JP6481334B2 - Purification method and manufacturing method of polymer for semiconductor lithography, manufacturing method of resist composition, and manufacturing method of substrate on which pattern is formed - Google Patents

Description

  The present invention relates to a method for purifying a polymer for semiconductor lithography, a method for producing a polymer for semiconductor lithography using the purification method, a method for producing a resist composition, and a method for producing a substrate on which a pattern is formed.

  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).

  In Patent Documents 4 and 5, a polymer solution adjusted to a specific polymer solid content is passed through a filter as a method for improving the foreign matter aging characteristics of a resist polymer solution and reducing pattern defects when forming a resist pattern. Thus, a production method for purifying a resist polymer has been proposed.

JP 10-319595 A JP 2003-295456 A JP 2004-31569 A JP 2005-189789 A JP 2006-83214 A

In recent years, in order to obtain an excellent resist pattern profile with the progress of miniaturization of resist patterns, it is required to highly remove foreign substances in a polymer solution for semiconductor lithography, but the conventional method is not necessarily sufficient. Absent.
For example, if a poorly soluble component contained in a polymer for semiconductor lithography is deposited when it is made into a polymer solution, it causes defects when a resist pattern is formed.

The present invention has been made in view of the above circumstances, and it is possible to highly remove a component having poor solubility contained in a polymer for semiconductor lithography, and to improve the stability over time when it is made into a polymer solution. Provided are a method for purifying a polymer for semiconductor lithography, and a method for producing a polymer for semiconductor lithography, whereby an excellent polymer can be obtained.
In addition, the present invention provides a method for producing a resist composition in which a poorly soluble component contained in a polymer for semiconductor lithography is highly removed and a resist pattern with few defects can be stably formed.
Further, the present invention provides a method for producing a substrate on which a pattern is formed, in which a poorly soluble component contained in a polymer for semiconductor lithography is highly removed and a resist pattern with few defects can be stably formed. For the purpose.

  In order to solve the above-mentioned problems, the method for purifying a polymer for semiconductor lithography according to the present invention is a method for rating filtration while controlling a solution containing a polymer having a polar group for a polymer for semiconductor lithography at a temperature of 35 ° C. or lower. It has the process of letting liquid pass through a filter with an accuracy of 0.1 μm or less.

  It is preferable to let the solution containing the polymer for semiconductor lithography pass through while maintaining the solution temperature within ± 5 ° C. at the time of starting to pass through the filter.

This invention provides the manufacturing method of the polymer for semiconductor lithography including the process of manufacturing the solution which contains the polymer for semiconductor lithography in the structural unit which has a polar group, and the refinement | purification method of this invention.
In the present invention, the process for producing a lithography polymer by the method for producing a lithography polymer of the present invention, and the resulting lithography polymer are mixed with 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 purifying a lithographic polymer of the present invention, a poorly soluble component contained in a lithographic polymer can be removed to a high degree, excellent in solubility stability, and used in a resist composition. It can be refined into a lithography polymer that can always form a resist pattern with few defects.
According to the method for producing a lithographic polymer of the present invention, a poorly soluble component is highly removed, the solubility is excellent, and a resist pattern with few defects is always formed when used in a resist composition. A lithographic polymer is obtained.
According to the method for producing a resist composition of the present invention, it is possible to obtain a resist composition that includes the lithography polymer produced by the production method of the present invention and can stably form a resist pattern with few defects.
According to the substrate manufacturing method of the present invention, a highly accurate fine resist pattern can be stably formed using a resist composition that can stably form a resist pattern with few defects.

In the present specification, “(meth) acrylic acid” means acrylic acid or methacrylic acid, and “(meth) acryloyloxy” means acryloyloxy or methacryloyloxy.
<Polymer for semiconductor lithography>
The polymer for semiconductor lithography in the present invention (hereinafter sometimes simply referred to as a polymer for lithography) is a polymer used in the lithography step and has at least 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.
The use of the polymer for lithography is not particularly limited as long as it is 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 polymer for the antireflection film include a structural unit having a light-absorbing group and an amino group, an amide group, a hydroxy group, an epoxy group, etc. that can be cured by reacting with a curing agent in order 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. A copolymer containing a structural unit having a group, specifically, a copolymer of a monomer such as styrene, alkyl (meth) acrylate, hydroxyalkyl (meth) acrylate, and hydroxystyrene.
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.

[Polymer for resist]
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.
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 further 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 resist polymer is preferably 5 to 30% by mole, more preferably 10 to 25% by mole, of the total structural unit (100% by mole) from the viewpoint of the resist pattern rectangularity. More preferred.

  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.

<Method for producing polymer>
In the present invention, the method for producing the polymer for lithography is not particularly limited. A known polymerization method can be used. For example, a solution polymerization method in which a monomer is radically polymerized using a polymerization initiator in the presence of a polymerization solvent can be suitably used.

<Polymerization solvent>
Examples of the polymerization solvent used in the solution polymerization method include the following.
Ethers: chain ether (diethyl ether, propylene glycol monomethyl ether (hereinafter referred to as “PGME”), etc.), cyclic ether (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: 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>
As the polymerization initiator, those that generate radicals efficiently by heat are preferable. 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.) and the like.
The suitability temperature of these polymerization initiators depending on the decomposition temperature is in the range of 50 to 150 ° C.

[Polymerization process]
In the polymerization step of the solution polymerization method, a polymerization solvent, a polymerization initiator, and a monomer are supplied into a polymerization vessel, and a radical polymerization reaction is performed while maintaining a predetermined polymerization temperature.
The supply of the monomer and the polymerization initiator to the polymerization vessel may be a continuous supply or a drop supply. A drop polymerization method in which a monomer and a polymerization initiator are dropped into a polymerization vessel is preferred because variations in average molecular weight and molecular weight distribution due to differences in production lots are small and a reproducible polymer can be easily obtained.

In the dropping polymerization method, the temperature in the polymerization vessel is adjusted 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 set within the range of the suitability temperature for the polymerization initiator. For example, 50-150 degreeC is preferable.

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 specification, a reaction solution in which a monomer is subjected to a polymerization reaction using a polymerization initiator in the presence of a polymerization solvent is referred to as a polymerization reaction solution. The polymerization reaction solution contains a 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 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.
The viscosity of the polymerization reaction solution can be adjusted to an arbitrary viscosity by diluting with a solvent. 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, isopropyl Examples thereof include alcohol, water, hexane, heptane, diisopropyl ether, and mixed solvents thereof.
The viscosity at 25 ° C. of the polymerization reaction solution is preferably 25 mPa · s or more from the viewpoint of production efficiency, 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 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 with a solvent can be performed during the polymerization step, and can also be performed during the stop step described below.

[Stop process]
In the polymerization step, a radical polymerization reaction is performed while maintaining a predetermined polymerization temperature for a preset polymerization time, and then the polymerization reaction of the obtained polymerization reaction solution is stopped.
In the radical polymerization reaction, polymerization proceeds by a chain mechanism comprising four elementary reactions of an initiation reaction, a growth reaction, a termination reaction, and a chain transfer reaction, and the molecular weight of the polymer to be formed is determined by the speed and mechanism of each elementary reaction. The growth reaction rate is proportional to the product of the monomer concentration and the radical concentration, and the termination reaction is proportional to the square of the radical concentration.
In the present invention, “stopping the polymerization reaction” means that the amount of radicals generated by the decomposition of the polymerization initiator is sufficiently reduced so as not to cause an initiation reaction and a growth reaction.
As a method for stopping the polymerization reaction, a process of cooling the reaction solution is generally used, but it can also be stopped by introducing a radical scavenger such as a polymerization inhibitor or oxygen.

[Reprecipitation process]
In the method for producing a polymer of the present invention, the polymerization reaction solution obtained through the storage step may be mixed with a poor solvent (preferably dropped in the poor solvent) to precipitate the polymer in the polymerization reaction solution. Good. 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 when 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 is 3 on a volume 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 15 times or less on a volume basis in 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.

[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 filtering operation may be repeated after the filtered wet powder is dispersed again in a poor solvent to obtain a polymer dispersion. This process is referred to as a re-dissolution process (restructuring process) 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 carry out purification only by the reprecipitation step without performing the remelting step.

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

[Purification method]
[Purification method]
In the method for purifying a polymer for semiconductor lithography of the present invention, the solution containing the polymer for semiconductor lithography is passed through a filter having a rated filtration accuracy of 0.1 μm or less while controlling the temperature to 35 ° C. or lower. The rated filtration accuracy is a particle diameter at which the filtration efficiency is 99.9% or more, and the filtration efficiency is a value obtained by the following formula (1).
(Number of particles before filtration−number of particles after filtration) / number of particles before filtration × 100 (1)
That is, the smaller the rated filtration accuracy, the finer the filter.
A polymer solution for semiconductor lithography is filtered by a filter having a rated filtration accuracy of 0.1 μm or less, and is produced as a by-product in the polymerization reaction. A polymer having poor properties can be removed. A polymer having a high molecular weight than the target weight average molecular weight or a polymer having poor solubility with a biased copolymer composition is often a gel-like substance in the polymer solution. It deforms without keeping its shape constant under the influence of heat and stress. Therefore, in order to carry out purification while maintaining stable filtration efficiency, it is necessary to perform filtration while controlling the temperature of the polymer solution during filtration at 35 ° C. or lower.
In order to maintain the filtration efficiency in a high state, the temperature of the polymer solution is preferably controlled to 30 ° C. or lower, more preferably 25 ° C. or lower. Further, the lower limit of the polymer solution temperature is not particularly limited, but is preferably 0 ° C. or higher, and more preferably 5 ° C. or higher from the viewpoint of increasing the solution viscosity and slowing the filtration rate and reducing the productivity.
Further, it is preferable to perform filtration while maintaining the temperature from the start of filtration to the end of filtration within ± 5 ° C. of the polymer solution temperature at the start of filtration. By maintaining the temperature within ± 5 ° C., it is possible to perform filtration while keeping the filtration accuracy during filtration constant, and it is possible to obtain a lithographic polymer solution for semiconductors exhibiting stable solubility. More preferably, it is within ± 4 ° C., and more preferably it is maintained within ± 3 ° C.
If a filter with a rated filtration accuracy of greater than 0.1 μm is used, a polymer with a higher molecular weight than the target weight average molecular weight or a polymer with poor solubility in the copolymer composition, which is a by-product of the polymerization reaction, is efficiently produced. There is a risk that it cannot be removed. For efficient removal, a filter having a rated filtration accuracy of 0.1 μm or less is used, a filter of 0.05 μm or less is preferable, a filter of 0.04 μm or less is more preferable, a filter of 0.02 μm or less is more preferable, and 0 A filter of .01 μm or less is particularly preferred, and 0.005 μm or less is most preferred. The filtration membrane of the filter is, for example, a filtration made of a polymer containing a fluorine polymer such as PTFE (polytetrafluoroethylene); a polyolefin polymer such as polyethylene or polypropylene; a polyamide polymer such as nylon 6, nylon 66, nylon 46, or the like. Mention may be made of membranes. An amide bond as a polar group can be efficiently removed as a by-product of the polymerization reaction, and a polymer having a higher molecular weight than the target weight average molecular weight or a polymer with poor solubility in the copolymer composition can be efficiently removed. It is preferable to use a filter having a filtration membrane containing the polyamide polymer.
As the shape of the filter, a known one can be used. For example, a filter in which a filtration membrane is accommodated in a disk type or cartridge type container can be used. The filter may have a plurality of filtration membranes of the same or different materials.
It is preferable to appropriately adjust the surface area of the filter, the filtration pressure, and the flow rate when the liquid is passed, depending on the amount, viscosity, etc. of the polymer solution for semiconductor lithography.
In the purification method of the present invention, filtration of a filter having a rated filtration accuracy of 0.1 μm or less can be divided into two or more stages. Moreover, the polymer solution for semiconductor lithography once filtered can be filtered by repeatedly passing through the same filter again.
When filtration is performed in two or more stages, the rated filtration accuracy and material of the filter can be used in any combination in the first stage filtration and the second stage filtration. It is preferable to use a filter with the highest rated filtration accuracy as the first stage filtration filter in terms of preventing a decrease in filterability due to clogging of the filter, and to use a filter with a lower rated filtration accuracy as the process proceeds to the second and subsequent stages.
In the case of performing circulation filtration in which the polymer solution for semiconductor lithography once filtered is repeatedly passed through the same filter, the number of circulation filtration is preferably 3 times or more and more preferably 4 times or more in terms of increasing filtration efficiency. Preferably, it is more preferably performed 5 times or more.

[Purification process]
The purification process of the polymer solution for semiconductor lithography using the purification method of the present invention is applied where the polymer is in a solution state during the production process of the polymer. The polymer production process is a period from the polymerization process until it is used as a composition for semiconductor lithography, and includes a process for storing the polymer solution for semiconductor lithography after the subsequent process in a container.
Specifically, the low boiling point compound was removed by concentrating the polymerization reaction solution in which the polymerization reaction was performed by solution polymerization, the solution in which the wet powder was redissolved in the subsequent step, and the solution in which the wet powder was redissolved in the subsequent step. Solution, a solution obtained by drying a wet powder in the subsequent process and then dissolving it in an appropriate solvent, and a solution obtained by concentrating the solution dissolved in an appropriate solvent after the dry powder is dried in the subsequent process and removing low-boiling compounds The purification method of the present invention can be applied to the polymer solution after the post-process. Thermal history such as drying and concentration in that it can efficiently remove polymers with a higher molecular weight than the intended weight average molecular weight and polymers with poor solubility in the copolymer composition, which are by-produced in the polymerization reaction. It is preferable to carry out a purification step after such a step.

<Method for producing resist composition>
A polymer for semiconductor lithography is obtained through a step (purification step) for purification by the purification method of the present invention, and the resulting polymer is mixed with a compound that generates an acid upon irradiation with actinic rays or radiation to form a resist. A composition can be produced. 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 may contain various additives such as a surfactant, 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 by spin coating or the like on the surface (processed surface) of a substrate to be processed such as a silicon wafer on which a desired fine pattern is to be formed. 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.

According to the present invention, as shown in the examples described later, not only the solubility in a solvent is excellent, but also the solubility over time is excellent, and good sensitivity is stable when used in a resist composition. The resulting polymer for semiconductor lithography is obtained.
This is because the high molecular weight and copolymer composition are biased by passing the liquid through a filter having a rated filtration accuracy of 0.1 μm or less while maintaining the differential pressure before and after filtration of the polymer for lithography in the purification process at 250 kPa or less. This is probably because the polymer was reduced.

  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]
Apparatus: Tosoh Corporation high-speed GPC apparatus HLC-8220GPC (trade name).
Separation column: manufactured by Showa Denko Co., Ltd., three 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 was 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 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%.

<Evaluation of polymer stability>
The concentration of the polymer solution to be measured was 20% by mass, and a poor solvent for the polymer was added and mixed to obtain a mixed solution. The addition amount A of the poor solvent when the turbidity of the mixed solution was 10.0 NTU was determined by changing the addition amount of the poor solvent.
The concentration of the polymer solution to be measured was 20% by mass, and a poor solvent having an amount of 80% of the addition amount A determined above was added to prepare a mixed solution. The mixture was stirred for 4 hours while maintaining the temperature at 25 ° C., and then the turbidity (referred to as 80% turbidity) of the mixture was measured.
Further, the concentration of the polymer solution to be measured was 20% by mass, stored for 30 days under light-shielding sealed conditions at 25 ° C., and then added with a poor solvent in an amount of 80% of the addition amount A determined above. A liquid was used. The mixture was stirred for 4 hours while maintaining the temperature at 25 ° C., and then the turbidity (referred to as 80% turbidity after 30 days) of the mixture was measured.
The turbidity was measured by measuring the turbidity of the mixture at 25 ° C. using a turbidimeter (manufactured by Orbeco-Helloge, product name: TB200).
By adding a poor solvent, a component having poor solubility in the polymer to be measured is precipitated, and the turbidity of the mixed solution is increased. The lower the value of 80% turbidity, the fewer the components with poor solubility in the polymer, and the higher the solubility stability of the polymer. In addition, the smaller the difference between “80% turbidity” and “80% turbidity after 30 days”, the smaller the components precipitated during storage of the polymer solution, and the better the stability over time.

<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 amount-residual film rate curve) was prepared, and Eth sensitivity (required exposure amount for setting the residual film rate to 0%, which represents sensitivity) was determined as follows. It shows that the sensitivity of a resist composition is so high that the value of Eth sensitivity is small.
Eth sensitivity: exposure amount (mJ / cm ² ) at which the exposure amount-residual film rate curve intersects with a residual film rate of 0%.

<Example 1>
In a flask (reactor) equipped with a nitrogen inlet, a stirrer, a condenser, a dropping funnel, and a thermometer, 67.8 parts of ethyl lactate was placed under a nitrogen atmosphere. The flask was placed in a hot water bath, and the solution temperature in the flask was raised to 80 ° C. while stirring the flask.
Thereafter, a dropping solution containing the following monomer mixture, solvent, and polymerization initiator was dropped into the flask at a constant dropping rate over 4 hours from the dropping funnel, and the temperature of 80 ° C. was maintained for 3 hours [ Polymerization step].
Seven hours after the start of dropping of the dropping solution, the reaction was stopped by cooling to 25 ° C. to obtain a polymerization reaction solution [stopping step].
28.56 parts (40 mol%) of monomer m-1;
32.93 parts (40 mol%) of monomer m-2,
19.82 parts (20 mol%) of monomer m-3,
122.0 parts ethyl lactate,
2.415 parts of dimethyl-2,2′-azobisisobutyrate (2.5 mol% with respect to the total monomer feed).

The obtained polymerization reaction solution was dropped into a 10-fold amount (volume basis, the same shall apply hereinafter) of the poor solvent while stirring to precipitate a polymer (white precipitate). A mixed solvent of methanol and water (methanol / water = 80/20 volume ratio) was used as a poor solvent [reprecipitation step].
The precipitate was filtered off to obtain a polymer wet powder. Again, the mixture was poured into a mixed solvent of methanol and water in the same amount as above (methanol / water = 85/15 volume ratio), and the precipitate was washed while stirring. And the precipitate after washing | cleaning was separated by filtration, and 160 parts of polymer wet powders were obtained [post process (remelting process)].

160 parts of the obtained polymer wet powder was mixed with 600 parts of PGMEA and dissolved, and the temperature of the resulting solution was controlled at 20 ° C., and the difference between before and after filtration was measured with a nylon cartridge filter with a rated filtration accuracy of 0.04 μm. Filtration is performed so that the pressure becomes 70 kPa, and the discharge pressure of the liquid feeding pump is controlled so that the differential pressure before and after filtration is 70 ± 10 kPa until 90% by mass of the polymer solution is passed through. The solution was filtered under pressure [purification step after re-dissolution].
The obtained filtrate (the polymer solution after filtration) was concentrated under the conditions of a pressure of 10 kPa and a temperature of 40 ° C., and when the distillate no longer came out, the pressure was changed to 5 kPa and the temperature of 55 ° C. Concentration was performed until the concentration reached 20% by mass [post step (concentration step)].
While controlling the temperature of the obtained polymer solution after concentration to 20 ° C., it is filtered by applying a pressure so that the differential pressure before and after filtration becomes 100 kPa with a cartridge filter made of nylon with a rated filtration accuracy of 0.04 μm, Until 90% by mass of the polymer solution passes, pressure filtration is performed while controlling the discharge pressure of the liquid feed pump so that the differential pressure before and after filtration is 100 ± 10 kPa, and the semiconductor has a polymer concentration of 20% by mass. A polymer solution for lithography (P1) was obtained [purification step after concentration].
At the end of filtration, the filter was not filled with the polymer solution, and the differential pressure before and after filtration was 0 kPa.
The weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the obtained polymer solution for semiconductor lithography (P1) were measured. The results are shown in Table 2.

[Evaluation of polymer solubility]
The obtained polymer solution for semiconductor lithography (P1) was used as a test solution, and n-heptane as a poor solvent was added in an amount shown in Table 1 to prepare a mixed solution, followed by stirring for 4 hours. After stirring, the turbidity of the mixed solution was measured using a turbidimeter (manufactured by Orbeco-Helige, product name: TB200, the same applies hereinafter). The liquid temperature during stirring and measurement was 25 ° C. The measurement results are shown in Table 1.
Based on the result of Table 1, when the addition amount A of the poor solvent (n-heptane) when the turbidity of the mixed solution was 10.0 NTU was determined, 13.7 mass relative to 100 mass% of the test solution. %Met. Therefore, 80% of the added amount A is 11.0% by mass.

  To the obtained polymer solution for semiconductor lithography (P1), 11.0% by mass of n-heptane as a poor solvent was added and stirred for 4 hours. After stirring, the turbidity of the solution (80% turbidity, unit: NTU) was measured using a turbidimeter. The liquid temperature during stirring and measurement was 25 ° C. Further, the obtained polymer solution for semiconductor lithography was stored for 30 days under a light-tight sealed condition at 25 ° C., and the turbidity of the solution (80% turbidity after 30 days, unit: NTU) was measured in the same manner. The measurement results are shown in Table 2.

[Evaluation of resist composition]
500 parts of the polymer solution for semiconductor lithography (P1) obtained, 2 parts of triphenylsulfonium triflate as a photoacid generator, and PGMEA as a solvent were brought to a polymer concentration of 12.5% by mass. The resulting mixture is mixed to make a uniform solution, and filtered through a polyethylene cartridge filter having a pore size of 0.02 μm while maintaining the temperature at 20 ° C. so that the filtration differential pressure is 200 kPa, thereby obtaining a resist composition. It was. Sensitivity (Eth sensitivity, unit: mJ / cm ² ) was measured for the obtained resist composition. The results are shown in Table 2.

<Example 2>
A polymer was produced and evaluated in the same manner as in Example 1 except that the filtration after re-dissolution and the filtration after concentration were changed to a cartridge filter made of nylon having a pore diameter of 0.1 μm. The results are shown in Tables 1 and 2. (Hereinafter the same)

<Example 3>
A polymer was produced in the same manner as in Example 1 except that only filtration after concentration was performed in the same manner without performing filtration after re-dissolution, and the obtained polymer solution for semiconductor lithography was similarly evaluated.
<Example 4>
The polymer was produced in the same manner as in Example 1 except that the temperature of the solution after filtration after actual re-dissolution and filtration after concentration was always controlled at 30 ° C. The polymer solution for semiconductor lithography was obtained in the same manner. evaluated.

< Reference Example 5>
Filtration after re-dissolution and filtration after concentration was controlled to 30 ° C, and filtration was started. After that, the solution temperature increased at a constant rate and the solution temperature at the end of filtration was 34 ° C. Produced a polymer in the same manner as in Example 1 and evaluated the obtained polymer solution for semiconductor lithography in the same manner.

<Comparative Example 1>
About the polymer solution for semiconductor lithography obtained by producing a polymer in the same manner as in Example 1 except that a polymer solution was produced without filtering with a nylon cartridge filter having a pore size of 0.04 μm in the subsequent step. Evaluation was performed in the same manner.
<Comparative example 2>
A polymer was produced in the same manner as in Example 1 except that the temperature of the solution after filtration after re-dissolution and filtration after concentration was always controlled at 40 ° C., and the obtained polymer solution for semiconductor lithography was similarly evaluated. did.

<Comparative Example 3>
Filtration after dissolution and filtration after concentration was controlled at 30 ° C, and filtration was started. Thereafter, the solution temperature increased at a constant rate, and the solution temperature at the end of filtration was 40 ° C. The polymer solution for semiconductor lithography obtained by producing a polymer in the same manner as in Example 1 was similarly evaluated.

As shown in the results of Table 2, Examples 1, 2, and 4, which were subjected to the purification step after re-dissolution and the purification step after concentration, Reference Example 5, and Example 3 that was subjected to the purification step after concentration were as follows: Compared with Comparative Example 1 in which none of these purification steps was performed, the solution turbidity was low when a poor solvent was added and the solubility of the polymer was good, and the polymer dissolved even after long-term storage The properties were hardly changed and the solubility stability was good.

In Comparative Example 2, the purification step after re-dissolution and the purification step after concentration were performed, but the temperature of the solution before and after filtration exceeded 35 ° C., and when a poor solvent was added as compared with Examples 1 to 5 The solution had a high turbidity, and the solubility of the polymer was clearly reduced by long-term storage.
In Comparative Example 3, the purification step after re-dissolution and the purification step after concentration were performed, but the differential pressure before and after filtration was an example in which the temperature of the solution before and after exceeded 35 ° C. Compared with Examples 1-5, the solution turbidity when a poor solvent was added was high, and the solubility of the polymer decreased clearly by long-term storage.

  When Example 1 is compared with Example 2, the rated filtration accuracy of the filter is small, and the finer the filter, the lower the solution turbidity when a poor solvent is added and the better the solubility of the polymer. I understand that.

Claims (4)

A solution containing a polymer for semiconductor lithography having a structural unit having a polar group,
Controlled to temperatures below and the temperature of the solution up to the end time from the start of filtration, while retaining within ± 3 ° C. filtration beginning, at the rated filtration precision 0.1μm or less, and polyamic
Having a step of passing liquid filter having a filter membrane comprising a de polymer, method for purifying semiconductor lithography polymer. The manufacturing method of the polymer for semiconductor lithography including the process of manufacturing the solution containing the polymer for semiconductor lithography which has a structural unit which has a polar group, and the process of performing the purification method of Claim 1. The process of manufacturing the polymer for lithography by the manufacturing method of the polymer for lithography of Claim 2, and the process of mixing the compound which produces | generates an acid by irradiation of actinic light or a radiation with the obtained polymer for lithography A method for producing a resist composition, comprising: A step of producing a resist composition by the method for producing a resist composition according to claim 3;
A step of applying the obtained resist composition onto a work surface of a substrate to form a resist film, a step of exposing the resist film, and a step of developing the exposed resist film using a developer The manufacturing method of the board | substrate with which the pattern was formed including these.