JP2001002735A - Production of copolymer for chemical amplification type resist - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a copolymer used as a resin for a resist of a chemical amplification type composition having extremely high sensitivity. SOLUTION: This method for producing a resin for a resist feathers carrying out polymerization by combinedly using at least one kind of chain transfer agent selected from compounds of the formula R-SH (R is a 1-20C saturated aliphatic hydrocarbon group) and a polymer initiator, in a method for producing a copolymer used as the resin for the resist changing solubility in an alkali by the action of an acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a copolymer suitably used for a chemically amplified resist composition useful for fine processing.

[0002]

2. Description of the Related Art In recent years, semiconductor devices or liquid crystal devices have been manufactured.
Lithography technology in the field of
The miniaturization is rapidly progressing due to the progress of the art. Its miniaturization
In general, a shorter wavelength of the exposure light source is used
The light source used is, specifically, a conventional g
From UV rays represented by X-ray and i-ray to DUV
I have. At present, KrF excimer laser (248n
m) Lithography technology is introduced to the market and shorter wavelength
ArF excimer laser (193nm) lithography
Graphic technology is about to be introduced. Further wavelength
As a short light source, F _TwoExcimer laser (157n
m) or X-rays, electron beams, etc.
ing.

[0003] As a high-resolution resist for such a short-wavelength light source, International Business Machines (IBM) has proposed a "chemically amplified resist". At present, improvement and development of this chemically amplified resist are energetically. Is being advanced.

[0004] Due to the shortening of the wavelength of the light source, the resin used for the resist has been forced to change its structure. In KrF excimer laser lithography, 248 nm
Although highly transparent polyhydroxystyrene and its hydroxyl groups protected by acid dissociable, dissolution inhibiting groups are used, these resins are not transparent at 193 nm in ArF excimer laser lithography. Acrylic resins or cycloolefin resins that are transparent at 193 nm have attracted attention because they are sufficient and almost unusable. Examples of the acrylic resin include JP-A-4-39665 and JP-A-10-207069.
JP-A-10-153864 and the like for cycloolefin resins.

The reaction mechanism of a chemically amplified resist is such that when light is irradiated to a photoacid generator incorporated in the resist, an acid is generated, and the acid changes the solubility of the resin. For example, if a protecting group that can be removed by an acid is added to the resin, the protecting group is removed only from the exposed portion, and the solubility in a developing solution is greatly changed. In general, heat treatment after exposure promotes the diffusion of acid in the resist,
Very high sensitivity can be obtained as compared with the conventional resist.

However, in order to further improve productivity,
Alternatively, in order to reduce the damage to the optical system, it is required to further reduce the exposure time. For that purpose, conventionally known photosensitive resins are still insufficient in performance, and higher sensitivity is required.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has been made in view of the above circumstances. It is an object of the present invention to provide a method for producing the same.

[0008]

The present invention relates to a process for producing a copolymer used as a resist resin whose solubility in alkali changes by the action of an acid. The present invention relates to a method for producing a resist resin, wherein polymerization is performed using at least one type of chain transfer agent selected from I).

R-SH (I) (wherein, R represents a saturated aliphatic hydrocarbon group having 1 to 20 carbon atoms.) The present inventors have intensively studied a method for producing a resin used in a resist composition. As a result, by using an appropriate chain transfer agent together with the polymerization initiator during the production, the amount of the initiator can be reduced at the time of synthesizing the low molecular weight copolymer, and the molecular weight distribution can be reduced. In addition to the advantages described above, the inventors have found that the sensitivity of the final resist is extremely greatly improved, unexpectedly.

[0010] In the present invention, the copolymer comprises (a)
Acrylic copolymer obtained by polymerizing a monomer having an alicyclic skeleton and other monomers, acrylic obtained by polymerizing a monomer having a (ii) lactone skeleton and other monomers It is preferable to use either a system copolymer or an acrylic copolymer obtained by polymerizing a monomer having an alicyclic skeleton and a monomer having a lactone skeleton.

[0011]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a mixture of monomers is subjected to radical polymerization by using at least one type of chain transfer agent selected from the above formula (I) in combination with a polymerization initiator. Is obtained.

First, the polymerization initiator used in the present invention is:
The compound is not particularly limited as long as it is a compound capable of efficiently generating a radical by heat and polymerizing a monomer.

Specifically, ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide; 1,1-bis (t-hexylperoxy) 3,3,5-trimethylcyclohexane, 1,1
Peroxy ketals such as -bis (t-hexylperoxy) cyclohexane; hydroperoxides such as P-menthane hydroperoxide, 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane or Dialkyl peroxides; diacyl peroxides such as isobutyryl peroxide and 3,5,5-trimethylhexanoyl peroxide;
Peroxyesters such as 3,3, -tetramethylbutylperoxyneodecanate and t-hexylperoxyneodecanate; peroxydicarbonates such as di-n-propylperoxydicarbonate and diisopropylperoxydicarbonate And azo compounds such as azobisisobutyronitrile and dimethyl-2,2'-azobisisobutyrate.

In the case of a resin for lithography using a short wavelength light source such as an ArF excimer laser, it is preferable that the initiator does not have an aromatic ring in the structure in consideration of the light transmittance. Taking into account the safety during polymerization, etc., those having a 10-hour half-life temperature of 60 ° C. or higher are preferred.

In the chain transfer agent represented by R-SH (formula (I)), the saturated aliphatic hydrocarbon group of R having 1 to 20 carbon atoms may be a linear or branched alkyl group or a cycloalkyl group. Linear, branched or cyclic, such as an alkyl-substituted cycloalkyl group, a cycloalkyl-substituted alkyl group, and the like, and these may be bonded to the other as a substituent.

Preferred are, specifically, 1-
Butanethiol, 2-butanethiol, 1-octanethiol, 1-decanethiol, 1-tetradecanethiol, cyclohexanethiol, 2-methyl-1-propanethiol, 2-methyl-2-propanethiol, and the like.

The chain transfer agents used in the present invention do not contain polar groups such as carboxyl groups and hydroxyl groups, so that their polymerization is stable and they do not contain aromatic rings.
Even when used for the production of a resin for lithography using a short wavelength light source such as an ArF excimer laser, a highly sensitive resist can be obtained without lowering the light transmittance.

The copolymer to which the production method of the present invention using a polymerization initiator and a chain transfer agent as described above is applied changes the solubility in alkali due to the action of an acid and enables alkali development. , Used as a resist resin.

The present invention can be applied to any copolymer production as long as it has an alkali-affinity group which is easily removed by an acid and has a protective group and can be produced by radical polymerization. When the copolymer is used as a resist resin, effects such as an improvement in sensitivity can be obtained.

For lithography where the wavelength of the exposure light source exceeds 200 nm, the hydroxyl group of hydroxystyrene is changed to t-
A copolymer having a structure protected by a butyloxycarbonyl group or the like is preferable.

For lithography in which the wavelength of the exposure light source is 200 nm or less, those having no aromatic ring are preferable in consideration of the light transmittance of the resin, and a monomer having an alicyclic skeleton and a monomer having a lactone skeleton are preferable. An acrylic copolymer obtained by polymerizing a monomer mixture containing at least one of the above is preferred.

In particular, (a) an acrylic copolymer obtained by polymerizing a monomer having an alicyclic skeleton and another monomer, (b) a monomer having a lactone skeleton and another monomer Either an acrylic copolymer obtained by polymerizing the polymer, or (c) an acrylic copolymer obtained by polymerizing a monomer having an alicyclic skeleton and a monomer having a lactone skeleton. Among them, (c) an acrylic copolymer obtained by polymerizing a monomer having an alicyclic skeleton and a monomer having a lactone skeleton is most preferable.

The monomer having an alicyclic skeleton used here can impart transparency and high dry etching resistance to a copolymer obtained by polymerization and a resin composition thereof. Particularly, those containing a protecting group which is eliminated by an acid (an alicyclic group may be directly a protecting group) are 19
High sensitivity at 3 nm can be provided.

As the monomer having an alicyclic skeleton, a (meth) acrylate ester containing an alicyclic skeleton in an ester portion is preferable. For example, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, adamantyl (meth) acrylate, tricyclodecanyl (meth)
Preferred are those selected from the group consisting of acrylates, dicyclopentadienyl (meth) acrylates, and derivatives having a substituent such as an alkyl group, a carboxyl group, or a hydroxyl group on the alicyclic ring of these monomers. Specific examples include 1-isobonyl methacrylate, 2-methacryloyloxy-2-methyladamantane, cyclohexyl methacrylate, adamantyl methacrylate, tricyclodecanyl methacrylate, and dicyclopentadienyl methacrylate. The monomer having an alicyclic skeleton can be used alone or in combination of two or more as needed.

The monomer having a lactone skeleton used herein imparts adhesion to a substrate to a copolymer obtained by polymerization and its resin composition. Also,
In particular, those containing a protecting group capable of leaving by an acid (a lactone group may be directly a protecting group) can provide high sensitivity at 193 nm.

As the monomer having a lactone skeleton, a (meth) acrylate ester having a lactone skeleton in the ester portion is preferable. For example, a (meth) acrylate having a δ-valerolactone ring, a (meth) acrylate having a γ-butyrolactone ring, and a substituent such as an alkyl group, a carboxyl group, or a hydroxyl group on the lactone ring of these monomers. Those selected from the group consisting of derivatives are preferred. Specifically, β-methacryloyloxy-β-methyl-δ-valerolactone, β-methacryloyloxy-γ-butyrolactone, β-methacryloyloxy-β-methyl-γ-butyrolactone, α-methacryloyloxy-γ-butyrolactone, 2- (1-methacryloyloxy) ethyl-4-butanolide and the like. The monomer having a lactone skeleton can be used alone or in combination of two or more as needed.

In the case of the above (a) or (b), the “other monomer” copolymerized with the monomer having an alicyclic skeleton or the monomer having a lactone skeleton.
As methyl methacrylate, ethyl methacrylate, butyl methacrylate, t-butyl methacrylate, ethoxyethyl methacrylate, maleic anhydride,
Examples thereof include methacrylic acid and hydroxyethyl methacrylate.

(A) In the case of an acrylic copolymer obtained by polymerizing a monomer having an alicyclic skeleton and another monomer, a monomer having an alicyclic skeleton is used as a copolymer composition. It is preferable that the unit is contained in the range of 40 to 60 mol%.

(B) In the case of an acrylic copolymer obtained by polymerizing a monomer having a lactone skeleton and other monomers, the copolymer composition has 40 to 100 monomer units having a lactone skeleton. Preferably, it is contained in the range of 60 mol%.

(C) In the case of an acrylic copolymer obtained by polymerizing a monomer having an alicyclic skeleton and a monomer having a lactone skeleton, the monomer unit having a lactone skeleton has
The range of 40 to 60 mol% of the whole monomer units is preferred.
When the average copolymer composition of the monomer having a lactone skeleton is within this range, the dry etching resistance and the adhesion to the substrate, the balance between sensitivity and resolution are improved, and the present invention is applied to the production of this copolymer. By applying the above, a resist composition having the best performance can be obtained without impairing sensitivity and resolution.

The weight-average molecular weight of the acrylic copolymers (a) to (c) is not particularly limited, but is 1,000 in consideration of dry etching resistance and resist shape.
The above is preferable, and the solubility is preferably 100,000 or less in consideration of the solubility in the resist solvent and the resolution.

In the production method of the present invention, a mixture of monomers constituting the above-mentioned copolymer is subjected to radical polymerization using the above-mentioned polymerization initiator and a chain transfer agent, thereby obtaining a copolymer used as a resin for resist. Obtain a polymer.

As the polymerization method, solution polymerization is generally preferable, and as a simple production method, a monomer solution in which a monomer and a polymerization initiator are dissolved in an organic solvent in an organic solvent in which a predetermined temperature is maintained in an organic solvent is used. A so-called drop polymerization method is preferable.

As the organic solvent used in the drop polymerization method, a solvent which can dissolve any of the monomer mixture, the polymerization initiator and the obtained copolymer is preferable.
4-dioxane, isopropyl alcohol, acetone,
Examples include tetrahydrofuran and methyl isobutyl ketone.

The polymerization conditions at this time can be appropriately set, but the polymerization temperature is usually preferably in the range of 50 to 150 ° C., and the dripping time is preferably slow, for example, 2 hours or more. , Preferably about 6 hours or more. Further, even after the completion of the dropwise addition, it is preferable to maintain the temperature if necessary in order to complete the polymerization, for example, 0.5 hours or more, preferably about 2 hours.

Next, the copolymer solution thus polymerized is diluted with a good solvent such as tetrahydrofuran or 1,4-dioxane to an appropriate solution viscosity, and then diluted in a large amount of a poor solvent such as methanol or water. Precipitate by dropping. afterwards,
The precipitate is filtered and sufficiently dried to obtain the acrylic copolymer used in the present invention. This reprecipitation step may be unnecessary in some cases, but is very effective for removing unreacted monomers remaining in the polymerization solution or a polymerization initiator. If these unreacted substances remain as they are, they may adversely affect the resist performance. Therefore, it is preferable to remove the unreacted substances if possible.

By using the thus obtained copolymer and dissolving it in a solvent together with a photoacid generator, a chemically amplified resist composition (solution) can be obtained.

The photoacid generator used here is not particularly limited, and can be arbitrarily selected from those which can be used as an acid generator for a chemically amplified resist composition. Specific examples include an onium salt compound, a sulfonimide compound, a sulfone compound, a sulfonate compound, a quinonediazide compound, and a diazomethane compound. Of these, onium salt compounds are preferred, and examples thereof include sulfonium salts, iodonium salts, phosphonium salts, diazonium salts, and pyridinium salts. Specific examples include triphenylsulfonium triflate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium naphthalene sulfonate, (hydroxyphenyl) benzylmethylsulfonium toluenesulfonate, diphenyliodonium triflate, diphenyliodonium pyrene sulfonate, diphenyliodonium dodecylbenzenesulfonate And diphenyliodonium hexafluoroantimonate.

The photoacid generators can be used alone or in combination of two or more. The amount of the photoacid generator to be used is appropriately selected depending on the type of the selected photoacid generator. Usually, 0.1 to 20 parts by weight per 100 parts by weight of the copolymer,
Particularly preferably, it is 0.5 to 10 parts by weight. in this case,
If the amount of the photoacid generator is less than 0.1 part by weight, it may be difficult to sufficiently cause a chemical reaction due to the catalytic action of the acid generated by the exposure. There is a possibility that uneven coating may occur when applying the varnish, or scum may occur during development.

The solvent to be used is arbitrarily selected according to the purpose. However, the solubility of the copolymer and the photoacid generator is taken into consideration, and at the same time, other reasons, such as uniformity of the coating film, It is preferable to select in consideration of the appearance, safety, and the like. Examples of the solvent satisfying these conditions include ethyl lactate, propylene glycol monomethyl ether acetate, cyclohexane, and diglyme.

In the resist composition (solution), if necessary, a surfactant, a sensitizer, an antihalation agent,
Various additives such as a storage stabilizer and an antifoaming agent may be blended.

In order to form a resist pattern using the thus obtained resist composition (solution), the resist composition is applied on a substrate to a predetermined thickness by a known coating means such as spin coating, and is appropriately dried. After that, exposure is performed using a predetermined light source. After the exposure, if necessary, a post-exposure bake is performed, and then development is performed with an alkali developing solution to obtain a predetermined pattern. The resist composition of the present invention comprises 1
Since it is transparent to 93 nm, it is possible to use an ArF excimer laser as an exposure source, and it shows high sensitivity, good dry etching resistance, good adhesion to a substrate, and a resist pattern having a high resolution and a good shape. can get.

Further, the copolymer produced by the production method of the present invention is not only a chemically amplified type but also a resist such as a negative type resist using a photopolymerization initiator and a crosslinking agent such as a polyfunctional (meth) acrylate in combination. It can also be used for compositions.

[0044]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. Here, “parts” means “parts by weight” unless otherwise specified.

The physical properties of the copolymer were measured using the following methods.

<Weight average molecular weight> Determined by gel permeation chromatography (GPC) in terms of polymethyl methacrylate. Chloroform was used as the solvent.

<Average copolymer composition (mol%) of copolymer>
^It was determined by ¹ H-NMR measurement. Heavy chloroform was used as the solvent.

Each resist was evaluated by the following method.

<Sensitivity> Immediately after exposing the resist film formed on the silicon wafer, post-exposure baking was performed, followed by development with an alkali developing solution, washing with water, and drying to form a resist pattern. The exposure was measured as the sensitivity to form a line and space pattern (L / S = 1/1) with a line width of 1/1.

<Resolution> The minimum dimension (μm) of the resist pattern resolved when exposed at the above exposure amount was defined as the resolution.

(Synthesis Example 1) A flask equipped with a nitrogen inlet, a stirrer, a condenser and a thermometer was charged with 20.0 parts of 1,4-dioxane under a nitrogen atmosphere. ° C. 2-methacryloyloxy-2-methyladamantane (abbreviation: MAdMA) 2
9.3 parts, β-methacryloyloxy-β-methyl-δ
Valerolactone (abbreviation: MLMA) 24.8 parts, 1,
A monomer solution obtained by mixing 62.5 parts of 4-dioxane, 0.2 parts of azobisisobutyronitrile, and 1.5 parts of cyclohexanethiol was dropped into the flask at a constant speed over a period of 6 hours. C. was maintained for 2 hours. Next, the obtained reaction solution was diluted about 2-fold with tetrahydrofuran, and added dropwise to about 10-fold amount of methanol while stirring to obtain a white precipitate (copolymer A-1). The obtained precipitate was separated by filtration and dried under reduced pressure at 60 ° C. for about 40 hours.

The weight average molecular weight of the obtained copolymer A-1 was 10,000 and the copolymer composition ratio was MAdMA / MLMA.
= 51/49 mol%.

Synthesis Example 2 Cyclohexanethiol
Synthesis was performed in the same manner as in Synthesis Example 1 except that 5 parts was changed to 1.5 parts of 1-octanethiol, to obtain a copolymer A-2.

The weight average molecular weight of the obtained copolymer A-2 was 11,000, and the copolymer composition ratio was MAdMA / MLMA.
= 50/50 mol%.

(Synthesis Example 3) β-methacryloyloxy-
β-methyl-δ-valerolactone (abbreviation: MLMA) 2
Synthesis was performed in the same manner as in Synthesis Example 1 except that 4.8 parts was changed to 21.2 parts of β-methacryloyloxy-γ-butyrolactone (abbreviation: HGBMA) to obtain a copolymer A-3.

The obtained copolymer A-3 had a weight average molecular weight of 10,000 and a copolymer composition ratio of MAdMA / HGBM.
A = 50/50 mol%.

(Synthesis Example 4) β-methacryloyloxy-
β-methyl-δ-valerolactone (abbreviation: MLMA) 2
Synthesis was performed in the same manner as in Synthesis Example 2 except that 4.8 parts was changed to 21.2 parts of β-methacryloyloxy-γ-butyrolactone (abbreviation: HGBMA) to obtain a copolymer A-4.

The weight average molecular weight of the obtained copolymer A-4 was 11,000, and the copolymer composition ratio was MAdMA / HGBM.
A = 50/50 mol%.

(Comparative Synthesis Example 1)
Synthesis was performed in the same manner as in Synthesis Example 1 using only 1.9 parts of azobisisobutyronitrile to obtain a copolymer A-5.

The weight average molecular weight of the obtained copolymer A-5 was 12,000, and the copolymer composition ratio was MAdMA / MLMA.
= 51/49 mol%.

(Comparative Synthesis Example 2) β-methacryloyloxy-β-methyl-δ-valerolactone (abbreviation: MLM)
A) Copolymer A was synthesized in the same manner as in Comparative Synthesis Example 1 except that 24.8 parts of β-methacryloyloxy-γ-butyrolactone (abbreviation: HGBMA) was changed to 21.2 parts.
-6 was obtained.

The weight average molecular weight of the obtained copolymer A-6 was 11,000, and the copolymer composition ratio was MAdMA / HGBM.
A = 50/50 mol%.

(Examples 1 to 4 and Comparative Examples 1 and 2)
After mixing the components shown in (1) and (2) to obtain a uniform solution, the pore size was adjusted to 0.
The solution was filtered through a 1 μm membrane filter to prepare a resist composition solution. Thereafter, each composition solution was spin-coated on a silicon wafer, and then prebaked at 120 ° C. for 60 seconds using a hot plate to form a film having a thickness of 0.1 μm.
A 5 μm resist film was formed. Next, after exposure using an ArF excimer laser exposure machine, post exposure bake was performed at 120 ° C. for 60 seconds using a hot plate.
Next, the resist film was developed with a 2.38% by weight aqueous solution of tetramethylammonium hydroxide at room temperature, washed with pure water, and dried to form a resist pattern. Table 2 shows the evaluation results of the obtained resist patterns.

[0064]

[Table 1]

[0065]

[Table 2] As described above, it can be seen that in the embodiment of the present invention, the sensitivity is greatly improved and the resolution is also improved.

[0066]

When the copolymer obtained by the production method of the present invention is used as a resist resin, a chemically amplified resist composition having very high sensitivity and good resolution can be obtained. By using this chemically amplified resist composition, a high-precision fine resist pattern can be formed stably, and it can be suitably used particularly for fine processing of semiconductors or liquid crystal elements.

When copolymerization is carried out using a monomer having an alicyclic skeleton as a monomer component, when used for a resist, transparency and dry etching resistance, particularly 193 nm
A copolymer having excellent characteristics in terms of sensitivity can be obtained.

Further, when copolymerization is carried out using a monomer having a lactone skeleton as a monomer component, a copolymer exhibiting excellent properties of adhesion to a substrate and resolution when used as a resist is obtained. be able to.

Further, when copolymerization is carried out using a monomer having an alicyclic skeleton and a monomer having a lactone skeleton as monomer components, the above-mentioned properties are well balanced when used in a resist. A copolymer exhibiting excellent properties can be obtained.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukiya Wakisaka 20-1 Miyukicho, Otake City, Hiroshima Prefecture Inside Mitsubishi Rayon Co., Ltd. Central Research Laboratory (72) Koji Nishida 201-1 Miyukicho, Otake City, Hiroshima Prefecture No. F-term in Central Research Laboratory of Mitsubishi Rayon Co., Ltd. (Reference) 2H025 AA01 AA02 AA09 AC04 AC08 AD03 BE00 BE10 BJ10 CB14 CB41 CB55 FA17 4J011 NA25 NB04 4J100 AJ02Q AK32Q AL03Q AL08P AL08Q AL09Q BA06P BA11PBA03P03 BC02 BC03 BC03 FA19 JA38

Claims (6)

[Claims] 1. A method for producing a copolymer used as a resist resin whose solubility in an alkali is changed by the action of an acid, wherein at least one selected from the following formula (I) in combination with a polymerization initiator: A method for producing a resin for a resist, comprising performing polymerization using the chain transfer agent of (1). R-SH (I) (wherein, R represents a saturated aliphatic hydrocarbon group having 1 to 20 carbon atoms.) 2. The copolymer according to claim 1, wherein the copolymer is an acrylic copolymer obtained by polymerizing a monomer having an alicyclic skeleton and another monomer. A method for producing a polymer. 3. The copolymer according to claim 1, wherein the copolymer is an acrylic copolymer obtained by polymerizing a monomer having a lactone skeleton and another monomer. Manufacturing method. 4. The copolymer according to claim 1, wherein the copolymer is an acrylic copolymer obtained by polymerizing a monomer having an alicyclic skeleton and a monomer having a lactone skeleton. A method for producing a copolymer of 5. The monomer having an alicyclic skeleton includes cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, adamantyl (meth) acrylate, tricyclodecanyl (meth) acrylate, dicyclopentadienyl ( 5. The method according to claim 2, wherein the copolymer is at least one selected from the group consisting of meth) acrylates and derivatives of these monomers having a substituent on the alicyclic ring. Method. 6. The monomer having a lactone skeleton is represented by δ
A (meth) acrylate having a valerolactone ring, γ
The (meth) acrylate having a -butyrolactone ring and at least one selected from the group consisting of derivatives of these monomers having a substituent on the lactone ring. A method for producing a polymer.