Positive-type resist composition and resist pattern formation method

Abstract

The present invention provides technology capable of forming a high-contrast resist pattern with minimal resist top loss. This positive resist composition comprises a copolymer A, a copolymer B, and a solvent, wherein the difference between the surface free energy of the copolymer A and the surface free energy of the copolymer B is 4 mJ / m2 or greater.

Description

[Technical Field]

[0001] The present invention relates to a positive-type resist composition and a resist pattern formation method. [Background technology]

[0002] Conventionally, in fields such as semiconductor manufacturing, polymers whose main chains are cleaved by irradiation with ionizing radiation such as electron beams or short-wavelength light such as ultraviolet light (hereinafter, ionizing radiation and short-wavelength light may be collectively referred to as "ionizing radiation, etc.") and whose solubility in developing solutions increases have been used as main-chain cleavage type positive resists.

[0003] For example, Patent Document 1 discloses a positive-type resist composition that includes a main-chain cleavage type positive-type resist having excellent sensitivity to ionizing radiation and heat resistance, comprising a copolymer containing α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-methylstyrene units. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-154754 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the resist patterns formed using the above-mentioned conventional positive-type resist compositions had room for improvement in terms of reducing top loss (reducing the wear of the top of the resist pattern) and increasing the contrast of the resist pattern.

[0006] Therefore, the present invention aims to provide a positive-type resist composition that exhibits minimal wear on the resist pattern top and can form a resist pattern with high contrast. Furthermore, the present invention aims to provide a method for forming a resist pattern that minimizes wear on the resist pattern top and enables the formation of a resist pattern with high contrast. [Means for solving the problem]

[0007] The inventors conducted diligent research to achieve the above objectives. They then discovered that by using a positive-type resist composition containing two predetermined copolymers as the positive-type resist, it is possible to form a resist pattern with less wear on the top of the resist pattern and high contrast, thus completing the present invention.

[0008] In other words, the present invention aims to advantageously solve the above problems, and the positive-type resist composition of the present invention comprises copolymer A, copolymer B, and a solvent, wherein the difference between the surface free energy of copolymer A and the surface free energy of copolymer B is 4 mJ / m 2 The above is a characteristic feature. Thus, it contains copolymer A, copolymer B, and a solvent, and the difference between the surface free energy of copolymer A and the surface free energy of copolymer B is 4 mJ / m 2 By using the positive-type resist composition described above, it is possible to form a resist pattern with minimal wear on the top of the resist pattern and high contrast. In this invention, the "surface free energy" can be measured using the method described in the examples of this specification.

[0009] Here, it is preferable that the positive resist composition of the present invention is such that at least one of copolymer A and copolymer B is a main-chain cleavage type copolymer containing halogen atoms. More preferably, at least one of copolymer A and copolymer B contains a fluorine substituent, at least one of the halogen atoms is a fluorine atom, and the fluorine atom is included in the fluorine substituent. If at least one of copolymer A and copolymer B is a main-chain cleavage type copolymer containing halogen atoms, and preferably at least one of copolymer A and copolymer B contains a fluorine substituent, and at least one of the halogen atoms is a fluorine atom, and the fluorine atom is included in the fluorine substituent, then it is possible to form a resist pattern with even less wear on the top of the resist pattern and even higher contrast. In this invention, the term "main chain severing type" of copolymer means that when the copolymer is irradiated with ionizing radiation such as electron beams or extreme ultraviolet (EUV) radiation, the main chain of the copolymer is severed.

[0010] In this context, it is preferable that the positive-type resist composition of the present invention substantially does not contain components with a weight-average molecular weight (Mw) of less than 1000. If the positive-type resist composition substantially does not contain components with a weight-average molecular weight (Mw) of less than 1000, the contrast of the resist pattern can be further enhanced. In this invention, the "weight-average molecular weight" can be measured using gel permeation chromatography as a value equivalent to standard polystyrene. Furthermore, in this invention, "substantially absent" means not actively incorporating a substance except in cases where it is inevitably present. Specifically, this refers to the content of a component with a weight-average molecular weight (Mw) of less than 1000 in the positive-type resist composition being less than 0.05% by mass.

[0011] Furthermore, the positive resist composition of the present invention comprises at least one of copolymer A and copolymer B, wherein the following formula (V): [ka] [In formula (V), X is a halogen atom, a cyano group, an alkylsulfonyl group, an alkoxy group, a nitro group, an acyl group, an alkyl ester group, or a halogenated alkyl group, R 1It is preferable that the monomer unit (V) represented by is an organic group having 3 to 10 fluorine atoms. If at least one of copolymer A and copolymer B has monomer unit (V), the contrast of the resist pattern can be further enhanced.

[0012] Furthermore, the positive resist composition of the present invention comprises copolymer A, wherein the copolymer A is of the following formula (I): [ka] [In formula (I), L is a divalent linking group having a fluorine atom, and Ar is an aromatic ring group which may have substituents.] A monomer unit (I) represented by the following formula (II): [ka] [In formula (II), R 1 R is an alkyl group, 2 R is a hydrogen atom, alkyl group, halogen atom, halogenated alkyl group, hydroxyl group, carboxyl group or halogenated carboxyl group, 3 It is preferable to have monomer unit (II) represented by ] and , where p and q are integers between 0 and 5, and p + q = 5. By using copolymer A having monomer unit (I) and monomer unit (II), the contrast of the resist pattern can be further enhanced. In this invention, "may have substituents" means "unsubstituted or substituted."

[0013] Furthermore, the positive resist composition of the present invention comprises copolymer B of the following formula (III): [ka] [In formula (III), R 1 This is an organic group with 5 to 7 fluorine atoms. The monomer unit (III) is represented by ] and the following formula (IV): [ka] 〔In formula (IV), R 1 is an alkyl group, R 2 is a hydrogen atom, a fluorine atom, an unsubstituted alkyl group or an alkyl group substituted with a fluorine atom, R 3 is a hydrogen atom, an unsubstituted alkyl group or an alkyl group substituted with a fluorine atom, p and q are integers of 0 or more and 5 or less, and p + q = 5.〕 It is preferable to have the monomer unit (IV) represented by. If the copolymer B having the monomer unit (III) and the monomer unit (IV) is used, the contrast of the resist pattern can be further enhanced.

[0014] Further, the present invention aims to advantageously solve the above problems, and the resist pattern forming method of the present invention includes a step of forming a resist film using any of the above-mentioned positive resist compositions, a step of exposing the resist film, and a step of developing the exposed resist film. Thus, by forming a resist film using the positive resist composition of the present invention, exposing the obtained resist film, and then developing the exposed resist film, a resist pattern with less reduction at the top of the resist pattern and high contrast can be formed.

[0015] And, in the resist pattern forming method of the present invention, it is preferable to perform the development using alcohol. By developing using alcohol, the contrast of the resist pattern can be further enhanced.

Effects of the Invention

[0016] According to the present invention, it is possible to provide a positive resist composition capable of forming a resist pattern with less reduction at the top of the resist pattern and high contrast. Further, according to the present invention, it is possible to provide a method for forming a resist pattern capable of forming a resist pattern with less reduction at the top of the resist pattern and high contrast.

Modes for Carrying Out the Invention

[0017] Embodiments of the present invention will be described in detail below. Here, the positive-type resist composition of the present invention is used to form a resist film when forming a resist pattern using ionizing radiation such as electron beams or EUV. The resist pattern formation method of the present invention forms a resist pattern using the positive-type resist composition of the present invention. Here, the resist pattern formation method of the present invention is not particularly limited and can be used, for example, when forming a resist pattern in manufacturing processes for semiconductors, photomasks, molds, etc.

[0018] (Positive-type resist composition) The positive-type resist composition of the present invention comprises copolymer A, copolymer B, and a solvent, as detailed below, and optionally further contains known additives that can be incorporated into the positive-type resist composition. Furthermore, the positive-type resist composition of the present invention comprises copolymer A and copolymer B, wherein the difference between the surface free energy of copolymer A and the surface free energy of copolymer B is 4 mJ / m 2 The above is required. Furthermore, the positive-type resist composition of the present invention has a surface free energy difference of 4 mJ / m 2 Since copolymer A and copolymer B described above are contained as positive-type resists, using this positive-type resist composition makes it possible to reduce the wear on the top of the resist pattern and form a resist pattern with high contrast. Furthermore, the positive-type resist composition of the present invention preferably contains substantially no components with a weight-average molecular weight (Mw) of less than 1000. Specifically, the content of components with a weight-average molecular weight (Mw) of less than 1000 in the positive-type resist composition is preferably less than 0.05% by mass, preferably less than 0.01% by mass, and more preferably less than 0.001% by mass.

[0019] <Copolymer A> The copolymer A contained in the positive-type resist composition of the present invention has a surface free energy difference of 4 mJ / m² between copolymer A and copolymer B. 2 The above is not particularly limited. Furthermore, in order to form a resist pattern with even less wear on the top of the resist pattern and even higher contrast, copolymer A is preferably a main-chain cleavage type copolymer containing halogen atoms, and more preferably contains a fluorine substituent, wherein at least one of the halogen atoms is a fluorine atom, and the fluorine atom is included in the fluorine substituent. Here, the fluorine substituent is not particularly limited as long as it is a substituent having a fluorine atom.

[0020] [Surface free energy of copolymer A] Here, the surface free energy of copolymer A is 28 mJ / m 2 Preferably, it is 29 mJ / m 2 It is more preferable that the concentration be 30 mJ / m 2 It is even more preferable that the concentration be 35 mJ / m 2 Preferably, it is 34 mJ / m 2 It is more preferable that the following is true: 33 mJ / m 2 The following is even more preferable:

[0021] Furthermore, copolymer A contained in the positive-type resist composition of the present invention is derived from the viewpoint of further enhancing the contrast of the resist pattern, and is based on the following formula (V): [ka] [In formula (V), X is a halogen atom, a cyano group, an alkylsulfonyl group, an alkoxy group, a nitro group, an acyl group, an alkyl ester group, or a halogenated alkyl group, R 1 It is an organic group having 3 to 10 fluorine atoms. It is preferable to have a monomer unit (V) represented by ].

[0022] Here, the monomer unit (V) is given by the following formula (e): [ka] [In equation (e), X and R 1 This is similar to formula (V). It is a structural unit derived from the monomer (e) represented by ].

[0023] Furthermore, the proportion of monomer units (e) in the total amount of polymer units constituting copolymer A is not particularly limited, but can be, for example, 30 moles or more, preferably 40 moles or more, more preferably 45 moles or more, can be 70 moles or less, preferably 60 moles or less, and more preferably 55 moles or less.

[0024] Here, examples of halogen atoms that can constitute X in formulas (V) and (e) include chlorine, fluorine, bromine, iodine, or astatine atoms. Examples of alkylsulfonyl groups that can constitute X in formulas (V) and (e) include methylsulfonyl or ethylsulfonyl groups. Examples of alkoxy groups that can constitute X in formulas (V) and (e) include methoxy, ethoxy, or propoxy groups. Examples of acyl groups that can constitute X in formulas (V) and (e) include formyl, acetyl, or propionyl groups. Examples of alkyl ester groups that can constitute X in formulas (V) and (e) include methyl or ethyl ester groups. Examples of halogenated alkyl groups that can constitute X in formulas (V) and (e) include methyl halides with one to three halogen atoms. In particular, X is preferably a halogen atom, and more preferably a chlorine atom.

[0025] Also, R in equations (V) and (e) 1 This is an organic group having 3 to 10 fluorine atoms, and R 1 The number of fluorine atoms contained is preferably 5 to 7. 1If the number of fluorine atoms contained within is greater than or equal to the above lower limit, copolymer A is useful as a main-chain cleavage type positive resist. Also, R 1 If the number of fluorine atoms contained within is below the above upper limit, the manufacturing efficiency of copolymer A is excellent.

[0026] Organic groups having 3 to 10 (preferably 5 to 7) fluorine atoms are not particularly limited and include, for example, fluoroalkyl groups having 3 to 10 fluorine atoms, such as (a-1) to (a-30) below; fluoroalkoxyalkyl groups having 3 to 10 fluorine atoms, such as (a-31) to (a-54) below; fluoroalkoxyalkenyl groups having 3 to 10 fluorine atoms, such as fluoroethoxyvinyl groups; and organic groups represented by the following formula (A) (hereinafter referred to as "organic group (A)"). -L-Ar ···(A) [In organic group (A), L is a divalent linking group, Ar is an aromatic ring group which may have substituents, and the number of fluorine atoms contained in organic group (A) is 3 to 10 (preferably 5 to 7).]

[0027] [ka]

[0028] [ka]

[0029] The divalent linking group that can constitute L in the organic group (A) is not particularly limited, but includes, for example, an alkylene group which may have substituents, an alkenylene group which may have substituents, and so on.

[0030] Furthermore, the alkylene group, which may have substituents, is not particularly limited and includes, for example, linear alkylene groups such as methylene, ethylene, propylene, n-butylene, and isobutylene groups, and cyclic alkylene groups such as 1,4-cyclohexylene groups. Among these, linear alkylene groups having 1 to 6 carbon atoms, such as methylene, ethylene, propylene, n-butylene, and isobutylene groups, are preferred as alkylene groups; linear alkylene groups having 1 to 6 carbon atoms, such as methylene, ethylene, propylene, and n-butylene groups, are more preferred; and linear alkylene groups having 1 to 3 carbon atoms, such as methylene, ethylene, and propylene groups, are even more preferred.

[0031] Furthermore, the alkenylene group, which may have substituents, is not particularly limited and includes, for example, linear alkenylene groups such as etenylene, 2-propenylene, 2-butenylene, and 3-butenylene, and cyclic alkenylene groups such as cyclohexenylene. Among these, linear alkenylene groups having 2 to 6 carbon atoms, such as etenylene, 2-propenylene, 2-butenylene, and 3-butenylene, are preferred as the alkenylene group.

[0032] Among the above, from the viewpoint of sufficiently improving the sensitivity of the resulting copolymer A to ionizing radiation, a divalent linking group is preferably an alkylene group which may have substituents, more preferably a linear alkylene group having 1 to 6 carbon atoms which may have substituents, even more preferably a linear alkylene group having 1 to 6 carbon atoms which may have substituents, and particularly preferably a linear alkylene group having 1 to 3 carbon atoms which may have substituents.

[0033] Furthermore, from the viewpoint of further improving the sensitivity of copolymer A to ionizing radiation, it is preferable that the divalent linking group that can constitute L of organic group (A) has one or more electron-withdrawing groups. In particular, when the divalent linking group is an alkylene group having an electron-withdrawing group as a substituent or an alkenylene group having an electron-withdrawing group as a substituent, it is preferable that the electron-withdrawing group is bonded to the carbon adjacent to the carbonyl carbon in formula (V) that is bonded to O.

[0034] Furthermore, the electron-withdrawing group that can sufficiently improve sensitivity to ionizing radiation and the like is not particularly limited, but includes, for example, at least one selected from the group consisting of a fluorine atom, a fluoroalkyl group, a cyano group, and a nitro group. The fluoroalkyl group is not particularly limited, but includes, for example, a fluoroalkyl group having 1 to 5 carbon atoms. Among these, a perfluoroalkyl group having 1 to 5 carbon atoms is preferred, and a trifluoromethyl group is more preferred.

[0035] Furthermore, from the viewpoint of further increasing the productivity of copolymer A, the L in the organic group (A) is preferably a divalent linking group having 3 to 10 fluorine atoms, more preferably a divalent linking group having 3 to 6 fluorine atoms, and even more preferably a trifluoromethylmethylene group, a pentafluoroethylmethylene group, or a bis(trifluoromethyl)methylene group.

[0036] Furthermore, examples of Ar in organic group (A) include aromatic hydrocarbon ring groups which may have substituents and aromatic heterocyclic groups which may have substituents.

[0037] Furthermore, the aromatic hydrocarbon ring group is not particularly limited, but examples include benzene ring group, biphenyl ring group, naphthalene ring group, azulene ring group, anthracene ring group, phenanthrene ring group, pyrene ring group, chrysene ring group, naphthacene ring group, triphenylene ring group, o-terphenyl ring group, m-terphenyl ring group, p-terphenyl ring group, acenaphthene ring group, coronene ring group, fluorene ring group, fluoranthrene ring group, pentacene ring group, perylene ring group, pentaphene ring group, picene ring group, pyranthrene ring group, and the like.

[0038] Furthermore, aromatic heterocyclic groups are not particularly limited, but include, for example, furan rings, thiophene rings, pyridine rings, pyridazine rings, pyrimidine rings, pyrazine rings, triazine rings, oxadiazole rings, triazole rings, imidazole rings, pyrazole rings, thiazole rings, indole rings, benzimidazole rings, benzothiazole rings, benzoxazole rings, quinoxaline rings, quinazoline rings, phthalazine rings, benzofuran rings, dibenzofuran rings, benzothiophene rings, dibenzothiophene rings, and carbazole rings.

[0039] Furthermore, the substituents that Ar may have are not particularly limited, but include, for example, alkyl groups, fluorine atoms, and fluoroalkyl groups. Examples of alkyl groups as substituents that Ar may have include chain alkyl groups having 1 to 6 carbon atoms, such as methyl groups, ethyl groups, propyl groups, n-butyl groups, and isobutyl groups. Examples of fluoroalkyl groups as substituents that Ar may have include fluoroalkyl groups having 1 to 5 carbon atoms, such as trifluoromethyl groups, trifluoroethyl groups, and pentafluoropropyl groups.

[0040] In particular, from the viewpoint of improving the ease of manufacturing copolymer A, the Ar in the organic group (A) is preferably an aromatic hydrocarbon ring group which may have substituents, more preferably an unsubstituted aromatic hydrocarbon ring group, and even more preferably a benzene ring group (phenyl group).

[0041] Furthermore, the monomer (e) represented by formula (V) is not particularly limited, and includes, for example, 2,2,2-trifluoroethyl α-chloroacrylate, 2,2,3,3,3-pentafluoropropyl α-chloroacrylate, 3,3,4,4,4-pentafluorobutyl α-chloroacrylate, 1H-1-(trifluoromethyl)trifluoroethyl α-chloroacrylate, 1H,1H,3H-hexafluorobutyl α-chloroacrylate, 1,2,2,2-tetrafluoro-1-(trifluoromethyl)ethyl α-chloroacrylate, 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylate, and other α-chloroacrylate compounds. Examples include fluoroalkyl esters; fluoroalkoxyalkyl esters of α-chloroacrylate such as pentafluoroethoxymethyl α-chloroacrylate and pentafluoroethoxyethyl α-chloroacrylate; fluoroalkoxyalkenyl esters of α-chloroacrylate such as pentafluoroethoxyvinyl α-chloroacrylate; and 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl α-chloroacrylate, 1-phenyl-2,2,2-trifluoroethyl α-chloroacrylate, and 1-phenyl-2,2,3,3,3-pentafluoropropyl α-chloroacrylate. Furthermore, from the viewpoint of further improving the production efficiency of copolymer A, the monomer (e) represented by formula (V) is preferably α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl, α-chloroacrylate-1-phenyl-2,2,2-trifluoroethyl, or α-chloroacrylate-1-phenyl-2,2,3,3,3-pentafluoropropyl, and more preferably α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl, or α-chloroacrylate-1-phenyl-2,2,3,3,3-pentafluoropropyl.

[0042] Furthermore, copolymer A contained in the positive-type resist composition of the present invention is derived from the viewpoint of further enhancing the contrast of the resist pattern, and is based on the following formula (I): [ka] A monomer unit (I) represented by the following formula (I): [In formula (I), L is a divalent linking group having a fluorine atom, and Ar is an aromatic group which may have substituents.] and the following formula (II): [ka] [In formula (II), R 1 R is an alkyl group, 2 R is a hydrogen atom, alkyl group, halogen atom, halogenated alkyl group, hydroxyl group, carboxyl group or halogenated carboxyl group, 3 It is more preferable that the monomer unit (II) represented by ] is an alkyl group substituted with a hydrogen atom, an unsubstituted alkyl group, or a fluorine atom, and p and q are integers between 0 and 5, with p + q = 5.

[0043] Copolymer A may contain any monomer units other than monomer unit (I) and monomer unit (II), but the proportion of monomer unit (I) and monomer unit (II) in total of the monomer units constituting copolymer A is preferably 90 mol% or more, and more preferably 100 mol% (i.e., copolymer A contains only monomer unit (I) and monomer unit (II)).

[0044] Furthermore, copolymer A contains monomer units (I) and (II), so when irradiated with an electron beam or the like, the main chain is cleaved, resulting in efficient reduction of molecular weight.

[0045] Here, the monomer unit (I) is given by the following formula (a): [ka] It is a structural unit derived from monomer (a) represented by [formula (a) in which L and Ar are the same as in formula (I)].

[0046] Here, examples of divalent linking groups having fluorine atoms that can constitute L in formulas (I) and (a) include divalent linear alkyl groups having 1 to 5 carbon atoms and containing fluorine atoms. The number of fluorine atoms is preferably 3 to 10, and more preferably 5 to 7.

[0047] Furthermore, examples of optionally substituted aromatic ring groups that can constitute Ar in formulas (I) and (a) include optionally substituted aromatic hydrocarbon ring groups and optionally substituted aromatic heterocyclic groups.

[0048] Furthermore, the aromatic hydrocarbon ring group is not particularly limited, and examples include groups similar to the aromatic hydrocarbon ring group that can constitute Ar in formulas (V) and (e) described above.

[0049] Furthermore, the aromatic heterocyclic group is not particularly limited, and examples include groups similar to the aromatic heterocyclic groups that can constitute Ar in formulas (V) and (e) described above.

[0050] Furthermore, the substituents that Ar may have are not particularly limited, and include, for example, groups similar to those that Ar may have in formulas (V) and (e) described above.

[0051] In particular, from the viewpoint of sufficiently improving sensitivity to electron beams and the like, the Ar in formula (I) and formula (a) is preferably an aromatic hydrocarbon ring group which may have substituents, more preferably an unsubstituted aromatic hydrocarbon ring group, and even more preferably a benzene ring group (phenyl group).

[0052] Furthermore, from the viewpoint of sufficiently improving sensitivity to electron beams and the like, the monomer (a) represented by formula (a) above, which can form the monomer unit (I) represented by formula (I) above, is preferably α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) and α-chloroacrylate-1-(4-methoxyphenyl)-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPhOMe), and more preferably α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl. In other words, copolymer A preferably has at least one of the α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and the α-chloroacrylate-1-(4-methoxyphenyl)-1-trifluoromethyl-2,2,2-trifluoroethyl units, and more preferably has the α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units.

[0053] The proportion of monomer unit (I) in the total monomer units constituting copolymer A is not particularly limited, and can be, for example, 30 moles or more, preferably 40 moles or more, more preferably 45 moles or more, can be 70 moles or less, preferably 60 moles or less, and more preferably 55 moles or less.

[0054] Furthermore, the monomer unit (II) is given by the following formula (b): [ka] [In formula (b), R 1 and R 2 Furthermore, p and q are the same as in formula (II). These are structural units derived from monomer (b) represented by ].

[0055] Here, R in equations (II) and (b) 1 ,R 2The alkyl groups that can constitute the R are not particularly limited, and examples include unsubstituted alkyl groups having 1 to 5 carbon atoms. 1 ,R 2 The alkyl group that can constitute the alkyl group is preferably a methyl group or an ethyl group.

[0056] Also, R in equations (II) and (b) 2 The halogen atoms that can constitute the halogen are not particularly limited, but include fluorine, chlorine, bromine, and iodine atoms. Among these, fluorine is preferred as the halogen atom.

[0057] Furthermore, R in equations (II) and (b) 2 The halogenated alkyl group that can constitute it is not particularly limited, but for example, a fluoroalkyl group having 1 to 5 carbon atoms can be cited. Among these, a perfluoroalkyl group having 1 to 5 carbon atoms is preferred as the halogenated alkyl group, and a trifluoromethyl group is more preferred.

[0058] Furthermore, R in equations (II) and (b) 2 The halogenated carboxyl groups that can constitute the halogenated carboxyl group are not particularly limited, but include, for example, carboxyl chloride group (-C(=O)-Cl), carboxyl fluoride group (-C(=O)-F), and carboxyl bromide group (-C(=O)-Br).

[0059] Furthermore, from the viewpoint of improving the ease of preparation of copolymer A and the cleavage of the main chain when irradiated with electron beams, etc., R in formulas (II) and (b) 1 It is preferably an alkyl group having 1 to 5 carbon atoms, and more preferably a methyl group.

[0060] Furthermore, from the viewpoint of ease of preparation of copolymer A and improvement of the main chain cleavage when irradiated with an electron beam or the like, it is preferable that p in formula (II)(b) is 0 or 1.

[0061] Furthermore, if p in equations (II) and (b) is any of 1 to 5, then R in equations (II) and (b)2 It is preferably an alkyl group having 1 to 5 carbon atoms, and more preferably a methyl group.

[0062] Also, R in equations (II) and (b) 3 Unsubstituted alkyl groups that can constitute the R are not particularly limited, but include unsubstituted alkyl groups having 1 to 5 carbon atoms. 3 The unsubstituted alkyl group that can constitute the group is preferably a methyl group or an ethyl group.

[0063] Furthermore, R in equations (II) and (b) 3 Examples of alkyl groups substituted with fluorine atoms that can constitute this group include, without any particular limitations, groups having a structure in which some or all of the hydrogen atoms in the alkyl group are replaced with fluorine atoms.

[0064] Furthermore, the monomer (b) represented by formula (b) above, which can form the monomer unit (II) represented by formula (II) above, is not particularly limited, but includes, for example, α-methylstyrene (AMS) and its derivatives such as the following monomers (b-1) to (b-12). [ka]

[0065] Furthermore, from the viewpoint of ease of preparation of copolymer A and improvement of the main chain cleavage when irradiated with an electron beam or the like, α-methylstyrene is preferred as the monomer (b) represented by the above formula (b) that can form monomer unit (II). In other words, copolymer A preferably has α-methylstyrene units.

[0066] Furthermore, the proportion of monomer unit (II) in the total monomer units constituting copolymer A is not particularly limited, but can be, for example, 30 moles or more, preferably 40 moles or more, more preferably 45 moles or more, can be 70 moles or less, preferably 60 moles or less, and more preferably 55 moles or less.

[0067] <Properties of copolymer A> [Weight average molecular weight (Mw)] The weight-average molecular weight (Mw) of copolymer A is preferably 100,000 or more, more preferably 125,000 or more, even more preferably 150,000 or more, preferably 600,000 or less, and more preferably 500,000 or less. If the weight-average molecular weight (Mw) of copolymer A is above the lower limit, the reduction of the resist pattern top can be further reduced, and a resist pattern with even better contrast can be formed. Also, if the weight-average molecular weight (Mw) of copolymer A is below the upper limit, the preparation of the positive-type resist composition can be facilitated.

[0068] [Number average molecular weight (Mn)] The number-average molecular weight (Mn) of copolymer A is preferably 100,000 or more, more preferably 110,000 or more, preferably 300,000 or less, and more preferably 200,000 or less. If the number-average molecular weight of copolymer A is above the lower limit, the wear on the top of the resist pattern can be further reduced, and a resist pattern with even better contrast can be formed. Furthermore, if the number-average molecular weight of copolymer A is below the upper limit, the preparation of the positive-type resist composition becomes even easier.

[0069] [Molecular weight distribution (Mw / Mn)] Furthermore, the molecular weight distribution (Mw / Mn) of copolymer A is preferably 1.20 or higher, more preferably 1.25 or higher, even more preferably 1.30 or higher, preferably 2.00 or lower, more preferably 1.80 or lower, and even more preferably 1.60 or lower. In this invention, the "number-average molecular weight" can be measured using gel permeation chromatography as a standard polystyrene equivalent, and the "molecular weight distribution" can be determined by calculating the ratio of the weight-average molecular weight to the number-average molecular weight (weight-average molecular weight / number-average molecular weight).

[0070] [Method for preparing copolymer A] The method for preparing copolymer A is not particularly limited. For example, copolymer A having the monomer unit (V) described above can be prepared by polymerizing a monomer composition containing monomer (e) and any monomer copolymerizable with monomer (e), recovering the resulting copolymer, and optionally purifying it. Furthermore, the composition, molecular weight distribution, number-average molecular weight, and weight-average molecular weight of copolymer A can be adjusted by changing the polymerization and purification conditions. Specifically, for example, the number-average molecular weight and weight-average molecular weight can be increased by lowering the polymerization temperature. Also, the number-average molecular weight and weight-average molecular weight can be increased by shortening the polymerization time. Moreover, the molecular weight distribution can be reduced by purification.

[0071] <Polymerization of monomeric compositions> Here, as the monomer composition used to prepare copolymer A, for example, a mixture of a monomer component containing monomer (e) and any monomer copolymerizable with monomer (e), an optional solvent, an optional polymerization initiator, and an optional additive can be used. The polymerization of the monomer composition can be carried out using known methods. Among these, cyclopentanone and water are preferred as the solvent.

[0072] Furthermore, polymers obtained by polymerizing monomer compositions can be recovered without particular limitation by adding a good solvent such as tetrahydrofuran to a solution containing the polymer, and then dropping the solution containing the good solvent dropwise into a poor solvent such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, or hexane to coagulate the polymer.

[0073] <Purification of polymers> The purification method used to purify the obtained polymer is not particularly limited and includes known purification methods such as reprecipitation and column chromatography. Among these, the reprecipitation method is preferred. Furthermore, the purification of the polymer may be repeated multiple times.

[0074] Furthermore, the purification of the polymer by reprecipitation is preferably carried out, for example, by dissolving the obtained polymer in a good solvent such as tetrahydrofuran, and then dropping the resulting solution dropwise into a mixed solvent of a good solvent such as tetrahydrofuran and a poor solvent such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, or hexane, thereby precipitating a portion of the polymer. By purifying the polymer by dropping the solution into a mixed solvent of a good solvent and a poor solvent in this way, the molecular weight distribution, number average molecular weight, and weight average molecular weight of the obtained copolymer A can be easily adjusted by changing the types and mixing ratios of the good and poor solvents. Specifically, for example, the higher the proportion of the good solvent in the mixed solvent, the higher the molecular weight of the copolymer precipitated in the mixed solvent can be.

[0075] When purifying polymers by reprecipitation, copolymer A may be a polymer precipitated in a mixed solvent of a good solvent and a poor solvent, or a polymer that did not precipitate in the mixed solvent (i.e., a polymer dissolved in the mixed solvent), provided that the desired properties are met. Here, polymers that did not precipitate in the mixed solvent can be recovered from the mixed solvent using known methods such as concentration to dryness.

[0076] <Copolymer B> The copolymer B contained in the positive-type resist composition of the present invention has a surface free energy difference of 4 mJ / m² between copolymer B and copolymer A. 2 The above is not particularly limited. Furthermore, in order to form a resist pattern with even less wear on the top of the resist pattern and even higher contrast, copolymer B is preferably a main chain cleavage type copolymer containing halogen atoms, and more preferably contains a fluorine substituent, wherein at least one of the halogen atoms is a fluorine atom, and said fluorine atom is included in the fluorine substituent. Here, the fluorine substituent is not particularly limited as long as it has a fluorine atom.

[0077] [Surface free energy of copolymer B] Here, the surface free energy of copolymer B is 18 mJ / m 2 Preferably, it is 19 mJ / m 2 It is more preferable that the concentration be 20 mJ / m 2 It is even more preferable that the concentration be 27 mJ / m 2 Preferably, it is 26 mJ / m 2 It is more preferable that the following is the case: 25 mJ / m 2 The following is even more preferable:

[0078] Furthermore, the difference between the surface free energy of copolymer B and the surface free energy of copolymer A [i.e., the value of (surface free energy of copolymer A) - (surface free energy of copolymer B)] is 4 mJ / m 2 It must be greater than or equal to 5.5 mJ / m 2 Preferably, it is 6 mJ / m 2 It is more preferable that the concentration be 6.5 mJ / m 2 It is even more preferable that the concentration be 12 mJ / m 2 Preferably, it is 11 mJ / m 2 It is more preferable that the following is true: 10 mJ / m 2 The following is even more preferable:

[0079] Furthermore, from the viewpoint of further enhancing the contrast of the resist pattern, it is preferable that copolymer B has monomer units (V) represented by formula (V), as described in the section on <Copolymer A>. Note that the monomer units (V) that copolymer B may have can be the same as the monomer units (V) described in the section on <Copolymer A>, so the explanation is omitted here.

[0080] Furthermore, the proportion of monomer units (e) in the total amount of polymer units constituting copolymer B is not particularly limited, but can be, for example, 30 moles or more, preferably 40 moles or more, more preferably 45 moles or more, can be 70 moles or less, preferably 60 moles or less, and more preferably 55 moles or less.

[0081] Furthermore, the copolymer B contained in the positive-type resist composition of the present invention is, from the viewpoint of further enhancing the contrast of the resist pattern, defined by the following formula (III): [ka] [In formula (III), R 1 This is an organic group with 5 to 7 fluorine atoms. The monomer unit (III) is represented by ] and the following formula (IV): [ka] [In formula (IV), R 1 R is an alkyl group, 2 R is a hydrogen atom, a fluorine atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom. 3 It is more preferable that the monomer unit (IV) represented by ] is a hydrogen atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom, and p and q are integers between 0 and 5, with p + q = 5.

[0082] Copolymer B may contain any monomer units other than monomer units (III) and monomer units (IV), but the proportion of monomer units (III) and monomer units (IV) in total of the monomer units constituting copolymer B is preferably 90 mol% or more, and more preferably 100 mol% (i.e., copolymer B contains only monomer units (III) and monomer units (IV)).

[0083] Furthermore, copolymer B contains monomer units (III) and (IV), so when irradiated with an electron beam or the like, the main chain is cleaved and the molecular weight is efficiently reduced. In addition, copolymer B preferably has a fluorine atom in monomer unit (III), so when the positive-type resist composition of the present invention is used, the surface free energy of copolymer B can be easily adjusted, and it can be resistant to forward scattering, backscattering, and stray light such as EUV from electron beams, and the contrast of the pattern can be further increased.

[0084] <Monomer unit (III)> Here, the monomer unit (III) is given by the following formula (c): [ka] [In formula (c), R 1 This is similar to equation (III). It is a structural unit derived from the monomer (c) represented by ].

[0085] Furthermore, in equations (II) and (c), R 1 The number of carbon atoms is preferably between 2 and 10, and more preferably 5 or less. If the number of carbon atoms is above the lower limit, the solubility in the developer can be sufficiently improved. If the number of carbon atoms is below the upper limit, the clarity of the resist pattern can be sufficiently ensured.

[0086] Specifically, R in equations (III) and (c) 1 It is preferably a fluoroalkyl group, a fluoroalkoxyalkyl group, or a fluoroalkoxyalkenyl group, and more preferably a fluoroalkyl group. 1 If the group is as described above, the cleavage ability of the main chain of copolymer B when irradiated with an electron beam or the like can be sufficiently improved.

[0087] Examples of fluoroalkyl groups include 2,2,3,3,3-pentafluoropropyl group (5 fluorine atoms, 3 carbon atoms), 3,3,4,4,4-pentafluorobutyl group (5 fluorine atoms, 4 carbon atoms), 1H-1-(trifluoromethyl)trifluoroethyl group (6 fluorine atoms, 3 carbon atoms), 1H,1H,3H-hexafluorobutyl group (6 fluorine atoms, 4 carbon atoms), 2,2,3,3,4,4,4-heptafluorobutyl group (7 fluorine atoms, 4 carbon atoms), and 1,2,2,2-tetrafluoro-1-(trifluoromethyl)ethyl group (7 fluorine atoms, 3 carbon atoms). Among these, the 2,2,3,3,3-pentafluoropropyl group (5 fluorine atoms, 3 carbon atoms) or the 2,2,3,3,4,4,4-heptafluorobutyl group (7 fluorine atoms, 4 carbon atoms) is preferred, and the 2,2,3,3,3-pentafluoropropyl group (5 fluorine atoms, 3 carbon atoms) is more preferred. Examples of fluoroalkoxyalkyl groups include fluoroethoxymethyl groups and fluoroethoxyethyl groups. Furthermore, examples of fluoroalkoxyalkenyl groups include fluoroethoxyvinyl groups.

[0088] Furthermore, the monomer (c) represented by formula (c) above, which can form the monomer unit (III) represented by formula (III) above, is not particularly limited and includes, for example, α-chloroacrylate fluoroalkyl esters such as 2,2,3,3,3-pentafluoropropyl α-chloroacrylate, 3,3,4,4,4-pentafluorobutyl α-chloroacrylate, 1H-1-(trifluoromethyl)trifluoroethyl α-chloroacrylate, 1H,1H,3H-hexafluorobutyl α-chloroacrylate, 1,2,2,2-tetrafluoro-1-(trifluoromethyl)ethyl α-chloroacrylate, and 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylate; α-chloroacrylate fluoroalkoxyalkyl esters such as pentafluoroethoxymethyl α-chloroacrylate and pentafluoroethoxyethyl α-chloroacrylate; and α-chloroacrylate fluoroalkoxyalkenyl esters such as pentafluoroethoxyvinyl α-chloroacrylate.

[0089] Furthermore, from the viewpoint of further improving the cleavage properties of the main chain of copolymer B when irradiated with an electron beam or the like, it is preferable that the monomer unit (III) is a structural unit derived from α-chloroacrylate fluoroalkyl ester. Furthermore, the proportion of monomer unit (III) in the total monomer units constituting copolymer B is not particularly limited, but can be, for example, 30 moles or more, preferably 40 moles or more, more preferably 45 moles or more, can be 70 moles or less, preferably 60 moles or less, and more preferably 55 moles or less.

[0090] Furthermore, the monomer unit (IV) is given by the following general formula (d): [ka] [In formula (d), R 1 ~R 3 Furthermore, p and q are the same as in formula (IV). ) are structural units derived from monomer (d) represented by ).

[0091] Here, R in equations (IV) and (d) 1 The alkyl groups that can constitute the R are not particularly limited, but include alkyl groups having 1 to 5 carbon atoms. 1 The alkyl group that can constitute the alkyl group is preferably a methyl group or an ethyl group.

[0092] Also, R in equations (IV) and (d) 2 ,R 3 Unsubstituted alkyl groups that can constitute the R are not particularly limited, but include unsubstituted alkyl groups having 1 to 5 carbon atoms. 2 ,R 3 The unsubstituted alkyl group that can constitute the group is preferably a methyl group or an ethyl group.

[0093] Furthermore, R in equations (IV) and (d) 2 , R 3 Examples of alkyl groups substituted with fluorine atoms that can constitute this group include, without any particular limitations, groups having a structure in which some or all of the hydrogen atoms in the alkyl group are replaced with fluorine atoms.

[0094] Furthermore, from the viewpoint of improving the ease of preparation of copolymer B, the multiple Rs present in formulas (IV) and (d) are 2 and / or R 3 Preferably, all of them are hydrogen atoms or unsubstituted alkyl groups, preferably hydrogen atoms or unsubstituted alkyl groups having 1 to 5 carbon atoms, and preferably hydrogen atoms.

[0095] Furthermore, the monomer (d) represented by formula (d) above, which can form the monomer unit (IV) represented by formula (IV) above, is not particularly limited and includes, for example, α-methylstyrene (AMS) and its derivatives such as monomers (d-1) to (d-11) below (e.g., 4-fluoro-α-methylstyrene: 4FAMS). [ka]

[0096] Furthermore, from the viewpoint of ease of preparation of copolymer B and improvement of the main chain cleavage when irradiated with an electron beam or the like, the monomer (d) represented by the above formula (d), which can form monomer units (IV), is preferably α-methylstyrene or 4-fluoro-α-methylstyrene. In other words, copolymer B is preferably composed of α-methylstyrene units or 4-fluoro-α-methylstyrene units.

[0097] Furthermore, the proportion of monomer unit (IV) in the total monomer units constituting copolymer B is not particularly limited, but can be, for example, 30 moles or more, preferably 40 moles or more, more preferably 45 moles or more, can be 70 moles or less, preferably 60 moles or less, and more preferably 55 moles or less.

[0098] <Properties of copolymer B> [Weight average molecular weight (Mw)] The weight-average molecular weight (Mw) of copolymer B is preferably 10,000 or more, more preferably 17,000 or more, even more preferably 25,000 or more, preferably 250,000 or less, more preferably 180,000 or less, and even more preferably 50,000 or less. If the weight-average molecular weight (Mw) of copolymer B is above the lower limit, it is possible to suppress the excessive increase in the solubility of the resist film in the developer at low irradiation doses. Furthermore, if the weight-average molecular weight (Mw) of copolymer B is below the upper limit, the preparation of the positive-type resist composition is easier.

[0099] [Number average molecular weight (Mn)] The number-average molecular weight (Mn) of copolymer B is preferably 7,000 or more, more preferably 10,000 or more, and preferably 150,000 or less. If the number-average molecular weight of copolymer B is above the lower limit, it is possible to further suppress the excessive increase in the solubility of the resist film in the developer at low irradiation doses, and a resist pattern with even better contrast can be formed. Furthermore, if the number-average molecular weight of copolymer B is below the upper limit, the preparation of the positive-type resist composition becomes even easier.

[0100] [Molecular weight distribution (Mw / Mn)] Furthermore, the molecular weight distribution (Mw / Mn) of copolymer B is preferably 1.10 or higher, more preferably 1.20 or higher, preferably 1.70 or lower, and more preferably 1.65 or lower. If the molecular weight distribution (Mw / Mn) of copolymer B is above the lower limit, the ease of manufacturing copolymer B can be improved. Also, if the molecular weight distribution (Mw / Mn) of copolymer B is below the upper limit, the contrast of the resulting resist pattern can be further improved.

[0101] [Method for preparing copolymer B] The method for preparing copolymer B is not particularly limited. For example, copolymer B having the monomer unit (V) described above can be prepared by polymerizing a monomer composition containing monomer (e) and any monomer copolymerizable with monomer (e), recovering the resulting copolymer, and optionally purifying it. Here, the polymerization method and purification method are not particularly limited and can be the same as those for copolymer A described above. Furthermore, when preparing copolymer B, it is preferable to use a polymerization initiator, and for example, a polymerization initiator such as azobisisobutyronitrile can be suitably used.

[0102] <Solvent> The solvent is not particularly limited as long as it is capable of dissolving copolymers A and B as described above, and known solvents such as the solvent described in Japanese Patent Publication No. 5938536 can be used. In particular, from the viewpoint of obtaining a positive-type resist composition with appropriate viscosity and improving the coating properties of the positive-type resist composition, it is preferable to use anisole, propylene glycol monomethyl ether acetate (PGMEA), cyclopentanone, cyclohexanone, or isoamyl acetate as the solvent.

[0103] <Preparation of positive-type resist composition> Positive resist compositions can be prepared by mixing copolymer A, copolymer B, a solvent, and any known additives that can be used. In this case, from the viewpoint of further reducing the wear of the resist pattern top and further increasing the contrast of the resist pattern, it is preferable that both copolymer A and copolymer B are main-chain cleavage type copolymers containing halogen atoms, more preferably that both copolymer A and copolymer B contain fluorine substituents, at least one of the halogen atoms is a fluorine atom, and that fluorine atom is included in the fluorine substituent. Even more preferably, it is preferable that either copolymer A or copolymer B has monomer units represented by formula (V) above, and more preferably that both copolymer A and copolymer B have monomer units represented by formula (V) above. Particularly preferably, copolymer A has monomer units (I) represented by formula (I) and monomer units (II) represented by formula (II) above, and copolymer B has monomer units (III) represented by formula (III) and monomer units (IV) represented by formula (IV) above. Here, the method of mixing the above components for preparing the positive resist composition is not particularly limited, and they may be mixed by known methods. Alternatively, the mixture may be filtered after mixing each component.

[0104] [filtration] Here, the method of filtering the mixture is not particularly limited, and for example, it can be filtered using a filter. The filter is not particularly limited, and examples include filtration membranes made of fluorocarbon, cellulose, nylon, polyester, hydrocarbon, etc. Among these, from the viewpoint of effectively preventing impurities such as metals from being mixed into the positive-type resist composition from metal piping, etc., which may be used when preparing copolymer A and copolymer B, polyethylene, polypropylene, polytetrafluoroethylene, polyfluorocarbons such as Teflon®, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), nylon, and composite membranes of polyethylene and nylon are preferred as materials constituting the filter. As a filter, for example, one disclosed in U.S. Patent No. 6,103,122 may be used. Alternatively, a commercially available filter such as Zeta Plus® 40Q manufactured by CUNO Incorporated may be used. Furthermore, the filter may contain a strongly cationic or weakly cationic ion exchange resin. Here, the average particle size of the ion exchange resin is not particularly limited, but is preferably 2 μm or more and 10 μm or less. Examples of cation exchange resins include sulfonated phenol-formaldehyde condensates, sulfonated phenol-benzaldehyde condensates, sulfonated styrene-divinylbenzene copolymers, sulfonated methacrylate-divinylbenzene copolymers, and other types of sulfonic acid or carboxylic acid group-containing polymers. + Counter-ion, NH4 + Counterions or alkali metal counterions, for example, K + and Na + A counterion is provided. The cation exchange resin preferably has a hydrogen counterion. Such a cation exchange resin may be H +Examples include counterion-containing sulfonated styrene-divinylbenzene copolymers, such as Microlite® PrCH from Purolite. Such cation exchange resins are commercially available as AMBERLYST® from Rohm and Haas.

[0105] Furthermore, the pore size of the filter is preferably 0.001 μm or more and 1 μm or less. If the pore size of the filter is within the above range, it is possible to sufficiently prevent impurities such as metals from being mixed into the positive-type resist composition.

[0106] <Ratio of copolymer A to copolymer B> Furthermore, the ratio of copolymer A to copolymer B in the positive-type resist composition of the present invention is not particularly limited, but the ratio of copolymer B is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less, based on 100% by mass of the total of copolymer A and copolymer B. If the ratio of copolymer B is above the lower limit, it is possible to suppress the excessive increase in the solubility of the resist film in the developer at a low irradiation dose, and a resist pattern with further improved contrast can be formed. Also, if the ratio of copolymer B is below the upper limit, it is possible to suppress the deterioration of the sensitivity of the positive-type resist.

[0107] (Method for forming resist patterns) The resist pattern formation method of the present invention comprises at least the steps of forming a resist film using the positive-type resist composition of the present invention described above (resist film formation step), exposing the resist film to light (exposure step), and developing the exposed resist film (development step). Furthermore, the resist pattern formation method of the present invention may further include steps other than the resist film formation step, exposure step, and development step described above. Specifically, the resist pattern formation method of the present invention may include a step of forming an underlayer film on the substrate on which the resist film is to be formed (underlayer film formation step) before the resist film formation step. Also, the resist pattern formation method of the present invention may include a step of heating the exposed resist film (post-exposure bake step) between the exposure step and the development step. Also, the resist pattern formation method of the present invention may further include a step of removing the developer solution (rinse step) after the development step. And, after the resist pattern is formed by the resist pattern formation method of the present invention, the method may further include a step of etching the underlayer film and / or the substrate (etching step).

[0108] Furthermore, in the resist pattern formation method of the present invention, a positive-type resist composition containing predetermined copolymers A and B is used as the positive-type resist composition, thereby reducing the wear on the top of the resist pattern and forming a resist pattern with high contrast.

[0109] (Resist film formation process) In the resist film formation process, the positive-type resist composition of the present invention is applied to a workpiece such as a substrate that will be processed using the resist pattern, and the applied positive-type resist composition is dried to form a resist film.

[0110] -substrate- Here, the substrate on which a resist film can be formed in the resist pattern formation method is not particularly limited, and substrates having an insulating layer and copper foil provided on the insulating layer, which are used in the manufacture of printed circuit boards, etc., and mask blanks having a light-shielding layer formed on the substrate can be used.

[0111] Examples of substrate materials include metals (silicon, copper, chromium, iron, aluminum, etc.), glass, titanium dioxide, silicon dioxide (SiO2), silica, mica, and other inorganic materials; nitrides such as SiN; oxidized nitrides such as SiON; and organic materials such as acrylic, polystyrene, cellulose, cellulose acetate, and phenolic resin. Among these, metal is preferred as the substrate material. By using, for example, a silicon substrate, a silicon dioxide substrate, or a copper substrate, preferably a silicon substrate or a silicon dioxide substrate, a cylindrical structure can be formed.

[0112] Furthermore, the size and shape of the substrate are not particularly limited. The surface of the substrate may be smooth, curved, or have an uneven shape, or it may be in the form of a thin sheet.

[0113] Furthermore, the surface of the substrate may be surface-treated as needed. For example, in the case of a substrate having hydroxyl groups on its surface, the substrate surface can be treated using a silane-based coupling agent that can react with hydroxyl groups. This changes the surface of the substrate from hydrophilic to hydrophobic, thereby improving the adhesion between the substrate and the underlying film, or between the substrate and the resist layer. In this case, the silane-based coupling agent is not particularly limited, but hexamethyldisilazane is preferred.

[0114] (Lower film formation process) In the optional underlayer film formation step, an underlayer film is formed on the substrate. By providing an underlayer film on the substrate, the surface of the substrate becomes hydrophobic. This increases the affinity between the substrate and the resist film, thereby improving the adhesion between the substrate and the resist film. The underlayer film may be an inorganic underlayer film or an organic underlayer film.

[0115] An inorganic underlayer film can be formed by coating an inorganic material onto a substrate and then firing it. Examples of inorganic materials include silicon-based materials.

[0116] An organic underlayer film can be formed by coating an organic material onto a substrate to form a coating film and then drying it. The organic material is not limited to those sensitive to light or electron beams; for example, resist materials and resin materials commonly used in the semiconductor and liquid crystal fields can be used. In particular, the organic material is preferably one that can form an etchable, especially dry-etchable, organic underlayer film. With such an organic material, the pattern can be transferred to the underlayer film by etching the organic underlayer film using a pattern formed by processing the resist film, thereby forming a pattern on the underlayer film. In particular, the organic material is preferably one that can form an etchable organic underlayer film, such as by oxygen plasma etching. An example of an organic material used for forming an organic underlayer film is AL412 from Brewer Science.

[0117] The application of the above-mentioned organic material can be carried out by conventionally known methods such as spin coating or using a spinner. The drying method for the coating film can be any method that can volatilize the solvent contained in the organic material, such as baking. While the baking conditions are not particularly limited, the baking temperature is preferably 80°C to 300°C, and more preferably 200°C to 300°C. The baking time is preferably 30 seconds or more, more preferably 60 seconds or more, preferably 500 seconds or less, more preferably 400 seconds or less, even more preferably 300 seconds or less, and particularly preferably 180 seconds or less. The thickness of the underlayer film after drying is not particularly limited, but is preferably 10 nm to 100 nm.

[0118] (Resist film formation process) In the resist film formation process, a positive-type resist composition is applied to a workpiece such as a substrate that will be processed using the resist pattern (or on top of the underlying film if an underlying film is formed), and the applied positive-type resist composition is dried to form a resist film.

[0119] Furthermore, the method for coating and drying the positive-type resist composition is not particularly limited, and methods commonly used for forming resist films can be used. Among these, heating (pre-baking) is preferred as the drying method. The pre-baking temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 140°C or higher, from the viewpoint of improving the film density of the resist film. Furthermore, the pre-baking temperature is preferably 250°C or lower, more preferably 220°C or lower, and even more preferably 200°C or lower, from the viewpoint of reducing changes in the molecular weight and molecular weight distribution of copolymer A and copolymer B in the resist film before and after pre-baking. Furthermore, the pre-baking time is preferably 10 seconds or more, more preferably 20 seconds or more, and even more preferably 30 seconds or more, from the viewpoint of improving the film density of the resist film formed after pre-baking. Furthermore, the pre-baking time is preferably 10 minutes or less, more preferably 5 minutes or less, and even more preferably 3 minutes or less, from the viewpoint of further reducing changes in the molecular weight and molecular weight distribution of copolymer A and copolymer B in the resist film before and after pre-baking.

[0120] (Exposure process) In the exposure process, the resist film formed in the resist film formation process is irradiated with electron beams, EUV or other ionizing radiation to create a desired pattern. For electron beam irradiation, known lithography equipment such as electron beam lithography systems or EUV lithography systems can be used.

[0121] (Post-freezing bake process) In an optional post-exposure bake process, the resist film exposed in the exposure process is heated. Performing a post-exposure bake process can reduce the surface roughness of the resist pattern.

[0122] Here, the heating temperature is preferably 70°C or higher, more preferably 80°C or higher, even more preferably 90°C or higher, preferably 200°C or lower, more preferably 170°C or lower, and even more preferably 150°C or lower. If the heating temperature is within the above range, the clarity of the resist pattern can be improved while the surface roughness of the resist pattern can be effectively reduced.

[0123] Furthermore, the heating time for the resist film in the post-exposure bake process is preferably 10 seconds or more, more preferably 20 seconds or more, and even more preferably 30 seconds or more. If the heating time is 10 seconds or more, the clarity of the resist pattern can be further improved while sufficiently reducing the surface roughness of the resist pattern. On the other hand, from the viewpoint of production efficiency, the heating time is preferably, for example, 10 minutes or less, more preferably 5 minutes or less, and even more preferably 3 minutes or less.

[0124] Furthermore, the method of heating the resist film in the post-exposure baking process is not particularly limited, and examples include heating the resist film on a hot plate, heating the resist film in an oven, or blowing hot air onto the resist film.

[0125] (Development process) In the development process, the exposed resist film (or the exposed and heated resist film if a post-exposure baking process is performed) is developed to form a developed film on the workpiece. Here, the resist film can be developed, for example, by bringing the resist film into contact with a developer. The method of bringing the resist film into contact with the developer is not particularly limited, and known methods such as immersing the resist film in the developer or applying the developer to the resist film can be used.

[0126] <Developer> The developer can be appropriately selected according to the properties of copolymers A and B described above. Specifically, when selecting the developer, it is preferable to select a developer that does not dissolve the resist film before the exposure process, but can dissolve the exposed areas of the resist film after the exposure process. Furthermore, one type of developer may be used alone, or two or more types may be mixed in any ratio. And as a developer, for example, hydrofluorocarbons such as 1,1,1,2,3,4,4,5,5,5-decafluoropentane (CF3CFHCFHCF2CF3), 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane, 1,1,1,2,2,3,4,5,5,5-decafluoropentane, 1,1,1,3,3-pentafluorobutane, 1,1,1,2,2,3,3,4,4-nonafluorohexane, 2,2-dichloro-1,1,1-trifluoroethane, 1,1-dichloro-1-fluoroethane, 1,1-dichloro-2,2,3,3,3-pentafluoro Hydrochlorofluorocarbons such as chloropropane (CF3CF2CHCl2) and 1,3-dichloro-1,1,2,2,3-pentafluoropropane (CClF2CF2CHClF), hydrofluoroethers such as methyl nonafluorobutyl ether (CF3CF2CF2CF2OCH3), methyl nonafluoroisobutyl ether, ethyl nonafluorobutyl ether (CF3CF2CF2CF2OC2H5), ethyl nonafluoroisobutyl ether, and perfluorohexyl methyl ether (CF3CF2CF(OCH3)C3F7), as well as CF4, C2F6, C3F8, C4F8, C4F 10 , C5F 12 , C6F 12 , C6F 14 , C7F 14 , C7F 16 , C8F 18 , C9F 20Fluorine-based solvents such as perfluorocarbons; alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, and 3-pentanol; acetate esters having alkyl groups such as amyl acetate and hexyl acetate; mixtures of fluorine-based solvents and alcohols; mixtures of fluorine-based solvents and acetate esters having alkyl groups; mixtures of alcohols and acetate esters having alkyl groups; mixtures of fluorine-based solvents, alcohols and acetate esters having alkyl groups; etc. can be used. Among these, from the viewpoint of further enhancing the contrast of the resist pattern, it is preferable to develop using alcohols such as 2-butanol and isopropyl alcohol.

[0127] The temperature of the developer solution during development is not particularly limited, but can be, for example, between 5°C and 40°C. The development time can also be, for example, between 10 seconds and 4 minutes.

[0128] (Rinsing process) In the resist pattern formation method of the present invention, a step of removing the developer solution can be performed after the development step. The developer solution can be removed, for example, using a rinsing solution. Specific examples of rinsing solutions include, for example, those similar to the developer solutions exemplified in the "developing process" section, as well as hydrocarbon solvents such as octane and heptane, and water. Here, the rinsing solution may contain a surfactant. When selecting a rinsing solution, it is preferable to select one that is less likely to dissolve the resist film before the exposure process than the developer solution used in the developing process, and that mixes easily with the developer solution.

[0129] The temperature of the rinsing solution during rinsing is not particularly limited, but can be, for example, between 5°C and 40°C. The rinsing time can be, for example, between 5 seconds and 3 minutes.

[0130] The developer and rinse solutions described above may be filtered before use. For example, one filtration method is the one using a filter, as described in the section "Preparation of Positive-Type Resist Composition" above.

[0131] (Etching process) In an optional etching process, the underlying film and / or substrate are etched using the resist pattern described above as a mask, thereby forming a pattern on the underlying film and / or substrate. In this process, the number of etching steps is not particularly limited and may be one or multiple times. Etching may be performed by dry etching or wet etching, but dry etching is preferred. Dry etching can be performed using a known dry etching apparatus. The etching gas used for dry etching can be appropriately selected depending on the elemental composition of the underlying film or substrate to be etched. Examples of etching gases include fluorine-based gases such as CHF3, CF4, C2F6, C3F8, and SF6; chlorine-based gases such as Cl2 and BCl3; oxygen-based gases such as O2, O3, and H2O; reducing gases such as H2, NH3, CO, CO2, CH4, C2H2, C2H4, C2H6, C3H4, C3H6, C3H8, HF, HI, HBr, HCl, NO, and BCl3; and inert gases such as He, N2, and Ar. These gases may be used individually or in mixtures of two or more. For dry etching of inorganic underlying films, oxygen-based gases are typically used. Furthermore, fluorine-based gases are typically used for dry etching of substrates, and a mixture of fluorine-based gas and an inert gas is preferably used.

[0132] Furthermore, if necessary, any remaining underlayer film on the substrate may be removed before or after etching the substrate. If the underlayer film is removed before etching the substrate, the underlayer film may be a patterned underlayer film or an underlayer film without a pattern.

[0133] Here, methods for removing the underlying film include, for example, the dry etching method described above. In the case of an inorganic underlying film, the underlying film may be removed by bringing it into contact with a liquid such as a basic solution or an acidic solution, preferably a basic liquid. Here, the basic solution is not particularly limited, and examples include alkaline hydrogen peroxide. Methods for removing the underlying film by wet peeling using alkaline hydrogen peroxide are not particularly limited as long as the underlying film and the alkaline hydrogen peroxide can be in contact for a certain period of time under heated conditions, and examples include immersing the underlying film in heated alkaline hydrogen peroxide, spraying alkaline hydrogen peroxide onto the underlying film in a heated environment, and coating the underlying film with heated alkaline hydrogen peroxide. After performing any of these methods, the substrate can be washed with water and dried to obtain a substrate from which the underlying film has been removed.

[0134] The following describes an example of a resist pattern formation method using the positive resist of the present invention and an etching method for the underlying film and substrate using the formed resist pattern. However, the substrate and conditions in each step used in the following example can be the same as those described above, so the explanation is omitted below. Note that the resist pattern formation method of the present invention is not limited to the method shown in the following example.

[0135] An example of a resist pattern formation method is a resist pattern formation method using an electron beam or EUV, which includes the above-described underlayer film formation step, resist film formation step, exposure step, development step, and rinsing step. Another example of an etching method is one which uses the resist pattern formed by the resist pattern formation method as a mask, and includes an etching step.

[0136] Specifically, in the underlayer film formation process, an inorganic material is applied to the substrate and then fired to form an inorganic underlayer film. Next, in the resist film formation step, the positive-type resist composition of the present invention is applied to the inorganic underlayer film formed in the underlayer film formation step and dried to form a resist film. Then, in the exposure process, the resist film formed in the resist film formation process is irradiated with EUV light to create the desired pattern. Furthermore, in the development process, the resist film exposed in the exposure process is brought into contact with a developer to develop the resist film and form a resist pattern on the underlying film. Then, in the rinsing process, the resist film developed in the developing process is brought into contact with the rinsing solution to rinse the developed resist film.

[0137] Then, in the etching process, the underlying film is etched using the above-mentioned resist pattern as a mask, and a pattern is formed on the underlying film. Next, the substrate is etched using the patterned underlayer film as a mask to form a pattern on the substrate.

[0138] (etching resistance of the resist film) The resist film obtained by the resist pattern formation method of the present invention exhibits excellent etching resistance, and in particular, excellent dry etching resistance. Furthermore, the higher the proportion of carbon per unit volume of copolymers A and B contained in the positive-type resist composition, the more the resist film tends to exhibit superior dry etching resistance.

[0139] Furthermore, according to the resist pattern formation method of the present invention, for example, a laminate comprising a resist film having a two-layer structure as described below can be obtained.

[0140] (Laminated structure) The laminate obtained by the resist pattern formation method of the present invention comprises a substrate and a resist film formed on the substrate, wherein the resist film comprises a lower layer provided on the substrate and an upper layer provided on the lower layer. The lower layer is composed of copolymer A as described above, and the upper layer is composed of copolymer B as described above. The resist film in the laminate of the present invention can be formed by the resist pattern formation method of the present invention. [Examples]

[0141] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, the number-average molecular weight, weight-average molecular weight, and molecular weight distribution of the copolymer were measured by the following methods.

[0142] <Number-average molecular weight, weight-average molecular weight, and molecular weight distribution> The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the obtained copolymers A and B were measured using gel permeation chromatography, and the molecular weight distribution (Mw / Mn) was calculated. Specifically, using a gel permeation chromatograph (HLC-8220, Tosoh Corporation) and tetrahydrofuran as the developing solvent, the number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the copolymer were determined as standard polystyrene equivalents. The molecular weight distribution (Mw / Mn) was then calculated. It was confirmed that both copolymer A and copolymer B contained substantially no components with a weight-average molecular weight (Mw) of less than 1000.

[0143] <Preparation of Copolymer A> <<Preparation Example 1: Preparation of Copolymer A1>> [Synthesis of polymers] A monomer composition containing 3 g of monomer (a) α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh), 2.493 g of monomer (b) α-methylstyrene, and 2.833 g of cyclopentanone as a solvent was added to a glass ampoule containing a stirring bar, sealed, and oxygen was removed from the system by repeatedly pressurizing and depressurizing with nitrogen gas 10 times. The system was then heated to 30°C and the reaction was carried out for 80 hours. Next, 10 g of tetrahydrofuran (THF) was added to the system, and the resulting solution was added dropwise to 100 g of methanol (MeOH) as a solvent to precipitate the polymer. The precipitated polymer was then recovered by filtration. The obtained polymer was a copolymer containing 50 mol% each of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-methylstyrene units. Subsequently, the number-average molecular weight, weight-average molecular weight, and molecular weight distribution of the obtained copolymer (copolymer A1 before purification) were measured. The results are shown in Table 1. [Purification of polymers] The polymer recovered by filtration was dissolved in 10 g of THF, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 29:71) to precipitate a white solidified product (a copolymer containing α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-methylstyrene units). Subsequently, the solution containing the precipitated copolymer was filtered using a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-methylstyrene units). Subsequently, the number-average molecular weight, weight-average molecular weight, and molecular weight distribution of the obtained copolymer (purified copolymer A1) were measured. The results are shown in Table 1.

[0144] <<Preparation Example 2: Preparation of Copolymer A2>> [Preparation of an aqueous solution of semi-hardened beef tallow fatty acid potassium soap with a solid content of 18%] 100g of deionized water was prepared and heated to 70°C while stirring, and 8.40g of potassium hydroxide (49% aqueous solution) was added. Next, 19.6g of 45° hardened beef tallow fatty acid HFA (manufactured by NOF Corporation) was added at an addition rate of 1.28g / min, and then 0.126g of potassium silicate was added. The mixture was then stirred at 80°C for more than 2 hours to obtain an aqueous solution of semi-hardened beef tallow fatty acid potassium soap with a solid content of 18%. [Synthesis of polymers] In a glass ampoule containing a stirring bar, 3 g of monomer (a) 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl chloroacrylate (ACAFPh) and 2.712 g of monomer (b) methylstyrene were added. Furthermore, to the same ampoule, 0.5463 g of an 18% solids aqueous solution of the semi-hardened beef tallow fatty acid potassium soap prepared above was mixed with 6.771 g of deionized water to form a monomer composition. The ampoule was then sealed, and oxygen in the system was removed by repeatedly pressurizing and depressurizing with nitrogen gas 10 times. The system was then heated to 40°C, and the polymerization reaction was carried out for 11 hours. Next, 10 g of THF was added to the system, and the resulting solution was added dropwise to 100 g of MeOH as a solvent to precipitate the polymer. The precipitated polymer was then recovered by filtration. The obtained polymer was a copolymer containing 50 mol% each of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-methylstyrene units. Subsequently, the obtained copolymer (copolymer A2 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 1. [Purification of polymers] The polymer recovered by filtration was dissolved in 10 g of THF, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 35:65) to precipitate a white solidified product (a copolymer containing α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-methylstyrene units). Subsequently, the solution containing the precipitated copolymer was filtered using a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-methylstyrene units). Subsequently, the obtained copolymer (purified copolymer A2) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 1.

[0145] <<Preparation Example 3: Preparation of Copolymer A3>> [Synthesis of polymers] A monomer composition containing 3 g of monomer (a) α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh), 1.066 g of monomer (b) α-methylstyrene, and 1.743 g of cyclopentanone as a solvent was added to a glass ampoule containing a stirring bar, sealed, and oxygen was removed from the system by repeatedly pressurizing and depressurizing with nitrogen gas 10 times. The system was then heated to 30°C and the reaction was carried out for 50 hours. Next, 10 g of tetrahydrofuran was added to the system, and the resulting solution was added dropwise to 100 g of MeOH as a solvent to precipitate the polymer. The precipitated polymer was then recovered by filtration. The obtained polymer was a copolymer containing 54 mol% of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and 46 mol% of α-methylstyrene units. Subsequently, the obtained copolymer (copolymer A3 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 1. [Purification of polymers] The polymer recovered by filtration was dissolved in 10 g of THF, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 30:70) to precipitate a white solidified product (a copolymer containing α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-methylstyrene units). Subsequently, the solution containing the precipitated copolymer was filtered using a Kiriyama funnel to obtain a white copolymer (a copolymer containing 54 mol% α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and 46 mol% α-methylstyrene units). Subsequently, the obtained copolymer (purified copolymer A3) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 1.

[0146] <<Preparation Example 4: Preparation of Copolymer A4>> [Synthesis of polymers] 3 g of monomer (a) α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) and 1.066 g of monomer (b) α-methylstyrene were added to a glass ampoule containing a stirring bar. Furthermore, 6.771 g of deionized water was added to 0.5463 g of an 18% solids aqueous solution of semi-hardened beef tallow fatty acid potassium soap prepared in Preparation Example 2 to the same ampoule to form a monomer composition. The ampoule was then sealed, and oxygen in the system was removed by repeatedly pressurizing and depressurizing with nitrogen gas 10 times. The system was then heated to 75°C, and the polymerization reaction was carried out for 1 hour. Next, 10 g of tetrahydrofuran was added to the system, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 30:70) to precipitate the polymer. The precipitated polymer was then recovered by filtration. The obtained polymer was a copolymer containing 54 mol% of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and 46 mol% of α-methylstyrene units. Subsequently, the obtained copolymer (copolymer A4 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 1. [Purification of polymers] The polymer recovered by filtration was dissolved in 10 g of THF, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 34:66) to precipitate a white solidified product (a copolymer containing α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-methylstyrene units). Subsequently, the solution containing the precipitated copolymer was filtered using a Kiriyama funnel to obtain a white copolymer (a copolymer containing 54 mol% α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and 46 mol% α-methylstyrene units). Subsequently, the obtained copolymer (purified copolymer A4) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 1.

[0147] <<Preparation Example 5: Preparation of Copolymer A5>> [Synthesis of polymers] The polymer was synthesized in the same manner as in Preparation Example 4, except that the mass ratio of THF to MeOH in the mixed solvent used for polymer precipitation was changed to 33:67, to obtain the copolymer (copolymer A5 before purification). Subsequently, the obtained copolymer (copolymer A5 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 1. [Purification of polymers] The copolymer was obtained by performing the same procedure as in Preparation Example 4, except that the mass ratio of THF to MeOH in the mixed solvent used for the purification of the polymer was changed to 33:67 and the purification was performed twice. Subsequently, the obtained copolymer (purified copolymer A5) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 1.

[0148] <<Preparation Example 6: Preparation of Copolymer A6>> [Synthesis of polymers] In a glass ampoule containing a stirring bar, 3 g of monomer (a) α-chloroacrylate-1-(4-methoxyphenyl)-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPhOMe) and 2.487 g of monomer (b) α-methylstyrene were added. Furthermore, in the same ampoule, 0.5463 g of an 18% solids aqueous solution of semi-hardened beef tallow fatty acid potassium soap prepared in Preparation Example 2 was mixed with 6.771 g of deionized water to form a monomer composition. The ampoule was then sealed, and oxygen in the system was removed by repeatedly pressurizing and depressurizing with nitrogen gas 10 times. The system was then heated to 75°C, and the polymerization reaction was carried out for 1 hour. Next, 10 g of tetrahydrofuran was added to the system, and the resulting solution was added dropwise to 100 g of methanol as a solvent to precipitate the polymer. The precipitated polymer was then recovered by filtration. The obtained polymer was a copolymer containing 50 mol% each of α-chloroacrylic acid-1-(4-methoxyphenyl)-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-methylstyrene units. Subsequently, the obtained copolymer (copolymer A6 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 1. [Purification of polymers] The polymer recovered by filtration was dissolved in 10 g of THF, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 30:70) to precipitate a white solidified product (a copolymer containing α-chloroacrylic acid-1-(4-methoxyphenyl)-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-methylstyrene units). Subsequently, the solution containing the precipitated copolymer was filtered using a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of α-chloroacrylic acid-1-(4-methoxyphenyl)-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-methylstyrene units). Subsequently, the obtained copolymer (purified copolymer A6) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 1.

[0149] <<Preparation Example 7: Preparation of Copolymer A7>> [Synthesis of polymers] 3 g of monomer (a) α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) and 1.066 g of monomer (b) α-methylstyrene were added to a glass ampoule containing a stirring bar. Furthermore, 6.771 g of deionized water was added to 0.5463 g of an 18% solids aqueous solution of semi-hardened beef tallow fatty acid potassium soap prepared in Preparation Example 2 to the same ampoule to form a monomer composition. The ampoule was then sealed, and oxygen in the system was removed by repeatedly pressurizing and depressurizing with nitrogen gas 10 times. The system was then heated to 40°C, and the polymerization reaction was carried out for 11 hours. Next, 10 g of tetrahydrofuran was added to the system, and the resulting solution was added dropwise to 100 g of methanol as a solvent to precipitate the polymer. The precipitated polymer was then recovered by filtration. The obtained polymer was a copolymer containing 54 mol% of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and 46 mol% of α-methylstyrene units. Subsequently, the obtained copolymer (copolymer A7 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 1. [Purification of polymers] The polymer recovered by filtration was dissolved in 10 g of THF, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 34:66) to precipitate a white solidified product (a copolymer containing α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-methylstyrene units). Subsequently, the solution containing the precipitated copolymer was filtered using a Kiriyama funnel to obtain a white copolymer (a copolymer containing 54 mol% α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and 46 mol% α-methylstyrene units). Subsequently, the obtained copolymer (purified copolymer A7) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 1.

[0150] <Preparation of Copolymer B> <<Preparation Example 8: Preparation of Copolymer B1>> [Synthesis of polymers] A monomer composition containing 3 g of 2,2,3,3,3-pentafluoropropyl chloroacrylate (ACAPFP) as monomer (c), 3.476 g of α-methylstyrene as monomer (d), 0.0055 g of azobisisobutyronitrile as a polymerization initiator, and 1.6205 g of cyclopentanone as a solvent was placed in a glass container, the glass container was sealed and nitrogen was purged, and the mixture was stirred for 6 hours in a constant temperature bath at 78°C under a nitrogen atmosphere. After returning the solution to room temperature and venting the glass container to the atmosphere, 10 g of THF was added to the resulting solution. The solution with THF added was then dropped dropwise into 100 g of MeOH as a solvent to precipitate the polymer. Subsequently, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white solidified substance (polymer). The obtained polymer was a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and α-methylstyrene units. Subsequently, the obtained copolymer (copolymer B1 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 2. [Purification of polymers] Next, the obtained polymer was dissolved in 100 g of THF, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 15:85) to precipitate a white solidified product (a copolymer containing α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and α-methylstyrene units). Subsequently, the solution containing the precipitated solidified product was filtered through a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and α-methylstyrene units). Subsequently, the obtained copolymer (purified copolymer B1) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 2.

[0151] <<Preparation Example 9: Preparation of Copolymer B2>> [Synthesis of polymers] A monomer composition containing 3 g of 2,2,3,3,3-pentafluoropropyl α-chloroacrylic acid (ACAPFP) as monomer (c), 3.468 g of α-methylstyrene as monomer (d), 0.0014 g of azobisisobutyronitrile as a polymerization initiator, and 6.4666 g of cyclopentanone as a solvent was placed in a glass container, the glass container was sealed and nitrogen was purged, and the mixture was stirred for 50 hours in a constant temperature bath at 40°C under a nitrogen atmosphere. After returning the solution to room temperature and venting the glass container to the atmosphere, 10 g of THF was added to the resulting solution. The solution with THF added was then dropped dropwise into 100 g of MeOH as a solvent to precipitate the polymer. Subsequently, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white solidified substance (polymer). The obtained polymer was a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and α-methylstyrene units. Subsequently, the obtained copolymer (polymer B2 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 2. [Purification of polymers] Next, the obtained polymer was dissolved in 100 g of THF, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 26:74) to precipitate a white solidified product (a polymer containing α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and α-methylstyrene units). Subsequently, the solution containing the precipitated solidified product was filtered through a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and α-methylstyrene units). Subsequently, the obtained copolymer (purified copolymer B2) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 2.

[0152] <<Preparation Example 10: Preparation of Copolymer B3>> [Synthesis of polymers] A monomer composition containing 3 g of 2,2,3,3,3-pentafluoropropyl α-chloroacrylic acid (ACAPFP) as monomer (c), 3.476 g of α-methylstyrene as monomer (d), 0.1103 g of azobisisobutyronitrile as a polymerization initiator, and 1.6205 g of cyclopentanone as a solvent was placed in a glass container, the glass container was sealed and nitrogen purged, and the mixture was stirred for 6 hours in a constant temperature bath at 78°C under a nitrogen atmosphere. After returning the solution to room temperature and venting the glass container to the atmosphere, 10 g of THF was added to the resulting solution. The solution with THF added was then dropped dropwise into 100 g of MeOH as a solvent to precipitate the polymer. Subsequently, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white solidified substance (polymer). The obtained polymer was a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and α-methylstyrene units. Subsequently, the obtained copolymer (copolymer B3 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 2. [Purification of polymers] Next, the obtained polymer was dissolved in 100 g of THF, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 5:95) to precipitate a white solidified product (a copolymer containing α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and α-methylstyrene units). Subsequently, the solution containing the precipitated solidified product was filtered through a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3-pentafluoropropyl units and α-methylstyrene units). Subsequently, the obtained copolymer (purified copolymer B3) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 2.

[0153] <<Preparation Example 11: Preparation of Copolymer B4>> [Synthesis of polymers] A monomer composition containing 3 g of 2,2,3,3,3-pentafluoropropyl α-chloroacrylic acid (ACAPFP) as monomer (c), 3.476 g of α-methylstyrene as monomer (d), 0.0005 g of azobisisobutyronitrile as a polymerization initiator, and 1.6205 g of cyclopentanone as a solvent was placed in a glass container, the glass container was sealed and nitrogen was purged, and the mixture was stirred for 2 hours in a constant temperature bath at 78°C under a nitrogen atmosphere. After returning the solution to room temperature and venting the glass container to the atmosphere, 10 g of THF was added to the resulting solution. The solution with THF added was then dropped dropwise into 100 g of MeOH as a solvent to precipitate the polymer. Subsequently, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white solidified substance (polymer). The obtained polymer was a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and α-methylstyrene units. Subsequently, the obtained copolymer (copolymer B4 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 2. [Purification of polymers] Next, the obtained polymer was dissolved in 100 g of THF, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 20:80) to precipitate a white solidified product (a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and α-methylstyrene units). Subsequently, the solution containing the precipitated solidified product was filtered through a Kiriyama funnel to obtain a white copolymer (a polymer containing α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and α-methylstyrene units). Subsequently, the obtained copolymer (purified copolymer B4) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 2.

[0154] <<Preparation Example 12: Preparation of Copolymer B5>> [Synthesis of polymers] A monomer composition containing 3 g of 2,2,3,3,3-pentafluoropropyl chloroacrylate (ACAPFP) as monomer (c), 3.476 g of α-methylstyrene as monomer (d), 0.0275 g of azobisisobutyronitrile as a polymerization initiator, and 1.6205 g of cyclopentanone as a solvent was placed in a glass container, the glass container was sealed and nitrogen was purged, and the mixture was stirred for 6 hours in a constant temperature bath at 78°C under a nitrogen atmosphere. After returning the solution to room temperature and venting the glass container to the atmosphere, 10 g of THF was added to the resulting solution. The solution with THF added was then dropped dropwise into 100 g of MeOH as a solvent to precipitate the polymer. Subsequently, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white solidified substance (polymer). The obtained polymer was a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and α-methylstyrene units. Subsequently, the obtained copolymer (copolymer B5 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 2. [Purification of polymers] Next, the obtained polymer was dissolved in 100 g of THF, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 10:90) to precipitate a white solidified product (a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and α-methylstyrene units). Subsequently, the solution containing the precipitated solidified product was filtered through a Kiriyama funnel to obtain a white copolymer (a polymer containing α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and α-methylstyrene units). Subsequently, the obtained copolymer (purified copolymer B5) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 2.

[0155] <<Preparation Example 13: Preparation of Copolymer B6>> [Synthesis of polymers] A monomer composition containing 3 g of 2,2,3,3,3-pentafluoropropyl α-chloroacrylic acid (ACAPFP) as monomer (c), 3.235 g of 4-fluoro-α-methylstyrene as monomer (d), 0.0014 g of azobisisobutyronitrile as a polymerization initiator, and 6.4666 g of cyclopentanone as a solvent was placed in a glass container, the glass container was sealed and nitrogen was purged, and the mixture was stirred for 50 hours in a constant temperature bath at 40°C under a nitrogen atmosphere. After returning the solution to room temperature and venting the glass container to the atmosphere, 10 g of THF was added to the resulting solution. The solution with THF added was then dropped dropwise into 100 g of MeOH as a solvent to precipitate the polymer. Subsequently, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white solidified substance (polymer). The obtained polymer was a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and 4-fluoro-α-methylstyrene units. Subsequently, the obtained copolymer (polymer B6 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 2. [Purification of polymers] Next, the obtained polymer was dissolved in 100 g of THF, and the resulting solution was added dropwise to a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 25:75) to precipitate a white solidified product (a copolymer containing α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and 4-fluoro-α-methylstyrene units). Subsequently, the solution containing the precipitated solidified product was filtered through a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and 4-fluoro-α-methylstyrene units). Subsequently, the obtained copolymer (purified copolymer B6) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 2.

[0156] <<Preparation Example 14: Preparation of Copolymer B7>> [Synthesis of polymers] A monomer composition containing 3 g of 2,2,2-trifluoroethyl α-chloroacrylate (ACATFE) as monomer (c), 4.399 g of α-methylstyrene as monomer (d), 0.0070 g of azobisisobutyronitrile as a polymerization initiator, and 1.8514 g of cyclopentanone as a solvent was placed in a glass container, the glass container was sealed and nitrogen was purged, and the mixture was stirred for 6 hours in a constant temperature bath at 78°C under a nitrogen atmosphere. After returning the solution to room temperature and venting the glass container to the atmosphere, 10 g of THF was added to the resulting solution. The solution with THF added was then added dropwise to 100 g of MeOH as a solvent to precipitate the polymer. Subsequently, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white solidified substance (polymer). The obtained polymer was a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,2-trifluoroethyl units and α-methylstyrene units. Subsequently, the obtained copolymer (purified copolymer B7) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 2. [Purification of polymers] Next, the obtained polymer was dissolved in 100 g of THF, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 15:85) to precipitate a white solid (a copolymer containing 50% each of α-chloroacrylic acid 2,2,2-trifluoroethyl units and α-methylstyrene units). Subsequently, the solution containing the precipitated solid was filtered through a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,2-trifluoroethyl units and α-methylstyrene units). Subsequently, the obtained copolymer (purified copolymer B7) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 2.

[0157] <<Preparation Example 15: Preparation of Copolymer B8>> [Synthesis of polymers] A monomer composition containing 3 g of 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylic acid (ACAHFB) as monomer (c), 2.8783 g of α-methylstyrene as monomer (d), 0.0046 g of azobisisobutyronitrile as a polymerization initiator, and 1.471 g of cyclopentanone as a solvent was placed in a glass container, the glass container was sealed and nitrogen was purged, and the mixture was stirred for 50 hours in a constant temperature bath at 40°C under a nitrogen atmosphere. After returning the solution to room temperature and venting the glass container to the atmosphere, 10 g of THF was added to the resulting solution. The solution with THF added was then dropped dropwise into 100 g of MeOH as a solvent to precipitate the polymer. Subsequently, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white solidified substance (polymer). The obtained polymer was a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl units and α-methylstyrene units. Subsequently, the obtained copolymer (polymer B8 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 3. [Purification of polymers] Next, the obtained polymer was dissolved in 100 g of THF, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 20:80) to precipitate a white solidified product (a copolymer containing α-chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl units and α-methylstyrene units). Subsequently, the solution containing the precipitated solidified product was filtered through a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl units and α-methylstyrene units). Subsequently, the obtained copolymer (purified copolymer B8) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 3.

[0158] <<Preparation Example 16: Preparation of Copolymer B9>> [Synthesis of polymers] A monomer composition containing 3 g of 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylic acid (ACAHFB) as monomer (c), 2.8783 g of α-methylstyrene as monomer (d), 0.0046 g of azobisisobutyronitrile as a polymerization initiator, and 1.471 g of cyclopentanone as a solvent was placed in a glass container, the glass container was sealed and nitrogen was purged, and the mixture was stirred for 6 hours in a constant temperature bath at 78°C under a nitrogen atmosphere. After returning the solution to room temperature and venting the glass container to the atmosphere, 10 g of THF was added to the resulting solution. The solution with THF added was then dropped dropwise into 100 g of MeOH as a solvent to precipitate the polymer. Subsequently, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white solidified substance (polymer). The obtained polymer was a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl units and α-methylstyrene units. Subsequently, the obtained copolymer (polymer B9 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 3. [Purification of polymers] Next, the obtained polymer was dissolved in 100 g of THF, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 10:90) to precipitate a white solidified product (a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl units and α-methylstyrene units). Subsequently, the solution containing the precipitated solidified product was filtered through a Kiriyama funnel to obtain a white copolymer (a polymer containing α-chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl units and α-methylstyrene units). Subsequently, the obtained copolymer (purified copolymer B9) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 3.

[0159] <<Preparation Example 17: Preparation of Copolymer B10>> [Synthesis of polymers] A monomer composition containing 3 g of 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylic acid (ACAHFB) as monomer (c), 2.8783 g of α-methylstyrene as monomer (d), 0.0046 g of azobisisobutyronitrile as a polymerization initiator, and 1.4813 g of cyclopentanone as a solvent was placed in a glass container, the glass container was sealed and nitrogen was purged, and the mixture was stirred for 6 hours in a constant temperature bath at 78°C under a nitrogen atmosphere. After returning the solution to room temperature and venting the glass container to the atmosphere, 10 g of THF was added to the resulting solution. The solution with THF added was then dropped dropwise into 100 g of MeOH as a solvent to precipitate the polymer. Subsequently, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white solidified substance (polymer). The obtained polymer was a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl units and α-methylstyrene units. Subsequently, the obtained copolymer (polymer B10 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 3. [Purification of polymers] Next, the obtained polymer was dissolved in 100 g of THF, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 9:91) to precipitate a white solidified product (a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl units and α-methylstyrene units). Subsequently, the solution containing the precipitated solidified product was filtered through a Kiriyama funnel to obtain a white copolymer (a polymer containing α-chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl units and α-methylstyrene units). Subsequently, the obtained copolymer (purified copolymer B10) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 3.

[0160] <<Preparation Example 18: Preparation of Copolymer B11>> [Synthesis of polymers] A monomer composition containing 3 g of 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylic acid (ACAHFB) as monomer (c), 2.8783 g of α-methylstyrene as monomer (d), 0.0913 g of azobisisobutyronitrile as a polymerization initiator, and 1.4927 g of cyclopentanone as a solvent was placed in a glass container, the glass container was sealed and nitrogen was purged, and the mixture was stirred for 6 hours in a constant temperature bath at 78°C under a nitrogen atmosphere. After returning the solution to room temperature and venting the glass container to the atmosphere, 10 g of THF was added to the resulting solution. The solution with THF added was then dropped dropwise into 100 g of MeOH as a solvent to precipitate the polymer. Subsequently, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white solidified substance (polymer). The obtained polymer was a copolymer containing 50 mol% each of α-chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl units and α-methylstyrene units. Subsequently, the obtained copolymer (polymer B11 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 3. [Purification of polymers] Next, the obtained polymer was dissolved in 100 g of THF, and the resulting solution was dropped into 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 7:93), to precipitate a white solid (a copolymer containing 50 mol% each of 2,2,3,3,4,4,4 - heptafluorobutyl α - chloroacrylate units and α - methylstyrene units). Then, the solution containing the precipitated solid was filtered through a Kiriyama funnel to obtain a white copolymer (a polymer containing 2,2,3,3,4,4,4 - heptafluorobutyl α - chloroacrylate units and α - methylstyrene units). Thereafter, various measurements were carried out on the obtained copolymer (copolymer B11 after purification) in the same manner as in Preparation Example 1. The results are shown in Table 3.

[0161] <<Preparation Example 19: Preparation of Copolymer B12>> [Synthesis of Polymer] A monomer composition containing 3 g of 2,2,3,3,4,4,4 - heptafluorobutyl α - chloroacrylate (ACAHFB) as monomer (c) and 2.8783 g of α - methylstyrene as monomer (d), 0.1827 g of azobisisobutyronitrile as a polymerization initiator, and 1.5155 g of cyclopentanone as a solvent was placed in a glass container. The glass container was sealed and purged with nitrogen, and then stirred in a constant - temperature bath at 78°C for 6 hours under a nitrogen atmosphere. Thereafter, after returning to room temperature and releasing the inside of the glass container to the atmosphere, 10 g of THF was added to the obtained solution. Then, the solution to which THF was added was dropped into 100 g of MeOH as a solvent to precipitate a polymer. Then, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white solid (polymer). The obtained polymer was a copolymer containing 50 mol% each of 2,2,3,3,4,4,4 - heptafluorobutyl α - chloroacrylate units and α - methylstyrene units. Thereafter, various measurements were carried out on the obtained copolymer (copolymer B12 before purification) in the same manner as in Preparation Example 1. The results are shown in Table 3. [Purification of Polymer] Next, the obtained polymer was dissolved in 100 g of THF, and the resulting solution was dropped into 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 4:96), to precipitate a white solid (a copolymer containing 50 mol% each of 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylate units and α-methylstyrene units). Then, the solution containing the precipitated solid was filtered through a Kiriyama funnel to obtain a white copolymer (a polymer containing 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylate units and α-methylstyrene units). Thereafter, various measurements were carried out on the obtained copolymer (copolymer B12 after purification) in the same manner as in Preparation Example 1. The results are shown in Table 3.

[0162] <<Preparation Example 20: Preparation of Copolymer B13>> [Synthesis of Polymer] A monomer composition containing 3 g of 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylate (ACAHFB) as monomer (c), 3.315 g of 4-fluoro-α-methylstyrene as monomer (d), 0.0457 g of azobisisobutyronitrile as a polymerization initiator, and 1.5902 g of cyclopentanone as a solvent was placed in a glass container. The glass container was sealed and purged with nitrogen, and then stirred in a constant temperature bath at 78 °C for 6 hours under a nitrogen atmosphere. Thereafter, after returning to room temperature and releasing the inside of the glass container to the atmosphere, 10 g of THF was added to the obtained solution. Then, the solution to which THF was added was dropped into 100 g of MeOH as a solvent to precipitate a polymer. Then, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white solid (polymer). The obtained polymer was a copolymer containing 50 mol% each of 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylate units and 4-fluoro-α-methylstyrene units. Thereafter, various measurements were carried out on the obtained copolymer (copolymer B13 before purification) in the same manner as in Preparation Example 1. The results are shown in Table 3. [Purification of Polymer] Next, the obtained polymer was dissolved in 100 g of THF, and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 8:92) to precipitate a white solidified product (a copolymer containing 2,2,3,3,4,4,4-heptafluorobutyl units and 4-fluoro-α-methylstyrene units of α-chloroacrylic acid). Subsequently, the solution containing the precipitated solidified product was filtered through a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of 2,2,3,3,4,4,4-heptafluorobutyl units and 4-fluoro-α-methylstyrene units of α-chloroacrylic acid). Subsequently, the obtained copolymer (purified copolymer B13) was subjected to various measurements in the same manner as in Preparation Example 1. The results are shown in Table 3.

[0163] (Example 1) <Preparation of positive-type resist composition> As a positive-type resist composition containing only copolymer A, copolymer A1 prepared as described above was dissolved in isoamyl acetate as a solvent to prepare a positive-type resist composition (A) with a concentration of 3% by mass. Furthermore, as a positive-type resist composition containing only copolymer B, copolymer B1 prepared as described above was dissolved in isoamyl acetate as a solvent to prepare a positive-type resist composition (B) with a concentration of 3% by mass. Furthermore, as a positive-type resist composition containing copolymer A and copolymer B, copolymer A1 prepared as described above and copolymer B1 prepared as described above were dissolved in isoamyl acetate as a solvent in such a mass ratio of copolymer A1 to copolymer B1 as 99:1 to prepare a positive-type resist composition (A-B mixed system) with a concentration of 3% by mass.

[0164] <gamma value> A spin coater (manufactured by Mikasa, MS-A150) was used to coat the positive resist composition (A·B mixed system) obtained as described above onto a 4-inch diameter silicon wafer to a thickness of 50 nm. Then, the coated positive resist composition (A·B mixed system) was heated on a hot plate at a temperature of 170 °C for 1 minute to form a resist film on the silicon wafer (resist film forming step). Then, using an electron beam lithography apparatus (manufactured by Elionix, ELS-S50), a plurality of patterns (dimensions 500 μm × 500 μm) with different electron beam irradiation amounts were drawn on the resist film (exposure step). Further, the resist film after exposure was heated on a hot plate at 100 °C for 1 minute (post-exposure bake step). For the heated resist film, development treatment was performed at a temperature of 23 °C for 1 minute using isopropyl alcohol as the developer (development step). Then, the developer was removed by nitrogen blowing. The irradiation amount of the electron beam was 4 μC / cm 2 to 200 μC / cm 2 and was varied by 4 μC / cm 2 each within the range. Next, the thickness of the resist film in the drawn portion was measured with an optical film thickness meter (manufactured by SCREEN Semiconductor Solutions, Lambda Ace), and a sensitivity curve showing the relationship between the common logarithm of the total irradiation amount of the electron beam and the remaining film ratio of the resist film after development (= film thickness of the resist film after development / film thickness of the resist film formed on the silicon wafer) was created. Then, for the obtained sensitivity curve (horizontal axis: common logarithm of the total irradiation amount of the electron beam, vertical axis: remaining film ratio of the resist film (0 ≤ remaining film ratio ≤ 1.00)), the sensitivity curve was fitted to a quadratic function in the range of remaining film ratio of 0.20 to 0.80, and a straight line (approximate line of the slope of the sensitivity curve) connecting the point with a remaining film ratio of 0 and the point with a remaining film ratio of 0.50 on the obtained quadratic function (function of the remaining film ratio and the common logarithm of the total irradiation amount) was created. Also, the total irradiation amount E th of the electron beam (μC / cm 2 ) when the remaining film ratio of the obtained straight line (function of the remaining film ratio and the common logarithm of the total irradiation amount) becomes 0 was determined. The smaller the value of E th , the higher the sensitivity, indicating that the copolymers A and B as positive resists can be well cut with a smaller irradiation amount. Furthermore, the γ value was calculated using the following formula. The results are shown in Table 4. In the following formula, E0 is the logarithm of the total irradiation dose obtained when the sensitivity curve is fitted to a quadratic function in the range of residual film percentages from 0.20 to 0.80, and a residual film percentage of 0 is substituted into the resulting quadratic function (a function of residual film percentage and the common logarithm of total irradiation dose). E1 is the logarithm of the total irradiation dose obtained when a residual film percentage of 1.00 is substituted into the resulting straight line (an approximation line of the slope of the sensitivity curve) connecting the point of residual film percentage 0 and the point of residual film percentage 0.50 on the obtained quadratic function. The following formula represents the slope of the above straight line between residual film percentages of 0 and 1.00. Note that a larger γ value indicates a steeper slope of the sensitivity curve, which allows for the formation of a clearer pattern.

number

[0165] <eth> A resist film was formed on a silicon wafer in the same manner as the evaluation method of the "γ value". The initial thickness T0 of the obtained resist film was measured film was measured with an optical film thickness meter (Lambda Ace, manufactured by SCREEN Semiconductor Solutions Co., Ltd.). Also, the total electron beam irradiation dose Eth (μC / cm 2 ) when the residual film ratio of the straight line (approximate line of the slope of the sensitivity curve) obtained during the calculation of the γ value becomes 0 was determined. The results are shown in Table 4. A smaller value of Eth means that the sensitivity of the resist film is higher and the formation efficiency of the resist pattern is higher.

[0166] <Residual film ratio (half pitch (hp): 25 nm)> Using a spin coater (MS-A150, manufactured by Mikasa), the positive resist composition (A·B mixed system) obtained as described above was applied onto a 4-inch silicon wafer to a thickness of 50 nm. Then, the applied positive resist composition was heated on a hot plate at a temperature of 170°C for 1 minute to form a positive resist film on the silicon wafer. Then, using an electron beam lithography apparatus (ELS-S50, manufactured by Elionix), a pattern of line and space 1:1 with a line width of 25 nm (that is, a half pitch of 25 nm) was electron beam lithographed at the optimum exposure dose (E op ) to obtain an electron beam lithographed wafer. The optimum exposure dose was appropriately set with a value approximately twice that of each E th as a guide. The electron beam lithographed wafer was developed by immersing it in isopropyl alcohol (IPA) as a resist developer at 23°C for 1 minute. Then, the developer was removed by nitrogen blowing to form a line and space pattern (half pitch: 25 nm). Then, the pattern portion was cleaved and observed with a scanning electron microscope (JMS-7800F PRIME, manufactured by JEOL Ltd.) at a magnification of 100,000 times, and the maximum height (T max The initial thickness T0 of the resist film was measured. Then, the "residual film rate (half pitch (hp): 25nm)" was calculated using the following formula and evaluated based on the following criteria. The results are shown in Table 4. A higher residual film rate (half pitch (hp): 25nm) indicates less wear on the top of the resist pattern. Remaining film rate (%)=(T max / T0)×100 A Over 98.5% B More than 96% and less than 98.5% C 96% or less

[0167] <Residue> The resist patterns formed during the evaluation of the <residual film rate> described above were observed at a magnification of 100,000x using a scanning electron microscope (SEM), and the extent of residual residue in the resist patterns was evaluated according to the following criteria. The results are shown in Table 4. Residue remaining in the resist pattern can be seen in the SEM image as high-brightness "dots," etc., compared to line pattern areas without residue. A smaller amount of residue in the resist pattern indicates a higher contrast of the resist pattern. A: No residue was detected within the hp25nm resist pattern. B: There is a very small amount of residue within the hp25nm resist pattern, but it is within acceptable limits. A large amount of residue was observed within the C:hp25nm resist pattern, which is outside the acceptable range.

[0168] <Dry etching resistance> Using a spin coater (Mikasa MS-A150), the positive-type resist composition (A / B mixed system) obtained as described above was coated onto a 4-inch diameter silicon wafer to a thickness of 500 nm. The coated positive-type resist composition was then heated on a hot plate at 170°C for 1 minute to form a resist film on the silicon wafer. Next, the resist film was etched using a plasma etching system (EXAM, manufactured by Shinko Seiki Co., Ltd.) (gas type: CF4, flow rate: 100 sccm, pressure: 10 Pa, power consumption: 200 W). Subsequently, the time it took for the film thickness to completely disappear was calculated using a step height, surface roughness, and micro-shape measuring device (P6, manufactured by KLA-Tencor Co., Ltd.). Then, the dry etching resistance was evaluated according to the following criteria. The results are shown in Table 4. Note that a longer time for the film to completely disappear (etching time) indicates better dry etching resistance. A: The time it takes for the membrane to disappear is 4 minutes and 40 seconds or longer. B: The time it takes for the membrane to disappear is 4 minutes or more, but less than 4 minutes and 40 seconds. C: The time it takes for the membrane to disappear is less than 4 minutes.

[0169] <Difference between the surface free energy of copolymer A and copolymer B, and surface free energy of the mixed system of copolymer A and copolymer B> Films were prepared using the positive-type resist composition (A), positive-type resist composition (B), and positive-type resist composition (A-B mixed system) prepared as described above, using the following method. Next, the contact angles of the obtained films were measured using a contact angle meter (Drop Master 700, Kyowa Interface Science Co., Ltd.) with two solvents (water and diiodomethane) whose surface tension, polarity term (p), and dispersion force term (d) were known, under the following conditions. The surface free energy was evaluated using the Owens-Wendt (extended Fowkes equation) method, and the surface free energy of the films was calculated. Then, the surface free energy of the film (film) prepared using positive-type resist composition (A) was defined as "surface free energy of copolymer A," and the surface free energy of the film (film) prepared using positive-type resist composition (B) was defined as "surface free energy of polymer B." The difference between the surface free energy of copolymer A and the surface free energy of copolymer B (= "surface free energy of copolymer A" - "surface free energy of copolymer B") was calculated. Also, the surface free energy of the film (membrane) produced using the positive resist composition (A·B mixed system) was defined as the "surface free energy of the mixed system of copolymer A and copolymer B". The results are shown in Tables 1, 2, and 4. <<Method for producing the film (membrane)>> Using a spin coater (manufactured by Mikasa Co., Ltd., MS-A150), the positive resist composition was applied onto a 4-inch diameter silicon wafer to a thickness of 50 nm. Then, the applied positive resist composition was heated on a hot plate at a temperature of 170 °C for 1 minute to form a resist film on the silicon wafer. <<Measurement conditions for contact angle measurement>> Needle: Metal needle 22G (water), Teflon (registered trademark) coating 22G (diiodomethane) Standby time: 1000 ms Liquid volume: 1.8 μL Liquid droplet recognition: Water 50 dat, diiodomethane 100 dat Temperature: 23 °C

[0170] (Examples 2 to 64) A positive resist composition was prepared in the same manner as in Example 1, except that the types of copolymer A and copolymer B and the mass ratio of copolymer A to copolymer B were changed as shown in Tables 4 to 9. Using the obtained positive resist composition, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Tables 4 to 9.

[0171] (Examples 65 to 67) A resist film was formed in the same manner as in Example 1, except that the type of copolymer A and the mass ratio of copolymer A to copolymer B were changed as shown in Table 9 and the post-exposure bake process was not performed. Using the obtained resist film, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 9.

[0172] (Examples 68 to 84) A positive-type resist composition was prepared in the same manner as in Example 1, except that the types of copolymer A and copolymer B, and the mass ratio of copolymer A to copolymer B were changed as shown in Table 10, and ethanol (EtOH) was used instead of isopropyl alcohol as the developer. The obtained positive-type resist composition was used for various measurements and evaluations in the same manner as in Example 1. The results are shown in Table 10.

[0173] (Examples 85-93) A positive-type resist composition was prepared in the same manner as in Example 1, except that the types of copolymer A and copolymer B, the mass ratio of copolymer A to copolymer B, and the developer were changed as shown in Table 11. The obtained positive-type resist composition was used for various measurements and evaluations in the same manner as in Example 1. The results are shown in Table 11.

[0174] (Comparative Examples 1-18) A positive-type resist composition was prepared in the same manner as in Example 1, except that the types of copolymer A and copolymer B, and the mass ratio of copolymer A to copolymer B were changed as shown in Table 12. The obtained positive-type resist composition was used for various measurements and evaluations in the same manner as in Example 1. The results are shown in Table 12.

[0175] (Comparative Examples 19-24) A positive-type resist composition was prepared in the same manner as in Example 1, except that copolymer A was not used and the developer was changed as shown in Table 13. The obtained positive-type resist composition was used for various measurements and evaluations in the same manner as in Example 1. The results are shown in Table 13.

[0176] Note that in the table, "ACAFPh" represents α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl, "ACAFPhOMe" represents α-chloroacrylate-1-(4-methoxyphenyl)-1-trifluoromethyl-2,2,2-trifluoroethyl, "KORR (18%) soap" refers to an aqueous solution of semi-hardened beef tallow fatty acid potassium soap with a solid content of 18%. "ACAPFP" indicates 2,2,3,3,3-pentafluoropropyl alpha-chloroacrylate. "ACAHFB" represents 2,2,3,3,4,4,4-heptafluorobutyl chloroacrylate, "ACATFE" indicates 2,2,2-trifluoroethyl α-chloroacrylate. "IPA" refers to isopropyl alcohol. "EtOH" indicates ethanol. "PrOH" indicates 1-propanol. "ButOH" indicates 1-butanol.

[0177] [Table 1]

[0178] [Table 2]

[0179] [Table 3]

[0180] [Table 4]

[0181] [Table 5]

[0182] [Table 6]

[0183] [Table 7]

[0184] [Table 8]

[0185] [Table 9]

[0186] [Table 10]

[0187] [Table 11]

[0188] [Table 12]

[0189] [Table 13]

[0190] Tables 4 to 11 show that in Examples 1 to 93, where a predetermined positive-type resist composition containing copolymer A and copolymer B was used as the positive-type resist composition, the wear on the top of the resist pattern was reduced and a high-contrast resist pattern was formed. On the other hand, Tables 12 and 13 show that when a positive-type resist composition containing only one of copolymer A or copolymer B was used (Comparative Examples 1-5, 7, 9, 11, 13, 15, 17, 19-24), and when the specified polymer was not used as copolymer B (Comparative Examples 6, 8, 10, 12, 14, 16, 18), it was not possible to form a resist pattern with less reduction in the top layer of the resist pattern and high contrast. [Industrial applicability]

[0191] According to the present invention, it is possible to provide a positive-type resist composition that exhibits minimal wear on the top of the resist pattern and can form a resist pattern with high contrast. Furthermore, according to the present invention, it is possible to provide a method for forming a resist pattern that minimizes wear on the top of the resist pattern and enables the formation of a resist pattern with high contrast.< / eth>

Claims

1. Copolymer A and Copolymer B and It contains a solvent, The difference between the surface free energy of copolymer A and the surface free energy of copolymer B is 4 mJ / m ２ That's all. The copolymer A is defined by the following formula (I): 【Chemistry 1】 [In formula (I), L is a divalent linking group having a fluorine atom, and Ar is an aromatic ring group which may have substituents.] A monomer unit (I) represented by the following formula (II): 【Chemistry 2】 [In formula (II), R1 is an alkyl group, R2 is a hydrogen atom, an alkyl group, a halogen atom, a halogenated alkyl group, a hydroxyl group, a carboxyl group, or a halogenated carboxyl group, R3 is a hydrogen atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom, and p and q are integers between 0 and 5, with p + q = 5.] A positive-type resist composition having monomer units (II) represented by .

2. Copolymer A and Copolymer B and It contains a solvent, The difference between the surface free energy of copolymer A and the surface free energy of copolymer B is 4 mJ / m ２ That's all. The copolymer B is of the following formula (III): 【Transformation 3】 [In formula (III), R1 is an organic group having 5 to 7 fluorine atoms.] The monomer unit (III) is represented by the following formula (IV): 【Chemistry 4】 [In formula (IV), R1 is an alkyl group, R2 is a hydrogen atom, a fluorine atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom, R3 is a hydrogen atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom, and p and q are integers between 0 and 5, with p + q = 5.] A positive-type resist composition having monomer units (IV) represented by .

3. The copolymer A is of the following formula (I): 【Transformation 5】 [In formula (I), L is a divalent linking group having a fluorine atom, and Ar is an aromatic ring group which may have substituents.] A monomer unit (I) represented by the following formula (II): 【Transformation 6】 [In formula (II), R1 is an alkyl group, R2 is a hydrogen atom, an alkyl group, a halogen atom, a halogenated alkyl group, a hydroxyl group, a carboxyl group, or a halogenated carboxyl group, R3 is a hydrogen atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom, and p and q are integers between 0 and 5, with p + q = 5.] A positive-type resist composition according to claim 2, comprising monomer unit (II) represented by .

4. The positive-type resist composition according to any one of claims 1 to 3, wherein at least one of copolymer A and copolymer B is a main-chain cleavage type copolymer containing halogen atoms.

5. The positive resist composition according to claim 4, wherein at least one of copolymer A and copolymer B contains a fluorine substituent, at least one of the halogen atoms is a fluorine atom, and the fluorine atom is included in the fluorine substituent.

6. The content of a component having a weight-average molecular weight (Mw) of less than 1000 in the copolymer A is less than 0.05% by mass, The positive-type resist composition according to any one of claims 1 to 5, wherein the content of a component having a weight-average molecular weight (Mw) of less than 1000 in the copolymer B is less than 0.05% by mass.

7. At least one of copolymer A and copolymer B is a copolymer of the following formula (V): 【Transformation 7】 [In formula (V), X is a halogen atom, a cyano group, an alkylsulfonyl group, an alkoxy group, a nitro group, an acyl group, an alkyl ester group, or a halogenated alkyl group, R １ This refers to an organic group having 3 to 10 fluorine atoms. The positive-type resist composition according to claim 1, having monomer units (V) represented by .

8. A step of forming a resist film using the positive-type resist composition according to any one of claims 1 to 7, The steps include: exposing the resist film, A step of developing the exposed resist film, A method for forming a resist pattern, including the method described above.

9. The resist pattern forming method according to claim 8, wherein the development is performed using alcohol.

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