Radiation-sensitive resin composition Number:7,144,675 from the United States Patent and Trademark Office (PTO) owispatent A radiation-sensitive resin composition comprising (A) a resin comprising at least two recurring units of the formulas (1) (6) in the total amount of 5 70 mol %, but each in the amount of 1 49 mol %, the resin being insoluble or scarcely soluble in alkali, but becoming easily soluble in alkali by the action of an acid, and (B) a photoacid generator. ##STR00001## ##STR00002## wherein R.sup.1 is a hydrogen or methyl and R.sup.2 is a substituted or unsubstituted alkyl group having 1 4 carbon atoms. The resin composition is useful as a chemically amplified resist having high transmittance of radiation, sensitivity, resolution, dry etching resistance, and pattern profile.<H composition, sensitive, Radiation, sensi, 7144675.html, Patent, pto, 7144675

Title: Radiation-sensitive resin composition

Abstract: A radiation-sensitive resin composition comprising (A) a resin comprising at least two recurring units of the formulas (1) (6) in the total amount of 5 70 mol %, but each in the amount of 1 49 mol %, the resin being insoluble or scarcely soluble in alkali, but becoming easily soluble in alkali by the action of an acid, and (B) a photoacid generator. ##STR00001## ##STR00002## wherein R.sup.1 is a hydrogen or methyl and R.sup.2 is a substituted or unsubstituted alkyl group having 1 4 carbon atoms. The resin composition is useful as a chemically amplified resist having high transmittance of radiation, sensitivity, resolution, dry etching resistance, and pattern profile.

Patent Number: 7,144,675 Issued on 12/05/2006 to Shima, et al.

Inventors: Shima; Motoyuki (Tokyo, JP), Ishii; Hiroyuki (Tokyo, JP), Yamamoto; Masafumi (Tokyo, JP), Matsuda; Daichi (Tokyo, JP), Nakamura; Atsushi (Tokyo, JP)
Assignee: JSR Corporation (Tokyo, JP)

Appl. No.: 10/648,243

Filed: August 27, 2003

Foreign Application Priority Data


Aug 29, 2002 [JP]			2002-251812
Apr 17, 2003 [JP]			2003-112902

Current U.S. Class: 430/270.1 ; 430/921

Current International Class: G03F 7/004 (20060101)

Field of Search: 430/270.1,910,921

References Cited [Referenced By]

U.S. Patent Documents


5215857	June 1993	Hosaka et al.
5238774	August 1993	Hosaka et al.
5405720	April 1995	Hosaka et al.
5494784	February 1996	Hosaka et al.
5925492	July 1999	Hosaka et al.
6020104	February 2000	Hosaka et al.
RE37179	May 2001	Yamachika et al.
6228554	May 2001	Hosaka et al.
6270939	August 2001	Hosaka et al.
6280900	August 2001	Chiba et al.
6337171	January 2002	Kobayashi et al.
6403280	June 2002	Yamahara et al.
6468714	October 2002	Kai et al.
6482568	November 2002	Douki et al.
6506537	January 2003	Kobayashi et al.
6517992	February 2003	Wang et al.
6517993	February 2003	Nakamura et al.
6531260	March 2003	Iwasawa et al.
6623907	September 2003	Numata et al.
6692887	February 2004	Suwa et al.
6692897	February 2004	Fujimori et al.
6806026	October 2004	Allen et al.
6824956	November 2004	Sato
6830866	December 2004	Kobayashi et al.
6962766	November 2005	Uenishi et al.
2002/0009667	January 2002	Nishimura et al.
2002/0009668	January 2002	Nishimura et al.
2002/0058201	May 2002	Miyaji et al.
2002/0090569	July 2002	Suzuki et al.
2002/0132181	September 2002	Nishimura et al.
2002/0172885	November 2002	Nagai et al.
2002/0192593	December 2002	Nagai et al.
2003/0022095	January 2003	Kai et al.
2003/0113658	June 2003	Ebata et al.
2003/0113660	June 2003	Yoneda et al.
2003/0157423	August 2003	Nagai et al.
2003/0170561	September 2003	Iwasawa et al.
2003/0191268	October 2003	Iwasawa et al.
2003/0194634	October 2003	Nagai et al.
2003/0203307	October 2003	Soyano et al.
2003/0203309	October 2003	Nishimura et al.
2003/0219680	November 2003	Nishimura et al.
2004/0072094	April 2004	Shima et al.

Foreign Patent Documents


02-027660	Jan., 1990	JP
04-226461	Aug., 1992	JP
07-234511	Sep., 1995	JP

Primary Examiner: Ashton; Rosemary
Attorney, Agent or Firm: Merchant & Gould, P.C. Kelber; Steven B.

Claims

What is claimed is:

1. A radiation-sensitive resin composition comprising: (A) a resin comprising a copolymer consisting of methacrylate or acrylate recurring units, wherein the copolymer comprises at least two recurring units of the following formulas (1) (6), ##STR00016## ##STR00017## wherein R.sup.1 represents a hydrogen atom or methyl group and R.sup.2 represents a substituted or unsubstituted alkyl group having 1 4 carbon atoms, two or more R.sup.2 groups that may be a first recurring unit of formula (5) and a second recurring unit of formula (5); a recurring unit of formula (5) and a recurring unit of formula (6); and a first recurring unit of formula (6) and a second recurring unit of formula (6).

2. The radiation-sensitive resin composition according to claim 1, wherein the photoacid generator (B) is compound shown by the formula (7), ##STR00018## wherein R.sup.3 represents a hydrogen atom, hydroxyl group, linear or branched alkyl group having 1 10 carbon atoms, linear or branched alkoxyl group having 1 10 carbon atoms, or linear or branched alkoxycarbonyl group having 2 11 carbon atoms, R.sup.4 represents a linear or branched alkyl group having 1 10 carbon atoms, R.sup.5 individually represents a linear or branched alkyl group having 1 10 carbon atoms, substituted or unsubstituted phenyl group, or substituted or unsubstituted naphthyl group, or two R.sup.5 groups bond to form a substituted or unsubstituted divalent group having 2 10 carbon atoms, k is an integer of 0 to 2, X.sup.- represents an anion represented by the formula R.sup.6C.sub.nF.sub.2nSO.sub.3.sup.- (wherein R.sup.6 represents a fluorine atom or substituted or unsubstituted monovalent hydrocarbon group and n is an integer of 1 to 10), and m is an integer of 0 to 10.

3. The radiation-sensitive resin composition according to claim 1, wherein the resin (A) and the photoacid generator (B) are dissolved in a solvent comprising at least one compound selected from the group consisting of propylene glycol mono-methyl ether acetate, 2-heptanone, and cyclohexanone.

4. A radiation-sensitive resin composition comprising, (A) a resin comprising a copolymer consisting of methacrylate or acrylate recurring units, wherein the copolymer comprises a first recurring unit of the following formulas (1) (3), ##STR00019## wherein R.sup.1 represents a hydrogen atom or methyl group and R.sup.2 is a methyl group, and a second recurring unit of the above formulas (1) (3), wherein R.sup.1 represents a hydrogen atom or methyl group and R.sup.2 represents a substituted or unsubstituted alkyl group having 1 4 carbon atoms, excluding a methyl group, two or more R.sup.2 groups that may be present being either the same or different, in the total amount of 5 70 mol %, but each in the amount of 1 49 mol %, the resin being insoluble or scarcely soluble in alkali, but becoming easily soluble in alkali by the action of an acid, and (B) a photoacid generator; wherein the copolymer comprises a combination of recurring units selected from the group consisting of: a recurring unit of formula (1) and a recurring unit of formula (2); a recurring unit of formula (1) and a recurring unit of formula (3); a first recurring unit of formula (2) and a second recurring unit of formula (2); a recurring unit of formula (2) and a recurring unit of formula (3); and a first recurring unit of formula (3) and a second recurring unit of formula (3).

5. The radiation-sensitive resin composition according to claim 4, wherein the photoacid generator (B) is the compound shown by the formula (7), ##STR00020## wherein R.sup.3 represents a hydrogen atom, hydroxyl group, linear or branched alkyl group having 1 10 carbon atoms, linear or branched alkoxyl group having 1 10 carbon atoms, or linear or branched alkoxycarbonyl group having 2 11 carbon atoms, R.sup.4 represents a linear or branched alkyl group having 1 10 carbon atoms, R.sup.5 individually represents a linear or branched alkyl group having 1 10 carbon atoms, substituted or unsubstituted phenyl group, or substituted or unsubstituted naphthyl group, or two R.sup.5 groups bond to form a substituted or unsubstituted divalent group having 2 10 carbon atoms, k is an integer of 0 to 2, X.sup.- represents an anion represented by the formula R.sup.6C.sub.nF.sub.2nSO.sub.3.sup.- (wherein R.sup.6 represents a fluorine atom or substituted or unsubstituted monovalent hydrocarbon group and n is an integer of 1 to 10), and m is an integer of 0 to 10.

6. The radiation-sensitive resin composition according to claim 4, wherein the resin (A) and the photoacid generator (B) are dissolved in a solvent comprising at least one compound selected from the group consisting of propylene glycol mono-methyl ether acetate, 2-heptanone, and cyclohexanone.

7. A radiation-sensitive resin composition comprising, (A) a resin comprising at least one recurring unit of the following formula (6), ##STR00021## wherein R.sup.2 is a methyl group, and at least one recurring unit selected from the group consisting of the recurring units of the formulas (1) (3), ##STR00022## wherein R.sup.1 represents a hydrogen atom or methyl group and R.sup.2 is a methyl group, in the total amount of 5 70 mol %, but each in the amount of 1 49 mol %, the resin being insoluble or scarcely soluble in alkali, but becoming easily soluble in alkali by the action of an acid, and (B) a photoacid generator.

8. The radiation-sensitive resin composition according to claim 7, wherein the photoacid generator (B) is the compound shown by the formula (7), ##STR00023## wherein R.sup.3 represents a hydrogen atom, hydroxyl group, linear or branched alkyl group having 1 10 carbon atoms, linear or branched alkoxyl group having 1 10 carbon atoms, or linear or branched alkoxycarbonyl group having 2 11 carbon atoms, R.sup.4 represents a linear or branched alkyl group having 1 10 carbon atoms, R.sup.5 individually represents a linear or branched alkyl group having 1 10 carbon atoms, substituted or unsubstituted phenyl group, or substituted or unsubstituted naphthyl group, or two R.sup.5 groups bond to form a substituted or unsubstituted divalent group having 2 10 carbon atoms, k is an integer of 0 to 2, X.sup.- represents an anion represented by the formula R.sup.6C.sub.nF.sub.2nSO.sub.3.sup.- (wherein R.sup.6 represents a fluroine atom or substituted or unsubstituted monovalent hydrocarbon group and n is an integer of 1 to 10), and m is an integer of 0 to 10.

9. The radiation-sensitive resin composition according to claim 7, wherein the resin (A) and the photoacid generator (B) are dissolved in a solvent comprising at least one compound selected from the group consisting of propylene glycol mono-methyl ether acetate, 2-heptanone, and cyclohexanone.

10. A radiation-sensitive resin composition comprising: (A) a resin comprising a first recurring unit of the following formulas (1) (3), ##STR00024## wherein R.sup.1 represents a hydrogen atom or methyl group and R.sup.2 is a methyl group, and a second recurring unit of the above formulas (1) (3), wherein R.sup.1 represents a hydrogen atom or methyl group and R.sup.2 represents a substituted or unsubstituted alkyl group having 1 4 carbon atoms, excluding a methyl group, two or more R.sup.2 groups that may be present being either the same or different, in the total amount of 5 70 mol %, but each in the amount of 1 49 mol %, the resin being insoluble or scarcely soluble in alkali, but becoming easily soluble in alkali by the action of an acid; and (B) a photoacid generator; wherein the resin further comprises the recurring unit shown by the following formula: ##STR00025## wherein R represents a hydrogen atom or a methyl group.

11. The radiation-sensitive resin composition according to claim 10, wherein the photoacid generator (B) is compound shown by the formula (7), ##STR00026## wherein: R.sup.3 represents a hydrogen atom, hydroxyl group, linear or branched alkyl group having 1 10 carbon atoms, linear or branched alkoxyl group having 1 10 carbon atoms, or linear or branched alkoxycarbonyl group having 2 11 carbon atoms; R.sup.4 represents a linear or branched alkyl group having 1 10 carbon atoms; R.sup.5 individually represents a linear or branched alkyl group having 1 10 carbon atoms, substituted or unsubstituted phenyl group, or substituted or unsubstituted naphthyl group, or two R.sup.5 groups bond to form a substituted or unsubstituted divalent group having 2 10 carbon atoms; k is an integer of 0 to 2; X.sup.- represents an anion represented by the formula R.sup.6C.sub.nF.sub.2nSO.sub.3.sup.- wherein R.sup.6 represents a fluorine atom or substituted or unsubstituted monovalent hydrocarbon group and n is an integer of 1 to 10; and m is an integer of 0 to 10.

12. The radiation-sensitive resin composition according to claim 10, wherein the resin (A) and the photoacid generator (B) are dissolved in a solvent comprising at least one compound selected from the group consisting of propylene glycol mono-methyl ether acetate, 2-heptanone, and cyclohexanone.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radiation-sensitive resin composition suitable as a chemically-amplified resist useful for microfabrication utilizing various types of radiation represented by deep ultraviolet rays such as a KrF excimer laser and ArF excimer laser, X-rays such as synchrotron radiation, and charged particle rays such as electron beams.

2. Description of Background Art

In the field of microfabrication represented by the manufacture of integrated circuit devices, lithographic technology enabling microfabrication with a line width of 0.20 .mu.m or less has been demanded in order to increase the degree of integration in recent years.

In a conventional lithographic process, near ultraviolet rays such as i-line radiation have been generally used. However, it is difficult to perform microfabrication with a line width of sub-quarter micron using near ultraviolet rays.

Therefore, in order to enable microfabrication with a line width of 0.20 .mu.m or less, utilization of radiation with a shorter wavelength has been studied. Deep ultraviolet rays represented by a bright line spectrum of a mercury lamp and an excimer laser, X-rays, electron beams, and the like can be given as radiation with a shorter wavelength. Of these, a KrF excimer laser (wavelength: 248 nm) and an ArF excimer laser (wavelength: 193 nm) have attracted attention.

As a resist applicable to the excimer laser radiation, a number of resists utilizing a chemical amplification effect between a component having an acid-dissociable functional group and a component generating an acid (hereinafter referred to as "photoacid generator") which generates an acid upon irradiation (hereinafter referred to as "exposure") has been proposed. Such a resist is hereinafter called a chemically-amplified resist.

As such a chemically-amplified resist, Japanese Patent Publication No. 2-27660 discloses a resist comprising a polymer containing a t-butyl ester group of carboxylic acid or a t-butylcarbonate group of phenol and a photoacid generator. The t-butoxycarbonyl group or t-butylcarbonate group in the polymer dissociates by the action of an acid generated upon exposure, whereby the polymer has an acidic group such as a carboxylic group or a phenolic hydroxyl group. As a result, exposed areas of the resist film become readily soluble in an alkaline developer.

Most of conventional chemically-amplified resists use a phenol resin as a base resin. Deep ultraviolet rays, if used for such a resin as radiation for exposure, are absorbed in the resin due to aromatic rings in the resin and cannot sufficiently reach the lower layers of the resist film. Because of this, the dose of the radiation is greater in the upper layers and smaller in the lower layers of the resist film. This causes a resist pattern profile to be thinner in the upper portion but thicker toward the lower portion, thereby forming a trapezoid shape after development. No sufficient resolution can be obtained from such a resist film. Such a trapezoid resist pattern profile formed after development cannot give a desirable dimensional accuracy in the succeeding steps such as an etching step and an ion implantation step. In addition, if the resist pattern profile is not a rectangle in which the upper side and the sidewall make almost right angle, the resist disappears faster during dry etching, making it difficult to control etching conditions.

A resist pattern profile can be improved by increasing the radiation transmittance through the resist film. For example, a (meth)acrylate resin represented by polymethylmethacrylate is a highly desirable resin from the viewpoint of radiation transmittance, because the (meth)acrylate resin has high transparency to deep ultraviolet rays. Japanese Patent Application Laid-open No. 4-226461 discloses a chemically-amplified resist using a methacrylate resin, for example.

However, this composition has insufficient dry etching resistance due to the absence of an aromatic ring, although the composition excels in microfabrication performance. This makes it difficult to perform etching with high accuracy. Therefore, a composition having both transparency to radiation and dry etching resistance cannot be provided.

As a means to improve dry etching resistance of the chemically-amplified resist without impairing transparency to radiation, a method of introducing an aliphatic ring into the resin component in the resist instead of an aromatic ring is known. For example, Japanese Patent Application Laid-open No. 7-234511 discloses a chemically-amplified resist using a (meth)acrylate resin having an aliphatic ring.

This resist includes groups which comparatively easily dissociate by conventional acids (acetal functional groups such as tetrahydropyranyl group, for example) and groups which are comparatively difficult to dissociate by acids (t-butyl functional groups such as t-butyl ester group or t-butylcarbonate group, for example) as acid-dissociable functional groups in the resin component. The resin component having the former acid-dissociable functional groups exhibits excellent basic characteristics as a resist, in particular, superior sensitivity and excellent pattern profile, but has poor storage stability as the composition. The resin component having the latter acid-dissociable functional groups has excellent storage stability, but exhibits impaired resist characteristics such as sensitivity and pattern shape. Moreover, inclusion of aliphatic rings in the resin component of this resist results in poor adhesion to substrates due to the extreme increase in hydrophobicity of the resin.

When forming a resist pattern by using a chemically-amplified resist, a heat treatment is usually performed after exposure in order to promote the dissociation of the acid-dissociable functional group. The line width of the resist pattern is inevitably changed to some extent as the heating temperature is changed. However, in order to deal with a recent decrease in size of integrated circuit devices, development of a resist which shows only a small change in line width due to a change in heating temperature after exposure (specifically, temperature dependency) has been demanded.

In addition, the photoacid generator is known to greatly affect the functions of a chemically-amplified resist. Presently, onium salt compounds which generate an acid upon exposure at a high quantum yield and exhibit high sensitivity are widely used as a photoacid generator for chemically-amplified resists.

As the onium salt compounds, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium naphthalenesulfonate, and cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate are used, for example. Most of these conventional onium salt compounds, however, do not exhibit satisfactory sensitivity. Although some compounds may exhibit comparatively high sensitivity, they are not necessarily satisfactory in overall resist performance such as resolution, pattern profile, and the like.

In view of development of technology capable of dealing with a recent progress in microfabrication of integrated circuit devices, a chemically-amplified resist which is applicable to short wavelength radiation represented by deep ultraviolet rays, exhibits high radiation transmittance, and excels in basic characteristics as a resist such as sensitivity, resolution, and pattern profile has been strongly demanded.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a radiation-sensitive resin composition useful as a chemically amplified resist having high transmittance of radiation and exhibiting superior basic properties as a resist such as high sensitivity, resolution, dry etching resistance, and pattern profile.

The above object can be achieved in the present invention by radiation-sensitive resin composition comprising:

(A) a resin comprising at least two recurring units of the following formulas (1) (6),

##STR00003## ##STR00004## wherein R.sup.1 represents a hydrogen atom or methyl group and R.sup.2 represents a substituted or unsubstituted alkyl group having 1 4 carbon atoms, two or more R.sup.2 groups that may be present being either the same or different, in the total amount of 5 70 mol %, but each in the amount of 1 49 mol %, the resin being insoluble or scarcely soluble in alkali, but becoming easily soluble in alkali by the action of an acid, and

(B) a photoacid generator.

In a preferred embodiment of the above radiation-sensitive resin composition, the photoacid generator (B) is a compound of the following formula (7),

##STR00005## wherein R.sup.3 represents a hydrogen atom, hydroxyl group, linear or branched alkyl group having 1 10 carbon atoms, linear or branched alkoxyl group having 1 10 carbon atoms, or linear or branched alkoxycarbonyl group having 2 11 carbon atoms, R.sup.4 represents a linear or branched alkyl group having 1 10 carbon atoms, R.sup.5 individually represents a linear or branched alkyl group having 1 10 carbon atoms, substituted or unsubstituted phenyl group, or substituted or unsubstituted naphthyl group, or two R.sup.5 groups bond to form a substituted or unsubstituted divalent group having 2 10 carbon atoms, k is an integer of 0 to 2, X.sup.- represents an anion represented by the formula R.sup.6C.sub.nF.sub.2nSO.sub.3.sup.- (wherein R.sup.6 represents a fluorine atom or substituted or unsubstituted monovalent hydrocarbon group and n is an integer of 1 to 10), and m is an integer of 0 to 10.

In another preferred embodiment of the above radiation-sensitive resin composition, the resin (A) and the photoacid generator (B) are dissolved in a solvent comprising at least one compound selected from the group consisting of propylene glycol mono-methyl ether acetate, 2-heptanone, and cyclohexanone.

In the above radiation-sensitive resin composition, the resin (A) preferably comprises at least two recurring units selected from the group consisting of the recurring units of the formulas (1) (3).

In the above radiation-sensitive resin composition, the resin (A) preferably comprises at least one recurring units selected from the group consisting of the recurring units of the formulas (1) (3) wherein R.sup.2 is a methyl group and at least one recurring units selected from the group consisting of the recurring units of the formulas (1) (3) wherein R.sup.2 is other than the methyl group.

In the above radiation-sensitive resin composition, the resin (A) preferably comprises at least one recurring unit of the formula (6) wherein R.sup.2 is a methyl group and at least one recurring unit selected from the group consisting of the recurring units of the formulas (1) (3).

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

The present invention will be described in detail below.

Component (A)

The component (A) in the present invention is a resin comprising at least two recurring units selected from the groups of the above formulas (1) (6), in the total amount of 5 70 mol %, but each group in the amount of 1 49 mol %. The resin is insoluble or scarcely soluble in alkali, but becomes easily soluble in alkali by the action of an acid. This resin is hereinafter referred to as "resin (A)".

If 50% or more of the initial film thickness of a resist film remains after development when a resist film made only from the resin (A) is developed under the same alkaline development conditions (in an aqueous alkaline solution concentration of pH 8 14, and more preferably pH 9 14) employed for forming a resist pattern using a resist film formed from a radiation-sensitive resin composition comprising the resin (A), such a characteristic of the resin (A) is referred to as "insoluble or scarcely soluble in alkali" in the present invention. The term "easily soluble in alkali" means the characteristics in which 50% or more of the initial film thickness of a resist film is lost.

The recurring units of the formulas (1), (2), (3), (4), (5), and (6) are hereinafter respectively referred to as a recurring unit (1), recurring unit (2), recurring unit (3), recurring unit (4), recurring unit (5), and recurring unit (6).

The recurring units (1) (6) are units respectively derived from the monomers of the following formulas (1m) to (6m),

##STR00006## ##STR00007## wherein R.sup.1 and R.sup.2 are the same as defined for the formulas (1) (6).

These monomers may be used either individually or in combination of two or more.

The resin (A) can comprise recurring units other than the recurring units (1) (6) (hereinafter referred to as "other recurring units").

Examples of the polymerizable unsaturated monomer to provide the other recurring units include: monofunctional monomers such as (meth)acrylates having a bridged hydrocarbon skeleton such as norbornyl (meth)acrylate, isobornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, tetracyclodecanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, adamantyl (meth)acrylate, 3-hydroxy-1-adamantyl (meth)acrylate, 3,5-dihydroxy-1-adamantyl (meth)acrylate, 3-oxo-1-adamantyl (meth)acrylate, and adamantylmethyl (meth)acrylate; carboxyl group-containing esters having a bridged hydrocarbon skeleton of an unsaturated carboxylic acid such as carboxynorbornyl (meth)acrylate, carboxytricyclodecanyl (meth)acrylate, and carboxytetracyclodecanyl (meth)acrylate; (meth)acrylates having no bridged hydrocarbon skeleton such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, 2-methylpropyl (meth)acrylate, 1-methylpropyl (meth)acrylate, t-butyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, cyclopropyl (meth)acrylate, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, 4-methoxycyclohexyl (meth)acrylate, 2-cyclopentyloxycarbonylethyl (meth)acrylate, 2-cyclohexyloxycarbonylethyl (meth)acrylate, and 2-(4-methoxycyclohexyl)oxycarbonylethyl (meth)acrylate; .alpha.-hydroxymethylacrylates such as methyl .alpha.-hydroxymethylacrylate, ethyl .alpha.-hydroxymethylacrylate, n-propyl .alpha.-hydroxymethylacrylate, and n-butyl .alpha.-hydroxymethylacrylate; unsaturated nitrile compounds such as (meth)acrylonitrile, .alpha.-chloroacrylonitrile, crotonitrile, maleinitrile, fumaronitrile, mesaconitrile, citraconitrile, and itaconitrile; unsaturated amide compounds such as (meth)acrylamide, N,N-dimethyl (meth)acrylamide, crotonamide, maleinamide, fumaramide, mesaconamide, citraconamide, and itaconamide; other nitrogen-containing vinyl compounds such as N-(meth)acryloylmorpholine, N-vinyl-.epsilon.-caprolactam, N-vinylpyrrolidone, vinylpyridine, and vinylimidazole; unsaturated carboxylic acids (anhydrides) such as a (meth)acrylic acid, crotonic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, itaconic anhydride, citraconic acid, citraconic anhydride, and mesaconic acid; carboxyl group-containing esters of unsaturated carboxylic acid having no bridged hydrocarbon skeleton such as 2-carboxyethyl (meth)acrylate, 2-carboxypropyl (meth)acrylate, 3-carboxypropyl (meth)acrylate, 4-carboxybutyl (meth)acrylate, and 4-carboxycyclohexyl (meth)acrylate; and (meth)acryloyloxylactone compounds having an acid-dissociable group such as .alpha.-(meth)acryloyloxy-.beta.-methoxycarbonyl-.gamma.-butyrolactone, .alpha.-(meth)acryloyloxy-.beta.-ethoxycarbonyl-.gamma.-butyrolactone, .alpha.-(meth)acryloyloxy-.beta.-n-propoxycarbonyl-.gamma.-butyrolactone, .alpha.-(meth)acryloyloxy-.beta.-i-propoxycarbonyl-.gamma.-butyrolactone, .alpha.-(meth)acryloyloxy-.beta.-n-butoxycarbonyl-.gamma.-butyrolactone, .alpha.-(meth)acryloyloxy-.beta.-(2-methylpropoxy)carbonyl-.gamma.-butyro- lactone, .alpha.-(meth)acryloyloxy-.beta.-(1-methylpropoxy)carbonyl-.gamma- .-butyrolactone, .alpha.-(meth)acryloyloxy-.beta.-t-butoxycarbonyl-.gamma.-butyrolactone, .alpha.-(meth)acryloyloxy-.beta.-cyclohexyloxycarbonyl-.gamma.-butyrolact- one, .alpha.-(meth)acryloyloxy-.beta.-(4-t-butylcyclohexyloxy) carbonyl-.gamma.-butyrolactone, .alpha.-(meth)acryloyloxy-.beta.-phenoxycarbonyl-.gamma.-butyrolactone, .alpha.-(meth)acryloyloxy-.beta.-(1-ethoxyethoxy)carbonyl-.gamma.-butyrol- actone, .alpha.-(meth)acryloyloxy-.beta.-(1-cyclohexyloxyethoxy)carbonyl-.- gamma.-butyrolactone, .alpha.-(meth)acryloyloxy-.beta.-t-butoxycarbonylmethoxycarbonyl-.gamma.-- butyrolactone, .alpha.-(meth)acryloyloxy-.beta.-tetrahydrofuranyloxycarbonyl-.gamma.-but- yrolactone, .alpha.-(meth)acryloyloxy-.beta.-tetrahydropyranyloxycarbonyl-.gamma.-but- yrolactone, .alpha.-methoxycarbonyl-.beta.-(meth)acryloyloxy-.gamma.-butyrolactone, .alpha.-ethoxycarbonyl-.beta.-(meth)acryloyloxy-.gamma.-butyrolactone, .alpha.-n-propoxycarbonyl-.beta.-(meth)acrylyloxy-.gamma.-butyrolactone, .alpha.-i-propoxycarbonyl-.beta.-(meth)acryloyloxy-.gamma.-butyrolactone, .alpha.-n-butoxycarbonyl-.beta.-(meth)acryloyloxy-.gamma.-butyrolactone, .alpha.-(2-methylpropoxy)carbonyl-.beta.-(meth)acryloyloxy-.gamma.-butyro- lactone, .alpha.-(1-methylpropoxy)carbonyl-.beta.-(meth)acryloyloxy-.gamma- .-butyrolactone, .alpha.-t-butoxycarbonyl-.beta.-(meth)acryloyloxy-.gamma.-butyrolactone, .alpha.-cyclohexyloxycarbonyl-.beta.-(meth)acryloyloxy-.gamma.-butyrolact- one, .alpha.-(4-t-butylcyclohexyloxy)carbonyl-.beta.-(meth)acryloyloxy-.ga- mma.-butyrolactone, .alpha.-phenoxycarbonyl-.beta.-(meth)acryloyloxy-.gamma.-butyrolactone, .alpha.-(1-ethoxyethoxy)carbonyl-.beta.-(meth)acryloyloxy-.gamma.-butyrol- actone, .alpha.-(1-cyclohexyloxyethoxy)carbonyl-.beta.-(meth)acryloyloxy-.- gamma.-butyrolactone, .alpha.-t-butoxycarbonylmethoxycarbonyl-.beta.-(meth)acryloyloxy-.gamma.-- butyrolactone, .alpha.-tetrahydrofuranyloxycarbonyl-.beta.-(meth)acryloyloxy-.gamma.-but- yrolactone, .alpha.-tetrahydropyranyloxycarbonyl-.beta.-(meth)acryloyloxy-.gamma.-but- yrolactone, and .beta.-(meth)acryloyloxy-.beta.-methyl-.delta.-valerolactone; and (meth)acryloyloxylactone compounds having no acid-dissociable group such as .alpha.-(meth)acryloyloxy-.gamma.-butylolactone, .beta.-(meth)acryloyloxy-.gamma.-butylolactone, .alpha.-(meth)acryloyloxy-.beta.-fluoro-.gamma.-butylolactone, .alpha.-(meth)acryloyloxy-.beta.-hydroxy-.gamma.-butylolactone, .alpha.-(meth)acryloyloxy-.beta.-methyl-.gamma.-butylolactone, .alpha.-(meth)acryloyloxy-.beta.-ethyl-.gamma.-butylolactone, .alpha.-(meth)acryloyloxy-.beta.,.beta.-dimethyl-.gamma.-butylolactone, .alpha.-(meth)acryloyloxy-.beta.-methoxy-.gamma.-butylolactone, .alpha.-fluoro-.beta.-(meth)acryloyloxy-.gamma.-butylolactone, .alpha.-hydroxy-.beta.-(meth)acryloyloxy-.gamma.-butylolactone, .alpha.-methyl-.beta.-(meth)acryloyloxy-.gamma.-butylolactone, .alpha.-ethyl-.beta.-(meth)acryloyloxy-.gamma.-butylolactone, .alpha.,.alpha.-dimethyl-.beta.-(meth)acryloyloxy-.gamma.-butylolactone, .alpha.-methoxy-.beta.-(meth)acryloyloxy-.gamma.-butylolactone, .alpha.-(meth)acryloyloxy-.delta.-valerolactone, .beta.-(meth)acryloyloxy-.delta.-valerolactone, .delta.-(meth)acryloyloxy-.gamma.-valerolactone, .delta.-(meth)acryloyloxy-.beta.-methyl-.gamma.-valerolactone, .delta.-(meth)acryloyloxy-.beta.,.beta.-dimethyl-.gamma.-valerolactone, 2-(meth)acryloyloxy-5-oxo-4-oxatricyclo[4.2.1.0.sup.3,7]nonane, 2-(meth)acryloyloxy-9-methoxycarbonyl-5-oxo-4-oxatricyclo[4.2.1..sup.3,7]- nonane, 4-(meth)acryloyloxy-7-oxo-6-oxabicyclo[3.2.1]octane, 4-(meth)acryloyloxy-2-methoxycarbonyl-7-oxo-6-oxabicyclo[3.2.1]octane, and 8(9)-(meth)acryloyloxy-3-oxo-4-oxatricyclo[5.2.1.0.sup.2,6]decane, and polyfunctional monomers such as polyfunctional monomers having a bridged hydrocarbon skeleton such as 1,2-adamantanediol di(meth)acrylate, 1,3-adamantanediol di(meth)acrylate, 1,4-adamantanediol di(meth)acrylate, and tricyclodecanyldimethylol di(meth)acrylate; and polyfunctional monomers having no bridged hydrocarbon skeleton such as methylene glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,6-hexanediol di-(meth)acrylate, 2,5-dimethyl-2,5-hexanediol di(meth)acrylate, 1,8-octanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,4-bis(2-hydroxypropyl)benzene di(meth)acrylate, and 1,3-bis(2-hydroxypropyl)benzene di(meth)acrylate.

Of these polymerizable unsaturated monomers providing the other recurring units, (meth)acrylates having a bridged hydrocarbon skeleton and the like are preferable.

Examples of the more preferable polymerizable unsaturated monomer include 3-hydroxy-1-adamantanyl (meth)acrylate, 3,5-dihydroxy-1-adamantanyl (meth)acrylate, 3-oxo-1-adamantanyl (meth)acrylate, 2-(meth)acryloyloxy-5-oxo-4-oxatricyclo[4.2.1.0.sup.3,7]nonane, 2-(meth)acryloyloxy-9-methoxycarbonyl-5-oxo-4-oxatricyclo[4.2.1.0.sup.3,7- ]nonane, 4-(meth)acryloyloxy-7-oxo-6-oxabicyclo[3.2.1]octane, 4-(meth)acryloyloxy-2-methoxycarbonyl-7-oxo-6-oxabicyclo[3.2.1]octane, and 8(9)-(meth)acryloyloxy-3-oxo-4-oxatricyclo[5.2.1.0.sup.2,6]decane.

In the resin (A), these other recurring units may be present either individually or in combination of two or more.

In the resin (A), the amount of each recurring unit of the at least two recurring units selected from the recurring units (1) (6) is preferably 1 49 mol %, and preferably 3 40 mol % of the total amount of all recurring units forming the resin. The total of the recurring units (1) (6) of the total amount of all recurring units forming the resin is preferably 5 70 mol %. If the amount of the recurring units (1) (6) is less than 5 mol %, not only a sufficient contrast cannot be obtained during development, but also resolution becomes poor, giving rise to development defects. If the amount exceeds 70 mol %, on the other hand, developability and sensitivity are significantly impaired, although contrast to developing solutions is improved.

The content of the other recurring units is usually 95 mol % or less, and preferably 80 mol % or less.

As preferable combinations of recurring units selected from the recurring units (1) (6), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (2) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (2) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (2) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.4H.sub.9), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (3) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (3) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (5) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (6) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (2) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (2) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (2) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.4H.sub.9), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (3) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (3) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (5) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (6) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (2) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (2) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (2) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (5) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (2) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (6) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (3) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (3) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (3) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (5) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (3) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (6) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (5) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (6) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (2) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (6) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (5) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (6) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (2) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (2) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (3) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (3) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (5) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (6) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (2) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (2) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (3) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (3) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (4) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (4) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (5) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (6) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (2) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (2) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (2) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (5) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (2) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (6) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (3) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (3) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (3) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (5) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (3) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (6) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (4) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (4) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (5) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (4) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (6) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (4) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (5) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (4) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (6) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (5) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (6) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (2) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (2) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (3) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (3) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (3) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (5) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (6) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (2) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (2) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (3) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (3) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (5) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (6) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (2) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (2) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (2) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (5) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (2) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (6) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (3) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (3) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (3) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (5) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (3) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (6) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (4) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (4) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (5) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (4) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (6) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (4) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (5) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (4) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (6) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (5) (R.sup.1: --H, R.sup.2: --CH.sub.3) and the recurring unit (6) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (1) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (2) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (2) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (2) (R.sup.1: --H, R.sup.2: --C.sub.4H.sub.9), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (3) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (3) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (4) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (5) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --CH.sub.3) and the recurring unit (6) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (2) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (2) (R.sup.1: --H, R.sup.2: --C.sub.2H.sub.5), a combination of the recurring unit (1) (R.sup.1: --CH.sub.3, R.sup.2: --C.sub.2H.sub.5) and the recurring unit (3) (R.sup.1: --H, R.sup.2: --CH.sub.3), a combination of the recurring unit (1) (R.sup.