JP2013006888A - Method of producing polymer for lithography, method of producing resist composition, and method of manufacturing substrate on which pattern is formed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a polymer for lithography, which can efficiently reduce a residual monomer contained in the polymer.SOLUTION: The method of producing the polymer for lithography includes: a step of radically polymerizing a monomer by using a polymerization initiator in the presence of a polymerization solvent to obtain a polymerization reaction solution having viscosity of >120 mPa s at 25°C; a step of diluting the polymerization reaction solution thus obtained, with a diluting solvent to obtain a post-dilution solution having viscosity of ≤120 mPa s at 25°C; and a step of dropping the post-dilution solution on a poor solvent for the polymer to precipitate the polymer in the post-dilution solution.

Description

  The present invention relates to a method for producing a lithography polymer, a method for producing a resist composition using the lithography polymer obtained by the production method, and a substrate on which a pattern is formed using the resist composition. Regarding the method.

  In recent years, a resist pattern formed in a manufacturing process of a semiconductor element, a liquid crystal element, or the like has been rapidly miniaturized due to progress in lithography technology. As a technique for miniaturization, there is a reduction in wavelength of irradiation light. Specifically, the irradiation light has become shorter from conventional ultraviolet rays typified by g-line (wavelength: 438 nm) and i-line (wavelength: 365 nm) to shorter wavelength DUV (Deep Ultra Violet). .

  Recently, 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 for further shortening the wavelength have been studied. . Furthermore, these immersion lithography techniques are also being studied. Also, as a different type of lithography technology, electron beam lithography technology has been energetically studied.

A “chemically amplified resist composition” containing a photoacid generator has been proposed as a highly sensitive resist composition used for forming a resist pattern using the irradiation light or electron beam of the short wavelength. Improvement and development of amplification resist compositions are underway.
For example, as a chemically amplified resist polymer used in ArF excimer laser lithography, an acrylic polymer that is transparent with respect to light having a wavelength of 193 nm has attracted attention. As the acrylic polymer, for example, a polymer of (meth) acrylic acid ester having an adamantane skeleton in an ester portion and (meth) acrylic acid ester having a lactone skeleton in an ester portion has been proposed (Patent Document 1). etc).
In addition, in order to prevent reflection from the substrate at the time of exposure, development of an antireflection film having a low light transmittance with respect to exposure light has been advanced, and an antireflection film using an acrylic polymer has been proposed ( Patent Documents 2 and 3).

  With the miniaturization of resist patterns, the demands on the quality of lithography polymers are becoming stricter. For example, it is known that in order to obtain an excellent resist pattern profile, it is better that the residual monomer contained in the polymer for lithography is low (Patent Document 4, etc.). Further, in order to reduce the residual monomer, it is generally known that a technique called reprecipitation, which is purified by adding a polymerization reaction solution to a poor solvent and precipitating a polymer, is used ( Patent Document 5).

JP 10-319595 A JP 2003-295456 A JP 2004-31569 A JP 2001-109153 A JP 2003-215806 A

However, the conventional reprecipitation method is not always sufficient, and a method capable of further reducing the residual monomer in the polymer is desired. In addition, if the polymer obtained by reprecipitation is added again to a poor solvent and subjected to a restructuring process to remove impurities, residual monomers can be reduced, but complicated operations increase and production efficiency is poor. Become.
The present invention has been made in view of the above circumstances, and a method for producing a lithography polymer capable of efficiently reducing the residual monomer contained in the polymer, and a lithography polymer obtained by the production method. It is an object of the present invention to provide a resist composition containing the same and a method for producing a substrate on which a pattern is formed using the resist composition.

In order to solve the above-mentioned problems, the method for producing a lithographic polymer according to the present invention comprises subjecting a monomer to radical polymerization using a polymerization initiator in the presence of a polymerization solvent, and having a viscosity at 25 ° C. of 120 mPa A step of obtaining a polymerization reaction solution higher than s; a step of diluting the obtained polymerization reaction solution with a diluting solvent to obtain a diluted solution having a viscosity at 25 ° C. of 120 mPa · s or less; It is characterized by including a step of dropping the polymer in a poor solvent for the coalescence to precipitate the polymer in the solution after the dilution.
The dilution solvent is preferably a poor solvent for the polymer.

  The present invention comprises a step of producing a polymer for lithography by the method for producing a polymer for lithography of the present invention, and the obtained polymer for semiconductor lithography and a compound that generates an acid upon irradiation with actinic rays or radiation. A method for producing a resist composition is provided.

  The present invention includes a step of producing a resist composition by the method for producing a resist composition of the present invention, a step of coating the obtained resist composition on a work surface of a substrate to form a resist film, and the resist Provided is a method for manufacturing a substrate on which a pattern is formed, which includes a step of exposing a film and a step of developing the exposed resist film using a developer.

According to the method for producing a polymer for lithography of the present invention, the removal efficiency when removing unreacted monomers and the like contained in the polymerization reaction solution can be improved by reprecipitation. Thereby, a polymer for lithography having a small residual amount of monomer and a narrow molecular weight distribution can be efficiently produced. Such a polymer for lithography with a small residual amount of monomer and a narrow molecular weight distribution is excellent in sensitivity when used in a resist composition.
According to the method for producing a resist composition of the present invention, a resist composition excellent in sensitivity can be obtained, which includes the lithography polymer produced by the production method of the present invention.
According to the substrate manufacturing method of the present invention, a highly accurate fine resist pattern can be stably formed using a resist composition having excellent sensitivity.

In the present specification, “(meth) acrylic acid” means acrylic acid or methacrylic acid, and “(meth) acryloyloxy” means acryloyloxy or methacryloyloxy.
The value of the viscosity of the solution in this specification is a value measured with an E-type viscometer at a measurement temperature of 25 ° C.

<Polymer for lithography>
The polymer for lithography in the present invention (hereinafter sometimes simply referred to as polymer) is not particularly limited as long as it is a polymer used in the lithography process. For example, a resist polymer used for forming a resist film, an antireflection film (TARC) formed on the upper layer of the resist film, or a reflection used for forming an antireflection film (BARC) formed on the lower layer of the resist film. Examples thereof include a polymer for prevention film, a gap fill film polymer used for forming a gap fill film, and a polymer for top coat film used for forming a top coat film.

  Examples of the resist polymer include a copolymer containing at least one structural unit having an acid leaving group and at least one structural unit having a polar group.

  Examples of the polymer for antireflection film include a structural unit having a light-absorbing group and an amino group, an amide group, a hydroxyl group, an epoxy group, etc. that can be cured by reacting with a curing agent to avoid mixing with the resist film. And a copolymer containing a structural unit having a reactive functional group. The light-absorbing group is a group having high absorption performance with respect to light in a wavelength region where the photosensitive component in the resist composition is sensitive. Specific examples include an anthracene ring, naphthalene ring, benzene ring, quinoline ring. , A group having a ring structure (optionally substituted) such as a quinoxaline ring and a thiazole ring. In particular, when KrF laser light is used as irradiation light, an anthracene ring or an anthracene ring having an arbitrary substituent is preferable, and when ArF laser light is used, a benzene ring or a benzene having an arbitrary substituent A ring is preferred.

  Examples of the optional substituent include a phenolic hydroxyl group, an alcoholic hydroxyl group, a carboxy group, a carbonyl group, an ester group, an amino group, and an amide group. Among these, those having a protected or unprotected phenolic hydroxyl group as the light absorbing group are preferable from the viewpoint of good developability and high resolution. Examples of the structural unit / monomer having the light-absorbing group include benzyl (meth) acrylate and p-hydroxyphenyl (meth) acrylate.

Examples of polymers for gap fill films are reactive functionalities that have a suitable viscosity for flowing into narrow gaps and can be cured by reacting with curing agents to avoid mixing with resist films and antireflection films. Examples thereof include a copolymer containing a structural unit having a group, specifically, a copolymer of hydroxystyrene and a monomer such as styrene, alkyl (meth) acrylate, or hydroxyalkyl (meth) acrylate.
Examples of the polymer for the topcoat film used in immersion lithography include a copolymer containing a structural unit having a carboxyl group, a copolymer containing a structural unit having a fluorine-containing group substituted with a hydroxyl group, and the like.

Hereinafter, the structural unit and the monomer corresponding thereto that are suitably used when the lithography polymer is a resist polymer will be described.
[Structural unit having a polar group]
The resist polymer preferably has a structural unit having a polar group.
The “polar group” is a group having a polar functional group or a polar atomic group. Specific examples include a hydroxy group, a cyano group, an alkoxy group, a carboxy group, an amino group, a carbonyl group, and a fluorine atom. A group containing a sulfur atom, a group containing a lactone skeleton, a group containing an acetal structure, a group containing an ether bond, and the like.
Among these, the resist polymer applied to the pattern forming method that is exposed to light having a wavelength of 250 nm or less preferably has a structural unit having a lactone skeleton as the structural unit having a polar group, It is preferable to have a structural unit having a functional group.

(Constitutional unit / monomer having a lactone skeleton)
Examples of the lactone skeleton include a lactone skeleton having about 4 to 20 members. The lactone skeleton may be a monocycle having only a lactone ring, or an aliphatic or aromatic carbocyclic or heterocyclic ring may be condensed with the lactone ring.
In the case where the polymer contains a structural unit having a lactone skeleton, the content thereof is preferably 20 mol% or more, more preferably 25 mol% or more of all structural units (100 mol%) from the viewpoint of adhesion to a substrate or the like. Is more preferable. Moreover, from the point of a sensitivity and resolution, 60 mol% or less is preferable, 55 mol% or less is more preferable, and 50 mol% or less is more preferable.

  As a monomer having a lactone skeleton, a (meth) acrylic acid ester having a substituted or unsubstituted δ-valerolactone ring, a substituted or unsubstituted γ-butyrolactone ring is used because of its excellent adhesion to a substrate or the like. Preferably, at least one selected from the group consisting of monomers having it is preferred, and monomers having an unsubstituted γ-butyrolactone ring are particularly preferred.

Specific examples of the monomer 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 pantoyl lactone, 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]} cited decan-3-one and the like . Examples of the monomer having a similar structure include methacryloyloxysuccinic anhydride.
Monomers having a lactone skeleton may be used alone or in combination of two or more.

(Structural unit / monomer having a hydrophilic group)
The “hydrophilic group” in the present specification is at least one of —C (CF ₃ ) ₂ —OH, a hydroxy group, a cyano group, a methoxy group, a carboxy group, and an amino group.
Among these, it is preferable that the resist polymer applied to the pattern forming method exposed to light having a wavelength of 250 nm or less has a hydroxy group or a cyano group as a hydrophilic group.
The content of the structural unit having a hydrophilic group in the polymer is preferably from 5 to 30 mol%, more preferably from 10 to 25 mol%, of the total structural units (100 mol%) from the viewpoint of the resist pattern rectangularity. .

  Examples of the monomer having a hydrophilic group include a (meth) acrylic acid ester having a terminal hydroxy group; a derivative having a substituent such as an alkyl group, a hydroxy group, or a carboxy group on the hydrophilic group of the monomer; Monomers having a cyclic hydrocarbon group (for example, cyclohexyl (meth) acrylate, 1-isobornyl (meth) acrylate, adamantyl (meth) acrylate, tricyclodecanyl (meth) acrylate, (meth) acrylic acid) Dicyclopentyl, 2-methyl-2-adamantyl (meth) acrylate, 2-ethyl-2-adamantyl (meth) acrylate, etc.) having a hydrophilic group such as a hydroxy group or a carboxy group as a substituent; Can be mentioned.

Specific examples of the monomer having a hydrophilic group include (meth) acrylic acid, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 2-hydroxy- (meth) acrylate. -Propyl, 4-hydroxybutyl (meth) acrylate, 3-hydroxyadamantyl (meth) acrylate, 2- or 3-cyano-5-norbornyl (meth) acrylate, 2-cyanomethyl-2-adamantyl (meth) acrylate, etc. Is mentioned. From the point of adhesion to a substrate or the like, 3-hydroxyadamantyl (meth) acrylate, 3,5-dihydroxyadamantyl (meth) acrylate, 2- or 3-cyano-5-norbornyl (meth) acrylate, 2-cyanomethyl- 2-adamantyl (meth) acrylate and the like are preferable.
The monomer which has a hydrophilic group may be used individually by 1 type, and may be used in combination of 2 or more type.

[Constitutional unit having acid leaving group]
The resist polymer preferably has a structural unit having an acid-leaving group in addition to the above-described structural unit having a polar group for use in resist applications. In addition to this, a known structural unit may be added if necessary. You may have.
The “acid leaving group” is a group having a bond that is cleaved by an acid, and a part or all of the acid leaving group is removed from the main chain of the polymer by cleavage of the bond.
In the 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, and has an effect of enabling resist pattern formation.
The proportion of the structural unit having an acid leaving group is preferably 20 mol% or more, more preferably 25 mol% or more, out of all the structural units (100 mol%) constituting the polymer from the viewpoint of sensitivity and resolution. . Moreover, 60 mol% or less is preferable from the point of the adhesiveness to a board | substrate etc., 55 mol% or less is more preferable, and 50 mol% or less is further more preferable.

The monomer having an acid leaving group may be any compound having an acid leaving group and a polymerizable multiple bond, and known ones can be used. The polymerizable multiple bond is a multiple bond that is cleaved during the polymerization reaction to form a copolymer chain, and an ethylenic double bond is preferable.
Specific examples of the monomer having an acid leaving group include (meth) acrylic acid esters having an alicyclic hydrocarbon group having 6 to 20 carbon atoms and having an acid leaving group. It is done. The alicyclic hydrocarbon group may be directly bonded to an oxygen atom constituting an ester bond of (meth) acrylic acid ester, or may be bonded via a linking group such as an alkylene group.
The (meth) acrylic acid ester has an alicyclic hydrocarbon group having 6 to 20 carbon atoms, and a tertiary carbon atom at the bonding site with the oxygen atom constituting the ester bond of the (meth) acrylic acid ester. A (meth) acrylic acid ester having an alicyclic group or an alicyclic hydrocarbon group having 6 to 20 carbon atoms and a -COOR group (R may have a substituent) on the alicyclic hydrocarbon group. (Meth) acrylic acid ester in which a tertiary hydrocarbon group, a tetrahydrofuranyl group, a tetrahydropyranyl group, or an oxepanyl group is bonded directly or via a linking group is included.

In particular, in the case of producing a resist composition that is applied to a pattern forming method that is exposed to light having a wavelength of 250 nm or less, as a preferred example of a monomer having an acid leaving group, for example, 2-methyl-2- Adamantyl (meth) acrylate, 2-ethyl-2-adamantyl (meth) acrylate, 1- (1′-adamantyl) -1-methylethyl (meth) acrylate, 1-methylcyclohexyl (meth) acrylate, 1-ethylcyclohexyl ( Examples include meth) acrylate, 1-methylcyclopentyl (meth) acrylate, 1-ethylcyclopentyl (meth) acrylate, isopropyl adamantyl (meth) acrylate, 1-ethylcyclooctyl (meth) acrylate, and the like.
As the monomer having an acid leaving group, one type may be used alone, or two or more types may be used in combination.

<Polymerization solvent>
Examples of the polymerization solvent used in the present invention include the following.
Ethers: chain ether (diethyl ether, propylene glycol monomethyl ether, etc.), cyclic ether (tetrahydrofuran (hereinafter referred to as “THF”), 1,4-dioxane, etc.) and the like.
Esters: methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, butyl lactate, propylene glycol monomethyl ether acetate (hereinafter referred to as “PGMEA”), γ-butyrolactone, and the like.
Ketones: acetone, methyl ethyl ketone (hereinafter referred to as “MEK”), methyl isobutyl ketone (hereinafter referred to as “MIBK”), cyclohexanone, and the like.
Amides: N, N-dimethylacetamide, N, N-dimethylformamide and the like.
Sulfoxides: dimethyl sulfoxide and the like.
Aromatic hydrocarbons: benzene, toluene, xylene and the like.
Aliphatic hydrocarbon: hexane and the like.
Alicyclic hydrocarbons: cyclohexane and the like.
An organic solvent may be used individually by 1 type, and may use 2 or more types together.

<Polymerization initiator>
The polymerization initiator used in the present invention is preferably one that generates radicals efficiently by heat. For example, an azo compound (2,2′-azobisisobutyronitrile, dimethyl-2,2′-azobisisobutyrate, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] Etc.), organic peroxides (2,5-dimethyl-2,5-bis (tert-butylperoxy) hexane, di (4-tert-butylcyclohexyl) peroxydicarbonate, etc.) and the like.

<Poor solvent>
The poor solvent used for reprecipitation in the present invention is a poor solvent for the polymer. That is, it is a solvent that has a small ability to dissolve the target polymer and from which the polymer can precipitate. According to the composition of the polymer, known ones can be appropriately selected and used. Methanol, isopropyl alcohol, diisopropyl ether, heptane, or water is preferable because unreacted monomers, polymerization initiators, and the like used in the polymer for semiconductor lithography can be efficiently removed. A poor solvent may be used individually by 1 type, and may use 2 or more types together.

<Method for producing polymer>
[Polymerization process]
As a polymerization method, a solution polymerization method in which a monomer is radically polymerized using a polymerization initiator in the presence of a polymerization solvent is used.
In the solution polymerization method, the monomer and the polymerization initiator may be supplied to the polymerization vessel either continuously or dropwise. As a solution polymerization method, a monomer and a polymerization initiator are dropped into a polymerization vessel from the viewpoint that a variation in average molecular weight and molecular weight distribution due to differences in production lots is small and a reproducible polymer can be easily obtained. The dropping polymerization method is preferred.

In the dropping polymerization method, the inside of the polymerization vessel is heated to a predetermined polymerization temperature, and then the monomer and the polymerization initiator are dropped into the polymerization vessel independently or in any combination.
A monomer may be dripped only with a monomer, and may be dripped as a monomer solution which melt | dissolved the monomer in the polymerization solvent.
A polymerization solvent and / or monomer may be charged into the polymerization vessel in advance.
The polymerization initiator may be dissolved directly in the monomer, may be dissolved in the monomer solution, or may be dissolved only in the polymerization solvent.
The monomer and the polymerization initiator may be dropped into the polymerization vessel after mixing in the same storage tank; they may be dropped into the polymerization container from each independent storage tank; They may be mixed immediately before the supply and dropped into the polymerization vessel.
One of the monomer and the polymerization initiator may be dropped first, and then the other may be dropped with a delay, or both may be dropped at the same timing.
The dropping rate may be constant until the end of dropping, or may be changed in multiple stages according to the consumption rate of the monomer or the polymerization initiator.
The dripping may be performed continuously or intermittently.
The polymerization temperature is preferably 50 to 150 ° C.

In the solution polymerization method, the viscosity of the reaction solution in which the polymerization reaction is performed increases as the monomer polymerization reaction proceeds. If the viscosity of the reaction solution becomes too high, a so-called runaway reaction may occur in which the polymerization reaction proceeds rapidly.
In the present invention, a reaction solution in which the polymerization reaction is stopped by causing a polymerization reaction of the monomer using a polymerization initiator in the presence of a polymerization solvent and then cooling is referred to as a polymerization reaction solution.
The viscosity of the polymerization reaction solution decreases when the amount of the polymerization solvent used in the polymerization reaction is large, and increases when the amount of the polymerization solvent used is small. The amount of the polymerization solvent used for the polymerization reaction may be set so that the viscosity of the reaction solution is low enough to prevent the above-mentioned runaway reaction, and the production amount becomes worse as the amount of the polymerization solvent used increases.
In the present invention, the viscosity at 25 ° C. of the polymerization reaction solution may be higher than 120 mPa · s, but is preferably 130 mPa · s or more, more preferably 150 mPa · s or more, more preferably 200 mPa · s or more from the viewpoint of production efficiency. Is particularly preferably 250 mPa · s or more. The upper limit of the viscosity of the polymerization reaction solution is not limited as long as the runaway reaction does not occur, and is preferably 10,000 mPa · s or less, and more preferably 9,000 mPa · s or less.

[Dilution process]
In the present invention, the polymerization reaction solution obtained by the solution polymerization method is diluted with a diluting solvent so that the viscosity at 25 ° C. is 120 mPa · s or less before purification by reprecipitation.
In the present invention, a solution obtained by adding a diluting solvent to the polymerization reaction solution and used for the first dropping into the poor solvent is referred to as a solution after dilution. The viscosity at 25 ° C. of the diluted solution is 120 mPa · s or less, preferably 100 mPa · s or less, preferably 90 mPa · s or less, and more preferably 80 mPa · s or less. When the viscosity of the solution after dilution is 120 mPa · s or less, the monomer removal efficiency when reprecipitation is performed can be sufficiently improved.
The lower limit of the viscosity of the solution after dilution is not particularly limited, but is preferably 5 mPa · s or more and more preferably 10 mPa · s or more in terms of not increasing the amount of the solution after dilution and reducing the productivity.
In the present invention, the viscosity of the polymerization reaction solution varies depending on the type and molecular weight of the polymer, the type of the polymerization solution, and the concentration of the polymerization reaction solution, but may be diluted as appropriate.

As a dilution solvent, the solvent mentioned as said polymerization solvent may be used, the solvent mentioned as said poor solvent may be used, and these may be combined.
Specific examples of the dilution solvent include 1,4-dioxane, acetone, THF, MEK, cyclopentanone, cyclohexanone, MIBK, γ-butyrolactone, PGMEA, PGME, ethyl lactate, methyl 2-hydroxyisobutyrate, methanol, ethanol, Examples thereof include isopropyl alcohol, water, hexane, heptane, diisopropyl ether, or a mixed solvent thereof.
In particular, when a poor solvent is used as a dilution solvent, the difference in solubility parameter from the poor solvent in the reprecipitation step described later is preferably reduced.

The difference between the solubility parameter (hereinafter also referred to as SP value) of the solvent (mixture of polymerization solvent and dilution solvent) in the solution after dilution and the SP value of the poor solvent used for reprecipitation is a good dispersion of the polymer solution. The smaller one is preferable from the viewpoint that the property can be obtained and the monomer can be efficiently removed.
The SP value of the solvent can be determined, for example, by the method described in “Polymer Handbook”, 4th edition, pages VII-675 to VII-711. Specifically, Table 1 (VII- 683), Tables 7 to 8 (VII-688 to VII-711). Further, the SP value in a mixed solvent of a plurality of solvents can be determined by a known method. For example, the SP value of the mixed solvent can be obtained as the sum of products of the SP value of each solvent and the volume fraction, assuming that additivity is established.

[Reprecipitation process]
A diluted solution obtained by diluting the polymerization reaction solution with a diluting solvent is dropped into a poor solvent to precipitate a polymer in the polymerization reaction solution. This step is called reprecipitation and is very effective for removing impurities such as unreacted monomers and polymerization initiator remaining in the polymer solution. If the unreacted monomer remains as it is, the sensitivity decreases when used as a resist composition, so it is preferable to remove it as much as possible.
The amount of the poor solvent at the time of dropping the diluted solution into the poor solvent is not particularly limited, but is preferably equal to or more than that of the diluted solution in terms of easier reduction of unreacted monomers, and 3 on a mass basis. Is preferably 4 times or more, more preferably 4 times or more, still more preferably 5 times or more, and particularly preferably 6 times or more. The upper limit is preferably 10 times or less on a mass basis from the viewpoint that the amount of the poor solvent used is not too large and productivity is not lowered.

Then, the target polymer is obtained in the state of a wet powder by filtering the deposit in a poor solvent.
The smaller the monomer content in the polymer, the better. According to the present invention, the monomer content in the polymer obtained by purification by reprecipitation is 0.5% by mass or less, preferably 0.2% by mass or less, more preferably 0.15% by mass or less, Particularly preferably, it can be reduced to 0.1% by mass or less.

[Post-process]
By drying the wet powder obtained by filtering the precipitate in the poor solvent, a dry powder of the target polymer can be obtained.
Alternatively, the operation of separating the filter after the filtered wet powder is again dispersed in a poor solvent to obtain a polymer dispersion can be repeated. This step is called a restructuring step and is effective for further reducing impurities such as unreacted monomers and polymerization initiator remaining in the polymer wet powder.
From the viewpoint that the polymer can be obtained while maintaining high productivity, it is preferable to perform the purification only by the reprecipitation step without performing the restructuring step.

Further, the wet powder may be used as a composition for semiconductor lithography by dissolving it in a suitable solvent without drying, and used as a composition for semiconductor lithography after concentration and removal of low boiling point compounds. May be. At that time, additives such as a storage stabilizer may be appropriately added.
Alternatively, the wet powder may be dried and then dissolved in a suitable solvent, and further concentrated to remove the low-boiling point compound, and then used as a composition for semiconductor lithography. At that time, additives such as a storage stabilizer may be added as appropriate.

<Method for producing resist composition>
The polymer thus obtained and a compound that generates an acid upon irradiation with actinic rays or radiation are mixed to produce a resist composition. The resist composition is a chemically amplified resist composition. Preferably, the polymer and a compound capable of generating an acid upon irradiation with actinic rays or radiation are dissolved in a resist solvent.

[Resist solvent]
As the resist solvent, the solvents listed above as the polymerization solvent can be used.
[Compound that generates acid upon irradiation with actinic ray or radiation]
The compound that generates an acid upon irradiation with actinic rays or radiation can be arbitrarily selected from those that can be used as a photoacid generator for a chemically amplified resist composition. A photo-acid generator may be used individually by 1 type, and may use 2 or more types together.
Examples of the photoacid generator include onium salt compounds, sulfonimide compounds, sulfone compounds, sulfonic acid ester compounds, quinone diazide compounds, diazomethane compounds, and the like.
0.1-20 mass parts is preferable with respect to 100 mass parts of polymers, and, as for the usage-amount of a photo-acid generator, 0.5-10 mass parts is more preferable.

[Nitrogen-containing compounds]
The chemically amplified resist composition may contain a nitrogen-containing compound. By including the nitrogen-containing compound, the resist pattern shape, the stability over time, and the like are further improved. That is, the cross-sectional shape of the resist pattern becomes closer to a rectangle, and the resist film is irradiated with light, then baked (PEB), and then left for several hours before the next development process. Although it is a line, the occurrence of the deterioration of the cross-sectional shape of the resist pattern is further suppressed when left as such (timed).
The nitrogen-containing compound is preferably an amine, more preferably a secondary lower aliphatic amine or a tertiary lower aliphatic amine.
As for the quantity of a nitrogen-containing compound, 0.01-2 mass parts is preferable with respect to 100 mass parts of polymers.

[Organic carboxylic acid, phosphorus oxo acid or derivative thereof]
The chemically amplified resist composition may contain an organic carboxylic acid, an oxo acid of phosphorus, or a derivative thereof (hereinafter collectively referred to as an acid compound). By including an acid compound, it is possible to suppress deterioration in sensitivity due to the blending of the nitrogen-containing compound, and further improve the resist pattern shape, stability with time of leaving, and the like.
Examples of the organic carboxylic acid include malonic acid, citric acid, malic acid, succinic acid, benzoic acid, and salicylic acid.
Examples of phosphorus oxo acids or derivatives thereof include phosphoric acid or derivatives thereof, phosphonic acid or derivatives thereof, phosphinic acid or derivatives thereof, and the like.
The amount of the acid compound is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the polymer.

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

<Manufacturing method of substrate on which fine pattern is formed>
An example of the manufacturing method of the board | substrate with which the fine pattern was formed of this invention is demonstrated.
First, the resist composition obtained by the production method of the present invention is applied to the surface of a substrate to be processed such as a silicon wafer on which a desired fine pattern is to be formed by spin coating or the like. And the resist film is formed on a board | substrate by drying the to-be-processed board | substrate with which this resist composition was apply | coated by baking process (prebaking) etc.

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 irradiation light, a KrF excimer laser, an ArF excimer laser, an F ₂ excimer laser, and an EUV excimer laser are preferable, and an ArF excimer laser is particularly preferable. Moreover, you may irradiate an electron beam.
In addition, immersion 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 apparatus. Exposure may be performed.

After the exposure, heat treatment is appropriately performed (post-exposure baking, PEB), an alkali developer is brought into contact with the resist film, and the exposed portion is dissolved in the developer and removed (development). Examples of the alkaline developer include known ones.
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 selectively etch the portion without the resist.
After the etching, the resist is removed with a release agent to obtain a substrate on which a fine pattern is formed.

  Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto. In addition, “part” in each example and comparative example means “part by mass” unless otherwise specified. The measurement method and evaluation method used the following methods.

<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: Tosoh Corporation, Tosoh High Speed GPC Equipment HLC-8220GPC (trade name),
Separation column: manufactured by Showa Denko, Shodex GPC K-805L (trade name) connected in series,
Measurement temperature: 40 ° C.
Eluent: Tetrahydrofuran (THF)
Sample: A solution in which about 20 mg of a polymer is dissolved in 5 mL of THF and filtered through a 0.5 μm membrane filter.
Flow rate: 1 mL / min,
Injection volume: 0.1 mL,
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, and the relationship between elution time and molecular weight was determined. As the standard polystyrene, the following standard polystyrene manufactured by Tosoh Corporation (both trade names) were 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).

<Measurement of viscosity>
The viscosity of the solution was measured with an E-type viscometer under the following conditions (viscosity measurement conditions).
[Viscosity measurement conditions]
Equipment: E-type viscometer RE80R (trade name) manufactured by Toki Sangyo,
Cone rotor: 1 ° 34 'x R24 (standard),
Measurement temperature: 25 ° C.
Sample volume: 1.2 mL.

<Quantification of unreacted monomer in polymer>
0.1 g of a dry powdery polymer and 4.0 g of acetonitrile were stirred and mixed for 1 hour, and the resulting mixture was filtered through a 0.2 μm membrane filter, and manufactured by Tosoh Corporation, high performance liquid chromatograph HPLC-8020 ( Product name), the unreacted monomer content in the polymer is determined for each monomer.

  In this measurement, the separation column is manufactured by GL Sciences, using one Inertsil ODS-2 (trade name), the mobile phase is a water / acetonitrile gradient system, the flow rate is 0.8 mL / min, and the detector is manufactured by Tosoh Corporation. Measurement is performed with an ultraviolet / visible absorptiometer UV-8020 (trade name), a detection wavelength of 220 nm, a measurement temperature of 40 ° C., and an injection amount of 4 μL. As the separation column, Inertsil ODS-2 (trade name) having a silica gel particle diameter of 5 μm, a column inner diameter of 4.6 mm × column length of 450 mm is used. The gradient conditions of the mobile phase are as follows, with the liquid A being water and the liquid B being acetonitrile. In order to quantify the monomer content, three types of monomer solutions having different concentrations are used as standard solutions.

Measurement time 0 to 3 minutes: A liquid / B liquid = 90 vol% / 10 vol%.
Measurement time: 3 to 24 minutes: A liquid / B liquid = 90 volume% / 10 volume% to 50 volume% / 50 volume%.
Measurement time: 24 to 36.5 minutes: A liquid / B liquid = 50 volume% / 50 volume% to 0 volume% / 100 volume%.
Measurement time: 36.5 to 44 minutes: Liquid A / liquid B = 0 volume% / 100 volume%.

<Measurement of light transmittance of polymer film>
10 parts of a polymer and 42 parts of propylene glycol monomethyl ether acetate (hereinafter referred to as PGMEA) as a solvent are mixed to obtain a uniform solution, and then filtered through a membrane filter having a pore size of 0.1 μm to obtain a polymer composition solution. Was prepared.
The prepared polymer composition solution was spin-coated on a quartz wafer and prebaked at 120 ° C. for 60 seconds using a hot plate to produce a polymer film having a thickness of 1.0 μm.
The polymer film produced on the quartz wafer was placed on the sample side, and the untreated quartz wafer was placed on the reference side, respectively, and the wavelength was measured using an ultraviolet / visible absorptiometer UV-3100 (trade name) manufactured by Shimadzu Corporation. Measurement was carried out with the range set to 192 to 194 nm, the scan speed set to medium speed, the sampling pitch set to automatic, and the slit width set to 2.0 to determine the light transmittance (%) at 193 nm.

<Evaluation of resist composition>
[Sensitivity and development contrast measurement]
The resist composition was spin-coated on a 6-inch silicon wafer and prebaked (PAB) at 120 ° C. for 60 seconds on a hot plate to form a thin film having a thickness of 300 nm. Using an ArF excimer laser exposure apparatus (product name: VUVES-4500, manufactured by RISOTEC Japan), 18 shots of 10 mm × 10 mm ² were exposed while changing the exposure amount. Then, after post-baking (PEB) at 110 ° C. for 60 seconds, 2.38 mass% tetramethylammonium hydroxide at 23 ° C. using a resist development analyzer (product name: RDA-800). Development was performed with an aqueous solution for 65 seconds, and the change with time in the resist film thickness during development at each exposure amount was measured.

[analysis]
A curve plotting the logarithm of the exposure amount (mJ / cm ² ) and the residual film thickness ratio (hereinafter referred to as the residual film ratio) (%) when developed for 60 seconds with respect to the initial film thickness, based on the obtained data (Hereinafter, exposure dose-residual film rate curve) is prepared, and Eth sensitivity (required exposure amount for setting the remaining film rate to 0%, which represents sensitivity) and γ value (exposure dose-residual film rate curve). (Denoting the development contrast). The smaller the Eth sensitivity value, the higher the sensitivity of the resist composition, and the larger the γ value, the better the development contrast.
Eth sensitivity: exposure amount (mJ / cm ² ) at which the exposure amount-residual film rate curve intersects with a residual film rate of 0%.
γ value: E50 (mJ / cm ² ) exposure amount at 50% of the remaining film rate of the exposure amount-residual film rate curve, and a tangent line at E50 of the exposure amount-residual film rate curve is a straight line with a remaining film rate of 100% The exposure amount intersecting with the straight line having a film rate of 0% was determined as E100 and E0, respectively, and the following formula was used.
γ = 1 / {log (E0 / E100)}

<Example 1>
243.6 g of ethyl lactate was placed in a 1 L SUS flask equipped with a nitrogen inlet, a stirrer, a condenser, a dropping funnel, and a thermometer. The inside of the flask was replaced with nitrogen, the flask was placed in a hot water bath while maintaining the nitrogen atmosphere, and the temperature of the hot water bath was raised to 80 ° C. while stirring the inside of the flask.
Thereafter, the following mixture 1 was dropped into the flask over 4 hours from the dropping funnel, and the temperature of 80 ° C. was further maintained for 3 hours.
Then, the reaction liquid in a flask was cooled to 25 degreeC, the polymerization reaction was stopped, and the polymerization reaction solution was obtained.
[Mixture 1]
95.20 g of a monomer of the following formula (m1),
131.04 g of a monomer of the following formula (m2),
66.08 g of a monomer of the following formula (m3),
438.5 g of ethyl lactate,
8.649 g of dimethyl-2,2′-azobisisobutyrate (manufactured by Wako Pure Chemical Industries, Ltd., V601 (trade name)).
The charge ratio (mol%) of each monomer is shown in Table 1. The viscosity at 25 ° C. of the obtained polymerization reaction solution was measured. The results are shown in Table 1.

Next, with respect to 100 parts by mass of the obtained polymerization reaction solution, 50 parts by mass of a diluting solvent was added to dilute the mass-based dilution ratio to be 1.5 times to obtain a diluted solution. . Ethyl lactate was used as a dilution solvent. The viscosity at 25 ° C. of the obtained diluted solution was measured. The results are shown in Table 1.
The obtained diluted solution was dropped into a 10-fold amount of a poor solvent while stirring the poor solvent to precipitate a polymer (white precipitate). Methanol was used as the poor solvent.
The precipitate was filtered off to obtain a polymer wet powder. The polymer wet powder was dried under reduced pressure at 40 ° C. for about 40 hours to obtain a dry powder of the polymer.
The weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the obtained polymer were measured. The monomer content of the polymer was determined for each monomer, and the proportion of the total monomer content in the entire polymer was determined as the residual monomer amount (unit: mass%). The light transmittance of the polymer film was measured. The results are shown in Table 2.

[Evaluation of resist composition]
100 parts of the obtained polymer, 2 parts of triphenylsulfonium triflate as a photoacid generator, and PGMEA as a solvent were mixed uniformly so that the polymer concentration was 12.5% by mass. After preparing the solution, it was filtered through a membrane filter having a pore size of 0.1 μm to obtain a resist composition. Eth sensitivity and γ value of the obtained resist composition were measured. The results are shown in Table 2.

<Examples 2, 3, and 4>
The same procedure as in Example 1 was performed except that the dilution solvent or dilution ratio was changed as follows. The results are shown in Tables 1 and 2.
In Example 2, ethyl lactate was used as a dilution solvent, and diluted such that the dilution ratio was 1.8 times.
In Example 3, ethyl lactate was used as a diluent solvent, and diluted to a dilution ratio of 2.1.
In Example 4, methanol was used as a diluent solvent, and diluted so that the dilution ratio was 2.0 times.

<Example 5>
In this example, a monomer of the following formula (m4) was used in place of the monomer of the formula (m2) in Example 1.
That is, 225.9 g of ethyl lactate was placed in the same flask as in Example 1. The inside of the flask was replaced with nitrogen, and the flask was placed in a hot water bath while maintaining the nitrogen atmosphere, and the temperature of the hot water bath was raised to 80 ° C. while stirring the inside of the flask.
Thereafter, the following mixture 2 was dropped into the flask over 4 hours from the dropping funnel, and the temperature of 80 ° C. was further maintained for 3 hours.
Then, the reaction liquid in a flask was cooled to 25 degreeC, the polymerization reaction was stopped, and the polymerization reaction solution was obtained.
[Mixture 2]
95.20 g of a monomer of the following formula (m1),
66.08 g of a monomer of the following formula (m3),
109.76 g of a monomer of the following formula (m4),
406.6 g of ethyl lactate,
8.372 g of dimethyl-2,2′-azobisisobutyrate (said V601 (trade name)).
The charge ratio (mol%) of each monomer is shown in Table 1. Table 1 shows the viscosity of the obtained polymerization reaction solution at 25 ° C.

  Next, in the same manner as in Example 1, it was diluted with ethyl lactate as a dilution solvent so that the dilution ratio was 1.5 times, and a diluted solution was obtained. Others were the same as in Example 1. The results are shown in Table 1 or Table 2.

<Example 6>
In this example, monomers of the following formulas (m6) and (m5) were used in place of the monomers of the formulas (m2) and (m3) in Example 1. Further, methanol was used as a dilution solvent, and water was used as a poor solvent.
That is, 161.0 g of ethyl lactate was placed in the same flask as in Example 1. The inside of the flask was replaced with nitrogen, and the flask was placed in a hot water bath while maintaining the nitrogen atmosphere, and the temperature of the hot water bath was raised to 80 ° C. while stirring the inside of the flask.
Thereafter, the following mixture 3 was dropped into the flask over 4 hours from the dropping funnel, and the temperature of 80 ° C. was further maintained for 3 hours.
Then, the reaction liquid in a flask was cooled to 25 degreeC, the polymerization reaction was stopped, and the polymerization reaction solution was obtained.
[Mixture 3]
136.1 g of the monomer of the following formula (m1),
70.5 g of a monomer of the following formula (m5),
104.0 g of the monomer of the following formula (m6),
310.6 g of ethyl lactate,
16.56 g of dimethyl-2,2'-azobisisobutyrate (said V601 (trade name)).
The charge ratio (mol%) of each monomer is shown in Table 1. Table 1 shows the viscosity of the obtained polymerization reaction solution at 25 ° C.

Next, the obtained polymerization reaction solution was diluted with methanol as a dilution solvent so that the dilution ratio was 2.0 times, and a diluted solution was obtained. Thereafter, a dry powder of the polymer was obtained in the same manner as in Example 1 except that water was used as the poor solvent.
In the same manner as in Example 1, Mw, Mw / Mn, residual monomer amount, and light transmittance of the obtained polymer were measured. The results are shown in Table 2.
The light transmittance of the polymer film in this example is remarkably low, and it absorbs light with a wavelength of 193 nm well, so that it can be seen that it can be suitably used as an antireflection film for ArF lithography. Therefore, evaluation as a resist composition (Eth sensitivity and γ value) was not performed.

<Comparative Example 1>
The same procedure as in Example 1 was performed, except that the polymerization reaction solution was not diluted and dropped directly into a poor solvent. The results are shown in Tables 1 and 2.
<Comparative example 2>
The same procedure as in Example 5 was carried out except that the polymerization reaction solution was not diluted and dropped directly into a poor solvent. The results are shown in Tables 1 and 2.
<Comparative Example 3>
The same procedure as in Example 6 was performed, except that the polymerization reaction solution was not diluted and dropped directly into a poor solvent.
When the polymerization reaction solution was dropped into a poor solvent, the precipitated polymers were fused together to obtain a uniform slurry, and the slurry could not be discharged from the bottom of the kettle and filtered. Therefore, the items shown in Table 2 were not measured and evaluated.

<Comparative example 4>
A polymerization reaction solution was obtained in the same manner as in Example 6.
Next, the obtained polymerization reaction solution was diluted with methanol as a dilution solvent so that the dilution ratio was 1.8 times, and a diluted solution was obtained. Thereafter, a polymer dry powder was obtained in the same manner as in Example 6.
In the same manner as in Example 6, Mw, Mw / Mn, residual monomer amount, and light transmittance of the obtained polymer were measured. The results are shown in Table 2.

As shown in the results of Tables 1 and 2, Examples 1-4 in which the polymer reaction solution was diluted to a viscosity of 120 mPa · s or less and dropped into a poor solvent were diluted with the same polymer reaction solution. The amount of the monomer remaining in the obtained polymer is much smaller than that of Comparative Example 1 dropped in a poor solvent, and the molecular weight distribution is narrow. Further, compared with Comparative Example 1, the light transmittance of the polymer film was improved, and the sensitivity and development contrast of the resist composition were improved.
Similarly, Example 5 in which the polymer reaction solution was diluted to a viscosity of 120 mPa · s or less and dropped into a poor solvent was Comparative Example 2 in which the same polymer reaction solution was dropped into the poor solvent without dilution. As a result, the amount of monomer remaining in the obtained polymer was remarkably small, the molecular weight distribution was narrow, the light transmittance of the polymer film was improved, and the sensitivity and development contrast of the resist composition were improved.
Further, from the result of Comparative Example 4, even when the polymer reaction solution was diluted and then dropped into the poor solvent, when the viscosity of the diluted solution to be dropped was larger than 120 mPa · s, Example 6 In comparison, it can be seen that the amount of monomer remaining in the polymer is remarkably increased.

Claims (4)

A step of radically polymerizing a monomer using a polymerization initiator in the presence of a polymerization solvent to obtain a polymerization reaction solution having a viscosity at 25 ° C. higher than 120 mPa · s;
A step of diluting the obtained polymerization reaction solution with a diluent solvent to obtain a diluted solution having a viscosity at 25 ° C. of 120 mPa · s or less,
A method for producing a polymer for lithography, comprising a step of dropping the diluted solution into a poor solvent for the polymer to precipitate the polymer in the diluted solution.   The method for producing a lithography polymer according to claim 1, wherein the dilution solvent is a poor solvent for the polymer.   A step of producing a polymer for lithography by the production method according to claim 1, a step of mixing the obtained polymer for semiconductor lithography and a compound that generates an acid upon irradiation with actinic rays or radiation. And a method for producing a resist composition.   A step of producing a resist composition by the production method according to claim 3, a step of applying the obtained resist composition on a work surface of a substrate to form a resist film, and the resist film, A method for producing a substrate on which a pattern is formed, comprising a step of exposing and a step of developing the exposed resist film using a developer.