Copolymer of hydroxystyrene-based monomer and (METH)acrylic acid ester-based monomer, and method for producing same

Abstract

[Problem] To provide a method for producing a copolymer of a hydroxystyrene-based monomer and a (meth)acrylic acid ester-based monomer, by which the compositional ratio uniformity and yield of the copolymer can be improved. [Solution] The present invention is a method for producing a copolymer by subjecting at least one type of hydroxystyrene-based monomer and at least one type of (meth)acrylic acid ester-based monomer to a polymerization reaction in the presence of a radical polymerization initiator and a solvent, the method being characterized in that the hydroxystyrene-based monomer is a hydroxystyrene compound in which the number of hydroxyl groups is 1-3 or a derivative in which at least some of the hydroxyl groups in these hydroxystyrene compounds are protected by groups that are dissociated by the action of an acid or a base, and the polymerization reaction is carried out while averaging differences in consumption rates of the monomers under conditions (1) to (4). (1) A plurality of monomer solutions which contain the hydroxystyrene-based monomer and the (meth)acrylic acid ester-based monomer and in which the compositional ratio of these monomers is different are prepared. Among the plurality of monomer solutions, a solution having the lowest compositional ratio of the monomer having the highest reactivity is denoted as a first monomer solution, a solution in which the compositional ratio of the monomer having the highest reactivity is at least 5 mol% higher than in the first monomer solution is denoted as an nth monomer solution (n is an integer of 2 or more), and the amount of monomer contained in the first monomer solution is 5-33 mol% of the total monomer amount. (2) The first monomer solution is initially supplied to a reaction vessel, and the nth monomer solutions are then successively supplied into the reaction vessel. (3) The compositional ratio of the monomer having the highest reactivity in the reaction system at the start point of the polymerization reaction is adjusted so as to be 30-90% of the compositional ratio of the monomer having the highest reactivity among all monomers. (4) At a point where the supply of all the monomer solutions is complete, the conversion rate of the monomer having the lowest reactivity is 75% or more.

Description

Copolymer of hydroxystyrene monomer and (meth)acrylic acid ester monomer and method for producing same

[0001] The present invention relates to a copolymer of a hydroxystyrene-based monomer and a (meth)acrylic acid ester-based monomer, and to a method for producing the copolymer.

[0002] Since their adoption for KrF lithography, chemically amplified resists have continued to be cutting-edge technologies, even as resolution continues to shrink with the development of ArF lithography, EUV (extreme ultraviolet) lithography, and EB (electron beam) lithography. Examples of resist resins for KrF lithography include copolymers of 4-hydroxystyrene and a monomer in which the hydroxy group of 4-hydroxystyrene is protected with an acid-labile protecting group, or copolymers of 4-hydroxystyrene and a (meth)acrylic monomer with an acid-labile group. The latter is expected to be useful for EUV and EB lithography as well. Regarding monomers that provide hydroxystyrene units, isomers such as 2-hydroxystyrene, 3-hydroxystyrene, and 3-4-dihydroxystyrene are also considered promising candidates.

[0003] However, since the target resolution of EUV resists is approximately one order of magnitude finer than that of KrF resists, there is a demand for the reduction of even finer defect sources. To achieve this, it is thought that the use of copolymers with higher uniformity would be effective for advanced resists.

[0004] Methods for producing hydroxystyrene-based polymers for photoresist applications are disclosed in the following patent documents. For example, Patent Document 1 discloses that a dropping polymerization method is effective for improving uniformity in the copolymerization of 4-acetoxystyrene, a precursor of the 4-hydroxystyrene structure, with an alicyclic (meth)acrylate containing an acid-decomposable functional group. By employing the dropping polymerization method described in this document, it is possible to synthesize a highly uniform copolymer in which the composition distribution in the molecular weight direction is controlled to an average of ±10% in GPC fractionation of the copolymer. Patent Documents 2 and 3 disclose that in copolymerization of a monomer in which 4-hydroxystyrene is protected with an acyl group or acetal group and an acid-decomposable alicyclic group-containing (meth)acrylate monomer, only the acid-decomposable alicyclic group-containing (meth)acrylate is introduced into a reaction vessel at the start of polymerization, with the other raw materials added later, followed by a deprotection step, thereby obtaining a 4-hydroxystyrene-based copolymer resin excellent for EB resist applications. Patent Document 4 describes that when a 4-hydroxystyrene polymer is subjected to acetalization protection by reacting it with a vinyl ether, the protected resin is fractionated by silica gel column chromatography, and a resist is prepared using only the fraction with a protection rate close to the average value, an effect of reducing surface roughness in EUV lithography is observed. Patent Document 5 describes that when a 4-hydroxystyrene copolymer is produced by performing both precipitation purification using a nonpolar solvent and precipitation purification using a polar solvent, a polymer with improved compositional uniformity can be obtained, in which the composition ratio of low molecular weight components, which accounts for 5% of the total, is close to the overall average value.

[0005] In the polymerization reaction of (meth)acrylic copolymers for ArF resists, primary or secondary ester monomers with polar groups, such as lactone, hydroxyadamantane, and sultone, tend to be highly reactive, while tertiary ester monomers with acid-labile groups tend to be less reactive. Therefore, copolymerization of these two monomers can result in nonuniform copolymer composition in the resulting polymer, which can become insoluble during development and cause defects. Patent Document 6 discloses a method for producing copolymers for photoresists in which the monomer composition ratio of unreacted monomers fluctuates within a range of ±15% in the polymerization reaction system from the start of the polymerization reaction to the end of the monomer solution supply. Patent Document 7 proposes preparing two or more types of monomer dropping solutions to be supplied to a reactor and varying the composition of the dropping solutions between the early and late stages of polymerization to achieve uniform copolymer composition in the resulting polymer.

[0006] Generally, when copolymerizing styrene-based monomers and (meth)acrylic acid ester-based monomers using the most common method of polymerization under solution conditions with a radical polymerization initiator, an ideal copolymerization composition specific to the monomer combination exists, and it is known that the monomer consumption rate is nearly identical around this ideal copolymerization composition, resulting in relatively easy and uniform polymerization. However, when producing copolymers with copolymerization ratios different from the ideal composition, significant differences in the monomer consumption rate often occur. In such cases, even when using a dropping polymerization method that easily achieves relatively uniform polymerization, considerable deviations in the composition of the copolymer produced in the early, middle, and late stages of polymerization occur.

[0007] Furthermore, in copolymerization of styrene-based monomers and (meth)acrylic ester-based monomers, the lower the molar ratio of the monomers present in the reaction system, the higher the reactivity tends to be. In this case, the monomers preferentially consumed in the early stages of polymerization remain in the reaction system in small amounts in the later stages of polymerization, resulting in the formation of copolymers with significantly lower compositions of highly reactive monomers, especially during the aging period after the monomer supply has ended. Terminating the reaction immediately after the monomer supply is completed can prevent the formation of copolymers with uneven compositions, but this significantly reduces the copolymer yield. Furthermore, because the polymers formed during the aging period have relatively low molecular weights, efforts have been focused on optimizing the purification process to remove them. However, severe purification is undesirable because it still reduces the copolymer yield.

[0008] Japanese Patent Application Laid-Open No. 2001-151823 Japanese Patent Application Laid-Open No. 2012-219162 Japanese Patent Application Laid-Open No. 2012-219164 Japanese Patent Application Laid-Open No. 2007-52193 Japanese Patent Application Laid-Open No. 2009-102659 Japanese Patent Application Laid-Open No. 2010-202699 International Publication WO2012 / 053434

[0009] An object of the present invention is to provide a method for producing a copolymer of a hydroxystyrene-based monomer and a (meth)acrylic acid ester-based monomer, which can improve the uniformity of the composition ratio of the copolymer and the yield of the copolymer. Steps to solve the problem

[0010] The present inventors have found that in a general solution radical polymerization method, particularly a dropping polymerization method which can produce a copolymer with a relatively high uniformity in composition ratio, the uniformity in composition ratio and yield of a copolymer of a hydroxystyrene-based monomer and a (meth)acrylic acid ester-based monomer can be improved by carrying out a polymerization reaction while averaging the difference in consumption rate of each monomer under specific conditions.

[0011] That is, the present invention provides the following inventions: [1] A method for producing a copolymer, comprising polymerizing at least one hydroxystyrene-based monomer and at least one (meth)acrylic acid ester-based monomer in the presence of a radical polymerization initiator and a solvent, wherein the hydroxystyrene-based monomer is a hydroxystyrene having one to three hydroxyl groups or a derivative of such a hydroxystyrene in which at least some of the hydroxyl groups are protected with a group that dissociates under the action of an acid or a base, and the polymerization reaction is carried out while averaging differences in the consumption rates of the individual monomers under the following conditions (1) to (4): (1) preparing a plurality of monomer solutions containing the hydroxystyrene-based monomer and the (meth)acrylic acid ester-based monomer and having different composition ratios thereof, wherein, among the plurality of monomer solutions, one having the lowest composition ratio of the most reactive monomer is designated as a first monomer solution, and one having a composition ratio of the most reactive monomer that is 5 mol % or more higher than that of the first monomer solution is designated as an nth monomer solution (n is an integer of 2 or more), and the amount of monomer contained in the first monomer solution is 5 mol % or more and 33 mol % or less with respect to the amount of all monomers; (2) supplying the first monomer solution to a reaction vessel first, and then sequentially supplying the nth monomer solutions to the reaction vessel; (3) adjusting the composition ratio of the most reactive monomer in the reaction system at the start of the polymerization reaction to be 30% to 90% with respect to the composition ratio of the most reactive monomer in all monomers; (4) When the supply of all the monomer solutions is completed, the conversion rate of the least reactive monomer is 75% or more. [2] A method for producing a copolymer according to [1], wherein the composition ratio of each monomer consumed in the polymerization reaction within one hour from the start of the polymerization reaction is within ±5 mol% of the composition ratio of each monomer in all the monomers. [3] A method for producing a copolymer according to [1] or [2], wherein the composition ratio of each monomer in the reaction system at the start of the polymerization reaction is adjusted to be within ±3 mol% of the test composition ratio calculated in the following preliminary test. (Procedure of preliminary test) Monomers having the monomer composition of the target copolymer, a radical polymerization initiator, and a solvent are mixed to prepare a dropping solution.A solvent is charged into a reaction vessel, heated, and once the predetermined reaction temperature is reached, the solution is added dropwise at a constant rate over at least 3 hours. After completion of the addition, the mixture is allowed to mature for at least 2 hours. Sampling is performed during the polymerization reaction to measure the unreacted monomer composition ratio in the polymerization reaction system, and a test composition is determined. Test composition = the monomer composition ratio when the unreacted monomer composition ratio is steady between 60% and 100% (at the end of addition). [4] A method for producing a copolymer according to any one of [1] to [3], wherein the composition ratio of each monomer consumed in the polymerization from the end of addition of all monomer solutions to the termination of polymerization is ±3 mol % of the total monomer composition ratio. [5] A method for producing a copolymer according to any one of [1] to [4], wherein the composition ratio of the highly reactive monomer in the composition ratio of each monomer consumed in the polymerization from the end of addition of all monomer solutions to the termination of polymerization is 80% or more of the composition ratio of the highly reactive monomer in the total monomer composition. [6] The method for producing a copolymer according to any one of [1] to [5], wherein the feed rate of the monomer solution is reduced from any time point between when the total monomer feed amount is 60 mol% and 85 mol% until the completion of dropwise addition of the monomer solution. [7] The method for producing a copolymer according to any one of [1] to [6], wherein, when polymerization is carried out using the same procedure as in the preliminary test, the monomer composition ratio consumed at any time during the polymerization reaction deviates from the monomer composition ratio of all monomers by ±10% or more. [8] The method for producing a copolymer according to any one of [1] to [7], wherein, when comparing the molar ratios of the styrene-based monomer and the (meth)acrylic acid ester-based monomer in the target copolymer, the smaller molar ratio is 10 mol% or more and 40 mol% or less. [9] The method for producing a copolymer according to any one of [1] to [8], wherein the conversion rate of each monomer after the start of the polymerization reaction is within ±20% of the average conversion rate of each monomer.

[10] The method for producing a copolymer according to any one of [1] to [9], wherein the hydroxystyrene-based monomer is at least one selected from the group consisting of 4-hydroxystyrene and 4-acetoxystyrene.

[11] A copolymer having structural units derived from at least one type of hydroxystyrene-based monomer and structural units derived from at least one type of (meth)acrylic acid ester-based monomer, wherein the hydroxystyrene-based monomer is a hydroxystyrene having 1 to 3 hydroxyl groups or a derivative of the hydroxystyrene in which at least a portion of the hydroxyl groups is protected with a group that dissociates under the action of an acid or a base, and the composition ratio of the structural units derived from the hydroxystyrene-based monomer to the structural units derived from the (meth)acrylic acid ester-based monomer in the copolymer is 10:90 to 45:55 or 55:45 to 90:10 in molar ratio, The copolymer according to

[11] , wherein, when the copolymer is subjected to gel permeation chromatography and the copolymer fraction is fractionated into three fractions of high, medium, and low molecular weight so that the weights of the copolymer contained therein are equal, the monomer composition ratio of the copolymer contained in the high molecular weight fraction is within a range of ±1% compared to the monomer composition ratio of the copolymer contained in the medium molecular weight fraction, and the monomer composition ratio of the copolymer contained in the low molecular weight fraction is within a range of ±2% compared to the monomer composition ratio of the copolymer contained in the medium molecular weight fraction.

[12] The copolymer according to

[11] , wherein the hydroxystyrene-based monomer is at least one selected from the group consisting of 4-hydroxystyrene and 4-acetoxystyrene.

[0012] According to the present invention, there is provided a method for producing a copolymer of a hydroxystyrene-based monomer and a (meth)acrylic acid ester-based monomer, which can improve the uniformity of the composition ratio of the copolymer and the yield of the copolymer. Furthermore, the production method of the present invention can provide the copolymer suitable for use in cutting-edge semiconductor resists.

[0013] [Method for Producing Copolymer] The method for producing the copolymer of the present invention uses at least one hydroxystyrene-based monomer and at least one (meth)acrylic acid ester-based monomer.

[0014] (Hydroxystyrene-based Monomer) The hydroxystyrene-based monomer used in the method for producing the copolymer of the present invention is a hydroxystyrene having 1 to 3 hydroxyl groups, or a derivative of such a hydroxystyrene in which at least some of the hydroxyl groups are protected with a group that dissociates under the action of an acid or a base. Specific examples of the hydroxystyrene-based monomer include 4-hydroxystyrene, 3-hydroxystyrene, 2-hydroxystyrene, 3,4-dihydroxystyrene, and trihydroxystyrene.

[0015] Furthermore, an acyl group is preferred as the protecting group for hydroxystyrene derivatives. For example, 4-acetoxystyrene is obtained by protecting the hydroxyl group of 4-hydroxystyrene with an acyl group. High-purity 4-acetoxystyrene suitable for photoresist applications is generally available on an industrial scale. Its use involves radical polymerization of an acyl-protected derivative such as 4-acetoxystyrene with a (meth)acrylic acid ester to produce a copolymer. The copolymer is then deprotected using a base or acid catalyst to obtain the desired copolymer of hydroxystyrene and a (meth)acrylic acid ester. In recent years, the isomers 2-acetoxystyrene and 3-acetoxystyrene have also become commercially available. Using these as raw materials, copolymers with 2-hydroxystyrene or 3-hydroxystyrene structures can be similarly synthesized.

[0016] Acetal groups can also be used as other protecting groups for hydroxystyrene derivatives. For example, 4-ethoxyethoxystyrene can be obtained by protecting the hydroxyl group of 4-hydroxystyrene with an acetal group. When an acetal group is used, the method of use is similar: a derivative protected with an acetal group, such as 4-ethoxyethoxystyrene, is copolymerized with a (meth)acrylic acid ester by radical polymerization. The copolymer is then deprotected with an acid catalyst to obtain the desired copolymer of hydroxystyrene and a (meth)acrylic acid ester. The advantage of the acetal type is that the deprotection reaction using an acid catalyst can be carried out under mild conditions, thereby suppressing side reactions during the deprotection step.

[0017] Further, examples of other protecting groups for hydroxystyrene derivatives include t-butyl and t-butoxycarbonyl groups. These protecting groups are acid-decomposable and require somewhat harsh treatment conditions for deprotection, but the aforementioned synthesis scheme can be applied depending on the type of (meth)acrylic acid ester to be copolymerized and the structure of the copolymer.

[0018] ((Meth)acrylic acid ester monomer) The (meth)acrylic acid ester monomer used in the method for producing the copolymer of the present invention can be a known compound that has been used conventionally for photoresists. Note that (meth)acrylic acid ester means acrylic acid ester and methacrylic acid ester. In particular, in the case of a chemically amplified resist, it is preferable to use a compound in which the carboxyl group of acrylic acid or methacrylic acid is protected with an acid-dissociable group, and the acid-dissociable group is preferably a tertiary hydrocarbon group or a group that forms an acetal structure. Specifically, tert-butyl group, tert-amyl group, 1-methyl-1-cyclopentyl group, 1-ethyl-1-cyclopentyl group, 1-methyl-1-cyclohexyl group, 1-ethyl-1-cyclohexyl group, 2-methyl-2-adamantyl group, 2-ethyl-2-adamantyl group, 2-propyl-2-adamantyl group, 2-(1-adamantyl)-2-propyl group, 8-methyl-8-tricyclo[5.2.1.02,6]decanyl group, 8-ethyl-8-tricyclo[5.2.1.02,6]decanyl group, 8-methyl-8-tetracyclo[4.4.0.12,5.17,10]dodecanyl group, 8-ethyl-8-tetracyclo[4.4.0.12,5.17,10]dodecanyl group saturated hydrocarbon groups such as 1-methoxyethyl group, 1-ethoxyethyl group, 1-iso-propoxyethyl group, 1-n-butoxyethyl group, 1-tert-butoxyethyl group, 1-cyclopentyloxyethyl group, 1-cyclohexyloxyethyl group, 1-tricyclo[5.2.1.02,6]decanyloxyethyl group, methoxymethyl group, ethoxymethyl group, iso-propoxymethyl group, n-butoxymethyl group, tert-butoxymethyl group, cyclopentyloxymethyl group, cyclohexyloxymethyl group, tricyclo[5.2.1.02,6]decanyloxymethyl group, 2-tetrahydrofuranyl group, 2-tetrahydropyranyl group, and other oxygen-containing hydrocarbon groups.

[0019] In addition, (meth)acrylic acid esters having a structure containing a polar group are also preferred in order to improve adhesion to semiconductor substrates and the like, and to adjust solubility in lithography solvents and alkaline developers. Examples of polar groups include groups having a lactone structure, alcoholic hydroxyl groups, groups having an ether structure, and nitrile groups. Among these, groups having a lactone structure and alcoholic hydroxyl groups are preferred. Specific examples of groups having a lactone structure include substituents containing a lactone structure such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, 1,3-cyclohexanecarbolactone, 2,6-norbornanecarbolactone, 4-oxatricyclo[5.2.1.02,6]decan-3-one, and mevalonic acid δ-lactone. Specific examples of alcoholic hydroxyl groups include hydroxyalkyl groups such as hydroxymethyl, hydroxyethyl, hydroxypropyl, 3-hydroxy-1-adamantyl, and 3,5-dihydroxy-1-adamantyl.

[0020] Furthermore, if necessary, in order to adjust the solubility in lithography solvents and alkaline developers, compounds in which the carboxyl group of (meth)acrylic acid is protected with a group that suppresses dissolution in alkaline developers and does not dissociate under the action of acid can also be used. Specific examples include methyl, ethyl, cyclopentyl, cyclohexyl, isobornyl, 1-adamantyl, 2-adamantyl, tricyclo[5.2.1.02,6]decanyl, tetracyclo[4.4.0.12,5.17,10]dodecyl, benzyl, and 9-anthracenemethyl groups.

[0021] (Polymerization Step) The polymerization step involves carrying out a polymerization reaction between at least one hydroxystyrene-based monomer and at least one (meth)acrylic acid ester-based monomer in the presence of a radical polymerization initiator and a solvent, and is characterized in that the polymerization reaction is carried out while averaging the difference in consumption rate of each monomer under the following conditions (1) to (4). This makes it possible to improve the uniformity of the composition ratio and yield of the copolymer of the hydroxystyrene-based monomer and the (meth)acrylic acid ester-based monomer.

[0022] Condition (1): Preparing multiple monomer solutions containing a hydroxystyrene-based monomer and a (meth)acrylic acid ester-based monomer, each having a different composition ratio. Among the multiple monomer solutions, the one with the lowest composition ratio of the most reactive monomer is designated the first monomer solution, and the one with a composition ratio of the most reactive monomer that is at least 5 mol% higher than that of the first monomer solution is designated the nth monomer solution (n is an integer of 2 or greater). For example, when multiple monomer solutions, first through fourth, are prepared (i.e., when n is 4), the composition ratios of the highly reactive monomer contained in the second, third, and fourth monomer solutions are at least 5 mol% higher than that of the first monomer solution, preferably at least 5 mol% and at most 20 mol%, more preferably at least 5 mol% and at most 15 mol% higher. Furthermore, n is preferably 2, 3, or 4, more preferably 2 or 3, and even more preferably 2.

[0023] In the copolymerization of a styrene-based monomer and a (meth)acrylate-based monomer, the polymerization rate of the monomer with a lower molar ratio present in the reaction system tends to be higher in many cases. Therefore, in the present invention, the composition ratio of the most reactive monomer in the first monomer solution supplied at the initial stage of polymerization is made lower than the target composition (the composition ratio of each monomer in all monomers), and the composition ratio of the most reactive monomer in the second monomer solution is made higher than the target composition by 5 mol % or more. From the middle stage of the polymerization reaction to the end of the dropwise addition, the composition ratio of the highly reactive monomer in the polymerization reaction system increases, and the composition ratio of the low reactive monomer decreases, so that it is presumed that the polymerization rate and conversion rate of the monomers increase.

[0024] Furthermore, the amount of the monomer contained in the first monomer solution is 5 mol% to 33 mol% relative to the total amount of monomers, preferably 8 mol% to 30 mol%, and more preferably 10 mol% to 25 mol%. By adjusting the amount of monomer contained in the first monomer solution within this range, the composition ratio of the monomers in the monomer solution is changed at least once during the period in which the amount of monomer solution supplied to the reaction vessel at the initial stage of polymerization is 5 mol% to 33 mol%. In order to average the consumption rates of each monomer (steady state) from the initial stage of polymerization, a first monomer solution containing a low composition ratio of the most reactive monomer is first supplied to the reaction vessel, and then the supply of a second monomer solution containing a composition ratio of the most reactive monomer that is 5 mol% or more higher than that of the first monomer solution is switched to. This switching averages the consumption rates of the most reactive monomer and the least reactive monomer, allowing the monomer composition ratio of the produced copolymer to approach the composition ratio of each monomer in the total monomers.

[0025] Condition (2): The first monomer solution is supplied to the reaction vessel first, and then the nth monomer solution is sequentially supplied to the reaction vessel. The method of supplying the first monomer solution to the reaction vessel is not particularly limited. The entire amount of the first monomer solution may be initially charged into the reaction vessel all at once, or a portion of the first monomer solution may be charged and the remainder may be added dropwise, or the entire amount of the first monomer solution may be added dropwise. A solvent may also be charged into the reaction vessel in advance. The nth monomer solution is preferably supplied dropwise to the reaction vessel. After the supply of the first monomer solution is completed, the second monomer solution, the third monomer solution, and the fourth monomer solution are sequentially added dropwise.

[0026] Condition (3): The composition ratio of the most reactive monomer in the reaction system at the start of the polymerization reaction is adjusted to be 30% to 90% of the composition ratio of the most reactive monomer in all monomers. The composition ratio of the most reactive monomer in the reaction system at the start of the polymerization reaction is preferably 40% to 85%, more preferably 50% to 80%, of the composition ratio of the most reactive monomer in all monomers. By adjusting the composition ratio of the most reactive monomer in the reaction system at the start of the polymerization reaction to fall within the above numerical range, it is possible to suppress the production of copolymers whose composition ratio deviates from the target, and improve the uniformity of the composition ratio of the copolymer.

[0027] Furthermore, it is preferable to adjust the composition ratio of each monomer consumed in the polymerization reaction within 1 hour from the start of the polymerization reaction to be preferably within ±5 mol %, more preferably within ±4 mol %, of the composition ratio of each monomer in the total monomers. By averaging the consumption rates of each monomer in the early stages of polymerization, it is possible to improve the uniformity of the composition ratio of the copolymer, and thereby improve the yield.

[0028] To achieve this, it is effective to adjust the composition ratio of each monomer in the reaction system at the start of the polymerization reaction so that it is within ±3 mol% of the test composition ratio calculated in the following preliminary test. (Preliminary Test Procedure) A dripping solution is prepared by mixing monomers having the monomer composition of the target copolymer, a radical polymerization initiator, and a solvent. A reaction vessel is charged with the solvent and heated until the predetermined reaction temperature is reached. The dripping solution is dripped at a constant rate over a period of at least three hours, and then the mixture is allowed to age for at least two hours after the dripping is complete. Sampling is performed during the polymerization reaction to measure the unreacted monomer composition ratio in the polymerization reaction system, and the test composition is determined. Test composition = The monomer composition ratio when the unreacted monomer composition ratio is at a steady state between 60% and 100% of the monomer supply (at the end of dripping). Note that "steady state" refers to a state in which the unreacted monomer composition ratio is constant or nearly constant.

[0029] Condition (4): When the supply of all the monomer solutions is completed, the conversion rate of the least reactive monomer is 75% or more. When the supply of all the monomer solutions is completed, the conversion rate of the least reactive monomer is preferably 77% or more. By adjusting the conversion rate of the least reactive monomer to the above value or higher, the consumption rate of each monomer can be averaged, a copolymer with a highly uniform composition ratio can be obtained, and the yield can be improved. In addition, it becomes easier to obtain a copolymer adjusted to the target weight average molecular weight and molecular weight distribution.

[0030] Furthermore, when the supply of the entire monomer solution is completed, the conversion rate of the most reactive monomer is preferably 80% or more, more preferably 85% or more.

[0031] Furthermore, it is preferable that the composition ratio of each monomer consumed in the polymerization from the end of the dropwise addition of all the monomer solutions to the termination of the polymerization is within ±3 mol % of the total monomer composition ratio. By satisfying this condition, the consumption rate of each monomer can be averaged, a copolymer with a highly uniform composition ratio can be obtained, and the yield can be improved.

[0032] Furthermore, it is preferable that the composition ratio of the highly reactive monomer in the composition ratio of each monomer consumed in the polymerization from the end of dropwise addition of all the monomer solutions to the termination of the polymerization is 80% or more of the composition ratio of the highly reactive monomer in all the monomers. By satisfying this condition, the consumption of the monomers after the termination of the polymerization can be reduced, and the production of a copolymer with an unbalanced composition ratio can be suppressed.

[0033] It is also preferable to reduce the feed rate of the monomer solution from any point between when the total monomer feed amount is 60 mol % and 85 mol % until the dropwise addition of the monomer solution is completed. By extending the dropwise addition time, the conversion rate at the end of the monomer feed can be increased. Furthermore, by extending the time until the dropwise addition of the total monomer solution is completed, the steady state of the polymerization reaction can be maintained for a long time, and the conversion rate of the monomer at the end of the dropwise addition of the total monomer solution can be increased. As a result, a copolymer with a highly uniform composition ratio can be obtained, and the yield can be improved.

[0034] Furthermore, when polymerization is carried out in the same manner as in the preliminary test, it is preferable to apply this method to the production of a copolymer in which the composition ratio of the monomers consumed at any time during the polymerization reaction deviates from the composition ratio of all the monomers by ±10% or more, because the effects of the present invention are more pronounced in the case of polymerization with such a monomer composition ratio.

[0035] Furthermore, when comparing the molar ratios of the styrene-based monomer and the (meth)acrylic acid ester-based monomer in the target copolymer, it is preferable to apply the present invention to the production of a copolymer in which the smaller molar ratio is 10 mol % or more and 40 mol % or less, because the effects of the present invention are more effectively exhibited in the case of polymerization with such a monomer composition ratio.

[0036] Furthermore, after the start of the polymerization reaction, it is preferable that the conversion rate of each monomer is within ±20% of the average value of the conversion rates of each monomer. By satisfying this condition, it is possible to reduce the consumption of monomers after the polymerization is stopped and to suppress the production of a copolymer with an unbalanced composition ratio.

[0037] Other polymerization conditions can be determined by reference to known methods for producing resist polymers by radical polymerization.

[0038] The solvent used in the method for producing the copolymer of the present invention is not particularly limited as long as it can stably dissolve the monomer, polymerization initiator, chain transfer agent, and polymerization reaction product. Specific examples of the polymerization solvent include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl isoamyl ketone, methyl amyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, and isopropanol; ether alcohols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether; esters such as methyl acetate, ethyl acetate, isopropyl acetate, propyl acetate, butyl acetate, methyl propionate, methyl lactate, and ethyl lactate; ether esters such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate; ethers such as tetrahydrofuran, 1,4-dioxane, and ethylene glycol dimethyl ether; aromatic hydrocarbons such as toluene and xylene; N,N-dimethylformamide, and acetonitrile. The amount of the polymerization solvent used is not particularly limited, but can be appropriately selected depending on the viscosity of the polymerization reaction system, the conversion rate of the monomers, and the like.

[0039] The radical polymerization initiator used in the method for producing the copolymer of the present invention may be a conventionally known initiator. Examples of the radical polymerization initiator include azo-based polymerization initiators and peroxide-based polymerization initiators. Specific examples of azo-based polymerization initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), dimethyl 2,2'-azobis(2-methylpropionate), 1,1'-azobis(cyclohexane-1-carbonitrile), and 4,4'-azobis(4-cyanovaleric acid). Azo-based polymerization initiators are preferred because of their excellent handling safety. Specific examples of peroxide-based polymerization initiators include decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, bis(3,5,5-trimethylhexanoyl) peroxide, succinic acid peroxide, tert-butylperoxy-2-ethylhexanoate, tert-butyl peroxypivalate, and 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate. These polymerization initiators can be used alone or in combination. The amount of polymerization initiator used can be appropriately selected depending on the target molecular weight, the types of monomers, polymerization initiators, chain transfer agents, solvents, etc., the structural unit composition, the polymerization temperature, the dropping rate, and the like.

[0040] The polymerization initiator may be mixed with any of the monomer solutions and then supplied to the reaction vessel, or may be supplied separately from the monomer solutions. In the initial stage, the reaction vessel may be pre-charged with a solution containing the polymerization initiator, or a solvent may be pre-charged into the reaction vessel, the solvent may be heated, and then the polymerization initiator may be supplied. The polymerization initiator may be supplied before, simultaneously with, or after the supply of the monomer solution. However, it is preferable to start the supply of the polymerization initiator before the supply amount of the monomer solution reaches 33 mol% of the total amount of monomers to initiate the polymerization reaction. In the present invention, by starting the polymerization reaction before the supply amount of the monomer solution reaches 33 mol% of the total amount of monomers, a steady state can be maintained for a long time. As a result, a copolymer with a highly uniform composition ratio can be obtained, and the yield can be improved.

[0041] The dropping time of the monomer solution is not particularly limited, but is typically selected from the range of 1 to 12 hours, preferably 2 to 10 hours, and more preferably 4 to 8 hours, from the viewpoint of maintaining the steady state of the polymerization reaction for a long period of time and maintaining production efficiency. Furthermore, it is preferable to reduce the dropping rate of the monomer during the dropping of the monomer solution of the second monomer or subsequent monomers. Specifically, it is preferable to reduce the dropping rate of the monomer from the time when the monomer supply amount reaches any point between 60 mol% and 85 mol% of the total monomer amount until the dropping of the monomer solution is completed. By reducing the dropping rate, the polymerization time during the dropping is extended, thereby increasing the conversion of each monomer. This allows the conversion of the least reactive monomer at the end of the dropping of all monomers to be 75% or more, thereby improving the yield of copolymers with good compositional uniformity.

[0042] In the dropping polymerization method, after the supply of the monomer solution is completed, it is preferable to carry out aging by maintaining the temperature for a certain period of time or further increasing the temperature, etc., to react the remaining unreacted monomers. The aging time is not particularly limited, but can be appropriately selected from the viewpoint of maintaining the uniformity of the composition ratio of the copolymer and the production efficiency.

[0043] The polymerization temperature can be appropriately selected depending on the boiling points of the solvent, monomer, chain transfer agent, etc., the half-life temperature of the polymerization initiator, etc. From the viewpoints of production efficiency and the stability of the monomer and copolymer, the polymerization temperature is preferably 40 to 160°C, and particularly preferably 60 to 120°C.

[0044] The polymerization pressure is not particularly limited and may be normal pressure, elevated pressure, or reduced pressure, but is usually normal pressure. In the case of an azo-based polymerization initiator, nitrogen gas is generated, so that the polymerization system is preferably an open system and carried out at near atmospheric pressure in order to suppress fluctuations in the polymerization pressure.

[0045] (Other Steps) The method for producing the copolymer of the present invention may include steps other than the polymerization step described above. These other steps will be specifically described below.

[0046] (Deprotection Step) In the method for producing the copolymer of the present invention, when a derivative in which at least a portion of the hydroxyl groups is protected is used as the hydroxystyrene-based monomer, a deprotection reaction is carried out after polymerization to produce hydroxystyrene units. The deprotection reaction is carried out using an acid or base catalyst depending on the type of protecting group. The deprotection reaction may be carried out by adding an acid or base to the polymerization reaction solution, or may be carried out after purifying the polymerization reaction solution by precipitation purification or the like, which will be described later.

[0047] When a deprotection reaction is carried out by adding an acid or a base to a polymerization reaction solution, a large amount of unreacted monomer usually remains, raising concerns about side reactions caused by the monomer. In the present invention, the amount of unreacted monomer remaining in the polymerization reaction solution is reduced as much as possible, thereby making it possible to suppress side reactions during the deprotection reaction.

[0048] (Purification Step) The copolymer solution obtained in the polymerization step of the present invention is subjected to a purification step following polymerization or deprotection. The polymer after the polymerization reaction contains low-molecular-weight impurities such as the polymerization solvent, unreacted monomers, oligomers, polymerization initiators, chain transfer agents, and their reaction by-products, as well as the deprotection catalyst and by-products of the deprotection reaction if the deprotection step is performed prior to purification. Therefore, it is preferable to remove these impurities through a purification step. Specifically, this is carried out by precipitation purification, in which the crude copolymer solution is diluted, if necessary, with a good solvent, and then brought into contact with a poor solvent to precipitate the copolymer, and the impurities are extracted and separated into the poor solvent phase, or by extracting the impurities into the poor solvent phase in a liquid-liquid two-phase system. These operations may be repeated in the same manner, or different operations may be combined.

[0049] Examples of poor solvents used in precipitation purification include water, compounds having a hydroxyl group such as methanol, ethanol, isopropanol, ethylene glycol, and ethyl lactate; linear, branched, or cyclic saturated hydrocarbons such as n-hexane, isohexane, n-heptane, cyclopentane, and methylcyclohexane; and aromatic hydrocarbons such as toluene and xylene. These solvents can be used alone or in combination of two or more. Examples of good solvents include the polymerization solvents described above and the resist solvents described below.

[0050] (Metal Impurity / Foreign Matter Removal Step) A step for removing trace amounts of metal impurities and foreign matter contained in the copolymer may be carried out. This may be achieved by washing a solution of the copolymer in an organic solvent with pure water, by contacting the solution with an ion exchange resin, or by passing the solution through a filter having ion exchange capacity. These methods may also be combined. The ion exchange resin and the filter having ion exchange capacity may be commercially available, and are known to be used for removing metals from resist polymers.

[0051] (Solvent Replacement / Vacuum Concentration Step) The solvent in the copolymer solution is preferably replaced with a solvent used in the resist composition. Solvent replacement can be performed by heating the polymer solution under reduced pressure to distill off low-boiling substances such as the solvent used in purification, and then supplying a resist solvent to the solution while further distilling off the initial solvent and the supplied solvent together. By removing low-boiling impurities such as the solvent used in purification, the copolymer can be completed into a solution suitable for preparing a resist composition.

[0052] The substitution solvent is not particularly limited as long as it dissolves the copolymer, but for resist applications, known solvents typically used in resist compositions can be used. Specific examples include solvents such as propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol n-butyl ether, dipropylene glycol n-propyl ether, dipropylene glycol n-butyl ether, ethyl lactate, methyl amyl ketone, γ-butyrolactone, cyclohexanone, and 4-methyl-2-pentanol.

[0053] [Copolymer] (Compositional Ratio) The copolymer of the present invention has structural units derived from at least one hydroxystyrene-based monomer and structural units derived from at least one (meth)acrylic acid ester-based monomer. In the composition of the copolymer, the compositional ratio of the structural units derived from the hydroxystyrene-based monomer to the structural units derived from the (meth)acrylic acid ester-based monomer is, on a molar basis, 10:90 to 45:55 or 55:45 to 90:10, preferably 15:85 to 45:55 or 55:45 to 85:15. The compositional ratio of the structural units in the polymer is analyzed by １３ Measurement can be performed by C-NMR under the measurement conditions described below.

[0054] (Weight-Average Molecular Weight / Molecular Weight Distribution) The weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the copolymer of the present invention are not particularly limited and can be appropriately set depending on the application. For example, from the viewpoint of exhibiting high molecular weight, the weight-average molecular weight (Mw) of the copolymer is preferably 1,000 to 50,000, more preferably 2,000 to 30,000, even more preferably 3,000 to 20,000, and even more preferably 4,000 to 10,000. Furthermore, from the viewpoint of uniform copolymer properties, the molecular weight distribution (Mw / Mn) of the copolymer is preferably 1.1 to 2.0, more preferably 1.2 to 1.80, and even more preferably 1.3 to 1.7. In the present invention, the weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the copolymer are measured by GPC (gel permeation chromatography) and can be measured under the measurement conditions described below.

[0055] (Method for Evaluating the Uniformity of Copolymer) The method for evaluating the uniformity of the copolymer of the present invention is to subject the copolymer to gel permeation chromatography (GPC), fractionate the copolymer fraction into three fractions of high, medium, and low molecular weight so that the weights of the copolymers contained therein are equal, and evaluate the homogeneity of the copolymers contained in each fraction. １３Examples of methods for determining the monomer composition ratio (mol %) include C-NMR. The copolymer fraction described above does not include low-molecular-weight fractions such as solvents and residual monomers. The closer the monomer composition ratios of the individual fractions, the higher the homogeneity of the copolymer can be evaluated. According to the present invention, it is possible to obtain copolymers in which the monomer composition ratio of the copolymer contained in the high-molecular-weight fraction is within ±1% of the monomer composition ratio of the copolymer contained in the medium-molecular-weight fraction, and the monomer composition ratio of the copolymer contained in the low-molecular-weight fraction is within ±2% of the monomer composition ratio of the copolymer contained in the medium-molecular-weight fraction.

[0056] The abbreviations for the compounds used in the following experiments are as follows: PACS: p-acetoxystyrene 4-HS: 4-hydroxystyrene MCPMA: 1-methyl-1-cyclopentyl methacrylate ECPMA: 1-ethyl-1-cyclopentyl methacrylate MEK: methyl ethyl ketone MTBE: methyl tertiary butyl ether PGME: propylene glycol monomethyl ether

[0057] [Measurement Method] [Weight-Average Molecular Weight and Molecular Weight Distribution of Copolymer] The weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the copolymer were measured by GPC (gel permeation chromatography) using polystyrene as a standard. Measuring device: HLC-8220GPC manufactured by Tosoh Corporation Detector: Differential refractive index (RI) detector Column: Shodex GPC KF804 x 3 (manufactured by Showa Denko KK) Eluent: Tetrahydrofuran Flow rate: 1.0 mL / min Temperature: 40°C Calibration curve: Prepared using a polystyrene standard sample (manufactured by Tosoh Corporation)

[0058] [Monomer Concentration] The monomer concentration was measured by GC (gas chromatography). Measuring device: GC-2010plus manufactured by Shimadzu Corporation. Carrier gas: N ２ Detector: FID Column: Aglent J&W DB-5 (15 m)

[0059] [Fraction of copolymer] The copolymer was subjected to GPC, and the copolymer fraction was fractionated into three fractions of high / middle / low molecular weight so that the weight of the copolymer contained was equal. Measuring device: LC-Forte / R manufactured by YMC Corporation Detector: Differential refractive index (RI) detector Column: YMC-GPCT60000 manufactured by YMC Corporation Eluent: MEK

[0060] [Composition ratio of monomers in copolymer] The composition ratio of monomers in copolymer is １３ Analysis was performed by C-NMR. Measurement device: AV400 manufactured by Bruker. Deuterated solvent: acetone-d6. Relaxation reagent: chromium (III) acetylacetonate. Measurement temperature: 40°C.

[0061] Reference Example 1 (Synthesis of 4-HS / MEK Solution) 7.9 kg of PACS and 23.4 kg of methanol were placed in a 100 L glass-lined reaction vessel equipped with a thermometer, a condenser, and a stirrer, and the vessel was sealed with nitrogen. The contents were cooled with stirring until the liquid temperature reached -5°C. The reaction vessel was then depressurized and then repressurized with nitrogen, a process repeated three times. In a separate vessel from the reaction vessel, an equimolar amount of 3 M aqueous sodium hydroxide solution relative to PACS was prepared, and this aqueous solution was bubbled with nitrogen for one hour. The nitrogen-bubbled aqueous sodium hydroxide solution was added dropwise to the reaction vessel over 100 minutes, and stirring was continued for an additional 30 minutes after the dropwise addition to carry out the reaction of deprotecting PACS and converting it to 4-HS.

[0062] Next, 0.97 molar equivalents of 6M hydrochloric acid relative to the PACS used was added dropwise to the reaction vessel over 60 minutes. After the addition, stirring was continued for an additional 30 minutes to neutralize the reaction solution. The 6M hydrochloric acid was added dropwise after previously bubbling with nitrogen for 1 hour. Next, the temperature of the neutralized reaction solution was raised to approximately 10-20°C, and MTBE was added in an amount three times the mass of PACS. The solution was stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discharged. Next, ion-exchanged water in an amount three times the mass of PACS was added, stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discharged. Next, MTBE in an amount two times the mass of PACS and ion-exchanged water in an amount three times the mass of PACS were added, stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discharged. Finally, ion-exchanged water in an amount three times the mass of PACS was added, stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discharged. This procedure was repeated twice.

[0063] The organic layer after washing with water was transferred to another 100 L reaction vessel, and MEK was added in an amount 13 times the mass of the initial PACS. Distillation was performed under reduced pressure at 5 kPa at 25°C or below to remove organic impurities other than 4-HS, such as tert-butyl methyl ether and reaction by-products, as well as excess MEK, ultimately yielding a solution with a 4-HS concentration of 25% by mass. The solution was then passed through a polytetrafluoroethylene (PTFE) hollow fiber membrane filter with a pore size of 50 nm, yielding 21 kg of a 24.9% by mass 4-HS / MEK solution.

[0064] Comparative Example 1 (Preliminary Test for Example 1) 56.6 g of the 4-HS / MEK solution of Reference Example 1, 78.9 g of MCPMA, 12.4 g of the polymerization initiator dimethyl 2,2-azobisisobutyrate, and 73.9 g of MEK were placed in a container and mixed to prepare a monomer solution. The molar ratio of 4-HS to MCPMA was 20:80.

[0065] 78.0 g of MEK was charged into a 500 mL four-neck glass flask reaction vessel equipped with a stirrer, a condenser, and a thermometer, and after creating a nitrogen atmosphere, the reaction vessel was heated to 79°C. Subsequently, the monomer solution was added dropwise to the reaction vessel at a constant rate over 4 hours, and after completion of the dropwise addition, the reaction was continued for another 2 hours (aging). The temperature during the polymerization reaction was controlled at 79.0 to 80.0°C, and after completion of the polymerization, the reaction vessel was cooled to room temperature.

[0066] During the polymerization reaction, a portion of the solution in the reaction vessel was sampled every hour to measure the concentration of unreacted monomer by GC, and the weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the copolymer by GPC. Furthermore, the monomer conversion (relative to the total amount supplied) and the molar ratio of unreacted monomer at each sampling time were determined from the changes over time in the monomer supply amount and unreacted monomer concentration up to each sampling time. The molar ratio of each monomer consumed every hour was also calculated from the same data. The measurement and calculation results are shown in Tables 1 and 2.

[0067]

[0068]

[0069] While the molar ratio of 4-HS to MCPMA supplied was 20:80, the composition of unreacted 4-HS in the system at the beginning of the polymerization was 17.7 to 13.0 mol %, and the 1-hour consumption of 4-HS exceeded 25 mol %, indicating that 4-HS is a highly polymerizable, i.e., highly reactive, monomer. Subsequently, between 3 and 4 hours, the composition of 4-HS in the polymerization system reached a roughly steady state of 10.4 to 9.5 mol %, and the composition of 4-HS and MCPMA consumed during this period was 19.6:80.4, suggesting that a copolymer close to the molar ratio of the supplied monomers (20:80) was being produced. After the entire monomer solution was completely supplied, the molar ratio of the monomers consumed per unit time gradually deviated significantly from 20:80 over the 2-hour maturation period, confirming the production of a copolymer with an extremely high MCPMA composition.

[0070] [Example 1] (Preparation of First Monomer Solution) The monomer composition of the first monomer solution was set to be the same as the monomer composition (4-HS:MCPMA=10.4:89.6) in the reaction system 3 hours after the start of polymerization, when the reaction had reached a substantially steady state in the preliminary test (Comparative Example 1), and the content of the monomers contained in the first monomer solution was set to 18 mol % of the total monomers. 5.2 g of a 25 mass % 4-HS / MEK solution, 15.7 g of MCPMA, 2.2 g of a polymerization initiator dimethyl 2,2-azobisisobutyrate, and 13.2 g of MEK were added to a vessel and mixed to prepare a first monomer solution.

[0071] (Preparation of Second Monomer Solution) In a separate container, 51.4 g of the same 4-HS / MEK solution, 63.2 g of MCPMA, 10.2 g of polymerization initiator dimethyl 2,2-azobisisobutyrate, and 60.7 g of MEK were mixed to prepare a second monomer solution. The composition ratio of each monomer in the second monomer solution was 4-HS:MCPMA=22.1:87.9, and the molar composition of the highly reactive monomer 4-HS was 5 mol% or more higher than that of the first monomer solution. The total amounts of each monomer and polymerization initiator contained in the first and second monomer solutions were the same as those used in the preliminary test (Comparative Example 1).

[0072] Next, 78.0 g of MEK was charged into a 500 mL four-neck glass flask reaction vessel equipped with a stirrer, condenser, and thermometer. The vessel was then placed under a nitrogen atmosphere and heated to 79°C. The first monomer solution was then added dropwise at a constant rate over 43 minutes. The second monomer solution was then added dropwise over 2 hours and 17 minutes, with the rate set to be the same as that of the first monomer solution on a monomer molar basis. Three hours after the start of monomer addition, 75% of the total monomer was added. At the 3-hour mark, the rate of addition of the second monomer solution was reduced to half, and the remaining monomer was added dropwise over 2 hours. The total addition time was 5 hours. The reaction was then continued for another hour. The temperature during the polymerization reaction was controlled between 79.0 and 80.0°C, and the mixture was cooled to room temperature after completion of the polymerization.

[0073] During the 6-hour polymerization reaction, a portion of the solution in the reaction vessel was sampled every hour to measure the concentration of unreacted monomer by GC, and the weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the copolymer by GPC. The monomer conversion (relative to the total amount supplied) and the molar ratio of unreacted monomer at each sampling time were determined from the changes over time in the monomer supply amount and unreacted monomer concentration up to each sampling time. The molar ratio of each monomer consumed every hour was also calculated from the same data. The measurement and calculation results are shown in Tables 3 and 4.

[0074]

[0075]

[0076] In Example 1, the conversion of the low-reactivity monomer MCPMA reached 84.6% at the end of the monomer solution supply, alleviating the uneven distribution of monomer consumption during the aging period (5 to 6 hours), i.e., suppressing the production of copolymers with an extremely high MCPMA composition. Furthermore, the final conversion of each monomer averaged 93.5%, achieving a high polymer yield.

[0077] Comparative Example 2 (Preliminary Test for Example 2) 30.0 g of PACS, 46.6 g of ECPMA, 11.9 g of a polymerization initiator dimethyl 2,2-azobisisobutyrate, and 83.7 g of PGME were mixed in a container to prepare a monomer solution. The molar ratio of PACS to ECPMA was 42:58.

[0078] A 500 mL glass four-neck flask reaction vessel equipped with a stirrer, a condenser, and a thermometer was charged with 60.0 g of PGME, and after a nitrogen atmosphere was created, the reaction vessel was heated to 79°C. Subsequently, the monomer solution was added dropwise to the reaction vessel at a constant rate over 4 hours, and after completion of the addition, the reaction was continued for another 2 hours (aging). The temperature during the polymerization reaction was controlled at 79.0 to 80.0°C, and after completion of the polymerization, the reaction vessel was cooled to room temperature.

[0079] During the polymerization reaction, a portion of the reaction solution was sampled every hour to measure the concentration of unreacted monomer by GC, and the weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the copolymer by GPC. Furthermore, the monomer conversion (relative to the total amount supplied) and the molar ratio of unreacted monomer at each sampling time were determined from the changes over time in the monomer supply amount and unreacted monomer concentration up to each sampling time. The molar ratio of each monomer consumed per hour was also calculated from the same data. The measurement and calculation results are shown in Tables 5 and 6.

[0080]

[0081]

[0082] While the molar ratio of PACS to ECPMA supplied was 42:58, the unreacted PACS composition in the system was 37.1-32.4% at the beginning of the polymerization, and the PACS consumption per hour was approximately 47-48%, indicating that PACS is a highly polymerizable, i.e., highly reactive, monomer. Subsequently, during the 3-4 hour period, the PACS composition in the polymerization system reached a roughly steady state of 29.6-32.4 mol%, and the PACS to ECPMA consumed during this period was 43.1:56.9, suggesting that a copolymer close to the molar ratio of the supplied monomers (42:58) was being produced. After the entire monomer solution was supplied, the molar ratio of the monomers consumed per unit time gradually deviated significantly from 42:58 over the 2-hour maturation period, indicating the production of a copolymer with an extremely high ECPMA composition.

[0083] [Example 2] (Preparation of First Monomer Solution) The monomer composition of the first monomer solution was the same as the monomer composition (PACS:ECPMA=32.4:67.6) in the reaction system at 3 hours from the start of polymerization, when the reaction had reached a substantially steady state in the preliminary test (Comparative Example 2), and the monomers contained in the first monomer solution were set to 15 mol % of the total monomers. 3.4 g of PACS, 7.9 g of ECPMA, 1.7 g of the polymerization initiator dimethyl 2,2-azobisisobutyrate, and 12.2 g of PGME were added to a container and mixed to prepare a first monomer solution.

[0084] (Preparation of Second Monomer Solution) 26.6 g of PACS, 38.7 g of ECPMA, 10.2 g of the polymerization initiator dimethyl 2,2-azobisisobutyrate, and 71.5 g of PGME were mixed in a separate container to prepare a second monomer solution. The composition ratio of each monomer in the second monomer solution was PACS:ECPMA = 43.6:56.4, and the molar composition of PACS, a highly reactive monomer, was 5 mol% or more higher than that of the first monomer solution. The total amounts of each monomer and polymerization initiator contained in the first and second monomer solutions were the same as those used in the preliminary test (Comparative Example 1).

[0085] Next, 78.0 g of PGME was charged into a 500 mL four-neck glass flask reaction vessel equipped with a stirrer, a condenser, and a thermometer. The vessel was then conditioned under a nitrogen atmosphere and heated to 79°C. The first monomer solution was then added dropwise at a constant rate over 35 minutes, followed by the second monomer solution, which was added dropwise at a constant rate over 2 hours and 25 minutes, with the rate set to be the same as the rate of addition of the first monomer solution on a monomer molar basis. Three hours after the start of monomer addition, 75% of the total monomer was added dropwise. At the 3-hour mark, the rate of addition of the second monomer solution was reduced to half, and the remainder was added dropwise over 2 hours. The total drop time was 5 hours. The reaction was then continued for another hour. The temperature during the polymerization reaction was controlled between 79.0 and 80.0°C, and the mixture was cooled to room temperature after completion of the polymerization.

[0086] During the 6-hour polymerization reaction, a portion of the solution in the reaction vessel was sampled every hour to measure the concentration of unreacted monomer by GC, and the weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the copolymer by GPC. The monomer conversion (relative to the total amount supplied) and the molar ratio of unreacted monomer at each sampling time were determined from the changes over time in the monomer supply amount and unreacted monomer concentration up to each sampling time. The molar ratio of each monomer consumed per hour was also calculated from the same data. The measurement and calculation results are shown in Tables 7 and 8.

[0087]

[0088]

[0089] In Example 2, the conversion of the low-reactivity monomer ECPMA reached 79.8% at the end of the monomer solution supply, mitigating the uneven distribution of monomer consumption during the aging period (5 to 6 hours) and preventing the formation of copolymers with extremely high ECPMA composition. Furthermore, the final conversion of each monomer averaged 91.0%, achieving a high polymer yield.

[0090] [Evaluation of Copolymer Composition Uniformity] With regard to the composition uniformity of the copolymers, the copolymers synthesized in Example 1 and Comparative Example 1 were compared, and the copolymers synthesized in Example 2 and Comparative Example 2 were compared.

[0091] Specifically, each copolymer was subjected to GPC by the above-mentioned measurement method, and the copolymer fraction was fractionated into three fractions of high / middle / low molecular weight so that the weight of the copolymer contained therein was equal. The monomer composition ratio of the copolymer contained in each fraction was １３ The copolymers were analyzed and evaluated by C-NMR. The evaluation results are shown in Tables 9 and 10. It was confirmed that the copolymers synthesized in Examples 1 and 2 had significantly improved uniformity compared to the copolymers synthesized in Comparative Examples 1 and 2, respectively.

[0092]

[0093]

[0094] Example 3 The method for supplying the first monomer solution was changed to a method in which the first monomer solution was charged into the reaction vessel before the start of polymerization, and polymerization was carried out using the same types and amounts of monomers as in Example 1.

[0095] (Preparation of First Monomer Solution) The monomer composition of the first monomer solution was the same as the monomer composition (4-HS:MCPMA=10.4:89.6) in the reaction system 3 hours after the start of polymerization, when the reaction had reached a substantially steady state in the preliminary test (Comparative Example 1), and the content of the monomers in the first monomer solution was set to 13.2 mol % of the total monomers. 3.9 g of a 24.9 mass % 4-HS / MEK solution, 11.7 g of MCPMA, and 99.6 g of MEK were added to a 500 mL four-neck glass flask reaction vessel equipped with a stirrer, a condenser, and a thermometer and mixed to prepare a first monomer solution.

[0096] (Preparation of Second Monomer Solution) In a separate container, 52.7 g of a 24.9% by mass 4-HS / MEK solution, 67.2 g of MCPMA, 12.4 g of the polymerization initiator dimethyl 2,2-azobisisobutyrate, and 52.3 g of MEK were mixed to prepare a second monomer solution. The composition ratio of each monomer in the second monomer solution was 4-HS:MCPMA=21.5:78.5, and the molar composition of the highly reactive monomer 4-HS was 5 mol% or more higher than that of the first monomer solution. The total amounts of each monomer and polymerization initiator contained in the first and second monomer solutions were the same as those used in the preliminary test (Comparative Example 1).

[0097] The reaction vessel containing the first monomer solution was conditioned under a nitrogen atmosphere and then heated to 79°C. The second monomer solution was then added dropwise at a constant rate over a period of 5 hours. The composition ratio of the highly reactive monomer (4-HS) in the reaction system at the start of polymerization was nearly equal to that of the first monomer solution, and was 52% of the composition ratio of 4-HS (20 mol%) in all monomers, since the effect of the addition of the second monomer solution was small, if any. After the addition of the second monomer solution was completed, the reaction was continued for 1 hour. The temperature during the polymerization reaction was controlled to 79.0 to 80.0°C, and the system was then cooled to room temperature after the completion of polymerization.

[0098] During the 6-hour polymerization reaction, a portion of the solution in the reaction vessel was sampled every hour to measure the concentration of unreacted monomer by GC, and the weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the copolymer by GPC. The monomer conversion (relative to the total amount supplied) and the molar ratio of unreacted monomer at each sampling time were determined from the changes over time in the monomer supply amount and unreacted monomer concentration up to each sampling time. The molar ratio of each monomer consumed per hour was also calculated from the same data. The measurement and calculation results are shown in Tables 11 and 12.

[0099]

[0100]

[0101] Example 3 is a method in which the first monomer solution is supplied to the reaction vessel before the start of polymerization. Compared with Comparative Example 1, the consumption of the monomers was made more uniform, that is, the composition uniformity of the produced copolymer was improved.

[0102] The copolymer of a hydroxystyrene-based monomer and a (meth)acrylic acid ester-based monomer obtained by the present invention can be suitably used as a photoresist for semiconductor manufacturing.

Claims

1. A method for producing a copolymer, comprising polymerizing at least one hydroxystyrene-based monomer and at least one (meth)acrylic acid ester-based monomer in the presence of a radical polymerization initiator and a solvent, The hydroxystyrene monomer is a hydroxystyrene having one to three hydroxyl groups, or a derivative of such a hydroxystyrene in which at least a part of the hydroxyl groups is protected with a group that dissociates under the action of an acid or a base, A method for producing a copolymer, characterized in that a polymerization reaction is carried out while averaging differences in the consumption rates of the individual monomers under the following conditions (1) to (4): (1) preparing a plurality of monomer solutions containing the hydroxystyrene-based monomer and the (meth)acrylic acid ester-based monomer, each having a different composition ratio; Among the plurality of monomer solutions, one having the lowest composition ratio of the most reactive monomer is designated as a first monomer solution, and one having a composition ratio of the most reactive monomer that is 5 mol % or more higher than that of the first monomer solution is designated as an n-th monomer solution (n is an integer of 2 or more), the amount of the monomer contained in the first monomer solution is 5 mol % or more and 33 mol % or less based on the amount of all the monomers; (2) first supplying the first monomer solution into the reaction vessel, and then sequentially supplying the nth monomer solution into the reaction vessel; (3) Adjusting the composition ratio of the most reactive monomer in the reaction system at the start of the polymerization reaction to be 30% to 90% of the composition ratio of the most reactive monomer in all monomers; (4) When the supply of all the monomer solutions is completed, the conversion rate of the least reactive monomer is 75% or more.

2. 2. The method for producing a copolymer according to claim 1, wherein the composition ratio of each monomer consumed in the polymerization reaction within 1 hour from the start of the polymerization reaction is within ±5 mol % of the composition ratio of each monomer in all the monomers.

3. 2. The method for producing the copolymer according to claim 1, wherein the composition ratio of each monomer in the reaction system at the start of the polymerization reaction is adjusted to be within ±3 mol % of the test composition ratio calculated in the following preliminary test. (Procedure for preliminary examination) A solution to be added is prepared by mixing monomers having the monomer composition of the target copolymer, a radical polymerization initiator, and a solvent. The solvent is charged into a reaction vessel and heated until the predetermined reaction temperature is reached. The solution is added dropwise at a constant rate over 3 hours or more, and the mixture is then allowed to age for another 2 hours or more after the addition. Sampling is carried out during the polymerization reaction to measure the composition ratio of unreacted monomers in the polymerization reaction system, and the test composition is determined. Test composition = Monomer composition ratio when the unreacted monomer composition ratio is in a steady state when the amount of monomer supplied is between 60% and 100% (at the end of dropping).

4. 2. The method for producing a copolymer according to claim 1, wherein the composition ratio of each monomer consumed in the polymerization from the time when the dropwise addition of all the monomer solutions is completed until the termination of the polymerization is ±3 mol % of the composition ratio of all the monomers.

5. 2. The method for producing a copolymer according to claim 1, wherein the composition ratio of the high-reactivity monomer in the composition ratios of each monomer consumed in the polymerization from the time when the dropwise addition of all the monomer solutions is completed until the termination of the polymerization is 80% or more of the composition ratio of the high-reactivity monomer in all the monomers.

6. 2. The method for producing a copolymer according to claim 1, wherein the feed rate of the monomer solution is reduced from any time point when the total amount of monomers fed is between 60 mol % and 85 mol % until the end of dropwise addition of the monomer solution.

7. The method for producing a copolymer according to claim 3, which is applied to the production of a copolymer such that, when polymerization is carried out in the same procedure as in the preliminary test, the composition ratio of the monomers consumed in any time period during the polymerization reaction deviates from the composition ratio of all the monomers by ±10% or more.

8. The method for producing a copolymer according to claim 1, which is applied to the production of a copolymer in which, when comparing the molar ratios of the styrene-based monomer and the (meth)acrylic acid ester-based monomer in the target copolymer, the smaller molar ratio is 10 mol % or more and 40 mol % or less.

9. 2. The method for producing a copolymer according to claim 1, wherein the conversion rate of each monomer after the start of the polymerization reaction is within ±20% of the average conversion rate of each monomer.

10. The method for producing a copolymer according to any one of claims 1 to 9, wherein the hydroxystyrene-based monomer is at least one selected from the group consisting of 4-hydroxystyrene and 4-acetoxystyrene.

11. A copolymer having structural units derived from at least one hydroxystyrene-based monomer and structural units derived from at least one (meth)acrylic acid ester-based monomer, The hydroxystyrene monomer is a hydroxystyrene having one to three hydroxyl groups, or a derivative of such a hydroxystyrene in which at least a part of the hydroxyl groups is protected with a group that dissociates under the action of an acid or a base, the composition ratio of the structural units derived from the hydroxystyrene-based monomer to the structural units derived from the (meth)acrylic acid ester-based monomer in the copolymer is, in terms of molar ratio, 10:90 to 45:55 or 55:45 to 90:10; When a copolymer is subjected to gel permeation chromatography and the copolymer fraction is fractionated into three fractions of high, medium and low molecular weight so that the weights of the copolymer contained therein are equal, the monomer composition ratio of the copolymer contained in the high molecular weight fraction is within a range of ±1% compared to the monomer composition ratio of the copolymer contained in the medium molecular weight fraction, and the monomer composition ratio of the copolymer contained in the low molecular weight fraction is within a range of ±2% compared to the monomer composition ratio of the copolymer contained in the medium molecular weight fraction.

12. The copolymer according to claim 11, wherein the hydroxystyrene-based monomer is at least one selected from the group consisting of 4-hydroxystyrene and 4-acetoxystyrene.