JP7809466B2 - Resin manufacturing method - Google Patents

Description

The present invention relates to a method for producing a resin, a resin, a resist composition, and a method for producing a resist pattern using the resist composition.

Patent Document 1 describes a method for producing a resin by copolymerizing a monomer containing the following compound, followed by reacting with an acid.

Japanese Patent Application Laid-Open No. 2018-012823

The present invention provides a method for producing a resin that forms a resist pattern with better CD uniformity (CDU) than a resist pattern formed with a resist composition containing a resin obtained by the above-mentioned resin production method.

The present invention includes the following inventions.
[1] a step of copolymerizing a monomer containing at least one selected from the group consisting of a compound represented by formula (a1-0), a compound represented by formula (a1-1), and a compound represented by formula (a1-2), and a compound represented by formula (a1-4), using a radical polymerization initiator in the presence of a base component, to obtain a resin (A0);
and reacting the resin (A0) with an acid component to obtain a resin (A) containing at least one structural unit selected from the group consisting of a structural unit represented by formula (a1-0), a structural unit represented by formula (a1-1), and a structural unit represented by formula (a1-2), and a structural unit represented by formula (a2-A).
[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 bonding site 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;
In formula (a1-4) and 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 the bonding site with 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.
md represents an integer of 1 to 3. When md is an integer of 2 or more, the plurality of R ^a34 , R ^a35 and R ^a36 may be the same or different from each other.
me represents an integer of 0 to 4. When me is an integer of 2 or more, multiple R ^a51 may be the same or different.
The relationship 1≦md+me≦5 is satisfied.
In formula (a1-4),
R ^a34 and R ^a35 each independently represent a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms, and 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—.]
[2] The method for producing a resin according to [1], wherein the radical polymerization initiator is an azo compound.
[3] The method for producing a resin according to [1] or [2], wherein the base is at least one base selected from the group consisting of pyridines, tertiary amines having an alkyl group of 1 to 4 carbon atoms, secondary amines having an alkyl group of 1 to 6 carbon atoms or a cycloalkyl group of 3 to 6 carbon atoms, and primary amines having an alkyl group of 1 to 8 carbon atoms, a cycloalkyl group of 3 to 6 carbon atoms, or an aryl group.
[4] The method for producing a resin according to [3], wherein the base is a pyridine or a tertiary amine having an alkyl group having 1 to 4 carbon atoms.
[5] The method for producing a resin according to any one of [1] to [4], wherein the acid is at least one selected from the group consisting of p-toluenesulfonic acid, oxalic acid, acetic acid, propionic acid, butanoic acid, formic acid, maleic acid, phthalic acid, sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid.
[6] The method for producing a resin according to [5], wherein the amount of the acid used is 0.1 to 10 parts by mass per part by mass of the total monomers used in copolymerization of the resin (A0).
[7] A resin obtained by the method for producing a resin according to any one of [1] to [6].
[8] A resist composition comprising the resin according to [7] and an acid generator.
[9] The resist composition according to [8], wherein the acid generator contains a salt represented by formula (B1):
[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—.
Z ⁺ represents an organic cation.
[10] The resist composition according to [8] or [9], further comprising a salt that generates an acid that is weaker in acidity than the acid generated from the acid generator.
[11] (1) A step of applying the resist composition according to any one of [8] to [10] 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 a resin obtained by the resin manufacturing method of the present invention, it is possible to produce resist patterns with good CD uniformity (CDU).

Unless otherwise specified, in this specification, "(meth)acrylate" means "at least one selected from the group consisting of acrylate and methacrylate." Terms such as "(meth)acrylic acid" and "(meth)acryloyl" have the same meaning. When a structural unit having "CH ₂ ═C(CH ₃ )—CO—" or "CH ₂ ═CH—CO—" is exemplified, structural units having both groups are also exemplified. 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 formed by combining two or more of the exemplified groups with their valences appropriately changed. "Derived from" or "derived from" refers to a polymerizable C═C bond contained in the molecule becoming a —C—C— group by polymerization. In addition, when stereoisomers exist, all stereoisomers are included.
In this specification, the term "solids content of a resist composition" refers to the sum of all components in the resist composition excluding the solvent (E), which will be described later.

[Method for producing resin and resin obtained by this method]
The method for producing a resin of the present invention includes the steps of copolymerizing a monomer containing at least one selected from the group consisting of a compound represented by formula (a1-0) (hereinafter may be referred to as "monomer (a1-0)"), a compound represented by formula (a1-1) (hereinafter may be referred to as "monomer (a1-1)"), and a compound represented by formula (a1-2) (hereinafter may be referred to as "monomer (a1-3)"), and a compound represented by formula (a1-4) (hereinafter may be referred to as "monomer (a1-4)") (these may be used alone or in combination of two or more), using a radical polymerization initiator in the presence of a base component, to obtain resin (A0);
and a step of reacting the resin (A0) with an acid component to obtain a resin (A) containing at least one structural unit selected from the group consisting of a structural unit represented by formula (a1-0) (hereinafter sometimes referred to as "structural unit (a1-0)"), a structural unit represented by formula (a1-1) (hereinafter sometimes referred to as "structural unit (a1-1)"), and a structural unit represented by formula (a1-2) (hereinafter sometimes referred to as "structural unit (a1-2)"), and a structural unit represented by formula (a2-A) (hereinafter sometimes referred to as "structural unit (a2-A)").
[In the formula, all symbols have the same meanings as defined above.]

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 ) _k1 -CO-O- (wherein k1 is preferably an integer of 1 to 4, more preferably 1), and more preferably an oxygen atom.
Examples of the alkyl group in R ^a02 , R ^a03 , R ^a04 , R ^a6 and R ^a7 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 ^a6 and R ^a7 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 in R ^a02 , R ^a03 , R ^a04 , R ^a6 and R ^a7 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 bonding site): The number of carbon atoms in the alicyclic hydrocarbon groups of ^{R a02} , R ^a03 , R ^a04 , R ^a6 and R ^a7 is preferably 3 to 16.
Examples of the aromatic hydrocarbon group in R ^a02 , R ^a03 , R ^a04 , R ^a6 and R ^a7 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, 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.
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 alkenyl group in R ^a6 and R ^a7 is preferably an alkenyl group having 2 to 6 carbon atoms, more preferably an ethenyl group, a propenyl group, an isopropenyl group, or a butenyl 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.
The combined group preferably has a total carbon number of 18 or less, and is more preferably a group combining an alkyl group and an alicyclic hydrocarbon group, or a group combining an alkyl group and an aromatic hydrocarbon group.
R ^a02 and R ^a03 are preferably alkyl groups having 1 to 6 carbon atoms or aromatic hydrocarbon groups having 6 to 12 carbon atoms, and more preferably methyl, ethyl, phenyl or naphthyl 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 each independently 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 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.
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, a methoxyethyl group, an ethoxyethyl group, and an ethoxymethyl group. The alkoxyalkyl group is preferably an alkoxyalkyl group having 2 to 8 carbon atoms, and more preferably an alkoxyalkyl group having 2 to 4 carbon atoms.
Examples of the alkoxyalkoxy group for R ^a51 include a methoxymethoxy group, a methoxyethoxy group, an ethoxymethoxy group, and an ethoxyethoxy group. The alkoxyalkoxy group is preferably an alkoxyalkoxy group having 2 to 8 carbon atoms, and more preferably an alkoxyalkoxy group having 2 to 4 carbon atoms.
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.

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 in A ⁵² 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.

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 in which the above-mentioned alkyl group and alicyclic hydrocarbon group are combined (for example, 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.
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 ^a35 and R ^a36 are bonded to each other to form a hydrocarbon group together with the —C—O— to which they are bonded, and examples of groups in which —CH ₂ — contained in these groups is replaced by —O— or —S— include the following groups. * represents a bonding site.
Specific examples of —OC(R ^a34 )(R ^a35 )—O—R ^a36 include the following groups: * represents a bonding site.
In addition, in the hydrocarbon groups of R ^a34 , R ^a35 and R ^a36 and the hydrocarbon group formed by bonding R ^a35 and R ^a36 together, —CH ₂ — contained in these groups may be replaced by —O— or —S—, in which case the number of carbon atoms before replacement is regarded as the number of carbon atoms of the hydrocarbon 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.
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-.
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 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 methoxy group, or an ethoxyethoxy group.
md is preferably 1 or 2. When md is 2, two —OC(R ^a34 )(R ^a35 )—O—R ^a36 are preferably the same.
As me, 0, 1 or 2 is preferable, 0 or 1 is more preferable, and 0 is even more preferable.
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 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.
When md is 1, the hydroxy group in the structural unit (a2-A) is preferably bonded to the o-position or p-position of the benzene ring, and more preferably bonded to the p-position. When md is 2, the two hydroxy groups are preferably bonded to the m-position and p-position of the benzene ring, respectively.

Examples of the monomer (a1-0) include a monomer represented by any one of formulas (a1-0-1) to (a1-0-18) and a monomer in which the methyl group corresponding to R ^a01 in the monomer (a1-0) has been replaced with a hydrogen atom, and a monomer represented by any one of formulas (a1-0-1) to (a1-0-10), (a1-0-13) and (a1-0-14) is preferred.

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, 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 monomer (a1-1) include the monomers described in JP-A-2010-204646. Among them, a monomer represented by any one of formulas (a1-1-1) to (a1-1-7) and a monomer in which the methyl group corresponding to R ^a4 in the monomer (a1-1) has been replaced with a hydrogen atom are preferred, and a monomer represented by any one of formulas (a1-1-1) to (a1-1-3) is more 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 (a1-1-3) are more preferred.

Examples of the monomer (a1-2) include a monomer represented by any one of formulas (a1-2-1) to (a1-2-12) and a monomer in which the methyl group corresponding to R ^a5 in the monomer (a1-2) has been replaced with a hydrogen atom, and the monomers represented by formulas (a1-2-2), (a1-2-5), (a1-2-6) and (a1-2-10) to (a1-2-12) are preferred.

Examples of the structural unit (a1-2) include structural units represented by any one of formulas (a1-2-1) to (a1-2-12) 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, and structural units represented by formulas (a1-2-2), (a1-2-5), (a1-2-6) and (a1-2-10) to (a1-2-12) are preferred.

When the monomer (a1-0) is used to polymerize the resin (A0), the amount used is preferably 5 to 80 mol %, more preferably 5 to 75 mol %, and even more preferably 10 to 70 mol %, based on the total amount of all the monomers constituting the resin (A0).
When the monomer (a1-1) and/or the monomer (a1-2) are used, the total amount used is preferably 10 to 90 mol %, more preferably 15 to 85 mol %, even more preferably 20 to 80 mol %, still more preferably 20 to 75 mol %, and still more preferably 20 to 70 mol %, based on the total amount of all monomers constituting the resin (A0).

When the resin (A) contains the structural unit (a1-0), the content thereof is preferably 5 to 80 mol %, more preferably 5 to 75 mol %, and even more preferably 10 to 70 mol %, based on all structural units of the resin (A).
When the resin (A) contains the structural unit (a1-1) and/or the structural unit (a1-2), the total content thereof is preferably 10 to 90 mol %, more preferably 15 to 85 mol %, even more preferably 20 to 80 mol %, still more preferably 20 to 75 mol %, and even more preferably 20 to 70 mol %, based on all structural units in the resin (A).
The total content of the structural units (a1-0), (a1-1) and (a1-2) in the resin (A) is 5 to 95 mol %, and preferably 25 to 80 mol %.

Examples of the monomer (a1-4) include the monomers described in JP 2010-204646 A. Preferred examples include the monomers represented by formulas (a1-4-1) to (a1-4-18) and monomers in which the hydrogen atom corresponding to R ^a50 has been replaced with a methyl group, and more preferred examples include the monomers represented by formulas (a1-4-1) to (a1-4-5), (a1-4-10), (a1-4-13), and (a1-4-14).

The amount of monomer (a1-4) used to polymerize resin (A0) is preferably 3 to 80 mol%, more preferably 5 to 75 mol%, even more preferably 7 to 70 mol%, even more preferably 7 to 65 mol%, and particularly preferably 10 to 60 mol%, based on the total amount of all monomers constituting resin (A0).

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 ^a50 has been replaced with a methyl 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 3 to 80 mol%, more preferably 5 to 75 mol%, even more preferably 7 to 70 mol%, even more preferably 7 to 65 mol%, and particularly preferably 10 to 60 mol%, based on the total of all structural units in resin (A).

Examples of the structural unit (a2-A) include structural units represented by formulas (a2-2-1) to (a2-2-16) and structural units in which the methyl group corresponding to R in the structural unit (a2-A) in the structural units represented by formulas ( ^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 preferably a structural unit in which a methyl group corresponding to R in the structural unit (a2-A) is replaced with a hydrogen atom in the structural unit represented by formula (a2-2-1), the structural unit represented by formula (a2-2-3), the structural unit represented by formula (a2-2-6), the structural unit represented by formula (a2-2-8), the structural unit represented by formulas (a2-2-12) to (a2-2-14), and the structural unit represented by formula (a2-2-1), the structural unit represented by formula ( ^a2-2-3 ), the structural unit represented by formula (a2-2-6), the structural unit represented by formula (a2-2-8), and the structural unit represented by formulas (a2-2-12) to (a2-2-14). More preferably, the structural unit is one in which a methyl group corresponding to ^a50 is replaced with a hydrogen atom.

The content of the structural unit (a2-A) in the resin (A) is preferably 3 to 80 mol %, more preferably 5 to 80 mol %, even more preferably 10 to 70 mol %, still more preferably 15 to 65 mol %, and even 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.

Resin (A0) may be polymerized using monomers other than monomer (a1-0), monomer (a1-1), monomer (a1-2), and monomer (a1-4). Thus, resin (A) may further contain structural units other than structural units (a1-0), structural unit (a1-1), structural unit (a1-2), and structural unit (a2-A). Examples of structural units other than the structural unit (a1-0), the structural unit (a1-1), the structural unit (a1-2), and the structural unit (a2-A) include structural units having an acid labile group (hereinafter may be referred to as "structural unit (a1)"), structural units 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. Here, the term "acid labile group" refers to a group that has a leaving group that is eliminated upon contact with an acid, resulting in conversion to a structural unit having a hydrophilic group (for example, a hydroxy group or a carboxy group).
In the method for producing a resin according to the present invention, a monomer that derives the following structural unit is used to polymerize resin (A0). In this case, it is preferable to use the monomer in an amount that leads to the content of the structural unit in resin (A).
The total amount of the monomers (a1-0), (a1-1), (a1-2) and (a1-4) used to polymerize the resin (A0) is preferably 10 to 99.9 mol %, more preferably 15 mol % to 95 mol %, and even more preferably 30 mol % to 90 mol %, based on the total amount of all the monomers constituting the resin (A0).

<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 ring having 6 to 18 carbon atoms, or a group combining these, or R ^a1 and R ^a2 bond to each other to form a non-aromatic hydrocarbon ring having 3 to 20 carbon atoms together with the carbon atoms to which they are bonded.]
ma and na each independently represent 0 or 1, and at least one of ma and na represents 1.
* indicates a binding site.]
[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 a heterocycle having 3 to 20 carbon atoms together with the carbon atom to which they are bonded and X, and —CH ₂ — contained in the hydrocarbon group and the heterocycle may be replaced by —O— or —S—.
X represents an oxygen atom or a sulfur atom.
na' represents 0 or 1.
* indicates a binding site.]

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 octenyl group, an isooctenyl 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 bonding site): 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, 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 a non-aromatic hydrocarbon ring, examples of -C(R ^a1 )(R ^a2 )(R ^a3 ) include the following rings. The non-aromatic hydrocarbon ring preferably has 3 to 12 carbon atoms. * represents the bonding site with -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 heterocycle together with the carbon atom to which they are bonded and X, —C(R ^a1′ )(R ^a2′ )—X—R ^a3′ includes the following rings: * represents the bonding site.
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 are alkyl groups, ma = 0 and na = 1 in formula (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 groups: * represents a binding site.

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

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.

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 a halogen atom, 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 the bonding site 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).

Further, examples of the structural unit (a1) include the following structural units.
When the resin (A) contains the structural units (a1-6-1) to (a1-6-3) described above, the content thereof is preferably 10 to 60 mol %, more preferably 15 to 55 mol %, even more preferably 20 to 50 mol %, still more preferably 20 to 45 mol %, and particularly preferably 20 to 40 mol %, based on the total structural units of the 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 above. 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.

An example of the structural unit (a2) having an alcoholic hydroxy group is 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 the bonding position with —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 position 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 a halogen atom, 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, multiple R ^a21 , R ^a22 , R ^a23 and/or R ^a25 may be the same or different from each other.]

Examples of the aliphatic hydrocarbon group for 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 formulas (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 preferably 1 to 70 mol %, more preferably 3 to 65 mol %, and even more preferably 5 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 1 to 60 mol%, more preferably 3 to 50 mol%, and even more preferably 5 to 50 mol%, based on all structural units in 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 halogen 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 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 saturated 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 bonding site):
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 structural unit (a4) include a structural unit represented by formula (a4-0), a structural unit represented by formula (a4-1), and a structural unit represented by formula (a4-4).
[In formula (a4-0),
R ⁵⁴ represents a hydrogen atom or a methyl group.
L ^4a represents a single bond or an alkanediyl 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.
R ⁶⁴ represents a hydrogen atom or a fluorine atom.

Examples of the alkanediyl 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 perfluoroethylfluoromethylene 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 ⁵⁴ 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 saturated 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.]
* indicates a binding site, and the * on the right side indicates the binding site with —O—CO—R ^a42 .]

Examples of the saturated hydrocarbon group for R ^a42 include chain hydrocarbon groups, monocyclic or polycyclic saturated alicyclic hydrocarbon groups, and groups formed by combining these groups.

Examples of the chain 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 saturated alicyclic hydrocarbon group include cycloalkyl 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 (* indicates a bonding site):
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 of R ^a42 include at least one selected from the group consisting of 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 a saturated hydrocarbon group having 1 to 17 carbon atoms which may have a halogen atom.
* indicates the binding site with ^Ra42 .]
However, in R ^a42 -X ^a43 -A ^a45 , when R ^a42 does not have a halogen atom, A ^a45 represents a saturated hydrocarbon group having 1 to 17 carbon atoms and at least one halogen atom.

Examples of the saturated 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 (* indicates a bonding site):
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 a saturated hydrocarbon group which may have a halogen atom, and more preferably a saturated hydrocarbon group having an alkyl group having a halogen atom and/or a group represented by formula (a-g3).
When R ^a42 is a saturated hydrocarbon group having a halogen atom, it is preferably a saturated 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 a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, a perfluorohexyl group, a perfluoroheptyl group, and a perfluorooctyl group. Examples of perfluorocycloalkyl groups include a perfluorocyclohexyl group.
When R ^a42 is a saturated 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 a saturated hydrocarbon group 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 saturated hydrocarbon group having 1 to 17 carbon atoms which may have a halogen atom.
X ^a44 represents **-O-CO- or **-CO-O- (** represents the bonding site to A ^a46 ).
A ^a47 represents a saturated 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.
* indicates the bonding site with the carbonyl group.]

The saturated hydrocarbon group of A ^a46 preferably has 1 to 6 carbon atoms, and more preferably 1 to 3 carbon atoms.
The saturated 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 (* indicates the bonding site with 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 represented by 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 saturated hydrocarbon group, and a divalent saturated hydrocarbon group formed by combining an alkanediyl group and a divalent alicyclic saturated hydrocarbon group. 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 bonding site, and ** is the bonding site 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.

Examples of the structural unit represented by formula (a4-1) include a structural unit represented by formula (a4-2) and a structural unit represented by formula (a4-3).
[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 for A ^a41 .
Examples of the saturated hydrocarbon group of R ^f6 include the same groups as those exemplified for R ⁴² .
The alkanediyl group in L ⁴⁴ is preferably an alkanediyl group having 2 to 4 carbon atoms, more preferably an ethylene group.

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.

[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 the bonding site 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 ^Aa41 .

The divalent saturated hydrocarbon group for A ^f13 which may have a fluorine atom is preferably a divalent chain 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 chain saturated 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 saturated 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 saturated hydrocarbon group having 1 to 6 carbon atoms and a divalent alicyclic saturated hydrocarbon group having 3 to 12 carbon atoms, and more preferably a divalent chain saturated hydrocarbon group having 2 to 3 carbon atoms.
The saturated hydrocarbon group of A ^f14 is preferably a group containing a chain saturated hydrocarbon group having 3 to 12 carbon atoms and a group containing an alicyclic saturated hydrocarbon group having 3 to 12 carbon atoms, and more preferably a group containing a chain saturated hydrocarbon group having 3 to 10 carbon atoms and a group containing an alicyclic saturated hydrocarbon group having 3 to 10 carbon atoms. Of these, A ^f14 is preferably a group containing an alicyclic saturated 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 saturated 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 bonding site, and * represents a bonding site with an oxygen atom.
In formula (L1-1),
X ^x1 represents *-O-CO- or *-CO-O- (* represents the bonding site 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.
mt represents an integer of 0 to 9. When mt 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 .
mt 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.
mt represents an integer of 0 to 9. When mt 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 mt are the same as those in formula (T1′).
Examples of the sultone ring include those mentioned above, and among these, 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 perfluoroalkyl group having 1 to 6 carbon atoms which may substitute for 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 groups; and branched alkanediyl groups such as butane-1,3-diyl, 2-methylpropane-1,3-diyl, 2-methylpropane-1,2-diyl, pentane-1,4-diyl, and 2-methylbutane-1,4-diyl groups.
divalent monocyclic alicyclic saturated hydrocarbon groups such as 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;
Examples include 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 the bonding site with 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.
z 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 z is 2 or greater, multiple R ^III2s and multiple 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 as the perfluoroalkyl group having 1 to 6 carbon atoms represented by Q ^b1 described below.

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 , z and ZA ⁺ have the same meanings as above.
R ^III5 represents a saturated hydrocarbon group having 1 to 12 carbon atoms.
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 .

The structural unit represented by formula (II-2-A-1) is preferably a structural unit represented by formula (II-2-A-2).
[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 alkyl group and the alicyclic hydrocarbon group include the same as those described above.
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, 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), aromatic hydrocarbon groups having an alicyclic hydrocarbon group (e.g., a p-cyclohexylphenyl group, a p-adamantylphenyl group), and aryl-cycloalkyl groups such as a phenylcyclohexyl group.
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 structural unit containing a cation in formula (II-1-1) include structural units represented by the following formulas, and structural units in which a group corresponding to the methyl group in R ^II4 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).

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 examples of the sulfonate anion include the same anions as those represented by formula (B1) described below.
Examples of the sulfonylimide anion represented by A 1 ^- include the following.
Examples of sulfonylmethide anions include the following:
Examples of carboxylate anions include the following:

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) (provided that it contains at least one selected from the group consisting of the structural unit represented by formula (a1-0), the structural unit (a1-1), and the structural unit (a1-2)) and the structural unit (s) (provided that it contains the structural unit represented by formula (a2-A)), i.e., a copolymer of the monomer (a1) and the monomer (a1-4).
The structural unit (a1) is preferably at least two types selected from the group consisting of the structural unit (a1-0), the structural unit (a1-1) and the structural unit (a1-2).
The structural unit (s) is preferably the structural unit (a2-A), the structural unit (a2-1) or the structural unit (a3-4).

The structural units constituting the resin (A) may be used singly or in combination of two or more, and the resin (A) can be produced by 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.

Examples of the base used in the step of obtaining the resin (A0) include hexylamine, heptylamine, octylamine, nonylamine, decylamine, aniline, 2-, 3-, or 4-methylaniline, 4-nitroaniline, 1- or 2-naphthylamine, ethylenediamine, tetramethylenediamine, hexamethylenediamine, 4,4'-diamino-1,2-diphenylethane, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 4,4'-diamino-3,3', dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, N-methylaniline, piperidine, diphenylamine, Phenylamine, triethylamine, trimethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, methyldibutylamine, methyldipentylamine, methyldihexylamine, methyldicyclohexylamine, methyldiheptylamine, methyldioctylamine, methyldinonylamine, methyldidecylamine, ethyldibutylamine, ethyldipentylamine, ethyldihexylamine, ethyldiheptylamine, ethyldioctylamine, ethyldinonylamine, ethyldidecylamine, dicyclohexylamine, triisopropanolamine, N,N-dimethylaniline, 2,6-isopropylaniline, imidazole, pyridine, 2-, 3-, or 4-methylpyridine, dimethylaminopyridine, 2,6-lutidine, 2,4,6-trimethylpyridine, pyrimidine, 4-methylimidazole, bipyridine, 2,2'-dipyridylamine, di-2-pyridyl ketone, 1,2-di(2-pyridyl)ethane, 1,2-di(4-pyridyl)ethane, 1,3-di(4-pyridyl)propane, 1,2-bis(2-pyridyl)ethylene, 1,2-bis(4-pyridyl) Examples of the alkyl ammonium hydroxide include ethylene, 1,2-bis(4-pyridyloxy)ethane, 4,4'-dipyridyl sulfide, 4,4'-dipyridyl disulfide, 1,2-bis(4-pyridyl)ethylene, 2,2'-dipicolylamine, 3,3'-dipicolylamine, tetramethylammonium hydroxide, tetraisopropylammonium hydroxide, tetrabutylammonium hydroxide, tetra-n-hexylammonium hydroxide, tetra-n-octylammonium hydroxide, phenyltrimethylammonium hydroxide, 3-(trifluoromethyl)phenyltrimethylammonium hydroxide, and choline.
Among these, a base having a boiling point higher than the polymerization temperature is preferred, a base having a boiling point of 85°C or higher is more preferred, and a nitrogen-containing basic organic compound is even more preferred. The nitrogen-containing basic organic compound is more preferably a pyridine, a tertiary amine having an alkyl group of 1 to 4 carbon atoms, a secondary amine having an alkyl group of 1 to 6 carbon atoms or a cycloalkyl group of 3 to 6 carbon atoms, or a primary amine having an alkyl group of 1 to 8 carbon atoms, a cycloalkyl group of 3 to 6 carbon atoms or an aryl group, and even more preferably a pyridine or a tertiary amine having an alkyl group of 1 to 4 carbon atoms. Preferred pyridines are pyridine, 2-, 3- or 4-methylpyridine, dimethylaminopyridine, 2,6-lutidine, 2,4,6-trimethylpyridine, and pyrimidine, and preferred tertiary amines are triethylamine, tripropylamine, trimethylamine, methyldiethylamine, ethyldipropylamine, and the like.
The amount of the base used in the step of obtaining Resin (A0) may be appropriately determined depending on the amount of the monomer having an acid labile group used, and is, for example, preferably 0.01 to 30 mol %, more preferably 0.02 to 20 mol %, and still more preferably 0.03 to 10 mol %, based on the total amount of the monomer having an acid labile group used.

Radical polymerization initiators used in the process to obtain resin (A0) include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl-2,2'-azobis(2-methylpropionate), 2,2'-azobis(2-hydroxymethylpropionitrile), and dimethyl azobis(isobutyrate). Examples of peroxides include organic peroxides such as lauryl peroxide, tert-butyl hydroperoxide, benzoyl peroxide, tert-butyl peroxybenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, tert-butyl peroxyneodecanoate, tert-butyl peroxypivalate, and (3,5,5-trimethylhexanoyl) peroxide; and inorganic peroxides such as potassium persulfate, ammonium persulfate, and hydrogen peroxide.

Of these, azo compounds are preferred, with 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), dimethyl-2,2'-azobis(2-methylpropionate) and dimethyl azobis(isobutyrate) being more preferred, and 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile) and dimethyl azobis(isobutyrate) being even more preferred. In addition, when two polymerization initiators are used in combination, a combination of 2,2'-azobis(2,4-dimethylvaleronitrile) and 2,2'-azobisisobutyronitrile, a combination of 2,2'-azobis(2,4-dimethylvaleronitrile) and 2,2'-azobis(2-methylbutyronitrile), a combination of 2,2'-azobis(2,4-dimethylvaleronitrile) and 1,1'-azobis(cyclohexane-1-carbonitrile), a combination of 2,2'-azobis(2,4-dimethylvaleronitrile) and dimethyl-2,2'-azobis(2-methylpropionate), or a combination of 2,2'-azobis(2,4-dimethylvaleronitrile) and dimethyl azobis(isobutyrate) is preferred, and the molar ratio thereof is preferably in the range of 1:1 to 1:10.
The amount of radical polymerization initiator used in the step of obtaining resin (A0) may be appropriately determined depending on the amount of monomer used, and is, for example, preferably 0.1 to 30 mol %, more preferably 1 to 15 mol %, based on the total amount of monomer used.

The temperature conditions in the radical polymerization method are not particularly limited and may be determined appropriately depending on, for example, the type of polymerization initiator. For example, 50 to 200°C is preferred, and 60 to 120°C is more preferred.

The radical polymerization method preferably uses an organic solvent. This organic solvent is typically one that can dissolve all of the monomers, polymerization initiator, and the resulting copolymer. Examples of such organic solvents include ketones such as methyl isopropyl ketone, methyl isobutyl ketone, ethyl isopropyl ketone, and methyl amyl ketone; ethers such as 1,4-dioxane, 1,3-dioxolane, diisopropyl ether, dimethoxyethane, diethoxyethane, and diethylene glycol dimethyl ether; and propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, and ethylene glycol monopropyl ether acetate. Examples of suitable solvents include glycol ether esters such as n-propyl formate, isopropyl formate, n-butyl formate, isobutyl formate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, and isobutyl propionate; aliphatic hydrocarbons such as heptane and octane; aromatic hydrocarbons such as benzene, toluene, xylene, and nitrobenzene; amides such as dimethylformamide and dimethylacetamide; aliphatic halogenated hydrocarbons such as dichloroethane and carbon tetrachloride; and water. These solvents may be used alone or in combination. Among these, ketones, ethers, glycol ether esters, alcohols, and esters are preferred.

The amount of the organic solvent used is preferably 1 to 5 times by weight relative to the total amount of the charged monomers.
The reaction time may be appropriately determined depending on the type of polymerization initiator, temperature conditions, etc., and is, for example, about 0.5 to 24 hours, preferably 0.5 to 8 hours.

The molecular weight of the resin (A0) produced in the present invention is typically approximately 2,000 to 500,000 in weight average molecular weight, and preferably 4,000 to 50,000.

The resin (A) can be obtained by reacting the resin (A0) with an acid component.
The reaction between the resin (A0) and the acid component can be carried out, for example, by adding the resin (A0) and the acid component to a solvent and mixing them.

The acid component is appropriately selected depending on the type of the structural unit represented by formula (a1-4) in resin (A0), and is preferably an acid component having an acid strength sufficient to dissociate the acid labile group from the structural unit represented by formula (a1-4) without dissociating the acid labile group from the structural unit represented by formula (a1-0), the structural unit represented by formula (a1-1), and the structural unit represented by formula (a1-2).
Examples of the acid component include p-toluenesulfonic acid, oxalic acid, acetic acid, propionic acid, butanoic acid, formic acid, maleic acid, phthalic acid, sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid. Of these, p-toluenesulfonic acid and sulfuric acid are preferred, and p-toluenesulfonic acid is more preferred.

The amount of acid component used can be determined appropriately depending on the type of acid component, concentration conditions, etc. For example, it is preferably 0.1 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, and more preferably 0.7 to 3 parts by mass per 1 part by mass of total monomers.

Solvents that can be used include those similar to those used in the synthesis of resin (A0). Among these, glycol ether esters, alcohols, and water are preferred.

The temperature conditions for the reaction of the resin (A0) with the acid component are not particularly limited and may be appropriately determined depending on the acid component, the type of acid-dissociable group in the resin (A0), and the like. For example, the temperature is preferably 0 to 60°C, more preferably 20 to 40°C.
The reaction time between the resin (A0) and the acid component may be appropriately determined depending on the acid component, the type of acid-dissociable group in the resin (A0), etc., and is, for example, about 1 to 24 hours, preferably 2 to 10 hours.
Resin (A) is obtained by reacting the above-mentioned resin (A0) with an acid component.
The above-described method for producing a resin can prevent a portion of the tertiary carbon atom-type acid labile groups from being eliminated to form carboxy groups, thereby providing a resin that can form a resist pattern with excellent CD uniformity (CDU).

[Resist Composition]
The resist composition of the present invention contains the resin (A) obtained by the above-mentioned production method and an acid generator (hereinafter, may be referred to as "acid generator (B)"). The resin (A) may be a single type, or two or more types of resins (A).
The resist composition of the present invention may contain a resin other than the resin (A).
The resist composition of the present invention preferably further contains a quencher (hereinafter sometimes referred to as "quencher (C)") and/or a solvent (hereinafter sometimes referred to as "solvent (E)").

<Resins other than resin (A)>
The resist composition of the present invention may contain a resin other than the resin (A).
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 (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), and more preferably a resin consisting only of the structural unit (a4).
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 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, still more preferably 1 to 30 parts by mass, and particularly preferably 1 to 8 parts by mass, relative to 100 parts by mass of resin (A).

The content of resin (A) in the resist composition is preferably 80% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 99% by mass or less, based on the solid content of the resist composition. Furthermore, when resins other than resin (A) are contained, the total content of resin (A) and the resins other than resin (A) is preferably 80% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 99% by mass or less, based on the solid content of the resist composition. 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.

<Acid Generator (B)>
The acid generator (B) may be either nonionic or ionic. Examples of 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), and the like. Examples of ionic acid generators include onium salts containing onium cations (e.g., diazonium salts, phosphonium salts, sulfonium salts, iodonium salts). Examples of the anion of the onium salt include a sulfonate anion, a sulfonylimide anion, and a sulfonylmethide anion.
As the acid generator (B), compounds that generate an acid when exposed to radiation, such as those described in JP-A-63-26653, JP-A-55-164824, JP-A-62-69263, JP-A-63-146038, JP-A-63-163452, JP-A-62-153853, JP-A-63-146029, U.S. Pat. No. 3,779,778, U.S. Pat. No. 3,849,137, German Patent No. 3,914,407, and European Patent No. 126,712, can be used. Compounds produced by known methods may also be used. Two or more types of acid generators (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)").
[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—.
Z ⁺ represents an organic cation.

Examples of the perfluoroalkyl group represented by Q ^b1 and Q ^b2 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 ^b1 and Q ^b2 each independently represent preferably a fluorine atom or a trifluoromethyl group, and more preferably both represent a fluorine atom.

Examples of the divalent saturated hydrocarbon group for L ^b1 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 L ^b1 in which one —CH ₂ — group is replaced by —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 —Y.

[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, 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 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, 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 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, 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 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—.

As the divalent saturated hydrocarbon group represented by L ^b1 in which one —CH ₂ — group is replaced by —O— or —CO—, a group represented by formula (b1-1) or formula (b1-3) is preferred.
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 with —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 formulae (b1-9) to (b1-11), when a hydrogen atom contained in the saturated hydrocarbon group is substituted with an alkylcarbonyloxy group, the number of carbon atoms before substitution is defined as the number of carbon atoms in the saturated hydrocarbon group.
Examples of the alkylcarbonyloxy group include an acetyloxy group, a propionyloxy group, a butyryloxy group, a cyclohexylcarbonyloxy group, and an adamantylcarbonyloxy group.

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 Y include groups represented by formulae (Y1) to (Y11) and (Y36) to (Y38).
When a —CH ₂ — contained in the alicyclic hydrocarbon group represented by Y 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).

The alicyclic hydrocarbon group represented by Y 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 Y is a spiro ring having an oxygen atom, 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 Y 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 combining these; -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, or the aromatic hydrocarbon group may be replaced by a hydroxy group or a fluorine atom; and ja represents an integer of 0 to 4).
Substituents of the alicyclic hydrocarbon group represented by Y 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, and —CH ₂ — contained in the alkyl group and the alicyclic hydrocarbon group is 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. ja represents an integer of 0 to 4.

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, and aromatic hydrocarbon groups having a chain hydrocarbon group of 1 to 18 carbon atoms (such as tolyl, xylyl, cumenyl, mesityl, p-methylphenyl, 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-adamantylphenyl and p-cyclohexylphenyl) are preferred. The number of carbon atoms in the aromatic hydrocarbon group is preferably 6 to 14, and more preferably 6 to 10.
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 6, and even 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 Y include the following:

Y 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, 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, Y is preferably an adamantyl group, a hydroxyadamantyl group, an oxoadamantyl group, or a group represented by formula (Y42), or formula (Y100) to formula (Y114).

The anion in the salt represented by formula (B1) is preferably an anion represented by formula (B1-A-1) to formula (B1-A-59) (hereinafter, these may be referred to as "anion (B1-A-1)" or the like depending on the formula number). An anion represented by any of formulas (B1-A-1) to (B1-A-4), (B1-A-9), (B1-A-10), (B1-A-24) to (B1-A-33), (B1-A-36) to (B1-A-40), and (B1-A-47) to (B1-A-59) is more preferred.

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 b1} and Q ^b2 have the same meaning as above.
Specific examples of the anion in the salt represented by formula (B1) include the anions described in JP-A-2010-204646.

Preferable anions in the salt represented by formula (B1) include anions represented by formulas (B1a-1) to (B1a-38).

Among these, anions represented by any of formulas (B1a-1) to (B1a-3), (B1a-7) to (B1a-16), (B1a-18), (B1a-19), and (B1a-22) to (B1a-38) are preferred.

Examples of the organic cation for Z ⁺ 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 with --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, a fluorinated alkyl 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 contain 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 contains 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 benzyl, phenethyl, phenylpropyl, trityl, naphthylmethyl, and naphthylethyl.
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 bonding site.
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 (B1a-1) to (B1a-3), (B1a-7) to (B1a-16), (B1a-18), (B1a-19), and (B1a-22) to (B1a-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.

In the resist composition of the present invention, the content of the acid generator 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, and even more preferably 3 parts by mass or more and 35 parts by mass or less, per 100 parts by mass of the resin (A). The resist composition of the present invention may contain one type of acid generator (B) alone, or may contain multiple types.

<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 the 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; cyclic esters such as γ-butyrolactone; etc. 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 salt that generates an acid that is weaker in acidity than the acid generated from the acid generator (B), and a basic nitrogen-containing organic compound. The content of the quencher (C) is preferably about 0.01 to 15 mass %, more preferably about 0.01 to 10 mass %, even more preferably about 0.1 to 8 mass %, and even more preferably about 0.1 to 5 mass %, based on the solids content of the resist composition.

<Salts that generate acids weaker in acidity than the acid generated from the acid generator>
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 with a weaker 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 with a weaker acidity than the acid generated from acid generator (B) is preferably a salt (salt having a carboxylic acid anion) that generates a carboxylic acid with a weaker acidity than the acid generated from acid generator (B), and more preferably a weak acid inner salt (D).

The weak acid inner salt (D) is not particularly limited as long as it is a diphenyliodonium salt having a phenyl group substituted with a carboxy anion, and specific examples thereof include the following salts:

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.
Examples of 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, and tributylamine. Amine, tripentylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, methyldibutylamine, methyldipentylamine, methyldihexylamine, methyldicyclohexylamine, methyldiheptylamine, methyldioctylamine, methyldinonylamine, methyldidecylamine, ethyldibutylamine, ethyldipentylamine, ethyldihexylamine, ethyldiheptylamine, ethyldioctylamine, ethyldinonylamine, ethyldidecylamine amine, 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-pyridyl)ethane Examples of the amines include 4,4'-dipyridyl 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. Preferred are aromatic amines such as diisopropylaniline, and more preferred is 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.

<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 resin (A) of the present invention, the acid generator (B), a salt that generates an acid weaker in acidity than the acid generated by the acid generator, and, if necessary, the resin (X), the quencher (C), the solvent (E), 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 having a resist film formed on their surfaces. 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 ArF excimer laser exposure, 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 conditions.
Apparatus: HLC-8120GPC model (manufactured by Tosoh Corporation)
Column: TSKgel Multipore H _XL -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".

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

Example 1 [Synthesis of Resin A1]
Monomer (a1-4-2), monomer (a1-2-6), and monomer (a2-2-11) were used as monomers, and they were mixed so that the molar ratio [monomer (a1-4-2):monomer (a1-2-6):monomer (a2-2-11)] was 29:65:6. Furthermore, propylene glycol monomethyl ether acetate was mixed with this monomer mixture in an amount of 2.5 times the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl was added as an initiator, relative to the total monomer amount, and 6 mol% of pyridine was added as a base, relative to the total monomer amount, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate. To the resulting solution, 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers was added, stirred for 3 hours, and then the mixture was separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then the mixture was separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding Resin A1 with a weight-average molecular weight of approximately 5.1 x ¹⁰³ in a 78% yield. This Resin A1 has the following structural units:

Synthesis Example 1 [Synthesis of Resin AX1]
Monomer (a1-4-2), monomer (a1-2-6), and monomer (a2-2-11) were used as monomers, and they were mixed so that the molar ratio [monomer (a1-4-2):monomer (a1-2-6):monomer (a2-2-11)] was 29:65:6. Furthermore, propylene glycol monomethyl ether acetate was mixed with this monomer mixture in an amount of 2.5 times the total mass of all monomers. Azobis(isobutyrate)dimethyl ester was added as an initiator to the resulting mixture in an amount of 9.2 mol% relative to the total monomer amount, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate, and the resulting solution was added with 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers. The mixture was stirred for 3 hours and then separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding resin AX1 with a weight-average molecular weight of approximately 5.1 x ¹⁰³ in an 82% yield. This resin AX1 has the following structural units. 0.4% of structural units derived from methacrylic acid was confirmed.

Example 2 [Synthesis of Resin A2]
Monomers (a1-4-2), (a1-2-10), and (a2-2-10) were used and mixed at a molar ratio of 29:65:6 [monomer (a1-4-2):monomer (a1-2-10):monomer (a2-2-10)]. Further, 2.5 times the mass of propylene glycol monomethyl ether acetate was mixed with this monomer mixture, based on the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl was added as an initiator, based on the total monomer amount, and 6 mol% of pyridine was added as a base, based on the total monomer amount, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate. To the resulting solution, 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers was added, stirred for 3 hours, and then separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding Resin A2 with a weight-average molecular weight of approximately 5.0 x ¹⁰³ in a 76% yield. This Resin A2 has the following structural units:

Synthesis Example 2 [Synthesis of Resin AX2]
Monomer (a1-4-2), monomer (a1-2-10), and monomer (a2-2-10) were used as monomers, and they were mixed so that the molar ratio [monomer (a1-4-2):monomer (a1-2-10):monomer (a2-2-10)] was 29:65:6. Furthermore, propylene glycol monomethyl ether acetate was mixed with this monomer mixture in an amount of 2.5 times the total mass of all monomers. Azobis(isobutyrate)dimethyl ester was added as an initiator to the resulting mixture in an amount of 9.2 mol% relative to the total monomer amount, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate, and the resulting solution was added with 2.0 times the mass of a 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers. The mixture was stirred for 3 hours and then separated. To the recovered organic layer, 2.0 times the mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding resin AX2 with a weight-average molecular weight of approximately 5.0 x ¹⁰³ in an 80% yield. This resin AX2 has the following structural units. 0.7% of structural units derived from methacrylic acid were confirmed.

Example 3 [Synthesis of Resin A3]
Monomer (a1-4-2), monomer (a1-2-11), and monomer (a2-2-12) were used as monomers, and they were mixed so that the molar ratio [monomer (a1-4-2):monomer (a1-2-11):monomer (a2-2-12)] was 29:65:6. Furthermore, propylene glycol monomethyl ether acetate was mixed with this monomer mixture in an amount of 2.5 times the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl was added as an initiator, relative to the total monomer amount, and 6 mol% of pyridine was added as a base, relative to the total monomer amount, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate. To the resulting solution, 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers was added, stirred for 3 hours, and then the mixture was separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then the mixture was separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding Resin A3 with a weight-average molecular weight of approximately 5.2 x ¹⁰³ in a 75% yield. This Resin A3 has the following structural units:

Synthesis Example 3 [Synthesis of Resin AX3]
Monomer (a1-4-2), monomer (a1-2-11), and monomer (a2-2-12) were used as monomers and mixed in a molar ratio of 29:65:6 [monomer (a1-4-2):monomer (a1-2-11):monomer (a2-2-12)]. Further, propylene glycol monomethyl ether acetate was mixed with this monomer mixture in an amount of 2.5 times the total mass of all monomers. Azobis(isobutyrate)dimethyl ester was added as an initiator to the resulting mixture in an amount of 9.2 mol% relative to the total monomer amount, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate, and the resulting solution was added with 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers. The mixture was stirred for 3 hours and then separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding resin AX3 with a weight-average molecular weight of approximately 5.1 x ¹⁰³ in a 77% yield. This resin AX3 has the following structural units. 1.1% of structural units derived from methacrylic acid were confirmed.

Example 4 [Synthesis of Resin A4]
Monomers (a1-4-13), (a1-2-12), and (a2-2-11) were used and mixed in a molar ratio of 29:65:6 [monomer (a1-4-13):monomer (a1-2-12):monomer (a2-2-11)]. Further, 2.5 times the mass of propylene glycol monomethyl ether acetate was mixed with this monomer mixture, based on the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl was added as an initiator, based on the total monomer amount, and 6 mol% of pyridine was added as a base, based on the total monomer amount, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate. To the resulting solution, 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers was added, stirred for 3 hours, and then the mixture was separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then the mixture was separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding Resin A4 with a weight-average molecular weight of approximately 5.3 x ^10⁻¹ in 70% yield. This Resin A4 has the following structural units:

Synthesis Example 4 [Synthesis of Resin AX4]
Monomer (a1-4-13), monomer (a1-2-12), and monomer (a2-2-11) were used as monomers and mixed so that the molar ratio [monomer (a1-4-13):monomer (a1-2-12):monomer (a2-2-11)] was 29:65:6. Furthermore, propylene glycol monomethyl ether acetate was mixed with this monomer mixture in an amount of 2.5 times the total mass of all monomers. Azobis(isobutyrate)dimethyl ester was added as an initiator to the resulting mixture in an amount of 9.2 mol% relative to the total monomer amount, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate, and the resulting solution was added with 2.0 times the mass of a 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers. The mixture was stirred for 3 hours and then separated. To the recovered organic layer, 2.0 times the mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding resin AX4 with a weight-average molecular weight of approximately 5.2 x ¹⁰³ in a 73% yield. This resin AX4 has the following structural units. 1.0% of structural units derived from methacrylic acid was confirmed.

Example 5 [Synthesis of Resin A5]
Monomers were used: Monomer (a1-4-2), Monomer (a1-1-3), Monomer (a1-2-6), and Monomer (a2-2-11). They were mixed in a molar ratio of 29:30:35:6 [monomer (a1-4-2): Monomer (a1-1-3): Monomer (a1-2-6): Monomer (a2-2-11)]. Furthermore, 2.5 times the mass of propylene glycol monomethyl ether acetate was mixed with this monomer mixture, based on the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl was added as an initiator, based on the total monomer amount, and 6 mol% of pyridine was added as a base, based on the total monomer amount. The mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate. To the resulting solution, 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers was added, stirred for 3 hours, and then separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding Resin A5 with a weight-average molecular weight of approximately 5.4 x ^10⁻¹ in a 62% yield. This Resin A5 has the following structural units:

Synthesis Example 5 [Synthesis of Resin AX5]
Monomers were used: Monomer (a1-4-2), Monomer (a1-1-3), Monomer (a1-2-6), and Monomer (a2-2-11). They were mixed in a molar ratio of 29:30:35:6 [monomer (a1-4-2): Monomer (a1-1-3): Monomer (a1-2-6): Monomer (a2-2-11)]. Furthermore, 2.5 times by mass of propylene glycol monomethyl ether acetate was mixed with this monomer mixture, based on the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl as an initiator, based on the total monomer amount, was added, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate, and the resulting solution was added with 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers. The mixture was stirred for 3 hours and then separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding resin AX5 with a weight-average molecular weight of approximately 5.1 x ¹⁰³ in a 64% yield. This resin AX5 has the following structural units. 0.3% of structural units derived from methacrylic acid was confirmed.

Example 6 [Synthesis of Resin A6]
Monomers used were monomer (a1-4-2), monomer (a1-0-13), monomer (a1-2-6), and monomer (a2-2-11), and the molar ratio [monomer (a1-4-2):monomer (a1-0-13):monomer (a1-2-6):monomer (a2-2-11)] was mixed at a ratio of 29:30:35:6. Furthermore, 2.5 times the mass of propylene glycol monomethyl ether acetate was mixed with this monomer mixture relative to the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl was added as an initiator relative to the total monomer amount, and 6 mol% of pyridine was added as a base relative to the total monomer amount, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate. To the resulting solution, 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers was added, stirred for 3 hours, and then the mixture was separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then the mixture was separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding Resin A6 with a weight-average molecular weight of approximately 5.1 x ¹⁰³ in an 80% yield. This Resin A6 has the following structural units:

Synthesis Example 6 [Synthesis of Resin AX6]
Monomers used were monomer (a1-4-2), monomer (a1-0-13), monomer (a1-2-6), and monomer (a2-2-11), and the molar ratio [monomer (a1-4-2):monomer (a1-0-13):monomer (a1-2-6):monomer (a2-2-11)] was mixed at a ratio of 29:30:35:6. Furthermore, 2.5 times by mass of propylene glycol monomethyl ether acetate was mixed with this monomer mixture relative to the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl as an initiator relative to the total monomer amount was added, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate, and the resulting solution was added with 2.0 times the mass of a 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers. The mixture was stirred for 3 hours and then separated. To the recovered organic layer, 2.0 times the mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding resin AX6 with a weight-average molecular weight of approximately 5.1 x ¹⁰³ in an 82% yield. This resin AX6 has the following structural units. 0.6% of structural units derived from methacrylic acid were confirmed.

Example 7 [Synthesis of Resin A7]
Monomers used were monomer (a1-4-2), monomer (a1-0-14), monomer (a1-2-6), and monomer (a2-2-11), and the molar ratio [monomer (a1-4-2):monomer (a1-0-14):monomer (a1-2-6):monomer (a2-2-11)] was mixed at a ratio of 29:30:35:6. Furthermore, 2.5 times the mass of propylene glycol monomethyl ether acetate was mixed with this monomer mixture relative to the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl was added as an initiator relative to the total monomer amount, and 6 mol% of pyridine was added as a base relative to the total monomer amount, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate. To the resulting solution, 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers was added, stirred for 3 hours, and then the mixture was separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then the mixture was separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding Resin A7 with a weight-average molecular weight of approximately 5.1 x ^10⁻¹ in 77% yield. This Resin A7 has the following structural units:

Synthesis Example 7 [Synthesis of Resin AX7]
Monomers used were monomer (a1-4-2), monomer (a1-0-14), monomer (a1-2-6), and monomer (a2-2-11), and the molar ratio [monomer (a1-4-2):monomer (a1-0-14):monomer (a1-2-6):monomer (a2-2-11)] was mixed at a ratio of 29:30:35:6. Furthermore, 2.5 times by mass of propylene glycol monomethyl ether acetate was mixed with this monomer mixture relative to the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl as an initiator relative to the total monomer amount was added, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate, and the resulting solution was added with 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers. The mixture was stirred for 3 hours and then separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding resin AX7 with a weight-average molecular weight of approximately 5.1 x ¹⁰³ in a 79% yield. This resin AX7 has the following structural units. 0.9% of structural units derived from methacrylic acid were confirmed.

Example 8 [Synthesis of Resin A8]
Monomers were used: Monomer (a1-2-6), Monomer (a2-1-3), Monomer (a3-4-2), Monomer (a1-4-13), and Monomer (a2-2-10). The molar ratio [monomer (a1-2-6): Monomer (a2-1-3): Monomer (a3-4-2): Monomer (a1-4-13): Monomer (a2-2-10)] was 50:3:12:32:3. Further, 2.5 times the mass of propylene glycol monomethyl ether acetate was added to this monomer mixture relative to the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl was added as an initiator relative to the total monomer amount, and 6 mol% of pyridine was added as a base relative to the total monomer amount. The mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate, and the resulting solution was added with 2.5% p-toluenesulfonic acid aqueous solution in an amount 2.0 times by mass relative to the total mass of all monomers. The mixture was stirred for 3 hours and then separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered and recovered, yielding Resin A8 with a weight-average molecular weight of approximately 5.2 x ^10⁻¹ in a 71% yield. This Resin A8 has the following structural units:

Synthesis Example 8 [Synthesis of Resin AX8]
Monomers (a1-2-6), (a2-1-3), (a3-4-2), (a1-4-13), and (a2-2-10) were used and mixed in a molar ratio of 50:3:12:32:3 [monomer (a1-2-6):monomer (a2-1-3):monomer (a3-4-2):monomer (a1-4-13):monomer (a2-2-10)]. Further, 2.5 times by mass of propylene glycol monomethyl ether acetate was mixed with this monomer mixture relative to the total mass of all monomers. Azobis(isobutyric acid)dimethyl ester was added as an initiator to the resulting mixture in an amount of 9.2 mol% relative to the total monomer amount, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate, and the resulting solution was added with 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers. The mixture was stirred for 3 hours and then separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding resin AX8 with a weight-average molecular weight of approximately 5.2 x ¹⁰³ in a 74% yield. This resin AX8 has the following structural units. 0.2% of structural units derived from methacrylic acid was confirmed.

Example 9 [Synthesis of Resin A9]
Monomers were used: Monomer (a1-4-2), Monomer (a1-1-3), Monomer (a1-2-6), and Monomer (a2-2-10). They were mixed in a molar ratio of 29:30:35:6 [monomer (a1-4-2): Monomer (a1-1-3): Monomer (a1-2-6): Monomer (a2-2-10)]. Furthermore, 2.5 times the mass of propylene glycol monomethyl ether acetate was mixed with this monomer mixture, based on the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl was added as an initiator, based on the total monomer amount, and 6 mol% of pyridine was added as a base, based on the total monomer amount. The mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate. To the resulting solution, 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers was added, stirred for 3 hours, and then the mixture was separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then the mixture was separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding Resin A9 with a weight-average molecular weight of approximately 5.3 x ¹⁰³ in a 66% yield. This Resin A9 has the following structural units:

Synthesis Example 9 [Synthesis of Resin AX9]
Monomers were used: Monomer (a1-4-2), Monomer (a1-1-3), Monomer (a1-2-6), and Monomer (a2-2-10). They were mixed in a molar ratio of 29:30:35:6 [monomer (a1-4-2): Monomer (a1-1-3): Monomer (a1-2-6): Monomer (a2-2-10)]. Furthermore, 2.5 times by mass of propylene glycol monomethyl ether acetate was mixed with this monomer mixture, based on the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl as an initiator, based on the total monomer amount, was added, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate, and the resulting solution was added with 2.0 times the mass of a 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers. The mixture was stirred for 3 hours and then separated. To the recovered organic layer, 2.0 times the mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding resin AX9 with a weight-average molecular weight of approximately 5.2 x ¹⁰³ in a 64% yield. This resin AX9 has the following structural units. 0.2% of structural units derived from methacrylic acid was confirmed.

Example 10 [Synthesis of Resin A10]
Monomer (a1-4-2), monomer (a1-2-6), and monomer (a2-2-10) were used as monomers, and they were mixed so that the molar ratio [monomer (a1-4-2):monomer (a1-2-6):monomer (a2-2-10)] was 29:65:6. Furthermore, propylene glycol monomethyl ether acetate was mixed with this monomer mixture in an amount of 2.5 times the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl as an initiator, based on the total monomer amount, and 6 mol% of pyridine as a base, based on the total monomer amount, were added, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate. To the resulting solution, 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers was added, stirred for 3 hours, and then the mixture was separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then the mixture was separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding Resin A10 with a weight-average molecular weight of approximately 5.3 x ¹⁰³ in an 84% yield. This Resin A10 has the following structural units:

Synthesis Example 10 [Synthesis of Resin AX10]
Monomer (a1-4-2), monomer (a1-2-6), and monomer (a2-2-10) were used as monomers and mixed so that the molar ratio [monomer (a1-4-2):monomer (a1-2-6):monomer (a2-2-10)] was 29:65:6. Furthermore, propylene glycol monomethyl ether acetate was mixed with this monomer mixture in an amount of 2.5 times the total mass of all monomers. Azobis(isobutyrate)dimethyl ester was added as an initiator to the resulting mixture in an amount of 9.2 mol% relative to the total monomer amount, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate, and the resulting solution was added with 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers. The mixture was stirred for 3 hours and then separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding resin AX10 with a weight-average molecular weight of approximately 5.3 x ¹⁰³ in an 83% yield. This resin AX10 has the following structural units. 0.2% of structural units derived from methacrylic acid was confirmed.

Example 11 [Synthesis of Resin A11]
Monomers were used: Monomer (a1-4-13), Monomer (a1-1-3), Monomer (a1-2-6), and Monomer (a2-2-10). They were mixed in a molar ratio of 29:30:35:6 [monomer (a1-4-13): Monomer (a1-1-3): Monomer (a1-2-6): Monomer (a2-2-10)]. Furthermore, 2.5 times the mass of propylene glycol monomethyl ether acetate was mixed with this monomer mixture, based on the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl was added as an initiator, based on the total monomer amount, and 6 mol% of pyridine was added as a base, based on the total monomer amount. The mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate, and the resulting solution was added with 2.5% p-toluenesulfonic acid aqueous solution in an amount 2.0 times by mass relative to the total mass of all monomers. The mixture was stirred for 3 hours and then separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding Resin A11 with a weight-average molecular weight of approximately 5.2 x ¹⁰³ in a 63% yield. This Resin A11 has the following structural units:

Synthesis Example 11 [Synthesis of Resin AX11]
Monomers were used: Monomer (a1-4-13), Monomer (a1-1-3), Monomer (a1-2-6), and Monomer (a2-2-10). They were mixed in a molar ratio of 29:30:35:6 [monomer (a1-4-13): Monomer (a1-1-3): Monomer (a1-2-6): Monomer (a2-2-10)]. Furthermore, 2.5 times by mass of propylene glycol monomethyl ether acetate was mixed with this monomer mixture, based on the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl as an initiator, based on the total monomer amount, was added, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate, and the resulting solution was added with 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers. The mixture was stirred for 3 hours and then separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding resin AX11 with a weight-average molecular weight of approximately 5.1 x 10 ³ in a 62% yield. This resin AX11 has the following structural units. 0.3% of structural units derived from methacrylic acid was confirmed.

Example 12 [Synthesis of Resin A12]
Monomer (a1-4-13), monomer (a1-2-6), and monomer (a2-2-10) were used as monomers, and they were mixed so that the molar ratio [monomer (a1-4-13):monomer (a1-2-6):monomer (a2-2-10)] was 29:65:6. Furthermore, propylene glycol monomethyl ether acetate was mixed with this monomer mixture in an amount of 2.5 times the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl as an initiator, based on the total monomer amount, and 6 mol% of pyridine as a base, based on the total monomer amount, were added, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate. To the resulting solution, 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers was added, stirred for 3 hours, and then the mixture was separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then the mixture was separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding Resin A12 with a weight-average molecular weight of approximately 5.2 x ¹⁰³ in an 82% yield. This Resin A12 has the following structural units:

Synthesis Example 12 [Synthesis of Resin AX12]
Monomer (a1-4-13), monomer (a1-2-6), and monomer (a2-2-10) were used as monomers and mixed in a molar ratio of 29:65:6 [monomer (a1-4-13):monomer (a1-2-6):monomer (a2-2-10)]. Furthermore, 2.5 times by mass of propylene glycol monomethyl ether acetate was mixed with this monomer mixture relative to the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl as an initiator relative to the total monomer amount was added, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate, and the resulting solution was added with 2.0 times by mass of 2.5% p-toluenesulfonic acid aqueous solution relative to the total mass of all monomers. The mixture was stirred for 3 hours and then separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding resin AX12 with a weight-average molecular weight of approximately 5.2 x ¹⁰³ in an 81% yield. This resin AX12 has the following structural units. 0.3% of structural units derived from methacrylic acid was confirmed.

Example 13 [Synthesis of Resin A13]
Monomers were used: Monomer (a1-2-6), Monomer (a2-1-3), Monomer (a3-4-2), Monomer (a1-4-2), and Monomer (a2-2-10). The molar ratio [monomer (a1-2-6): Monomer (a2-1-3): Monomer (a3-4-2): Monomer (a1-4-2): Monomer (a2-2-10)] was 50:3:12:32:3. Further, 2.5 times the mass of propylene glycol monomethyl ether acetate was added to this monomer mixture, based on the total mass of all monomers. To the resulting mixture, 9.2 mol% of azobis(isobutyrate)dimethyl was added as an initiator, based on the total monomer amount, and 6 mol% of pyridine was added as a base, based on the total monomer amount. The mixture was heated at 85°C for approximately 5 hours. The polymerization reaction mixture was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate, to which a 2.5% p-toluenesulfonic acid aqueous solution was added in an amount 2.0 times by mass relative to the total mass of all monomers. The solution was stirred for 3 hours and then separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate a resin, which was then filtered and recovered, yielding Resin A13 with a weight-average molecular weight of approximately 5.3 x ^10⁻¹ in a 75% yield. This Resin A13 has the following structural units:

Synthesis Example 13 [Synthesis of Resin AX13]
Monomers (a1-2-6), (a2-1-3), (a3-4-2), (a1-4-2), and (a2-2-10) were used and mixed in a molar ratio of 50:3:12:32:3 [monomer (a1-2-6):monomer (a2-1-3):monomer (a3-4-2):monomer (a1-4-2):monomer (a2-2-10)]. Further, 2.5 times by mass of propylene glycol monomethyl ether acetate was mixed with this monomer mixture relative to the total mass of all monomers. Azobis(isobutyric acid)dimethyl ester was added as an initiator to the resulting mixture in an amount of 9.2 mol% relative to the total monomer amount, and the mixture was heated at 85°C for approximately 5 hours. The polymerization reaction solution was then cooled to 23°C. The resulting polymerization reaction solution was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered. The resulting resin was again dissolved in propylene glycol monomethyl ether acetate, and a 2.5% p-toluenesulfonic acid aqueous solution was added to the resulting solution in an amount 2.0 times by mass relative to the total mass of all monomers. The mixture was stirred for 3 hours and then separated. To the recovered organic layer, 2.0 times by mass of ion-exchanged water relative to the total mass of all monomers was added, stirred, and then separated. This water tapping operation was repeated five times. The recovered organic layer was poured into a large amount of a methanol/water (weight ratio: 6/4) mixed solvent to precipitate the resin, which was then filtered and recovered, yielding resin AX13 with a weight-average molecular weight of approximately 5.4 x ¹⁰³ in a 74% yield. This resin AX13 has the following structural units. 0.4% of structural units derived from methacrylic acid was confirmed.

<Preparation of Resist Composition>
The components shown in Table 1 were mixed and dissolved to obtain a mixture, which was then filtered through a fluororesin filter with a pore size of 0.2 μm to prepare a resist composition.

<Resin>
A1 to A13, AX1 to AX13: Resins A1 to A13, Resins AX1 to AX13
<Acid Generator (B)>
B1-43: Salt represented by formula (B1-43) (synthesized according to the examples in JP 2016-47815 A)
<Quencher (C)>
(Salts that generate acids that are weaker in acidity than the acid generated by the acid generator)
D1: Synthesized by the method described in JP-A-2011-39502
<Solvent>
Propylene glycol monomethyl ether acetate 400 parts Propylene glycol monomethyl ether 150 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 the silicon wafer so that the composition layer had a thickness of 0.04 μm. The wafer was then pre-baked on a direct hot plate at the temperature shown in the "PB" column of Table 1 for 60 seconds to form a composition layer. A contact hole pattern (hole pitch 40 nm/hole diameter 17 nm) was directly written on 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 1, 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 resist pattern obtained after development, the exposure amount at which the diameter of the formed hole was 17 nm was defined as the effective sensitivity.

<CD Uniformity (CDU) Evaluation>
For the effective sensitivity, the hole diameter of a pattern formed with a hole diameter of 17 nm was measured 24 times per hole, and the average value was taken as the average hole diameter of one hole. The standard deviation was calculated using the population of 400 measurements of the average hole diameter of patterns formed with a hole diameter of 17 nm on the same wafer.
The results are shown in Table 2. The values in the table indicate standard deviations (nm).

Compared with the comparative compositions 1 to 7 and 9 to 12, the standard deviations of the compositions 1 to 7 and 9 to 12 were small, and the CD uniformity (CDU) evaluation was good.

(Electron beam exposure evaluation of resist composition: butyl acetate 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 the silicon wafer so that the composition layer had a thickness of 0.04 μm. The wafer was then pre-baked on a direct hot plate at the temperature shown in the "PB" column of Table 1 for 60 seconds to form a composition layer. An electron beam lithography machine (ELS-F125 125 keV, manufactured by Elionix Corporation) was used to directly write the composition layer formed on the wafer, gradually changing the exposure dose so that a contact hole pattern (hole pitch 50 nm/hole diameter 23 nm) would result after development.
After exposure, post-exposure baking was performed on a hot plate for 60 seconds at the temperature shown in the "PEB" column of Table 1. 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 resist pattern obtained after development, the exposure amount at which the diameter of the formed hole was 23 nm was defined as the effective sensitivity.

<CD Uniformity (CDU) Evaluation>
For the effective sensitivity, the hole diameter of a pattern formed with a hole diameter of 23 nm was measured 24 times per hole, and the average value was taken as the average hole diameter of one hole. The standard deviation was calculated using the population of 400 measurements of the average hole diameter of patterns formed with a hole diameter of 23 nm on the same wafer.
The results are shown in Table 3. The values in the table indicate standard deviations (nm).

Compared with the comparative compositions 8 and 13, the compositions 8 and 13 had smaller standard deviations and better CD uniformity (CDU) ratings.

The resin of the present invention and the resist composition containing it can produce resist patterns with excellent CD uniformity (CDU), making them suitable for semiconductor microfabrication and extremely useful industrially.

Claims (5)

a step of copolymerizing a monomer containing at least one compound selected from the group consisting of a compound represented by formula (a1-0), a compound represented by formula (a1-1), and a compound represented by formula (a1-2), a compound represented by formula (a1-4), and a compound represented by formula (a2-A) using a radical polymerization initiator in the presence of a base component to obtain a resin (A0);
a step of reacting the resin (A0) with an acid component to obtain a resin (A) containing at least one structural unit selected from the group consisting of a structural unit represented by formula (a1-0), a structural unit represented by formula (a1-1), and a structural unit represented by formula (a1-2), and two structural units represented by formula (a2-A),
In the step of obtaining the resin (A0), the compound represented by the formula (a1-4) is such that R ^a51 is not an iodine atom, and
In the compound represented by formula (a2-A), me is an integer of 1 or more, and at least one of the plurality of R ^a51 is an iodine atom;
In the step of obtaining the resin (A), one of the two structural units represented by formula (a2-A) has me as an integer of 1 or more, and at least one of the plurality of R ^a51 is an iodine atom, and the other has R ^a51 as not an iodine atom,
the amount of the base component used is 0.01 to 30 mol % based on the total amount of the monomers having an acid labile group used in the step of obtaining the resin (A0),
the amount of the acid component used is 0.1 to 10 parts by mass relative to 1 part by mass of the total monomers used in the step of obtaining the resin (A0),
the temperature condition for the reaction of the resin (A0) with the acid component is 0°C to 60°C;
The method for producing a resin , wherein the reaction time of the reaction between the resin (A0) and the acid component is 1 hour to 24 hours .
[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 bonding site 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 5 to 10 carbon atoms, an aromatic hydrocarbon group having 6 to 10 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 10 carbon atoms, an aromatic hydrocarbon group having 6 to 10 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;
In formula (a1-4) and 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, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an alkoxyalkyl group having 2 to 12 carbon atoms.
A ^a50 represents a single bond.
md represents an integer of 1 to 3. When md is an integer of 2 or more, a plurality of R ^a34 , R ^a35 and R ^a36 may be the same or different from each other.
me represents an integer of 0 to 4. When me is an integer of 2 or more, multiple R ^a51 may be the same or different.
The relationship 1≦md+me≦5 is satisfied.
In formula (a1-4),
R ^a34 represents a hydrogen atom;
R ^a35 represents a hydrogen atom, a methyl group, or an ethyl group;
R ^a36 represents a monovalent hydrocarbon group having 1 to 20 carbon atoms, and the monovalent hydrocarbon group represents a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a cyclohexyl group, a cyclopentyl group, a cyclohexyl group, an adamantyl group, a norbornyl group, a phenyl group, a naphthyl group, or a combination thereof.] The method for producing a resin according to claim 1, wherein the radical polymerization initiator is an azo compound. The method for producing a resin according to claim 1 or 2, wherein the base is at least one base selected from the group consisting of pyridines, tertiary amines having an alkyl group of 1 to 4 carbon atoms, secondary amines having an alkyl group of 1 to 6 carbon atoms or a cycloalkyl group of 3 to 6 carbon atoms, and primary amines having an alkyl group of 1 to 8 carbon atoms, a cycloalkyl group of 3 to 6 carbon atoms, or an aryl group. The method for producing a resin according to claim 3, wherein the base is a pyridine or a tertiary amine having an alkyl group having 1 to 4 carbon atoms. The method for producing a resin according to any one of claims 1 to 4, wherein the acid is at least one selected from the group consisting of p-toluenesulfonic acid, oxalic acid, acetic acid, propionic acid, butanoic acid, formic acid, maleic acid, phthalic acid, sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid.