High-purity o- / m-hydroxystyrene solution, method for preparing same, and method for producing o- / m-hydroxystyrene-based polymer

Abstract

[Problem] To provide: an o- / m-hydroxystyrene solution that is desirable as a raw material for the commercial-scale production of an o- / m-hydroxystyrene-based polymer and has a high purity and good storage stability; and a method for efficiently preparing same. [Solution] This method for preparing an o- / m-hydroxystyrene solution comprises the following steps (i) to (iv): (i) a deprotection step for bringing o- / m-acetoxystyrene into contact with a base in a solvent to generate o- / m-hydroxystyrene; (ii) a neutralization step for adding an acid to a deprotected o- / m-hydroxystyrene-containing solution to neutralize the solution; (iii) a step for washing the neutralized o- / m-hydroxystyrene-containing solution with water; and (iv) a solvent substitution step for adding a solvent, which can dissolves o- / m-hydroxystyrene, to the o- / m-hydroxystyrene-containing solution and distilling the solution at 40°C or lower to distill off an excess solvent and components other than o- / m-hydroxystyrene.

Description

High-purity o- / m-hydroxystyrene solution, method for producing same, and method for producing o- / m-hydroxystyrene polymer

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

[0002] While p-hydroxystyrene has traditionally been widely used as a resist polymer, its isomers, o- and m-hydroxystyrene, are also attracting attention as raw materials for resist polymers for cutting-edge EUV lithography. Like p-hydroxystyrene, o-hydroxystyrene and m-hydroxystyrene have long been known, but they are extremely unstable compounds that undergo polymerization during storage at room temperature, making it difficult to mass-produce and store them as raw materials for industrial polymer production. Patent Document 1 describes a method for stabilizing the storage of p-hydroxystyrene, but no stable storage methods for o-hydroxystyrene and m-hydroxystyrene have yet been reported.

[0003] As a method for producing a p-hydroxystyrene-based polymer, there is known a method in which, instead of p-hydroxystyrene, a monomer in which the hydroxy group of p-hydroxystyrene is protected, such as p-acetoxystyrene, is polymerized as a raw material, and then the protecting group is removed by the action of an acid or a base to produce a hydroxy group (Patent Documents 2 and 3).

[0004] International Publication No. 2021 / 256551 JP 02-047109 JP 63-023902

[0005] Following this example, when an o- / m-hydroxystyrene-based polymer was produced by polymerizing o- / m-acetoxystyrene or the like with other monomers as a raw material and then removing the acetyl group by the action of an acid or base, the deprotection reaction of the o- / m-acetoxystyrene unit in the polymer unexpectedly proceeded more slowly than that of the p-acetoxystyrene unit, and it could not be said to be an efficient method. Furthermore, in the production of a polymer containing a monomer unit having a lactone structure, which is often used in polymers as resist polymers to improve substrate adhesion, the lactone structure decomposed during the deprotection reaction of the acetyl group.

[0006] The present invention provides a highly pure o- / m-hydroxystyrene solution with excellent storage stability suitable as a raw material for commercial-scale production of an o- / m-hydroxystyrene polymer, and an efficient method for producing the same. The present invention also provides a method for efficiently producing an o- / m-hydroxystyrene polymer suitable for resists for cutting-edge lithography, particularly an o- / m-hydroxystyrene polymer containing both a unit that decomposes under the action of an acid and a unit that decomposes under the action of a base, by a simple process that does not require a deprotection step and that enables efficient commercial-scale production.

[0007] As a result of extensive research to achieve the above-mentioned object, the present inventors have found that an o- / m-hydroxystyrene solution having an o- / m-hydroxystyrene concentration of 10 to 70% and an o- / m-hydroxystyrene polymer content relative to the o- / m-hydroxystyrene of 0.5% or less can be stably stored over an extended period of time while suppressing the formation of polymerization products. Furthermore, the present inventors have found that, in producing the o- / m-hydroxystyrene solution, o- / m-acetoxystyrene is used as a starting material, o- / m-hydroxystyrene is produced by a base-catalyzed deprotection reaction, neutralization is performed, and then a solvent capable of dissolving o- / m-hydroxystyrene is added to the solution containing o- / m-hydroxystyrene, and the mixture is subjected to reduced-pressure distillation at 40°C or less to distill off components other than o- / m-hydroxystyrene and the solvent, as well as excess solvent, thereby performing solvent replacement without crystallizing o- / m-hydroxystyrene, thereby enabling efficient production of a high-purity, storage-stable o- / m-hydroxystyrene solution on a commercial scale. The present inventors also found that by carrying out polymerization using the o- / m-hydroxystyrene solution, it is possible to produce a polymer having structural units derived from o- / m-hydroxystyrene, in which the inclusion of insoluble components and metal impurities is highly suppressed, particularly a polymer containing an o- / m-hydroxystyrene unit together with a unit that decomposes under the action of an acid or a unit that decomposes under the action of a base, and this finding led to the completion of the present invention.

[0008] That is, the present invention provides the following inventions. [1] A method for producing an o- / m-hydroxystyrene solution, comprising the following steps (i) to (iv): (i) a deprotection step of contacting o- / m-acetoxystyrene with a base in a solvent to produce o- / m-hydroxystyrene, (ii) a neutralization step of adding an acid to a solution containing the deprotected o- / m-hydroxystyrene to neutralize it, (iii) a step of washing the neutralized solution containing o- / m-hydroxystyrene with water, and (iv) a solvent replacement step of adding a solvent capable of dissolving o- / m-hydroxystyrene to the solution containing o- / m-hydroxystyrene and distilling the mixture at 40°C or less to remove components other than o- / m-hydroxystyrene and excess solvent. [2] A method for producing an o- / m-hydroxystyrene solution according to [1], wherein the base used in the deprotection step has been bubbling with an inert gas to remove dissolved oxygen before use, and the deprotection step is carried out under a nitrogen atmosphere. [3] The method for producing an o- / m-hydroxystyrene solution according to [1] or [2], wherein the acid used in the neutralization step has been subjected to bubbling with an inert gas to remove dissolved oxygen before use. [4] The method for producing an o- / m-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 an o- / m-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] A method for producing an o- / m-hydroxystyrene solution according to any one of [1] to [5], wherein the solvent substitution step is carried out to achieve an o- / m-hydroxystyrene concentration of 10% by mass or more and 70% by mass or less. [7] A method for producing an o- / m-hydroxystyrene solution according to any one of [1] to [6], further comprising a step of passing the o- / m-hydroxystyrene solution through a filter having a nominal pore size of 1 micron or less before and / or after the solvent substitution step. [8] An o- / m-hydroxystyrene solution having an o- / m-hydroxystyrene concentration of 10% by mass or more and 70% by mass or less, wherein, in gel permeation chromatography analysis of the solution, the chromatogram area of ​​o- / m-hydroxystyrene accounts for 99.5% or more of the total area of ​​chromatograms of components other than the organic solvent, taken as 100. [9] The o- / m-hydroxystyrene solution according to [8], wherein, in a gel permeation chromatography analysis of the solution, the chromatogram area of ​​the o- / m-hydroxystyrene polymer is 0.5% or less relative to the chromatogram area of ​​the o- / m-hydroxystyrene.

[10] An o- / m-hydroxystyrene solution having an o- / m-hydroxystyrene concentration of 10% by mass or more and 70% by mass or less, 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 ​​the o- / m-hydroxystyrene is 99.7% or more.

[11] An o- / m-hydroxystyrene solution having an o- / m-hydroxystyrene concentration of 10% by mass or more and 70% by mass or less, wherein, in a gel permeation chromatography analysis of the solution, the chromatogram area of ​​o- / m-hydroxystyrene is 99.9% or more when the total area of ​​the chromatograms of components other than the organic solvent is set to 100.

[12] The o- / m-hydroxystyrene solution according to any 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 o- / m-hydroxystyrene solution according to any one of [8] to

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

[14] A method for producing a polymer having structural units derived from o- / m-hydroxystyrene, comprising polymerizing the o- / m-hydroxystyrene solution according to any one of [8] to

[13] as a polymerization raw material, either alone or with another monomer copolymerizable therewith.

[15] A method for producing a polymer having structural units derived from o- / m-hydroxystyrene according to

[14] , wherein the other monomer copolymerizable with o- / m-hydroxystyrene comprises a monomer having an acid-dissociable group.

[16] A method for producing a polymer having structural units derived from o- / m-hydroxystyrene according to

[14] , wherein the other monomer copolymerizable with o- / m-hydroxystyrene comprises a monomer having an acid-dissociable group and at least one selected from the group consisting of a monomer having a lactone structure, a monomer having a sultone structure, and a monomer having a cyclic carbonate structure.

[17] A method for producing a polymer having structural units derived from o- / m-hydroxystyrene, comprising polymerizing an o- / m-hydroxystyrene solution produced by the method of any one of [1] to [7] as a polymerization raw material, either alone or with another monomer copolymerizable with o- / m-hydroxystyrene.

[18] A method for producing a polymer having structural units derived from o- / m-hydroxystyrene, comprising the steps of: producing an o- / m-hydroxystyrene solution by the method of any one of [1] to [7]; and polymerizing the o- / m-hydroxystyrene solution produced in the above step as a polymerization raw material, either alone or with another monomer copolymerizable with o- / m-hydroxystyrene.

[19] A method for producing a polymer having structural units derived from o- / m-hydroxystyrene according to any one of

[14] to

[18] , which is applicable to polymerization using a polymerization vessel with a capacity of 30 L or more.

[20] A polymer comprising a structural unit derived from o- / m-hydroxystyrene, a structural unit having an acid-dissociable group, and a structural unit having at least one structure selected from the group consisting of lactone, sultone, and cyclic carbonate, wherein the polymer does not contain a structural unit resulting from decomposition of the lactone, sultone, or cyclic carbonate.

[0009] According to the present invention, a highly pure o- / m-hydroxystyrene solution having excellent storage stability can be produced simply and efficiently on a commercial scale. Furthermore, an o- / m-hydroxystyrene-based polymer suitable for resists for cutting-edge lithography can be produced efficiently on a commercial scale by a simple process that does not require a deprotection step. In the present invention, the efficient production of an o- / m-hydroxystyrene solution and an o- / m-hydroxystyrene-based polymer can reduce production costs.

[0010] The process for producing an o- / m-hydroxystyrene solution, the process for producing an o- / m-hydroxystyrene solution, and the process for producing an o- / m-hydroxystyrene-based polymer of the present invention will be described in detail below.

[0011] <Method for Producing an o- / m-Hydroxystyrene Solution> (i) Deprotection Step The deprotection step is a step in which o- / m-acetoxystyrene is contacted with a base in a solvent to eliminate the acetyl group and produce o- / m-hydroxystyrene.

[0012] 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.

[0013] The amount of the base used is preferably 0.1 to 10.0 molar equivalents, more preferably 0.5 to 3.0 molar equivalents, relative to o- / m-acetoxystyrene. If the amount of the base used is within the above range, a sufficient reaction rate is likely to be obtained.

[0014] 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.

[0015] 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 o- / m-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; 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 o- / m-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.

[0016] The reaction temperature for the deprotection reaction is usually from -20 to 50°C, preferably from -10 to 20°C, more preferably from -5 to 10°C, from the viewpoint of inhibiting the polymerization reaction.

[0017] The reaction time is not particularly limited as long as it is long enough for the o- / m-acetoxystyrene to be completely converted into o- / m-hydroxystyrene. １ This can be confirmed by analyzing the product by methods such as H-NMR, gas chromatography, gel permeation chromatography, etc. The deprotection reaction of o- / m-acetoxystyrene is preferably carried out in an inert gas atmosphere such as nitrogen.

[0018] (ii) Neutralization Step The neutralization step is a step in which an acid is added to the base catalyst remaining in the reaction solution after the deprotection reaction to neutralize it. 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. It is preferable to dilute the acid used for neutralization with a solvent as needed and bubble the acid with an inert gas such as nitrogen gas beforehand. This has the effect of suppressing the formation of o- / m-hydroxystyrene polymers.

[0019] (iii) Water-washing step: The water-washing step is a step of washing the solution containing o- / m-hydroxystyrene after neutralization. The solution containing o- / m-hydroxystyrene is preferably extracted into an organic solvent that can dissolve o- / m-hydroxystyrene and is separable from water, and then washed with deionized water to remove impurities such as by-products and salts.

[0020] The solvent used to extract o- / m-hydroxystyrene may be any solvent that dissolves o- / m-hydroxystyrene and is separable from water, and more preferably has the same boiling point as or a lower boiling point than 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.

[0021] 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.

[0022] 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.

[0023] The water used to wash the resulting o- / m-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., the amount of waste liquid, etc.

[0024] 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.

[0025] (iv) Solvent Replacement Step The solvent replacement step is a step in which the o- / m-hydroxystyrene extract is replaced with the desired solvent. That is, a replacement solvent capable of dissolving o- / m-hydroxystyrene is added to the o- / m-hydroxystyrene extract, and the mixture is distilled to remove reaction by-products, components other than o- / m-hydroxystyrene, such as the extraction solvent, and excess replacement solvent. By performing solvent replacement without crystallization to obtain an o- / m-hydroxystyrene solution, rather than crystallizing o- / m-hydroxystyrene using a conventional crystallization method and then dissolving it in a solvent, the formation of o- / m-hydroxystyrene polymers can be suppressed.

[0026] The substitution solvent may be added to the o- / m-hydroxystyrene extract before or after the start of distillation, or preferably added as needed during the distillation. When the concentration of the o- / m-hydroxystyrene extract is high, it is preferable to add the substitution solvent before distillation in order to suppress polymerization of o- / m-hydroxystyrene.

[0027] 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 suppressing polymerization of o- / m-hydroxystyrene.

[0028] 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 o- / m-hydroxystyrene, such as reaction by-products and the extraction solvent, as well as excess substitution solvent. The pressure of the reduced pressure distillation is, for example, 1 to 100 kPa, and preferably 1 to 30 kPa.

[0029] The type of solvent to be substituted is not particularly limited as long as it can dissolve o- / m-hydroxystyrene. When the resulting o- / m-hydroxystyrene solution is used as a polymerization raw material in producing a polymer, a solvent that can be used as a polymerization solvent is more preferable. Specific examples of the solvent 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, and acetonitrile. 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.

[0030] 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 o- / m-hydroxystyrene.

[0031] (v) Filtration The o- / m-hydroxystyrene solution is preferably filtered through a fine filter to remove insoluble matters such as polymers generated in small amounts during the production process. Filtration through a filter may be carried out before, after, or both before and after the solvent replacement.

[0032] 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 materials for membrane filters, hollow fiber membrane filters, and pleated membrane filters are preferably 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 o- / m-hydroxystyrene.

[0033] 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.

[0034] (vi) Storage of o- / m-hydroxystyrene solution The temperature at which the produced o- / m-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.

[0035] <o- / m-Hydroxystyrene Solution> The o- / m-hydroxystyrene solution of the present invention is a solution in which o- / m-hydroxystyrene is dissolved in a solvent at a specific concentration. By adjusting the o- / m-hydroxystyrene concentration, the storage stability of o- / m-hydroxystyrene can be improved. The production method for the o- / m-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 o- / m-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 o- / m-hydroxystyrene.

[0036] The o- / m-hydroxystyrene concentration in the o- / m-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. When the o- / m-hydroxystyrene concentration in the o- / m-hydroxystyrene solution is 10% by mass or more, a decrease in polymerization efficiency can be prevented when the o- / m-hydroxystyrene is used as a polymerization raw material, and when the concentration is 70% by mass or less, precipitation of o- / m-hydroxystyrene can be prevented, which is preferable. Furthermore, when long-term storage stability is particularly important, an o- / m-hydroxystyrene concentration of 50% by mass or less is particularly preferable.

[0037] Furthermore, in an o- / m-hydroxystyrene solution having an o- / m-hydroxystyrene concentration of 10% by mass or more and 70% by mass or less, when the solution is analyzed by gel permeation chromatography, the chromatogram area of ​​o- / m-hydroxystyrene is preferably 99.5% or more, more preferably 99.7% or more, and even more preferably 99.9% or more, when the total area of ​​the chromatogram of components other than the organic solvent is taken as 100.

[0038] In an o- / m-hydroxystyrene solution having an o- / m-hydroxystyrene concentration of 10% by mass or more and 70% by mass or less, the content of o- / m-hydroxystyrene polymers is preferably 0.5% or less, more preferably 0.3% or less, and even more preferably 0.1% or less, relative to the o- / m-hydroxystyrene. If the content of o- / m-hydroxystyrene polymers is the above-mentioned numerical value or less, it can be said that the progress of the polymerization reaction during storage is sufficiently suppressed.

[0039] The o- / m-hydroxystyrene solution preferably does not contain a polymerization inhibitor. When using the o- / m-hydroxystyrene solution to produce a resist polymer for cutting-edge lithography, this can avoid the risk of impurities derived from the polymerization inhibitor being mixed into the resist polymer. Furthermore, even without adding a polymerization inhibitor, the progress of the polymerization reaction during storage can be suppressed.

[0040] The solvent used for the o- / m-hydroxystyrene solution is not particularly limited as long as it can dissolve o- / m-hydroxystyrene. When the resulting o- / m-hydroxystyrene solution is used as it is as a polymerization raw material for producing a polymer, it is more preferable that the solvent be one that 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, and acetonitrile. 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.

[0041] <Method for producing a polymer having structural units derived from o- / m-hydroxystyrene> The method for producing a polymer having structural units derived from o- / m-hydroxystyrene of the present invention includes a step of polymerizing o- / m-hydroxystyrene as a polymerization raw material, either alone or with another monomer copolymerizable therewith. As the polymerization raw material, the o- / m-hydroxystyrene solution obtained by the production method described in the above <Method for producing an o- / m-hydroxystyrene solution> and the o- / m-hydroxystyrene solution described in the above <O- / m-hydroxystyrene solution> can be used as they are. When the o- / m-hydroxystyrene solution is subjected to the polymerization step as is, the organic solvent in which the o- / m-hydroxystyrene is dissolved can be used as the polymerization solvent as it is.

[0042] (Other Copolymerizable Monomers) The other copolymerizable monomers are not particularly limited as long as they are polymerizable with o- / m-hydroxystyrene. In the case of resist applications, known monomers used in the production of resist polymers can be used. As the other copolymerizable monomer, for example, it is preferable to use a monomer having an acid-dissociable group. The acid-dissociable group is preferably a group having a tertiary carbon atom bonded to an oxygen atom. Furthermore, since the present invention uses o- / m-hydroxystyrene in which the phenolic hydroxyl group is not protected, a deprotection reaction using a base is not required. Therefore, as the other copolymerizable monomer, it is also possible to use a monomer having a lactone structure, a sultone structure, or a cyclic carbonate structure, which are labile to bases.

[0043] According to the method for producing a polymer having structural units derived from o- / m-hydroxystyrene of the present invention, it is possible to produce a polymer containing structural units derived from o- / m-hydroxystyrene, structural units having an acid-dissociable group, and structural units having at least one structure selected from the group consisting of lactone, sultone, and cyclic carbonate, the polymer not containing structural units resulting from decomposition of the lactone, sultone, or cyclic carbonate. In the present invention, polymerization is carried out using o- / m-hydroxystyrene in which the phenolic hydroxyl group is not protected, which eliminates the need for a deprotection reaction with a base and prevents decomposition of the lactone, sultone, or cyclic carbonate by a base, which is preferable.

[0044] (Resist Polymer) The resist polymer is a polymer whose solubility in a developer changes under the action of acid, and has 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 refers to a group that inhibits the dissolution of the copolymer in an alkaline developer and dissociates under the action of acid to dissolve the copolymer in the alkaline developer. Furthermore, in order to improve the polymer's adhesion to a substrate, the polymer may contain a repeating unit (B) having a lactone ring structure or a repeating unit (C) having a hydroxy group. If necessary, the polymer may further contain other repeating units, such as a repeating unit (D) having a structure that inhibits dissolution in an alkaline developer and is stable to the action of acid (hereinafter sometimes referred to as an "acid-stable, dissolution-inhibiting structure").

[0045] (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, the repeating unit (A) is a repeating unit derived from (meth)acrylic acid, hydroxystyrene, or the like in which an OH group such as a carboxyl group, a phenolic hydroxyl group, or a sulfonic acid group is protected with an acid-dissociable, dissolution-inhibiting group.

[0046] Examples of the acid dissociable, dissolution inhibiting group include structures represented by formula (a1) or (a2). In formula (a1), * represents a bonding 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 is R ２０ Or R ２１ When 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, a tetracyclo[4.4.0.12,5.17,10]dodecane ring, or the like, is bonded to the above, the difference in solubility in an alkaline developer before and after lithography is large, which is preferable for drawing a fine pattern. 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. ２５represents 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 is 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 is R ２５ Specific examples of the ring bonded to include a hydrofuran ring and a hydropyran ring.

[0047] 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 of repeating units with different structures can be selected and used from the repeating units (A). (Wherein, Rx is H, CH ３ or CF ３ Represents.)

[0048] (Wherein, Rx is H, CH ３ or CF ３ Represents.)

[0049] (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). In formula (B1), R ３０R 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). In formula (b), R ３０１ ~R ３０８ Any one of R ３２ represents a single bond that is a bonding site as 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 Any one of 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 bonds with one or two of R to form an alicyclic ring having 5 to 15 carbon atoms, and the remaining 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.

[0050] 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, and specific examples of the alkoxy group having 1 to 4 carbon atoms include a methoxy group and an ethoxy group.

[0051] In formula (b), R ３０１ ~R ３０８ One of the following is R ３２ represents a single bond having a bonding 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 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 bonds with one or two of the remaining R ３０１ ~R ３０８ Particularly preferred examples of the lactone structure in which represents a hydrogen atom, a hydrocarbon group or an alkoxy group having 1 to 4 carbon atoms 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.

[0052] Specific examples of the repeating unit (B) are given below, but the present invention is not limited thereto. 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). (Wherein, Rx is H, CH３ or CF ３ Represents.)

[0053] (Repeating Unit (C)) The repeating unit (C) is a repeating unit having a hydroxy group or a carboxy group in a side chain, and has the functions of increasing the adhesion of the polymer to a substrate or an undercoat film, controlling the solubility in a lithography solvent or an alkaline developer, and reacting with a curing agent to form a crosslinked structure.

[0054] As the structure of the repeating unit (C), structures represented by formulae (C1) to (C3) are particularly preferred. In formula (C1), R １０ 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 is a substituted or unsubstituted aromatic hydrocarbon group. １２ represents a single bond, or 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 include a single bond, and 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 is 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 is particularly preferably a single bond. i represents an integer of 1 or 2. In formula (C2), R １３represents 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. １４ 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, and specific examples thereof 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 and which have a cyclohexane ring, a norbornane ring, a 7-oxa-norbornane ring, a 7-thia-norbornane ring, an adamantane ring, a tetracyclo[4.4.0.12,5.17,10]dodecane ring, etc., and are preferably a cyclohexane ring, a norbornane ring, or an adamantane ring. 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 preferred are a single bond, a 1,1,1,3,3,3-hexafluoro-2,2-propylene group, and 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. In formula (C3), R １６ 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 thereof 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.

[0055] Specific examples of the repeating unit (C) are given below, but the present invention is not limited thereto. One type of repeating unit (C) or multiple types of repeating units with different structures can be selected and used. (Wherein, Rx is H, CH ３ or CF ３ Represents.)

[0056] (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 the action of acid. Preferably, it is a repeating unit in which a carboxyl group or a phenolic hydroxyl group in a repeating unit derived from (meth)acrylic acid or hydroxystyrene, etc., 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.

[0057] 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 the carboxyl group or phenolic hydroxyl group and is bonded to the oxygen atom is a primary or secondary carbon, aromatic hydrocarbon groups, or structures to which methyl and 1-adamantyl groups are bonded. Specific examples include methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, cyclopentyl, cyclohexyl, 2-norbornyl, 2-isobornyl, 8-tricyclo[5.2.1.02,6]decanyl, 1-adamantyl, 2-adamantyl, 4-tetracyclo[4.4.0.12,5.17,10]dodecanyl, phenyl, benzyl, naphthyl, and anthracenyl groups.

[0058] 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 of repeating units with different structures can be selected and used from the repeating units (D). (Wherein, Rx is H, CH ３ or CF ３ Represents.)

[0059] Furthermore, an example of a repeating unit having the same effect as the repeating unit (D) is a repeating unit represented by formula (D'). In formula (D'), R ６０ 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 ６２ R 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.

[0060] Specific examples of the repeating unit (D') are given below.

[0061] The polymerization can be carried out by a conventionally known polymerization method such as radical polymerization, cationic polymerization, or anionic polymerization.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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 o- / m-hydroxystyrene solution can be used. These can be used alone or in combination of two or more.

[0067] 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. Usually, the amount of the solvent is 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight, per part by weight of the monomer.

[0068] The amount of polymerization solvent initially charged into the reaction vessel (hereinafter sometimes referred to as the "initial charged solvent") may be at least the minimum amount that allows stirring, but an amount greater than necessary is not preferred because it reduces the amount of monomer solution that can be supplied and reduces production efficiency. Typically, the volume ratio of the initial charged solvent to the final charged amount (i.e., the total amount of the initial charged solvent and the monomer solution and initiator solution to be added dropwise) is selected, for example, from a range of 1 / 30 or more, preferably 1 / 20 to 1 / 2, and particularly preferably 1 / 10 to 1 / 3. Incidentally, a portion of the monomer and / or polymerization initiator may be premixed with the initial charged solvent.

[0069] The dropping time of the monomer solution is not preferred because a short time tends to broaden the molecular weight distribution and a large amount of solution is dropped at once, causing a drop in the temperature of the polymerization solution. Conversely, a long time is not preferred 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.

[0070] 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. An excessively 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.

[0071] 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, particularly preferably 60 to 120°C. The polymerization temperature significantly affects the molecular weight and copolymer composition of the copolymer and therefore must be precisely controlled. However, since the polymerization reaction is generally an exothermic reaction, it is difficult to control the temperature at a constant value. For this reason, it is preferable to include 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.

[0072] 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.

[0073] 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, and these impurities are preferably removed by a purification step. 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 polymerization reaction solution is prepared as a liquid-liquid two-phase solution, and the impurities are extracted into the poor solvent phase. 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 a step of redissolving the solid in a good solvent and then adding a poor solvent to reprecipitate, or by a step of washing the precipitated solid with a poor solvent. In the case of liquid-liquid two-phase separation, the poor solvent phase is 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 steps may be repeated in the same manner, or different steps may be combined.

[0074] 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.

[0075] 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 becomes insufficient, while if it is too large, waste liquid increases, 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.

[0076] 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 low molecular weight region of the copolymer 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] The temperature of the heat source during reduced pressure heating is not particularly limited as long as it is a temperature at which the copolymer does not 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 step, low-boiling point components and the final solvent are evaporated under reduced pressure, so the copolymer solution during the step 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.

[0081] Furthermore, when replacing the solvent, if the amount of solvent supplied later is too small, the low-boiling compounds cannot be sufficiently removed, whereas if the amount is too large, the replacement takes a long time and the copolymer is subjected to more heat history 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.

[0082] 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.

[0083] Furthermore, in order 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.

[0084] 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 each metal is below the lower detection limit of an analytical device.

[0085] The metal content is measured by inductively coupled plasma mass spectrometry (ICP-MS).

[0086] 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.

[0087] [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. Procedure (i): Dilute the polymer solution with a good solvent to prepare a test solution with a polymer concentration of 10.0% by mass. Procedure (ii): Place the test solution in the flask of a non-contact turbidimeter for orbital shaking culture (ODMonitor A&S manufactured by Taitec Corporation, attached to a shaker NR-2). While orbital shaking is performed, add a poor solvent dropwise at a constant speed, recording the change in weight of the test solution and the change in turbidity at a measurement wavelength of 950 nm. Procedure (iii): Continue adding the poor solvent until the turbidity reaches 0.20 OD (optical density). Record the amount of poor solvent 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.

[0088] The above-mentioned method for evaluating insoluble or slightly soluble components can be applied to the above-mentioned o- / m-hydroxystyrene polymer solution and other polymer solutions.

[0089] 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.

[0090] The analyses in this example were carried out as follows. [Purity of o- / m-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 o- / m-hydroxystyrene solution synthesized below were measured by GPC (gel permeation chromatography) using polystyrene as a standard. The analytical sample used was a tetrahydrofuran solution prepared so that the polymer solids concentration was 2% by mass. The amount of sample injected into the apparatus was 50 μL. Measuring apparatus: HLC-8220GPC manufactured by Tosoh Corporation Detector: Differential refractive index (RI) detector Column: Shodex GPC KF804 x 3 (manufactured by Showa Denko KK) Eluent: Tetrahydrofuran Flow rate: 1.0 mL / min Temperature: 40°C Calibration curve: Prepared using a polystyrene standard sample (manufactured by Tosoh Corporation)

[0091] [Water Content of o- / m-Hydroxystyrene Solution] The water content of the o- / m-hydroxystyrene solution synthesized below was measured using a Karl Fischer trace moisture analyzer AQ-7 (manufactured by Hiranuma Sangyo Co., Ltd.).

[0092] [Monomer Composition Ratio of Polymer] The monomer composition ratio of the polymer synthesized below is １３ Analysis was performed by C-NMR. Apparatus: AV400 manufactured by Bruker. Deuterated solvent: acetone-d6. Relaxation reagent: chromium (III) acetylacetonate. Measurement temperature: 40°C.

[0093] The abbreviations for the compounds used in the following experiments are as follows: OACS: o-acetoxystyrene MACS: m-acetoxystyrene PACS: p-acetoxystyrene OHS: o-hydroxystyrene MHS: m-hydroxystyrene ECpMA: 1-ethyl-1-cyclopentyl methacrylate GBLMA: γ-butyrolactone-α-methacrylate CCMA: (2-oxo-1,3-dioxolan-4-yl)methyl methacrylate MEK: methyl ethyl ketone PGMEA: propylene glycol monomethyl ether acetate

[0094] <Production of OHS (o-hydroxystyrene) Solution> [Example 1] 162.0 g of OACS and 486.0 g of methanol were placed in a reaction vessel equipped with a thermometer, a condenser, and a stirrer, and the vessel was sealed with nitrogen. The contents were cooled with stirring to a liquid temperature of -5°C. Thereafter, the pressure in the reaction vessel was reduced and then repressurized with nitrogen, which was repeated three times. In a vessel separate from the reaction vessel, an equimolar amount of 3 M aqueous sodium hydroxide solution relative to OACS was prepared, and this was bubbled with nitrogen for 1 hour. The nitrogen-bubbled aqueous sodium hydroxide solution was added dropwise to the reaction vessel over 60 minutes, and after the dropwise addition, stirring was continued for an additional 30 minutes to carry out a reaction in which OACS was deprotected and converted to OHS.

[0095] Next, 0.97 molar equivalents of 6M hydrochloric acid relative to OACS was added dropwise to the reaction vessel over 45 minutes. After the addition, stirring was continued for an additional 30 minutes to neutralize the reaction solution. The 6M hydrochloric acid was previously bubbled with nitrogen for 1 hour before the dropwise addition. Next, the temperature of the neutralized reaction solution was raised to approximately 10-20°C, and 500g of methyl tert-butyl ether was added, stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discharged. Next, 500g of ion-exchanged water was added, stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discharged. Next, 330g of methyl tert-butyl ether and 500g of ion-exchanged water were added, stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discharged. Finally, 500g of ion-exchanged water was added, stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discharged. This procedure was repeated twice.

[0096] The organic layer after washing with water was transferred to another reaction vessel, and 500 g of PGMEA was added. Additional PGMEA was gradually added while performing vacuum distillation at 25°C or below, and impurities other than OHS, such as methyl tert-butyl ether and reaction by-products, as well as excess PGMEA, were distilled off, ultimately resulting in a PGMEA solution with an OHS concentration of 40% by mass. The solution was then passed through a polytetrafluoroethylene (PTFE) membrane filter with a pore size of 50 nm. Analysis of the resulting OHS solution revealed that in GPC analysis, the chromatogram area of ​​OHS was 99.23% when the total chromatogram area of ​​components other than PGMEA was taken as 100, and the water content was 0.01%.

[0097] Example 2 A PGMEA solution with an OHS concentration of 40% by mass was prepared in the same manner as in Example 1, except that the amounts of monomers, solvents, and other reagents used were 100 times that of Example 1. Analysis of the resulting OHS solution revealed that in GPC analysis, the chromatogram area of ​​OHS was 99.99% when the total chromatogram area of ​​components other than PGMEA was taken as 100, and the water content was 0.00%. The metal content was also Na = 2 ppb, and the other metal elements were 0.1 ppb or less.

[0098] <Production of MHS (3-hydroxystyrene) Solution> [Example 3] 162.0 g of MACS and 486.0 g of methanol were placed in a reaction vessel equipped with a thermometer, a condenser, and a stirrer, and the vessel was sealed with nitrogen. The contents were cooled with stirring to a liquid temperature of -5°C. Thereafter, the pressure in the reaction vessel was reduced and then repressurized with nitrogen, which was repeated three times. In a vessel separate from the reaction vessel, an equimolar amount of 3 M aqueous sodium hydroxide solution relative to OACS was prepared, and this was bubbled with nitrogen for 1 hour. The nitrogen-bubbled aqueous sodium hydroxide solution was added dropwise to the reaction vessel over 60 minutes, and after the dropwise addition, stirring was continued for an additional 30 minutes to carry out a reaction in which MACS was deprotected and converted to MHS.

[0099] Next, 0.97 molar equivalents of 6M hydrochloric acid relative to MACS was added dropwise to the reaction vessel over 45 minutes. After the addition, stirring was continued for an additional 30 minutes to neutralize the reaction solution. The 6M hydrochloric acid was previously bubbled with nitrogen for 1 hour before the dropwise addition. Next, the temperature of the neutralized reaction solution was raised to approximately 10-20°C, and 500g of methyl tert-butyl ether was added thereto. The mixture was stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discharged. Next, 500g of ion-exchanged water was added thereto. The mixture was stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discharged. Next, 330g of methyl tert-butyl ether and 500g of ion-exchanged water were added thereto. The mixture was stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discharged. Finally, 500g of ion-exchanged water was added thereto. The mixture was stirred for 15 minutes, allowed to stand for 15 minutes, and the aqueous layer was discharged. This procedure was repeated twice.

[0100] The organic layer after washing with water was transferred to another reaction vessel, and 500 g of methyl ethyl ketone (hereinafter referred to as MEK) was added. MEK was gradually added while distilling under reduced pressure at 25°C or below, and impurities other than MHS, such as methyl tert-butyl ether and reaction by-products, and excess MEK were distilled off, ultimately resulting in an MEK solution with an MHS concentration of 25% by mass. Thereafter, the solution was passed through a polytetrafluoroethylene (PTFE) membrane filter with a pore size of 50 nm. Analysis of the obtained MHS solution revealed that in GPC analysis, the chromatogram area of ​​MHS was 99.8% when the total chromatogram area of ​​components other than MEK was taken as 100, and the water content was 0.01%.

[0101] Example 4 An MEK solution with an MHS concentration of 25% by mass was prepared in the same manner as in Example 3, except that the amounts of monomers, solvents, and other reagents used were 100 times that of Example 3. Analysis of the resulting MHS solution revealed that in GPC analysis, the chromatogram area of ​​MHS was 99.99% when the total chromatogram area of ​​components other than MEK was taken as 100, and the water content was 0.02%. The metal contents were Na = 3 ppb, K = 0.5 ppb, and the amounts of other metal elements were 0.1 ppb or less.

[0102] <Storage Stability Test> [Example 5] A portion of the 40% by mass OHS / PGMEA solution obtained in Example 1 was divided into small portions and placed in containers for storage tests at -15°C, 5°C, 20°C, and 40°C, and the changes in the OHS concentration and OHS polymer concentration in the solution were measured by GPC. The results are shown in Table 1. It was confirmed that the OHS / PGMEA solution of the present invention was stable for 6 months when stored at 5°C or below.

[0103]

[0104] Example 6 A portion of the 25% by mass MHS / MEK solution obtained in Example 4 was divided into small portions and placed in containers for storage tests at -20°C, 10°C, 20°C, and 40°C, and the changes in the MHS concentration and MHS polymer concentration in the solution were measured by GPC. The results are shown in Table 2. It was confirmed that the MHS / MEK solution of the present invention is stable for 6 months when stored at 20°C or below.

[0105]

[0106] <Production of Copolymer> [Example 7] Production of OHS / ECpMA Copolymer A monomer solution was prepared by adding 65.0 g of the 40 mass % OHS / PGMEA solution obtained in Example 2, 63.2 g of ECpMA, 18.2 g of dimethyl 2,2-azobisisobutyrate, and 19.1 g of MEK to a vessel and mixing them.

[0107] 57.4 g of MEK was charged into a four-neck glass flask reaction vessel equipped with a stirrer, a condenser, and a thermometer. After creating a nitrogen atmosphere, the vessel was heated to 79°C. The monomer solution was then added dropwise at a constant rate over 4 hours, and the polymerization reaction was continued for another 2 hours. After polymerization was completed, the vessel was cooled to room temperature. The polymerization solution was mixed with 483 g of n-hexane and stirred to precipitate a polymer. The mixture was then allowed to stand, and the polymer was separated by decantation. The polymer was redissolved in 52.5 g of acetone, to which 420 g of n-hexane was added and stirred to precipitate the polymer. This procedure of separating the polymer by decantation was repeated twice. 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 then subjected to NMR analysis. NMR analysis revealed that the monomer composition ratio (molar ratio) of the polymer was OHS:ECpMA = 39.5:60.5.

[0108] The remaining polymer solution was washed with 78 g of a 1% by weight aqueous oxalic acid solution using a separatory funnel, followed by adding 78 g of pure water and 6 g of ethyl acetate. This washing and separation procedure was repeated four times. 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 OHS / ECpMA copolymer with a polymer concentration of 30% by weight. Analysis of the resulting polymer solution by GPC revealed Mw = 5100 and Mw / Mn = 1.39.

[0109] Example 8 Production of MHS / ECpMA Copolymer A monomer solution was prepared by adding 50.0 g of the 25% by mass MHS / PGMEA solution obtained in Example 4, 28.2 g of ECpMA, 5.4 g of dimethyl 2,2-azobisisobutyrate, and 2.7 g of MEK to a vessel and mixing them.

[0110] 36.7 g of MEK was charged into a four-neck glass flask reaction vessel equipped with a stirrer, a condenser, and a thermometer. After creating a nitrogen atmosphere, the vessel was heated to 79°C. The monomer solution was then added dropwise at a constant rate over 4 hours, and the polymerization reaction was continued for another 2 hours. After completion of the polymerization, the vessel was cooled to room temperature. The polymerization solution was mixed with 220 g of n-hexane and stirred to precipitate a polymer. The mixture was then allowed to stand, and the polymer was separated by decantation. The polymer was redissolved by adding 16.5 g of acetone and 16.5 g of methanol, to which 220 g of n-hexane was added and stirred to precipitate the polymer. This procedure of separating the polymer by decantation was repeated three times. The recovered polymer was dissolved in 77 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 then subjected to NMR analysis. The monomer composition ratio (molar ratio) of the polymer as determined by NMR analysis was MHS:ECpMA=43.0:53.0.

[0111] The remaining polymer solution was washed with 37 g of a 1 wt% aqueous oxalic acid solution using a separatory funnel, followed by adding 37 g of pure water and 6 g of ethyl acetate. This washing and separation procedure was repeated four times. 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 MHS / ECpMA copolymer with a polymer concentration of 30 wt%. Analysis of the resulting polymer solution by GPC revealed Mw = 5500 and Mw / Mn = 1.36.

[0112] Example 9 Production of OHS / ECpMA / GBLMA Copolymer A monomer solution was prepared by adding 68.0 g of the 40% by mass OHS / PGMEA solution obtained in Example 2, 52.2 g of ECpMA, 10.5 g of GBLMA, 9.2 g of dimethyl 2,2-azobisisobutyrate, and 21.3 g of MEK to a vessel and mixing them.

[0113] A glass four-neck flask reaction vessel equipped with a stirrer, a condenser, and a thermometer was charged with 63.9 g of MEK, and the vessel was then placed in a nitrogen atmosphere and heated to 79°C. The monomer solution was then added dropwise at a constant rate over 4 hours, after which the polymerization reaction was continued for another 2 hours. After completion of the polymerization, the vessel was cooled to room temperature. The polymerization solution was mixed with 460 g of n-hexane and stirred to precipitate a polymer. The mixture was then allowed to stand, and the polymer was separated by decantation. The polymer was redissolved in 50 g of acetone, to which 400 g of n-hexane was added and stirred to precipitate the polymer, and the polymer was then separated by decantation. This procedure was repeated three 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 then subjected to NMR analysis. The monomer composition ratio (molar ratio) of the polymer as determined by NMR analysis was OHS:ECpMA:GBLMA=40.8:48.3:10.9.

[0114] The remaining polymer solution was washed with 88 g of a 1% by weight aqueous solution of oxalic acid using a separatory funnel, followed by adding 87 g of pure water and 7 g of ethyl acetate. This washing and separation procedure was repeated four times. 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 an OHS / ECpMA / GBLMA copolymer with a polymer concentration of 30% by weight. Analysis of the resulting polymer solution by GPC revealed Mw = 7900 and Mw / Mn = 1.58.

[0115] Example 10 Production of OHS / ECpMA / CCMA Copolymer A monomer solution was prepared by adding 58.7 g of the 40% by mass OHS / PGMEA solution obtained in Example 2, 45.0 g of ECpMA, 9.2 g of CCMA, 15.9 g of dimethyl 2,2-azobisisobutyrate, 13.7 g of PGMEA, and 9.3 g of methanol to a vessel and mixing them.

[0116] A four-necked glass flask reactor equipped with a stirrer, a condenser, and a thermometer was charged with 59.6 g of PGMEA and 11.4 g of methanol. The reactor was then placed under a nitrogen atmosphere and heated to 79°C. The monomer solution was then added dropwise at a constant rate over 4 hours, after which the polymerization reaction was continued for another 2 hours. After polymerization was complete, the mixture was cooled to room temperature. The polymerization solution was mixed with 440 g of n-hexane and stirred to precipitate the polymer. After allowing to stand, the polymer was separated by decantation. The polymer was redissolved in 55 g of acetone and 33 g of methanol, to which 400 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 170 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 then subjected to NMR analysis. The monomer composition ratio (molar ratio) of the polymer as determined by NMR analysis was OHS:ECpMA:CCMA=41.2:47.1:11.7.

[0117] The remaining polymer solution was washed with 92 g of a 1 wt% aqueous oxalic acid solution using a separatory funnel, followed by adding 92 g of purified water and 7 g of ethyl acetate. This washing and separation procedure was repeated four times. 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 an OHS / ECpMA / CCMA copolymer with a polymer concentration of 30 wt%. Analysis of the resulting polymer solution by GPC revealed Mw = 5700 and Mw / Mn = 1.43.

[0118] Reference Example: Production of PHS / ECpMA copolymer using PACS 28.6 g of PACS, 60.0 g of ECpMA, 19.1 g of dimethyl 2,2-azobisisobutyrate, 29.9 g of PGMEA, and 5.7 g of methanol were mixed in a vessel to prepare a monomer solution.

[0119] 44.7 g of PGMEA and 8.6 g of methanol were charged into a four-neck glass flask reaction vessel equipped with a stirrer, condenser, and thermometer. The vessel was then placed under a nitrogen atmosphere and heated to 79°C. The monomer solution was then added dropwise at a constant rate over 4 hours, after which the polymerization reaction was continued for another 2 hours. After polymerization was complete, the vessel was cooled to room temperature. 0.7 g of DBU and 40 g of methanol were added to the cooled polymerization solution, and the temperature was raised to 70°C while stirring under a nitrogen atmosphere to carry out the deprotection reaction of the PACS unit. During the reaction, a portion of the reaction solution was sampled and the deprotection rate of the PACS was monitored by NMR. A reaction time of 7 hours was required to achieve a 100% deprotection rate of the PACS.

[0120] The polymer solution after the deprotection reaction was mixed with 420 g of n-hexane and stirred to precipitate the polymer. After standing, the polymer was separated by decantation. 20 g of acetone and 30 g of MeOH were added to the polymer to redissolve it, and 400 g of n-hexane was added thereto and stirred to precipitate the polymer. This procedure of separating the polymer by decantation was repeated twice. 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. The composition ratio (molar ratio) of the polymer according to NMR analysis was PHS:ECpMA = 40.1:59.9.

[0121] The remaining polymer solution was neutralized with 92 g of 1% by weight oxalic acid aqueous solution using a separatory funnel, followed by washing with 92 g of purified water and 7 g of ethyl acetate. This procedure was repeated four times. 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 PHS / ECpMA copolymer with a polymer concentration of 30% by weight. Analysis of the resulting polymer solution by GPC revealed Mw = 5,080 and Mw / Mn = 1.39.

[0122] Comparative Example 1: Preparation of OHS / ECpMA Copolymer Using OACS The PACS used in the Reference Example was replaced with OACS, and the polymerization reaction was carried out in the same manner. The subsequent deprotection reaction was carried out in the same manner, using 1.0 g of DBU, which was more than in the Reference Example. During the reaction, a portion of the reaction solution was sampled, and the deprotection rate of OACS was monitored by NMR. Complete deprotection of OACS required 14 hours, twice as long as that required with PACS.

[0123] The polymer solution after the deprotection reaction was subjected to precipitation purification, neutralization, water washing, and solvent substitution in the same manner as in Reference Example, to finally obtain a PGMEA solution of an OHS / ECpMA copolymer with a polymer concentration of 30% by mass. The monomer composition ratio (molar ratio) of the obtained polymer was OHS:ECpMA = 38.7:61.3, Mw = 5,450, and Mw / Mn = 1.41.

[0124] Comparative Example 2 Production of OHS / ECpMA / GBLMA Copolymer Using OACS 28.5 g of OACS, 40.0 g of ECpMA, 7.5 g of GBLMA, 17.2 g of dimethyl 2,2-azobisisobutyrate, 46.8 g of PGMEA, and 8.9 g of methanol were added to a vessel and mixed to prepare a monomer solution.

[0125] 57.3 g of PGMEA and 10.9 g of methanol were charged into a four-neck glass flask reaction vessel equipped with a stirrer, condenser, and thermometer. The vessel was then placed under a nitrogen atmosphere and heated to 79°C. The monomer solution was then added dropwise at a constant rate over 4 hours, after which the polymerization reaction was continued for another 2 hours. After polymerization was complete, the mixture was cooled to room temperature. 1.1 g of DBU and 33 g of methanol were added to the cooled polymerization solution, and the mixture was heated to 70°C under stirring under a nitrogen atmosphere to carry out the deprotection reaction of the OACS units. During the reaction, a portion of the reaction solution was sampled and the OACS deprotection rate was monitored by NMR. It took 14 hours to deprotect all of the OACS units. At the same time, a side reaction in which part of the lactone structure of the GBLMA unit decomposed was detected.

[0126] The polymer solution after the deprotection reaction was mixed with 420 g of n-hexane and stirred to precipitate the polymer. After standing, the polymer was separated by decantation. 20 g of acetone and 30 g of MeOH were added to the polymer to redissolve it, and 400 g of n-hexane was added thereto and stirred to precipitate the polymer. This procedure of separating the polymer by decantation was repeated twice. 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 ratio (molar ratio) of the polymer was OHS:ECpMA:GBLMA:by-product = 43.7:45.8:2.9:7.6, indicating that approximately 70% of the GBLMA units had decomposed.

[0127] The remaining polymer solution was washed with 46 g of a 1% by weight aqueous solution of oxalic acid using a separatory funnel, followed by adding 46 g of pure water and 6 g of ethyl acetate. This washing and separation procedure was repeated four times. 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 resulting in a PGMEA solution with a polymer concentration of 30% by weight. GPC analysis of the resulting polymer solution showed Mw = 4,720 and Mw / Mn = 1.39.

[0128] Comparative Example 3 Production of OHS / ECpMA / CCMA Copolymer Using OACS 28.5 g of OACS, 40.0 g of ECpMA, 8.1 g of CCMA, 17.2 g of dimethyl 2,2-azobisisobutyrate, 47.3 g of PGMEA, and 9.3 g of methanol were placed in a vessel and mixed to prepare a monomer solution.

[0129] 57.9 g of PGMEA and 11.1 g of methanol were charged into a four-neck glass flask reaction vessel equipped with a stirrer, condenser, and thermometer. The vessel was then placed under a nitrogen atmosphere and heated to 79°C. The monomer solution was then added dropwise at a constant rate over 4 hours, after which the polymerization reaction was continued for another 2 hours. After polymerization was complete, the vessel was cooled to room temperature. 1.1 g of DBU and 36 g of methanol were added to the cooled polymerization solution, and the temperature was raised to 70°C with stirring under a nitrogen atmosphere to carry out the deprotection reaction of the OACS unit. During the reaction, a portion of the reaction solution was sampled and the OACS deprotection rate was monitored by NMR. A reaction time of 14 hours was required to achieve a 100% OACS deprotection rate. At the same time, a side reaction in which a portion of the cyclic carbonate structure of the CCMA unit decomposed was detected.

[0130] The polymer solution after the deprotection reaction was mixed with 420 g of n-hexane and stirred to precipitate the polymer. After standing, the polymer was separated by decantation. 20 g of acetone and 30 g of MeOH were added to the polymer to redissolve it, and 400 g of n-hexane was added thereto and stirred to precipitate the polymer. This procedure of separating the polymer by decantation was repeated twice. 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. The monomer composition ratio (molar ratio) of the polymer according to NMR analysis was OHS:ECpMA:CCMA:by-product = 43.6:45.5:0.5:10.4, and 95% of the CCMA units had decomposed.

[0131] The remaining polymer solution was washed with 46 g of a 1% by weight aqueous oxalic acid solution using a separatory funnel, followed by adding 46 g of pure water and 6 g of ethyl acetate. This washing and separation procedure was repeated four times. 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 resulting in a PGMEA solution with a polymer concentration of 30% by weight. GPC analysis of the resulting polymer solution showed Mw = 4,450 and Mw / Mn = 1.39.

[0132] From the above results, in the production of polymers having o-hydroxystyrene units, applying a known method for producing p-hydroxystyrene polymers by deprotecting the corresponding acetoxystyrene copolymer results in an extremely slow and inefficient deprotection reaction, whereas the method of the present invention for direct polymerization with a comonomer using an o- / m-hydroxystyrene solution can efficiently produce polymers having o- / m-hydroxystyrene units. Furthermore, when producing polymers containing lactone structures or cyclic carbonate structures, the method of the present invention, which does not involve a deprotection reaction, does not decompose these structures and can produce polymers of high purity.

[0133] The highly pure and storage-stable o- / m-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 this solution, o- / m-hydroxystyrene-based polymers suitable for resists for EUV lithography and electron beam lithography can be efficiently produced on a commercial scale by a simple process that does not require a deprotection step.

Claims

1. A method for producing a solution of o- / m-hydroxystyrene comprising the following steps (i) to (iv): (i) a deprotection step of contacting o- / m-acetoxystyrene with a base in a solvent to produce o- / m-hydroxystyrene; (ii) a neutralization step of adding an acid to a solution containing o- / m-hydroxystyrene after deprotection to neutralize it; (iii) a step of washing the solution containing neutralized o- / m-hydroxystyrene with water; and (iv) a solvent replacement step of adding a solvent capable of dissolving o- / m-hydroxystyrene to the solution containing o- / m-hydroxystyrene, and distilling the mixture at 40°C or less to remove components other than o- / m-hydroxystyrene and excess solvent.

2. The method for producing an o- / m-hydroxystyrene solution according to claim 1, wherein the base used in the deprotection step is one from which dissolved oxygen has been removed by bubbling with an inert gas prior to use, and the deprotection step is carried out under a nitrogen atmosphere.

3. The method for producing an o- / m-hydroxystyrene solution according to claim 1 or 2, wherein the acid used in the neutralization step has had dissolved oxygen removed by bubbling with an inert gas before use.

4. The method for producing an o- / m-hydroxystyrene solution according to any one of claims 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. A method for producing an o- / m-hydroxystyrene solution according to any one of claims 1 to 4, wherein the organic solvent used in the solvent replacement step is any type of organic solvent selected from the group consisting of alcohols, ketones, ethers, glycol ethers, glycol ether esters, and esters.

6. A method for producing an o- / m-hydroxystyrene solution according to any one of claims 1 to 5, wherein the o- / m-hydroxystyrene concentration is adjusted to 10% by mass or more and 70% by mass or less in the solvent replacement step.

7. A method for producing an o- / m-hydroxystyrene solution according to any one of claims 1 to 6, further comprising a step of passing the o- / m-hydroxystyrene solution through a filter having a nominal pore size of 1 micron or less before and / or after the solvent replacement step.

8. An o- / m-hydroxystyrene solution having an o- / m-hydroxystyrene concentration of 10% by mass or more and 70% by mass or less, in which, in a gel permeation chromatography analysis of the solution, the chromatogram area of ​​o- / m-hydroxystyrene is 99.5% or more when the total area of ​​the chromatograms of components other than the organic solvent is taken as 100.

9. The o- / m-hydroxystyrene solution according to claim 8, wherein in a gel permeation chromatography analysis of the solution, the chromatogram area of ​​o- / m-hydroxystyrene polymer is 0.5% or less relative to the chromatogram area of ​​o- / m-hydroxystyrene.

10. An o- / m-hydroxystyrene solution having an o- / m-hydroxystyrene concentration of 10% by mass or more and 70% by mass or less, in which, in a gel permeation chromatography analysis of the solution, the chromatogram area of ​​o- / m-hydroxystyrene is 99.7% or more when the total area of ​​the chromatograms of components other than the organic solvent is taken as 100.

11. An o- / m-hydroxystyrene solution having an o- / m-hydroxystyrene concentration of 10% by mass or more and 70% by mass or less, in which, in a gel permeation chromatography analysis of the solution, the chromatogram area of ​​o- / m-hydroxystyrene is 99.9% or more when the total area of ​​the chromatograms of components other than the organic solvent is taken as 100.

12. The o- / m-hydroxystyrene solution according to any one of claims 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 o- / m-hydroxystyrene solution according to any one of claims 8 to 12, which does not contain a polymerization inhibitor.

14. A method for producing a polymer having structural units derived from o- / m-hydroxystyrene, comprising polymerizing the o- / m-hydroxystyrene solution according to any one of claims 8 to 13 as a polymerization raw material, either alone or together with another monomer copolymerizable therewith.

15. A method for producing a polymer having structural units derived from o- / m-hydroxystyrene according to claim 14, wherein the other monomer copolymerizable with o- / m-hydroxystyrene includes a monomer having an acid-dissociable group.

16. A method for producing a polymer having a structural unit derived from o- / m-hydroxystyrene according to claim 14, wherein the other monomer copolymerizable with o- / m-hydroxystyrene includes a monomer having an acid dissociable group and at least one monomer selected from the group consisting of a monomer having a lactone structure, a monomer having a sultone structure, and a monomer having a cyclic carbonate structure.

17. A method for producing a polymer having structural units derived from o- / m-hydroxystyrene, comprising polymerizing the o- / m-hydroxystyrene solution produced by the method according to any one of claims 1 to 7 as a polymerization raw material, either alone or together with another monomer copolymerizable therewith.

18. A method for producing a polymer having structural units derived from o- / m-hydroxystyrene, comprising the steps of: producing an o- / m-hydroxystyrene solution by the method according to any one of claims 1 to 7; and using the o- / m-hydroxystyrene solution produced in the above step as a polymerization raw material, polymerizing it alone or together with another monomer copolymerizable with o- / m-hydroxystyrene.

19. A method for producing a polymer having a structural unit derived from o- / m-hydroxystyrene according to any one of claims 14 to 18, which is applied to polymerization using a polymerization tank having a capacity of 30 L or more.

20. A polymer comprising a structural unit derived from o- / m-hydroxystyrene, a structural unit having an acid dissociable group, and a structural unit having at least one structure selected from the group consisting of lactone, sultone, and cyclic carbonate, the polymer not comprising a structural unit resulting from decomposition of the lactone, sultone, or cyclic carbonate.

Images