High-purity 4-hydroxystyrene solution, method for producing same, and method for producing 4-hydroxystyrene polymer

Abstract

To provide a 4-hydroxystyrene solution that is suitable as a raw material for commercial-scale production of 4-hydroxystyrene-based polymers, and has a high purity and good storage stability, and a production method for the 4-hydroxystyrene solution.SOLUTION: A production method for a 4-hydroxystyrene solution according to the present invention comprises the following (i) to (iv): (i) a deprotection step of bringing 4-acetoxystyrene into contact with a base in a solvent to generate 4-hydroxystyrene; (ii) a neutralization step of neutralizing the deprotected solution containing 4-hydroxystyrene by adding an acid to the solution; (iii) a step of washing the neutralized solution containing 4-hydroxystyrene with water; and (iv) a solvent substitution step of adding a solvent capable of dissolving 4-hydroxystyrene to the solution containing 4-hydroxystyrene, and performing distillation at 40°C or lower to remove excess solvent and components other than 4-hydroxystyrene.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a high-purity 4-hydroxystyrene solution having good storage stability and a method for producing the same, and also to a method for producing a 4-hydroxystyrene polymer in which polymerization is carried out using the 4-hydroxystyrene solution as a raw material. [Background technology]

[0002] Polymers containing structural units derived from 4-hydroxystyrene (hereinafter referred to as "4-hydroxystyrene-based polymers") are used in many products, including photoresists, printed wiring boards, adhesives, PS printing plates, metal surface treatment agents, and sealants. In particular, when used in photoresists, as patterns become finer, there is a demand for highly reduced impurities, such as insoluble components and metals, contained in the polymer. To meet the demand for ever finer pattern rules in future technologies such as EUV lithography and electron beam lithography, even stricter control of the properties of resist polymers will be required.

[0003] Known methods for producing 4-hydroxystyrene polymers include a method using 4-hydroxystyrene as a starting material and a method using a monomer in which the hydroxyl group of 4-hydroxystyrene has been substituted with a protecting group.

[0004] Known methods using a monomer in which the hydroxyl group of 4-hydroxystyrene is substituted with a protecting group include, for example, polymerizing 4-acetoxystyrene as a raw material and then removing the protecting group by the action of an acid or base to reveal the hydroxyl group (Patent Documents 1 and 2). This method allows for the stable commercial production of polymers because high-purity acetoxystyrene is readily available. However, since post-polymerization deprotection reactions using an acid or base and subsequent neutralization reactions are required, the number of manufacturing steps increases, which has the disadvantage of correspondingly higher manufacturing costs. Furthermore, the increased number of steps may increase the risk of impurity contamination. Furthermore, polymers for chemically amplified resists contain structural units with acid-labile groups that dissociate under the action of acid, and some of the acid-labile groups may be eliminated during the deprotection reaction of the acetoxystyrene units.

[0005] On the other hand, a method using 4-hydroxystyrene as a starting material has also been investigated (Patent Document 3), but the purity of 4-hydroxystyrene is not mentioned at all. Furthermore, the production of the polymer is also only on a laboratory scale. This is because 4-hydroxystyrene is an extremely unstable compound and polymerization proceeds rapidly even at room temperature, making it difficult to mass-produce and store it as a raw material for industrial polymer production.

[0006] A known method for producing high-purity 4-hydroxystyrene is to react 4-acetoxystyrene with an alcohol in the presence of a catalytic amount of a suitable base (Patent Document 4).

[0007] Furthermore, as a method for stably storing unstable 4-hydroxystyrene, a method of adding 3 to 1000% by weight of an alcohol such as methanol to 4-hydroxystyrene (Patent Document 5) is known, but this method does not sufficiently inhibit polymerization, and it is necessary to mix in an alcohol. Furthermore, a polymerization raw material composition in which methanol is added to a 4-hydroxystyrene composition obtained by dehydrogenating 4-ethylphenol (Patent Document 6) has been disclosed, but since this composition contains a large amount of impurities such as catalyst residues from the dehydrogenation of 4-ethylphenol and residual ethylphenol, it is not a method suitable for producing resist resins for cutting-edge lithography.

[0008] Other methods disclosed for producing 4-hydroxystyrene in high yield and storing it stably include a method in which a protected monomer of 4-hydroxystyrene is deprotected with a base catalyst in the presence of 1,3,5-trihydroxybenzene, followed by crystallization to obtain 4-hydroxystyrene crystals, and a method in which 4-hydroxystyrene is stored with 0.01% by mass or more and 10% by mass or less of 1,3,5-trihydroxybenzene added (Patent Document 7). However, these methods are not suitable for use as resists for cutting-edge lithography because 1,3,5-trihydroxybenzene is mixed into the polymer as an impurity. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 02-047109 [Patent Document 2] Japanese Patent Application Publication No. 63-023902 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-157401 [Patent Document 4] Japanese Patent Application Publication No. 4-283529 [Patent Document 5] Special Publication No. 51-29137 [Patent Document 6] Japanese Patent Application Publication No. 10-251315 [Patent Document 7] Japanese Patent Application Publication No. 2016-098181 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention provides a highly pure and storage-stable 4-hydroxystyrene solution suitable as a raw material for commercial-scale production of a 4-hydroxystyrene polymer, and a method for producing the same. The present invention also provides a method for producing a 4-hydroxystyrene polymer suitable for use in resists for cutting-edge lithography on a commercial scale by a simple process that does not require a deprotection step. [Means for solving the problem]

[0011] As a result of extensive research to achieve the above-mentioned object, the present inventors have found that a 4-hydroxystyrene solution having a 4-hydroxystyrene concentration of 10 to 70% and a 4-hydroxystyrene polymer content of 0.5% or less relative to 4-hydroxystyrene can be stably stored over a long period of time while suppressing the formation of polymerization products. Furthermore, the present inventors have found that, in producing the 4-hydroxystyrene solution, 4-acetoxystyrene is used as a starting material, 4-hydroxystyrene is produced by a deprotection reaction using a base catalyst, and after neutralization, a solvent capable of dissolving 4-hydroxystyrene is added to the solution containing 4-hydroxystyrene, and the mixture is subjected to reduced pressure distillation at 40°C or less to remove components other than 4-hydroxystyrene and the solvent, as well as excess solvent, thereby performing solvent replacement without crystallizing 4-hydroxystyrene, thereby enabling the commercial production of a high-purity, storage-stable 4-hydroxystyrene solution. The present inventors also found that by carrying out polymerization using the 4-hydroxystyrene solution, it is possible to produce a polymer having structural units derived from 4-hydroxystyrene, in which the inclusion of insoluble components and metal impurities is highly suppressed, by a simple process that does not require a deprotection step, and on a commercial scale, and thus completed the present invention.

[0012] That is, according to the present invention, the following inventions are provided. [1] The following steps (i) to (iv): (i) a deprotection step of contacting 4-acetoxystyrene with a base in a solvent to form 4-hydroxystyrene; (ii) a neutralization step of adding an acid to a solution containing 4-hydroxystyrene after deprotection to neutralize it; (iii) washing the solution containing 4-hydroxystyrene after neutralization with water; (iv) a solvent replacement step in which a solvent capable of dissolving 4-hydroxystyrene is added to a solution containing 4-hydroxystyrene, and the mixture is distilled at 40°C or less to remove components other than 4-hydroxystyrene and excess solvent; A method for producing a 4-hydroxystyrene solution, comprising: [2] The method for producing a 4-hydroxystyrene solution according to [1], wherein the base used in the deprotection step is one from which dissolved oxygen has been removed by bubbling with an inert gas before use, and the deprotection step is carried out under a nitrogen atmosphere. [3] The method for producing a 4-hydroxystyrene solution according to [1] or [2], wherein the acid used in the neutralization step has been bubbling with an inert gas to remove dissolved oxygen before use. [4] The method for producing a 4-hydroxystyrene solution according to any one of [1] to [3], wherein the base used in the deprotection step is selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, potassium tert-butoxide, trimethylamine, triethylamine, ethanolamine, diazabicycloundecene, diazabicyclononene, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,1,3,3-tetramethylguanidine, and tetramethylammonium hydroxide. [5] The method for producing a 4-hydroxystyrene solution according to any one of [1] to [4], wherein the organic solvent used in the solvent substitution step is any type of organic solvent selected from the group consisting of alcohols, ketones, ethers, glycol ethers, glycol ether esters, and esters. [6] The method for producing a 4-hydroxystyrene solution according to any one of [1] to [5], wherein the solvent substitution step is carried out to adjust the 4-hydroxystyrene concentration to 10 to 70 mass %. [7] The method for producing a 4-hydroxystyrene solution according to any one of [1] to [6], further comprising a step of passing the 4-hydroxystyrene solution through a filter having a nominal pore size of 1 micron or less before and / or after the solvent substitution step. [8] A 4-hydroxystyrene solution having a 4-hydroxystyrene concentration of 10 to 70 mass%, wherein in a gel permeation chromatography analysis of the solution, when the total area of ​​the chromatograms of components other than the organic solvent is taken as 100, the chromatogram area of ​​4-hydroxystyrene is 99.5% or more. [9] The 4-hydroxystyrene solution according to [8], wherein, in a gel permeation chromatography analysis of the solution, the chromatogram area of ​​4-hydroxystyrene polymers relative to the chromatogram area of ​​4-hydroxystyrene is 0.5% or less.

[10] The 4-hydroxystyrene solution according to [8] or [9], wherein the chromatogram area of ​​the 4-hydroxystyrene is 99.7% or more.

[11] The 4-hydroxystyrene solution according to [8] or [9], wherein the chromatogram area of ​​the 4-hydroxystyrene is 99.9% or more.

[12] The 4-hydroxystyrene solution according to any one of [8] to

[11] , wherein the organic solvent is any type of organic solvent selected from the group consisting of alcohols, ketones, ethers, glycol ethers, glycol ether esters, and esters.

[13] The 4-hydroxystyrene solution according to any one of [8] to

[12] , which does not contain a polymerization inhibitor.

[14] A polymerization raw material for a resist polymer, comprising the 4-hydroxystyrene solution according to any one of [8] to

[13] .

[15] A method for producing a polymer having structural units derived from 4-hydroxystyrene, in which the 4-hydroxystyrene solution according to any one of [8] to

[13] is used as a polymerization raw material and polymerized alone or together with other monomers copolymerizable therewith.

[16] A method for producing a polymer having structural units derived from 4-hydroxystyrene, in which a 4-hydroxystyrene solution produced by the method according to any one of [1] to [7] is used as a polymerization raw material and polymerized alone or with other monomers copolymerizable therewith.

[17] A step of producing a 4-hydroxystyrene solution by the method according to any one of [1] to [7]; a step of polymerizing the 4-hydroxystyrene solution produced in the above step as a polymerization raw material by itself or by polymerizing it with other monomers copolymerizable with 4-hydroxystyrene; A method for producing a polymer having structural units derived from 4-hydroxystyrene, comprising:

[18] The method for producing a polymer according to any one of

[15] to

[17] , wherein the other copolymerizable monomer includes a monomer having an acid-dissociable group.

[19] The method for producing a polymer according to

[18] , wherein the monomer having an acid-dissociable group is a group having a tertiary carbon atom bonded to an oxygen atom.

[20] The method for producing a polymer according to any one of

[15] to

[19] , which is applied to polymerization using a polymerization vessel with a capacity of 30 L or more. [Effects of the Invention]

[0013] According to the present invention, a highly pure 4-hydroxystyrene solution with excellent storage stability can be easily produced on a commercial scale. Furthermore, a 4-hydroxystyrene-based polymer suitable for resists for cutting-edge lithography can be produced on a commercial scale by a simple process that does not require a deprotection step. DETAILED DESCRIPTION OF THE INVENTION

[0014] The method for producing a 4-hydroxystyrene solution, the 4-hydroxystyrene solution, and the 4-hydroxystyrene-based polymer of the present invention will be described in detail below.

[0015] <Method of producing 4-hydroxystyrene solution> (i) Deprotection step The deprotection step is a step in which 4-acetoxystyrene is contacted with a base in a solvent to remove the acetyl group and produce 4-hydroxystyrene.

[0016] The base used in the deprotection reaction is not particularly limited, and specific examples include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; alkali metal alkoxides such as sodium methoxide, potassium methoxide, sodium ethoxide, and potassium tert-butoxide; trimethylamine, triethylamine, ethanolamine, diazabicycloundecene, diazabicyclononene, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,1,3,3-tetramethylguanidine, and tetramethylammonium hydroxide. Among these, sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, potassium tert-butoxide, trimethylamine, triethylamine, diazabicycloundecene, diazabicyclononene, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,1,3,3-tetramethylguanidine, and tetramethylammonium hydroxide are preferred, and sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, diazabicycloundecene, diazabicyclononene, and tetramethylammonium hydroxide are more preferred. The above bases may be used alone or in combination of two or more.

[0017] The amount of base used is preferably 0.1 to 10.0 molar equivalents, more preferably 0.5 to 3.0 molar equivalents, relative to 4-acetoxystyrene. If the amount of base used is within the above range, a sufficient reaction rate is likely to be obtained.

[0018] The base is preferably supplied to the reaction system in the form of a solution, and it is further preferred to previously bubble the base solution with an inert gas such as nitrogen gas. Use of a degassed base solution has the effect of suppressing the formation of a hydroxystyrene polymer during the deprotection reaction.

[0019] The deprotection reaction is preferably carried out in an organic solvent, and the organic solvent is not particularly limited as long as it can dissolve 4-acetoxystyrene. Specific examples include alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, isobutyl alcohol, n-amyl alcohol, isoamyl alcohol, n-hexyl alcohol, n-heptyl alcohol, n-octyl alcohol, n-nonyl alcohol, n-decyl alcohol, lauryl alcohol, cetyl alcohol, stearyl alcohol, benzyl alcohol, triphenylcarbinol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, and 1,4-butanediol; methyl ether; Examples of suitable organic solvents include ketones such as methyl ketone, diethyl ketone, methyl isobutyl ketone, and cyclohexanone; hydrocarbons such as pentane, hexane, heptane, octane, isooctane, decane, cyclopentane, cyclohexane, benzene, toluene, and xylene; ethers such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, tetrahydrofuran, diethyl ether, diisopropyl ether, and methyl tert-butyl ether; and nitrile solvents such as acetonitrile and propionitrile. These organic solvents may be used alone or in combination. Among these, alcohols are preferred, with methanol, ethanol, n-propyl alcohol, and isopropyl alcohol being particularly preferred. It is preferable to previously bubble a solution of 4-acetoxystyrene in the above organic solvent with an inert gas such as nitrogen gas. This has the effect of suppressing the formation of hydroxystyrene polymers during the deprotection reaction.

[0020] The reaction temperature for the deprotection reaction is usually from -20 to 50°C, preferably from -10 to 20°C, and more preferably from -5 to 10°C, from the viewpoint of inhibiting the polymerization reaction.

[0021] The reaction time is not particularly limited as long as it is long enough for 4-acetoxystyrene to be completely converted into 4-hydroxystyrene. 1 This can be confirmed by analyzing the product using methods such as H-NMR, gas chromatography, and gel permeation chromatography. The deprotection reaction of 4-acetoxystyrene is preferably carried out in an inert gas atmosphere such as nitrogen.

[0022] (ii) Neutralization process The neutralization step is a step in which an acid is added to neutralize the base catalyst remaining in the reaction solution after the deprotection reaction. The type of acid used for neutralization is not particularly limited, but specific examples include formic acid, hydrochloric acid, acetic acid, oxalic acid, sulfuric acid, trifluoroacetic acid, and methanesulfonic acid. The acid used for neutralization is preferably diluted with a solvent as needed and bubbled with an inert gas such as nitrogen gas beforehand. This has the effect of suppressing the formation of a polymer of 4-hydroxystyrene.

[0023] (iii)Water washing process The water-washing step is a step of washing the solution containing 4-hydroxystyrene after neutralization with water. The solution containing 4-hydroxystyrene is preferably extracted into an organic solvent that can dissolve 4-hydroxystyrene and is separable from water, and then washed with deionized water to remove impurities such as by-products and salts.

[0024] The solvent used to extract 4-hydroxystyrene may be any solvent that dissolves 4-hydroxystyrene and is separable from water, and more preferably, it is a solvent with a boiling point that is the same as or lower than that of the solvent used in the solvent substitution step described below. This allows the extraction solvent to be easily distilled off in the subsequent solvent substitution step, preventing the extraction solvent from remaining in the final product.

[0025] Specific examples include ethers such as diisopropyl ether, ditertiary butyl ether, methyl tert-butyl ether, ethyl tert-butyl ether, and diethylene glycol dimethyl ether; ketones such as methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone; esters such as methyl acetate and ethyl acetate; and hydrocarbons such as pentane, hexane, heptane, cyclohexane, and methylcyclohexane. Ethers are preferred, and methyl tert-butyl ether is particularly preferred. These extraction solvents may be used alone or in combination.

[0026] The temperature during extraction is preferably in the range of -20 to less than 50°C, but from the viewpoint of inhibiting the polymerization reaction, it is more preferably in the range of -10 to 30°C.

[0027] The water used to wash the resulting 4-hydroxystyrene extract is preferably deionized water to prevent metal ions from getting mixed in. There are no particular restrictions on the amount of water used or the number of times of washing, but these can be determined appropriately taking into consideration operability, extraction efficiency of metal ions, etc., amount of waste liquid, etc.

[0028] The temperature during washing with water is preferably 0°C or higher and 50°C or lower, and more preferably 0°C or higher and 30°C or lower.

[0029] (iv) Solvent substitution step The solvent substitution step is a step in which the 4-hydroxystyrene extract is substituted with the target solvent. That is, a substitution solvent capable of dissolving 4-hydroxystyrene is added to the 4-hydroxystyrene extract, and the mixture is distilled to remove reaction by-products, components other than 4-hydroxystyrene, such as the extraction solvent, and excess substitution solvent. By performing solvent substitution without crystallization to obtain a 4-hydroxystyrene solution, rather than by crystallizing 4-hydroxystyrene using a conventional crystallization method and then dissolving it in a solvent, the formation of 4-hydroxystyrene polymers can be suppressed.

[0030] The substitution solvent may be added to the 4-hydroxystyrene extract before or after the start of distillation, or preferably added as needed during the distillation. When the concentration of the 4-hydroxystyrene extract is high, it is preferable to add the substitution solvent before distillation in order to suppress polymerization of 4-hydroxystyrene.

[0031] The temperature during distillation is preferably 40°C or lower, more preferably 20 to 35°C, and even more preferably 20 to 30°C, from the viewpoint of inhibiting polymerization of 4-hydroxystyrene.

[0032] The distillation may be carried out under atmospheric pressure, but is preferably carried out under reduced pressure. The pressure of the reduced pressure distillation is not particularly limited and can be appropriately adjusted so as to distill off components other than 4-hydroxystyrene, such as reaction by-products and extraction solvents, and excess substitution solvent. The pressure of the reduced pressure distillation is, for example, 1 to 100 kPa, and preferably 1 to 30 kPa.

[0033] The type of solvent to be substituted is not particularly limited as long as it can dissolve 4-hydroxystyrene. When the resulting 4-hydroxystyrene solution is used as a polymerization raw material in the production of a polymer, it is more preferable that the solvent can be used as a polymerization solvent. Specific examples include alcohols such as methanol, ethanol, propanol, butanol, and octanol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketone, and cyclohexanone; ethers such as ethyl tert-butyl ether, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, and diethylene glycol dimethyl ether; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether; glycol 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; esters such as ethyl acetate and ethyl lactate; N,N-dimethylformamide, acetonitrile, and the like. Preferred are alcohols, ketones, ethers, ether alcohols, ether esters, and esters, more preferred are methanol, ethanol, propanol, butanol, octanol, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, ethyl acetate, and ethyl lactate, and particularly preferred are methanol, ethanol, 2-propanol, 2-butanol, n-octanol, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate.

[0034] The amount of the substitution solvent to be used is not particularly limited, but is determined in consideration of the cost and an amount that can sufficiently distill off impurities other than 4-hydroxystyrene.

[0035] (v) Filtration The 4-hydroxystyrene solution is preferably filtered through a fine filter to remove insoluble matters such as polymers generated in trace amounts during the production process. Filtration through a filter may be carried out before, after, or both before and after the solvent replacement.

[0036] Examples of filter configurations that can be used include membrane filters, hollow fiber membrane filters, pleated membrane filters, and filters filled with filter media such as highly purified cellulose or diatomaceous earth. The membrane filters, hollow fiber membrane filters, and pleated membrane filters are preferably made of polyolefins such as polyethylene, ultra-high density polyethylene, and polypropylene, fluororesins such as PTFE, and nylon, with nylon being particularly preferred. These filters may also contain ion exchange groups or cationic charge regulators that generate a zeta potential in the filter. The ion exchange groups are preferably weakly acidic or weakly basic. Weakly acidic or weakly basic ion exchange groups can inhibit the polymerization of 4-hydroxystyrene.

[0037] The nominal pore size of the filter is preferably 1 μm or less, more preferably 0.2 μm or less, and even more preferably 0.05 μm or less. The lower limit of the nominal pore size of the filter is not particularly limited, but is usually 0.01 μm.

[0038] (vi) Storage of 4-hydroxystyrene solution The temperature at which the produced 4-hydroxystyrene solution is stored is preferably −15° C. or higher and 40° C. or lower, more preferably −15° C. or higher and 20° C. or lower, and even more preferably −15° C. to 5° C., in order to suppress polymerization during storage.

[0039] <4-hydroxystyrene solution> The 4-hydroxystyrene solution of the present invention is one in which 4-hydroxystyrene is dissolved in a solvent at a specific concentration. Adjusting the 4-hydroxystyrene concentration can improve the storage stability of 4-hydroxystyrene. The production method for the 4-hydroxystyrene solution is not particularly limited, and a solution obtained by a production method including the above-mentioned steps (i) to (iv) can be used. Alternatively, instead of the solvent substitution step (iv), a solution obtained by a method in which high-purity 4-hydroxystyrene crystals are obtained by a conventionally known crystallization method and then dissolved in a solvent may be used. In particular, a solution obtained by a production method including the above-mentioned steps (i) to (iv) is preferred because it can increase the purity of 4-hydroxystyrene.

[0040] The 4-hydroxystyrene concentration in the 4-hydroxystyrene solution is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 60% by mass or less, and even more preferably 20% by mass or more and 50% by mass or less. A 4-hydroxystyrene concentration of 10% by mass or more in the 4-hydroxystyrene solution can prevent a decrease in polymerization efficiency when used as a polymerization raw material, and a concentration of 70% by mass or less can prevent precipitation of 4-hydroxystyrene, which is preferable. Furthermore, when long-term storage stability is particularly important, a concentration of 50% by mass or less is particularly preferable.

[0041] Furthermore, in a 4-hydroxystyrene solution having a 4-hydroxystyrene concentration of 10 to 70 mass %, when the total area of ​​the chromatogram of components other than the organic solvent is taken as 100 in a gel permeation chromatography analysis of the solution, the chromatogram area of ​​4-hydroxystyrene is preferably 99.5% or more, more preferably 99.7% or more, and even more preferably 99.9% or more.

[0042] The content of 4-hydroxystyrene polymer in a 4-hydroxystyrene solution having a 4-hydroxystyrene concentration of 10 to 70% by mass is preferably 0.5% or less, more preferably 0.3% or less, and even more preferably 0.1% or less, relative to the 4-hydroxystyrene content. If the content of 4-hydroxystyrene polymer is less than the above numerical value, it can be said that the progress of the polymerization reaction during storage is sufficiently suppressed.

[0043] The 4-hydroxystyrene solution preferably does not contain a polymerization inhibitor. This avoids the risk of impurities from the polymerization inhibitor being mixed into the resist polymer when using the 4-hydroxystyrene solution to produce resist polymers for cutting-edge lithography. Furthermore, the progress of the polymerization reaction during storage can be suppressed without adding a polymerization inhibitor.

[0044] The solvent used for the 4-hydroxystyrene solution is not particularly limited as long as it can dissolve 4-hydroxystyrene. When the resulting 4-hydroxystyrene solution is used as a polymerization raw material for producing a polymer, it is more preferable that it be usable as a polymerization solvent. Specific examples include alcohols such as methanol, ethanol, propanol, butanol, and octanol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketone, and cyclohexanone; ethers such as ethyl tert-butyl ether, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, and diethylene glycol dimethyl ether; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether; glycol 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; esters such as ethyl acetate and ethyl lactate; N,N-dimethylformamide, acetonitrile, and the like. Preferred are alcohols, ketones, ethers, ether alcohols, ether esters, and esters, more preferred are methanol, ethanol, propanol, butanol, octanol, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, ethyl acetate, and ethyl lactate, and particularly preferred are methanol, ethanol, 2-propanol, 2-butanol, n-octanol, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate.

[0045] <Method of producing a polymer having structural units derived from 4-hydroxystyrene> The method of the present invention for producing a polymer having structural units derived from 4-hydroxystyrene includes a step of polymerizing 4-hydroxystyrene as a polymerization raw material, either alone or with another monomer copolymerizable therewith. As the polymerization raw material, the 4-hydroxystyrene solution obtained by the production method described in the above <Production Method of 4-Hydroxystyrene Solution> and the 4-hydroxystyrene solution described in the above <4-Hydroxystyrene Solution> can be used as they are. When the 4-hydroxystyrene solution is subjected to the polymerization step as it is, the organic solvent in which 4-hydroxystyrene is dissolved can be used as the polymerization solvent as it is.

[0046] (Other copolymerizable monomers) The copolymerizable other monomer is not particularly limited as long as it is polymerizable with 4-hydroxystyrene, and in the case of resist applications, known monomers used in the production of resist polymers can be used.

[0047] The resist polymer is a polymer whose solubility in a developer solution changes under the action of acid and contains at least one repeating unit (A) having a structure in which an alkali-soluble group is protected by an acid-dissociable, dissolution-inhibiting group. The acid-dissociable, dissolution-inhibiting group is a group that inhibits the dissolution of the copolymer in an alkaline developer solution and dissociates under the action of acid to dissolve the copolymer in the alkaline developer solution. To improve the polymer's adhesion to substrates, the resist polymer may also contain a repeating unit (B) having a lactone ring structure or a repeating unit (C) having a hydroxy group. If necessary, the resist polymer may further contain other repeating units, such as a repeating unit (D) having a structure that inhibits dissolution in an alkaline developer solution and is stable to the action of acid (hereinafter sometimes referred to as an "acid-stable, dissolution-inhibiting structure").

[0048] (Repeating unit (A)) The repeating unit (A) is a repeating unit having a structure in which an alkali-soluble group such as a carboxyl group, a phenolic hydroxyl group, or a sulfonic acid group is protected with an acid-dissociable, dissolution-inhibiting group that dissociates under the action of acid, preferably a repeating unit in which a carboxyl group, a phenolic hydroxyl group, or an OH group such as a sulfonic acid group in a repeating unit derived from (meth)acrylic acid or hydroxystyrene is protected with an acid-dissociable, dissolution-inhibiting group.

[0049] Examples of the acid dissociable, dissolution inhibiting group include structures represented by formula (a1) or (a2). [ka] In formula (a1), * represents a binding site as formula (a1), and R 20 and R 21 R each independently represents a hydrocarbon group having 1 to 4 carbon atoms, and specific examples thereof include alkyl groups having 1 to 4 carbon atoms, such as a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, and an i-butyl group. 22 represents a hydrocarbon group having 1 to 12 carbon atoms, and specific examples thereof include linear, branched, or cyclic alkyl groups having 1 to 12 carbon atoms, such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, cyclopentyl, cyclohexyl, norbornyl, tricyclo[5.2.1.02,6]decanyl, adamantyl, and tetracyclo[4.4.0.12,5.17,10]dodecanyl, and aryl groups having 6 to 12 carbon atoms, such as phenyl and naphthyl. 22 is R 20 or R 21 and may bond to form a ring, specifically an alicyclic ring having 5 to 12 carbon atoms such as a cyclopentane ring, a cyclohexane ring, a norbornane ring, a tricyclo[5.2.1.02,6]decane ring, an adamantane ring, or a tetracyclo[4.4.0.12,5.17,10]dodecane ring. 22 To, or R 22 R 20 or R 21When a saturated alicyclic ring, specifically a cyclopentane ring, a cyclohexane ring, a norbornane ring, a tricyclo[5.2.1.02,6]decane ring, an adamantane ring, or a tetracyclo[4.4.0.12,5.17,10]dodecane ring is bonded to the above ring, the difference in solubility in an alkaline developer before and after lithography is large, which is preferable for drawing fine patterns. [ka] In formula (a2), * represents a binding site as formula (a2), and R 23 and R 24 R each independently represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms, and specific examples thereof include a hydrogen atom and an alkyl group having 1 to 4 carbon atoms, such as a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, and an i-butyl group. 25 represents a hydrocarbon group having 1 to 12 carbon atoms, and specific examples thereof include a linear, branched, or cyclic alkyl group having 1 to 12 carbon atoms, such as a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a t-butyl group, a 2-ethylhexyl group, a cyclopentyl group, a cyclohexyl group, a norbornyl group, a tricyclo[5.2.1.02,6]decanyl group, an adamantyl group, or a tetracyclo[4.4.0.12,5.17,10]dodecanyl group. 23 is R 24 or R 25 may be bonded to form a ring, and R 23 R 24 Specific examples of the ring bonded to R include a cyclopentane ring, a cyclohexane ring, a norbornane ring, a tricyclo[5.2.1.02,6]decane ring, an adamantane ring, and a tetracyclo[4.4.0.12,5.17,10]dodecane ring. 23 R 25 Specific examples of the ring bonded to include a hydrofuran ring and a hydropyran ring.

[0050] Specific examples of the repeating unit (A) are given below, but the present invention is not limited to these. One type of repeating unit (A) or multiple types with different structures can be selected and used from the repeating units (A). [ka] (In the formula, Rx represents H, CH3, or CF3.) [ka] JPEG0007743664000005.jpg98150 (wherein Rx represents H, CH3, or CF3.)

[0051] (Repeating unit (B)) The repeating unit (B) is a repeating unit having a lactone structure or a sultone structure, and serves to improve adhesion to a substrate or an undercoat film, and to control solubility in a lithography solvent or an alkaline developer. A preferred example is a structure represented by formula (B1). [ka] In formula (B1), R 30 R represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, and specific examples thereof include a hydrogen atom, and an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, or a trifluoromethyl group, and is preferably a hydrogen atom, a methyl group, or a trifluoromethyl group. 31 represents a single bond or a divalent linking group. The divalent linking group represents an alkylene group having 1 to 4 carbon atoms or a group in which the alkylene group is substituted with an oxygen atom, a carbonyl group, or a carbonyloxy group. R 32 represents a lactone structure-containing group represented by formula (b). [ka] In formula (b), R 301 ~R 308 One of the following is R 32The remaining R represents the single bond that is the binding site. 301 ~R 308 represents a hydrogen atom, a hydrocarbon group having 1 to 4 carbon atoms, or an alkoxy group, or R 301 ~R 308 One of the following is R 32 and other, R 301 ~R 308 represents a hydrocarbon group having 3 to 14 carbon atoms which may contain an oxygen atom or a sulfur atom and which forms an alicyclic ring having 5 to 15 carbon atoms by bonding with one or two of R 301 ~R 308 represents a single bond for forming the alicyclic ring having 5 to 15 carbon atoms, and the other R 301 ~R 308 represents a hydrogen atom, a hydrocarbon group having 1 to 4 carbon atoms, or an alkoxy group. m represents an integer of 0 or 1.

[0052] Specific examples of the alicyclic ring include a cyclopentane ring, a cyclohexane ring, a norbornane ring, a 7-oxa-norbornane ring, a 7-thia-norbornane ring, and a tetracyclo[4.4.0.12,5.17,10]dodecane ring, preferably a norbornane ring or a 7-oxa-norbornane ring. Specific examples of the hydrocarbon group having 1 to 4 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, and an i-butyl group. Specific examples of the alkoxy group having 1 to 4 carbon atoms include a methoxy group and an ethoxy group.

[0053] In formula (b), R 301 ~R 308 One of the following is R 32 represents a single bond with the binding site as 301 ~R 308 represents a hydrogen atom, or a hydrocarbon group or alkoxy group having 1 to 4 carbon atoms. Particularly preferred examples of the lactone structure include a γ-butyrolactone structure and a δ-valerolactone structure. 301 ~R 308 One of the following is R 32 It has a binding site as a301 ~R 308 represents a hydrocarbon group having 3 to 14 carbon atoms which may contain an oxygen atom or a sulfur atom and which forms an alicyclic ring having 5 to 15 carbon atoms by bonding with one or two of the remaining R 301 ~R 308 represents a hydrogen atom, or a hydrocarbon group or alkoxy group having 1 to 4 carbon atoms. Particularly preferred examples of the lactone structure include a 1,3-cyclohexanecarbolactone structure, a 2,6-norbornanecarbolactone structure, a 7-oxa-2,6-norbornanecarbolactone structure, and a 4-oxa-tricyclo[5.2.1.02,6]decan-3-one structure.

[0054] Specific examples of the repeating unit (B) are given below, but the present invention is not limited to them. One type of repeating unit (B) or multiple types of repeating units with different structures can be selected and used from the repeating units (B). [ka] JPEG0007743664000009.jpg186150 (wherein Rx represents H, CH3, or CF3.)

[0055] (Repeating unit (C)) The repeating unit (C) is a repeating unit having a hydroxy group or a carboxy group in the side chain, and functions to increase the adhesion of the polymer to the substrate or the undercoat film, to control the solubility in lithography solvents or alkaline developers, and to form a crosslinked structure by reacting with a curing agent.

[0056] As the structure of the repeating unit (C), structures represented by formulae (C1) to (C3) are particularly preferred. [ka] In formula (C1), R 10R represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, and specific examples thereof include a hydrogen atom, and an alkyl group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, such as a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, or a trifluoromethyl group, and is preferably a hydrogen atom, a methyl group, or a trifluoromethyl group. 11 R is a substituted or unsubstituted aromatic hydrocarbon group. 12 represents a single bond, a divalent hydrocarbon group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, or a carbonyl group, and specific examples thereof include a single bond, an alkylene group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, such as a methylene group, a 1,1-ethylene group, a 2,2-propylene group, a 1,1,1,3,3,3-hexafluoro-2,2-propylene group, or a 1,1,1-trifluoro-2-trifluoromethyl-2,3-propylene group, and are preferably a single bond, a 1,1,1,3,3,3-hexafluoro-2,2-propylene group, or a 1,1,1-trifluoro-2-trifluoromethyl-2,3-propylene group, and are particularly preferably a single bond. i represents an integer of 1 or 2. [ka] In formula (C2), R 13 R represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, and specific examples thereof include a hydrogen atom, and an alkyl group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, such as a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, or a trifluoromethyl group, and is preferably a hydrogen atom, a methyl group, or a trifluoromethyl group. 14R represents a divalent to tetravalent hydrocarbon group having 2 to 14 carbon atoms which may contain a fluorine atom, an oxygen atom, or a sulfur atom. Specific examples include linear or branched saturated hydrocarbon groups having 2 to 4 carbon atoms, such as an ethylene group or an isopropylene group, and saturated alicyclic hydrocarbon groups having 5 to 14 carbon atoms which may contain an oxygen atom or a sulfur atom, such as a cyclohexane ring, a norbornane ring, a 7-oxa-norbornane ring, a 7-thia-norbornane ring, an adamantane ring, or a tetracyclo[4.4.0.12,5.17,10]dodecane ring. A cyclohexane ring, a norbornane ring, or an adamantane ring is preferred. 15 represents a single bond or a divalent hydrocarbon group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, and specific examples thereof include a single bond, a methylene group, a 1,1-ethylene group, a 2,2-propylene group, a 1,1,1,3,3,3-hexafluoro-2,2-propylene group, a 1,1,1-trifluoro-2-trifluoromethyl-2,3-propylene group, and other alkylene groups having 1 to 4 carbon atoms which may be substituted with a fluorine atom, and preferably a single bond, a 1,1,1,3,3,3-hexafluoro-2,2-propylene group, or a 1,1,1-trifluoro-2-trifluoromethyl-2,3-propylene group. 14 is an adamantyl group, R 15 A combination in which j is a single bond is particularly preferred. [ka] In formula (C3), R 16 R represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, and specific examples thereof include a hydrogen atom, and an alkyl group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, such as a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, or a trifluoromethyl group, and is preferably a hydrogen atom, a methyl group, or a trifluoromethyl group. 17represents a divalent alicyclic hydrocarbon group having 6 to 12 carbon atoms which may contain an oxygen atom or a sulfur atom, and specific examples include alicyclic hydrocarbon groups which may contain an oxygen atom or a sulfur atom and have a norbornane ring, a 7-oxa-norbornane ring, a 7-thia-norbornane ring, a tetracyclo[4.4.0.12,5.17,10]dodecane ring, etc., and are preferably a norbornane ring or a tetracyclo[4.4.0.12,5.17,10]dodecane ring. k represents an integer of 0 or 1.

[0057] Specific examples of the repeating unit (C) are given below, but the present invention is not limited to them. One type of repeating unit (C) or multiple types of repeating units with different structures can be selected and used. [ka] (In the formula, Rx represents H, CH3, or CF3.)

[0058] (Repeating unit (D)) The repeating unit (D) is a repeating unit having a structure in which an alkali-soluble group, such as a carboxyl group or a phenolic hydroxyl group, is protected with an acid-stable, dissolution-inhibiting group that does not dissociate even when exposed to acid. It is preferably a repeating unit derived from (meth)acrylic acid or hydroxystyrene, in which the carboxyl group or phenolic hydroxyl group is protected with an acid-stable, dissolution-inhibiting group. This repeating unit functions to control the solubility in lithography solvents and alkaline developers, and the optical properties of the thin film, such as the refractive index and light transmittance.

[0059] Examples of the acid-stable dissolution-inhibiting group include aliphatic hydrocarbon groups having 1 to 12 carbon atoms, in which the carbon atom that replaces the hydrogen atom of a carboxyl group or phenolic hydroxyl group and is bonded to the oxygen atom is a primary or secondary carbon, aromatic hydrocarbon groups, or structures in which methyl groups and 1-adamantyl groups are bonded. Specific examples include methyl groups, ethyl groups, n-propyl groups, i-propyl groups, n-butyl groups, i-butyl groups, cyclopentyl groups, cyclohexyl groups, 2-norbornyl groups, 2-isobornyl groups, 8-tricyclo[5.2.1.02,6]decanyl groups, 1-adamantyl groups, 2-adamantyl groups, 4-tetracyclo[4.4.0.12,5.17,10]dodecanyl groups, phenyl groups, benzyl groups, naphthyl groups, and anthracenyl groups.

[0060] Specific examples of the repeating unit (D) are given below, but the present invention is not limited to these. One type of repeating unit (D) or multiple types with different structures can be selected and used from the repeating units (D). [ka] (In the formula, Rx represents H, CH3, or CF3.)

[0061] Furthermore, an example of a repeating unit having the same effect as the repeating unit (D) is a repeating unit represented by formula (D'). [ka] In formula (D'), R 60 R represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, and specific examples thereof include a hydrogen atom, and an alkyl group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, such as a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, or a trifluoromethyl group, and is preferably a hydrogen atom, a methyl group, or a trifluoromethyl group. 61 is a hydrogen atom, or R 62R is a single bond or an alkylene group having 1 to 4 carbon atoms, and specific examples thereof include a hydrogen atom, a single bond, a methylene group, an ethylene group, and an isopropylene group. 62 is an aromatic hydrocarbon group having 6 to 14 carbon atoms, and specific examples thereof include a benzene ring, a naphthalene ring, and an anthracene ring.

[0062] Specific examples of the repeating unit (D') are given below. [ka]

[0063] The polymerization can be carried out by a conventionally known polymerization method such as radical polymerization, cationic polymerization, or anionic polymerization.

[0064] In the case of radical polymerization, raw material monomers, a radical polymerization initiator, and optionally a chain transfer agent are dissolved in a solvent and heated and stirred, preferably under an inert gas atmosphere such as nitrogen. For example, the polymerization can be carried out by a so-called bulk polymerization method in which all raw materials, such as the monomer, polymerization initiator, and chain transfer agent, are dissolved in a solvent and heated to the polymerization temperature, or a so-called dropwise polymerization method in which a solution of the monomer and polymerization initiator dissolved in a solvent is added dropwise to a solvent heated to the polymerization temperature. Among these, the dropwise polymerization method is preferred because of its high reproducibility for each production lot. The so-called independent dropwise method in which the monomer and the polymerization initiator, which is a radical generating source, are added dropwise separately is particularly preferred. It should be noted that the monomer, polymerization initiator, chain transfer agent, etc. can each be partially supplied to the polymerization system in advance. In the dropwise method, the molecular weight distribution and composition distribution of the copolymer can be controlled by changing the composition and supply rate of each supply solution depending on the concentration and composition of the monomers, the radical concentration, etc. in the polymerization system.

[0065] Conventional radical polymerization initiators can be used. For example, radical polymerization initiators such as azo compounds and peroxides are preferred. Specific examples of azo compound 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). Specific examples of peroxide polymerization initiators include decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, bis(3,5,5-trimethylhexanoyl) peroxide, succinic acid peroxide, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxypivalate, and 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate. These can be used alone or in combination.

[0066] The amount of the polymerization initiator used can be selected depending on the target molecular weight, the types of monomer, polymerization initiator, chain transfer agent, solvent, etc., the repeating unit composition, polymerization temperature, dropping rate, etc.

[0067] The chain transfer agent may be any known chain transfer agent, as needed. Among them, thiol compounds are preferred, and a wide range of known thiol compounds can be selected. The amount of chain transfer agent used can be selected depending on the target molecular weight, the types of monomers, polymerization initiators, chain transfer agents, and solvents, the repeating unit composition, the polymerization temperature, the dropping rate, etc.

[0068] The solvent used in the polymerization reaction is not particularly limited as long as it can stably dissolve the monomer, polymerization initiator, chain transfer agent, and polymerization reaction product. Specifically, the solvents exemplified above for the 4-hydroxystyrene solution can be used. These can be used alone or in combination of two or more.

[0069] There is no particular restriction on the amount of the polymerization solvent used, but if the amount of solvent used is too small, the monomer may precipitate or the viscosity may become too high, making it impossible to maintain a uniform polymerization system, while if the amount of solvent used is too large, the conversion rate of the monomer may be insufficient or the molecular weight of the copolymer may not be increased to the desired value. The amount of the solvent is usually 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight, per part by weight of the monomer.

[0070] The amount of polymerization solvent initially charged into the reaction vessel (hereinafter sometimes referred to as the "initial solvent") should be at least the minimum amount necessary to allow stirring. However, an amount greater than necessary is undesirable because it reduces the amount of monomer solution that can be supplied and reduces production efficiency. Typically, the volume ratio of the initial solvent to the final charge amount (i.e., the total amount of the initial solvent and the monomer and initiator solutions to be added dropwise) is selected to be, for example, 1 / 30 or more, preferably 1 / 20 to 1 / 2, and particularly preferably 1 / 10 to 1 / 3. It is also possible to premix a portion of the monomer and / or polymerization initiator with the initial solvent.

[0071] The dropping time of the monomer solution is not preferable because a short time tends to broaden the molecular weight distribution and the temperature of the polymerization solution drops due to the large amount of solution being dropped at once. Conversely, a long time is not preferable because the copolymer is subjected to more heat than necessary and productivity decreases. Therefore, the dropping time is usually selected from the range of 0.5 to 24 hours, preferably 1 to 12 hours, and particularly preferably 2 to 8 hours.

[0072] After the dropwise addition is complete, it is preferable to maintain the temperature for a certain period of time or further increase the temperature to carry out aging, thereby allowing the remaining unreacted monomers to react. A too long aging time is undesirable because it reduces the production efficiency per unit time and subjects the copolymer to excessive heat history. Therefore, the aging time is usually selected within 12 hours, preferably within 6 hours, and particularly preferably within the range of 1 to 4 hours.

[0073] 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. Preferably, it is selected within the range of 40 to 160°C, and particularly preferably 60 to 120°C. The polymerization temperature has a significant effect on the molecular weight and copolymer composition of the copolymer and therefore needs to be precisely controlled. However, since the polymerization reaction is generally an exothermic reaction, it is difficult to control the temperature at a constant level. For this reason, it is preferable to use at least one compound having a boiling point close to the target polymerization temperature as the polymerization solvent and to set the polymerization temperature at or above the initial boiling point of the compound at the polymerization pressure. This method allows the latent heat of vaporization of the polymerization solvent to suppress an increase in the polymerization temperature.

[0074] The polymerization pressure can be set as appropriate. However, when radicals are generated from the initiator, nitrogen gas is generated in the case of an azo-based initiator, and oxygen gas is generated in the case of a peroxide-based initiator. Therefore, in order to suppress fluctuations in the polymerization pressure, it is preferable to make the polymerization system an open system and carry out the polymerization at near atmospheric pressure.

[0075] The polymer obtained after the polymerization reaction contains low-molecular-weight impurities such as the polymerization solvent, unreacted monomers, oligomers, polymerization initiators, chain transfer agents, and reaction by-products thereof. These impurities are preferably removed by a purification process. Specifically, the polymerization reaction solution is diluted, if necessary, by adding a good solvent, and then contacted with a poor solvent to precipitate the copolymer as a solid, and the impurities are extracted into the poor solvent phase (hereinafter referred to as reprecipitation). Alternatively, the impurities are extracted into the poor solvent phase from a liquid-liquid two-phase system. In the case of reprecipitation, the precipitated solid is separated from the poor solvent by a method such as filtration or decantation, and the solid can be further purified by redissolving the solid in a good solvent and then adding a poor solvent to reprecipitate, or by washing the precipitated solid with a poor solvent. In the case of liquid-liquid two-phase separation, the poor solvent phase can be separated by liquid-liquid separation, and the resulting copolymer solution can be further purified by adding a poor solvent to reprecipitate or by liquid-liquid two-phase separation. These procedures may be repeated in the same manner, or different procedures may be combined.

[0076] Examples of poor solvents used in this purification step 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 pentane, 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 solvents exemplified as coating film-forming solvents described below. A good solvent can also be mixed with a poor solvent.

[0077] The type and amount of poor solvent used in the purification step are not particularly limited as long as the copolymer can be separated from low-molecular-weight compounds, but can be appropriately selected depending on the solubility of the copolymer in the poor solvent, the type and amount of solvent used in the polymerization, the type and amount of impurities, etc. If the amount of poor solvent is too small, separation of impurities such as the polymerization solvent and unreacted monomers will be insufficient, while if it is too large, waste liquid will increase, which is undesirable in terms of workability and cost. Generally, the amount of poor solvent is 0.5 to 50 times, preferably 1 to 20 times, and more preferably 2 to 10 times by weight of the total amount of the polymerization reaction solution diluted with a good solvent as needed.

[0078] The temperature of the purification step must be strictly controlled because it significantly affects the molecular weight and molecular weight distribution of the copolymer, the removal rate of impurities such as residual monomers and initiator residues, and various lithography properties. If the temperature of the purification step is too low, the solubility of impurities in the reprecipitation solvent and washing solvent will be insufficient, and impurities will not be sufficiently removed, resulting in inefficiency. Conversely, if the temperature is too high, the copolymer will dissolve in the reprecipitation solvent and washing solvent, resulting in an imbalance in the composition of the copolymer in the low molecular weight region and a decrease in yield, which is undesirable. For this reason, the purification step is preferably carried out at a temperature in the range of 0 to 40°C, preferably 0 to 30°C.

[0079] A treatment for removing metal impurities contained in the polymer may be carried out. This may be achieved by washing a solution of the polymer in an organic solvent with pure water, by contacting the polymer 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 or filter having ion exchange capacity may be a commercially available known product used for removing metals from resist polymers.

[0080] The purified polymer can be dried and extracted as a powder, or can be redissolved in a good solvent before or after drying and extracted as a solution. It is also preferable to replace the solvent in the polymer solution with a solvent used in a resist composition or the like by the method described below to obtain a polymer solution.

[0081] The substitution method is to heat the polymer solution under reduced pressure to distill off low-boiling substances such as the solvent used in purification, and then to distill off the initial solvent together with the supplied solvent while supplying a resist solvent to the polymer solution. By removing the low-boiling impurities such as the solvent used in purification, the copolymer can be completed as a resist solution.

[0082] The temperature of the heat source during reduced pressure heating is not particularly limited as long as it does not cause the copolymer to deteriorate, but is usually preferably 100°C or lower, more preferably 70°C or lower, even more preferably 60°C or lower, and particularly preferably 50°C or lower. In the solvent substitution process, low-boiling point components and the final solvent are evaporated under reduced pressure, so the copolymer solution during the process is cooled by the heat of vaporization, and its temperature becomes lower than that of the heat source. By limiting the heat source temperature, deterioration of the copolymer due to overheating can be prevented.

[0083] Furthermore, when replacing the solvent, if the amount of solvent supplied later is too small, the low-boiling compounds cannot be sufficiently removed, and if it is too large, the replacement takes too long and the copolymer is subjected to more heat than necessary, which is undesirable. The amount supplied can usually be selected from the range of 1.05 to 10 times, preferably 1.1 to 5 times, and particularly preferably 1.2 to 3 times the amount required as solvent for the finished solution.

[0084] 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.

[0085] Furthermore, to remove undesirable microgels such as high polymers, which can cause resist pattern defects, it is preferable to filter the copolymer solution (or the above-mentioned coating film-forming solution). The filtration accuracy of the filter is 0.2 μm or less, preferably 0.1 μm or less, and particularly preferably 0.05 μm or less. Examples of filter materials include polyolefins such as polyethylene and polypropylene, polar group-containing resins such as polyamide, polyester, and polyacrylonitrile, and fluorine-containing resins such as fluorinated polyethylene, with polyamide being particularly preferred. Examples of polyamide-based filters include (hereinafter referred to as trademarks), Ultipleat P-Nylon 66 and Ultipore N66 manufactured by Nippon Pall Co., Ltd., and the LifeAsure PSN series and LifeAsure EF series manufactured by Cuno Corporation. Examples of polyolefin-based filters include Microguard Plus HC10 and Optimizer D manufactured by Nippon Entegris Co., Ltd. These filters may be used alone or in combination of two or more types.

[0086] The polymer obtained by the production method of the present invention preferably has a highly reduced level of metal contamination. Specifically, the total metal content is preferably 50 ppb or less, more preferably 10 ppb or less, and even more preferably 3 ppb or less, based on the mass of the polymer, and it is particularly preferable that all metals are below the lower detection limit of an analytical instrument.

[0087] Metal content is measured by inductively coupled plasma mass spectrometry (ICP-MS).

[0088] The metal content is typically the sum of the contents of Na, K, Mg, Al, Ca, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sn, Co, Li, Ti, Ag, W, V, Ba, Pt, Au, As, Cd, Mo, and Zr. The content of each of the metals is preferably 1 ppb or less.

[0089] [Method for evaluating insoluble or poorly soluble components] Insoluble or poorly soluble components contained in a polymer solution can be analyzed by the following procedure. Step (i): The polymer solution is diluted with a good solvent to prepare a test solution having a polymer concentration of 10.0% by mass. Procedure (ii): The above test solution is placed in the flask of a non-contact turbidity meter for gyratory shaking culture (ODMonitor A&S manufactured by Taitec Co., Ltd., attached to the shaker NR-2). While gyratory shaking is performed, the poor solvent is added dropwise at a constant speed, and the change in weight of the test solution and the change in turbidity at a measurement wavelength of 950 nm are recorded. Step (iii): Continue adding the antisolvent until the turbidity reaches 0.20 OD (optical density), and record the amount of antisolvent added until the turbidity reaches 0.10 OD, 0.15 OD, and 0.20 OD. Using the above procedure, the smaller the amount of poor solvent added until each turbidity is reached, the smaller the amount of insoluble or poorly soluble components.

[0090] The above-mentioned method for evaluating insoluble or slightly soluble components can be applied to the above-mentioned 4-hydroxystyrene polymer solution and other polymer solutions. [Example]

[0091] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples. In the following examples, parts are by mass unless otherwise specified.

[0092] The analysis in this example was carried out as follows. [Purity of 4-hydroxystyrene solution] and [Weight average molecular weight and molecular weight distribution of polymer] The purity, polymer content, and weight-average molecular weight and molecular weight distribution of the 4-hydroxystyrene solution synthesized below were measured by GPC (gel permeation chromatography) using polystyrene as the standard. The analytical sample was prepared to a tetrahydrofuran solution with a polymer solids concentration of 2% by mass. The sample injection volume into the instrument was 50 μL. Measuring device: Tosoh HLC-8220GPC Detector: Refractive index (RI) detector Column: Shodex GPC KF804 x 3 (Showa Denko) Eluent: tetrahydrofuran Flow rate: 1.0mL / min Temperature: 40℃ Calibration curve: Created using polystyrene standard samples (manufactured by Tosoh)

[0093] [Water content of 4-hydroxystyrene solution] The water content of the 4-hydroxystyrene solution synthesized below was measured using the following device. Measuring device: Karl Fischer moisture analyzer AQ-7 (manufactured by Hiranuma Sangyo Co., Ltd.)

[0094] [Quantitative analysis of low molecular weight components in polymers] The amount of low molecular weight components contained in the polymer synthesized below was determined by LC (liquid chromatography). Measuring device: Tosoh HLC-8320GPC Detector: Refractive index (RI) detector Column: TOSOH TSKgel superHZ1000 x 4 Eluent: tetrahydrofuran Flow rate: 0.35mL / min Temperature: 40℃

[0095] [Monomer composition ratio of polymer] The monomer composition ratio of the polymer synthesized below is: 13 The product was analyzed by C-NMR. Equipment: Bruker AV400 Deuterated solvent: acetone-d6 Relaxation Reagent: Chromium(III) Acetylacetonate Measurement temperature: 40℃

[0096] [Metal analysis of polymer solutions] The metal content of the polymer synthesized below was analyzed using an inductively coupled plasma mass spectrometer (ICP-MS). The metals measured were a total of 26 elements: Na, K, Mg, Al, Ca, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sn, Co, Li, Ti, Ag, W, V, Ba, Pt, Au, As, Cd, Mo, and Zr. The analytical values ​​are based on the mass of the polymer solids. Apparatus: ICP mass spectrometer (Agilent Technologies, product name: Agilent7500cs) Sample preparation: Dilute the polymer solution with N-methyl-2-pyrrolidone

[0097] 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 TBMA: tert butyl methacrylate GBLMA: gamma-butyrolactone-alpha-methacrylate NLM: 3,5-norbornane lacton-2-yl methacrylate MEK: Methyl ethyl ketone MTBE: Methyl tertiary butyl ether PGMEA: Propylene glycol monomethyl ether acetate PGME: Propylene glycol monomethyl ether MeOH: Methanol IPA: 2-propanol SBA: 2-butanol EtOAc: ethyl acetate THF: tetrahydrofuran

[0098] <Method of producing 4-hydroxystyrene solution> [Example 1] A 100 L glass-lined reactor equipped with a thermometer, condenser, and stirrer was charged with 7.9 kg of PACS and 23.4 kg of methanol and sealed with nitrogen. The contents were cooled with stirring to a liquid temperature of -5°C. The reactor was then depressurized and repressurized with nitrogen three times. A 3 M aqueous solution of sodium hydroxide (equimolar to PACS) was prepared in a separate vessel, and nitrogen was bubbled through this solution for 1 hour. The nitrogen-bubbled aqueous solution was added dropwise to the reactor over 100 minutes. After addition, stirring was continued for another 30 minutes to deprotect PACS and convert it to 4-HS.

[0099] Next, 0.97 molar equivalents of 6M hydrochloric acid relative to the PACS used was added dropwise to the reaction vessel over 60 minutes, and the reaction solution was neutralized by stirring for an additional 30 minutes. Note that the 6M hydrochloric acid had been previously bubbled with nitrogen for 1 hour before addition.

[0100] Next, the temperature of the neutralized reaction solution was raised to approximately 10-20°C, and MTBE (three times the mass of PACS) was added, stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discarded. Next, ion-exchanged water (three times the mass of PACS) was added, stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discarded. Next, MTBE (two times the mass of PACS) and ion-exchanged water (three times the mass of PACS) were added, stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discarded. Finally, ion-exchanged water (three times the mass of PACS) was added, stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discarded. This procedure was repeated twice.

[0101] The washed organic layer was transferred to another 100 L reactor, and MEK, 13 times the mass of the original PACS, was added. Distillation was carried out 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 resulting in 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 25% by mass 4-HS / MEK solution (yield: 92%).

[0102] A portion of the resulting 4-HS solution was divided into several containers and subjected to storage tests at temperatures of -15°C, -5°C, and 40°C. In the storage tests, the 4-HS and polymers in the 4-HS solution were analyzed by gel permeation chromatography (GPC) immediately after production, and after 20, 40, 90, and 180 days. The results are shown in Table 1.

[0103] [Table 1]

[0104] The 25% by mass 4-HS / MEK solution obtained in Example 1 could be stored stably for 6 months at −15° C. with almost no polymerization. Furthermore, in an accelerated test at 40° C., the formation of polymerized products was suppressed to 0.5% or less for up to 20 days.

[0105] [Example 2] A four-neck flask equipped with a thermometer, condenser, and stirrer was charged with 53.52 g of PACS and 160.5 g of methanol and sealed with nitrogen. The contents were cooled with stirring to a liquid temperature of -5°C. The reaction vessel was then depressurized and repressurized with nitrogen three times. A 3 M aqueous solution of sodium hydroxide was prepared in a separate vessel to an equimolar amount relative to PACS, and nitrogen was bubbled through this solution for 15 minutes. The nitrogen-bubbled aqueous solution was added dropwise to the reaction vessel over 70 minutes, and stirring was continued for an additional 30 minutes after addition to deprotect PACS and convert it to 4-HS.

[0106] Next, 0.97 molar equivalents of 6N hydrochloric acid relative to the PACS used was added dropwise to the reaction vessel over 45 minutes, and the reaction solution was neutralized by stirring for an additional 30 minutes. Note that the 6N hydrochloric acid had been previously bubbled with nitrogen for 1 hour before addition.

[0107] Next, the temperature of the neutralized reaction solution was raised to approximately 10-20°C, and MTBE (three times the mass of PACS) was added, stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discarded. Next, ion-exchanged water (three times the mass of PACS) was added, stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discarded. Next, MTBE (two times the mass of PACS) and ion-exchanged water (three times the mass of PACS) were added, stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discarded. Finally, ion-exchanged water (three times the mass of PACS) was added, stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discarded. This procedure was repeated twice.

[0108] The washed organic layer was transferred to another reaction vessel and MEK (13 times the mass of the original PACS) was added. The mixture was distilled under reduced pressure at 25°C or below to remove organic impurities other than 4-HS, such as MTBE and reaction by-products, as well as excess MEK, resulting in a solution with a 4-HS concentration of 50% by mass. The 4-HS solution was then passed through a polytetrafluoroethylene (PTFE) membrane filter with a pore size of 50 nm.

[0109] A portion of the resulting 4-HS solution was divided into small containers and subjected to a storage test at -15°C. In the storage test, the 4-hydroxylene and polymers in the 4-HS solution were analyzed by GPC immediately after production and after 30 days. The results are shown in Table 2.

[0110] [Table 2]

[0111] [Example 3] An experiment was carried out in the same manner as in Example 2, except that propylene glycol methyl ether acetate (hereinafter, PGMEA) was used instead of MEK as the substitution solvent, and a 25% by mass 4-HS / PGMEA solution was finally obtained.

[0112] A portion of the resulting 4-HS solution was divided into small containers and subjected to a storage test at -15°C. Immediately after production and 30 days later, the 4-HS and polymer in the 4-HS solution were analyzed by GPC. The results are shown in Table 3.

[0113] [Table 3]

[0114] [Comparative Example 1] The PACS was deprotected, neutralized, and washed with water in the same manner as in Example 2 to obtain a MTBE solution of 4-HS. This was transferred to a 1 L glass container, and the solvent was removed by vacuum distillation at 20°C or below. The resulting polymer was further dried under vacuum at 40°C for 4 hours to obtain 32 g of 4-HS crystals. The resulting 4-HS crystals were then dissolved in MEK to prepare a 25% by mass 4-HS / MEK solution.

[0115] A portion of the resulting 4-HS solution was divided into small containers and subjected to a storage test at -15°C. The 4-HS and polymers in the 4-HS solution were analyzed by GPC immediately after production, and after 4 and 7 days. The results are shown in Table 4. [Table 4]

[0116] In Comparative Example 1, the solvent substitution step was not performed, and the MTBE solvent was removed by vacuum distillation and vacuum drying. The resulting 4-HS crystals were then dissolved in MEK to obtain a solution. The generation of 4-HS polymers could not be suppressed, and the storage stability was also insufficient.

[0117] <Storage stability test of 4-hydroxystyrene solution> [Example 4] In the same manner as in Example 1, the deprotection reaction of PACS, neutralization of the reaction solution, and washing with water were carried out to obtain a MTBE solution of 4-HS.

[0118] The MTBE solution was concentrated in an evaporator until the 4-HS concentration reached 70% by mass, and then added dropwise to n-hexane at 0°C. The mixture was stirred while cooling the bottom of the container in an ice bath to crystallize 4-HS. The recovered 4-HS crystals were washed with n-hexane and then dried under reduced pressure at room temperature.

[0119] A portion of the obtained 4-HS crystals was dissolved in MEK to adjust the 4-HS concentration to 25% by mass. This was divided into several containers and a storage stability test was performed. The results are shown in Table 5.

[0120] [Example 5] to [Example 13] 4-HS crystals were synthesized in the same manner as in Example 4, and 4-HS solutions were prepared in the solvents and at the concentrations shown in Table 5. Storage stability tests were performed at storage temperatures of -5°C, 15°C, or 40°C. The results are shown in Table 5.

[0121] [Table 5]

[0122] <Method of producing 4-hydroxystyrene polymer> [Example 14] Preparation of 4-HS / MCpMA copolymer A monomer solution was prepared by mixing 80.0 g of the 25% by mass 4-HS / MEK solution obtained in Example 1 (in GPC analysis, the chromatogram area of ​​4-HS was 99.9% when the total chromatogram area of ​​components other than MEK was set to 100), 45.6 g of MCpMA, 8.4 g of dimethyl 2,2-azobisisobutyrate, and 13.0 g of MEK in a container.

[0123] A 500 mL four-neck glass flask reaction vessel equipped with a stirrer, condenser, and thermometer was charged with 52.7 g of MEK, and after creating a nitrogen atmosphere, the temperature was raised to 79°C. The monomer solution was added dropwise at a constant rate over 4 hours, and the reaction was continued for another 2 hours. The temperature during the polymerization reaction was controlled at 79.0 to 80.5°C, and after completion of the polymerization, the vessel was cooled to room temperature.

[0124] The polymerization solution was mixed with 460 g of n-hexane and stirred to precipitate the polymer. After standing, the polymer was separated by decantation. The polymer was redissolved in a mixture containing 40 g of acetone and 30 g of 2-propanol, to which 460 g of n-hexane was added and stirred to precipitate the polymer. This procedure of separating the polymer by decantation was repeated four times. The recovered polymer was dissolved in 140 g of ethyl acetate. A portion of the polymer solution was sampled and dried under reduced pressure at 40°C to obtain a polymer powder, which was subjected to NMR analysis. NMR analysis revealed that the monomer composition (molar ratio) of the polymer was 4-HS:MCpMA = 41.0:59.0.

[0125] The remaining polymer solution was washed with a 1% by weight aqueous solution of oxalic acid using a separatory funnel, followed by five washes with pure water. The washed polymer solution was distilled under reduced pressure at a heat source temperature of 45°C while adding PGMEA while distilling off ethyl acetate, ultimately yielding a PGMEA solution of 4-HS / MCpMA copolymer with a polymer concentration of 15% by weight. Analysis of the resulting polymer solution by GPC and LC revealed a Mw of 5800, Mw / Mn of 1.40, and a residual low-molecular-weight component of less than 200 Mw of 0.01% (LC area %).

[0126] [Example 15] Preparation of 4-HS / MCpMA copolymer The procedure was the same as in Example 14, except that the volume of the reaction vessel used in the polymerization reaction was changed to 2 L and the amounts of the monomer, solvent, reagents, etc. used were changed to four times those in Example 14.

[0127] The analysis results of the obtained polymer were 4-HS:MCpMA=40.3:59.7, Mw=5810, Mw / Mn=1.39, and the residual low molecular weight component of Mw less than 200=0.00% (LC area %).

[0128] [Example 16] Preparation of 4-HS / MCpMA copolymer The procedure was the same as in Example 14, except that the volume of the reaction vessel used in the polymerization reaction was changed to 10 L and the amounts of the monomers, solvents, reagents, etc. used were changed to 25 times those in Example 14.

[0129] The analysis results of the obtained polymer were 4-HS:MCpMA=40.5 / 59.5, Mw=5,800, Mw / Mn=1.40, and the residual low molecular weight component of less than Mw 200=0.00% (LC area %).

[0130] The results of Examples 15 and 16 show that this method can produce polymers with good reproducibility of properties even when the production scale is changed significantly.

[0131] [Example 17] Preparation of 4-HS / ECpMA copolymer A monomer solution was prepared by mixing 400.0 g of a 25.9 mass % 4-HS / MEK solution (in GPC analysis, the chromatogram area of ​​4-HS was 100.0% when the total chromatogram area of ​​components other than MEK was set to 100) produced by the same procedure as in Example 1, 280.6 g of ECpMA, 29.6 g of dimethyl 2,2-azobisisobutyrate, and 86.0 g of MEK.

[0132] A 2L glass four-neck flask reaction vessel equipped with a stirrer, condenser, and thermometer was charged with 302 g of MEK, and after creating a nitrogen atmosphere, the temperature was raised to 79°C. The monomer solution was added dropwise at a constant rate over 4 hours, and the reaction was continued for another 2 hours. The temperature during the polymerization reaction was controlled at 79.0 to 80.5°C, and after completion of the polymerization, the vessel was cooled to room temperature.

[0133] 1000 g of the polymerization solution was mixed with a mixed solution of 2300 g of n-hexane and 100 g of methanol, stirred to precipitate the polymer, and then allowed to stand. The polymer was then separated by decantation. The polymer was redissolved in a mixed solution of 200 g of acetone and 100 g of methanol, to which 2000 g of n-hexane was added and stirred to precipitate the polymer. This procedure of separating the polymer by decantation was repeated four times. The recovered polymer was dissolved in 400 g of acetone. A portion of the polymer solution was sampled and dried under reduced pressure at 40 °C to obtain a polymer powder, which was then subjected to NMR analysis. NMR analysis revealed that the monomer composition (molar ratio) of the polymer was 4-HS:ECpMA = 39.5:60.5.

[0134] The remaining polymer solution was distilled under reduced pressure at a heat source temperature of 45°C while adding PGMEA and distilling off acetone, and the solvent was replaced with PGMEA to finally obtain a PGMEA solution of 4-HS / ECpMA copolymer with a polymer concentration of 20% by mass. The obtained polymer solution was analyzed by GPC and LC, and the results were Mw = 7430, Mw / Mn = 1.46, and the residual low-molecular-weight component with Mw less than 200 = 0.01% (LC area %).

[0135] [Example 18] Preparation of 4-HS / ECpMA copolymer A 100-liter glass-lined reactor equipped with a stirrer, a heat medium circulation jacket, a vacuum line, a nitrogen line, and a cooler was used as the reactor for the polymerization reaction. Polymerization, purification, and solvent substitution were carried out in the same manner as in Example 17, except that the amounts of monomers, solvents, reagents, and the like used were changed to 55 times the amounts used in Example 17.

[0136] The analysis results of the obtained polymer were 4-HS:ECpMA=39.8:60.2, Mw=7450, Mw / Mn=1.46, and the residual low molecular weight component of Mw less than 200=0.01% (LC area %).

[0137] Furthermore, the metal content of the PGMEA solution of the 4-HS / ECpMA copolymer with a polymer concentration of 20% by mass obtained in Example 18 was determined by ICP mass spectrometry to be 8 ppb for Na and less than 1.0 ppb for all other elements based on the polymer weight.

[0138] The results of Examples 17 and 18 demonstrate that this method can produce polymers with good reproducibility of polymer properties and with extremely low levels of low-molecular-weight impurities and metal impurities, even on a commercial scale.

[0139] Comparative Example 2: Preparation of 4-HS / MCpMA copolymer The same procedure as in Example 15 was carried out except that a 25% by mass 4-HS / MEK solution (in GPC analysis, the chromatogram area of ​​4-HS was 97.3% when the total chromatogram area of ​​components other than MEK was taken as 100) was used.

[0140] The analytical results of the obtained polymer were 4-HS:MCpMA=40.4:59.6, Mw=5860, Mw / Mn=1.40, and the residual low molecular weight component of Mw less than 200=0.00% (LC area %). These physical properties were almost the same as those of the polymer obtained in Example 15.

[0141] [Evaluation of insoluble or poorly soluble components] To compare the insoluble or poorly soluble components contained in the PGMEA solutions of 4-HS / MCpMA copolymer obtained in Example 15 and Comparative Example 2, test solutions were prepared and the change in turbidity of the test solutions was measured in real time as a poor solvent was added to the test solutions. The detailed test method is described below.

[0142] The test liquids were prepared by further diluting the polymer solutions obtained in Example 15 and Comparative Example 2 with PGMEA to adjust the polymer concentration to 10.0% by mass.

[0143] Turbidity measurements were performed using a non-contact turbidity meter for orbital shaking culture (OD-Monitor A&S manufactured by Taitec, attached to the shaker NR-2). 100.0 g of test solution was placed in a glass Erlenmeyer flask, and the opening of the Erlenmeyer flask was sealed with a stopper equipped with a tube for dripping the poor solvent to prevent evaporation of the solvent. The zero point of the turbidity meter was corrected while the Erlenmeyer flask containing the test solution was being orbitally shaken. While the Erlenmeyer flask was being orbitally shaken, n-hexane, a poor solvent, was dripped at a rate of 0.3 g / min, and the weight change and turbidity change of the test solution during this time were measured. The measured value OD (optical density; OD = common logarithm of the transmittance of transmitted light) of the turbidity meter used here was calculated by calculating the amount of infrared light (950 nm) transmitted to the OD of E. coli. 600 The values ​​are expressed in terms of the amount of n-hexane added. The dropping of n-hexane was continued until the turbidity reached 0.50 OD. In the test solution with a turbidity of 0.50 OD, slight turbidity was visually observed in the solution, but no polymer precipitation was observed. The measurement was carried out three times, and the average values ​​of the amount of n-hexane added until the turbidity reached 0.10 OD, 0.15 OD, 0.20 OD, 0.30 OD, and 0.50 OD are summarized in Table 1.

[0144] [Table 6]

[0145] The experimental results showed no difference between the two at turbidity levels of 0.30 OD or higher, but a difference was observed in the amount of n-hexane added dropwise between 0.10 OD and 0.20 OD, i.e., to produce very slight turbidity, with a larger amount of n-hexane added in Example 15. The copolymer of Example 15 is substantially the same as the copolymer of Comparative Example 2 in physical properties such as monomer composition ratio, Mw, Mw / Mn, and amount of residual low-molecular-weight components, but can be evaluated as having a smaller amount of insoluble or poorly soluble components that can cause development defects.

[0146] [Example 19] Preparation of 4-HS / MCpMA / GBLMA copolymer A monomer solution was prepared by mixing 48.3 g of the 25% by mass 4-HS / MEK solution obtained in Example 1 (in GPC analysis, the chromatogram area of ​​4-HS was 99.9% when the total chromatogram area of ​​components other than MEK was set to 100), 55.5 g of MCpMA, 28.6 g of GBLMA, 6.9 g of dimethyl 2,2-azobisisobutyrate, and 61.2 g of MEK.

[0147] 74.8 g of MEK was placed in a 500 mL four-neck glass flask reaction vessel equipped with a stirrer, condenser, and thermometer, and after creating a nitrogen atmosphere, the vessel was heated to 79°C. The monomer solution was added dropwise at a constant rate over 4 hours, and the reaction was continued for another 2 hours. The temperature during the polymerization reaction was controlled at 79.0 to 80.5°C, and after completion of the polymerization, the vessel was cooled to room temperature.

[0148] 275 g of the polymerization solution was mixed with 620 g of n-hexane and 67 g of methanol, stirred to precipitate the polymer, allowed to stand, and then separated by decantation. The polymer was redissolved in a mixture containing 67 g of MEK and 67 g of methanol, to which 540 g of n-hexane was added and stirred to precipitate the polymer, and the polymer was separated by decantation. This procedure was repeated twice.

[0149] The recovered polymer was dissolved in 270 g of ethyl acetate. A portion of the polymer solution was sampled and dried under reduced pressure at 40°C to obtain a polymer powder, which was subjected to NMR analysis. The monomer composition ratio (molar ratio) of the polymer according to NMR analysis was 4-HS:MCpMA:GBLMA = 18.8:51.8:29.4.

[0150] The remaining polymer solution was washed with a 1% by weight aqueous solution of oxalic acid using a separatory funnel, followed by five washes with pure water. The washed polymer solution was distilled at 45°C under reduced pressure while adding PGMEA while distilling off ethyl acetate, ultimately yielding a PGMEA solution of 4-HS / MCpMA / GBLMA copolymer with a polymer concentration of 20% by weight. Analysis of the resulting polymer solution by GPC and LC revealed Mw = 9720, Mw / Mn = 1.59, and residual low-molecular-weight components less than Mw 200 = 0.01% (LC area %).

[0151] [Example 20] Preparation of 4-HS / MCpMA / NLM copolymer A monomer solution was prepared by adding 52.8 g of the 25% by mass 4-HS / MEK solution obtained in Example 1 (in GPC analysis, the chromatogram area of ​​4-HS was 99.9% when the total chromatogram area of ​​components other than MEK was set to 100), 66.7 g of MCpMA, 24.5 g of NLM, 18.4 g of dimethyl 2,2-azobisisobutyrate, and 61.7 g of MEK to a container and mixing them.

[0152] 75.4 g of MEK was placed in a 500 mL four-neck glass flask reaction vessel equipped with a stirrer, condenser, and thermometer, and after creating a nitrogen atmosphere, the vessel was heated to 79°C. The monomer solution was added dropwise at a constant rate over 4 hours, and the reaction was continued for another 2 hours. The temperature during the polymerization reaction was controlled between 79.0 and 80.5°C, and after completion of the polymerization, the vessel was cooled to room temperature.

[0153] The polymerization solution was mixed with 690 g of n-hexane and stirred to precipitate the polymer, and after standing, the polymer was separated by decantation. The polymer was redissolved in a mixed solvent of 120 g of MEK and 45 g of methanol, to which 690 g of n-hexane was added and stirred to precipitate the polymer, and the polymer was separated by decantation. This procedure was repeated four times.

[0154] The recovered polymer was dissolved in 450 g of ethyl acetate. A portion of the polymer solution was sampled and dried under reduced pressure at 40°C to obtain a polymer powder, which was subjected to NMR analysis. The monomer composition ratio (molar ratio) of the polymer according to NMR analysis was 4-HS:MCpMA:NLM = 20.2:59.4:20.4.

[0155] The remaining polymer solution was washed with a 1% by weight aqueous solution of oxalic acid using a separatory funnel, followed by five washes with pure water. The washed polymer solution was distilled at 45°C under reduced pressure while adding PGMEA while distilling off ethyl acetate, ultimately yielding a PGMEA solution of 4-HS / MCpMA / NLM copolymer with a polymer concentration of 15% by weight. Analysis of the resulting polymer solution by GPC and LC revealed a Mw of 5240, Mw / Mn of 1.39, and 0.00% (LC area %) of residual low-molecular-weight components less than Mw 200.

[0156] [Example 21] Preparation of 4-HS / TBMA copolymer A monomer solution was prepared by adding 200.0 g of the 25% by mass 4-HS / MEK solution obtained in Example 1 (in GPC analysis, the chromatogram area of ​​4-HS was 99.9% when the total chromatogram area of ​​components other than MEK was set to 100), 81.8 g of TBMA, 16.8 g of dimethyl 2,2-azobisisobutyrate, and 17.0 g of MEK to a container and mixing them.

[0157] A 1000 mL four-neck glass flask reaction vessel equipped with a stirrer, condenser, and thermometer was charged with 105.1 g of MEK, and after creating a nitrogen atmosphere, the temperature was raised to 79°C. The monomer solution was added dropwise at a constant rate over 4 hours, and the reaction was continued for another 2 hours. The temperature during the polymerization reaction was controlled at 79.0 to 80.5°C, and after completion of the polymerization, the vessel was cooled to room temperature.

[0158] The polymerization solution was mixed with 880 g of n-hexane and 20 g of methanol, stirred to precipitate the polymer, allowed to stand, and then separated by decantation. The polymer was redissolved in a mixture containing 176 g of acetone and 12 g of methanol, to which 800 g of n-hexane was added and stirred to precipitate the polymer, and the polymer was separated by decantation. This procedure was repeated four times.

[0159] The recovered polymer was dissolved in 180 g of acetone. A portion of the polymer solution was sampled and dried under reduced pressure at 40°C to obtain a polymer powder, which was subjected to NMR analysis. The monomer composition ratio (molar ratio) of the polymer according to NMR analysis was 4-HS:TBMA = 42.4:57.6.

[0160] The washed polymer solution was distilled at 45°C under reduced pressure while adding PGMEA and distilling off acetone, finally obtaining a PGMEA solution of 4-HS / TBMA copolymer with a polymer concentration of 20% by mass. The obtained polymer solution was analyzed by GPC and LC, and the results were Mw = 6,090, Mw / Mn = 1.44, and the residual low molecular weight component of Mw less than 200 = 0.00% (LC area %).

[0161] [Example 22] Preparation of 4-HS / TBMA copolymer A glass container was charged with 589 g of a 25% by mass 4-HS / MEK solution (in GPC analysis, the chromatogram area of ​​4-HS was 99.8% when the total chromatogram area of ​​components other than MEK was taken as 100), 267 g of TBMA, 55 g of dimethyl 2,2′-azobis(2-methylpropionate), and 84 g of MEK, and dissolved to prepare a dropping solution.

[0162] 325 g of MEK was fed to another 2 L glass vessel and heated to 79°C with stirring. The above-mentioned dripping solution was added dropwise to the vessel over 4 hours, and the reaction was continued for another 2 hours, after which the vessel was cooled to room temperature. A hexane mixture containing 2% by mass of methanol was added to the polymerization solution to precipitate a polymer, followed by stirring, and then the polymer was separated by decantation. The polymer was redissolved in an acetone mixture containing 7% by mass of methanol, and hexane was added to the mixture to precipitate the polymer, followed by stirring, and the polymer was separated by decantation. This procedure was repeated four times.

[0163] The polymer was redissolved in acetone, PGMEA was added, and the mixture was distilled under reduced pressure to finally obtain 1580 g of a PGMEA solution containing 20% ​​by mass of the polymer. 13 C-NMR analysis revealed that the composition ratio of the resulting copolymer was 4-HS / TBMA=38.8 / 61.2.

[0164] [Example 23] Preparation of 4-HS / ECpMA copolymer A monomer solution was prepared by adding 83.6 g of the 25% by mass 4-HS / PGMEA solution obtained in Example 3 (in GPC analysis, the chromatogram area of ​​4-HS was 99.9% when the total chromatogram area of ​​components other than PGMEA was set to 100), 46.2 g of ECpMA, 11.4 g of dimethyl 2,2-azobisisobutyrate, and 15.4 g of PGMEA to a container and mixing them.

[0165] A 500 mL four-neck glass flask reaction vessel equipped with a stirrer, condenser, and thermometer was charged with 67.1 g of PGMEA, and after creating a nitrogen atmosphere, the temperature was raised to 79°C. The monomer solution was added dropwise at a constant rate over 4 hours, and the reaction was continued for another 2 hours. The temperature during the polymerization reaction was controlled between 79.0 and 80.5°C, and after completion of the polymerization, the vessel was cooled to room temperature.

[0166] 200 g of the polymerization solution was mixed with a mixed solution of 460 g of n-hexane and 20 g of methanol, stirred to precipitate the polymer, allowed to stand, and then separated by decantation. The polymer was redissolved in a mixed solution of 40 g of acetone and 20 g of methanol, to which 400 g of n-hexane was added and stirred to precipitate the polymer, and the polymer was separated by decantation. This procedure was repeated four times.

[0167] The recovered polymer was dissolved in 80 g of acetone. A portion of the polymer solution was sampled and dried under reduced pressure at 40°C to obtain a polymer powder, which was subjected to NMR analysis. The monomer composition ratio (molar ratio) of the polymer according to NMR analysis was 4-HS:ECpMA = 42.6:57.4.

[0168] The remaining polymer solution was distilled under reduced pressure at a heat source temperature of 45°C while adding PGMEA and distilling off acetone, replacing the solvent with PGMEA. Finally, a PGMEA solution of 4-HS / ECpMA copolymer with a polymer concentration of 20% by mass was obtained. Analysis of the resulting polymer solution by GPC and LC revealed that Mw = 5810, Mw / Mn = 1.47, and the residual low-molecular-weight component with Mw less than 200 was 0.01% (LC area %). [Industrial Applicability]

[0169] The highly pure and storage-stable 4-hydroxystyrene solution of the present invention can be used as a raw material for resist polymers for EUV lithography and electron beam lithography. Furthermore, by using the solution, 4-hydroxystyrene-based polymers suitable for resists for EUV lithography and electron beam lithography can be produced on a commercial scale by a simple process that does not require a deprotection step.

Claims

1. A method for producing a polymer having structural units derived from 4-hydroxystyrene, comprising: A process for producing a 4-hydroxystyrene solution containing no polymerization inhibitor and having a concentration of 10 to 70 mass %, comprising the following steps (i) to (iv): (i) a deprotection step in which 4-acetoxystyrene is contacted with a base in a solvent to produce 4-hydroxystyrene; (ii) a neutralization step of adding an acid to a solution containing the deprotected 4-hydroxystyrene to neutralize it; (iii) washing the solution containing 4-hydroxystyrene after neutralization with water; (iv) a solvent substitution step in which a solvent capable of dissolving 4-hydroxystyrene is added to a solution containing 4-hydroxystyrene, and the resulting mixture is distilled at 40°C or less to remove components other than 4-hydroxystyrene and excess solvent, thereby achieving a 4-hydroxystyrene concentration of 10 to 70% by mass, wherein the dissolving solvent is any type of organic solvent selected from the group consisting of alcohols, ketones, ethers, glycol ethers, glycol ether esters, and esters; a process for producing a 4-hydroxystyrene solution, comprising: a step of polymerizing the 4-hydroxystyrene solution obtained in the step of producing the 4-hydroxystyrene solution as a polymerization raw material, either alone or with a monomer copolymerizable with 4-hydroxystyrene; A method for producing a polymer having structural units derived from 4-hydroxystyrene, comprising:

2. 2. The method for producing a polymer having structural units derived from 4-hydroxystyrene according to claim 1, wherein the steps (i) to (iv) are carried out in the absence of a polymerization inhibitor.

3. 3. The method for producing a polymer having a structural unit derived from 4-hydroxystyrene according to claim 1 or 2, wherein the base used in the deprotection step is a base from which dissolved oxygen has been removed by bubbling with an inert gas before use, and the deprotection step is carried out under a nitrogen atmosphere.

4. The method for producing a polymer having a structural unit derived from 4-hydroxystyrene according to any one of claims 1 to 3, wherein the acid used in the neutralization step has been subjected to bubbling with an inert gas to remove dissolved oxygen before use.

5. The method for producing a polymer having a structural unit derived from 4-hydroxystyrene according to any one of claims 1 to 4, wherein the base used in the deprotection step is selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, potassium tert-butoxide, trimethylamine, triethylamine, ethanolamine, diazabicycloundecene, diazabicyclononene, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,1,3,3-tetramethylguanidine, and tetramethylammonium hydroxide.

6. The method for producing a polymer having structural units derived from 4-hydroxystyrene according to any one of claims 1 to 5, wherein the organic solvent used in the solvent substitution step is any one organic solvent selected from the group consisting of methanol, ethanol, propanol, butanol, octanol, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, ethyl acetate, and ethyl lactate.

7. The method for producing a polymer having structural units derived from 4-hydroxystyrene according to any one of claims 1 to 6, further comprising a step of passing the 4-hydroxystyrene solution through a filter having a nominal pore size of 1 micron or less before and / or after the solvent substitution step.

8. A method for producing a polymer having structural units derived from 4-hydroxystyrene, comprising: The method includes a step of polymerizing a 4-hydroxystyrene solution as a polymerization raw material, either alone or with a monomer copolymerizable with 4-hydroxystyrene, The 4-hydroxystyrene solution does not contain a polymerization inhibitor, has a 4-hydroxystyrene concentration of 10 to 70% by mass, and in gel permeation chromatography analysis, when the total area of ​​a chromatogram of components other than the organic solvent is taken as 100, the chromatogram area of ​​4-hydroxystyrene is 99.9% or more, and the chromatogram area of ​​4-hydroxystyrene polymers relative to the chromatogram area of ​​4-hydroxystyrene is 0.1% or less.

9. 9. The method for producing a polymer having structural units derived from 4-hydroxystyrene according to claim 8, wherein the organic solvent contained in the 4-hydroxystyrene solution is any one organic solvent selected from the group consisting of methanol, ethanol, propanol, butanol, octanol, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, ethyl acetate, and ethyl lactate.

10. The method for producing a polymer having a structural unit derived from 4-hydroxystyrene according to claim 8 or 9, wherein the other copolymerizable monomer includes a monomer having an acid-dissociable group.

Images