyl groups such as a benzyl group, aromatic hydrocarbon groups having an alkyl group (e.g., a p-methylphenyl group, a p-tert-butylphenyl group, a tolyl group, a xylyl group, a cumenyl group, a mesityl group, a 2,6-diethylphenyl group, a 2-methyl-6-ethylphenyl group, etc.), aromatic hydrocarbon groups having an alicyclic hydrocarbon group (e.g., a p-cyclohexylphenyl group, a p-adamantylphenyl group, etc.), and aryl-cycloalkyl groups such as a phenylcyclohexyl group. In particular, R ^a36 may be an alkyl group having 1 to 18 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, or a group formed by combining these.

R ^a34 is preferably a hydrogen atom.
R ^a35 is preferably a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an alicyclic hydrocarbon group having 3 to 12 carbon atoms, and more preferably a methyl group or an ethyl group.
The hydrocarbon group for R ^a36 is preferably an alkyl group having 1 to 18 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, or a group formed by combining these, and more preferably an alkyl group having 1 to 18 carbon atoms, an alicyclic aliphatic hydrocarbon group having 3 to 18 carbon atoms, or an aralkyl group having 7 to 18 carbon atoms. The alkyl group and the alicyclic hydrocarbon group for R ^a36 are preferably unsubstituted. The aromatic hydrocarbon group for ^{R a36} is preferably an aromatic ring having an aryloxy group having 6 to 10 carbon atoms.

The —OC(R ^a34 )(R ^a35 )—O—R ^a36 in the structural unit (a1-4) is eliminated upon contact with an acid (for example, p-toluenesulfonic acid) to form a hydroxy group.
--OC(R ^a34 )(R ^a35 )--O--R ^a36 is preferably bonded to the o-position or p-position of the benzene ring, and more preferably bonded to the p-position.

Examples of the structural unit (a1-4) include structural units derived from monomers described in JP 2010-204646 A. Preferred examples include structural units represented by formulas (a1-4-1) to (a1-4-18) and structural units in which the hydrogen atom corresponding to R ^a32 in the structural unit (a1-4) is replaced with a methyl group, a halogen atom, a haloalkyl group, or an alkyl group, and more preferred examples include structural units represented by formulas (a1-4-1) to (a1-4-5), (a1-4-10), (a1-4-13), and (a1-4-14).

When resin (A) contains structural unit (a1-4), its content is preferably 10 to 95 mol%, more preferably 15 to 90 mol%, even more preferably 20 to 85 mol%, even more preferably 20 to 70 mol%, and particularly preferably 20 to 60 mol%, based on the total of all structural units in resin (A).

Examples of the structural unit derived from a (meth)acrylic monomer having the group (2) include a structural unit represented by formula (a1-5) (hereinafter, sometimes referred to as "structural unit (a1-5)").
In formula (a1-5),
R ^a8 represents an alkyl group having 1 to 6 carbon atoms which may have one or more halogen atoms, a hydrogen atom, or a halogen atom.
Z ^a1 represents a single bond or *-(CH ₂ ) _h3 -CO-L ⁵⁴ -, where h3 represents an integer of 1 to 4, and * represents a bond to L ⁵¹ .
L ⁵¹ , L ⁵² , L ⁵³ and L ⁵⁴ each independently represent —O— or —S—.
s1 represents an integer of 1 to 3.
s1' represents an integer of 0 to 3.

Examples of halogen atoms include fluorine atoms and chlorine atoms, with fluorine atoms being preferred.
Examples of the alkyl group having 1 to 6 carbon atoms which may have a halogen atom include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a fluoromethyl group, and a trifluoromethyl group.
In formula (a1-5), R ^a8 is preferably a hydrogen atom, a methyl group or a trifluoromethyl group.
L ⁵¹ is preferably an oxygen atom.
It is preferred that one of L ⁵² and L ⁵³ is —O— and the other is —S—.
s1 is preferably 1.
s1' is preferably an integer of 0 to 2.
Z ^a1 is preferably a single bond or *-CH ₂ -CO-O-.

Examples of the structural unit (a1-5) include structural units derived from monomers described in JP-A-2010-61117. Among these, structural units represented by formulas (a1-5-1) to (a1-5-4) are preferred, and structural units represented by formula (a1-5-1) or (a1-5-2) are more preferred.

When resin (A) contains structural unit (a1-5), its content is preferably 1 to 50 mol%, more preferably 3 to 45 mol%, even more preferably 5 to 40 mol%, and even more preferably 5 to 30 mol%, based on the total structural units of resin (A).

Further, examples of the structural unit (a1) include the following structural units.

When resin (A) contains structural units such as (a1-3-1) to (a1-3-7) above, the content thereof is preferably 10 to 95 mol%, more preferably 15 to 90 mol%, even more preferably 20 to 85 mol%, even more preferably 20 to 70 mol%, and particularly preferably 20 to 60 mol%, based on the total structural units of resin (A).

<Structural unit (s)>
The structural unit (s) is derived from a monomer having no acid labile group (hereinafter, may be referred to as "monomer (s)"). As the monomer from which the structural unit (s) is derived, a monomer having no acid labile group known in the resist field can be used.
The structural unit (s) preferably has a hydroxy group or a lactone ring. By using a resin having a structural unit that has a hydroxy group but no acid labile group (hereinafter sometimes referred to as "structural unit (a2)") and/or a structural unit that has a lactone ring but no acid labile group (hereinafter sometimes referred to as "structural unit (a3)") in the resist composition of the present invention, the resolution of the resist pattern and adhesion to the substrate can be improved.

<Structural Unit (a2)>
The hydroxy group contained in the structural unit (a2) may be an alcoholic hydroxy group or a phenolic hydroxy group.
When producing a resist pattern from the resist composition of the present invention, if a high-energy ray such as a KrF excimer laser (248 nm), an electron beam, or EUV (extreme ultraviolet) is used as an exposure light source, the structural unit (a2) preferably has a phenolic hydroxy group, and it is more preferable to use the structural unit (a2-A) described below. Furthermore, if an ArF excimer laser (193 nm) or the like is used, the structural unit (a2) preferably has an alcoholic hydroxy group, and it is more preferable to use the structural unit (a2-1) described below. The structural unit (a2) may contain one type alone, or two or more types.

The structural unit (a2) having a phenolic hydroxy group includes a structural unit represented by formula (a2-A) (hereinafter, sometimes referred to as "structural unit (a2-A)").
[In formula (a2-A),
R ^a50 represents a hydrogen atom, a halogen atom or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom.
R ^a51 represents a halogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkoxyalkyl group having 2 to 12 carbon atoms, an alkoxyalkoxy group having 2 to 12 carbon atoms, an alkylcarbonyl group having 2 to 4 carbon atoms, an alkylcarbonyloxy group having 2 to 4 carbon atoms, an acryloyloxy group, or a methacryloyloxy group.
A ^a50 represents a single bond or *-X ^a51 -(A ^a52 -X ^a52 ) _nb -, where * represents a bond to the carbon atom to which -R ^a50 is bonded.
A ^a52 represents an alkanediyl group having 1 to 6 carbon atoms.
X ^a51 and X ^a52 each independently represent —O—, —CO—O—, or —O—CO—.
nb represents 0 or 1.
mb represents an integer of 0 to 4. When mb is an integer of 2 or more, multiple R ^a51 may be the same or different.]

Examples of the halogen atom in R ^a50 and R ^a51 include a fluorine atom, a chlorine atom, and a bromine atom.
Examples of the alkyl group having 1 to 6 carbon atoms which may have a halogen atom for R ^a50 include a trifluoromethyl group, a difluoromethyl group, a methyl group, a perfluoroethyl group, a 2,2,2-trifluoroethyl group, a 1,1,2,2-tetrafluoroethyl group, an ethyl group, a perfluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group, a propyl group, a perfluorobutyl group, a 1,1,2,2,3,3,4,4-octafluorobutyl group, a butyl group, a perfluoropentyl group, a 2,2,3,3,4,4,5,5,5-nonafluoropentyl group, a pentyl group, a hexyl group, and a perfluorohexyl group.
R ^a50 is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom, a methyl group or an ethyl group, and even more preferably a hydrogen atom or a methyl group.
Examples of the alkyl group for R ^a51 include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, and a hexyl group. The alkyl group is preferably an alkyl group having 1 to 4 carbon atoms, more preferably a methyl group or an ethyl group, and even more preferably a methyl group.
Examples of the alkoxy group for R ^a51 include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, a sec-butoxy group, and a tert-butoxy group. The alkoxy group is preferably an alkoxy group having 1 to 4 carbon atoms, more preferably a methoxy group or an ethoxy group, and even more preferably a methoxy group.
Examples of the alkoxyalkyl group for R ^a51 include a methoxymethyl group, an ethoxyethyl group, a propoxymethyl group, an isopropoxymethyl group, a butoxymethyl group, a sec-butoxymethyl group, and a tert-butoxymethyl group. The alkoxyalkyl group is preferably an alkoxyalkyl group having 2 to 8 carbon atoms, more preferably a methoxymethyl group or an ethoxyethyl group, and even more preferably a methoxymethyl group.
Examples of the alkoxyalkoxy group for R ^a51 include a methoxymethoxy group, a methoxyethoxy group, an ethoxymethoxy group, an ethoxyethoxy group, a propoxymethoxy group, an isopropoxymethoxy group, a butoxymethoxy group, a sec-butoxymethoxy group, and a tert-butoxymethoxy group. The alkoxyalkoxy group is preferably an alkoxyalkoxy group having 2 to 8 carbon atoms, and more preferably a methoxyethoxy group or an ethoxyethoxy group.
Examples of the alkylcarbonyl group for R ^a51 include an acetyl group, a propionyl group, a butyryl group, etc. The alkylcarbonyl group is preferably an alkylcarbonyl group having 2 to 3 carbon atoms, and more preferably an acetyl group.
Examples of the alkylcarbonyloxy group for R ^a51 include an acetyloxy group, a propionyloxy group, and a butyryloxy group. The alkylcarbonyloxy group is preferably an alkylcarbonyloxy group having 2 to 3 carbon atoms, and more preferably an acetyloxy group.
R ^a51 is preferably a halogen atom, a hydroxy group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an alkoxyalkoxy group having 2 to 8 carbon atoms, more preferably a fluorine atom, an iodine atom, a hydroxy group, a methyl group, a methoxy group, an ethoxy group, an ethoxyethoxy group, or an ethoxymethoxy group, and still more preferably a fluorine atom, an iodine atom, a hydroxy group, a methyl group, a methoxy group, or an ethoxyethoxy group.

Examples of *-X ^a51 -(A ^a52 -X ^a52 ) _nb - include *-O-, *-CO-O-, *-O-CO-, *-CO-O-A ^a52 -CO-O-, *-O-CO-A ^a52 -O-, *-O-A ^a52 -CO-O-, *-CO-O-A ^a52 -O-CO-, *-O-CO-A ^a52 -O-CO-. Of these, *-CO-O-, *-CO-O-A ^a52 -CO-O- or *-O-A ^a52 -CO-O- are preferred.

Examples of the alkanediyl group include a methylene group, an ethylene group, a propane-1,3-diyl group, a propane-1,2-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diyl group, a butane-1,3-diyl group, a 2-methylpropane-1,3-diyl group, a 2-methylpropane-1,2-diyl group, a pentane-1,4-diyl group, and a 2-methylbutane-1,4-diyl group.
A ^a52 is preferably a methylene group or an ethylene group.

A ^a50 is preferably a single bond, *-CO-O- or *-CO-O-A ^a52 -CO-O-, more preferably a single bond, *-CO-O- or *-CO-O-CH ₂ -CO-O-, and even more preferably a single bond or *-CO-O-.

mb is preferably 0, 1 or 2, more preferably 0 or 1, and particularly preferably 0.
The hydroxy group is preferably bonded to the ortho- or para-position of the benzene ring, more preferably to the para-position.

Examples of the structural unit (a2-A) include structural units derived from monomers described in JP-A Nos. 2010-204634 and 2012-12577.
Examples of the structural unit (a2-A) include structural units represented by formulae (a2-2-1) to (a2-2-16) and structural units in which the methyl group corresponding to R ^a50 in the structural unit (a2-A) in the structural units represented by formulae (a2-2-1) to (a2-2-16) is replaced with a hydrogen atom, a halogen atom, a haloalkyl group, or another alkyl group. The structural unit (a2-A) is a structural unit represented by formula (a2-2-1), a structural unit represented by formula (a2-2-3), a structural unit represented by formula (a2-2-6), a structural unit represented by formula (a2-2-8), a structural unit represented by formulas (a2-2-12) to (a2-2-14), and a structural unit represented by formula (a2-2-1), a structural unit represented by formula (a2-2-3), a structural unit represented by formula (a2-2-6), a structural unit represented by formula (a2-2-8), and a structural unit represented by formulas (a2-2-12) to (a2-2-14). In these structural units, R Preferably, it is a structural unit in which a methyl group corresponding to ^a50 in the structural unit (a2-A) is replaced with a hydrogen atom, and more preferably, it is a structural unit in which a methyl group corresponding to R a50 in the structural unit (a2-A) is replaced with a hydrogen atom in the structural unit represented by formula (a2-2-3), the structural unit represented by formula (a2-2-8), the structural units represented by formulas (a2-2-12) to (a2-2-14), or the structural units represented by formula (a2-2-3) or (a2-2-8), or the structural units represented by formulas (a2-2-12) to (a2-2-14), and it is even more preferably, it is a structural unit in which a methyl group corresponding to R ^a50 in the structural unit (a2-A) is replaced with a hydrogen atom in the structural unit represented by formula ( ^a2-2-8 ) and the structural unit represented by formula (a2-2-8).

When the structural unit (a2-A) is contained in the resin (A), the content of the structural unit (a2-A) is preferably 5 to 80 mol %, more preferably 10 to 70 mol %, even more preferably 15 to 65 mol %, and still more preferably 20 to 65 mol %, based on all structural units.
The structural unit (a2-A) can be incorporated into the resin (A) by, for example, polymerizing the structural unit (a1-4) and then treating with an acid such as p-toluenesulfonic acid. Alternatively, the structural unit (a2-A) can be incorporated into the resin (A) by polymerizing the structural unit (a1-4) and then treating with an alkali such as tetramethylammonium hydroxide.

The structural unit (a2) having an alcoholic hydroxy group includes a structural unit represented by formula (a2-1) (hereinafter, sometimes referred to as "structural unit (a2-1)").
In formula (a2-1),
L ^a3 represents —O— or *—O—(CH ₂ ) _k2 —CO—O—;
k2 represents an integer of 1 to 7. * represents a bond to —CO—.
R ^a14 represents a hydrogen atom or a methyl group.
R ^a15 and R ^a16 each independently represent a hydrogen atom, a methyl group or a hydroxy group.
o1 represents an integer of 0 to 10.

In formula (a2-1), L ^a3 is preferably —O— or —O—(CH ₂ ) _f1 —CO—O— (wherein f1 represents an integer of 1 to 4), and more preferably —O—.
R ^a14 is preferably a methyl group.
R ^a15 is preferably a hydrogen atom.
R ^a16 is preferably a hydrogen atom or a hydroxy group.
o1 is preferably an integer of 0 to 3, more preferably 0 or 1.

Examples of the structural unit (a2-1) include structural units derived from monomers described in JP 2010-204646 A. A structural unit represented by any one of formulas (a2-1-1) to (a2-1-6) is preferred, a structural unit represented by any one of formulas (a2-1-1) to (a2-1-4) is more preferred, and a structural unit represented by formula (a2-1-1) or formula (a2-1-3) is even more preferred.

When resin (A) contains structural unit (a2-1), its content is typically 1 to 45 mol%, preferably 1 to 40 mol%, more preferably 1 to 35 mol%, even more preferably 1 to 20 mol%, and even more preferably 1 to 10 mol%, based on all structural units in resin (A).

<Structural Unit (a3)>
The lactone ring contained in the structural unit (a3) may be a monocyclic ring such as a β-propiolactone ring, a γ-butyrolactone ring, or a δ-valerolactone ring, or may be a condensed ring of a monocyclic lactone ring with another ring. Preferred examples include a γ-butyrolactone ring, an adamantane lactone ring, or a bridged ring containing a γ-butyrolactone ring structure (for example, a structural unit represented by the following formula (a3-2)).

The structural unit (a3) is preferably a structural unit represented by formula (a3-1), formula (a3-2), formula (a3-3), or formula (a3-4). One of these may be contained alone, or two or more may be contained.
[In formula (a3-1), formula (a3-2), formula (a3-3) and formula (a3-4),
L ^a4 , L ^a5 and L ^a6 each independently represent a group represented by —O— or *-O—(CH ₂ ) _k3 —CO—O— (k3 represents an integer of 1 to 7).
L ^a7 represents -O-, *-OL ^a8 -O-, *-OL ^a8 -CO-O-, *-OL ^a8 -CO-O-L ^a9 -CO-O-, or *-OL ^a8 -O-CO-L ^a9 -O-.
L ^a8 and L ^a9 each independently represent an alkanediyl group having 1 to 6 carbon atoms.
* indicates the bonding site with the carbonyl group.
R ^a18 , R ^a19 and R ^a20 each independently represent a hydrogen atom or a methyl group.
R ^a24 represents an alkyl group having 1 to 6 carbon atoms which may have one or more halogen atoms, a hydrogen atom, or a halogen atom.
X ^a3 represents —CH ₂ — or an oxygen atom.
R ^a21 represents an aliphatic hydrocarbon group having 1 to 4 carbon atoms.
R ^a22 , R ^a23 and R ^a25 each independently represent a carboxy group, a cyano group or an aliphatic hydrocarbon group having 1 to 4 carbon atoms.
p1 represents an integer of 0 to 5.
q1 represents an integer of 0 to 3.
r1 represents an integer of 0 to 3.
w1 represents an integer of 0 to 8.
When p1, q1, r1 and/or w1 is 2 or more, a plurality of R ^a21 , R ^a22 , R ^a23 and/or R ^a25 may be the same as or different from one another.]

Examples of the aliphatic hydrocarbon group in R ^a21 , R ^a22 , R ^a23 and R ^a25 include alkyl groups such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group and a tert-butyl group.
The halogen atom in R ^a24 includes a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.
Examples of the alkyl group for R ^a24 include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, and a hexyl group, and are preferably alkyl groups having 1 to 4 carbon atoms, and more preferably a methyl group or an ethyl group.
Examples of the alkyl group having a halogen atom for R ^a24 include a trifluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluoroisopropyl group, a perfluorobutyl group, a perfluorosec-butyl group, a perfluorotert-butyl group, a perfluoropentyl group, a perfluorohexyl group, a trichloromethyl group, a tribromomethyl group, and a triiodomethyl group.
Examples of the alkanediyl group in L ^a8 and L ^a9 include a methylene group, an ethylene group, a propane-1,3-diyl group, a propane-1,2-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diyl group, a butane-1,3-diyl group, a 2-methylpropane-1,3-diyl group, a 2-methylpropane-1,2-diyl group, a pentane-1,4-diyl group, and a 2-methylbutane-1,4-diyl group.

In formulae (a3-1) to (a3-3), L ^a4 to L ^a6 each independently represent preferably —O— or *—O—(CH ₂ ) _k3 —CO—O—, where k3 is an integer of 1 to 4, more preferably —O— and *—O—CH ₂ —CO—O—, and even more preferably an oxygen atom.
R ^a18 to R ^a21 are preferably methyl groups.
R ^a22 and R ^a23 each independently represent preferably a carboxy group, a cyano group, or a methyl group.
p1, q1 and r1 each independently represent an integer of preferably 0 to 2, and more preferably 0 or 1.

In formula (a3-4), R ^a24 is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom, a methyl group or an ethyl group, and even more preferably a hydrogen atom or a methyl group.
R ^a25 is preferably a carboxy group, a cyano group or a methyl group.
L ^a7 is preferably —O— or *-OL ^a8 —CO—O—, and more preferably —O—, —O—CH ₂ —CO—O— or —OC ₂ H ₄ —CO—O—.
w1 is preferably an integer of 0 to 2, and more preferably 0 or 1.
In particular, the formula (a3-4) is preferably the formula (a3-4)'.
(In the formula, R ^a24 and L ^a7 have the same meanings as above.)

Examples of the structural unit (a3) include structural units derived from the monomers described in JP-A No. 2010-204646, JP-A No. 2000-122294, and JP-A No. 2012-41274. Preferred structural units (a3) are structural units represented by any one of formulas (a3-1-1), (a3-1-2), (a3-2-1), (a3-2-2), (a3-3-1), (a3-3-2), and (a3-4-1) to (a3-4-12), and structural units in which the methyl groups corresponding to R ^a18 , R ^a19 , R ^a20 , and R ^a24 in formulas (a3-1) to (a3-4) in the structural units are replaced with hydrogen atoms.

When the resin (A) contains the structural unit (a3), the total content thereof is usually 5 to 70 mol %, preferably 10 to 65 mol %, and more preferably 10 to 60 mol %, based on all structural units in the resin (A).
Furthermore, the content of the structural unit (a3-1), the structural unit (a3-2), the structural unit (a3-3), or the structural unit (a3-4) is preferably 5 to 60 mol%, more preferably 5 to 50 mol%, and even more preferably 10 to 50 mol%, based on the total structural units of the resin (A).

<Structural unit (a4)>
Examples of the structural unit (a4) include the following structural units.
[In formula (a4),
R ⁴¹ represents a hydrogen atom or a methyl group.
R ⁴² represents a saturated hydrocarbon group having 1 to 24 carbon atoms and containing a fluorine atom, and —CH ₂ — contained in the saturated hydrocarbon group may be replaced by —O— or —CO—.]
Examples of the saturated hydrocarbon group represented by R ⁴² include chain hydrocarbon groups, monocyclic or polycyclic alicyclic hydrocarbon groups, and groups formed by combining these groups.

Examples of the chain hydrocarbon group include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, decyl, dodecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl groups. Examples of the monocyclic or polycyclic alicyclic hydrocarbon group include cycloalkyl groups such as cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl groups; decahydronaphthyl, adamantyl, norbornyl, and polycyclic alicyclic hydrocarbon groups such as the following groups (* represents a bond):
Examples of groups formed by combination include groups formed by combining one or more alkyl groups or one or more alkanediyl groups with one or more alicyclic hydrocarbon groups, such as -alkanediyl group-alicyclic hydrocarbon group, -alicyclic hydrocarbon group-alkyl group, and -alkanediyl group-alicyclic hydrocarbon group-alkyl group.

Examples of the structural unit (a4) include at least one structural unit selected from the group consisting of formula (a4-0), formula (a4-1), formula (a4-2), formula (a4-3), and formula (a4-4).
[In formula (a4-0),
^R5 represents a hydrogen atom or a methyl group.
L ^4a represents a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 4 carbon atoms.
^L3a represents a perfluoroalkanediyl group having 1 to 8 carbon atoms or a perfluorocycloalkanediyl group having 3 to 12 carbon atoms.
^R6 represents a hydrogen atom or a fluorine atom.

Examples of the divalent aliphatic saturated hydrocarbon group for ^L4a include linear alkanediyl groups such as a methylene group, an ethylene group, a propane-1,3-diyl group, and a butane-1,4-diyl group, and branched alkanediyl groups such as an ethane-1,1-diyl group, a propane-1,2-diyl group, a butane-1,3-diyl group, a 2-methylpropane-1,3-diyl group, and a 2-methylpropane-1,2-diyl group.
Examples of the perfluoroalkanediyl group in ^L3a include a difluoromethylene group, a perfluoroethylene group, a perfluoropropane-1,1-diyl group, a perfluoropropane-1,3-diyl group, a perfluoropropane-1,2-diyl group, a perfluoropropane-2,2-diyl group, a perfluorobutane-1,4-diyl group, a perfluorobutane-2,2-diyl group, a perfluorobutane-1,2-diyl group, a perfluoropentane-1,5-diyl group, a perfluoropentane-2,2-diyl group, a perfluoropentane- perfluorohexane-3,3-diyl group, perfluorohexane-1,6-diyl group, perfluorohexane-2,2-diyl group, perfluorohexane-3,3-diyl group, perfluoroheptane-1,7-diyl group, perfluoroheptane-2,2-diyl group, perfluoroheptane-3,4-diyl group, perfluoroheptane-4,4-diyl group, perfluorooctane-1,8-diyl group, perfluorooctane-2,2-diyl group, perfluorooctane-3,3-diyl group, and perfluorooctane-4,4-diyl group.
Examples of the perfluorocycloalkanediyl group in ^L3a include a perfluorocyclohexanediyl group, a perfluorocyclopentanediyl group, a perfluorocycloheptanediyl group, and a perfluoroadamantanediyl group.

L ^4a is preferably a single bond, a methylene group or an ethylene group, more preferably a single bond or a methylene group.
^L3a is preferably a perfluoroalkanediyl group having 1 to 6 carbon atoms, and more preferably a perfluoroalkanediyl group having 1 to 3 carbon atoms.

Examples of the structural unit (a4-0) include the structural units shown below and structural units in which the methyl group corresponding to R ⁵ in the structural unit (a4-0) is replaced with a hydrogen atom.

[In formula (a4-1),
R ^a41 represents a hydrogen atom or a methyl group.
R ^a42 represents a saturated hydrocarbon group having 1 to 20 carbon atoms which may have a substituent, and one --CH ₂ -- contained in the saturated hydrocarbon group may be replaced by --O-- or --CO--.
A ^a41 represents an alkanediyl group having 1 to 6 carbon atoms which may have a substituent or a group represented by formula (a-g1), provided that at least one of A ^a41 and R ^a42 has a halogen atom (preferably a fluorine atom) as a substituent.
[In formula (a-g1),
s represents 0 or 1.
A ^a42 and A ^a44 each independently represent a divalent saturated hydrocarbon group having 1 to 5 carbon atoms which may have a substituent.
A ^a43 represents a single bond or a divalent aliphatic hydrocarbon group having 1 to 5 carbon atoms which may have a substituent.
X ^a41 and X ^a42 each independently represent —O—, —CO—, —CO—O— or —O—CO—.
However, the total number of carbon atoms of A ^a42 , A ^a43 , A ^a44 , X ^a41 and X ^a42 is 7 or less.]
* represents a bond, and the * on the right is a bond to —O—CO—R ^a42 .]

Examples of the saturated hydrocarbon group for R ^a42 include a chain saturated hydrocarbon group, a monocyclic or polycyclic alicyclic saturated hydrocarbon group, and groups formed by combining these groups.
Examples of the chain saturated hydrocarbon group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a decyl group, a dodecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, and an octadecyl group.
Examples of the monocyclic or polycyclic alicyclic hydrocarbon group include cycloalkyl groups such as a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, and a cyclooctyl group; and polycyclic alicyclic saturated hydrocarbon groups such as a decahydronaphthyl group, an adamantyl group, a norbornyl group, and the following groups (* represents a bond):
Examples of groups formed by this combination include groups formed by combining one or more alkyl groups or one or more alkanediyl groups with one or more alicyclic saturated hydrocarbon groups, such as -alkanediyl group-alicyclic saturated hydrocarbon group, -alicyclic saturated hydrocarbon group-alkyl group, and -alkanediyl group-alicyclic saturated hydrocarbon group-alkyl group.

Examples of the substituent that R ^a42 may have include at least one selected from a halogen atom and a group represented by formula (a-g3): Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and a fluorine atom is preferred.
[In formula (a-g3),
X ^a43 represents an oxygen atom, a carbonyl group, *-O-CO- or *-CO-O-.
A ^a45 represents an aliphatic hydrocarbon group having 1 to 17 carbon atoms which may have a halogen atom. * represents a bond to R ^a42 .]
However, in R ^a42 -X ^a43 -A ^a45 , when R ^a42 does not have a halogen atom, A ^a45 represents an aliphatic hydrocarbon group having 1 to 17 carbon atoms and at least one halogen atom.

Examples of the aliphatic hydrocarbon group for A ^a45 include alkyl groups such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a decyl group, a dodecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, and an octadecyl group;
Examples include monocyclic alicyclic hydrocarbon groups such as a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, and a cyclooctyl group; and polycyclic alicyclic hydrocarbon groups such as a decahydronaphthyl group, an adamantyl group, a norbornyl group, and the following groups (* represents a bond):
Examples of groups formed by combination include groups formed by combining one or more alkyl groups or one or more alkanediyl groups with one or more alicyclic hydrocarbon groups, such as -alkanediyl group-alicyclic hydrocarbon group, -alicyclic hydrocarbon group-alkyl group, and -alkanediyl group-alicyclic hydrocarbon group-alkyl group.

R ^a42 is preferably an aliphatic hydrocarbon group which may have a halogen atom, and more preferably an aliphatic hydrocarbon group having an alkyl group having a halogen atom and/or a group represented by formula (a-g3).
When R ^a42 is an aliphatic hydrocarbon group having a halogen atom, it is preferably an aliphatic hydrocarbon group having a fluorine atom, more preferably a perfluoroalkyl group or a perfluorocycloalkyl group, still more preferably a perfluoroalkyl group having 1 to 6 carbon atoms, and particularly preferably a perfluoroalkyl group having 1 to 3 carbon atoms. Examples of perfluoroalkyl groups include perfluoromethyl group, perfluoroethyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group, perfluorohexyl group, perfluoroheptyl group, and perfluorooctyl group. Examples of perfluorocycloalkyl groups include a perfluorocyclohexyl group.
When R ^a42 is an aliphatic hydrocarbon group having a group represented by formula (a-g3), the total number of carbon atoms in R ^a42 , including the number of carbon atoms contained in the group represented by formula (a-g3), is preferably 15 or less, and more preferably 12 or less. When R a42 has a group represented by formula (a-g3) as a substituent, the number thereof is preferably 1.

When R ^a42 is an aliphatic hydrocarbon having a group represented by formula (a-g3), R ^a42 is more preferably a group represented by formula (a-g2).
[In formula (a-g2),
A ^a46 represents a divalent aliphatic hydrocarbon group having 1 to 17 carbon atoms which may have a halogen atom.
X ^a44 represents **-O-CO- or **-CO-O- (** represents a bond to A ^a46 ).
A ^a47 represents an aliphatic hydrocarbon group having 1 to 17 carbon atoms which may have a halogen atom.
However, the total number of carbon atoms of A ^a46 , A ^a47 and X ^a44 is 18 or less, and at least one of A ^a46 and A ^a47 has at least one halogen atom.
* represents a bond to the carbonyl group.

The aliphatic hydrocarbon group of A ^a46 preferably has 1 to 6 carbon atoms, and more preferably 1 to 3 carbon atoms.
The aliphatic hydrocarbon group of A ^a47 preferably has 4 to 15 carbon atoms, more preferably 5 to 12 carbon atoms, and A ^a47 is even more preferably a cyclohexyl group or an adamantyl group.

A preferred structure of the group represented by formula (a-g2) is the following structure (* represents a bond to the carbonyl group):

Examples of the alkanediyl group for A ^a41 include linear alkanediyl groups such as a methylene group, an ethylene group, a propane-1,3-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group, and a hexane-1,6-diyl group; and branched alkanediyl groups such as a propane-1,2-diyl group, a butane-1,3-diyl group, a 2-methylpropane-1,2-diyl group, a 1-methylbutane-1,4-diyl group, and a 2-methylbutane-1,4-diyl group.
Examples of the substituent in the alkanediyl group of A ^a41 include a hydroxy group and an alkoxy group having 1 to 6 carbon atoms.
A ^a41 is preferably an alkanediyl group having 1 to 4 carbon atoms, more preferably an alkanediyl group having 2 to 4 carbon atoms, and even more preferably an ethylene group.

Examples of the divalent saturated hydrocarbon group represented by A ^a42 , A ^a43 , and A ^a44 in the group represented by formula (a-g1) include a linear or branched alkanediyl group, a monocyclic divalent alicyclic hydrocarbon group, and a group formed by combining an alkanediyl group and a divalent alicyclic hydrocarbon group, etc. Specific examples include a methylene group, an ethylene group, a propane-1,3-diyl group, a propane-1,2-diyl group, a butane-1,4-diyl group, a 1-methylpropane-1,3-diyl group, a 2-methylpropane-1,3-diyl group, and a 2-methylpropane-1,2-diyl group.
Examples of the substituent of the divalent saturated hydrocarbon group represented by A ^a42 , A ^a43 and A ^a44 include a hydroxy group and an alkoxy group having 1 to 6 carbon atoms.
Preferably, s is 0.

In the group represented by formula (a-g1), examples of the group in which X ^a42 is —O—, —CO—, —CO—O—, or —O—CO— include the following groups: In the following examples, * and ** each represent a bond, and ** is a bond to —O—CO—R ^a42 .

Examples of the structural unit represented by formula (a4-1) include the structural units shown below and structural units in which the methyl group corresponding to R ^a41 in the structural unit represented by formula (a4-1) in the following structural units is replaced with a hydrogen atom.

The structural unit represented by formula (a4-1) is preferably a structural unit represented by formula (a4-2).
[In formula (a4-2),
R ^f5 represents a hydrogen atom or a methyl group.
L ⁴⁴ represents an alkanediyl group having 1 to 6 carbon atoms, and one --CH ₂ -- contained in the alkanediyl group may be replaced by --O-- or --CO--.
R ^f6 represents a saturated hydrocarbon group having 1 to 20 carbon atoms and containing a fluorine atom.
However, the upper limit of the total number of carbon atoms in L ⁴⁴ and R ^f6 is 21.]

Examples of the alkanediyl group having 1 to 6 carbon atoms for L ⁴⁴ include the same groups as those exemplified as the alkanediyl group for A ^a41 .
Examples of the saturated hydrocarbon group of R ^f6 include the same groups as those exemplified for R ^a42 .
As the alkanediyl group having 1 to 6 carbon atoms in L ⁴⁴ , an alkanediyl group having 2 to 4 carbon atoms is preferred, and an ethylene group is more preferred.

Examples of the structural unit represented by formula (a4-2) include structural units represented by formulas (a4-1-1) to (a4-1-11). Examples of the structural unit represented by formula (a4-2) include a structural unit in which the methyl group corresponding to R ^f5 in the structural unit (a4-2) is replaced with a hydrogen atom.

Examples of the structural unit (a4) include a structural unit represented by formula (a4-3).
[In formula (a4-3),
R ^f7 represents a hydrogen atom or a methyl group.
^L5 represents an alkanediyl group having 1 to 6 carbon atoms.
A ^f13 represents a divalent saturated hydrocarbon group having 1 to 18 carbon atoms which may have a fluorine atom.
X ^f12 represents *-O-CO- or *-CO-O- (* represents a bond to A ^f13 ).
A ^f14 represents a saturated hydrocarbon group having 1 to 17 carbon atoms which may have a fluorine atom.
However, at least one of A ^f13 and A ^f14 has a fluorine atom, and the upper limit of the total number of carbon atoms of L ⁵ , A ^f13 and A ^f14 is 20.]

Examples of the alkanediyl group in ^L5 include the same groups as those exemplified as the alkanediyl group in the divalent saturated hydrocarbon group of ^Aa41 .
The divalent saturated hydrocarbon group for A ^f13 which may have a fluorine atom is preferably a divalent aliphatic saturated hydrocarbon group which may have a fluorine atom and a divalent alicyclic saturated hydrocarbon group which may have a fluorine atom, and more preferably a perfluoroalkanediyl group.
Examples of the divalent aliphatic hydrocarbon group which may have a fluorine atom include alkanediyl groups such as a methylene group, an ethylene group, a propanediyl group, a butanediyl group, and a pentanediyl group; and perfluoroalkanediyl groups such as a difluoromethylene group, a perfluoroethylene group, a perfluoropropanediyl group, a perfluorobutanediyl group, and a perfluoropentanediyl group.
The divalent alicyclic hydrocarbon group optionally having a fluorine atom may be either monocyclic or polycyclic. Examples of the monocyclic group include a cyclohexanediyl group and a perfluorocyclohexanediyl group. Examples of the polycyclic group include an adamantanediyl group, a norbornanediyl group, and a perfluoroadamantanediyl group.
Examples of the saturated hydrocarbon group and the saturated hydrocarbon group which may have a fluorine atom of A ^f14 include the same groups as those exemplified for R ^a42 . Among them, a trifluoromethyl group, a difluoromethyl group, a methyl group, a perfluoroethyl group, a 2,2,2-trifluoroethyl group, a 1,1,2,2-tetrafluoroethyl group, an ethyl group, a perfluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group, a propyl group, a perfluorobutyl group, a 1,1,2,2,3,3,4,4-octafluorobutyl group, a butyl group, a perfluoropentyl group, a 2,2,3,3,4,4,5,5,5-nonafluoropentyl group, a pentyl group, Preferred are fluorinated alkyl groups such as a hexyl group, a perfluorohexyl group, a heptyl group, a perfluoroheptyl group, an octyl group, and a perfluorooctyl group, a cyclopropylmethyl group, a cyclopropyl group, a cyclobutylmethyl group, a cyclopentyl group, a cyclohexyl group, a perfluorocyclohexyl group, an adamantyl group, an adamantylmethyl group, an adamantyldimethyl group, a norbornyl group, a norbornylmethyl group, a perfluoroadamantyl group, and a perfluoroadamantylmethyl group.

In formula (a4-3), L ⁵ is preferably an ethylene group.
The divalent saturated hydrocarbon group for A ^f13 is preferably a group containing a divalent chain hydrocarbon group having 1 to 6 carbon atoms and a divalent alicyclic hydrocarbon group having 3 to 12 carbon atoms, more preferably a divalent chain hydrocarbon group having 2 to 3 carbon atoms.
The saturated hydrocarbon group of A ^f14 is preferably a group containing a chain hydrocarbon group having 3 to 12 carbon atoms and an alicyclic hydrocarbon group having 3 to 12 carbon atoms, and more preferably a group containing a chain hydrocarbon group having 3 to 10 carbon atoms and an alicyclic hydrocarbon group having 3 to 10 carbon atoms. Of these, A ^f14 is preferably a group containing an alicyclic hydrocarbon group having 3 to 12 carbon atoms, and more preferably a cyclopropylmethyl group, a cyclopentyl group, a cyclohexyl group, a norbornyl group, or an adamantyl group.

Examples of the structural unit represented by formula (a4-3) include structural units represented by formulas (a4-1'-1) to (a4-1'-11). Examples of the structural unit represented by formula (a4-3) include a structural unit in which the methyl group corresponding to ^Rf7 in the structural unit (a4-3) is replaced with a hydrogen atom.

The structural unit (a4) also includes a structural unit represented by formula (a4-4).
[In formula (a4-4),
R ^f21 represents a hydrogen atom or a methyl group.
A ^f21 represents --(CH ₂ ) _j1 --, --(CH ₂ ) _j2 --O--(CH ₂ ) _j3 --, or --(CH ₂ ) _j4 --CO--O--(CH ₂ ) _j5 --.
j1 to j5 each independently represent an integer of 1 to 6.
R ^f22 represents a saturated hydrocarbon group having 1 to 10 carbon atoms and a fluorine atom.]

Examples of the saturated hydrocarbon group for R ^f22 include the same as the saturated hydrocarbon group represented by R ^a42 . ^{R f22} is preferably an alkyl group having 1 to 10 carbon atoms and containing a fluorine atom or an alicyclic hydrocarbon group having 1 to 10 carbon atoms and containing a fluorine atom, more preferably an alkyl group having 1 to 10 carbon atoms and containing a fluorine atom, and even more preferably an alkyl group having 1 to 6 carbon atoms and containing a fluorine atom.

In formula (a4-4), A ^f21 is preferably —(CH ₂ ) _j1 —, more preferably an ethylene group or a methylene group, and even more preferably a methylene group.

Examples of the structural unit represented by formula (a4-4) include the following structural units and structural units represented by the following formulas in which a methyl group corresponding to R ^f21 in the structural unit (a4-4) is replaced with a hydrogen atom:

When resin (A) contains structural unit (a4), its content is preferably 1 to 20 mol %, more preferably 2 to 15 mol %, and even more preferably 3 to 10 mol %, based on the total structural units of resin (A).

<Structural unit (a5)>
The non-leaving hydrocarbon group contained in the structural unit (a5) may be a group containing a linear, branched, or cyclic hydrocarbon group. Among these, the structural unit (a5) is preferably a group containing an alicyclic hydrocarbon group.
Examples of the structural unit (a5) include a structural unit represented by formula (a5-1).
[In formula (a5-1),
R ⁵¹ represents a hydrogen atom or a methyl group.
R ⁵² represents an alicyclic hydrocarbon group having 3 to 18 carbon atoms, and a hydrogen atom contained in the alicyclic hydrocarbon group may be substituted with an aliphatic hydrocarbon group having 1 to 8 carbon atoms.
L ⁵⁵ represents a single bond or a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, and one —CH ₂ — contained in the saturated hydrocarbon group may be replaced by —O— or —CO—.]

The alicyclic hydrocarbon group for ^R52 may be either monocyclic or polycyclic. Examples of monocyclic alicyclic hydrocarbon groups include cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl. Examples of polycyclic alicyclic hydrocarbon groups include adamantyl and norbornyl.
Examples of the aliphatic hydrocarbon group having 1 to 8 carbon atoms include alkyl groups such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, an octyl group, and a 2-ethylhexyl group.
Examples of the alicyclic hydrocarbon group having a substituent include a 3-methyladamantyl group.
R ⁵² is preferably an unsubstituted alicyclic hydrocarbon group having 3 to 18 carbon atoms, and more preferably an adamantyl group, a norbornyl group, or a cyclohexyl group.
The divalent saturated hydrocarbon group for L ⁵⁵ includes a divalent chain saturated hydrocarbon group and a divalent alicyclic saturated hydrocarbon group, and is preferably a divalent chain saturated hydrocarbon group.
Examples of the divalent chain saturated hydrocarbon group include a methylene group, an ethylene group, and an alkanediyl group such as a propanediyl group, a butanediyl group, and a pentanediyl group.
The divalent alicyclic saturated hydrocarbon group may be either monocyclic or polycyclic. Examples of the monocyclic alicyclic saturated hydrocarbon group include cycloalkanediyl groups such as cyclopentanediyl and cyclohexanediyl. Examples of the polycyclic divalent alicyclic saturated hydrocarbon group include adamantanediyl and norbornanediyl.

Examples of the divalent saturated hydrocarbon group represented by L ⁵⁵ in which —CH ₂ — is replaced by —O— or —CO— include groups represented by formulae (L1-1) to (L1-4). In the following formulae, * and ** each represent a bond, and * represents a bond to an oxygen atom.
In formula (L1-1),
X ^x1 represents *-O-CO- or *-CO-O- (* represents a bond to L ^x1 ).
L ^x1 represents a divalent aliphatic saturated hydrocarbon group having 1 to 16 carbon atoms.
L ^x2 represents a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 15 carbon atoms.
However, the total number of carbon atoms in L ^x1 and L ^x2 is 16 or less.
In formula (L1-2),
L ^x3 represents a divalent aliphatic saturated hydrocarbon group having 1 to 17 carbon atoms.
L ^x4 represents a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 16 carbon atoms.
However, the total number of carbon atoms in L ^x3 and L ^x4 is 17 or less.
In formula (L1-3),
L ^x5 represents a divalent aliphatic saturated hydrocarbon group having 1 to 15 carbon atoms.
L ^x6 and L ^x7 each independently represent a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 14 carbon atoms.
However, the total number of carbon atoms in L ^x5 , L ^x6 and L ^x7 is 15 or less.
In formula (L1-4),
L ^x8 and L ^x9 each represent a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 12 carbon atoms.
W ^x1 represents a divalent alicyclic saturated hydrocarbon group having 3 to 15 carbon atoms.
However, the total number of carbon atoms in L ^x8 , L ^x9 and W ^x1 is 15 or less.

L ^x1 is preferably a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms, more preferably a methylene group or an ethylene group.
L ^x2 is preferably a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms, more preferably a single bond.
L ^x3 is preferably a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms.
L ^x4 is preferably a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms.
L ^x5 is preferably a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms, more preferably a methylene group or an ethylene group.
L ^x6 is preferably a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms, more preferably a methylene group or an ethylene group.
L ^x7 is preferably a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms.
L ^x8 is preferably a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms, more preferably a single bond or a methylene group.
L ^x9 is preferably a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms, more preferably a single bond or a methylene group.
W ^x1 is preferably a divalent alicyclic saturated hydrocarbon group having 3 to 10 carbon atoms, more preferably a cyclohexanediyl group or an adamantanediyl group.

Examples of the group represented by formula (L1-1) include the divalent groups shown below.

Examples of the group represented by formula (L1-2) include the divalent groups shown below.

Examples of the group represented by formula (L1-3) include the divalent groups shown below.

Examples of the group represented by formula (L1-4) include the divalent groups shown below.

L ⁵⁵ is preferably a single bond or a group represented by formula (L1-1).

Examples of the structural unit (a5-1) include the structural units shown below and structural units in which the methyl group corresponding to R ⁵¹ in the structural unit (a5-1) has been replaced with a hydrogen atom.
When the resin (A) has the structural unit (a5), the content thereof is preferably 1 to 30 mol %, more preferably 2 to 20 mol %, and even more preferably 3 to 15 mol %, based on all structural units of the resin (A).
<Structural Unit (a6)>
The structural unit (a6) is a structural unit having an —SO ₂ — group, and preferably has an —SO ₂ — group in a side chain.
The structural unit having an —SO ₂ — group may have a linear structure having an —SO ₂ — group, a branched structure having an —SO ₂ — group, or a cyclic structure (monocyclic or polycyclic structure) having an —SO ₂ — group. A structural unit having a cyclic structure having an —SO ₂ — group is preferred, and a structural unit having a cyclic structure containing —SO ₂ —O— (sultone ring) is more preferred.

Examples of the sultone ring include rings represented by the following formulae (T ¹ -1), (T ¹ -2), (T ¹ -3), and (T ¹ -4). The bonding site can be at any position. The sultone ring may be monocyclic, but is preferably polycyclic. A polycyclic sultone ring refers to a bridged ring containing —SO ₂ —O— as an atomic group constituting the ring, and examples include rings represented by formulae (T ¹ -1) and (T ¹ -2). The sultone ring, like the ring represented by formula (T ¹ -2), may further contain a heteroatom in addition to —SO ₂ —O— as an atomic group constituting the ring. Examples of the heteroatom include an oxygen atom, a sulfur atom, or a nitrogen atom, and an oxygen atom is preferred.

The sultone ring may have a substituent, and examples of the substituent include an alkyl group having 1 to 12 carbon atoms which may have a halogen atom or a hydroxy group, a halogen atom, a hydroxy group, a cyano group, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, a glycidyloxy group, an alkoxycarbonyl group having 2 to 12 carbon atoms, and an alkylcarbonyl group having 2 to 4 carbon atoms.

Halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.
Examples of the alkyl group include methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, and decyl groups, and are preferably alkyl groups having 1 to 6 carbon atoms, more preferably methyl groups.
Examples of the alkyl group having a halogen atom include a trifluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluoroisopropyl group, a perfluorobutyl group, a perfluorosec-butyl group, a perfluorotert-butyl group, a perfluoropentyl group, a perfluorohexyl group, a trichloromethyl group, a tribromomethyl group, and a triiodomethyl group, and preferably a trifluoromethyl group.
Examples of the alkyl group having a hydroxy group include a hydroxymethyl group and a 2-hydroxyethyl group.
Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group, an octyloxy group, a decyloxy group, and a dodecyloxy group.
Examples of the aryl group include a phenyl group, a naphthyl group, an anthryl group, a p-methylphenyl group, a p-tert-butylphenyl group, a p-adamantylphenyl group, a tolyl group, a xylyl group, a cumyl group, a mesityl group, a biphenyl group, a phenanthryl group, a 2,6-diethylphenyl group, and a 2-methyl-6-ethylphenyl group.
Aralkyl groups include benzyl, phenethyl, phenylpropyl, naphthylmethyl, and naphthylethyl groups.
Examples of the alkoxycarbonyl group include groups in which an alkoxy group, such as a methoxycarbonyl group or an ethoxycarbonyl group, is bonded to a carbonyl group, and preferred are alkoxycarbonyl groups having 6 or less carbon atoms, more preferably methoxycarbonyl groups.
Alkylcarbonyl groups include acetyl, propionyl and butyryl groups.

From the viewpoint of ease of production of the monomer from which the structural unit (a6) is derived, a sultone ring having no substituent is preferred.
The sultone ring is preferably a ring represented by the following formula (T1').
[In formula (T1'),
^X11 represents an oxygen atom, a sulfur atom or a methylene group.
R ⁴¹ represents an alkyl group having 1 to 12 carbon atoms which may have a halogen atom or a hydroxy group, a halogen atom, a hydroxy group, a cyano group, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, a glycidyloxy group, an alkoxycarbonyl group having 2 to 12 carbon atoms, or an alkylcarbonyl group having 2 to 4 carbon atoms.
ma represents an integer of 0 to 9. When ma is 2 or more, multiple R ⁴¹ may be the same or different.
The binding site is at any position.]
X ¹¹ is preferably an oxygen atom or a methylene group, more preferably a methylene group.
Examples of R ⁴¹ include the same substituents as those on the sultone ring, and are preferably alkyl groups having 1 to 12 carbon atoms which may have a halogen atom or a hydroxyl group.

The sultone ring is more preferably a ring represented by formula (T1).
[In formula (T1),
^R8 represents an alkyl group having 1 to 12 carbon atoms which may have a halogen atom or a hydroxy group, a halogen atom, a hydroxy group, a cyano group, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, a glycidyloxy group, an alkoxycarbonyl group having 2 to 12 carbon atoms, or an alkylcarbonyl group having 2 to 4 carbon atoms.
m represents an integer of 0 to 9. When m is 2 or more, multiple R ^8s may be the same or different.
The binding site is at any position.]

Examples of ^R8 include the same as those of ^R41 .
ma in formula (T1′) and m in formula (T1) are preferably 0 or 1, and more preferably 0.

Examples of the ring represented by formula (T1') and the ring represented by formula (T1) include the following rings: The binding site is at any position.

The structural unit having a sultone ring preferably has the following group: In the following group, * represents a bonding site.

The structural unit having an —SO ₂ — group preferably further has a group derived from a polymerizable group, such as a vinyl group, an acryloyl group, a methacryloyl group, an acryloyloxy group, a methacryloyloxy group, an acryloylamino group, a methacryloylamino group, an acryloylthio group, or a methacryloylthio group.
Among these, the monomer from which the structural unit (a6) is derived is preferably a monomer having an ethylenically unsaturated bond, and more preferably a (meth)acrylic monomer.

The structural unit (a6) is preferably a structural unit represented by formula (Ix).
In formula (Ix), R ^x represents an alkyl group having 1 to 6 carbon atoms which may have one or more halogen atoms, a hydrogen atom, or a halogen atom.
A ^xx represents an oxygen atom, —N(R ^c )— or a sulfur atom.
A ^x represents a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, and one —CH ₂ — contained in the saturated hydrocarbon group may be replaced by —O—, —CO— or —N(R ^d )—.
^X11 represents an oxygen atom, a sulfur atom or a methylene group.
R ⁴¹ represents an alkyl group having 1 to 12 carbon atoms which may have a halogen atom or a hydroxy group, a halogen atom, a hydroxy group, a cyano group, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, a glycidyloxy group, an alkoxycarbonyl group having 2 to 12 carbon atoms, or an alkylcarbonyl group having 2 to 4 carbon atoms.
ma represents an integer of 0 to 9. When ma is 2 or more, multiple R ⁴¹ may be the same or different.
^Rc and ^Rd each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.

The halogen atom of R ^x includes a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.
Examples of the alkyl group for R ^x include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, and an n-hexyl group, and are preferably alkyl groups having 1 to 4 carbon atoms, and more preferably a methyl group or an ethyl group.
Examples of the alkyl group having a halogen atom for R ^x include a trifluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluoroisopropyl group, a perfluorobutyl group, a perfluorosec-butyl group, a perfluorotert-butyl group, a perfluoropentyl group, a perfluorohexyl group, a trichloromethyl group, a tribromomethyl group, and a triiodomethyl group.
R ^x is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom, a methyl group or an ethyl group, and even more preferably a hydrogen atom or a methyl group.

Examples of the divalent saturated hydrocarbon group for ^Ax include a linear alkanediyl group, a branched alkanediyl group, and a monocyclic or polycyclic divalent alicyclic saturated hydrocarbon group, and Ax may be a combination of two or more of these groups.
Specifically, methylene group, ethylene group, propane-1,3-diyl group, propane-1,2-diyl group, butane-1,4-diyl group, pentane-1,5-diyl group, hexane-1,6-diyl group, heptane-1,7-diyl group, octane-1,8-diyl group, nonane-1,9-diyl group, decane-1,10-diyl group, undecane-1,11-diyl group linear alkanediyl groups such as a dodecane-1,12-diyl group, a tridecane-1,13-diyl group, a tetradecane-1,14-diyl group, a pentadecane-1,15-diyl group, a hexadecane-1,16-diyl group, a heptadecane-1,17-diyl group, an ethane-1,1-diyl group, a propane-1,1-diyl group, and a propane-2,2-diyl group;
branched alkanediyl groups such as butane-1,3-diyl group, 2-methylpropane-1,3-diyl group, 2-methylpropane-1,2-diyl group, pentane-1,4-diyl group, and 2-methylbutane-1,4-diyl group;
a monocyclic divalent alicyclic saturated hydrocarbon group such as a cycloalkanediyl group, such as a cyclobutane-1,3-diyl group, a cyclopentane-1,3-diyl group, a cyclohexane-1,4-diyl group, or a cyclooctane-1,5-diyl group;
Examples include polycyclic divalent alicyclic saturated hydrocarbon groups such as norbornane-1,4-diyl group, norbornane-2,5-diyl group, adamantane-1,5-diyl group, and adamantane-2,6-diyl group.

R ⁴¹ , X ¹¹ and ma are the same as those in formula (T1′).
Examples of the sultone ring include those mentioned above, and among them, those having a specific bonding position are preferred.

Examples of the structural unit (a6) include the following structural units.

Of these, structural units represented by formula (a6-1), formula (a6-2), formula (a6-6), formula (a6-7), formula (a6-8), and formula (a6-12) are preferred, and structural units represented by formula (a6-1), formula (a6-2), formula (a6-7), and formula (a6-8) are more preferred.
When the resin (A) has the structural unit (a6), the content thereof is preferably 1 to 50 mol %, more preferably 2 to 40 mol %, and even more preferably 3 to 30 mol %, based on all structural units of the resin (A).

<Structural Unit (II)>
Resin (A) may further contain a structural unit that decomposes upon exposure to generate an acid (hereinafter, sometimes referred to as "structural unit (II)"). Specific examples of structural unit (II) include the structural units described in JP-A-2016-79235, and are preferably structural units having a sulfonate group or carboxylate group and an organic cation in the side chain, or a structural unit having a sulfonio group and an organic anion in the side chain.

The structural unit having a sulfonate group or carboxylate group and an organic cation in the side chain is preferably a structural unit represented by formula (II-2-A').
[In formula (II-2-A'),
X ^III3 represents a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, in which —CH ₂ — contained in the saturated hydrocarbon group may be replaced by —O—, —S— or —CO—, and in which a hydrogen atom contained in the saturated hydrocarbon group may be replaced by a halogen atom, an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, or a hydroxy group.
A ^x1 represents an alkanediyl group having 1 to 8 carbon atoms, and a hydrogen atom contained in the alkanediyl group may be substituted with a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms.
RA ^- represents a sulfonate group or a carboxylate group.
R ^III3 represents a hydrogen atom, a halogen atom or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom.
ZA ⁺ represents an organic cation.

Examples of the halogen atom represented by R ^III3 include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.
Examples of the alkyl group having 1 to 6 carbon atoms which may have a halogen atom and which is represented by R ^III3 include the same as the alkyl group having 1 to 6 carbon atoms which may have a halogen atom and which is represented by R ^a8 .
Examples of the alkanediyl group having 1 to 8 carbon atoms represented by A ^x1 include a methylene group, an ethylene group, a propane-1,3-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diyl group, an ethane-1,1-diyl group, a propane-1,1-diyl group, a propane-1,2-diyl group, a propane-2,2-diyl group, a pentane-2,4-diyl group, a 2-methylpropane-1,3-diyl group, a 2-methylpropane-1,2-diyl group, a pentane-1,4-diyl group, and a 2-methylbutane-1,4-diyl group.
Examples of the optionally substituted perfluoroalkyl group having 1 to 6 carbon atoms in A ^X1 include a trifluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluoroisopropyl group, a perfluorobutyl group, a perfluorosec-butyl group, a perfluorotert-butyl group, a perfluoropentyl group, and a perfluorohexyl group.
Examples of the divalent saturated hydrocarbon group having 1 to 18 carbon atoms represented by ^XIII3 include linear or branched alkanediyl groups, and monocyclic or polycyclic divalent alicyclic saturated hydrocarbon groups, and combinations of these may also be used.
Specific examples thereof include linear alkanediyl groups such as methylene, ethylene, propane-1,3-diyl, propane-1,2-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl, nonane-1,9-diyl, decane-1,10-diyl, undecane-1,11-diyl, and dodecane-1,12-diyl; butane-1,3-diyl, 2-methylpropane-1,3-diyl, and 2-methylpropane-1,3-diyl; Examples thereof include branched alkanediyl groups such as pentane-1,2-diyl group, pentane-1,4-diyl group, and 2-methylbutane-1,4-diyl group; cycloalkanediyl groups such as cyclobutane-1,3-diyl group, cyclopentane-1,3-diyl group, cyclohexane-1,4-diyl group, and cyclooctane-1,5-diyl group; and divalent polycyclic alicyclic saturated hydrocarbon groups such as norbornane-1,4-diyl group, norbornane-2,5-diyl group, adamantane-1,5-diyl group, and adamantane-2,6-diyl group.
Examples of saturated hydrocarbon groups in which —CH ₂ — is replaced by —O—, —S— or —CO— include divalent groups represented by formulae (X1) to (X53), where the number of carbon atoms before —CH ₂ — is replaced by —O—, —S— or —CO— is 17 or less. In the following formulae, * and ** represent bonding sites, and * represents a bond to A ^x1 .

^X3 represents a divalent saturated hydrocarbon group having 1 to 16 carbon atoms.
X ⁴ represents a divalent saturated hydrocarbon group having 1 to 15 carbon atoms.
^X5 represents a divalent saturated hydrocarbon group having 1 to 13 carbon atoms.
^X6 represents a divalent saturated hydrocarbon group having 1 to 14 carbon atoms.
^X7 represents a trivalent saturated hydrocarbon group having 1 to 14 carbon atoms.
^X8 represents a divalent saturated hydrocarbon group having 1 to 13 carbon atoms.

Examples of ZA ⁺ in formula (II-2-A') include the same as the cation Z1 ⁺ in the salt represented by formula (B1).

The structural unit represented by formula (II-2-A') is preferably a structural unit represented by formula (II-2-A).
[In formula (II-2-A),
R ^III3 , X ^III3 and ZA ⁺ have the same meanings as above.
z2A represents an integer of 0 to 6.
R ^III2 and R ^III4 each independently represent a hydrogen atom, a fluorine atom, or a perfluoroalkyl group having 1 to 6 carbon atoms, and when z2A is 2 or greater, a plurality of R ^III2s and R ^III4s may be the same or different.
Q ^a and Q ^b each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms.]
Examples of the perfluoroalkyl group having 1 to 6 carbon atoms represented by R ^III2 , R ^III4 , Q ^a and Q ^b include the same perfluoroalkyl groups having 1 to 6 carbon atoms represented by Q ^b1 described above.

The structural unit represented by formula (II-2-A) is preferably a structural unit represented by formula (II-2-A-1).
[In formula (II-2-A-1),
R ^III2 , R ^III3 , R ^III4 , Q ^a , Q ^b and ZA ⁺ have the same meanings as above.
R ^III5 represents a saturated hydrocarbon group having 1 to 12 carbon atoms.
z2A1 represents an integer of 0 to 6.
X ^I2 represents a divalent saturated hydrocarbon group having 1 to 11 carbon atoms, in which —CH ₂ — contained in the saturated hydrocarbon group may be replaced by —O—, —S—, or —CO—, and in which a hydrogen atom contained in the saturated hydrocarbon group may be substituted by a halogen atom or a hydroxy group.]
Examples of the saturated hydrocarbon group having 1 to 12 carbon atoms represented by R ^III5 include linear or branched alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and dodecyl groups.
Examples of the divalent saturated hydrocarbon group represented by X ^I2 include the same as the divalent saturated hydrocarbon group represented by X ^III3 .

As the structural unit represented by formula (II-2-A-1), a structural unit represented by formula (II-2-A-2) is more preferred.
[In formula (II-2-A-2),
R ^III3 , R ^III5 and ZA ⁺ have the same meanings as above.
m and nA each independently represent 1 or 2.

Examples of the structural unit represented by formula (II-2-A') include the following structural units, structural units in which the group corresponding to the methyl group in R ^III3 is replaced with a hydrogen atom, a halogen atom (e.g., a fluorine atom), or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom (e.g., a trifluoromethyl group), and structural units described in WO 2012/050015. ZA ⁺ represents an organic cation.

The structural unit having a sulfonio group and an organic anion on the side chain is preferably a structural unit represented by formula (II-1-1).
[In formula (II-1-1),
A ^II1 represents a single bond or a divalent linking group.
R ^II1 represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms.
R ^II2 and R ^II3 each independently represent a hydrocarbon group having 1 to 18 carbon atoms, and R ^II2 and R ^II3 may be bonded to each other to form a ring together with the sulfur atom to which they are bonded.
R ^II4 represents a hydrogen atom, a halogen atom or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom.
A ⁻ represents an organic anion.
Examples of the divalent aromatic hydrocarbon group having 6 to 18 carbon atoms represented by R ^II1 include a phenylene group and a naphthylene group.
Examples of the hydrocarbon group represented by R ^II2 and R ^II3 include an alkyl group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, and a group formed by combining these groups.
Examples of the halogen atom represented by R ^II4 include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.
Examples of the alkyl group having 1 to 6 carbon atoms which may have a halogen atom and which is represented by R ^II4 include the same as the alkyl group having 1 to 6 carbon atoms which may have a halogen atom and which is represented by R ^a8 .
Examples of the divalent linking group represented by A ^II1 include divalent saturated hydrocarbon groups having 1 to 18 carbon atoms, in which —CH ₂ — may be replaced by —O—, —S— or —CO—. Specific examples include the same as the divalent saturated hydrocarbon groups having 1 to 18 carbon atoms represented by X ^III3 .

Examples of the cation-containing structural unit in formula (II-1-1) include structural units represented by the following formulas and structural units in which the group corresponding to the methyl group in R ^II4 is replaced with a hydrogen atom, a fluorine atom, a trifluoromethyl group, or the like.

Examples of the organic anion represented by ^A- include a sulfonate anion, a sulfonylimide anion, a sulfonylmethide anion, and a carboxylate anion. The organic anion represented by ^A- is preferably a sulfonate anion, and the sulfonate anion is more preferably an anion contained in the salt represented by the above formula (B1). The sulfonylimide anion, sulfonylmethide anion, and carboxylate anion are more preferably an anion ^AI- contained in the salt represented by the above formula (I).

Examples of the structural unit represented by formula (II-1-1) include structural units represented by the following formulas:

When the structural unit (II) is contained in the resin (A), the content of the structural unit (II) is preferably 1 to 20 mol %, more preferably 2 to 15 mol %, and even more preferably 3 to 10 mol %, based on the total structural units of the resin (A).

Resin (A) may contain structural units other than those described above, including structural units well known in the art.

The resin (A) is preferably a resin composed of the structural unit (a1) and the structural unit (s), that is, a copolymer of the monomer (a1) and the monomer (s).
The structural unit (a1) is preferably at least one selected from the group consisting of the structural unit (a1-0), the structural unit (a1-1), and the structural unit (a1-2) (preferably the structural unit having a cyclohexyl group and a cyclopentyl group), more preferably at least two selected from the group consisting of the structural unit (a1-1) and the structural unit (a1-2).
The structural unit (s) is preferably at least one selected from the group consisting of the structural unit (a2) and the structural unit (a3). The structural unit (a2) is preferably the structural unit (a2-1) or the structural unit (a2-A). The structural unit (a3) is preferably at least one selected from the group consisting of the structural unit represented by formula (a3-1), the structural unit represented by formula (a3-2), and the structural unit represented by formula (a3-4).
The structural units constituting the resin (A) may be used singly or in combination of two or more, and can be produced by a known polymerization method (e.g., radical polymerization) using monomers that lead to these structural units. The content of each structural unit in the resin (A) can be adjusted by the amount of monomer used in the polymerization.
The weight average molecular weight of the resin (A) is preferably 2,000 or more (more preferably 2,500 or more, even more preferably 3,000 or more) and 50,000 or less (more preferably 30,000 or less, even more preferably 15,000 or less). In this specification, the weight average molecular weight is a value determined by gel permeation chromatography under the conditions described in the Examples.

<Resins other than resin (A)>
The resist composition of the present invention may contain a resin other than the resin (A) in combination.
Examples of resins other than resin (A) include resins containing the structural unit (a4) or the structural unit (a5) (hereinafter, sometimes referred to as resin (X)).
Of these, the resin (X) is preferably a resin containing the structural unit (a4).
In the resin (X), the content of the structural unit (a4) is preferably 30 mol % or more, more preferably 40 mol % or more, and even more preferably 45 mol % or more, based on the total amount of all structural units in the resin (X).
Examples of structural units that the resin (X) may further have include the structural unit (a1), the structural unit (a2), the structural unit (a3), and structural units derived from other known monomers. Among these, the resin (X) is preferably a resin consisting only of the structural unit (a4) and/or the structural unit (a5).
The structural units constituting the resin (X) may be used singly or in combination of two or more, and can be produced by a known polymerization method (e.g., radical polymerization) using monomers that derive these structural units. The content of each structural unit in the resin (X) can be adjusted by the amount of monomer used in the polymerization.
The weight average molecular weight of resin (X) is preferably 6,000 or more (more preferably 7,000 or more) and 80,000 or less (more preferably 60,000 or less). The method for measuring the weight average molecular weight of resin (X) is the same as that for resin (A).

When the resist composition of the present invention contains resin (X), the content thereof is preferably 1 to 60 parts by mass, more preferably 1 to 50 parts by mass, even more preferably 1 to 40 parts by mass, even more preferably 1 to 30 parts by mass, and particularly preferably 1 to 8 parts by mass, per 100 parts by mass of resin (A).

The content of resin (A) in the resist composition is preferably 80% to 99% by mass, and more preferably 90% to 99% by mass, based on the solid content of the resist composition. Furthermore, when a resin other than resin (A) is contained, the total content of resin (A) and the resin other than resin (A) is preferably 80% to 99% by mass, and more preferably 90% to 99% by mass, based on the solid content of the resist composition. In this specification, the "solid content of the resist composition" refers to the sum of all components in the resist composition excluding solvent (E), which will be described later. The solid content of the resist composition and the resin content relative to the solid content can be measured using known analytical methods such as liquid chromatography or gas chromatography.

<Solvent (E)>
The content of the solvent (E) in the resist composition is usually from 90% by mass to 99.9% by mass, preferably from 92% by mass to 99% by mass, and more preferably from 94% by mass to 99% by mass. The content of the solvent (E) can be measured by known analytical means such as liquid chromatography or gas chromatography.

Examples of solvent (E) include glycol ether esters such as ethyl cellosolve acetate, methyl cellosolve acetate, and propylene glycol monomethyl ether acetate; glycol ethers such as propylene glycol monomethyl ether; esters such as ethyl lactate, butyl acetate, amyl acetate, and ethyl pyruvate; ketones such as acetone, methyl isobutyl ketone, 2-heptanone, and cyclohexanone; and cyclic esters such as gamma-butyrolactone. One type of solvent (E) may be used alone, or two or more types may be used.

<Quencher (C)>
Examples of the quencher (C) include a basic nitrogen-containing organic compound and a salt that generates an acid that is weaker in acidity than the acid generated from the acid generator (B). When the resist composition contains the quencher (C), the content of the quencher (C) is preferably from about 0.01 to 15 mass%, more preferably from about 0.01 to 10 mass%, even more preferably from about 0.1 to 5 mass%, and even more preferably from about 0.1 to 3 mass%, based on the solids content of the resist composition.
The basic nitrogen-containing organic compound includes amines and ammonium salts. The amines include aliphatic amines and aromatic amines. The aliphatic amines include primary amines, secondary amines, and tertiary amines.

Amines include 1-naphthylamine, 2-naphthylamine, aniline, diisopropylaniline, 2-, 3-, or 4-methylaniline, 4-nitroaniline, N-methylaniline, N,N-dimethylaniline, diphenylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, triethylamine, trimethylamine, tripropylamine, tributamine, ethylamine, tripentylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, methyldibutylamine, methyldipentylamine, methyldihexylamine, methyldicyclohexylamine, methyldiheptylamine, methyldioctylamine, methyldinonylamine, methyldidecylamine, ethyldibutylamine, ethyldipentylamine, ethyldihexylamine, ethyldiheptylamine, ethyldioctylamine, ethyldinonylamine, ethyldi Decylamine, dicyclohexylmethylamine, tris[2-(2-methoxyethoxy)ethyl]amine, triisopropanolamine, ethylenediamine, tetramethylenediamine, hexamethylenediamine, 4,4'-diamino-1,2-diphenylethane, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 4,4'-diamino-3,3'-diethyldiphenylmethane, 2,2'-methylenebisaniline, imidazole, 4-methylimidazole, pyridine, 4-methylpyridine, 1,2-di(2-pyridinyl)-2-methylpropanol ... Examples include 4,4'-dipyridyl)ethane, 1,2-di(4-pyridyl)ethane, 1,2-di(2-pyridyl)ethene, 1,2-di(4-pyridyl)ethene, 1,3-di(4-pyridyl)propane, 1,2-di(4-pyridyloxy)ethane, di(2-pyridyl)ketone, 4,4'-dipyridyl sulfide, 4,4'-dipyridyl disulfide, 2,2'-dipyridylamine, 2,2'-dipicolylamine, and bipyridine, preferably diisopropylaniline, and more preferably 2,6-diisopropylaniline.

Examples of ammonium salts include tetramethylammonium hydroxide, tetraisopropylammonium hydroxide, tetrabutylammonium hydroxide, tetrahexylammonium hydroxide, tetraoctylammonium hydroxide, phenyltrimethylammonium hydroxide, 3-(trifluoromethyl)phenyltrimethylammonium hydroxide, tetra-n-butylammonium salicylate, and choline.

The acidity of a salt that generates an acid weaker than the acid generated from the acid generator (B) is indicated by its acid dissociation constant (pKa). A salt that generates an acid weaker than the acid generated from the acid generator (B) is a salt whose acid dissociation constant of the acid generated from the salt is usually −3<pKa, preferably −1<pKa<7, and more preferably 0<pKa<5.
Examples of salts that generate an acid that is weaker in acidity than the acid generated from acid generator (B) include salts represented by the following formula, salts represented by formula (D) described in JP 2015-147926 A (hereinafter, sometimes referred to as "weak acid inner salt (D)"), and salts described in JP 2012-229206 A, JP 2012-6908 A, JP 2012-72109 A, JP 2011-39502 A, and JP 2011-191745 A. The salt that generates an acid that is weaker in acidity than the acid generated from acid generator (B) is preferably a salt that generates a carboxylic acid that is weaker in acidity than the acid generated from acid generator (B) (salt having a carboxylic acid anion), and more preferably a weak acid inner salt (D).

Examples of the weak acid inner salt (D) include the following salts.

<Other ingredients>
The resist composition of the present invention may optionally contain components other than those described above (hereinafter, these may be referred to as "other components (F)"). There are no particular limitations on the other components (F), and additives known in the resist field, such as sensitizers, dissolution inhibitors, surfactants, stabilizers, and dyes, can be used.

<Preparation of Resist Composition>
The resist composition of the present invention can be prepared by mixing the salt (I), resin (A), acid generator (B), and, if necessary, a resin other than the resin (A), solvent (E), quencher (C), and other components (F). The order of mixing is arbitrary and is not particularly limited. The temperature during mixing can be selected from 10 to 40°C, depending on the type of resin, the solubility of the resin in the solvent (E), and other factors. The mixing time can be selected from 0.5 to 24 hours, depending on the mixing temperature. The mixing means is also not particularly limited, and stirring and mixing can be used.
After mixing the components, it is preferable to filter the mixture using a filter with a pore size of about 0.003 to 0.2 μm.

<Method for producing a resist pattern>
The method for producing a resist pattern of the present invention comprises the steps of:
(1) applying the resist composition of the present invention onto a substrate;
(2) a step of drying the applied composition to form a composition layer;
(3) exposing the composition layer to light;
(4) a step of heating the composition layer after exposure; and (5) a step of developing the composition layer after heating.
The resist composition can be applied to a substrate using a commonly used device such as a spin coater. Examples of the substrate include inorganic substrates such as silicon wafers and organic substrates such as those with a pre-formed resist film. Before applying the resist composition, the substrate may be cleaned, and an anti-reflective film or the like may be formed on the substrate.
The composition after coating is dried to remove the solvent and form a composition layer. Drying is carried out, for example, by evaporating the solvent using a heating device such as a hot plate (so-called pre-baking), or by using a vacuum device. The heating temperature is preferably 50 to 200°C, and the heating time is preferably 10 to 180 seconds. The pressure during vacuum drying is preferably about 1 to 1.0 x ¹⁰⁵ Pa.
The obtained composition layer is usually exposed using an exposure machine. The exposure machine may be an immersion exposure machine. As the exposure light source, various types can be used, such as those that emit ultraviolet laser light such as KrF excimer laser (wavelength 248 nm), ArF excimer laser (wavelength 193 nm), and _F2 excimer laser (wavelength 157 nm), those that emit harmonic laser light in the far ultraviolet or vacuum ultraviolet region by wavelength conversion of laser light from a solid laser light source (YAG or semiconductor laser, etc.), and those that irradiate electron beams or extreme ultraviolet light (EUV). In this specification, irradiation with these types of radiation may be collectively referred to as "exposure". During exposure, exposure is usually performed through a mask corresponding to the desired pattern. When the exposure light source is an electron beam, exposure may be performed by direct writing without using a mask.
The composition layer after exposure is subjected to a heat treatment (so-called post-exposure bake) to promote the deprotection reaction of the acid labile groups. The heating temperature is usually about 50 to 200°C, preferably about 70 to 150°C. A chemical treatment (silylation) may be performed to adjust the hydrophilicity or hydrophobicity of the resin on the surface side of the composition after heating. Furthermore, before development, the steps of applying a resist composition, drying, exposing, and heating may be repeatedly performed on the composition layer after exposure.
The heated composition layer is usually developed using a developer in a developing device. Development methods include dipping, puddling, spraying, and dynamic dispensing. The development temperature is preferably, for example, 5 to 60°C, and the development time is preferably, for example, 5 to 300 seconds. By selecting the type of developer as follows, a positive resist pattern or a negative resist pattern can be produced.
When producing a positive resist pattern from the resist composition of the present invention, an alkaline developer is used as the developer. The alkaline developer may be any of various alkaline aqueous solutions used in this field. Examples include aqueous solutions of tetramethylammonium hydroxide and (2-hydroxyethyl)trimethylammonium hydroxide (commonly known as choline). The alkaline developer may also contain a surfactant.
After development, the resist pattern is preferably washed with ultrapure water, and then water remaining on the substrate and pattern is removed.
When a negative resist pattern is produced from the resist composition of the present invention, a developer containing an organic solvent (hereinafter sometimes referred to as an "organic developer") is used as the developer.
Examples of the organic solvent contained in the organic developer include ketone solvents such as 2-hexanone and 2-heptanone; glycol ether ester solvents such as propylene glycol monomethyl ether acetate; ester solvents such as butyl acetate; glycol ether solvents such as propylene glycol monomethyl ether; amide solvents such as N,N-dimethylacetamide; and aromatic hydrocarbon solvents such as anisole.
The content of the organic solvent in the organic developer is preferably 90% by mass or more and 100% by mass or less, more preferably 95% by mass or more and 100% by mass or less, and even more preferably substantially only the organic solvent.
Among these, the organic developer is preferably a developer containing butyl acetate and/or 2-heptanone. The total content of butyl acetate and 2-heptanone in the organic developer is preferably 50% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and even more preferably the organic developer contains substantially only butyl acetate and/or 2-heptanone.
The organic developer may contain a surfactant and a small amount of water.
During development, development may be stopped by replacing the organic developer with a different type of solvent.
The developed resist pattern is preferably washed with a rinse solution. There are no particular limitations on the rinse solution as long as it does not dissolve the resist pattern, and a solution containing a general organic solvent can be used, preferably an alcohol solvent or an ester solvent.
After cleaning, it is preferable to remove the rinse liquid remaining on the substrate and the pattern.

<Application>
The resist composition of the present invention is suitable as a resist composition for KrF excimer laser exposure, a resist composition for ArF excimer laser exposure, a resist composition for electron beam (EB) exposure, or a resist composition for EUV exposure, and is particularly suitable as a resist composition for electron beam (EB) exposure or a resist composition for EUV exposure, and is useful for semiconductor microfabrication.

The present invention will be explained in more detail with reference to examples. In the examples, "%" and "parts" representing the content or amount used are by mass unless otherwise specified.
The weight-average molecular weight is a value determined by gel permeation chromatography under the following analytical conditions:
Column: TSKgel Multipore HXL-M x 3 + guard column (Tosoh Corporation)
Eluent: tetrahydrofuran Flow rate: 1.0 mL/min
Detector: RI detector Column temperature: 40°C
Injection volume: 100μl
Molecular weight standard: Standard polystyrene (Tosoh Corporation)
The structure of the compound was confirmed by measuring the molecular ion peak using mass spectrometry (LC: Agilent 1100 model, MASS: Agilent LC/MSD model). In the following examples, the value of this molecular ion peak is indicated by "MASS".

Example 1: Synthesis of salt represented by formula (I-8)
20 parts of the compound represented by formula (I-8-a), 2.28 parts of the compound represented by formula (I-8-c), 100 parts of ethyl acetate, and 15 parts of tetrahydrofuran were mixed and stirred at 23°C for 30 minutes. 6.55 parts of the compound represented by formula (I-8-b) were added to the resulting mixed solution, and the mixture was stirred at 23°C for 18 hours. 20 parts of n-heptane and 70 parts of ion-exchanged water were added to the resulting reaction mass, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. 60 parts of ion-exchanged water was added to the recovered organic layer, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. This water washing procedure was repeated four times. The resulting organic layer was concentrated, and the concentrated mass was separated using a column (silica gel 60N (spherical, neutral) 100-210 μm; Kanto Chemical Co., Inc., developing solvent: n-heptane/ethyl acetate=1/1) to obtain 7.48 parts of the compound represented by formula (I-8-d).
0.95 parts of the compound represented by formula (I-8-d) and 10 parts of tetrahydrofuran were mixed and stirred at 23°C for 30 minutes, then cooled to 5°C, and 0.14 parts of sodium hydride was added. To the resulting mixture, 1.81 parts of the salt represented by formula (I-8-e) was added, and the mixture was stirred at 5°C for 3 hours. To the resulting mixture, 6.30 parts of 1N hydrochloric acid was added, and the mixture was heated to 23°C and stirred at 23°C for 6 hours. To the resulting mixture, 30 parts of chloroform and 15 parts of ion-exchanged water were added, and the mixture was stirred at 23°C for 30 minutes, followed by separation and isolation of the organic layer. The resulting organic layer was concentrated, and then 1 part of acetonitrile and 30 parts of tert-butyl methyl ether were added to the concentrated residue, and the mixture was stirred at 23°C for 30 minutes. The supernatant was removed, and the mixture was concentrated to obtain 1.52 parts of the salt represented by formula (I-8-f).
0.95 parts of the salt represented by formula (I-8-f) and 30 parts of dimethylformamide were mixed and stirred at 23°C for 30 minutes, after which 0.16 parts of potassium carbonate and 0.05 parts of potassium iodide were added, and the mixture was heated to 75°C. 0.57 parts of the compound represented by formula (I-8-g) was added to the resulting mixture, and the mixture was stirred at 75°C for 5 hours, and then cooled to 23°C. 50 parts of chloroform and 20 parts of a 5% aqueous oxalic acid solution were added to the resulting mixture, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. 20 parts of ion-exchanged water was added to the resulting organic layer, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. This water-washing operation was repeated five times. The resulting organic layer was concentrated to obtain 1.14 parts of the salt represented by formula (I-8-h).
0.98 parts of the salt represented by formula (I-8-h), 1.02 parts of the salt represented by formula (I-8-i), 30 parts of chloroform, and 15 parts of ethyl acetate were mixed and stirred at 23°C for 2 hours. 20 parts of ion-exchanged water was added to the obtained mixture, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. This water washing procedure was repeated five times. The obtained organic layer was concentrated, and 30 parts of tert-butyl methyl ether was added to the concentrated residue, followed by stirring at 23°C for 30 minutes and filtration to obtain 1.39 parts of the salt represented by formula (I-8).
MASS (ESI (+) Spectrum): M ⁺ 577.2
MASS (ESI(-)Spectrum): M ^- 517.1

Example 2: Synthesis of salt represented by formula (I-4)
0.98 parts of the salt represented by formula (I-8-h), 0.66 parts of the salt represented by formula (I-4-i), 30 parts of chloroform, and 15 parts of ethyl acetate were mixed and stirred at 23°C for 2 hours. 20 parts of ion-exchanged water was added to the obtained mixture, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. This water washing procedure was repeated five times. The obtained organic layer was concentrated, and 30 parts of tert-butyl methyl ether was added to the concentrated residue, followed by stirring at 23°C for 30 minutes, and then filtration was performed to obtain 0.92 parts of the salt represented by formula (I-4).
MASS (ESI (+) Spectrum): M ⁺ 577.2
MASS (ESI (-) Spectrum): M ^- 311.0

Example 3: Synthesis of salt represented by formula (I-16)
0.98 parts of the salt represented by formula (I-8-h), 0.91 parts of the salt represented by formula (I-16-i), 30 parts of chloroform, and 15 parts of ethyl acetate were mixed and stirred at 23°C for 2 hours. 20 parts of ion-exchanged water was added to the obtained mixture, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. This water washing procedure was repeated five times. The obtained organic layer was concentrated, and 30 parts of tert-butyl methyl ether was added to the concentrated residue, followed by stirring at 23°C for 30 minutes and filtration to obtain 1.26 parts of the salt represented by formula (I-16).
MASS (ESI (+) Spectrum): M ⁺ 577.2
MASS (ESI(-)Spectrum): M ^- 467.1

Example 4: Synthesis of salt represented by formula (I-472)
0.95 parts of the salt represented by formula (I-8-f) and 30 parts of dimethylformamide were mixed and stirred at 23°C for 30 minutes, after which 0.16 parts of potassium carbonate and 0.05 parts of potassium iodide were added, and the temperature was raised to 75°C. 0.80 parts of the compound represented by formula (I-472-g) was added to the resulting mixture, and the mixture was stirred at 75°C for 5 hours and then cooled to 23°C. 50 parts of chloroform and 20 parts of a 5% aqueous oxalic acid solution were added to the resulting mixture, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. 20 parts of ion-exchanged water was added to the resulting organic layer, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. This water-washing procedure was repeated five times. The resulting organic layer was concentrated to obtain 1.39 parts of the salt represented by formula (I-472-h).
1.14 parts of the salt represented by formula (I-472-h), 0.91 parts of the salt represented by formula (I-16-i), 30 parts of chloroform, and 15 parts of ethyl acetate were mixed and stirred at 23°C for 2 hours. 20 parts of ion-exchanged water was added to the obtained mixture, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. This water-washing procedure was repeated five times. The obtained organic layer was concentrated, and 30 parts of tert-butyl methyl ether was added to the concentrated residue, followed by stirring at 23°C for 30 minutes and filtration to obtain 1.53 parts of the salt represented by formula (I-472).
MASS (ESI (+) Spectrum): M ⁺ 677.3
MASS (ESI(-)Spectrum): M ^- 467.1

Example 5: Synthesis of salt represented by formula (I-1004)
2.10 parts of the compound represented by formula (I-8-d) and 20 parts of tetrahydrofuran were mixed and stirred at 23°C for 30 minutes, then cooled to 5°C, and 0.28 parts of sodium hydride was added. To the resulting mixture, 1.91 parts of the salt represented by formula (I-1004-e) was added, and the mixture was stirred at 5°C for 3 hours. To the resulting mixture, 12.60 parts of 1N hydrochloric acid was added, and the mixture was heated to 23°C and stirred at 23°C for 6 hours. To the resulting mixture, 50 parts of chloroform and 25 parts of ion-exchanged water were added, and the mixture was stirred at 23°C for 30 minutes, followed by separation and extraction of the organic layer. The resulting organic layer was concentrated, and then 3 parts of acetonitrile and 30 parts of tert-butyl methyl ether were added to the concentrated residue, and the mixture was stirred at 23°C for 30 minutes, after which the supernatant was removed and the mixture was concentrated to obtain 2.42 parts of the salt represented by formula (I-1004-f).
1.20 parts of the salt represented by formula (I-1004-f) and 30 parts of dimethylformamide were mixed and stirred at 23°C for 30 minutes, after which 0.32 parts of potassium carbonate and 0.10 parts of potassium iodide were added and the temperature was raised to 75°C. To the resulting mixture, 1.37 parts of the compound represented by formula (I-8-g) was added, and the mixture was stirred at 75°C for 5 hours and then cooled to 23°C. To the resulting mixture, 50 parts of chloroform and 20 parts of a 5% aqueous oxalic acid solution were added, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. To the resulting organic layer, 20 parts of ion-exchanged water was added, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. This water-washing operation was repeated five times. The resulting organic layer was concentrated to obtain 1.66 parts of the salt represented by formula (I-1004-h).
1.43 parts of the salt represented by formula (I-1004-h), 0.91 parts of the salt represented by formula (I-16-i), 30 parts of chloroform, and 15 parts of ethyl acetate were mixed and stirred at 23°C for 2 hours. 20 parts of ion-exchanged water was added to the obtained mixture, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. This water-washing procedure was repeated five times. The obtained organic layer was concentrated, and 30 parts of tert-butyl methyl ether was added to the concentrated residue, followed by stirring at 23°C for 30 minutes, and then filtration was performed to obtain 1.89 parts of the salt represented by formula (I-1004).
MASS (ESI (+) Spectrum): M ⁺ 893.3
MASS (ESI(-)Spectrum): M ^- 467.1

Example 6: Synthesis of salt represented by formula (I-1042)
3.15 parts of the compound represented by formula (I-8-d) and 30 parts of tetrahydrofuran were mixed and stirred at 23°C for 30 minutes, then cooled to 5°C, and 0.42 parts of sodium hydride was added. 2.01 parts of the salt represented by formula (I-1042-e) was added to the resulting mixture, and the mixture was stirred at 5°C for 3 hours. 18.90 parts of 1N hydrochloric acid was added to the resulting mixture, and the temperature was raised to 23°C and the mixture was stirred at 23°C for 6 hours. 100 parts of chloroform and 50 parts of ion-exchanged water were added to the resulting mixture, and the mixture was stirred at 23°C for 30 minutes, followed by separation and extraction of the organic layer. The resulting organic layer was concentrated, and then 5 parts of acetonitrile and 30 parts of tert-butyl methyl ether were added to the concentrated residue, and the mixture was stirred at 23°C for 30 minutes, after which the supernatant was removed and the mixture was concentrated to obtain 3.11 parts of the salt represented by formula (I-1042-f).
1.45 parts of the salt represented by formula (I-1042-f) and 30 parts of dimethylformamide were mixed and stirred at 23°C for 30 minutes, after which 0.48 parts of potassium carbonate and 0.15 parts of potassium iodide were added and the temperature was raised to 75°C. To the resulting mixture, 2.05 parts of the compound represented by formula (I-8-g) were added, and the mixture was stirred at 75°C for 5 hours and then cooled to 23°C. To the resulting mixture, 50 parts of chloroform and 20 parts of a 5% aqueous oxalic acid solution were added, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. To the resulting organic layer, 20 parts of ion-exchanged water was added, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. This water-washing operation was repeated five times. The resulting organic layer was concentrated to obtain 2.05 parts of the salt represented by formula (I-1042-h).
1.99 parts of the salt represented by formula (I-1042-h), 0.91 parts of the salt represented by formula (I-16-i), 30 parts of chloroform, and 15 parts of ethyl acetate were mixed and stirred at 23°C for 2 hours. 20 parts of ion-exchanged water was added to the obtained mixture, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. This water washing procedure was repeated five times. The obtained organic layer was concentrated, and 30 parts of tert-butyl methyl ether was added to the concentrated residue, followed by stirring at 23°C for 30 minutes, and then filtration was performed to obtain 2.32 parts of the salt represented by formula (I-1042).
MASS (ESI (+) Spectrum): M ⁺ 1209.5
MASS (ESI(-)Spectrum): M ^- 467.1

Example 7: Synthesis of salt represented by formula (I-1802)
6.57 parts of the compound represented by formula (I-1802-a), 0.23 parts of the compound represented by formula (I-8-c), 30 parts of ethyl acetate, and 15 parts of tetrahydrofuran were mixed and stirred at 23°C for 30 minutes. 0.66 parts of the compound represented by formula (I-8-b) was added to the resulting mixed solution, and the mixture was stirred at 23°C for 18 hours. 100 parts of n-heptane and 20 parts of ion-exchanged water were added to the resulting reaction mass, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. 20 parts of ion-exchanged water was added to the recovered organic layer, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. This water washing procedure was repeated four times. The obtained organic layer was concentrated, and the concentrated mass was separated through a column (silica gel 60N (spherical, neutral) 100-210 μm; manufactured by Kanto Chemical Co., Inc., developing solvent: n-heptane/ethyl acetate=1/1) to obtain 6.28 parts of the compound represented by formula (I-1802-d).
2.26 parts of the compound represented by formula (I-1802-d) and 10 parts of tetrahydrofuran were mixed and stirred at 23°C for 30 minutes, then cooled to 5°C, and 0.14 parts of sodium hydride was added. To the resulting mixture, 1.81 parts of the salt represented by formula (I-8-e) was added, and the mixture was stirred at 5°C for 3 hours. To the resulting mixture, 6.30 parts of 1N hydrochloric acid was added, and the mixture was heated to 23°C and stirred at 23°C for 6 hours. To the resulting mixture, 30 parts of chloroform and 15 parts of ion-exchanged water were added, and the mixture was stirred at 23°C for 30 minutes, followed by separation and isolation of the organic layer. The resulting organic layer was concentrated, and then 1 part of acetonitrile and 30 parts of tert-butyl methyl ether were added to the concentrated residue, and the mixture was stirred at 23°C for 30 minutes, after which the supernatant was removed and concentrated to obtain 2.58 parts of the salt represented by formula (I-1802-f).
1.54 parts of the salt represented by formula (I-1802-f) and 30 parts of dimethylformamide were mixed and stirred at 23°C for 30 minutes, after which 0.16 parts of potassium carbonate and 0.05 parts of potassium iodide were added, and the temperature was raised to 75°C. To the resulting mixture, 0.57 parts of the compound represented by formula (I-8-g) was added, and the mixture was stirred at 75°C for 5 hours, and then cooled to 23°C. To the resulting mixture, 50 parts of chloroform and 20 parts of a 5% aqueous oxalic acid solution were added, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. To the resulting organic layer, 20 parts of ion-exchanged water was added, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. This water-washing operation was repeated five times. The resulting organic layer was concentrated to obtain 1.78 parts of the salt represented by formula (I-1802-h).
1.38 parts of the salt represented by formula (I-1802-h), 0.91 parts of the salt represented by formula (I-16-i), 30 parts of chloroform, and 15 parts of ethyl acetate were mixed and stirred at 23°C for 2 hours. 20 parts of ion-exchanged water was added to the obtained mixture, and the mixture was stirred at 23°C for 30 minutes, followed by separation to separate the organic layer. This water washing procedure was repeated five times. The obtained organic layer was concentrated, and 30 parts of tert-butyl methyl ether was added to the concentrated residue, followed by stirring at 23°C for 30 minutes, and then filtration was performed to obtain 1.54 parts of the salt represented by formula (I-1802).
MASS (ESI (+) Spectrum): M ⁺ 829.0
MASS (ESI(-)Spectrum): M ^- 467.1

Synthesis of Resin The compounds (monomers) used in the synthesis of Resin (A) are shown below. Hereinafter, these compounds will be referred to as "monomers (a1-1-3)" etc. according to their formula numbers.

Synthesis Example 1 [Synthesis of Resin A1]
Monomer (a1-4-2), monomer (a1-1-3), and monomer (a1-2-6) were used as monomers, and the molar ratio [monomer (a1-4-2):monomer (a1-1-3):monomer (a1-2-6)] was mixed at a ratio of 38:24:38. Furthermore, 1.5 times by mass of methyl isobutyl ketone was mixed with this monomer mixture, based on the total mass of all monomers. Azobisisobutyronitrile was added as an initiator to the resulting mixture, based on the total number of moles of all monomers, at 7 mol%, and the mixture was heated at 85°C for approximately 5 hours to carry out polymerization. Thereafter, 2.0 times by mass of an aqueous p-toluenesulfonic acid solution (2.5 wt%) was added to the polymerization reaction solution, based on the total mass of all monomers, and the mixture was stirred for 6 hours, followed by separation. The resulting organic layer was poured into a large amount of n-heptane to precipitate a resin, which was then filtered and recovered to obtain Resin A1 (copolymer) with a weight-average molecular weight of approximately 5.3 × 10 ³ in a yield of 78%. This Resin A1 has the following structural units:

Synthesis Example 2 [Synthesis of Resin A2]
Monomer (a1-4-2) and monomer (a1-2-6) were used as monomers, and they were mixed so that the molar ratio [monomer (a1-4-2):monomer (a1-2-6)] was 38:62. Furthermore, 1.5 times by mass of methyl isobutyl ketone was mixed with this monomer mixture, based on the total mass of all monomers. Azobisisobutyronitrile was added as an initiator to the resulting mixture, in an amount of 7 mol% based on the total moles of all monomers, and the mixture was heated at 85°C for approximately 5 hours to polymerize. Subsequently, 2.0 times by mass of an aqueous p-toluenesulfonic acid solution (2.5 wt%) based on the total mass of all monomers was added to the polymerization reaction solution, stirred for 6 hours, and then separated. The resulting organic layer was poured into a large amount of n-heptane to precipitate the resin, which was then filtered and recovered, yielding resin A2 (copolymer) with a weight average molecular weight of approximately 5.4 x ¹⁰³ in an 89% yield. This resin A2 has the following structural units.

Synthesis Example 3 [Synthesis of Resin A3]
Monomers (a1-1-3), (a1-2-6), (a2-1-3), (a3-4-2), and (aa1-4-2) were used and mixed in a molar ratio of 20:35:3:15:27 [monomer (a1-1-3):monomer (a1-2-6):monomer (a2-1-3):monomer (a3-4-2):monomer (a1-4-2)]. This monomer mixture was then mixed with 1.5 times the mass of methyl isobutyl ketone relative to the total mass of all monomers. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the resulting mixture in amounts of 1.2 mol% and 3.6 mol%, respectively, relative to the total monomer amount, and the mixture was heated at 73°C for approximately 5 hours. Thereafter, an aqueous solution of p-toluenesulfonic acid (2.5 wt%) was added to the polymerization reaction solution in an amount 2.0 times the total mass of all monomers, and the mixture was stirred for 12 hours and then separated. The recovered organic layer was poured into a large amount of n-heptane to precipitate a resin, which was then filtered and recovered to obtain Resin A3 with a weight-average molecular weight of approximately 5.3 x ¹⁰³ in a yield of 63%. This Resin A3 has the following structural units:

Synthesis Example 4 [Synthesis of Resin A4]
Monomers (a1-1-3), (a1-2-6), (a2-1-3), (a3-4-2), and (a1-4-13) were used and mixed in a molar ratio of 20:35:3:15:27 [monomer (a1-1-3):monomer (a1-2-6):monomer (a2-1-3):monomer (a3-4-2):monomer (a1-4-13)]. This monomer mixture was then mixed with 1.5 times the mass of methyl isobutyl ketone relative to the total mass of all monomers. Azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile) were added as initiators to the resulting mixture in amounts of 1.2 mol% and 3.6 mol%, respectively, relative to the total monomer amount, and the mixture was heated at 73°C for approximately 5 hours. Thereafter, an aqueous solution of p-toluenesulfonic acid (2.5 wt%) was added to the polymerization reaction solution in an amount 2.0 times the total mass of all monomers, and after stirring for 12 hours, the layers were separated. The recovered organic layer was poured into a large amount of n-heptane to precipitate a resin, which was then filtered and recovered to obtain Resin A4 with a weight-average molecular weight of approximately 5.1 x ¹⁰³ in a yield of 61%. This Resin A4 has the following structural units:

<Preparation of Resist Composition>
As shown in Table 2, the following components were mixed and the resulting mixture was filtered through a fluororesin filter with a pore size of 0.2 μm to prepare a resist composition.

<Resin>
A1 to A4: Resin A1 to Resin A4
<Salt (I)>
I-4: Salt represented by formula (I-4) I-8: Salt represented by formula (I-8) I-16: Salt represented by formula (I-16) I-472: Salt represented by formula (I-472) I-1004: Salt represented by formula (I-1004) I-1042: Salt represented by formula (I-1042) I-1802: Salt represented by formula (I-1802) <Acid Generator>
IX-1
IX-2
IX-3
<Quencher (C)>
C1: Synthesized by the method described in JP 2011-39502 A
<Solvent>
Propylene glycol monomethyl ether acetate 400 parts Propylene glycol monomethyl ether 100 parts γ-butyrolactone 5 parts

(Electron Beam Exposure Evaluation of Resist Composition: Alkaline Development)
A 6-inch silicon wafer was treated with hexamethyldisilazane on a direct hot plate at 90°C for 60 seconds. The resist composition was spin-coated onto this silicon wafer so that the film thickness of the composition layer was 0.04 μm. The wafer was then pre-baked on a direct hot plate for 60 seconds at the temperature shown in the "PB" column in Table 2 to form a composition layer. A line and space pattern (pitch 36 to 72 nm/line width 18 to 36 nm) was directly written onto the composition layer formed on the wafer using an electron beam lithography machine (ELS-F125 125 keV, manufactured by Elionix Co., Ltd.) by gradually changing the exposure dose.
After exposure, post-exposure baking was performed on a hot plate for 60 seconds at the temperature shown in the "PEB" column of Table 2, and then puddle development was performed for 60 seconds using a 2.38% by mass aqueous solution of tetramethylammonium hydroxide to obtain a resist pattern.
In the obtained resist pattern, the exposure amount at which the line width and space width of a 36 nm line and space pattern became 1:1 was defined as effective sensitivity.

<Resolution evaluation>
At the effective sensitivity, the resist pattern was observed with a scanning electron microscope, and the minimum line width that could be resolved was taken as the resolution. The results are shown in Table 3. The resolution (nm) is shown.
In comparison with the comparative compositions 1 to 3, the compositions 1 to 8 were evaluated as being good in terms of resolution.

The above results show that the salt of the present invention and the resist composition containing said salt provide good resolution.

(Electron Beam Exposure Evaluation of Resist Composition: Organic Solvent Development)
A 6-inch silicon wafer was treated with hexamethyldisilazane on a direct hot plate at 90°C for 60 seconds. The resist composition was spin-coated onto this silicon wafer so that the film thickness of the composition layer was 0.04 μm. The wafer was then pre-baked on a direct hot plate for 60 seconds at the temperature shown in the "PB" column in Table 2 to form a composition layer. A line and space pattern (pitch 36 to 72 nm/line width 18 to 36 nm) was directly written onto the composition layer formed on the wafer using an electron beam lithography machine (ELS-F125 125 keV, manufactured by Elionix Co., Ltd.) by gradually changing the exposure dose.
After exposure, post-exposure baking was performed on a hot plate for 60 seconds at the temperature shown in the "PEB" column in Table 2. Next, the composition layer on the silicon wafer was developed by a dynamic dispensing method using butyl acetate (manufactured by Tokyo Chemical Industry Co., Ltd.) as a developer at 23°C for 20 seconds, thereby obtaining a resist pattern.
In the obtained resist pattern, the exposure amount at which the line width and space width of a 36 nm line and space pattern became 1:1 was defined as effective sensitivity.

<Resolution evaluation>
For the effective sensitivity, the resist pattern was observed with a scanning electron microscope, and the minimum line width that could be resolved was taken as the resolution. The results are shown in Table 4. The resolution (nm) is shown.
In comparison with the comparative compositions 4 to 6, the compositions 9 to 16 were evaluated as being good in terms of resolution.

The above results show that the salt of the present invention and the resist composition containing said salt provide good resolution in both alkaline development and organic solvent development.

The salt of the present invention and the resist composition containing said salt have good resolution and are useful for semiconductor microfabrication.

Claims (13)

A salt represented by formula (I):
[In formula (I),
R ¹ , R ² and R ³ each independently represent -O-R ¹⁰ , -O-CO-R ¹⁰ , -O-CO-O-R ¹⁰ or -OL ¹ -CO-O-R ¹⁰ .
R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ and R ⁹ each independently represent a halogen atom, a hydroxy group, a fluorinated alkyl group having 1 to 12 carbon atoms or a hydrocarbon group having 1 to 18 carbon atoms, the hydrocarbon group may have a substituent, and -CH ₂ - contained in the hydrocarbon group may be replaced by -O-, -S-, -CO- or -SO ₂ -.
^L1 represents an alkanediyl group having 1 to 6 carbon atoms.
R ¹⁰ represents an alicyclic hydrocarbon group having one or more —OR ¹¹ groups.
R ¹¹ represents a hydrogen atom , an acid labile group represented by formula (1a) or an acid labile group represented by formula (2a) .
X ¹ , X ² and X ³ each independently represent an oxygen atom or a sulfur atom.
m1 represents an integer of 0 to 5, and when m1 is 2 or more, the groups in the parentheses may be the same or different.
m2 represents an integer of 0 to 4, and when m2 is 2 or more, the groups in the parentheses may be the same or different.
m3 represents an integer of 0 to 4, and when m3 is 2 or more, the groups in the parentheses may be the same or different.
m4 represents an integer of 0 to 4, and when m4 is 2 or greater, multiple R ^4s may be the same or different.
m5 represents an integer of 0 to 4, and when m5 is 2 or more, the multiple ^R5s may be the same or different.
m6 represents an integer of 0 to 4, and when m6 is 2 or greater, multiple R ^6s may be the same or different.
m7 represents an integer of 0 to 5, and when m7 is 2 or greater, the multiple ^R7s may be the same or different.
m8 represents an integer of 0 to 4, and when m8 is 2 or greater, multiple R ^8s may be the same or different.
m9 represents an integer of 0 to 4, and when m9 is 2 or more, the multiple R ^9s may be the same or different.
However, 0≦m1+m7≦5, 0≦m2+m8≦4, 0≦m3+m9≦4, and at least one of m1, m2, and m3 represents an integer of 1 or more.
X ⁴ represents a single bond, —CH ₂ —, —O—, —S—, —CO—, —SO— or —SO ₂ —.
AI ⁻ represents an organic sulfonate anion.
[In formula (1a), R ^aa1 , R ^aa2 and R ^aa3 each independently represent an alkyl group of 1 to 8 carbon atoms which may have a substituent, an alkenyl group of 2 to 8 carbon atoms which may have a substituent, an alicyclic hydrocarbon group of 3 to 20 carbon atoms which may have a substituent, or an aromatic hydrocarbon group of 6 to 18 carbon atoms which may have a substituent, or R aa1 and R ^aa2 are ^bonded to each other to form an alicyclic hydrocarbon group of 3 to 20 carbon atoms together with the carbon atom to which they are bonded.]
naa represents 0 or 1.
* represents a bond.
[In formula (2a), R ^aa1′ and R ^aa2′ each independently represent a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms; R ^aa3′ represents a hydrocarbon group having 1 to 20 carbon atoms; or R ^aa2′ and R ^aa3′ are bonded to each other to form, together with —C-X ^a — to which they are bonded, a heterocyclic group having 3 to 20 carbon atoms; and —CH ₂ — contained in the hydrocarbon group and the heterocyclic group may be replaced by —O— or —S—.]
Xa represents an oxygen atom or a sulfur atom ^.
* represents a bond. The salt according to claim 1, wherein X ¹ , X ² and X ³ are oxygen atoms. The salt according to claim 1 or 2, wherein R ¹ , R ² and R ³ are —O—CO—O—R ¹⁰ — or —OL ¹ —CO—O—R ^{10 —} . 4. The salt according to claim 1, wherein R ¹⁰ is an adamantyl group having an —OR ¹¹ group (R ¹¹ represents a hydrogen atom or an acid labile group). The salt according to any one of claims 1 to 4, wherein R ¹¹ is a hydrogen atom. m1 is an integer of 0 to 2,
When m1 is 1 or 2, m2 and m3 each represent 0 or 1;
The salt according to any one of claims 1 to 5 , wherein when m1 is 0, m2 and m3 are 1. The salt according to any one of claims 1 to 6 , wherein the organic sulfonate anion of AI ^- is an anion represented by formula (IA):
[In formula (IA),
Q ¹ and Q ² each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms.
^L1 represents a saturated hydrocarbon group having 1 to 24 carbon atoms, in which —CH ₂ — contained in the saturated hydrocarbon group may be replaced by —O— or —CO—, and in which a hydrogen atom contained in the saturated hydrocarbon group may be replaced by a fluorine atom or a hydroxy group.
^Y1 represents an optionally substituted methyl group or an optionally substituted alicyclic hydrocarbon group having 3 to 24 carbon atoms, and one —CH ₂ — contained in the alicyclic hydrocarbon group may be replaced by —O—, —SO ₂ — or —CO—.] An acid generator comprising the salt according to any one of claims 1 to 7 . A resist composition comprising the acid generator according to claim 8 and a resin having an acid labile group. 10. The resist composition according to claim 9 , wherein the resin having an acid labile group comprises at least one structural unit selected from the group consisting of structural units represented by formula (a1-1) and structural units represented by formula (a1-2):
[In formula (a1-1) and formula (a1-2),
L ^a1 and L ^a2 each independently represent —O— or *-O—(CH ₂ ) _k1 —CO—O—, where k1 represents an integer of 1 to 7, and * represents a bond to —CO—.
R ^a4 and R ^a5 each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom.
R ^a6 and R ^a7 each independently represent an alkyl group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, or a combination thereof.
m1 represents an integer of 0 to 14.
n1 represents an integer of 0 to 10.
n1′ represents an integer of 0 to 3. 11. The resist composition according to claim 9 , wherein the resin having an acid labile group comprises a structural unit represented by formula (a2-A).
[In formula (a2-A),
R ^a50 represents a hydrogen atom, a halogen atom or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom.
R ^a51 represents a halogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkoxyalkyl group having 2 to 12 carbon atoms, an alkoxyalkoxy group having 2 to 12 carbon atoms, an alkylcarbonyl group having 2 to 4 carbon atoms, an alkylcarbonyloxy group having 2 to 4 carbon atoms, an acryloyloxy group, or a methacryloyloxy group.
A ^a50 represents a single bond or *-X ^a51 -(A ^a52 -X ^a52 ) _nb -, where * represents a bond to the carbon atom to which -R ^a50 is bonded.
A ^a52 represents an alkanediyl group having 1 to 6 carbon atoms.
X ^a51 and X ^a52 each independently represent —O—, —CO—O—, or —O—CO—.
nb represents 0 or 1.
mb represents an integer of 0 to 4. When mb is an integer of 2 or more, multiple R ^a51 may be the same or different.] 12. The resist composition according to claim 9, further comprising a salt that generates an acid that is weaker in acidity than the acid generated from the acid generator. (1) a step of applying the resist composition according to any one of claims 9 to 12 onto a substrate;
(2) a step of drying the applied composition to form a composition layer;
(3) exposing the composition layer to light;
(4) a step of heating the composition layer after exposure; and (5) a step of developing the composition layer after heating.
A method for producing a resist pattern comprising: