JP2012184381A - Polymer for semiconductor lithography and method for producing the same, resist composition, and method for manufacturing substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a polymer for semiconductor lithography, by which variation among lots of the polymer is reduced.SOLUTION: The method for producing a polymer for semiconductor lithography uses a polymerization initiator in the presence of a polymerization solvent to perform radical polymerization of a monomer, and includes a gas purge process comprising precharging at least a portion of the polymerization solvent and/or at least a portion of the monomer into a polymerization reaction vessel, and after reducing the pressure in the polymerization reaction vessel to 20 kPa or lower, substituting the gas in the polymerization reaction vessel with an inert gas before starting the polymerization reaction.

Description

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

  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 advances in semiconductor 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).

With the miniaturization of resist patterns, demands for quality of polymers for semiconductor lithography have become stricter. For example, a lot variation in manufacturing a polymer for semiconductor lithography may cause a minute defect during development, which may cause a defect in device design.
Patent Document 2 listed below describes a method of synthesizing a resin having an acid-dissociable group using a living radical polymerization initiator as a method for reducing fluctuations in molecular weight distribution due to lot differences.

JP 10-319595 A JP 2009-175746 A

However, in the method described in Patent Document 2, it is necessary to use a specific polymerization initiator, and it is also necessary to optimize the manufacturing conditions accompanying the change of the polymerization initiator.
The present invention has been made in view of the above circumstances, and a method for producing a polymer for semiconductor lithography, which can reduce variation between lots of polymers in a method different from the conventional method described in Patent Document 2, It is an object to provide a polymer for semiconductor lithography obtained by the production method, a resist composition using the polymer for semiconductor lithography, and a method for producing a substrate on which a pattern is formed using the resist composition. And

  The inventors of the present invention have found that variation between lots can be reduced by controlling the conditions for purging the inert gas in the reaction vessel before starting the polymerization reaction, and have reached the present invention.

The method for producing a polymer for semiconductor lithography according to the present invention is a method for producing a polymer by radical polymerization of a monomer using a polymerization initiator in the presence of a polymerization solvent, and a polymerization reaction in advance. After charging at least a part of the polymerization solvent and / or at least a part of the monomer in the container and before starting the polymerization reaction, the pressure inside the polymerization reaction container is reduced to 20 kPa or less and then the polymerization reaction container is filled. And a gas purge step of replacing the gas with an inert gas.
In the gas purge step, it is preferable to repeat the operation of supplying the inert gas after depressurizing the inside of the polymerization reaction vessel twice or more.

The present invention comprises a step of producing a polymer for semiconductor lithography by the production method of the present invention,
Provided is a method for producing a resist composition, comprising a step of mixing the obtained polymer for semiconductor lithography with a compound that generates an acid upon irradiation with actinic rays or radiation.
The present invention includes a step of applying a resist composition obtained by the method for producing a resist composition of the present invention on a work surface of a substrate to form a resist film, and a step of exposing the resist film. And a step of developing the exposed resist film using a developer, and a method for producing a substrate on which a pattern is formed.

According to the present invention, a polymer for semiconductor lithography having a small lot-to-lot variation can be obtained.
The resist composition using the polymer for semiconductor lithography of the present invention is excellent in stability of performance because the lot-to-lot variation of the polymer is small.
According to the substrate manufacturing method of the present invention, a highly accurate fine pattern can be stably formed.

In the present specification, “(meth) acrylic acid” means acrylic acid or methacrylic acid, and “(meth) acryloyloxy” means acryloyloxy or methacryloyloxy.
<Polymer>
[Structural unit (a)]
The polymer for semiconductor lithography of the present invention (hereinafter sometimes simply referred to as a polymer) preferably has a structural unit (a) having a polar group.
The “polar group” is a group having a polar functional group or a polar atomic group. Specific examples include a hydroxy group, a cyano group, an alkoxy group, a carboxy group, an amino group, a carbonyl group, and a fluorine atom. A group containing a sulfur atom, a group containing a lactone skeleton, a group containing an acetal structure, a group containing an ether bond, and the like.
Among these, the polymer used in the resist composition in 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 the structural unit having a polar group, and further described below. It is preferable to have a structural unit having a hydrophilic group.

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

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

Specific examples of the monomer having a lactone skeleton include β- (meth) acryloyloxy-β-methyl-δ-valerolactone, 4,4-dimethyl-2-methylene-γ-butyrolactone, β- (meth) acryloyl. Oxy-γ-butyrolactone, β- (meth) acryloyloxy-β-methyl-γ-butyrolactone, α- (meth) acryloyloxy-γ-butyrolactone, 2- (1- (meth) acryloyloxy) ethyl-4-butanolide , (Meth) acrylic acid pantoyl lactone, 5- (meth) acryloyloxy-2,6-norbornanecarbolactone, 8-methacryloxy-4-oxatricyclo [5.2.1.0 ^2,6 ] decane-3 - one, 9-methacryloxy-4-oxatricyclo [5.2.1.0 ^{2, 6]} cited decan-3-one and the like . Examples of the monomer having a similar structure include methacryloyloxysuccinic anhydride.
Monomers having a lactone skeleton may be used alone or in combination of two or more.

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

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

Specific examples of the monomer having a hydrophilic group include (meth) acrylic acid, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 2-hydroxy- (meth) acrylate. -Propyl, 4-hydroxybutyl (meth) acrylate, 3-hydroxyadamantyl (meth) acrylate, 2- or 3-cyano-5-norbornyl (meth) acrylate, 2-cyanomethyl-2-adamantyl (meth) acrylate, etc. Is mentioned. From the viewpoint of adhesion to a substrate or the like, 3-hydroxyadamantyl (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.

[Structural unit (a)]
The polymer of the present invention preferably has a structural unit (b) having an acid-eliminable group in addition to the above-mentioned structural unit (a) having a polar group when used for resist applications. Accordingly, it may have a known structural unit.
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 formation of a resist pattern.
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>
The method for producing a polymer of the present invention is a solution polymerization method in which a monomer is radically polymerized using a polymerization initiator in the presence of a polymerization solvent.
In the solution polymerization method, the monomer and the polymerization initiator may be supplied to the polymerization reaction vessel either continuously or dropwise. Dropping a dropping solution containing a monomer and a polymerization initiator into a polymerization reaction vessel from the point that dispersion of average molecular weight, molecular weight distribution, etc. due to differences in production lots is small and a polymer having good reproducibility is easily obtained. A polymerization method is preferred.

Examples of the polymerization solvent 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”), 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.
A polymerization solvent may be used individually by 1 type, and may use 2 or more types together.

  As the polymerization initiator, those that generate radicals efficiently by heat are preferable. Examples of the polymerization initiator include azo compounds (2,2′-azobisisobutyronitrile, dimethyl-2,2′-azobisisobutyrate, 2,2′-azobis [2- (2-imidazoline). -2-yl) propane], etc.), organic peroxides (2,5-dimethyl-2,5-bis (tert-butylperoxy) hexane, di (4-tert-butylcyclohexyl) peroxydicarbonate, etc. Etc.).

In the production method of the present invention, at least a part of the polymerization solvent and / or at least a part of the monomer are charged in advance into the polymerization reaction vessel.
It is preferable that a part of the polymerization solvent is put in the polymerization reaction vessel in advance, and the rest is supplied into the polymerization reaction vessel as a solvent for the dropping solution.
When the monomer is charged into the polymerization reaction vessel in advance, a part of the total monomer used for the polymerization reaction is put into the polymerization reaction vessel, and the remainder is added to the dropping solution and supplied into the polymerization reaction vessel. It is preferable.
In the polymerization reaction vessel, only the polymerization solvent may be put in advance, only the monomer may be put, or a mixture thereof may be put.
In this way, by performing the gas purging step in a state in which at least a part of the polymerization solvent and / or at least a part of the monomer is charged in advance in the polymerization reaction container, only the gas layer part in the polymerization reaction container is obtained. In addition, oxygen in the liquid layer composed of the polymerization solvent and / or monomer can also be efficiently removed.

  In the production method of the present invention, a pressure-resistant reaction vessel is preferable in that the vessel used for the polymerization reaction can be pressure-controlled, and it has excellent thermal conductivity and can easily control reaction temperature and suppress variation between lots of the reaction. A pressure-resistant metal reaction vessel is more preferable. As the metal, stainless steel (hereinafter also referred to as SUS) is preferable because it has high corrosion resistance and can reduce the mixing of metal impurities into the polymer.

After charging the polymerization solvent and / or monomer into the polymerization reaction vessel and before starting the polymerization reaction, the polymerization reaction vessel is filled with a predetermined pressure (hereinafter referred to as “final pressure reduction degree”). After that, the gas purge step is performed to replace the gas in the polymerization reaction vessel with an inert gas.
Specifically, after depressurizing the inside of the polymerization reaction vessel to an ultimate pressure reduction degree, an operation of supplying an inert gas into the polymerization reaction vessel (hereinafter sometimes referred to as “purging operation after depressurization”) is performed. By supplying an inert gas, the pressure in the polymerization reaction vessel is increased.
As the inert gas, a gas inert to radicals is used. As a specific example, nitrogen or a rare gas element is preferable, and nitrogen or argon is more preferable because it is generally used industrially.

In the gas purging step, the inside of the polymerization reaction vessel is decompressed and degassed, and then the inert gas is supplied to efficiently replace the air present in the polymerization reaction vessel with the inert gas. Oxygen, one of the agents, can be removed efficiently.
By reducing the radical scavenger in the polymerization reaction vessel, the reproducibility of the radical polymerization reaction is improved, and the molecular weight variation of the polymer can be reduced even when lots or production scales are different.
The ultimate reduced pressure is 20 kPa or less, preferably 15 kPa or less, and more preferably 10 kPa or less. In the gas purging step, the inside of the polymerization reaction vessel is depressurized to 20 kPa or less and degassed, so that the effect of reducing the molecular weight variation of the polymer can be favorably obtained. The lower the ultimate pressure reduction, the smaller the molecular weight variation of the polymer. The lower limit value of the ultimate pressure reduction degree is not particularly limited, but is preferably 0.01 kPa or more from the viewpoint that the time required to reach the desired pressure reduction degree can be implemented in a short time.

In the gas purge step, in order to further reduce the oxygen in the polymerization reaction vessel, it is preferable to repeat the operation of supplying an inert gas after depressurizing the inside of the polymerization reaction vessel (purging operation after depressurization) two or more times. It is more preferable to repeat the above, and it is more preferable to repeat four or more times.
When the purge operation after pressure reduction is repeated, the ultimate pressure reduction every time may be uniform or may vary, but it is preferable that the ultimate pressure reduction at all times is 20 kPa or less.

In the gas purge step, the degree of pressure increase (attainment pressure increase degree) when the inert gas is supplied to increase the pressure after the pressure reduction is not particularly limited, but when starting the polymerization reaction after the gas purge step, the pressure in the polymerization reaction vessel However, it adjusts so that it may become the pressure (polymerization pressure) which performs a polymerization reaction.
When the polymerization pressure varies, the boiling point of the solution of the polymerization solvent and / or monomer varies, and the reaction temperature during the polymerization reaction is not stable. Therefore, the polymerization pressure is preferably within a certain range. A preferable polymerization pressure is 70 to 130 kPa, more preferably 90 to 110 kPa.
When the pressure reduction and pressure increase are repeated, the ultimate pressure increase every time may be uniform or may vary, but it is preferable that the ultimate pressure increase of all times is equal to or lower than the polymerization pressure, More preferably, it is about the same as the polymerization pressure. Specifically, the polymerization pressure is more preferably within a range of ± 30 kPa.

  After the gas purge step, the polymerization reaction is started. Specifically, by heating a liquid (polymerization solvent and / or monomer) charged in advance in the polymerization reaction vessel to a predetermined polymerization temperature, and supplying a polymerization initiator in the presence of the monomer, The polymerization reaction is started. The polymerization temperature is preferably 50 to 150 ° C.

In the dropping polymerization method, the monomer may be dropped only with the monomer or may be dropped as a monomer solution in which the monomer is dissolved in the polymerization solvent.
The polymerization initiator may be dropped directly after being dissolved in the monomer, may be dropped after being dissolved in the monomer solution, or may be dropped after being dissolved only in the polymerization solvent.
The monomer and the polymerization initiator may be mixed in the same storage tank and then dropped into the polymerization reaction container; they may be dropped from the independent storage tank into the polymerization reaction container; respectively, polymerization from the independent storage tank They may be mixed immediately before being supplied to the reaction vessel and dropped into the polymerization reaction 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.

A predetermined amount of a monomer and a polymerization initiator are supplied and a polymerization reaction is performed for a predetermined time. Then, the reaction solution is cooled to stop the polymerization reaction, thereby obtaining a polymer solution.
The obtained polymer solution is purified as necessary. For example, after diluting to a suitable solution viscosity with a diluting solvent such as 1,4-dioxane, acetone, THF, MEK, MIBK, γ-butyrolactone, PGMEA, PGME, ethyl lactate, etc., methanol, ethanol, isopropyl alcohol, water, hexane In a poor solvent such as heptane, diisopropyl ether, or a mixed solvent thereof, the polymer is precipitated. This process is called a reprecipitation process, and is very effective for removing unreacted monomers, polymerization initiators and the like 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 monomer content as an impurity in the polymer is more preferably 2.0% by mass or less, further preferably 1.0% by mass or less, particularly preferably 0.29% by mass or less, and 0.25% by mass or less. Most preferred.

As the poor solvent, any solvent may be used as long as the polymer to be produced is not dissolved, and any known solvent can be used, but unreacted monomers, polymerization initiators and the like used in the polymer for semiconductor lithography can be used. Methanol, isopropyl alcohol, diisopropyl ether, heptane, water, or a mixed solvent thereof is preferable because it can be efficiently removed.
Since the amount of the poor solvent used can further reduce the remaining unreacted monomer, it can be used in the same mass or more as the polymer solution, preferably 3 times or more, more preferably 4 times or more, and further more preferably 5 times or more. Preferably, 6 times or more is particularly preferable.

Thereafter, the precipitate is filtered off to obtain a wet powder.
Further, after the wet powder is dispersed again in a poor solvent to obtain a polymer dispersion, an operation of filtering the polymer can be repeated. This step is called a restructuring step and is very effective for further reducing unreacted monomers, polymerization initiators and the like remaining in the polymer wet powder.
It is preferable to purify the polymer only by the reprecipitation step without performing the restructuring step in that the polymer can be obtained while maintaining high productivity.

The obtained wet powder can be sufficiently dried to obtain a dry powder polymer.
In addition, after filtration, it may be used as a composition for semiconductor lithography by dissolving it in a suitable solvent without drying and as a composition for semiconductor lithography. After concentration to remove low-boiling compounds, the composition for semiconductor lithography is used. It may be used. At that time, additives such as a storage stabilizer may be appropriately added.
Further, after drying, it may be dissolved in an appropriate solvent and further concentrated to remove the low boiling point compound, and then used as a composition for semiconductor lithography. At that time, additives such as a storage stabilizer may be appropriately added.

<Resist composition>
The resist composition of the present invention contains a polymer obtained by the production method of the present invention and a compound that generates an acid upon irradiation with actinic rays or radiation (hereinafter sometimes referred to as “photoacid generator”). A chemically amplified resist composition.
The resist composition of the present invention is obtained by dissolving a polymer and a compound that generates an acid upon irradiation with actinic rays or radiation in a resist solvent.

[Resist solvent]
Examples of the resist solvent include the same solvents as the polymerization solvent.
[Compound that generates acid upon irradiation with actinic ray or radiation (photoacid generator)]
As the photoacid generator, known photoacid generators for the chemically amplified resist composition can be appropriately selected and used. 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 content of the photo-acid generator in a resist composition, 0.5-10 mass parts is more preferable.

[Nitrogen-containing compounds]
The chemically amplified resist composition may contain a nitrogen-containing compound. By including the nitrogen-containing compound, the resist pattern shape, the stability over time, and the like are further improved. That is, the cross-sectional shape of the resist pattern becomes closer to a rectangle, and the resist film is irradiated with light, then baked (PEB), and then left for several hours before the next development process. Although it is a line, the occurrence of the deterioration of the cross-sectional shape of the resist pattern is further suppressed when left as such (timed).

The nitrogen-containing compound is preferably an amine, more preferably a secondary lower aliphatic amine or a tertiary lower aliphatic amine.
As for the quantity of a nitrogen-containing compound, 0.01-2 mass parts is preferable with respect to 100 mass parts of polymers.

[Organic carboxylic acid, phosphorus oxo acid or derivative thereof]
The chemically amplified resist composition may contain an organic carboxylic acid, an oxo acid of phosphorus, or a derivative thereof (hereinafter collectively referred to as an acid compound). By including an acid compound, it is possible to suppress deterioration in sensitivity due to the blending of the nitrogen-containing compound, and further improve the resist pattern shape, stability with time of leaving, and the like.

Examples of the organic carboxylic acid include malonic acid, citric acid, malic acid, succinic acid, benzoic acid, and salicylic acid.
Examples of phosphorus oxo acids or derivatives thereof include phosphoric acid or derivatives thereof, phosphonic acid or derivatives thereof, phosphinic acid or derivatives thereof, and the like.
The amount of the acid compound is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the polymer.

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

<Manufacturing method of substrate on which fine pattern is formed>
The method for producing a substrate on which a fine pattern is formed according to the present invention comprises a step of applying a resist composition of the present invention on a processed surface of a substrate to form a resist film, and exposing the resist film to the substrate. And a step of developing the exposed resist film using a developer.
Hereinafter, an example of the manufacturing method of the substrate will be described.

  First, the resist composition of the present invention is applied by spin coating or the like to 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). A well-known thing can be used as an alkali developing solution.
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 pattern is formed.

In the polymer for semiconductor lithography obtained by the production method of the present invention, variations in molecular weight among lots and variations in the molecular weight of the polymer due to different production scales are suppressed.
The resist composition of the present invention is excellent in stability of resist performance such as sensitivity and development contrast because the molecular weight variation of the polymer for semiconductor lithography contained in the resist composition is small.
Therefore, according to the substrate manufacturing method of the present invention, a highly accurate fine resist pattern can be stably formed by using the resist composition of the present invention. In addition, it is also suitable for pattern formation by photolithography using exposure light having a wavelength of 250 nm or less or lithography using electron beam lithography such as ArF excimer laser (193 nm), which requires use of a highly sensitive resist composition. be able to.

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

<Measurement of weight average molecular weight>
The weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the polymer were determined in terms of polystyrene by gel permeation chromatography under the following conditions (GPC conditions).
[GPC conditions]
Equipment: Tosoh Corporation, Tosoh High Speed GPC Equipment HLC-8220GPC (trade name),
Separation column: manufactured by Showa Denko, Shodex GPC K-805L (trade name) connected in series,
Measurement temperature: 40 ° C.
Eluent: Tetrahydrofuran (THF)
Sample: A solution in which about 20 mg of a polymer is dissolved in 5 mL of THF and filtered through a 0.5 μm membrane filter.
Flow rate: 1 mL / min,
Injection volume: 0.1 mL,
Detector: differential refractometer.

Calibration curve I: About 20 mg of standard polystyrene was dissolved in 5 mL of THF, and the solution was filtered through a 0.5 μm membrane filter and injected into a separation column under the above conditions, and the relationship between elution time and molecular weight was determined. As the standard polystyrene, the following standard polystyrene manufactured by Tosoh Corporation (both trade names) were used.
F-80 (Mw = 706,000),
F-20 (Mw = 190,000),
F-4 (Mw = 37,900),
F-1 (Mw = 10,200),
A-2500 (Mw = 2,630),
A-500 (mixture of Mw = 682, 578, 474, 370, 260).

<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 (VUVES-4500, manufactured by RISOTEC Japan), 18 shots of 10 mm × 10 mm ² were exposed while changing the exposure amount. Next, after post-baking (PEB) at 110 ° C. for 60 seconds, using a resist development analyzer (RDA-800 manufactured by RISOTEC Japan), development is performed with an aqueous 2.38 mass% tetramethylammonium hydroxide solution at 23 ° C. for 65 seconds. The change with time of the resist film thickness during development at each exposure amount was measured.

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

[Difference in weight average molecular weight between lots]
In each example, a polymer for semiconductor lithography was synthesized five times under the same conditions, and the weight average molecular weight of each polymer obtained was measured. The standard deviation of the number of measurements 5 was determined and used as the difference between the lots in the weight average molecular weight. The smaller the difference between lots, the better the reproducibility of the polymerization reaction, and the smaller the lot-to-lot variation in the weight average molecular weight.

[Example 1]
243.6 g of ethyl lactate was added as a polymerization solvent to a 1 L SUS flask equipped with a nitrogen inlet, a stirrer, a condenser, one dropping funnel, and a thermometer. After reducing the pressure in the flask to 18 kPa (final pressure reduction degree), nitrogen gas was supplied to increase the pressure to 101 kPa (gas purge step). That is, in the gas purge step, an operation of supplying an inert gas after depressurizing the inside of the polymerization reaction vessel (hereinafter referred to as a purge operation after depressurization) was performed only once. The polymerization pressure is normal pressure (101 kPa).
Next, the flask was placed in a hot water bath while keeping the inside of the flask in a nitrogen atmosphere, and the temperature of the hot water bath was raised to 80 ° C. while stirring the inside of the flask.
Subsequently, the following mixture 1 was dropped into the flask over 4 hours from the dropping funnel, and the temperature of 80 ° C. was further maintained for 3 hours. Thereafter, the reaction solution was cooled to 25 ° C., the polymerization reaction was stopped, and a polymer solution was obtained.

(Mixture 1)
95.20 g of a monomer of the following formula (m1),
131.04 g of a monomer of the following formula (m2),
66.08 g of a monomer of the following formula (m3),
438.5 g of ethyl lactate,
8.649 g of dimethyl-2,2′-azobisisobutyrate (manufactured by Wako Pure Chemical Industries, Ltd., V601 (trade name)).
The charge ratio (mol%) of each monomer is shown in Table 1.

  The obtained polymer solution was dropped into 7.0 times of a mixed solvent of methanol and water (methanol / water = 95/5 volume ratio) with stirring, and a white precipitate (polymer P1) was precipitated. Obtained. The precipitate was filtered off to obtain a polymer wet powder. The polymer powder was dried at 40 ° C. under reduced pressure for about 40 hours. Table 2 shows the weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the obtained polymer P1.

  100 parts of the polymer P1, 2 parts of triphenylsulfonium triflate as a photoacid generator, and PGMEA as a solvent are mixed so that the polymer concentration becomes 12.5% by mass to obtain a uniform solution. And filtered through a membrane filter having a pore size of 0.1 μm to obtain a resist composition. The sensitivity (Eth) and development contrast (γ value) of the obtained resist composition were evaluated. The results are shown in Table 2.

The polymer P1 was manufactured five times (manufacturing 1 to 5) under the same conditions. The weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the polymer obtained each time were measured. The standard deviation of the polymerization average molecular weight of production 1-5 was calculated | required, and it was set as the difference between lots of a weight average molecular weight (Mw).
A resist composition was prepared using the polymer obtained in each round under the same conditions, and the sensitivity (Eth) and development contrast (γ value) were evaluated.
Table 1 shows the main production conditions (material and volume of the polymerization reaction vessel, degree of ultimate pressure reduction, number of vacuum purge operations), and Table 2 shows the results.

[Examples 2 and 3]
A polymer was produced and evaluated in the same manner as in Example 1 except that the conditions were changed as shown in Table 1.
That is, in Example 2, the degree of pressure reduction was changed to 10 kPa.
In Example 3, the purge operation after depressurization was repeated twice. The ultimate reduced pressure during the first decompression and the ultimate reduced pressure during the second decompression were both 5 kPa. The ultimate pressure increase when the pressure was increased by supplying nitrogen gas after depressurization was 101 kPa for both the first time and the second time.
The main production conditions are shown in Table 1, and the results are shown in Table 2 (hereinafter the same).

[Example 4]
In Example 1, the polymerization reaction vessel was changed to a 100 L capacity. The amount of each raw material used was scaled up 100 times on a mass basis. Otherwise, the polymer was produced and evaluated in the same manner as in Example 1.
That is, 24360 g of ethyl lactate charged in the polymerization reaction vessel in advance, and the blending amount in the mixture 1 is 9520 g of the monomer of the formula (m1), 13104 g of the monomer of the formula (m2), and the monomer of the formula (m3) Was 6608 g, ethyl lactate was 43850 g, and dimethyl-2,2′-azobisisobutyrate was 864.9 g.

[Example 5]
In this example, a polymerization reaction vessel having a capacity of 100 L was used, and a monomer of the following formula (m4) was used instead of the monomer of the formula (m2). Further, the purge operation after depressurization was repeated three times, and the first to third ultimate pressure reductions were all 4 kPa, and the ultimate pressure increase was 101 kPa.
That is, 2.259 kg of ethyl lactate was placed in a 100 L SUS flask equipped with a nitrogen inlet, a stirrer, a condenser, one dropping funnel, and a thermometer. After reducing the pressure in the flask to 4 kPa, the operation of supplying nitrogen gas and increasing the pressure to 101 kPa was repeated three times. The flask was placed in a hot water bath while keeping the inside of the flask under a nitrogen atmosphere, and the temperature of the hot water bath was raised to 80 ° C. while stirring the flask.
Thereafter, the following mixture 2 was dropped into the flask over 4 hours from the dropping funnel, and the temperature of 80 ° C. was further maintained for 3 hours. Thereafter, the reaction solution was cooled to 25 ° C., the polymerization reaction was stopped, and a polymer solution was obtained.

(Mixture 2)
9520 g of a monomer of the following formula (m1),
6608 g of a monomer of the following formula (m3),
10976 g of a monomer of the following formula (m4),
40660 g of ethyl lactate,
837.2 g of dimethyl-2,2′-azobisisobutyrate (manufactured by Wako Pure Chemical Industries, Ltd., V601 (trade name)).
The charge ratio (mol%) of each monomer is shown in Table 1.

The obtained polymer solution was added dropwise to a 7.0 times amount of methanol and water mixed solvent (methanol / water = 80/20 volume ratio) with stirring to obtain a white precipitate (polymer P5). It was. The precipitate was filtered off to obtain a polymer wet powder. The polymer powder was dried at 40 ° C. under reduced pressure for about 40 hours. Table 21 shows the weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the obtained polymer P5.
Moreover, the same evaluation as Example 1 was performed.

[Comparative Examples 1 and 2]
A polymer was produced and evaluated in the same manner as in Example 1 except that the conditions were changed as shown in Table 1.
That is, Comparative Example 1 changed the degree of pressure reduction to 35 kPa, and Comparative Example 2 changed the degree of pressure reduction to 55 kPa.

[Comparative Example 3]
In this example, the gas in the polymerization reaction vessel was replaced with nitrogen gas by supplying nitrogen gas under normal pressure (101 kPa) without reducing pressure in the gas purge step.
That is, 243.6 g of ethyl lactate as a polymerization solvent was placed in a glass flask having a capacity of 1 L equipped with a nitrogen inlet, a stirrer, a condenser, one dropping funnel, and a thermometer. Next, nitrogen gas was purged by flowing nitrogen gas into the flask at a flow rate of 200 ml / min for 10 minutes under normal pressure (101 kPa).
Next, the flask was placed in a hot water bath while keeping the inside of the flask in a nitrogen atmosphere, and the temperature of the hot water bath was raised to 80 ° C. while stirring the inside of the flask. Thereafter, a polymer was produced and evaluated in the same manner as in Example 1.

From the results of Tables 1 and 2, Examples 1 to 1 in which the pressure inside the polymerization reaction vessel was reduced to 20 kPa or less and the pressure was increased by supplying nitrogen gas before starting the polymerization reaction (purging operation after pressure reduction). In No. 5, a polymer having a small difference in lot of polymerization average molecular weight was obtained. In addition, the resist composition prepared using the polymer also exhibited stable resist performance with small lot-to-lot variations and sensitivity.
In Example 4, even when the capacity of the polymerization reaction vessel was scaled up to 100 L, the molecular weight (Mw and Mw / Mn) of the obtained polymer was equivalent to those in Examples 1 to 3, and the resist performance was also in Example. It was equivalent to 1-3. This shows that the reproducibility of the polymerization reaction is good even when the scale of the polymerization reaction changes.
On the other hand, although the purge operation was performed after depressurization, Comparative Examples 1 and 2 having an ultimate depressurization degree of greater than 20 kPa had a much larger difference in lot of polymerization average molecular weight than Examples 1 to 5, and the resist composition Also in the sensitivity and the development contrast, the variation between lots was large.
Further, Comparative Example 3 in which the nitrogen gas purge was performed without reducing the pressure in the polymerization reaction vessel also had a large lot-to-lot difference in polymerization average molecular weight.

Claims (4)

A method for producing a polymer by radical polymerization of a monomer using a polymerization initiator in the presence of a polymerization solvent,
Prior to starting the polymerization reaction after charging at least part of the polymerization solvent and / or at least part of the monomer in the polymerization reaction vessel in advance,
A method for producing a polymer for semiconductor lithography, comprising a gas purge step of depressurizing the inside of the polymerization reaction vessel to 20 kPa or less and then substituting the gas in the polymerization reaction vessel with an inert gas.   2. The method for producing a polymer for semiconductor lithography according to claim 1, wherein in the gas purging step, after the pressure in the polymerization reaction vessel is reduced, the operation of supplying the inert gas is repeated twice or more. A step of producing a polymer for semiconductor lithography by the production method according to claim 1,
The manufacturing method of a resist composition which has the process of mixing the obtained polymer for semiconductor lithography, and the compound which generate | occur | produces an acid by irradiation of actinic light or a radiation.   Applying a resist composition obtained by the method for producing a resist composition according to claim 3 on a work surface of a substrate to form a resist film; and exposing the resist film; And a step of developing the exposed resist film using a developing solution.