JP2023135842A - Production method of copolymer, production method of resist composition, and production method of substrate having pattern formed - Google Patents

Abstract

To provide a copolymer which, with regard to a copolymer generated during a polymerization process period, can make a copolymerization composition ratio during the process get closer to a target composition ratio.SOLUTION: Provided is a method for producing a copolymer by subjecting 2 or more kinds of monomers to a polymerization reaction, comprising step (2) and step (3), where step (3) is started after step (2) is initiated. Step (2): a step of feeding a monomer composition, comprising a monomer (a2) containing an acid dissociable group and a monomer (b2) containing a phenolic hydroxyl group, in a reactor and subjecting the same to a polymerization reaction. Step (3): a step of feeding a monomer composition (z), comprising at least one selected from the group consisting of a monomer (a3) containing an acid dissociable group and a monomer (b3) containing a phenolic hydroxyl group and having a composition different from the monomer composition (y), in the reactor and subjecting the same to a polymerization reaction.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a copolymer, a method for producing a resist composition, and a method for producing a substrate on which a pattern is formed.

In recent years, resist patterns formed in the manufacturing process of semiconductor elements, liquid crystal elements, etc. have been rapidly becoming finer due to advances in lithography technology. One method of miniaturization is to shorten the wavelength of irradiation light.
For example, KrF excimer laser (wavelength: 248 nm) lithography technology has been introduced, and ArF excimer laser (wavelength: 193 nm) lithography technology and EUV (wavelength: 13.5 nm) lithography technology, which aim to further shorten the wavelength, are being researched.

In the example of Patent Document 1, a methanol solution of parahydroxystyrene and methyl ethyl ketone are supplied to a polymerization container, a methanol solution of 2-hydroxyadamantyl methacrylate is introduced into a dropping device A, and a polymerization initiation method is introduced into a dropping device B. By introducing a methanol solution of agent and chain transfer agent, and maintaining the copolymer obtained through the dropwise polymerization step and purification step as a copolymer solution containing a specific amount of water, fluctuations in molecular weight during storage can be prevented. It describes how to suppress it.

Japanese Patent Application Publication No. 2010-202698

According to the findings of the present inventors, in the method for producing a copolymer described in Patent Document 1, due to the difference in copolymerization reactivity of the monomers to be copolymerized, the copolymer produced during the polymerization process It is difficult to bring the ratio of structural units (period copolymerization composition ratio) in each period into which the polymerization process period is divided close to the design value (target composition ratio).
An object of the present invention is to provide a method for producing a copolymer that can bring the periodic copolymerization composition ratio closer to the target composition ratio for the copolymer produced during the polymerization process.

[1] A method for producing a copolymer by polymerizing two or more monomers, which includes the following steps (2) and (3), and after the start of step (2), the step (3) A method for producing a copolymer.
Step (2): A monomer composition (y) containing a monomer (a2) containing an acid-dissociable group and a monomer (b2) containing a phenolic hydroxyl group is supplied into a reactor, and polymerization is carried out. The process of reacting.
Step (3): The monomer composition (y) contains at least one selected from the group consisting of a monomer (a3) containing an acid-dissociable group and a monomer (b3) containing a phenolic hydroxyl group. A step in which a monomer composition (z) having a different composition from the above is supplied into a reactor and subjected to a polymerization reaction.
[2] 30 minutes elapse from the time when 80% by mass of the total mass of the monomer composition (y) supplied into the reactor in step (2) is completed, and after the completion of supplying 100% by mass. The method for producing a copolymer according to [1], wherein the step (3) is started before the point in time.
[3] The method for producing a copolymer according to [1] or [2], wherein the monomer (a2) and the monomer (a3) each contain a compound represented by the following formula (ai).

(In formula (ai), R ₁₁ represents a hydrogen atom or a methyl group, and R ₂₁ represents an alkyl group having 1 to 5 carbon atoms that may have an etheric oxygen atom between the carbon-carbon bonds. , R ₂₂ and R ₂₃ each represent an alkyl group having 1 to 5 carbon atoms which may have an etheric oxygen atom between the carbon-carbon bonds, and R ₂₂ and R ₂₃ are bonded to each other to form a ring. (You may do so.)
[4] Production of the copolymer according to any one of [1] to [3], wherein the monomer (b2) and the monomer (b3) each contain a compound represented by the following formula (bi). Method.

(In formula (bi), R ₁₂ represents a hydrogen atom or a methyl group, Y represents a linking group containing a single bond or an ester bond, and R ₃₁ represents a hydrogen atom, a hydrocarbon group having an acyl group, or a carbon -Represents a hydrocarbon group having an etheric oxygen atom between carbon bonds, and k represents an integer from 1 to 5.)
[5] At least one selected from the monomer composition (y) and the monomer composition (z) further comprises a monomer having a lactone skeleton and a monomer having a sultone skeleton. The method for producing a copolymer according to any one of [1] to [4], comprising at least one selected from the following.
[6] At least one selected from the monomer composition (y) and the monomer composition (z) further contains a monomer having a hydrophilic group other than the monomer (b2). The method for producing a copolymer according to any one of [1] to [5], comprising:
[7] The method for producing a copolymer according to any one of [1] to [6], further comprising the following step (1), and starting the step (2) after starting the step (1).
Step (1): A monomer composition containing a monomer (a1) containing an acid-dissociable group and having a different composition from the monomer composition (y) and the monomer composition (z). x) into the reactor.
[8] The method for producing a copolymer according to [7], wherein the step (2) is started after the supply of the monomer composition (x) is completed in the step (1).
[9] The method for producing a copolymer according to [7] or [8], wherein the monomer (a1) contains a compound represented by the following formula (ai).

(In formula (ai), R ₁₁ represents a hydrogen atom or a methyl group, and R ₂₁ represents an alkyl group having 1 to 5 carbon atoms that may have an etheric oxygen atom between the carbon-carbon bonds. , R ₂₂ and R ₂₃ each represent an alkyl group having 1 to 5 carbon atoms which may have an etheric oxygen atom between the carbon-carbon bonds, and R ₂₂ and R ₂₃ are bonded to each other to form a ring. (You may do so.)
[10] The monomer composition (x) further contains at least one selected from the group consisting of a monomer having a lactone skeleton and a monomer having a sultone skeleton [7] to [9] A method for producing any of the copolymers.
[11] The copolymer according to any one of [7] to [10], wherein the monomer composition (x) further contains a monomer having a hydrophilic group other than the monomer (b2). manufacturing method.
[12] After completing the supply of the monomer composition (z) in the step (3), the copolymer according to any one of [1] to [11] further includes the following step (4). manufacturing method.
Step (4): A step of cooling the reactor.
[13] After completing the supply of the monomer composition (z) in the step (3), the copolymer according to any one of [1] to [12] further includes the following step (5). manufacturing method.
Step (5): A step of supplying oxygen into the reactor.
[14] After completing the supply of the monomer composition (z) in the step (3), the copolymer according to any one of [1] to [13] further includes the following step (6). manufacturing method.
Step (6): A step of adding the reaction product in the reactor to a poor solvent.
[15] The method for producing a copolymer according to [14], wherein the poor solvent contains at least one selected from the group consisting of isopropyl ether, isopropanol, heptane, hexane, cyclohexane, and toluene.
[16] A method for producing a resist composition, comprising producing a copolymer by the production method according to any one of [1] to [15] above, and producing a resist composition using the obtained copolymer.
[17] A step of manufacturing a resist composition by the manufacturing method of [16] above, a step of applying the obtained resist composition onto a substrate to form a resist film, and a step of exposing the resist film to light. A method for manufacturing a substrate on which a pattern is formed, the method comprising: developing the exposed resist film using a developer.

According to the present invention, the periodic copolymerization composition ratio of the copolymer produced during the polymerization process can be brought closer to the target composition ratio.

As used herein, "(meth)acrylic acid" means acrylic acid or methacrylic acid, and "(meth)acryloyloxy" means acryloyloxy or methacryloyloxy.
As used herein, the term "constituent unit" of a polymer means a unit (atomic group) formed from one monomer molecule.
In this specification, "~" indicating a numerical range means that the numerical values described before and after it are included as lower and upper limits.
The weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of the polymer in the present invention are values determined in terms of polystyrene by gel permeation chromatography.

≪Copolymer≫
The copolymer in the present invention (hereinafter also referred to as "this copolymer") comprises a structural unit based on one or more monomers (a) containing an acid-dissociable group and a monomer containing a phenolic hydroxyl group. It has a structural unit based on one or more types of structure (b). Furthermore, it may have a structural unit based on one or more types of other monomers.
This copolymer is preferably a resist polymer, and is suitably used for producing a resist composition.

<Monomer (a) containing acid-dissociable group>
The "acid-leaving group" is a group having a bond that is cleaved by an acid, and part or all of the acid-leaving group is released from the main chain of the polymer by cleavage of the bond.
In a resist composition, a polymer having a structural unit having an acid-eliminable group reacts with an acid component to become soluble in an alkaline solution, thereby making it possible to form a resist pattern.

The monomer (a) having an acid-eliminating group (hereinafter also referred to as "monomer (a)") may be any compound having an acid-eliminating group and a polymerizable multiple bond, and may be any known compound. can use things. The polymerizable multiple bond is a multiple bond that is cleaved during a polymerization reaction to form a copolymer chain, and ethylenic double bonds are preferred.
As the monomer (a), for example, a known (meth)acrylic ester having an acid-eliminating group can be used. From the viewpoint of acid removability, it is preferable that the monomer (a) contains a compound represented by the following formula (ai) (hereinafter also referred to as "compound (ai)").

In formula (ai), R ₁₁ represents a hydrogen atom or a methyl group, R ₂₁ represents an alkyl group having 1 to 5 carbon atoms that may have an etheric oxygen atom between the carbon-carbon bonds, R ₂₂ and R ₂₃ each represent an alkyl group having 1 to 5 carbon atoms that may have an etheric oxygen atom between the carbon-carbon bonds, and R ₂₂ and R ₂₃ combine with each other to form a ring. It's okay.

The alkyl group that is R ₂₁ may be linear or branched.
The alkyl group represented by R ₂₁ preferably has 1 to 4 carbon atoms, more preferably 1 to 3 carbon atoms.
Specific examples of R ₂₁ include methyl group, ethyl group, isopropyl group, and tert-butyl group.

When R ₂₂ and R ₂₃ do not form a ring, R ₂₂ and R ₂₃ may be the same or different.
The alkyl group that is R ₂₂ or R ₂₃ may be linear or branched.
The alkyl group represented by R ₂₂ preferably has 1 to 4 carbon atoms, more preferably 1 to 3 carbon atoms.
The alkyl group represented by R ₂₃ preferably has 1 to 4 carbon atoms, more preferably 1 to 3 carbon atoms.
Specific examples of R ₂₂ or R ₂₃ include a methyl group and an ethyl group.

When R ₂₂ and R ₂₃ are bonded to each other to form a ring, the ring is a monocyclic or polycyclic alicyclic group that may have an etheric oxygen atom between the carbon-carbon bonds. . The number of carbon atoms constituting the ring includes carbon atoms bonded to R ₂₁ , R ₂₂ and R ₂₃ . The number of carbon atoms constituting the ring is 3 to 11, preferably 4 to 10, and more preferably 5 to 6.

Specific examples of compound (ai) include 1-methylcyclopentyl (meth)acrylate,
1-ethylcyclopentyl (meth)acrylate, 1-isopropylcyclopentyl (meth)acrylate, 1-tert-butyl-1-cyclopentyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, 2-ethyl-2- Examples include adamantyl (meth)acrylate and isopropyl adamantyl (meth)acrylate.
Among these, 1-methylcyclopentyl methacrylate, 1-ethylcyclopentyl (meth)acrylate, 1-isopropylcyclopentyl (meth)acrylate, and 1-tert-butyl-1-cyclopentyl (meth)acrylate are more preferred in terms of lithography properties. .
In the production of this copolymer, the monomer (a) may be used alone or in combination of two or more.

<Monomer (b) containing phenolic hydroxyl group>
The monomer (b) containing a phenolic hydroxyl group (hereinafter also referred to as "monomer (b)") has a hydroxy group that is a "polar group" and a "hydrophilic group", and has a hydroxyl group that is a "polar group" and a "hydrophilic group". Contributes to the solubility of the film in developer. It also has an aromatic ring and contributes to the etching resistance of the resist film.

The monomer (b) may be any compound having a phenolic hydroxyl group and a polymerizable multiple bond, and known monomers can be used. The polymerizable multiple bond is preferably an ethylenic double bond.
From the viewpoint of solubility in a developer and etching resistance, it is preferable that monomer (b) contains a compound represented by the following formula (bi) (hereinafter also referred to as "compound (bi)").

In formula (bi), R ₁₂ represents a hydrogen atom or a methyl group, Y represents a linking group containing a single bond or an ester bond, and R ₃₁ represents a hydrogen atom, a hydrocarbon group having an acyl group, or a carbon- It represents a hydrocarbon group having an etheric oxygen atom between carbon bonds, and k represents an integer of 1 to 5.

A specific example of the linking group containing an ester bond, which is Y, is -C(O)O-.
Specific examples of the hydrocarbon group having an acyl group, which is R ₃₁ , include an acetyl group, a benzoyl group, and a pivaloyl group.
Specific examples of R ₃₁ , a hydrocarbon group having an etheric oxygen atom between carbon-carbon bonds, include -C(CH ₃ )O-CH ₃ , -C(CH ₃ )O-CH ₂ -CH ₃ can be mentioned.
k is 1 to 5, preferably 1 to 3, and more preferably 1 to 2.

Specific examples of compound (bi) include p-hydroxystyrene, m-hydroxystyrene, o-hydroxystyrene, 3,4-dihydroxystyrene, and 4-hydroxyphenyl (meth)acrylate.
Among these, p-hydroxystyrene is more preferred in terms of solubility in developer and etching resistance.
In the production of the present copolymer, the monomer (b) may be used alone or in combination of two or more.

<Other monomers>
Other monomers are monomers that do not fall under either monomer (a) or monomer (b). Examples include monomers having polar groups (excluding monomer (b)) and monomers having hydrophilic groups (excluding monomer (b)).
The term "polar group" as used herein refers to a polar functional group or a group having a polar atomic group, and specific examples include a hydroxy group, a cyano group, an alkoxy group, a carboxy group, an amino group, and a carbonyl group. , a group containing a fluorine atom, a group containing a sulfur atom, a group containing a lactone skeleton, a group containing a sultone skeleton, a group containing an acetal structure, a group containing an ether bond, and the like. Among these, groups containing a lactone skeleton or a sultone skeleton are preferred from the viewpoint of adhesion to substrates and the like.
The "hydrophilic group" in this specification is at least one of -C(CF ₃ ) ₂ -OH, hydroxy group, cyano group, methoxy group, carboxy group, sulfo group, and amino group.
In this specification, a hydroxy group, a cyano group, a methoxy group, a carboxy group, a sulfo group, and an amino group are polar groups and hydrophilic groups.
In a polymer for resist, a structural unit having a polar group contributes to adhesion to a substrate etc., and a structural unit having a hydrophilic group contributes to solubility in a developer.
In particular, from the viewpoint of solubility in a developer, it is preferable that a resist polymer applied to a pattern forming method that involves exposure to light with a wavelength of 250 nm or less has a hydroxy group or a cyano group; More preferred.

[Monomer (c) having lactone skeleton or sultone skeleton]
Other monomers may include a monomer selected from the group consisting of a monomer having a lactone skeleton and a monomer having a sultone skeleton (hereinafter also referred to as "monomer (c)"). preferable.
Examples of the lactone skeleton include 4- to 20-membered ring lactone skeletons. The lactone skeleton may be a monocyclic lactone ring, or an aliphatic or aromatic carbon ring or heterocycle may be fused to the lactone ring.
Examples of the sultone skeleton include a 4- to 20-membered sultone (cyclic sulfonic acid ester) skeleton. The sultone skeleton may be a monocyclic structure including only the sultone ring, or may have an aliphatic or aromatic carbon ring or heterocycle fused to the sultone ring.
The monomer (c) may be any compound having a lactone skeleton or sultone skeleton and a polymerizable multiple bond, and any known monomer can be used. The polymerizable multiple bond is preferably an ethylenic double bond.
As the monomer (c), for example, a (meth)acrylic acid ester having a lactone skeleton or a sultone skeleton can be used.

Monomers having a lactone skeleton include (meth)acrylic acid esters having a substituted or unsubstituted δ-valerolactone ring, and substituted or unsubstituted γ-butyrolactone, since they have an excellent effect of improving adhesion to substrates, etc. A (meth)acrylic ester having a ring and a (meth)acrylic ester having a norbornane lactone ring are preferred.
Specific examples of monomers having a lactone skeleton include β-(meth)acryloyloxy-β-methyl-δ-valerolactone, 4,4-dimethyl-2-methylene-γ-butyrolactone, β-(meth)acryloyl Oxy-γ-butyrolactone, β-(meth)acryloyloxy-β-methyl-γ-butyrolactone, α-(meth)acryloyloxy-γ-butyrolactone, 2-(1-(meth)acryloyloxy)ethyl-4-butanolide , (meth)acrylic acid pantoyllactone, 5-(meth)acryloyloxy-2,6-norbornanecarbolactone, 8-methacryloxy-4-oxatricyclo[5.2.1.0 ^2,6 ]decane-3 -one, 9-methacryloxy-4-oxatricyclo[5.2.1.0 ^2,6 ]decane-3-one, and the like.
Among these, α-(meth)acryloyloxy-γ-butyrolactone is preferred, and α-methacryloyloxy-γ-butyrolactone is more preferred.
The monomers having a lactone skeleton may be used singly or in combination of two or more.

The monomer having a sultone skeleton is preferably a (meth)acrylic ester having a norbornane sultone ring from the viewpoint of adhesion to a substrate or the like.
Specific examples of monomers having a sultone skeleton include β-(meth)acryloyloxy-β-methyl-δ-valerosultone, 4,4-dimethyl-2-methylene-γ-butyrosultone, β-(meth)acryloyloxy -γ-Butyrosultone, β-(meth)acryloyloxy-β-methyl-γ-butyrosultone, α-(meth)acryloyloxy-γ-butyrosultone, (meth)acrylic acid pantoylsultone, 5-(meth)acryloyloxy- Examples include 2,6-norbornane carbosultone, 2-methacryloyloxyacetoxy-4,5-oxathiatricyclo[4.2.1.0 ^3,7 ]nonane 5,5-dioxide, and the like.

[Monomer (d) having a hydrophilic group]
The other monomers preferably include monomers having a hydrophilic group (excluding monomer (b)) (hereinafter also referred to as "monomer (d)").
The monomer (d) may be any compound having a hydrophilic group and a polymerizable multiple bond, and known monomers can be used. The polymerizable multiple bond is preferably an ethylenic double bond.
Monomer (d) is a (meth)acrylic acid ester having a terminal hydroxy group from the viewpoint of solubility in a developer; substitution of an alkyl group, hydroxy group, carboxy group, etc. on the hydrophilic group of the monomer Derivatives having a group; compounds in which a (meth)acrylic acid ester having a cyclic hydrocarbon group has a hydrophilic group such as a hydroxy group or a carboxy group as a substituent are preferable.
The (meth)acrylic acid ester having a cyclic hydrocarbon group includes cyclohexyl (meth)acrylate, 1-isobornyl (meth)acrylate, adamantyl (meth)acrylate, tricyclodecanyl (meth)acrylate, Examples include dicyclopentyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

Specific examples of monomer (d) include (meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 2-hydroxy-n-propyl (meth)acrylate. , 4-hydroxybutyl (meth)acrylate, 3-hydroxyadamantyl (meth)acrylate, 2- or 3-cyano-5-norbornyl (meth)acrylate, 2-cyanomethyl-2-adamantyl (meth)acrylate, etc. Can be mentioned.
Among these, from the viewpoint of adhesion to substrates etc., 3-hydroxyadamantyl (meth)acrylate, 3,5-dihydroxyadamantyl (meth)acrylate, 2- or 3-cyano-5-norbornyl (meth)acrylate, 2-cyanomethyl-2-adamantyl (meth)acrylate is preferred, and 3-hydroxyadamantyl (meth)acrylate is more preferred.
The monomers having a hydrophilic group may be used alone or in combination of two or more.

<Copolymer composition ratio>
The proportion of the structural unit (a) based on the monomer (a) with respect to all the structural units constituting the present copolymer is preferably 20 to 70 mol%, more preferably 25 to 60 mol%, and 30 to 70 mol%. More preferably 50 mol%. If it is above the lower limit of the above range, the sensitivity and resolution of the resist film will be excellent, and if it is below the upper limit, the properties due to constituent units other than monomer (a) will be excellent, and the adhesion of the resist film to the substrate etc. and development will be improved. Excellent solubility in liquids.
The proportion of the structural unit (b) based on the monomer (b) with respect to all the structural units constituting the present copolymer is preferably 10 to 70 mol%, more preferably 15 to 60 mol%, and 20 to 70 mol%. More preferably 50 mol%. When it is at least the lower limit of the above range, it has excellent etching resistance, and when it is at most the upper limit, it has excellent properties due to structural units other than the monomer (b).
The proportion of the structural unit (c) based on the monomer (c) with respect to all the structural units constituting the present copolymer is preferably 0 to 60 mol%, more preferably 0 to 50 mol%, and 0 to 50 mol%. 40 mol% is more preferred. When it is below the above upper limit, properties due to structural units other than the monomer (c) are excellent.
The proportion of the structural unit (d) based on the monomer (d) with respect to all the structural units constituting the present copolymer is preferably 0 to 40 mol%, more preferably 0 to 30 mol%, and 0 to 30 mol%. 20 mol% is more preferred. When it is below the above upper limit, properties due to structural units other than the monomer (d) are excellent.

The total ratio of the structural unit (a) and the structural unit (b) to all the structural units constituting the present copolymer is preferably 40 to 100 mol%, more preferably 50 to 95 mol%, and 60 to 95 mol%. More preferably 90 mol%.
When this copolymer has structural units (other structural units) based on other monomers other than structural unit (a) and structural unit (b), for all the structural units constituting this copolymer, The total ratio of the structural unit (a), the structural unit (b), and other structural units is 100 mol%.

<Molecular weight>
The molecular weight of this copolymer is not particularly limited. When the present copolymer is a resist polymer, the weight average molecular weight (Mw) is preferably 1,000 to 200,000, more preferably 2,000 to 40,000. The molecular weight distribution (Mw/Mn) is preferably 1.0 to 3.0, more preferably 1.1 to 2.5.

≪Method for producing copolymer≫
The method for producing a copolymer of the present invention (hereinafter also referred to as "this production method") is a method for producing a copolymer by subjecting two or more types of monomers to a polymerization reaction.
Radical polymerization is preferred as the polymerization method. Specifically, a method of radically polymerizing monomers using a polymerization initiator is preferred. Radical polymerization is preferably carried out in the presence of a polymerization solvent.
The monomer polymerization reaction is preferably carried out in an atmosphere in which the oxygen concentration in the gas phase in the reactor is 1% by volume or less. When the oxygen concentration is 1% by volume or less, the inhibitory effect on the polymerization reaction is small. The oxygen concentration is more preferably 0.1% by volume or less, and even more preferably 0.01% by volume or less. It can be zero.
Specifically, before the start of the polymerization reaction, it is preferable to replace the gas phase in the reactor with an inert gas having an oxygen concentration of 1% by volume or less. Examples of the inert gas include nitrogen, rare gas, and the like. Nitrogen and argon are preferred because they are inert to radicals and are commonly used industrially, and nitrogen is more preferred.

The polymerization initiator is preferably one that efficiently generates radicals when heated. For example, azo compounds (2,2'-azobisisobutyronitrile, dimethyl-2,2'-azobisisobutyrate, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] ), organic peroxides (2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, di(4-tert-butylcyclohexyl)peroxydicarbonate, etc.), and the like.
The suitable temperature for use of these polymerization initiators is in the range of 50 to 150°C depending on the decomposition temperature.

Examples of the polymerization solvent include the following.
Ethers: chain ethers (diethyl ether, propylene glycol monomethyl ether (hereinafter referred to as "PGME"), etc.), cyclic ethers (tetrahydrofuran (hereinafter referred to as "THF"), etc.), 1,4-dioxane, etc. )etc.
Esters: methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, butyl lactate, propylene glycol monomethyl ether acetate (hereinafter referred to as "PGMEA"), γ-butyrolactone, methyl 2-hydroxyisobutyrate, etc.
Ketones: acetone, methyl ethyl ketone (hereinafter referred to as "MEK"), methyl isobutyl ketone (hereinafter referred to as "MIBK"), cyclohexanone, etc.
Amides: N,N-dimethylacetamide, N,N-dimethylformamide, etc.
Sulfoxides: dimethyl sulfoxide, etc.
Aromatic hydrocarbons: benzene, toluene, xylene, etc.
Aliphatic hydrocarbons: hexane, etc.
Alicyclic hydrocarbons: cyclohexane, etc.
One type of polymerization solvent may be used alone, or two or more types may be used in combination.

This manufacturing method includes at least the following steps (2) and (3). Furthermore, it is preferable to include the following step (1). Step (2) is started after step (1) is started. Step (3) is started after step (2) is started.
After completion of step (3), it is preferable to perform the following steps (4), (5), or (6).
Two or more steps selected from steps (4) to (6) may be combined. In this case, step (6) is started after steps (4) and (5) are completed. Step (5) is started after or simultaneously with the start of step (4).
Step (1): A step of supplying a monomer composition (x) containing a monomer (a1) containing an acid-dissociable group (hereinafter also referred to as "monomer (a1)") into a reactor. . The monomer composition (x) may be divided into two or more parts and supplied.
Step (2): A monomer (a2) containing an acid-dissociable group (hereinafter also referred to as "monomer (a2)") and a monomer (b2) containing a phenolic hydroxyl group (hereinafter referred to as "monomer (a2)") A step of supplying a monomer composition (y) containing a monomer (y) (also referred to as "mer (b2)") into a reactor and causing a polymerization reaction. The monomer composition (y) may be divided into two or more parts and supplied.
Step (3): A monomer (a3) containing an acid-dissociable group (hereinafter also referred to as "monomer (a3)") and a monomer (b3) containing a phenolic hydroxyl group (hereinafter referred to as "monomer (a3)") A step of supplying a monomer composition (z) containing at least one member selected from the group consisting of "compound (b3)" into a reactor and causing a polymerization reaction. The monomer composition (z) may be divided into two or more parts and supplied.
Step (4): Step of cooling the reactor.
Step (5): A step of supplying oxygen into the reactor.
Step (6): A step of adding the reaction product in the reactor to a poor solvent.

Monomers (a1), (a2), and (a3) are each a part of monomer (a) used for producing the present copolymer.
Monomer (a1) and monomer (a2) may be the same or different from each other.
Monomer (a1) and monomer (a3) may be the same or different from each other.
Monomer (a2) and monomer (a3) may be the same or different from each other.

Monomers (b2) and (b3) are each a part of monomer (b) used in the production of the present copolymer.
The monomer (b2) and the monomer (b3) may be the same or different from each other.

The monomer composition (x) and the monomer composition (y) have different compositions from each other.
The monomer composition (x) and the monomer composition (z) have different compositions.
The monomer composition (y) and the monomer composition (z) have different compositions.

[Step (1)]
The monomer composition (x) in step (1) contains monomer (a1). It may also contain a polymerization solvent. It may contain one or more types of monomers other than monomer (a).
The monomer (a1) contained in the monomer composition (x) is more than 0% by mass and 30% by mass or less based on the total mass of the monomer (a) used in the production of the present copolymer. It is preferably 0.5 to 20% by weight, more preferably 1 to 10% by weight.

When the present copolymer has a structural unit (b), the monomer composition (x) contains a monomer (b1) that is a part of the monomer (b) used in the production of the present copolymer. May include.
The monomer (b1) contained in the monomer composition (x) is preferably 0 to 30% by mass, and 0 to 30% by mass based on the total mass of the monomer (b) used in the production of the present copolymer. It is more preferably 20% by mass, and even more preferably 0 to 10% by mass.

When the present copolymer has a structural unit (c), the monomer composition (x) includes a monomer (c1) that is a part of the monomer (c) used in the production of the present copolymer. It is preferable to include.
The monomer (c1) contained in the monomer composition (x) is preferably 0 to 30% by mass, based on the total mass of the monomer (c) used in the production of the present copolymer, and 0. It is more preferably 5 to 20% by weight, even more preferably 1 to 10% by weight.

When the present copolymer has a structural unit (d), the monomer composition (x) includes a monomer (d1) that is a part of the monomer (d) used in the production of the present copolymer. It is preferable to include.
The monomer (d1) contained in the monomer composition (x) is preferably 0 to 30% by mass, based on the total mass of the monomer (d) used in the production of the present copolymer. It is more preferably 5 to 20% by weight, even more preferably 1 to 10% by weight.

When the monomer composition (x) contains two or more types of monomers, the content ratio (monomer composition, unit: mol%) of each monomer in the monomer composition (x) is It is preferable that the target composition of the present copolymer be within a range of ±20%.
In addition, if the monomer composition does not contain all types of monomers constituting the present copolymer, the content ratio (mole) of the monomers contained in the monomer composition in the target composition %) (the same applies hereinafter). For example, the target composition of the present copolymer is structural unit (a): structural unit (b): structural unit (c) = 35:30:35 (mol%) When the monomer composition (x) contains the monomer (a1) and the monomer (c1), the monomer (a1) and the monomer contained in the monomer composition (x) The content ratio of (c1) is 50:50 (mol%). It is preferably within the range of 40 to 60:60 to 40 (mol %), which is within the range of ±20% based on this 50:50 (mol %).

In step (1), before starting step (2), part or all of the monomer composition (x) is supplied into the reactor. The monomer composition (x) may be fed into the reactor all at once, may be gradually fed into the reactor by dropwise addition, or a combination of these may be used. Step (1) is ended before step (2) is ended. It is preferable to start step (2) after completing the supply of monomer composition (x).

[Step (2)]
The monomer composition (y) in step (2) contains monomer (a2) and monomer (b2). It may contain one or more monomers other than monomer (a2) and monomer (b2). It may also contain a polymerization solvent.
The monomer (a2) contained in the monomer composition (y) is preferably 30 to 100% by mass, and 50 to 100% by mass based on the total mass of the monomer (a) used in the production of the present copolymer. 98% by mass is more preferred, and 70 to 95% by mass is even more preferred.
The monomer (b2) contained in the monomer composition (y) is preferably 30 to 100% by mass, and 50 to 100% by mass based on the total mass of the monomer (b) used in the production of the present copolymer. 98% by mass is more preferred, and 70 to 95% by mass is even more preferred.

When the present copolymer has a structural unit (c), the monomer composition (y) contains a monomer (c2) that is a part of the monomer (c) used in the production of the present copolymer. It is preferable to include.
The monomer (c2) contained in the monomer composition (y) is preferably 30 to 100% by mass, and 50 to 100% by mass based on the total mass of the monomer (c) used in the production of the present copolymer. 98% by mass is more preferred, and 70 to 95% by mass is even more preferred.

When the present copolymer has a structural unit (d), the monomer composition (y) contains a monomer (d2) that is a part of the monomer (d) used in the production of the present copolymer. It is preferable to include.
The monomer (d2) contained in the monomer composition (y) is preferably 30 to 100% by mass, and 50 to 100% by mass based on the total mass of the monomer (d) used in the production of the present copolymer. 98% by mass is more preferred, and 70 to 95% by mass is even more preferred.

The content ratio of the monomers (monomer composition, unit: mol%) in the monomer composition (y) is within a range of ±10% with respect to the target composition of the present copolymer to be obtained. It is preferably within the range of ±5%, more preferably within the range of ±2%.

In step (2), it is preferable to gradually supply the monomer composition (y) to the reactor by dropping or the like.
In step (2), it is preferable that the polymerization reaction starts at the same time as the supply of monomer composition (y) into the reactor is started. For this reason, it is preferable to start supplying the polymerization initiator simultaneously with the start of supplying the monomer composition (y). For example, the monomer composition (y) may contain a polymerization initiator, a polymerization initiator solution may be supplied separately from the monomer composition (y), or these may be combined.

When providing step (1), the monomer composition (y) and the polymerization initiator are supplied into the reactor with the monomer composition (x) previously supplied into the reactor adjusted to the polymerization temperature. It is preferable to start.
When step (1) is not provided, a polymerization solvent is supplied into the reactor in advance, and the monomer composition (y) and the polymerization initiator are supplied into the reactor while the polymerization solvent is adjusted to the polymerization temperature. It is preferable to start.

[Step (3)]
The monomer composition (z) in step (3) contains at least one of monomer (a3) and monomer (b3). It may include both. It may contain one or more monomers other than monomer (a3) and monomer (b3). It may also contain a polymerization solvent.
The monomer (a3) contained in the monomer composition (z) is preferably 0 to 50% by mass, and 0. More preferably 5 to 30% by weight, even more preferably 1 to 10% by weight.
The monomer (b3) contained in the monomer composition (z) is preferably 0 to 50% by mass, and 0. More preferably 5 to 30% by weight, even more preferably 1 to 10% by weight.

When the present copolymer has a structural unit (c), the monomer composition (z) contains a monomer (c3) that is a part of the monomer (c) used in the production of the present copolymer. It is preferable to include.
The monomer (c3) contained in the monomer composition (z) is preferably 0 to 50% by mass, and 0. More preferably 5 to 30% by weight, even more preferably 1 to 10% by weight.

When the present copolymer has a structural unit (d), the monomer composition (z) contains a monomer (d3) that is a part of the monomer (d) used in the production of the present copolymer. It is preferable to include.
The monomer (d3) contained in the monomer composition (z) is preferably 0 to 50% by mass, and 0. More preferably 5 to 30% by weight, even more preferably 1 to 10% by weight.

The monomer content ratio (monomer composition, unit: mol%) in the monomer composition (z) is within ±20% of the target composition of the present copolymer to be obtained. It is preferably within the range of ±15%, and even more preferably within the range of ±10%.
Monomer composition (y) and monomer composition (z) are different in monomer composition.
When the monomer composition (z) contains the monomer (a3), the content ratio (mol%) of the monomer (a2) in the monomer composition (y) and the monomer composition (z ) is preferably 5 mol% or more, more preferably 10 mol% or more.
When the monomer composition (z) contains the monomer (b3), the content ratio (mol%) of the monomer (b2) in the monomer composition (y) and the monomer composition (z ) is preferably 5 mol% or more, and more preferably 10 mol% or more.

The monomer compositions of monomer composition (y) and monomer composition (z) are preferably designed by the following method.
The monomer composition (y) has the same composition or a composition close to the target composition ratio, and step (2) is performed. During the progress of step (2), periodically measure the amount of monomer remaining in the polymerization reaction solution, and after confirming the periodic copolymerization composition ratio, design the composition of monomer composition (z). do. Specifically, for monomers with fast copolymerization reactivity and a low copolymerization composition ratio during the late stage of polymerization, the content ratio in the monomer composition (z) is the content ratio in the monomer composition (y). For monomers whose copolymerization reactivity is slow and whose copolymerization composition ratio is high in the late stage of polymerization, the content ratio in the monomer composition (z) is the content ratio in the monomer composition (y). By making it less than , the period copolymerization composition ratio can be brought closer to the target composition ratio.

In step (3), it is preferable to gradually supply the monomer composition (z) to the reactor by dropping or the like.
From the time when 80% by mass of the total mass of the monomer composition (y) supplied into the reactor in step (2) is completed to the time when 30 minutes have passed after the completion of supplying 100% by mass. , it is preferred to start step (3). It is more preferable to start step (3) within 15 minutes after the supply of monomer composition (y) is completed.
In step (3), it is preferable to supply a polymerization initiator into the reactor. For example, the monomer composition (z) may contain a polymerization initiator, a polymerization initiator solution may be supplied separately from the monomer composition (z), or these may be combined. It is preferable to start supplying the polymerization initiator simultaneously with the start of supplying the monomer composition (z).
The time when 100% by mass of the monomer composition (y) has been completely supplied is defined as the end of step (2). The reaction solution in the reactor is maintained at the polymerization temperature from the end of step (2) to the start of step (3).
The time when 100% by mass of the monomer composition (z) has been completely supplied is defined as the end of step (3).
A reaction product is present in the reactor at the end of step (3). The reaction product includes unreacted monomers and polymerization initiators in addition to the produced polymer. For example, when monomers are subjected to a polymerization reaction in the presence of a polymerization solvent, a polymerization reaction solution containing the polymerization solvent and a reaction product is obtained.

[Step (4)]
Step (4) is a step (stopping step) of actively lowering the temperature of the polymerization reaction solution (reaction product) by cooling the reactor after the completion of (3) and stopping the polymerization reaction. Step (4) may be started immediately after step (3) is completed, or step (4) may be started after the polymerization temperature (reaction temperature) in step (3) is maintained for a predetermined period of time.
A radical polymerization reaction proceeds through a chain mechanism consisting of four elementary reactions: initiation reaction, propagation reaction, termination reaction, and chain transfer reaction, and the molecular weight of the resulting polymer is determined by the rate and mechanism of each elementary reaction. The growth reaction rate is proportional to the product of the monomer concentration and the radical concentration, and the termination reaction rate is proportional to the square of the radical concentration.
In the present invention, "stopping the polymerization reaction" means bringing the amount of radicals generated due to decomposition of the polymerization initiator to a sufficiently low level so as not to cause initiation and propagation reactions.
The temperature of the polymerization reaction solution after cooling is preferably 30°C or lower, more preferably 25°C or lower, even more preferably 20°C or lower, and particularly preferably 15°C or lower. The lower limit of the temperature after cooling is preferably −20° C. or higher from the viewpoint of ease of handling the polymerization reaction solution.

[Step (5)]
In step (5), oxygen is supplied into the reactor and the reaction product in the reactor is brought into contact with oxygen.
Step (5) starts after the end of step (3). When performing step (4), step (5) is started after or simultaneously with the start of step (4). When step (4) is not performed, step (5) may be started immediately after step (3) is completed, or after maintaining the polymerization temperature (reaction temperature) in step (3) for a predetermined time, step ( 5) may be started.

The temperature of the reaction product at the start of step (5), that is, the temperature T of the reaction product (polymerization reaction solution) immediately before starting oxygen supply into the reactor, is preferably 25°C or higher, and preferably 30°C or higher. The temperature is more preferably 45°C or higher, even more preferably 50°C or higher. The upper limit of the temperature T is preferably equal to or lower than the polymerization temperature (reaction temperature) in step (3). The difference between the temperature T and the polymerization temperature (polymerization temperature -T) is preferably 0 to 50°C, more preferably 0 to 35°C, even more preferably 0 to 30°C.

In step (5), a gas containing oxygen is introduced into the reactor, and part or all of the gas phase in the reactor is replaced with the gas.
As the gas introduced into the reactor, oxygen gas or air (oxygen concentration of 1 volume % or more and 22 volume % or less) can be used. It is preferable to use air from the viewpoint of workability and economy.
The oxygen concentration in the gas phase in the reactor after completion of step (5) is preferably 1% by volume or more, more preferably 3% by volume or more. The upper limit of the oxygen concentration is preferably 22% by volume or less from the viewpoint of workability and economic efficiency.
The reaction product (polymerization reaction solution) may be stored in contact with an oxygen-containing gas for a period of time after the completion of step (5) and before the start of step (6). The storage time is, for example, one hour or more.

Step (5) contributes to suppressing the polymerization reaction caused by the polymerization initiator remaining in the reaction product.
Specifically, unreacted monomers and polymerization initiators remain in the reaction product (polymerization reaction solution) after completion of step (3). By bringing the reaction product into contact with oxygen after the completion of the polymerization reaction, it is possible to suppress the reinitiation of the polymerization reaction caused by radicals generated from the remaining polymerization initiator, and it is possible to suppress the reinitiation of the polymerization reaction due to radicals generated from the remaining polymerization initiator. Generation can be suppressed.

[Step (6)]
Step (6) is a step (re-precipitation step) of adding the reaction product produced in the polymerization reaction to a poor solvent and precipitating the polymer in the reaction product.
The poor solvent is preferably one or a mixed solvent of two or more selected from the group consisting of methanol, isopropyl ether, isopropanol, heptane, hexane, cyclohexane, and toluene.

The reprecipitation step is very effective in purifying the reaction product by removing impurities such as unreacted monomers and polymerization initiators remaining in the reaction product. If unreacted monomers remain, the sensitivity will decrease when used as a resist composition, so it is preferable to remove them as much as possible.
By filtering out the precipitate in the poor solvent, the desired copolymer can be obtained in the form of a wet powder. The content of unreacted monomers remaining in the present copolymer is preferably as small as possible.

The desired dry powder of the present copolymer can be obtained by drying the wet powder obtained by filtering off the precipitate in the poor solvent.
Alternatively, the operation of dispersing the filtered wet powder in a poor solvent again to form a polymer dispersion and then filtering it can be repeated. This step is called a reslurry step, and is effective for further reducing impurities such as unreacted monomers and polymerization initiators remaining in the wet polymer powder.
In terms of obtaining a polymer while maintaining high productivity, it is preferable to perform purification only by a reprecipitation process without performing a reslurry process.

Further, the wet powder may be used as a resist composition by dissolving the wet powder in a solvent without drying, or may be used as a resist composition after being concentrated to remove low-boiling compounds. At that time, additives such as storage stabilizers may be added as appropriate.
Alternatively, the wet powder may be dried, then dissolved in a solvent, further concentrated to remove low-boiling compounds, and then used as a resist composition. Also in this case, additives such as storage stabilizers may be added as appropriate.

≪Method for producing resist composition≫
A resist polymer can be manufactured by this manufacturing method, and a resist composition can be manufactured using the obtained resist polymer.
The resist composition includes a resist polymer and a resist solvent. The chemically amplified resist composition further includes a compound that generates an acid upon irradiation with actinic rays or radiation (hereinafter also referred to as a "photoacid generator").
For example, a resist composition can be manufactured by dissolving a resist polymer and an optional photoacid generator in a resist solvent.
As the resist solvent, the solvents listed above as polymerization solvents can be used.

As the photoacid generator, compounds known in the art can be appropriately selected and used in chemically amplified resist compositions. One type of photoacid generator may be used alone, or two or more types may be used in combination.
Specific examples of the photoacid generator include onium salt compounds, sulfonimide compounds, sulfone compounds, sulfonic acid ester compounds, quinonediazide compounds, diazomethane compounds, and the like.
The amount of the photoacid generator used is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the polymer.

The chemically amplified resist composition may contain a nitrogen-containing compound. As the nitrogen-containing compound, amines are preferred, and secondary lower aliphatic amines and tertiary lower aliphatic amines are more preferred.
The amount of the nitrogen-containing compound is preferably 0.01 to 2 parts by weight based on 100 parts by weight of the polymer.

The chemically amplified resist composition may contain an organic carboxylic acid, a phosphorus oxoacid, or a derivative thereof (hereinafter, these will be collectively referred to as an acid compound).
Examples of organic carboxylic acids include malonic acid, citric acid, malic acid, succinic acid, benzoic acid, and salicylic acid.
Examples of the phosphorus oxoacid or its derivative include phosphoric acid or its derivative, phosphonic acid or its derivative, phosphinic acid or its derivative, and the like.
The amount of the acid compound is preferably 0.01 to 5 parts by weight based on 100 parts by weight of the polymer.

The resist composition may contain various additives such as a surfactant, other quenchers, sensitizers, antihalation agents, storage stabilizers, and antifoaming agents, as necessary. Any additive known in the art can be used. Further, the amount of these additives is not particularly limited and may be determined as appropriate.

≪Method for producing a substrate on which a fine pattern is formed≫
The method for manufacturing a substrate of this embodiment includes a step of coating the resist composition obtained above on a substrate to form a resist film, a step of exposing the resist film to light, and a step of transferring the exposed resist film to a developer. This is a method of manufacturing a substrate on which a pattern is formed, through a step of developing using a method.
An example of the method for manufacturing the substrate of this embodiment will be described below.

First, a resist composition is applied by spin coating or the like to the surface of a substrate to be processed, such as a silicon wafer, on which a desired fine pattern is to be formed. Then, the substrate to be processed coated with the resist composition is dried by baking treatment (prebaking) or the like to form a resist film on the substrate.

Next, the resist film is irradiated with light having a wavelength of 250 nm or less through a photomask to form a latent image (exposure). As the irradiation light, KrF excimer laser, ArF excimer laser, F ₂ excimer laser, and EUV excimer laser are preferable, and ArF excimer laser and EUV excimer laser are more preferable. Alternatively, an electron beam may be irradiated.
In addition, a liquid immersion method in which light is irradiated with a high refractive index liquid such as pure water, perfluoro-2-butyltetrahydrofuran, or perfluorotrialkylamine interposed between the resist film and the final lens of the exposure device. Exposure may also be performed.

After exposure, the resist film is appropriately heat-treated (post-exposure bake, PEB), and the resist film is brought into contact with an alkaline developer to dissolve the exposed portion in the developer and remove it (development). As the alkaline developer, known ones can be mentioned.
After development, the substrate is appropriately rinsed with pure water or the like. In this way, a resist pattern is formed on the substrate to be processed.

The substrate on which the resist pattern is formed is appropriately heat-treated (post-baked) to strengthen the resist, and portions without resist are selectively etched.
After etching, the resist is removed using a stripping agent to obtain a substrate on which a fine pattern is formed.

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

The following measurement method was used.
<Measurement of weight average molecular weight>
The weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of the polymer were determined in terms of polystyrene by gel permeation chromatography under the following conditions (GPC conditions).
[GPC conditions]
Equipment: Manufactured by Tosoh Corporation, Tosoh High Speed GPC equipment HLC-8320GPC (product name),
Separation column: 3 Shodex GPC K-805L (trade name) manufactured by Showa Denko Co., Ltd. connected in series,
Measurement temperature: 40℃,
Eluent: tetrahydrofuran (THF),
Sample: A solution in which about 20 mg of the polymer was dissolved in 5 mL of THF and filtered with a 0.5 μm membrane filter.
Flow rate: 1mL/min,
Injection volume: 0.1mL,
Detector: Differential refractometer.
Calibration curve I: About 20 mg of standard polystyrene was dissolved in 5 mL of THF, and the solution was filtered through a 0.5 μm membrane filter and injected into a separation column under the above conditions to determine the relationship between elution time and molecular weight. As the standard polystyrene, the following standard polystyrene manufactured by Tosoh Corporation (all trade names) was used.
F-80 (Mw=706,000),
F-20 (Mw=190,000),
F-4 (Mw=37,900),
F-1 (Mw=10,200),
A-2500 (Mw=2,630),
A-500 (mixture of Mw=682, 578, 474, 370, 260).

<Quantification of monomer>
The amount of monomer remaining in the polymerization reaction solution was determined by the following method.
At 1, 2, 3, 4, 5, 6, and 7 hours after the start of dropping in step (2), 0.1 g of the polymerization reaction solution in the reaction container was collected, diluted with acetonitrile, and added using a volumetric flask. The total volume was made 10 mL. This diluted solution was filtered through a 0.2 μm membrane filter, and the amount of monomer in the diluted solution was determined for each monomer using ACQUITY H-Class (trade name) manufactured by Waters.
In this measurement, one ACQUITY UPLC BEH C18 Column (trade name) manufactured by Waters was used as the separation column, the mobile phase was a water/acetonitrile gradient system, the flow rate was 0.5 mL/min, and the detector was The measurement was performed using an ACQUITY UPLC photodiode array (trade name) manufactured by Waters Inc., the detection wavelength was 220 nm, the measurement temperature was 40° C., and the injection amount was 2 μL.
The separation column ACQUITY UPLC BEH C18 Column (trade name) used had a silica gel particle size of 1.7 μm and a column inner diameter of 2.1 mm×column length of 50 mm.
The gradient conditions of the mobile phase were as follows, with water as liquid A and acetonitrile as liquid B. Furthermore, in order to quantify the amount of unreacted monomer, three types of monomer solutions with different concentrations were used as standard solutions.
Measurement time 0 to 4 minutes: A liquid/B liquid = 90 volume %/10 volume %.
Measurement time 4 to 6 minutes: A liquid/B liquid = 90 vol%/10 vol% to 70 vol%/30 vol%.
Measurement time 6 to 7 minutes: A liquid/B liquid = 70 vol%/30 vol% to 0 vol%/100 vol%.
Measurement time 7 to 7.1 minutes: Liquid A/Liquid B = 0% by volume/100% by volume.
Measurement time 7.1 to 9 minutes: A liquid/B liquid = from 0 volume%/100 volume% to 90 volume%/10 volume%.

<Calculation of period copolymerization composition ratio>
For the difference in the amount of monomer in each period determined by the above method, each amount is calculated from the sum of the amounts of monomer composition (y) and monomer composition (z) dropped during each period. The period copolymerization composition ratio in the period was calculated.

<Raw materials>
The following raw materials were used.
[Monomer composition (x)]
Monomer (a1-1): 1-methylcyclopentyl methacrylate (in formula (ai), R ₁₁ is a methyl group, R ₂₁ is a methyl group, R ₂₂ and R ₂₃ are bonded to each other to form a cyclopentyl ring) Compound)
Monomer (c1-1): α-methacryloyloxy-γ-butyrolactone [monomer composition (y)]
Monomer (a2-1): 1-methylcyclopentyl methacrylate Monomer (b2-1): p-hydroxystyrene (in formula (bi), R ₁₂ is a hydrogen atom, Y is a single bond, R ₃₁ is a hydrogen atom , k is 1, and the hydroxyl group -OR ₃₁ is bonded to the para position)
Monomer (c2-1): α-methacryloyloxy-γ-butyrolactone [monomer composition (z)]
Monomer (a3-1): 1-methylcyclopentyl methacrylate Monomer (b3-1): p-hydroxystyrene Monomer (c3-1): α-methacryloyloxy-γ-butyrolactone [polymerization solvent]
Polymerization solvent (1): PGMEA
[Polymerization initiator]
Polymerization initiator (1): dimethyl-2,2'-azobisisobutyrate

<Example 1>
A resist copolymer was produced using monomer compositions (x), (y), and (z) having the formulations shown in Table 1, by a method including the following steps (1) to (6).
Table 2 shows the monomer composition (unit: mol %) in each monomer composition.

[Step (1)]
A reactor equipped with a gas inlet, a stirrer, a condenser, two dropping devices, and a thermometer contained the entire amount of the monomer composition (x), and the monomer composition was placed in the first dropping device. (y), and the second dropping device contained the entire amount of monomer composition (z).
The gas phase in the reactor was replaced with nitrogen, and the reactor was placed in a hot water bath while maintaining the nitrogen atmosphere. The temperature of the water bath was raised while stirring the liquid in the reactor, and the temperature of the monomer composition (x) in the reactor was adjusted to 80° C., which is the polymerization temperature.

[Step (2)]
While stirring the liquid in the reactor, the entire amount of monomer composition (y) was added dropwise thereto at a constant rate over 360 minutes.
[Step (3)]
360 minutes after the start of dropping monomer composition (y), dropping of monomer composition (z) was started. The entire amount of monomer composition (z) was dropped at a constant rate over 60 minutes.

[Step (4)]
After the monomer composition (z) was added dropwise, heating of the water bath was stopped to obtain a polymerization reaction solution.
Subsequently, the hot water in the hot water bath was continuously replaced with water at 20°C to cool the polymerization reaction solution in the reactor to 25°C to stop the polymerization reaction.

[Step (5)]
Simultaneously with the start of cooling in step (4), a mixed gas of nitrogen (97% by volume)/oxygen (3% by volume) was supplied from the gas inlet to adjust the gas phase in the flask to an oxygen concentration of 3% by volume. Replaced.

[Step (6)]
The obtained polymerization reaction solution was added to 10 times the amount (by volume) of the poor solvent. Specifically, the polymerization reaction solution was added dropwise while stirring the poor solvent to precipitate the polymer (white precipitate). Isopropyl ether was used as a poor solvent.
The precipitate was filtered off to obtain a wet polymer powder. The wet polymer powder was dried at 40° C. under reduced pressure for about 40 hours to obtain a dry polymer powder.
The weight average molecular weight (Mw) of the obtained polymer was 5900, and the molecular weight distribution (Mw/Mn) was 1.52.
The period copolymerization composition ratio was measured using the method described above. The results are shown in Table 3. Table 3 also shows the ratio of the period copolymerization composition ratio to the target composition (period copolymerization composition ratio/target composition) for each structural unit as a percentage (the same applies hereinafter).

<Comparative example 1>
A resist copolymer was produced in the same manner as in Example 1, except that step (3) was not performed and the temperature was maintained for 60 minutes.
That is, monomer compositions (x) and (y) having the formulations shown in Table 1 were used. The monomer compositions in monomer compositions (x) and (y) are the same as in Example 1, as shown in Table 2.

Steps (1) and (2) were carried out in the same manner as in Example 1. Step (3) was not performed, and in step (4), after the monomer composition (y) was added dropwise, the temperature was maintained for 60 minutes, and then the heating of the hot water bath was stopped to obtain a polymerization reaction solution. The subsequent steps were carried out in the same manner as in Example 1 to obtain a dry polymer powder.
The weight average molecular weight (Mw) of the obtained polymer was 5800, and the molecular weight distribution (Mw/Mn) was 1.51. The period copolymerization composition ratio was measured using the method described above.

As shown in the results in Table 3, compared to Comparative Example 1 in which step (3) was not performed after step (2), in Example 1 in which step (3) was performed, the amount of The period copolymerization composition ratio of the copolymer was close to the target composition.
A possible reason for this effect is that each monomer was supplied in step (3) in consideration of the copolymerization reactivity of each monomer used in the polymerization reaction.

Claims (17)

A method for producing a copolymer by polymerizing two or more monomers, the method comprising:
A method for producing a copolymer, comprising the following steps (2) and (3), and starting the step (3) after starting the step (2).
Step (2): A monomer composition (y) containing a monomer (a2) containing an acid-dissociable group and a monomer (b2) containing a phenolic hydroxyl group is supplied into a reactor, and polymerization is carried out. The process of reacting.
Step (3): The monomer composition (y) contains at least one selected from the group consisting of a monomer (a3) containing an acid-dissociable group and a monomer (b3) containing a phenolic hydroxyl group. A step in which a monomer composition (z) having a different composition from the above is supplied into a reactor and subjected to a polymerization reaction. From the time when 80% by mass of the total mass of the monomer composition (y) supplied into the reactor in the step (2) is completed to the time when 30 minutes have passed after the completion of supplying 100% by mass. The method for producing a copolymer according to claim 1, wherein the step (3) is started during this period. The method for producing a copolymer according to claim 1 or 2, wherein the monomer (a2) and the monomer (a3) each contain a compound represented by the following formula (ai).

(In formula (ai), R ₁₁ represents a hydrogen atom or a methyl group, and R ₂₁ represents an alkyl group having 1 to 5 carbon atoms that may have an etheric oxygen atom between the carbon-carbon bonds. , R ₂₂ and R ₂₃ each represent an alkyl group having 1 to 5 carbon atoms which may have an etheric oxygen atom between the carbon-carbon bonds, and R ₂₂ and R ₂₃ are bonded to each other to form a ring. (You may do so.) The method for producing a copolymer according to any one of claims 1 to 3, wherein the monomer (b2) and the monomer (b3) each contain a compound represented by the following formula (bi). .

(In formula (bi), R ₁₂ represents a hydrogen atom or a methyl group, Y represents a linking group containing a single bond or an ester bond, and R ₃₁ represents a hydrogen atom, a hydrocarbon group having an acyl group, or a carbon -Represents a hydrocarbon group having an etheric oxygen atom between carbon bonds, and k represents an integer from 1 to 5.) At least one selected from the monomer composition (y) and the monomer composition (z) is further selected from the group consisting of a monomer having a lactone skeleton and a monomer having a sultone skeleton. The method for producing a copolymer according to any one of claims 1 to 4, comprising at least one copolymer. At least one selected from the monomer composition (y) and the monomer composition (z) further contains a monomer having a hydrophilic group other than the monomer (b2). A method for producing a copolymer according to any one of Items 1 to 5. The method for producing a copolymer according to any one of claims 1 to 6, further comprising the following step (1), and starting the step (2) after starting the step (1).
Step (1): A monomer composition containing a monomer (a1) containing an acid-dissociable group and having a different composition from the monomer composition (y) and the monomer composition (z). x) into the reactor. The method for producing a copolymer according to claim 7, wherein the step (2) is started after the supply of the monomer composition (x) is completed in the step (1). The method for producing a copolymer according to claim 7 or 8, wherein the monomer (a1) contains a compound represented by the following formula (ai).

(In formula (ai), R ₁₁ represents a hydrogen atom or a methyl group, and R ₂₁ represents an alkyl group having 1 to 5 carbon atoms that may have an etheric oxygen atom between the carbon-carbon bonds. , R ₂₂ and R ₂₃ each represent an alkyl group having 1 to 5 carbon atoms which may have an etheric oxygen atom between the carbon-carbon bonds, and R ₂₂ and R ₂₃ are bonded to each other to form a ring. (You may do so.) Any one of claims 7 to 9, wherein the monomer composition (x) further contains at least one selected from the group consisting of a monomer having a lactone skeleton and a monomer having a sultone skeleton. A method for producing a copolymer as described in . The copolymer according to any one of claims 7 to 10, wherein the monomer composition (x) further contains a monomer having a hydrophilic group other than the monomer (b2). Production method. After completing the supply of the monomer composition (z) in the step (3), the copolymer according to any one of claims 1 to 11 further includes the following step (4). Production method.
Step (4): A step of cooling the reactor. After completing the supply of the monomer composition (z) in the step (3), the copolymer according to any one of claims 1 to 12 further includes the following step (5). Production method.
Step (5): A step of supplying oxygen into the reactor. After completing the supply of the monomer composition (z) in the step (3), the copolymer according to any one of claims 1 to 13 further includes the following step (6). Production method.
Step (6): A step of adding the reaction product in the reactor to a poor solvent. The method for producing a copolymer according to claim 14, wherein the poor solvent contains at least one selected from the group consisting of isopropyl ether, isopropanol, heptane, hexane, cyclohexane, and toluene. A method for producing a resist composition, comprising producing a copolymer by the production method according to any one of claims 1 to 15, and producing a resist composition using the obtained copolymer. A step of manufacturing a resist composition by the manufacturing method according to claim 16, a step of applying the obtained resist composition onto a substrate to form a resist film, a step of exposing the resist film to light, and a step of exposing the resist composition to light. Developing the resist film using a developer.