JP7127267B2 - Method for producing polymer solution for lithography, method for producing resist composition, and method for producing patterned substrate - Google Patents

Description

The present invention provides a method for producing a polymer solution for lithography, a method for producing a resist composition using the polymer solution for lithography obtained by the production method, and a substrate having a pattern formed thereon using the resist composition. It relates to a method of manufacturing.

2. Description of the Related Art In recent years, resist patterns formed in the manufacturing process of semiconductor devices, liquid crystal devices, etc. have been rapidly miniaturized due to advances in lithography technology. As a technique for miniaturization, there is shortening of the wavelength of irradiation light.
For example, lithography techniques using KrF excimer laser (wavelength: 248 nm), ArF excimer laser (wavelength: 193 nm) or EUV (wavelength: 13.5 nm), and electron beam lithography techniques are being studied.

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

In Patent Documents 4 and 5, as a method for improving foreign matter aging characteristics of a resist polymer solution and reducing pattern defects during resist pattern formation, a polymer solution adjusted to a specific polymer solid content is filtered with a filter. A manufacturing method has been proposed in which a resist polymer is purified by

JP-A-10-319595 JP-A-2003-295456 JP-A-2004-31569 Japanese Patent Application Laid-Open No. 2005-189789 JP 2006-83214 A

In recent years, the miniaturization of resist patterns has progressed, and in order to obtain an excellent resist pattern profile, it is desirable to reduce foreign matter in the resist polymer solution as much as possible, but conventional methods are not necessarily sufficient.

The present invention has been made in view of the above circumstances. It is an object of the present invention to provide a method for producing a composition and a method for producing a patterned substrate using the resist composition.

The present invention has the following aspects.
[1] A polymerization step of polymerizing a monomer in the presence of a polymerization solvent to obtain a polymerization reaction solution containing the polymer, and mixing the polymerization reaction solution with a poor solvent to obtain a precipitate containing the polymer. A method for producing a polymer solution for lithography, comprising a purification step and a dissolving step of dissolving the precipitate in a good solvent for 7 hours or more to obtain a polymer solution.
[2] The method for producing a polymer solution for lithography according to [1], comprising a concentration step of concentrating the polymer solution to obtain a concentrate.
[3] The method for producing a polymer solution for lithography of [1], comprising a first filtering step of filtering the polymer solution.
[4] The method for producing a polymer solution for lithography according to [2], comprising at least one of a first filtration step of filtering the polymer solution and a second filtration step of filtering the concentrate.
[5] The method for producing a polymer solution for lithography according to [3] or [4], wherein the filter used for filtration has a pore size of 0.1 μm or less.
[6] A step of producing a polymer solution for lithography by the production method of any one of [1] to [5], and generating an acid by irradiating the obtained polymer solution for lithography with actinic rays or radiation. A method for producing a resist composition, comprising the step of mixing with a compound.
[7] A step of producing a resist composition by the production method of [6], a step of applying the obtained resist composition on a surface to be processed of a substrate to form a resist film, and 1. A method of manufacturing a patterned substrate, comprising the steps of exposing and developing the exposed resist film using a developer.

According to the method for producing a polymer solution for lithography of the present invention, a polymer solution for lithography containing less foreign substances can be obtained.
According to the method for producing a resist composition of the present invention, a resist composition capable of forming a resist pattern with few defects can be obtained.
According to the substrate manufacturing method of the present invention, a highly accurate fine resist pattern can be stably formed.

4 is a graph showing the results of Examples and Comparative Examples.

As used herein, "(meth)acrylic acid" means acrylic acid or methacrylic acid, and "(meth)acryloyloxy" means acryloyloxy or methacryloyloxy.

Embodiments of the present invention will be described.
≪Polymer solution for lithography≫
The polymer solution for lithography (sometimes simply referred to as "polymer solution") of the present embodiment contains a polymer for lithography and a good solvent.

<Polymer for lithography>
The polymer for lithography (sometimes simply referred to as "polymer") in the present embodiment can be applied without particular limitation as long as it is a polymer used in the lithography process. For example, a resist polymer used to form a resist film, an anti-reflective coating (TARC) formed on the upper layer of the resist film, or a reflective polymer used to form an anti-reflective coating (BARC) formed on the lower layer of the resist film Polymers for preventing films, polymers for gap fill films used for forming gap fill films, and polymers for top coat films used for forming top coat films can be mentioned.

Examples of resist polymers include copolymers containing one or more structural units having an acid-labile group and one or more structural units having a polar group.
Examples of polymers for antireflection films include constitutional units having light-absorbing groups, and amino groups, amide groups, hydroxyl groups, epoxy groups, etc. that can be cured by reacting with a curing agent to avoid mixing with the resist film. and a structural unit having a reactive functional group. The light-absorbing group is a group having high absorption performance with respect to light in the wavelength region to which the photosensitive component in the resist composition is sensitive, and specific examples thereof include anthracene ring, naphthalene ring, benzene ring, and quinoline ring. , a quinoxaline ring, a group having a ring structure (which may have an arbitrary substituent) such as a thiazole ring. In particular, when KrF laser light is used as the 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 benzene having an arbitrary substituent A ring is preferred.

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

Examples of polymers for gap fill films include reactive functionalities that can be cured by reacting with curing agents, etc., to avoid mixing with resist films and anti-reflection films, and to have appropriate viscosity to flow into narrow gaps. Copolymers containing a structural unit having a group, specifically copolymers of hydroxystyrene and monomers such as styrene, alkyl (meth)acrylates, and hydroxyalkyl (meth)acrylates can be mentioned.
Examples of topcoat film polymers used in immersion lithography include copolymers containing a structural unit having a carboxyl group, copolymers containing a structural unit having a fluorine-containing group substituted with a hydroxyl group, and the like.

[Structural Unit Having Polar Group]
The lithographic polymer may have constitutional units having polar groups.
A "polar group" is a group having a polar functional group or a polar atomic group, and 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 of exposing with light having a wavelength of 250 nm or less preferably has a structural unit having a lactone skeleton as a structural unit having a polar group, and furthermore has a hydrophilic structure as described later. It is preferable to have a structural unit having a functional group.

(Structural unit/monomer having a lactone skeleton)
Examples of the lactone skeleton include lactone skeletons having about 4- to 20-membered rings. The lactone skeleton may be a monocyclic lactone ring only, or the lactone ring may be condensed with an aliphatic or aromatic carbocyclic or heterocyclic ring.
When the polymer contains a structural unit having a lactone skeleton, the content thereof is preferably 20 mol% or more, preferably 25 mol% or more, of the total structural units (100 mol%) from the viewpoint of adhesion to a substrate or the like. is more preferred. From the viewpoint of sensitivity and resolution, it is preferably 60 mol % or less, more preferably 55 mol % or less, and even more preferably 50 mol % or less.

As the monomer having a lactone skeleton, a (meth)acrylic acid ester having a substituted or unsubstituted δ-valerolactone ring and a substituted or unsubstituted γ-butyrolactone ring are used because of their excellent adhesion to substrates. γ-butyrolactone ring-containing monomers are particularly 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 pantoyl lactone, 5-(meth)acryloyloxy-2,6-norbornanecarboractone, 8-methacryloxy-4-oxatricyclo[5.2.1.0 ^2,6 ]decane-3 -one, 9-methacryloxy-4-oxatricyclo[5.2.1.0 ^2,6 ]decan-3-one and the like. In addition, methacryloyloxysuccinic anhydride and the like can also be mentioned as a monomer having a similar structure.
The monomer 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” used herein is at least one of —C(CF ₃ ) ₂ —OH, hydroxy group, cyano group, methoxy group, carboxy group and amino group.
Among these, it is preferable that the resist polymer applied to the pattern forming method of exposing with 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 5 to 30 mol%, more preferably 10 to 25 mol%, of the total structural units (100 mol%) from the viewpoint of resist pattern rectangularity. .

Examples of the monomer having a hydrophilic group include (meth)acrylate having a terminal hydroxy group; derivatives having a substituent such as an alkyl group, a hydroxy group, and a carboxy group on the hydrophilic group of the monomer; Monomers having a cyclic hydrocarbon group (e.g., 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; mentioned.

Specific examples of monomers having a hydrophilic group include (meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 2-hydroxy-n (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 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 and the like are preferred.
A monomer having a hydrophilic group may be used alone or in combination of two or more.

[Structural Unit Having Acid Leaving Group]
The resist polymer preferably has a structural unit having an acid-leaving group in addition to the structural unit having a polar group described above for use in resist applications, and may optionally contain known structural units. may have.
An "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 cleaved from the main chain of the polymer by cleaving the bond.
In a resist composition, a polymer having a structural unit having an acid-leaving group reacts with an acid component to become soluble in an alkaline solution, thereby enabling formation of a resist pattern.
From the viewpoint of sensitivity and resolution, the proportion of structural units having an acid-leaving group is preferably 20 mol% or more, more preferably 25 mol% or more, of the total structural units (100 mol%) constituting the polymer. . From the viewpoint of adhesion to a substrate or the like, it is preferably 60 mol % or less, more preferably 55 mol % or less, and even more preferably 50 mol % or less.

The monomer having an acid-leaving group may be any compound having an acid-leaving group and a polymerizable multiple bond, and known monomers can be used. A polymerizable multiple bond is a multiple bond that is cleaved during a polymerization reaction to form a copolymer chain, and is preferably an ethylenic double bond.
Specific examples of monomers having an acid-leaving group include (meth)acrylic acid esters having an alicyclic hydrocarbon group having 6 to 20 carbon atoms and an acid-leaving group. be done. The alicyclic hydrocarbon group may be directly bonded to the oxygen atom constituting the ester bond of the (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. or having an alicyclic hydrocarbon group having 6 to 20 carbon atoms, and a —COOR group (R may have a substituent a tertiary hydrocarbon group, a tetrahydrofuranyl group, a tetrahydropyranyl group, or an oxepanyl group) is bonded directly or via a linking group (meth)acrylic acid esters.

In particular, when producing a polymer to be applied to a pattern forming method in which exposure is performed with light having a wavelength of 250 nm or less, preferable examples of the monomer having an acid-leaving group include 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 (meth) ) acrylate, 1-methylcyclopentyl (meth)acrylate, 1-ethylcyclopentyl (meth)acrylate, isopropyladamantyl (meth)acrylate, 1-ethylcyclooctyl (meth)acrylate and the like.
The monomer having an acid-leaving group may be used alone or in combination of two or more.

<Good solvent>
Examples of good solvents used in the production of polymer solutions for lithography 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"), 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 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: dimethylsulfoxide and the like.
Aromatic hydrocarbons: benzene, toluene, xylene and the like.
Aliphatic hydrocarbon: hexane and the like.
Alicyclic hydrocarbons: cyclohexane and the like.
The good solvent in the polymer solution for lithography may be used singly or in combination of two or more.

<<Method for producing polymer solution for lithography>>
The method for producing a polymer solution for lithography according to the present embodiment includes a polymerization step of polymerizing a monomer in the presence of a polymerization solvent to obtain a polymerization reaction solution containing a polymer, and and a dissolving step of dissolving the precipitate containing the polymer in a good solvent.

[Polymerization step]
As a polymerization method, a solution polymerization method can be used in which monomers are radically polymerized using a polymerization initiator in the presence of a polymerization solvent.
As the polymerization solvent, those mentioned as the good solvent can be used.

As the polymerization initiator, those that efficiently generate radicals by heat are preferred. For example, azo compounds (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.).
The temperature suitable for use of these polymerization initiators is in the range of 50 to 150° C. depending on the decomposition temperature.

In the polymerization step, it is preferable to feed a polymerization solvent, a polymerization initiator, and a monomer into a polymerization vessel and maintain a predetermined polymerization temperature to carry out a radical polymerization reaction.
The supply of the monomers and the polymerization initiator to the polymerization vessel may be continuous supply or dropwise supply. A dropping polymerization method in which a monomer and a polymerization initiator are added dropwise into a polymerization vessel is preferred because variations in average molecular weight, molecular weight distribution, etc. due to differences in production lots are small and reproducible polymers can be easily obtained.

In the dropping polymerization method, the inside of the polymerization vessel is temperature-controlled to a predetermined polymerization temperature, and then the monomers and the polymerization initiator are dropped into the polymerization vessel independently or in any combination.
The monomer may be added dropwise as a monomer alone, or may be added dropwise as a monomer solution in which the monomer is dissolved in a polymerization solvent.
A polymerization solvent and/or a monomer may be charged in advance into the polymerization vessel.
The polymerization initiator may be dissolved directly in the monomer, dissolved in the monomer solution, or dissolved only in the polymerization solvent.
The monomer and the polymerization initiator may be mixed in the same reservoir and then dropped into the polymerization vessel; they may be dropped into the polymerization vessel from separate storage tanks; and from separate storage tanks into the polymerization vessel. They may be mixed just before feeding and added dropwise into the polymerization vessel.
One of the monomers and the polymerization initiator may be dropped first and then the other may be dropped later, 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 polymerization initiator.
Dropping may be performed continuously or intermittently.
The polymerization temperature is preferably set within the temperature range suitable for use of the polymerization initiator. For example, 50 to 150°C is preferred.

In the solution polymerization method, the viscosity of the reaction liquid in which the polymerization reaction is performed increases as the polymerization reaction of the monomer proceeds. If the viscosity of the reaction solution becomes too high, a so-called runaway reaction, in which the polymerization reaction proceeds rapidly, may occur.
In the present specification, a reaction solution in which monomers are polymerized in the presence of a polymerization solvent is referred to as a polymerization reaction solution. The polymerization reaction solution contains the polymer produced by the polymerization reaction.
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 in the polymerization reaction may be set so that the viscosity of the reaction solution is low enough to prevent the above-mentioned runaway reaction from occurring.
Further, the viscosity of the polymerization reaction solution can be adjusted to an arbitrary viscosity by diluting it with a solvent. Specific examples of diluent solvents include 1,4-dioxane, acetone, THF, MEK, cyclopentanone, cyclohexanone, MIBK, γ-butyrolactone, PGMEA, PGME, ethyl lactate, methyl 2-hydroxyisobutyrate, methanol, ethanol, and isopropyl. Examples include alcohol, water, hexane, heptane, diisopropyl ether, and mixed solvents thereof.
From the viewpoint of production efficiency, the viscosity of the polymerization reaction solution at 25° C. is preferably 25 mPa·s or more, more preferably 50 mPa·s or more, 100 mPa·s or more, and particularly preferably 150 mPa·s or more. The upper limit of the viscosity of the polymerization reaction solution may be any range in which the runaway reaction does not occur, and is preferably 10,000 mPa·s or less, more preferably 9,000 mPa·s or less.
Dilution with a solvent can be performed at any timing during the polymerization process.

In the polymerization step, a predetermined polymerization temperature is maintained for a preset polymerization time to carry out a radical polymerization reaction, and then the polymerization reaction is terminated to obtain a polymerization reaction solution.
Radical polymerization 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 propagation rate is proportional to the product of the monomer concentration and the radical concentration, and the termination rate is proportional to the square of the radical concentration.
As used herein, the phrase "to terminate the polymerization reaction" means to bring about a state in which the amount of radicals generated by decomposition of the polymerization initiator is sufficiently reduced to the extent that initiation and propagation reactions do not occur.
As a technique for stopping the polymerization reaction, a step of cooling the reaction solution is generally used, but the polymerization reaction can also be stopped by adding a radical scavenger such as a polymerization inhibitor or oxygen.

[Purification process]
The polymerization reaction solution obtained in the polymerization step is mixed with a poor solvent (preferably dropped into the poor solvent) to precipitate the polymer in the polymerization reaction solution. This step is called reprecipitation, and is very effective for removing impurities such as unreacted monomers and polymerization initiators remaining in the polymerization reaction solution. If the unreacted monomer remains as it is, the sensitivity of the resist composition is lowered, so it is preferable to remove the unreacted monomer as much as possible.
The poor solvent is preferably methanol, isopropyl alcohol, diisopropyl ether, heptane, or water because it can efficiently remove unreacted monomers, polymerization initiators, and the like. The poor solvent may be used alone or in combination of two or more.
The amount of the poor solvent when dropping the polymerization reaction solution into the poor solvent is not particularly limited, but is preferably equal to or more than the same mass as the polymerization reaction solution in that the amount of unreacted monomers can be more easily reduced. It is preferably at least 4 times, more preferably at least 4 times, further preferably at least 5 times, and particularly preferably at least 6 times. The upper limit is preferably 10 times or less on the basis of mass from the viewpoint that the amount of the poor solvent to be used is not too large and productivity is not lowered.

After that, the precipitate containing the target polymer is obtained in the state of wet powder by filtering the precipitate in the poor solvent. The smaller the monomer content in the precipitate, the better.

The wet powder obtained by filtering off the precipitate in the poor solvent may be dispersed again in the poor solvent to obtain a polymer dispersion, and then filtering may 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 powder.
From the point of view that the polymer can be obtained while maintaining high productivity, it is preferable to carry out the purification only by the reprecipitation step without performing the reslurry step.

[Dissolving process]
A polymer-containing precipitate obtained in the purification step is dissolved in a good solvent to obtain a polymer solution. The polymer solution obtained can be used as a polymer solution for lithography.
The precipitate may be dissolved in a good solvent in the state of wet powder, or the concentrated wet powder obtained by concentrating the wet powder to remove low boiling point compounds may be dissolved in a good solvent. Alternatively, the dry powder obtained by drying the wet powder may be dissolved in a good solvent. When dissolving the precipitate in the good solvent, additives such as a storage stabilizer may be added as appropriate.

Specifically, the good solvent and the precipitate are mixed and dissolved. The dissolution time is defined as the time from the start of mixing of the good solvent and the precipitate to the use of the resulting polymer solution in the next step. The next step includes a filtration step or a concentration step, which will be described later.
For example, the precipitate may be put into a good solvent and dissolved by continuous stirring from the start to the end of the dissolution time, or may be dissolved by intermittent stirring. In the case of intermittent stirring, stirring may be performed immediately after adding the precipitate to the good solvent, and then the mixture may be allowed to stand still, or one or more times of standing and one or more times of stirring may be alternately performed. good. Alternatively, the precipitate may be allowed to stand immediately after being put into a good solvent, and then stirred continuously, or one or more times of stirring and one or more times of standing may be alternately performed.
The dissolution time should be 7 hours or longer. By setting the dissolution time to 7 hours or more, the solubility of the polymer can be sufficiently improved. Over 7 hours, the improvement in polymer solubility slows down. Although the upper limit of the dissolution time is not particularly limited, it is preferably 30 hours or less, more preferably 20 hours or less, from the viewpoint of production efficiency.

As the stirring means, a stirrer equipped with stirring blades can be used. The shape of the stirring blade is not particularly limited, and examples thereof include anchor blades, paddle blades, propeller blades, turbine blades, edged turbine blades, and ribbon blades. Maxblend (registered trademark) blades manufactured by Sumitomo Heavy Industries Co., Ltd. can also be used.
The rotational speed of the stirring blade is, for example, preferably 1-1000 rpm, more preferably 2-500, even more preferably 3-100.

[Concentration step]
The polymer solution obtained in the dissolution step may be concentrated to remove low boiling point compounds. The concentrate obtained can be used as a polymer solution for lithography.

[Filtration process]
It is preferable to filter the polymer solution obtained in the dissolving step (also referred to as a first filtering step) to remove foreign substances in the polymer solution.
When performing the concentration step, the polymer solution before concentration may be filtered (first filtration step), or the concentrated solution may be filtered (also referred to as a second filtration step). It is preferable to perform at least one, and both may be performed.

The following are common to the first filtration step and the second filtration step.
In the filtration step, the polymer solution is preferably passed through a filter having a pore size of 0.1 μm or less.
The filtration differential pressure during filtration is not particularly limited, but if it is too low, the filtration rate will slow down and the productivity will drop, so it is preferably 10 kPa or more, more preferably 20 kPa or more.
Filtration differential pressure is the value obtained by subtracting the pressure applied to the polymer solution after passing through the filter from the pressure applied to the polymer solution before passing through the filtration membrane. be. Normally, the pressure before and after the filtration is high due to the passage resistance of the filtration membrane, so the differential pressure before and after the filtration is a positive value.
Filtration efficiency is excellent in the filtration differential pressure being more than the said lower limit. Filtration efficiency (unit: %) is a value obtained by the following formula (1).
(Number of particles before filtration - Number of particles after filtration) / Number of particles before filtration x 100 (1)

The filtration membrane of the filter is, for example, a fluoropolymer such as PTFE (polytetrafluoroethylene); a polyolefin polymer such as polyethylene and polypropylene; a polyamide polymer such as nylon 6, nylon 66 and nylon 46. Mention may be made of membranes.
Amide bond as a polar group in that it can efficiently remove polymers with a higher molecular weight than the target weight average molecular weight and poorly soluble polymers with a biased copolymer composition, which are by-produced in the polymerization reaction. It is preferred to use a filter having a filtration membrane comprising a polyamide polymer having
As for the shape of the filter, a known one can be used, and for example, a disk-type, cartridge-type, or other container in which a filtration membrane is housed can be used. The filter may have a plurality of filtration membranes made of the same or different materials.
It is preferable that the surface area of the filter, the temperature of the polymer solution, and the flow rate when passing the solution are appropriately adjusted according to the amount, viscosity, and the like of the polymer solution.

Filtration by the filter can also be performed in two or more steps. Alternatively, the polymer solution that has been filtered once can be repeatedly passed through the same filter for filtration.
When the filtration is performed in two or more stages, the pore size and material of the filter can be arbitrarily combined in the first stage of filtration and the second stage or more of the filtration. It is preferable to use a filter with the largest pore size in the first stage, and use filters with smaller pore sizes in the second and subsequent stages, in order to prevent deterioration of filterability due to clogging of the filter.

<<Method for producing resist composition>>
A resist composition is produced by mixing a polymer solution for lithography and a compound that generates an acid upon exposure to actinic rays or radiation. Specifically, a resist solvent is added, if necessary, to the polymer solution for lithography, and a compound that generates an acid upon exposure to actinic rays or radiation is added and dissolved.
As the resist solvent, the solvents listed above as good solvents can be used.

The compound that generates an acid upon irradiation with actinic rays or radiation can be arbitrarily selected from those that can be used as photoacid generators for chemically amplified resist compositions. The photoacid generators may be used singly or in combination of two or more.
Examples of photoacid generators include onium salt compounds, sulfonimide compounds, sulfone compounds, sulfonate ester compounds, quinonediazide compounds, and diazomethane compounds.
The amount of the photoacid generator used is preferably 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, per 100 parts by mass of the polymer.

The chemically amplified resist composition may contain a nitrogen-containing compound. Containing a nitrogen-containing compound further improves the resist pattern shape, storage stability over time, and the like. In other words, the cross-sectional shape of the resist pattern becomes closer to a rectangle, and after the resist film is irradiated with light and then baked (PEB), it is allowed to stand for several hours before the next development process. Although it is a line, the occurrence of deterioration of the cross-sectional shape of the resist pattern is further suppressed when left unattended (with the passage of time).
As the nitrogen-containing compound, amines are preferable, and secondary lower aliphatic amines and tertiary lower aliphatic amines are more preferable.
The amount of the nitrogen-containing compound is preferably 0.01 to 2 parts by mass with respect to 100 parts by mass of the polymer.

The chemically amplified resist composition may contain an organic carboxylic acid, a phosphorus oxoacid, or a derivative thereof (hereinafter collectively referred to as an acid compound). By containing an acid compound, it is possible to suppress deterioration in sensitivity due to the addition of a nitrogen-containing compound, and further improve the resist pattern shape, storage stability over time, and the like.
Organic carboxylic acids include malonic acid, citric acid, malic acid, succinic acid, benzoic acid, salicylic acid and the like.
Phosphorus oxoacids 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.

The resist composition may contain various additives such as surfactants, other quenchers, sensitizers, antihalation agents, storage stabilizers and antifoaming agents, if necessary. Any additives known in the art can be used.

<Method for producing a substrate having a fine pattern formed>
An example of a method for manufacturing a substrate on which a fine pattern is formed will be described.
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 (pre-baking) 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). The irradiation light is preferably a KrF excimer laser, an ArF excimer laser, an F2 excimer laser, or an EUV excimer laser, and particularly preferably an ArF excimer laser. Moreover, you may irradiate an electron beam.
Further, liquid immersion in which light is irradiated while a high refractive index liquid such as pure water, perfluoro-2-butyltetrahydrofuran, or perfluorotrialkylamine is interposed between the resist film and the final lens of the exposure device. Exposure may be performed.

After the exposure, heat treatment (post-exposure bake, PEB) is applied as appropriate, the resist film is brought into contact with an alkaline developer, and the exposed portion is dissolved in the developer and removed (development). A well-known thing is mentioned as an alkali developing solution.
After development, the substrate is appropriately rinsed with pure water or the like. Thus, 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 the portions without resist are selectively etched.
After etching, the resist is removed with a stripping agent to obtain a substrate on which a fine pattern is formed.

According to the present invention, a polymer solution for lithography can be obtained which has excellent solubility in a polymer solvent and exhibits good sensitivity when used in a resist composition, as shown in the examples below.
Specifically, by dissolving the precipitate containing the polymer in a good solvent for 7 hours or longer, the ratio of large particles with a particle size of 10 nm or more to the total particles dispersed in the polymer solution. can be sufficiently reduced. That is, it is possible to obtain a polymer solution having excellent polymer solubility and sufficiently reduced foreign matter in the solution.
Such a polymer solution has sufficiently reduced foreign matters in the solution, so that the filtration time is shortened during filter filtration. Moreover, a resist composition using such a polymer solution has excellent sensitivity.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these. Also, "parts" in each example and comparative example means "mass parts" unless otherwise specified.
The following methods were used for the measurement and evaluation methods.

<Method for evaluating solubility>
The particle size distribution of the polymer solution was measured using a high-sensitivity FPAR-1000 (manufactured by Otsuka Electronics) equipped with a dilute probe. The obtained autocorrelation function was analyzed by the Marquardt method to obtain a particle size distribution curve in terms of mass. From the obtained particle size distribution curve in terms of mass, the ratio (% by mass) of large particle size particles having a particle size of 10 nm or more was obtained.

<Method for measuring 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]
Apparatus: manufactured by Tosoh Corporation, Tosoh high-speed GPC apparatus HLC-8220GPC (trade name),
Separation column: three Shodex GPC K-805L (trade name), manufactured by Showa Denko KK, connected in series;
Measurement temperature: 40°C,
Eluent: tetrahydrofuran (THF),
Sample: about 20 mg of polymer 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, filtered through a 0.5 μm membrane filter, and the solution was injected into the 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 (both 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).

<Evaluation of resist composition (sensitivity)>
The resist composition was spin-coated on a 6-inch silicon wafer and pre-baked (PAB) on a hot plate at 120° C. for 60 seconds to form a thin film with a thickness of 300 nm. Using an ArF excimer laser exposure apparatus (manufactured by Litho Tech Japan, trade name: VUVES-4500), 18 shots of 10 mm×10 mm were exposed with varying exposure doses. Then, after performing post-baking (PEB) at 110 ° C. for 60 seconds, using a resist development analyzer (manufactured by Litho Tech Japan, product name: RDA-800), tetramethylammonium hydroxyl at a concentration of 2.38% by mass at 23 ° C. The resist film was developed with an aqueous solution for 65 seconds, and the change in the resist film thickness over time during development at each exposure dose was measured.

[analysis]
Based on the obtained data, the logarithm of the exposure dose (mJ/cm ² ) and the ratio of the residual film thickness after 60 seconds of development to the initial film thickness (hereinafter referred to as residual film ratio) (%) were plotted. A curve (hereinafter referred to as an exposure amount-remaining film ratio curve) was prepared, and the Eth sensitivity (required exposure amount for a film remaining ratio of 0%, representing sensitivity) was determined as follows. A smaller Eth sensitivity value indicates a higher sensitivity of the resist composition.
Eth sensitivity: the exposure dose (mJ/cm ² ) at which the exposure dose-remaining film ratio curve intersects with a residual film ratio of 0%.

<Examples 1 to 6>
Examples 1 to 4 are comparative examples, and Examples 5 and 6 are examples.

(Polymerization process)
1740 parts of PGMEA was placed in a 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, and the flask was placed in a hot water bath while maintaining the nitrogen atmosphere.
After that, the following mixture 1 was added dropwise into the flask from the dropping funnel over 4 hours, and the temperature was maintained at 80°C for 3 hours. After that, the heating of the hot water bath was stopped, and the hot water in the hot water bath was continuously replaced with water of 20° C. to cool the flask and stop the polymerization reaction, thereby obtaining a polymerization reaction solution containing a polymer.
[Mixture 1]
680 parts (40 mol%) of a monomer of the following formula (m1),
936 parts (40 mol%) of a monomer of the following formula (m2),
472 parts (20 mol%) of a monomer of the following formula (m3),
PGMEA 3132 parts,
Dimethyl-2,2'-azobisisobutyrate (manufactured by Wako Pure Chemical Industries, Ltd., V601 (trade name)) 276 parts.

(Refining process)
Next, the polymerization reaction solution was added dropwise to 7.2 times the amount (by volume) of the poor solvent while stirring the poor solvent to precipitate a polymer (white precipitate). A mixed solvent of methanol/water=80/20 (vol %) was used as a poor solvent. The precipitate was filtered off to obtain a precipitate in the form of wet powder.
In this example, a reslurry step was further performed. Specifically, the wet powder obtained by filtration is dispersed in the same amount of poor solvent as in the reprecipitation step (7.2 times the amount of the polymerization reaction solution) to obtain a polymer dispersion, and then filtered. was performed to obtain 3720 parts of wet powder (wet powder after refining) having a solid content concentration of 46% by mass. In the reslurry process, a mixed solvent of methanol/water=85/15 (vol %) was used as a poor solvent.

(Melting process)
The wet powder obtained in the reslurry step and a good solvent were mixed to dissolve the wet powder to obtain a polymer solution. Specifically, 30 parts of the wet powder and 141 parts of PGMEA were placed in a stirring vessel and continuously stirred while maintaining the temperature at 25° C. to obtain a polymer solution. Stirring was performed using a stirrer equipped with anchor blades at a stirring speed of 30 rpm. The dissolution time from the time when the wet powder and PGMEA were put into the stirring tank until the end of stirring was changed as shown in Table 1, and immediately after the end of stirring, the particle size distribution of the polymer solution was evaluated by the above solubility evaluation method. was measured, and the ratio (% by mass) of large particles having a particle size of 10 nm or more was obtained. Table 1 shows the results.
In Example 1, in which the dissolution time was 1 hour, the particle size distribution was not measured because an insoluble polymer was visually observed.

(First filtration step (filter filtration))
The polymer solution obtained in each example was filtered through a nylon cartridge filter (10 inches) with a pore size of 0.04 μm. Specifically, 360 kg of the polymer solution was passed through the cartridge filter while maintaining the filtration differential pressure at 50 kPa.
Filtration time was measured from the beginning to the end of filtration. Table 1 shows the results.
The polymer solution of Example 1 caused clogging after the start of filtration, and the entire amount could not be filtered.

(Concentration process)
The filtrates of Examples 2 to 6 (polymer solutions after filtration) obtained in the first filtration step were concentrated under conditions of a pressure of 10 kPa and a temperature of 40° C., and the pressure was 5 kPa when no more distillate was produced. , the temperature was changed to 55° C., and concentration was carried out until the concentration of the polymer reached 20% by mass to obtain a concentrated liquid.
The weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of the obtained concentrate were measured. Table 1 shows the results.

[Production of resist composition]
Using the concentrate obtained in the concentration step as a polymer solution for lithography, a resist composition was produced.
Specifically, 500 parts of the concentrate, 2 parts of triphenylsulfonium triflate as a photoacid generator, and PGMEA as a solvent were mixed so that the polymer concentration was 12.5% by mass. After making a uniform solution by heating, the solution was filtered through a polyethylene cartridge filter with a pore size of 0.02 μm while controlling the temperature at 20° C., applying pressure so that the filtration differential pressure was 200 kPa to obtain a resist composition. Eth sensitivity was measured for the obtained resist composition. Table 1 shows the results.

The solid line in FIG. 1 is a graph showing the relationship between the stirring time and the proportion of large-diameter particles, and the dashed line is the graph showing the relationship between the stirring time and the filtration time during filter filtration.
As shown in the results of Table 1 and FIG. 1, by setting the dissolution time to 7 hours or more, the content of large-diameter particles is sufficiently low, and the filtration time is sufficient when the polymer solution is filtered. It can be seen that the sensitivity is improved when it is made into a resist composition.

Claims (7)

A monomer having a lactone skeleton, a monomer having an acid-leaving group, and —C(CF ₃ ) ₂ —OH, a hydroxy group, a cyano group, a methoxy group, a carboxy group and an amino group in the presence of a polymerization solvent. A polymerization step of obtaining a polymerization reaction solution containing a polymer by polymerizing a monomer containing a monomer having a hydrophilic group selected from the group consisting of
A purification step of mixing the polymerization reaction solution with a poor solvent to obtain a precipitate containing a polymer;
A dissolving step of dissolving the precipitate in a wet powder state in a good solvent over a period of time exceeding 7.5 hours to obtain a polymer solution,
A method for producing a polymer solution for lithography. 2. The method for producing a polymer solution for lithography according to claim 1, further comprising a concentration step of concentrating the polymer solution to obtain a concentrated liquid. 2. The method for producing a polymer solution for lithography according to claim 1, comprising a first filtering step of filtering said polymer solution. 3. The method for producing a polymer solution for lithography according to claim 2, comprising at least one of a first filtering step of filtering said polymer solution and a second filtering step of filtering said concentrate. 5. The method for producing a polymer solution for lithography according to claim 3, wherein the filter used for filtering has a pore size of 0.1 [mu]m or less. A step of producing a polymer solution for lithography by the production method according to any one of claims 1 to 5, the obtained polymer solution for lithography, and a compound that generates an acid upon exposure to actinic rays or radiation. A method for producing a resist composition, comprising the step of mixing A step of producing a resist composition by the production method according to claim 6, a step of applying the obtained resist composition on a surface to be processed of a substrate to form a resist film, and A method of manufacturing a patterned substrate, comprising the steps of exposing and developing the exposed resist film using a developer.

Images