JP7729294B2 - Negative photosensitive resin composition and dry film resist - Google Patents

Description

The present invention relates to a negative-type photosensitive resin composition and a dry film resist.

In recent years, as electronic devices have become more compact, semiconductor packages have become increasingly dense. In the semiconductor package manufacturing process, a resist film is formed using a resist material on a support such as a film, sheet, metal substrate, or ceramic substrate. However, as circuits become finer due to increased density, the steps on the support surface are also becoming finer. When liquid resist material is applied to such a stepped support surface, it is difficult to obtain a resist film of uniform thickness, and defects such as voids can occur near the steps. Therefore, attention is being focused on negative-tone photosensitive dry film resists, which can produce resist films of uniform thickness and without defects near the steps.

Conventionally, negative photosensitive dry film resists have mainly been solvent-developable, using organic solvents. However, solvent development causes the resist resin to swell due to solvent absorption during development, making it unsuitable for drawing fine patterns.
Therefore, instead of solvent development, fine pattern writing using an alkali-developable negative photosensitive dry film resist incorporating an alkali-soluble component has been investigated (for example, Patent Document 1). However, in the pattern formation of Patent Document 1, since a parahydroxystyrene skeleton or a functional group such as a carboxyl group is used as the alkali-soluble component, it is difficult to control the alkali dissolution rate, and post-development residues are left in the exposed areas and film loss occurs in the unexposed areas, making it difficult to form fine patterns of 10 or so μm or less, and also the chemical resistance is insufficient.

Therefore, the development of negative dry film resists that incorporate phenol novolac resins to control the alkaline dissolution rate is being considered (see, for example, Patent Document 2). However, the pattern formation in Patent Document 2 does not solve the problem of post-development residue in exposed areas because the alkaline development rate of phenol novolac resins is insufficient. Furthermore, it is difficult to draw fine patterns of less than 10 μm, and there are problems with film formation defects when forming a resist film on a film and adhesion to the support inside a semiconductor package.

As described above, with the increasing density of semiconductor packages, there is a demand for the development of negative-tone photosensitive dry film resists that can print finer patterns without leaving residue, can form coatings on substrate films without film formation defects, and have solvent resistance and substrate adhesion.

Japanese Patent Application Laid-Open No. 2018-151489 JP 2019-128438 A

The object of the present invention is to provide a dry film resist and a negative photosensitive resin composition in which the resist layer before exposure is alkali-soluble, has excellent film-forming properties and adhesion, and the cured resist after exposure has excellent chemical resistance.

As a result of extensive research to solve the above-mentioned problems, the inventors discovered that by using a negative-tone photosensitive resin composition that combines a novolac-type phenolic resin composition having specific structural units, a radically polymerizable compound, and a photopolymerization initiator, it is possible to obtain a dry film resist that improves the alkaline solubility of the resist layer before exposure, has excellent film-forming properties and adhesion, and exhibits excellent chemical resistance in the cured resist, thereby completing the present invention.

That is, the present invention relates to a negative photosensitive resin composition containing the following components (A) to (C):
(A) a novolak-type phenolic resin in which the molar ratio of the structural unit (a1) derived from m-cresol, the structural unit (a2) derived from benzaldehyde, and the structural unit (a3) derived from salicylaldehyde [(a1):(a2):(a3)] is 1.0:0.3-0.8:0.3-0.8; (B) a radically polymerizable compound; and (C) a photopolymerization initiator.

The present invention further relates to a dry film resist comprising a substrate film and a resist layer containing the negative photosensitive resin composition.
The present invention further relates to a cured product of the resist layer.

The present invention provides a dry film resist and a negative photosensitive resin composition in which the resist layer before exposure is alkali-soluble, has excellent film-forming properties and adhesion, and the cured resist has excellent chemical resistance.

1 is a GPC chart of the novolak phenolic resin obtained in Synthesis Example 1. 1 is a GPC chart of the novolak phenolic resin obtained in Synthesis Example 2. 1 is a GPC chart of the novolak phenolic resin obtained in Synthesis Example 3. 1 is a GPC chart of the novolak phenolic resin obtained in Synthesis Example 4. 1 is a GPC chart of the novolak phenolic resin obtained in Synthesis Example 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes the embodiments of the present invention.
In this specification, "x to y" represents a numerical range of "x or more and y or less." The upper and lower limits of the numerical ranges can be combined in any combination.
Furthermore, a combination of two or more of the individual aspects of the present invention described below is also an aspect of the present invention.

[Negative Photosensitive Resin Composition]
A negative photosensitive resin composition according to one embodiment of the present invention contains the following components (A) to (C).
(A) a novolak-type phenolic resin in which the molar ratio of the structural unit (a1) derived from m-cresol, the structural unit (a2) derived from benzaldehyde, and the structural unit (a3) derived from salicylaldehyde [(a1):(a2):(a3)] is 1.0:0.3-0.8:0.3-0.8; (B) a radically polymerizable compound; and (C) a photopolymerization initiator.

In this embodiment, the use of the novolac phenolic resin (A) can suppress the occurrence of film formation defects on the substrate film. Furthermore, the alkali solubility of the unexposed areas is high, resulting in a resist with excellent adhesion. Furthermore, the chemical resistance of the cured resist is improved.
The components of the negative photosensitive resin composition will be described below.

Component (A)
The novolac phenolic resin, which is component (A), has a molar ratio [(a1):(a2):(a3)] of the structural unit (a1) derived from m-cresol, the structural unit (a2) derived from benzaldehyde, and the structural unit (a3) derived from salicylaldehyde of 1.0:0.3-0.8:0.3-0.8.

The molar ratio of the structural unit (a1) derived from m-cresol, the structural unit (a2) derived from benzaldehyde, and the structural unit (a3) derived from salicylaldehyde in component (A) [(a1):(a2):(a3)] is preferably 1.0:0.5-0.7:0.3-0.5, and more preferably 1.0:0.55-0.65:0.35-0.45, from the viewpoint of obtaining a cured film that not only has high sensitivity but also exhibits chemical resistance when cured at low temperatures.

Component (A) may contain structural units other than the structural unit (a1) derived from m-cresol, the structural unit (a2) derived from benzaldehyde, and the structural unit (a3) derived from salicylaldehyde. Examples of structural units other than (a1) to (a3) include structural units derived from phenols and aldehydes other than m-cresol, benzaldehyde, and salicylaldehyde.

Examples of the phenols include phenol, o-cresol, p-cresol, 2,3-xylenol, 2,5-xylenol, 3,4-xylenol, 3,5-xylenol, 2,3,5-trimethylphenol, and 3,4,5-trimethylphenol.

Examples of the above aldehydes include formalin, paraformaldehyde, acetaldehyde, chloroacetaldehyde, 4-hydroxybenzaldehyde, and 3-hydroxybenzaldehyde.

From the viewpoint of obtaining a cured film that not only has high sensitivity but also has chemical resistance when cured at low temperature, the total content of the structural units (a1), (a2), and (a3) in component (A) is preferably 30% by mass or more, more preferably 50% by mass or more, and even more preferably 90% by mass or more.
The total content of the structural units (a1), (a2), and (a3) may be substantially 100% by mass, which means that structural units other than the structural units (a1), (a2), and (a3) are inevitably contained.

The weight-average molecular weight of the novolac phenolic resin, component (A), is preferably 1,000 or more, more preferably 1,500 or more. It is also preferably 7,000 or less, more preferably 6,000 or less, and even more preferably 5,000 or less. A weight-average molecular weight of 1,000 or more is preferred because it provides high heat resistance. On the other hand, a weight-average molecular weight of 7,000 or less is preferred because it provides high sensitivity. In this specification, the weight-average molecular weight is measured according to the conditions described in the examples.

Component (A) is obtained by polycondensing m-cresol, benzaldehyde, and salicylaldehyde in an organic solvent using an acid catalyst in a molar ratio (m-cresol:benzaldehyde:salicylaldehyde) of 1.0:0.3-0.8:0.3-0.8.

The molar ratio of m-cresol, benzaldehyde, and salicylaldehyde (m-cresol:benzaldehyde:salicylaldehyde) in the reaction solvent is preferably in the range of 1.0:0.5-0.7:0.3-0.5, more preferably 1.0:0.55-0.65:0.35-0.45, from the viewpoint of obtaining a cured film that not only has high sensitivity but also chemical resistance when cured at low temperatures.

The molar ratio of salicylaldehyde is preferably smaller than the molar ratio of benzaldehyde , i.e., it is preferable that the molar ratio satisfies salicylaldehyde < benzaldehyde .

When m-cresol, benzaldehyde, and salicylaldehyde are polycondensed in an organic solvent to obtain the novolac phenolic resin (component (A)), as described above, the organic solvent may contain phenols and aldehydes other than m-cresol, benzaldehyde, and salicylaldehyde.

The ratio of the total mass of m-cresol, benzaldehyde, and salicylaldehyde in the reaction solvent to the total mass of all starting materials that can become structural units constituting component (A) is preferably 30% by mass or more, more preferably 50% by mass or more, and even more preferably substantially 100% by mass, from the viewpoint of obtaining a cured film that not only has high sensitivity but also exhibits chemical resistance when cured at low temperatures.

Reaction solvents used in the production of component (A) include, for example, methanol, ethanol, 1-propanol, 2-propanol, butanol, hexanol, ethylene glycol, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, methyl ethyl ketone, methyl isobutyl ketone, and toluene. Among these, one or more selected from ethanol, 1-propanol, and 2-propanol are preferred, and ethanol is more preferred.

From the viewpoint of reaction uniformity, the amount of the reaction solvent used is preferably 20 parts by mass or more, more preferably 50 parts by mass or more, per 100 parts by mass of the raw materials used to derive the structural units that constitute component (A). It is also preferably 500 parts by mass or less, more preferably 300 parts by mass or less.

Examples of the acid catalyst used in producing component (A) include inorganic acids such as hydrochloric acid, sulfuric acid, phosphoric acid, boric acid, etc., and organic acids such as oxalic acid, acetic acid, paratoluenesulfonic acid, etc. Among these, inorganic acids and paratoluenesulfonic acid are preferred, and paratoluenesulfonic acid is more preferred, in order to further promote the reaction.
The amount of acid catalyst added is not particularly limited, but is preferably 5 parts by mass or more, more preferably 20 parts by mass or more, per 100 parts by mass of the raw materials from which the structural units constituting component (A) are derived, and is preferably 150 parts by mass or less, more preferably 100 parts by mass or less.

The reaction temperature during polycondensation of the raw materials for component (A) is preferably 30° C. or higher, more preferably 40° C. or higher, since this allows the reaction to be promoted and the resulting polymer to be efficiently polymerized. The reaction temperature is also preferably 100° C. or lower, more preferably 80° C. or lower.
The reaction time is preferably 4 hours or more, more preferably 12 hours or more, and is preferably 32 hours or less, more preferably 24 hours or less.

・Component (B)
The radical polymerizable compound of component (B) refers to a compound having multiple ethylenically unsaturated groups in the molecule. By incorporating the radical polymerizable compound, curing of the exposed area is promoted, improving sensitivity during exposure. In addition, the crosslink density after thermal curing is improved, improving the hardness of the resist.

As the radically polymerizable compound, a compound having a (meth)acrylic group, which easily undergoes radical polymerization, is preferred.
From the viewpoint of improving sensitivity during exposure and hardness of the cured film, a compound having two or more (meth)acrylic groups in the molecule is more preferred.

Examples of radically polymerizable compounds include diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane di(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tri(meth)acrylate, and ditrimethylolpropane tetra(meth)acrylate. , 1,3-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, ethoxylated glycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tri(meth)acrylate ester, ethoxylated pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tripentaerythritol hepta(meth)acrylate, tripentaerythritol octa(meth)acrylate, tetrapentaerythritol nona(meth)acrylate, tetrapentaerythritol deca(meth)acrylate, pentaerythritol undeca(meth)acrylate, pentaerythritol dodeca(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate ester, 2,2-bis[4-(3-(meth)acryloxy-2-hydroxypropoxy)phenyl]propane, 1,3,5-tris((meth)acryloxyethyl)isocyanuric acid, 1,3-bis((meth)acryloxyethyl)isocyanuric acid, 9,9-bis[4-(2-(meth)acryloxyethoxy)phenyl]fluorene, 9,9-bis[4-(3-(meth)acryloxypropoxy)phenyl]fluorene, 9,9-bis(4-(meth)acryloxyphenyl)fluorene, or acid-modified, ethylene oxide-modified, or propylene oxide-modified versions thereof.

In one embodiment, the negative-type photosensitive resin composition does not contain, as a radical polymerizable compound, one or more resins or compounds selected from an ethylenically unsaturated group-containing polyimide, an ethylenically unsaturated group-containing polyimide precursor, an ethylenically unsaturated group-containing polybenzoxazole, and an ethylenically unsaturated group-containing polybenzoxazole precursor.
In one embodiment, the negative photosensitive resin composition is for use in a dry film resist.

The amount of radically polymerizable compound is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, and particularly preferably 5 parts by mass or more, per 100 parts by mass of component (A). A content within the above range can improve sensitivity during exposure. On the other hand, the content of the radically polymerizable compound is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 80 parts by mass or less, and particularly preferably 70 parts by mass or less.

・Component (C)
The photopolymerization initiator, component (C), refers to a compound that generates radicals through bond cleavage and/or reaction upon exposure. By incorporating a photopolymerization initiator, the exposed areas of the film of the negative-tone photosensitive resin composition become insoluble in an alkaline developer, thereby forming a negative-tone pattern. Furthermore, curing of the exposed areas is accelerated, improving sensitivity.

The photopolymerization initiator is not particularly limited, and known photopolymerization initiators can be used. Examples of photopolymerization initiators include benzyl ketal photopolymerization initiators, α-hydroxyketone photopolymerization initiators, α-aminoketone photopolymerization initiators, acylphosphine oxide photopolymerization initiators, oxime ester photopolymerization initiators, acridine photopolymerization initiators, titanocene photopolymerization initiators, benzophenone photopolymerization initiators, acetophenone photopolymerization initiators, aromatic ketoester photopolymerization initiators or benzoate ester photopolymerization initiators, and α-aminoalkylphenone photopolymerization initiators.

The photopolymerization initiator may be used alone or in combination of two or more kinds.
The amount of the photopolymerization initiator to be blended is preferably 0.1 parts by mass or more, more preferably 5 parts by mass or more, and preferably 30 parts by mass or less, more preferably 20 parts by mass or less, per 100 parts by mass of component (A), since this allows for good sensitivity and the desired pattern to be obtained.

Solvent In this embodiment, a solvent may be used in addition to the above-described components (A) to (C).
Examples of the solvent include polar aprotic solvents such as N-methyl-2-pyrrolidone, γ-butyrolactone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide, ethers such as tetrahydrofuran, dioxane, propylene glycol monomethyl ether, and propylene glycol monoethyl ether, ketones such as acetone, methyl ethyl ketone, and diisobutyl ketone, esters such as ethyl acetate, butyl acetate, isobutyl acetate, propyl acetate, propylene glycol monomethyl ether acetate, and 3-methyl-3-methoxybutyl acetate, alcohols such as ethyl lactate, methyl lactate, diacetone alcohol, and 3-methyl-3-methoxybutanol, and aromatic hydrocarbons such as toluene and xylene. These solvents may be used alone or in combination of two or more.

The amount of solvent blended in the negative-type photosensitive resin composition of this embodiment is such that the solids concentration in the composition is preferably 5% by mass or more, since the fluidity of the composition allows a uniform coating to be obtained by a coating method such as spin coating. Also, the amount is preferably such that the solids concentration in the composition is 65% by mass or less.

In one embodiment, in addition to the above-described components (A) to (C) and the solvent, various additives may be blended into the negative photosensitive resin composition to the extent that the effects of the present invention are not impaired. Examples of additives include fillers, pigments, surfactants such as leveling agents, adhesion improvers, and dissolution promoters.

The negative photosensitive resin composition of the present embodiment can be prepared by stirring and mixing the above-described components (A) to (C), and, if necessary, a solvent and various additives, in a conventional manner to form a homogeneous liquid.
When solid materials such as fillers and pigments are blended into the composition, they are preferably dispersed and mixed using a dispersing device such as a dissolver, homogenizer, triple roll mill, etc. In addition, the composition can be filtered using a mesh filter, membrane filter, etc. to remove coarse particles and impurities.
The negative photosensitive resin composition of this embodiment can be suitably used for dry film resist applications.

[Dry film resist]
A dry film resist according to one embodiment of the present invention has a base film and a resist layer (hereinafter, sometimes referred to as a resist layer or a resist film) containing the negative photosensitive resin composition of the present invention.

The substrate film can be a single-layer film made of a single polymer film or a multilayer film made by laminating multiple polymer films. Specific examples include plastic films such as nylon film, polyethylene (PE) film, polyethylene terephthalate (PET) film, polyethylene naphthalate film, polyphenylene sulfide (PPS) film, polypropylene (PP) film, polystyrene film, polymethylpentene (TPX) film, polycarbonate film, fluorine-containing film, special polyvinyl alcohol (PVA) film, and polyester film with a release treatment. Of these, polyethylene terephthalate (PET) film is preferred.

The resist layer can be obtained, for example, by forming a film of the negative-type photosensitive resin composition of the present invention on a substrate film using an applicator, bar coater, wire bar coater, roll coater, curtain flow coater, etc.

In one embodiment of the dry film resist, in addition to the above-described base film and resist layer, known layers such as a film for protecting the resist layer may be laminated.
The protective film is not particularly limited as long as it can be peeled off without damaging the shape of the resist layer. Specific examples include plastic films such as nylon film, polyethylene (PE) film, polyethylene terephthalate (PET) film, polyethylene naphthalate film, polyphenylene sulfide (PPS) film, polypropylene (PP) film, polystyrene film, polymethylpentene (TPX) film, polycarbonate film, fluorine-containing film, special polyvinyl alcohol (PVA) film, and polyester film subjected to a release treatment.

The dry film resist of this embodiment can be attached to an object such as a semiconductor substrate or a semiconductor package using various laminators such as a vacuum laminator or a roll laminator, and the base film can be peeled off to transfer the resist layer to the object.
The semiconductor substrate, semiconductor package, etc. may or may not have a stepped structure. By appropriately adjusting the thickness of the resist layer according to the height of the step, it is possible to fill the step with the resist layer. The dry film resist of this embodiment can be suitably used for semiconductor substrates, semiconductor packages, etc. that have steps.
After the transfer, the transfer medium is subjected to heat treatment, if necessary, on a hot plate or in an oven at 60 to 150° C. for 1 to 30 minutes, preferably 80 to 130° C. for 1 to 10 minutes.

The transferred resist layer is irradiated (exposed) with actinic rays or radiation through a negative mask capable of forming a pattern of a predetermined shape, thereby obtaining a cured resist. Examples of radiation sources that can be used include low-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, and argon gas lasers. Examples of radiation include microwaves, infrared rays, visible light, ultraviolet rays, X-rays, gamma rays, electron beams, proton beams, neutron beams, and ion beams. Among these light sources, ultraviolet light is preferred, with the g-rays (wavelength 436 nm) and i-rays (wavelength 365 nm) of high-pressure mercury lamps being preferred. The radiation dose varies depending on the composition of the negative-type photosensitive resin composition and the film thickness of the photosensitive layer, but is preferably about 100 to 1,000 mJ/ ^cm² .

After exposure, the desired resist pattern can be formed by developing the resist in accordance with a known method to dissolve and remove unnecessary portions.
In this embodiment, the resist layer before exposure has high alkali solubility, and therefore the difference in alkali solubility between the exposed portion and the resist layer is large, making it possible to perform patterning with high resolution.

The developer is appropriately selected depending on the composition of the negative photosensitive resin composition. Examples of the developer include alkaline aqueous solutions of inorganic alkaline substances such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate, and aqueous ammonia; primary amines such as ethylamine and n-propylamine; secondary amines such as diethylamine and di-n-butylamine; tertiary amines such as triethylamine and methyldiethylamine; alcohol amines such as dimethylethanolamine and triethanolamine; quaternary ammonium salts such as tetramethylammonium hydroxide and tetraethylammonium hydroxide; and cyclic amines such as pyrrole and piheridine.
The alkaline developer may be used by appropriately adding alcohol, surfactant, etc., as needed. The alkaline concentration of the alkaline developer is usually preferably in the range of 2 to 5% by mass, and a 2.38% by mass aqueous solution of tetramethylammonium hydroxide is generally preferably used.

The development time varies depending on the composition of the negative-type photosensitive resin composition and the film thickness of the layer containing the negative-type photosensitive resin composition, but is typically 1 to 30 minutes. The development method may be any of the following: puddle method, dipping method, puddle method, spray development method, etc. Development may be carried out in multiple stages, with the developer being replaced between each stage.

After development with an alkaline developer, the resist pattern is washed with running water for 30 to 90 seconds, and if necessary, further heated at a temperature of 50° C. to 200° C. to obtain a cured resist pattern.
A cured resist formed using the dry film resist of this embodiment has excellent chemical resistance.

The present invention will be described in more detail below with reference to specific examples. The weight average molecular weight (Mw) of the synthesized resin was measured under the following GPC measurement conditions.
[GPC measurement conditions]
Measuring device: "HLC-8220 GPC" manufactured by Tosoh Corporation
Column: "Shodex KF802" manufactured by Showa Denko K.K.: 8.0 mmΦ x 300 mm
+ Showa Denko "Shodex KF802": 8.0mmΦ x 300mm
+ Showa Denko K.K. "Shodex KF803": 8.0mmΦ x 300mm
+ Showa Denko "Shodex KF804": 8.0mmΦ x 300mm
Column temperature: 40°C
Detector: RI (differential refractometer)
Data processing: Tosoh Corporation "GPC-8020 Model II Version 4.30"
Developing solvent: tetrahydrofuran Flow rate: 1.0 mL/min Sample: 0.5% by mass tetrahydrofuran solution in terms of resin solid content filtered through a microfilter Injection amount: 0.1 mL
Standard sample: Monodisperse polystyrene (standard sample: monodisperse polystyrene)
"A-500" manufactured by Tosoh Corporation
Tosoh Corporation "A-2500"
Tosoh Corporation "A-5000"
"F-1" manufactured by Tosoh Corporation
"F-2" manufactured by Tosoh Corporation
Tosoh Corporation "F-4"
"F-10" manufactured by Tosoh Corporation
"F-20" manufactured by Tosoh Corporation

Synthesis Example 1 (Synthesis of Novolac Phenolic Resin (A-1))
A 2000 mL four-neck flask equipped with a condenser was charged with 164 g (1.52 mol) of m-cresol, 103 g (0.97 mol) of benzaldehyde, 74 g (0.61 mol) of salicylaldehyde, and 8 g of paratoluenesulfonic acid, which were then dissolved in 300 g of ethanol as a reaction solvent. The mixture was then heated to 80°C using a mantle heater and stirred under reflux for 16 hours to allow the reaction to proceed. After the reaction, ethyl acetate and water were added and the mixture was washed five times with a separation wash. The solvent was removed from the remaining resin solution by distillation under reduced pressure, followed by vacuum drying, yielding 281 g of a pale red powder of novolac phenolic resin (A1).
The Mw of the novolac phenolic resin (A-1) was 3,100. The GPC chart of the novolac phenolic resin (A-1) is shown in FIG.

Synthesis Example 2 (Synthesis of Novolac Phenolic Resin (A-2))
Except for changing the amounts of starting materials to 164 g (1.52 mol) of m-cresol, 80 g (0.75 mol) of benzaldehyde, and 92 g (0.75 mol) of salicylaldehyde, 280 g of powder of novolac phenolic resin (A-2) was obtained in the same manner as in Synthesis Example 1. The Mw of the novolac phenolic resin (A-2) was 2,370.
The GPC chart of the novolak phenolic resin (A-2) is shown in FIG.

Synthesis Example 3 (Synthesis of Novolac Phenolic Resin (A-3))
Except for changing the amounts of starting materials to 164 g (1.52 mol) of m-cresol, 117 g (1.10 mol) of benzaldehyde, and 58 g (0.47 mol) of salicylaldehyde, the same procedure as in Synthesis Example 1 was repeated to obtain 279 g of powder of novolac phenolic resin (A-3). The Mw of the novolac phenolic resin (A-3) was 2,700.
The GPC chart of the novolak phenolic resin (A-3) is shown in FIG.

Synthesis Example 4 (Synthesis of Novolac Phenolic Resin (A-4))
Except for changing the amounts of starting materials to 164 g (1.52 mol) of m-cresol, 67 g (0.63 mol) of benzaldehyde, and 115 g (0.94 mol) of salicylaldehyde, the same procedure as in Synthesis Example 1 was repeated to obtain 282 g of powder of novolac phenolic resin (A-4). The Mw of the novolac phenolic resin (A-4) was 2,900.
The GPC chart of the novolak phenolic resin (A-4) is shown in FIG.

Synthesis Example 5 (Synthesis of Novolac Phenolic Resin (A-5))
Except for changing the reaction solvent to 250 g of ethanol, 30 g of 1-propanol, and 15 g of 2-propanol, the same procedure as in Synthesis Example 1 was repeated to obtain 282 g of powder of novolac phenolic resin (A-5). The Mw of the novolac phenolic resin (A-5) was 3,200.
The GPC chart of the novolak phenolic resin (A-5) is shown in FIG.

Comparative Synthesis Example 1 (Synthesis of Novolac Phenolic Resin (A-6))
Under a dry nitrogen stream, a 2000 mL three-neck flask equipped with a condenser was charged with 140 g (1.30 mol) of m-cresol, 76 g (0.7 mol) of p-cresol, 151 g of 37 wt % aqueous formaldehyde solution (1.86 mol of formaldehyde), and 1 g (0.01 mol) of oxalic acid dihydrate. The mixture was dissolved in 528 g of methyl isobutyl ketone (MIBK), and the reaction mixture was refluxed using a mantle heater for 4 hours while stirring. After the reaction, water was added, and the mixture was subjected to five separation washings. The methyl isobutyl ketone was distilled off under reduced pressure at 60°C using an evaporator, followed by vacuum drying, yielding 212 g of a pale red powder of phenol novolac resin (A-6). GPC analysis of the phenol novolac resin (A-6) showed a weight average molecular weight (Mw) of 3,500.

[Negative Photosensitive Resin Composition]
Example 1
A negative photosensitive resin composition (E-1) was obtained by dissolving 10.0 g of the phenol novolak resin (A-1) powder obtained in Synthesis Example 1, 6.0 g of a radical polymerizable compound (B) (dipentaerythritol hexaacrylate manufactured by Nippon Kayaku Co., Ltd.), 1.2 g of a photopolymerization initiator (C) powder (Irgacure 369 manufactured by Sigma-Aldrich Co., Ltd.), and 25.8 g of propylene glycol monomethyl ether acetate.

Examples 2 to 5, Comparative Example 1
In Examples 2 to 5 and Comparative Example 1, negative photosensitive resin compositions (E-2) to (E-6) were obtained in the same manner as in Example 1, except that phenol novolak resin (A-2) to (A-6) powder shown in Table 1 was used as component (A).

Comparative Example 2
A negative photosensitive resin composition (E-7) was obtained in the same manner as in Example 1, except that a resin (A-7) represented by the following formula was used as component (A) instead of the phenol novolak resin. In the following formula showing the structural structure of the alkali-soluble resin, the number to the right of the parentheses indicates the content (mass%) of the unit in the parentheses in the resin.

Comparative Example 3
A negative photosensitive resin composition (E-8) was obtained in the same manner as in Example 1, except that component (A) was not used.

[evaluation]
Dry film resists were prepared using the negative photosensitive resin compositions prepared in the Examples and Comparative Examples, and the film-forming properties on the substrate film, the alkali solubility and adhesion of the resist film before exposure, and the chemical resistance of the cured resist film after exposure were evaluated.
(1) Film Formability The negative photosensitive resin composition was applied to a PET film to a thickness of approximately 5 μm using a bar coater (manufactured by Daiichi Rika Co., Ltd.: No. 02), and the applied film was dried at 100° C. for 60 seconds to obtain a PET film with a photosensitive film formed thereon. The photosensitive film formed on the PET film surface was observed using an optical microscope to evaluate repellency and unevenness during film formation.
Those without repellency or unevenness were rated as having good film-forming properties (◯), and those with repellency or unevenness were rated as having insufficient film-forming properties (×). The evaluation results are shown in Table 1.

(2) Alkali Solubility The negative photosensitive resin composition was applied to a PET film to a thickness of approximately 5 μm using a bar coater (manufactured by Daiichi Rika Co., Ltd.: No. 02), and the applied film was dried at 100° C. for 60 seconds to obtain a PET film with a photosensitive film. The obtained PET film was immersed for 10 seconds in a tray containing 250 mL of a developer (2.38% aqueous tetramethylammonium hydroxide solution). The PET film was then removed and rinsed with pure water for 10 seconds, and the residue on the PET film was evaluated.
Those with no residue were rated as good (◯), and those with residue were rated as poor (×). The evaluation results are shown in Table 1.

(3) Adhesion The negative photosensitive resin composition was applied to a copper plate (Standard Test Piece Co., Ltd.: C1020) to a thickness of approximately 5 μm using a bar coater (Daiichi Rika Co., Ltd.: No. 02), and the applied film was dried at 100°C for 60 seconds to obtain a copper plate with a photosensitive film. The obtained photosensitive film was divided into a grid pattern of 25 squares spaced 2 mm apart using a cutter knife. Cellophane tape was firmly attached to the grid pattern portion of the photosensitive film, and the cellophane tape was peeled off within 1 second within 5 minutes. The peeling of the grid pattern portion was observed (based on the JIS 5400 cross-cut test).
The evaluation results are shown in Table 1.

(4) Chemical Resistance of Cured Film A negative photosensitive resin composition was applied to a silicon wafer having a diameter of 5 inches using a bar coater (No. 02, manufactured by Daiichi Rika Co., Ltd.) to a thickness of approximately 5 μm, and then dried at 100° C. for 60 seconds. The wafer was then irradiated with light at 200 mJ/cm ² using a UV irradiation device (UVE-1001SD, manufactured by Minei Electric Co., Ltd.) and baked at 130° C. for 180 seconds to obtain a wafer having a cured film formed thereon.
The film thickness of the obtained wafer was measured, and then the wafer was divided into two. One of the two pieces was immersed in a 50 wt % aqueous solution of sulfuric acid (simulating a plating solution), and the other in a 2.38 wt % aqueous solution of TMAH for 15 minutes. The wafer was removed from the solution, washed with pure water, and the film thickness was measured again.
Chemical resistance was evaluated based on the rate of change in film thickness before and after immersion in a solvent. A rate of change of less than 2% was rated as good (◯), and a rate of change of 2% or more was rated as insufficient (×). The evaluation results are shown in Table 1.

In Table 1, the molar ratio of structural units in component (A), "(a1)/(a2)/(a3)," is the molar ratio of structural units (a1) derived from m-cresol, structural units (a2) derived from benzaldehyde, and structural units (a3) derived from salicylaldehyde.

From Table 1, it can be seen that dry film resists using the negative-tone photosensitive resin composition of the present invention do not suffer from film formation defects. It can also be seen that the resist film is alkali-soluble and has high adhesion. Furthermore, it can be seen that the cured resist film has excellent chemical resistance.

Claims (5)

A negative photosensitive resin composition comprising the following components (A) to (C):
(A) a novolak-type phenolic resin in which the molar ratio of the structural unit (a1) derived from m-cresol, the structural unit (a2) derived from benzaldehyde, and the structural unit (a3) derived from salicylaldehyde [(a1):(a2):(a3)] is 1.0:0.5-0.7:0.3-0.5; (B) a radically polymerizable compound; and (C) a photopolymerization initiator. 2. The negative photosensitive resin composition according to claim 1, wherein the total content of the structural unit (a1) derived from m-cresol, the structural unit (a2) derived from benzaldehyde, and the structural unit (a3) derived from salicylaldehyde in component (A ) is 30% by mass or more. The negative-type photosensitive resin composition according to claim 1 or 2, further containing a solvent. A dry film resist comprising a substrate film and a resist layer containing the negative photosensitive resin composition described in claim 1 or 2. A cured product of the resist layer according to claim 4 .