JP7725850B2 - Novolac phenolic resin, method for producing novolac phenolic resin, and photoresist composition - Google Patents

Description

The present invention relates to a novolac phenolic resin, a method for producing a novolac phenolic resin, and a photoresist composition.

Phenol resins such as novolac resins are used in adhesives, molding compounds, paints, photoresist materials, epoxy resin raw materials, and epoxy resin curing agents. For example, epoxy resin compositions using novolac phenolic resins as epoxy resin curing agents have excellent heat resistance and moisture resistance in the cured products, and are therefore widely used in the electrical and electronic fields, such as semiconductor encapsulants and insulating materials for printed wiring boards.

In the field of photoresist materials, novolac-type phenolic resins are used as alkali-soluble resins in positive-tone photoresists. In recent years, a wide variety of resist pattern formation methods have been developed, each tailored to specific uses and functions. As a result, the performance requirements for photoresist resin materials have become more sophisticated and diverse.

For example, in the field of flexible printed wiring boards such as those used in mobile phones, negative photoresists are used as dry film resists, but the use of positive dry film resists, which are advantageous for fine patterns in terms of resolution, is being considered. However, novolac phenolic resins are hard, and their films are brittle and inflexible, making them difficult to make into rolled positive dry film resists. Furthermore, solder resists also require flexibility to be compatible with flexible substrates. Therefore, novolac phenolic resins used as alkali-soluble resins are required to have a low modulus of elasticity when made into a film.

Furthermore, in etching processes such as dry etching for dry film resists and solder resists, the resist film must have sufficient hardness to withstand physical etching to prevent chipping after patterning. Therefore, novolac-type phenolic resins are required to have high hardness in addition to a low modulus of elasticity when formed into a film.

An example of the novolac type phenolic resin that is most widely used as an alkali-soluble resin for positive photoresists is a cresol novolac type phenolic resin (see, for example, Patent Document 1).
However, the cresol novolac phenolic resin described in Patent Document 1 cannot meet the above-mentioned increasingly sophisticated and diverse performance requirements, and the flexibility and film hardness of the resulting resin film are insufficient.

Patent Document 2 discloses a novolac phenolic resin containing specific ratios of phenols essentially containing alkyl-substituted phenols and a crosslinker composed of a compound containing a biphenyl ring or a benzene ring and/or formaldehyde, as well as a photoresist composition containing this novolac phenolic resin. The novolac phenolic resin in Patent Document 2 is specified to have a weight-average molecular weight of 1,000 or more but less than 4,500 when the phenols consist solely of alkyl-substituted phenols, and a weight-average molecular weight of 1,000 or more but less than 5,500 when the phenols contain both alkyl-substituted and unsubstituted phenols.

It is disclosed that the use of this novolac phenolic resin enables the production of a photoresist composition that has high sensitivity, a high film retention rate, and high resolution, and that the resulting resist (protective film, mask) has high heat resistance and is also able to exhibit stable adhesion to the substrate by suppressing peeling at the edges of the resist.
However, the novolac phenolic resin used therein required alkyl-substituted phenols as phenols and had a relatively low weight-average molecular weight.Furthermore, Patent Document 2 does not suggest anything about the flexibility or film hardness of the resulting resin film.

Japanese Unexamined Patent Publication No. 62-270951 JP 2013-133345 A

The present invention aims to provide a photoresist composition that can form a photoresist film that is flexible and has high film hardness, a novolac phenolic resin used therein, and a method for producing the novolac phenolic resin.

As a result of extensive research to solve the above-mentioned problems, the inventors discovered that a photoresist composition using a novolac phenolic resin synthesized from phenol, formaldehyde, and a specific biphenyl aralkyl resin can form a photoresist film that is flexible and has high film hardness, leading to the completion of the present invention.

That is, the present invention relates to the following items.
1. A novolac-type phenolic resin characterized by containing a first segment (S1) and a second segment (S2) and being represented by the following general formula (NP):

In the above general formula,
(SB) is a block represented by (S2) _n (S1) _m (n and m are integers of 0 or more, but not 0 at the same time), j is an integer of 1 or more, (SB) may be the same or different, and includes at least (SB) where n is 1 or more and (SB) where m is 1 or more,
(S1) is a divalent group represented by the following formula (1-2):

(S2) is a divalent group represented by the following formula (2):

The terminal groups (TM1) and (TM2) may be the same or different and are any of the following:

However, in the above formulas (1-2), (2) and (3), the bond ** is bonded to the bond *.

2. A novolac phenolic resin which is a reaction product of phenol, formaldehyde, and a biphenyl aralkyl resin represented by the following formula (1), wherein the biphenyl aralkyl resin is a reaction product of a phenol compound represented by the following formula (4) and a biphenyl compound represented by the following formula (5):

3. A method for producing a novolac phenolic resin by reacting phenol, formaldehyde, and a biphenyl aralkyl resin represented by the following formula (1), wherein the ratio ((w(rS1))/(w(rS2))) of the mass of the phenol (w(rS2)) to the mass of the biphenyl aralkyl resin (w(rS1)) is 0.5 or more and 9 or less.

4. A photoresist composition containing the phenolic resin composition for photoresists described in 1 above and a photosensitizer.

The present invention provides a photoresist composition capable of forming a photoresist film that is flexible and has high film hardness, a novolac phenolic resin used therein, and a method for producing the novolac phenolic resin.

The novolac phenolic resin of the present invention contains a first segment (S1) and a second segment (S2) and is represented by the following general formula (NP). The novolac phenolic resin of the present invention can be suitably used as a base resin for photoresist compositions.

(SB) is a block represented by (S2) _n (S1) _m (n and m are integers of 0 or more, but not 0 at the same time), j is an integer of 1 or more, and multiple (SB)s may be different, but in at least one (SB), n and m are 1 or more.

The first segment (S1) is a divalent group represented by the following general formula (1-2) and is derived from a biphenyl aralkyl resin (rS1) represented by the following formula (1). Because the first segment (S1) contains a biphenyl structure, "m" can be used as an indicator of the proportion of biphenyl structures in the general formula (NP).

The second segment (S2) is a divalent group represented by the following formula (2) and is derived from phenol (rS2).

The terminal groups (TM1) and (TM2) may be the same or different and are any of the following:

The bond * and bond ** in formulas (1-2), (2), and (3) indicate that the different symbols * and ** are bonded together.

Since the biphenyl structure is contained in the first segment (S1), the mass of (S1) _m in general formula (NP) corresponds to the mass (W(bpa)) derived from the biphenyl aralkyl resin (rS1). Meanwhile, phenol is contained in the second segment (S2) and at least one of the terminal groups, allowing the mass (W(ph)) of the phenol structure derived from these to be calculated. The mass ratio ((W(bpa))/(W(ph))) is preferably 0.5 or more and 9 or less.

By using a novolac phenolic resin with the above-mentioned mass ratio ((W(bpa))/(W(ph))) of 0.5 or greater, a photoresist composition capable of forming a flexible photoresist film can be obtained. The mass ratio ((W(bpa))/(W(ph))) is preferably 1.0 or greater.

By using a novolac phenolic resin with a mass ratio ((W(bpa))/(W(ph))) of 9.0 or less, it is possible to easily obtain a photoresist composition that can form a photoresist film that has a good balance of flexibility, hardness, and solubility in alkaline aqueous solutions. The mass ratio ((W(bpa))/(W(ph))) is more preferably 4.0 or less, even more preferably 2.3 or less, and especially preferably 1.5 or less.

The weight average molecular weight (Mw) of the novolac phenolic resin of the present invention, measured by GPC (gel permeation chromatography) in terms of polystyrene, is preferably 3,000 to 50,000, more preferably 5,500 to 40,000, even more preferably 8,000 to 35,000, particularly preferably 9,000 to 30,000, and most preferably 9,500 to 28,000.

Novolac phenolic resins with a polystyrene-equivalent weight-average molecular weight (Mw) measured by GPC within the above range are preferred in terms of ease of handling during manufacturing, sensitivity when made into a photoresist composition, rate of dissolution in alkali, heat resistance, and flexibility. If the weight-average molecular weight is less than 3,000, the sensitivity may be too high, heat resistance may be poor, or flexibility may be poor. If it is greater than 50,000, the sensitivity may be low and the rate of dissolution in alkali may be slow.

The softening point of the novolac phenolic resin of the present invention is preferably 90°C to 160°C, more preferably 100°C to 150°C, even more preferably 110°C to 145°C, and particularly preferably 120°C to 145°C. By keeping the softening point within the above range, it is possible to obtain a novolac phenolic resin that satisfies the heat resistance requirements when made into a photoresist composition.

[Method for producing novolac phenolic resin represented by general formula (NP)]
The novolac phenolic resin of the present invention can be produced by condensation polymerization of the biphenyl aralkyl resin represented by the formula (1), phenol, and formaldehyde in the presence of an acid catalyst. The phenol is a benzene ring having a phenolic hydroxyl group and has no substituent. By using such a phenol as a raw material, it is possible to produce a novolac phenolic resin having a high proportion of biphenyl structures.

<Method of producing biphenyl aralkyl resin>
The biphenyl aralkyl resin represented by formula (1) can be suitably obtained by subjecting a phenol compound (b1) represented by the following formula (4) to a condensation reaction with a biphenyl compound (b2) represented by the following formula (5) in the absence of a catalyst or preferably in the presence of an acid catalyst.

Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and a t-butyl group, with a methyl group being preferred. Examples of the phenol compound (b1) include monohydric phenol compounds such as phenol, m-cresol, p-cresol, o-cresol, ethylphenol, propylphenol, butylphenol, and hexylphenol. Of these, phenol is preferred. That is, a hydrogen atom is most preferred as R.
These phenol compounds may be used alone or in combination of two or more. From the viewpoint of providing a photoresist composition with a good balance of sensitivity, alkali dissolution rate, and flexibility, it is particularly preferred to use phenol alone.

The biphenyl compound (b2) is a component that crosslinks the phenol compound (b1) represented by the formula (4) above, and is represented by the following formula (5):

Specific examples of alkoxyl groups include methoxy and ethoxy groups, with methoxy groups being preferred due to their reactivity with phenolic compounds and ease of availability. Examples of halogen atoms include fluorine, chlorine, bromine, and iodine atoms, with chlorine atoms being preferred due to their reactivity with phenolic compounds and ease of availability.

Specific examples of preferred biphenyl compounds (b2) include 4,4'-di(chloromethyl)biphenyl, 4,4'-di(methoxymethyl)biphenyl, and 4,4'-di(ethoxymethyl)biphenyl.

Furthermore, as a component that crosslinks the phenol compound (b1) represented by the formula (4), formaldehyde can be used together with the biphenyl compound (b2) within the range that does not impair the effects of the present invention.

The amount of biphenyl compound (b2) used is preferably 0.1 to 1.0 mol, more preferably 0.3 to 0.6 mol, per 1 mol of phenol compound (b1). By using 0.1 to 1.0 mol of biphenyl compound (b2) per 1 mol of phenol compound (b1), a biphenyl aralkyl resin having a weight-average molecular weight (Mw) within the preferred range can be obtained.

The conditions for the condensation reaction between the phenol compound (b1) and the biphenyl compound (b2) are exemplified below, but are not limited to these. The conditions for the acid catalyst, reaction solvent, reaction temperature, reaction time, reaction pressure, and post-treatment can be those conventionally known for the production process.

<Acid catalyst>
The acid catalyst is not particularly limited and can be selected from organic sulfonic acids such as benzenesulfonic acid, paratoluenesulfonic acid, methanesulfonic acid, etc., inorganic acids such as hydrochloric acid, sulfuric acid, etc. The acid catalysts can be used alone or in combination of two or more, with sulfuric acid, oxalic acid, or paratoluenesulfonic acid being particularly preferred.

The amount of the acid catalyst used is generally about 0.01 to 1% by weight based on the phenol. For example, it is recommended to use about 0.3 to 1.0% by weight for oxalic acid, about 0.05 to 0.1% by weight for sulfuric acid, and about 0.1 to 0.3% by weight for paratoluenesulfonic acid.
When used in a photoresist composition, it is desirable to use as little acid catalyst as possible. If the acid catalyst remains in the resin, the photoresist properties may be impaired, so it is preferable to neutralize the acid catalyst with an amine or inorganic alkali.

<Reaction temperature>
If the reaction temperature is too low, the polymerization will not proceed, and if it is too high, it may be difficult to control the reaction, making it difficult to obtain the desired biphenylaralkyl resin. Generally, a temperature of 50 to 200°C will allow the reaction to proceed appropriately. The reaction temperature is preferably 70 to 180°C, and more preferably 80 to 170°C.

<Reaction Solvent>
Examples of the organic solvent include ethers such as diethylene glycol dimethyl ether, 1,2-dimethoxyethane, and 1,2-diethoxyethane; esters such as propylene glycol monomethyl ether acetate; and cyclic ethers such as tetrahydrofuran and dioxane. The amount of these organic solvents used is usually 20 to 1,000 parts by mass per 100 parts by mass of the reaction raw materials.

<Reaction time, reaction pressure>
The reaction time varies depending on the reaction temperature, but is usually from 0.1 to 20 hours. The reaction is usually carried out under normal pressure, but may also be carried out under slightly elevated or reduced pressure.

<Post-processing>
As a post-treatment, it is preferable to add a base to neutralize the acid catalyst in order to terminate the reaction, and then add water to wash the reaction mixture to remove the acid catalyst. The base used to neutralize the acid catalyst is not particularly limited, and any base can be used as long as it neutralizes the acid catalyst and forms a salt that is soluble in water.

Bases include inorganic bases such as metal hydroxides and metal carbonates, as well as organic bases such as amines and organic amines. Specific examples of inorganic bases include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, sodium bicarbonate, and calcium carbonate. Specific examples of organic base amines or organic amines include ammonia, trimethylamine, triethylamine, diethylamine, and tributylamine. Organic amines are preferred. The amount used depends on the amount of acid catalyst, but it is preferable to use an amount that neutralizes the acid catalyst and brings the pH of the reaction system into the range of 4 to 8.

The amount and number of washes are not particularly limited, but from an economical perspective, 1 to 5 washes are preferred to remove the acid catalyst to an extent that it does not affect practical use. The wash temperature is also not particularly limited, but from the perspective of catalyst species removal efficiency and workability, 40 to 95°C is preferred. If separation of the resin and wash water is poor during washing, it is effective to add a solvent that reduces the viscosity of the resin or increase the wash temperature. The type of solvent is not particularly limited, but any solvent that dissolves the phenolic resin and reduces viscosity can be used.

After removing the acid catalyst, the temperature of the reaction system is typically raised to 130°C to 230°C, and volatile components remaining in the reaction mixture, such as unreacted raw materials and organic solvents, are distilled off under a reduced pressure of, for example, 20 to 50 torr. This allows the desired biphenyl aralkyl resin to be efficiently separated and recovered.

In this way, the biphenylaralkyl resin represented by formula (1) is produced. In formula (1), k represents the repeating number and is an integer greater than or equal to 0. Because the obtained biphenylaralkyl resin is an aggregate of polymers with various molecular weights, the value of k in formula (1) can be expressed as the average value k' of the aggregate.

The average value k' is preferably such that the weight average molecular weight (Mw) of the biphenyl aralkyl resin, measured by GPC (gel permeation chromatography) in terms of polystyrene, is 800 to 4000, more preferably 1300 to 3500, still more preferably 1500 to 3000, particularly preferably 1800 to 2500, and most preferably 1900 to 2300.
If the weight average molecular weight is less than 800, the sensitivity may be too high, the heat resistance may be poor, or the flexibility may be poor. If the weight average molecular weight is more than 4000, the sensitivity may be low and the dissolution rate in alkali may be slow.

As explained above for the phenol compound (b1) represented by formula (4), it is preferable for R in formula (1) to have a hydrogen atom introduced therein, from the viewpoint of achieving a balance between sensitivity, alkali dissolution rate, heat resistance, and flexibility when the photoresist composition is prepared.

The novolac phenolic resin of the present invention, represented by general formula (NP), can be produced by subjecting a biphenyl aralkyl resin represented by formula (1), phenol, and formaldehyde to a condensation polymerization reaction in the presence of an acid catalyst. Phenol is not only a raw material, but also functions as a solvent to dissolve other components in the reaction. Furthermore, the use of phenol makes it possible to produce novolac phenolic resins with desired properties.

One preferred embodiment of the reaction is as follows: First, phenol and, if necessary, a solvent are added to a reactor, followed by the biphenyl aralkyl resin. After the biphenyl aralkyl resin is completely dissolved with phenol, an aqueous solution of formaldehyde is added dropwise to react the three raw materials.

The ratio of the mass of the biphenyl aralkyl resin (w(rS1)) represented by formula (1) to the mass of the phenol (w(rS2)) (the mass ratio of the raw material charges ((w(rS1))/(w(rS2)))) is 0.5 or greater, and preferably 1.0 or greater. By setting the mass ratio of the raw material charges ((w(rS1))/(w(rS2)))) to 0.5 or greater, a phenolic resin composition for photoresists can be obtained that has flexibility and hardness when made into a photoresist film.

The upper limit of the mass ratio ((w(rS1))/(w(rS2))) of the raw material charges is preferably 9.0 or less, more preferably 4.0 or less, even more preferably 2.3 or less, and particularly preferably 1.5 or less. By keeping this mass ratio at 9.0 or less, it is possible to easily obtain a phenolic resin composition for photoresists that has a good balance of flexibility, hardness, and alkali dissolution rate.

There are no particular restrictions on the formaldehyde, but an aqueous formaldehyde solution may be used, or a polymer that decomposes to form formaldehyde in the presence of acid, such as paraformaldehyde or trioxane, may also be used. An aqueous formaldehyde solution is preferred, as it is easy to handle, and commercially available 42% aqueous formaldehyde solution can be used as is.

The amount of formaldehyde used is preferably 0.2 to 1.0 moles per mole of phenol, and more preferably 0.5 to 0.9 moles. By using 0.2 to 1 mole of formaldehyde per mole of phenol, the weight-average molecular weight (Mw) of the novolac phenolic resin of the present invention can be adjusted to fall within the above-mentioned preferred range.

When producing the novolac phenolic resin represented by general formula (NP), the conditions for the acid catalyst, reaction solvent, reaction temperature, reaction time, reaction pressure, and post-treatment can be the same as those used in the production of the biphenyl aralkyl resin described above.

Since the novolac phenolic resin of the present invention is produced by the above-described method, it is presumed to be blocked containing a first segment (S1) derived from the biphenyl aralkyl resin (rS1) represented by the above-described formula (1) and a segment derived from the second segment (S2) derived from phenol (rS2). The above-described reaction is illustrated in the following formulas (6) and (7), which will be explained below.

First, as shown in formula (6) below, a biphenyl aralkyl resin (rS1), which is a phenolic resin having a biphenyl structure, is obtained by reacting a phenolic compound with a biphenyl compound.

Next, as shown in formula (7) below, phenol (rS2), formaldehyde, and biphenyl aralkyl resin (rS1) are reacted to produce first and second segments. The first segment (S1) is formed by blocking polymerization units of biphenyl aralkyl resin (rS1). The second segment (S2) is formed by blocking polymerization units of phenol resin obtained by condensation polymerization of phenol (rS2) and formaldehyde.

However, the molecular ends are one of the following:

In the above formula, m is the degree of polymerization when the first segments (S1) are polycondensed together, and n is the degree of polymerization of the second segment (S2) formed by polycondensation of phenol and formaldehyde. j represents the degree of polymerization when the first segment (S1) and the second segment (S2) are polycondensed. n and m are integers of 0 or greater, but are not both 0. There is always a combination where n is an integer of 1 or greater and m is an integer of 1 or greater. Also, j is an integer of 1 or greater.

Since the novolac phenolic resin of the present invention is an aggregate of polymers having various molecular weights, the values of m, n, and j can be expressed as their respective average values m', n', and j'. The average values m', n', and j' are a combination of values that result in a polystyrene-equivalent weight average molecular weight (Mw) of the novolac phenolic resin of the present invention measured by GPC (gel permeation chromatography) within a preferred range.

As shown in formula (7), in the novolac phenolic resin of the present invention, a segment ((S2) _n (S1) _m ) comprising a first segment (S1) and a second segment (S2) is blocked. That is, the novolac phenolic resin of the present invention represented by general formula (NP) has a structure such as (S2S2)(S1S1S1)S2 or S2(S1S1)S2S1(S2S2)S1.

Such blocked novolac phenolic resins cannot be obtained by a single-step random polycondensation reaction (co-condensation reaction) between a phenol component, an aldehyde component, and BCMB (4,4'-di(chloromethyl)biphenyl). In the present invention, a specific biphenyl aralkyl resin obtained from specific raw materials is reacted with phenol and formaldehyde, enabling the production of a novolac phenolic resin with a different chemical structure from conventional resins.

In the novolak phenolic resin of the present invention, the first segment (S1) having a biphenyl structure is believed to mainly contribute to the flexibility and hardness of the photoresist film, while the second segment (S2) derived from phenol is believed to contribute to the alkali dissolution rate of the photoresist film.
Therefore, the novolac phenolic resin of the present invention can be suitably used as a base resin for a photoresist composition.

The photoresist composition of the present invention contains the novolac phenolic resin of the present invention and a photosensitizer. By using the photoresist composition of the present invention, a flexible resist film can be obtained, which can be developed with an alkaline solution to form a good resist pattern.

The photosensitizer is not limited to, but is preferably a photosensitizer containing a quinone diazide compound having a quinone diazide group, and is particularly preferably a photosensitizer containing a 1,2-quinone diazide compound. As a photosensitizer containing a quinone diazide group, any photosensitizer that has been used in quinone diazide-novolac photoresists can be suitably used.

Preferred photosensitizers are compounds obtained by reacting naphthoquinone diazide sulfonic acid chloride, benzoquinone diazide sulfonic acid chloride, or the like with a low-molecular-weight or high-molecular-weight compound having a functional group capable of condensation with these acid chlorides. Examples of functional groups capable of condensation with acid chlorides include hydroxyl groups and amino groups, with hydroxyl groups being particularly preferred.

Examples of compounds having a hydroxyl group that can condense with acid chlorides include hydroquinone, resorcinol, hydroxybenzophenones such as 2,4-dihydroxybenzophenone, 2,3,4-trihydroxybenzophenone, 2,4,6-trihydroxybenzophenone, 2,4,4'-trihydroxybenzophenone, 2,3,4,4'-tetrahydroxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, and 2,2',3,4,6'-pentahydroxybenzophenone, bis(2,4-dihydrobenzophenone), Examples of suitable hydroxyphenylalkanes include hydroxyphenylalkanes such as 4,4',3",4"-tetrahydroxy-3,5,3',5'-tetramethyltriphenylmethane and 4,4',2",3",4"-pentahydroxy-3,5,3',5'-tetramethyltriphenylmethane. These may be used alone or in combination of two or more.

Furthermore, examples of acid chlorides include naphthoquinone diazide sulfonic acid chloride and benzoquinone diazide sulfonic acid chloride. Specific examples of preferred examples of these include 1,2-naphthoquinone diazide-5-sulfonyl chloride and 1,2-naphthoquinone diazide-4-sulfonyl chloride.

In the photoresist composition of the present invention, the content of the photosensitizer is typically 5 to 50 parts by weight, and preferably 10 to 40 parts by weight, per 100 parts by weight of the novolac phenolic resin. If the content of the photosensitizer is 5 parts by weight or more, sufficient sensitivity as a photosensitive composition can be ensured. Furthermore, if the content of the photosensitizer is 50 parts by weight or less, the problem of component precipitation can be substantially avoided.

The photoresist composition of the present invention is preferably uniformly dissolved in a solvent. There are no particular limitations on the type or amount of solvent used in the photoresist composition, but the type and amount are selected so that the solvent evaporates at an appropriate drying rate when a coating film is formed, resulting in a uniform, smooth coating film. Suitable solvents include, for example, glycol ether esters such as ethyl cellosolve acetate and propylene glycol monomethyl ether acetate; esters such as ethyl pyruvate, n-amyl acetate, and ethyl lactate; and ketones such as 2-heptanone and γ-butyrolactone. These solvents may be used alone or in combination of two or more.

In addition to the novolac phenolic resin and photosensitizer described above, the resist composition of the present invention can also contain, as appropriate, conventional components of resist compositions, such as stabilizers such as antioxidants, plasticizers, surfactants, adhesion improvers, dissolution promoters, and dissolution inhibitors.

The photoresist composition of the present invention can be suitably used as a positive photoresist composition. Conventional methods can be used, one example of which is as follows. A silicon wafer having an oxide film formed on its surface is used as a substrate, and a coating film of the photoresist composition of the present invention is formed on the surface using a spin coater or similar. After pre-baking as needed, the coating film is subjected to pattern exposure using a reduced projection exposure device or similar. The exposed portions of the coating film are then developed using a developer such as a 2.38% aqueous solution of tetramethylammonium hydroxide to remove them. After rinsing with pure water or similar as needed, the coating is post-baked to form a resist pattern on the substrate.

Then, for example, the oxide film exposed by the resist pattern is removed by etching, leaving the oxide film patterned. The resist pattern on the oxide film is then removed to obtain a silicon wafer with a patterned oxide film. Next, a donor element, for example, is diffused into the silicon wafer exposed by the oxide film pattern by ion implantation, resulting in an n-type semiconductor.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

The biphenyl aralkyl resin (hereinafter referred to as biphenyl aralkyl resin (rS1)) used in the examples is as follows:

Biphenyl aralkyl resin (rS1):
Biphenyl aralkyl resin represented by the following general formula (8) (softening point: 83°C, weight average molecular weight (Mw): 2100)

Example 1
A 500 mL glass flask equipped with a thermometer, a feed/distillation outlet, and a stirrer was charged with 50 g (0.53 mol) of phenol, 50 g of biphenyl aralkyl resin (rS1) (hereinafter sometimes abbreviated as resin (rS1)), 0.05 g of paratoluenesulfonic acid (hereinafter sometimes abbreviated as PTS), and 10 g of propylene glycol monomethyl ether acetate (hereinafter sometimes abbreviated as PGMA) as a solvent. The flask was heated to 85°C, and then 30.4 g (0.43 mol) of 42% formalin was added over 1 hour.

After adding formalin, the temperature was raised to 95°C and the reaction was allowed to proceed for 16 hours. The temperature was then raised to 160°C to dehydrate the mixture, after which it was subjected to vacuum distillation at 30 Torr for 1 hour to remove unreacted raw materials, yielding the novolac phenolic resin of Example 1.

Example 2
A 500 mL glass flask equipped with a thermometer, a charging/distillation outlet, and a stirrer was charged with 50 g (0.53 mol) of phenol, 50 g of resin (rS1), 0.05 g of PTS, and 10 g of PGMA as a solvent. The flask was heated to 85°C, and then 34.2 g (0.48 mol) of 42% formalin was added over 1 hour.
After the formalin was added, the temperature was raised to 95° C. and the reaction was carried out for 16 hours. Thereafter, the temperature was raised to 160° C. to dehydrate the mixture, and then vacuum distillation was carried out at 30 Torr for 1 hour to remove unreacted raw materials, thereby obtaining a novolac phenolic resin of Example 2.

Comparative Example 1
A cresol novolac resin (metacresol and paracresol in a ratio of 4/6) was used as Comparative Example 1. This cresol novolac resin is used as the base novolac of a photoresist.

Comparative Example 2
The biphenyl aralkyl resin (rS1) (softening point: 83° C., weight average molecular weight (Mw): 2100) used as the raw material for the novolac type phenolic resins in Examples 1 and 2 was used as Comparative Example 2.

The novolak-type phenolic resins obtained in the examples and the resins of the comparative examples were examined for weight-average molecular weight (Mw), softening point, and alkali dissolution rate.
The resin analysis and evaluation methods are as follows.

(1) Weight average molecular weight (Mw)
GPC measurement was carried out under the following conditions to determine the weight average molecular weight in terms of polystyrene.
Model: Waters e2695 manufactured by Waters Corporation Column: Shodex LF-804 (1 unit) Measurement conditions: Column pressure 2.7 MPa
Eluent: tetrahydrofuran (THF)
Flow rate: 1 mL/min
Temperature: 40℃
Detector: UV-Visible Detector 2489
WAVE LENGTH: 254nm
Injection volume: 100 μmL
Sample concentration: 5 mg/mL

(2) Softening point (SP)
The softening point was measured by the ring and ball method in accordance with JIS K0070.

(3) Alkaline dissolution rate (DR)
A resin solution was prepared by dissolving 3 g of each resin in 9 g of PGMEA (propylene glycol monomethyl ether acetate). The solution was filtered through a 0.2 micron membrane filter. The solution was applied to a 4-inch silicon wafer using a spin coater to a thickness of approximately 1.5 μm and dried on a hot plate at 110°C for 60 seconds. A developer (1.60% aqueous tetramethylammonium hydroxide solution) was then used to measure the time until the film completely disappeared. The dissolution rate was calculated by dividing the initial film thickness by the time required for dissolution.

The results obtained, along with the formulation of each resin, are summarized in Table 1 below.

As shown in Table 1 above, when only the biphenyl aralkyl resin is used without using phenol (Comparative Example 2), it cannot be dissolved in an alkaline developer.
The results of Examples 1 and 2 show that by using a biphenyl aralkyl resin together with a predetermined amount of formaldehyde, a high molecular weight novolak type phenolic resin having an appropriate softening point and alkali dissolution rate can be obtained.

Coating films were formed using the novolac phenolic resin of the example and the resins of comparative examples 1 and 2, and the coating films were subjected to pencil hardness tests and evaluated for flexibility. The test and evaluation methods were as follows:

(1) Pencil Hardness Test Five grams of each resin was dissolved in PGMEA to prepare a resin solution with a solid content of 40%. Using a 50 μm applicator, a film was formed on a substrate (aluminum plate (5052 material)). This was dried at 110° C. for 10 minutes to obtain a coating film with a thickness of approximately 10 μm after drying.
The scratch hardness of the resulting coating film was measured by the pencil method described in JIS-K5400.

(2) Flexibility evaluation (evaluation of hardness and elastic modulus using a microhardness tester)
Five grams of each resin was dissolved in PGMEA to prepare a resin solution with a solid content of 25%. The solution was applied to a silicon wafer with a spin coater to a thickness of 5.0 μm, and then dried on a hot plate at 110° C. for 90 seconds.
The resulting coating film was tested using an Elionix ENT-1100a (ultra-microindentation hardness tester) at a test load of 2 mN. First, an indenter was pressed into the sample, and the load and indentation depth on the indenter were continuously measured during loading and unloading. A load-indentation depth curve was obtained from the measurement results, and hardness and elastic modulus data were obtained from this curve.

The results are summarized in Table 2 below. Note that the resin in Comparative Example 2 was insoluble and therefore could not be evaluated.

As shown in Table 2 above, the coating films of the novolac type phenolic resins of the present invention (Examples 1 and 2) had a pencil hardness test result of 2H, which indicates that the film surface is harder than the coating film of the cresol resin (Comparative Example 1).
When comparing the hardness and elastic modulus measured by a microhardness meter, the coating films of the novolac phenolic resins of the present invention (Examples 1 and 2) were smaller than those of the cresol resin (Comparative Example 1). It was shown that the coating films of the novolac phenolic resins of the present invention have a hard and strong surface, but are flexible against a small indentation force. In other words, it is believed that the coating films of the novolac phenolic resins of the present invention are hard yet flexible and resistant to cracking.

In the above, the coating film of the novolak type phenolic resin was evaluated, but the same results were obtained for the coating film of the photoresist composition prepared by blending components such as a photosensitizer.

Claims (5)

A novolak-type phenolic resin comprising a first segment (S1) and a second segment (S2) and represented by the following general formula (NP) (excluding (SB) represented by (S2) _n (S1) _m , where all m k's in (S1) are 0).

In the above general formula,
(SB) is a block represented by (S2) _n (S1) _m (n and m are integers of 0 or more, but not 0 at the same time), j is an integer of 1 or more, (SB) may be the same or different, and includes at least (SB) where n is 1 or more and (SB) where m is 1 or more,
(S1) is a divalent group represented by the following formula (1-2):

(S2) is a divalent group represented by the following formula (2):

The terminal groups (TM1) and (TM2) may be the same or different and are any of the following:

However, in the above formulas (1-2), (2) and (3), the bond ** is bonded to the bond *. A novolac phenolic resin, which is a reaction product of phenol, formaldehyde, and a biphenyl aralkyl resin represented by the following formula (1), wherein the biphenyl aralkyl resin is a reaction product of a phenol compound represented by the following formula (4) and a biphenyl compound represented by the following formula (5):


A method for producing a novolak phenolic resin by reacting phenol, formaldehyde, and a biphenyl aralkyl resin represented by the following formula (1), wherein the ratio ((w(rS1))/(w(rS2))) of the mass of the phenol (w(rS2)) to the mass of the biphenyl aralkyl resin (w(rS1)) is 0.5 or more and 9 or less.
The method according to claim 3, wherein the biphenyl aralkyl resin represented by formula (1) is obtained by reacting a phenol compound represented by formula (4) with a biphenyl compound represented by formula (5):

A photoresist composition containing a novolac phenolic resin and a photosensitizer ,
The novolac phenolic resin contains a first segment (S1) and a second segment (S2), and is represented by the following general formula (NP):

In the above general formula,
(SB) is a block represented by (S2) _n (S1) _m (n and m are integers of 0 or more, but not 0 at the same time), j is an integer of 1 or more, (SB) may be the same or different, and includes at least (SB) where n is 1 or more and (SB) where m is 1 or more,
(S1) is a divalent group represented by the following formula (1-2):

(S2) is a divalent group represented by the following formula (2):

The terminal groups (TM1) and (TM2) may be the same or different and are any of the following:

However, in the above formulas (1-2), (2) and (3), the bond ** is bonded to the bond *.