Copolymer, copolymer mixture, and positive resist composition

Abstract

The purpose of the present invention is to provide a copolymer capable of raising the pattern collapse resistance while maintaining the clarity of a resist pattern. The present invention is a copolymer having a monomer unit (I) represented by formula (I), a monomer unit (II) represented by formula (II) different from the monomer unit (I), and a monomer unit (III) represented by formula (III). Furthermore, in the formulas, L1, Ar1, X1, R1, X2, R2, R3, and R4 are predetermined groups, p and q are integers of 0-5 inclusive, and p + q = 5.

Description

Copolymer, copolymer mixture, and positive resist composition

[0001] The present invention relates to a copolymer, a copolymer mixture, and a positive resist composition.

[0002] BACKGROUND ART In the field of semiconductor manufacturing and the like, polymers whose main chains are scissed and whose solubility in a developer is increased by irradiation with ionizing radiation such as an electron beam or short-wavelength light such as ultraviolet light (hereinafter, ionizing radiation and short-wavelength light may be collectively referred to as "ionizing radiation, etc.") have conventionally been used as main-chain scission-type positive resists.

[0003] For example, Patent Document 1 discloses a main chain scission type positive resist that is excellent in sensitivity to ionizing radiation and heat resistance, and that is made of a copolymer containing α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-methylstyrene units.

[0004] JP 2018-154754 A

[0005] Here, in a main chain scission type positive resist, it is required that the resulting resist pattern be clear, i.e., that there be a clear boundary between the portion where the resist film remains (residual film) and the portion where it has dissolved. Specifically, from the viewpoint of enabling the formation of a resist pattern with higher clarity, the resist is required to have the property that it will not dissolve in a developer unless the exposure dose reaches a specific amount, and once the specific amount is reached, the main chain is quickly scissed and it becomes soluble in the developer, i.e., it is required to increase the γ value, which represents the magnitude of the slope of the sensitivity curve that shows the relationship between the common logarithm of the exposure dose of ionizing radiation or the like and the remaining film thickness of the resist after development.

[0006] Furthermore, in a main chain scission type positive resist, when a resist pattern is formed after irradiation with ionizing radiation or the like and development treatment using a developer, the resist pattern may collapse (pattern collapse). Therefore, in a main chain scission type positive resist, it is required to suppress this pattern collapse (in other words, to improve the resistance to pattern collapse).

[0007] Therefore, an object of the present invention is to provide a copolymer that can enhance resistance to pattern collapse while ensuring the clarity of the resist pattern. Another object of the present invention is to provide a copolymer mixture that can enhance resistance to pattern collapse while ensuring the clarity of the resist pattern. Another object of the present invention is to provide a positive resist composition that can form a resist pattern that has high resistance to pattern collapse while ensuring clarity.

[0008] The present inventors have conducted extensive research in order to achieve the above object, and have newly discovered that the above-mentioned problems can be solved by using a copolymer having three specific types of monomer units in a positive resist composition, which has led to the completion of the present invention.

[0009] That is, an object of the present invention is to advantageously solve the above-mentioned problems, and [1] the present invention provides a compound represented by the following formula (I): [In formula (I), L １ is a divalent linking group having a fluorine atom, and Ar １ represents an aromatic ring group which may have a substituent, and X １ 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, and a monomer unit (I) represented by the following formula (II): [In formula (II), R １ is an organic group having 3 to 10 fluorine atoms, and X ２ 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, and a monomer unit (II) represented by the following formula (III): [In formula (III), R ２ is an alkyl group, and R ３ is a hydrogen atom, a fluorine atom, an unsubstituted alkyl group or an alkyl group substituted with a fluorine atom, and R ４is a hydrogen atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom, and p and q are integers of 0 to 5, and p+q=5. The copolymer has a monomer unit (III) represented by the formula: [wherein p and q are integers of 0 to 5, and p+q=5.]. The copolymer can improve resistance to pattern collapse while ensuring the clarity of the resist pattern. In this specification, "optionally having a substituent" means "unsubstituted or having a substituent."

[0010] [2] In the copolymer of [1] above, the R １ The number of fluorine atoms in R is preferably 5 or more. １ When the number of fluorine atoms is equal to or greater than the lower limit, the sensitivity of the copolymer to ionizing radiation and the like can be improved.

[0011] [3] In the copolymer of [1] or [2] above, the L １ The number of fluorine atoms in L is preferably 4 or more. １ When the number of fluorine atoms is equal to or greater than the lower limit, the sensitivity of the copolymer to ionizing radiation and the like can be improved.

[0012] [4] In any of the copolymers [1] to [3] above, the total proportion of the monomer units (I) and the monomer units (II) is preferably 45 mol% or more and 70 mol% or less, when the total monomer units in the copolymer is 100 mol%. When the total proportion of the monomer units (I) and the monomer units (II) is equal to or more than the lower limit, when the total monomer units in the copolymer is 100 mol%, the clarity of the resist pattern can be improved. On the other hand, when the total proportion of the monomer units (I) and the monomer units (II) is equal to or less than the upper limit, when the total monomer units in the copolymer is 100 mol%, the pattern collapse resistance can be improved. Furthermore, the amount of residues (hereinafter sometimes referred to as "resist residues") unintentionally remaining in the space portions of the resist pattern can be reduced. In this specification, the proportion of the monomer units in the copolymer is defined as: １ It can be measured using a nuclear magnetic resonance (NMR) method such as H-NMR.

[0013] Another object of the present invention is to advantageously solve the above-mentioned problems. [5] The present invention provides a method for producing a polymer film comprising a copolymer A and a copolymer B, wherein the copolymer A is any one of the copolymers [1] to [4] above, and the difference in surface free energy between the copolymer B and the copolymer A is 3 mJ / m ２ The copolymer mixture is as described above. The above copolymer mixture can improve the resistance to pattern collapse while ensuring the clarity of the resist pattern. In this specification, the "surface free energy" can be measured using the method described in the examples of this specification.

[0014] Another object of the present invention is to advantageously solve the above-mentioned problems, and [6] the present invention provides a copolymer A and a copolymer B, wherein the copolymer A is any one of the copolymers [1] to [4] above, and the copolymer B is represented by the following formula (IV): [In formula (IV), L ２ is a divalent linking group having a fluorine atom, and Ar ２ represents an aromatic ring group which may have a substituent, and X ３ 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, and a monomer unit (IV) represented by the following formula (V): [In formula (V), R ５ is an alkyl group, and R ６ 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, and R ７ is a hydrogen atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom, and r and s are integers of 0 to 5, and r+s=5. The copolymer mixture has a monomer unit (V) represented by the formula: [wherein r is a hydrogen atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom, and r and s are integers of 0 to 5, and r+s=5.] The copolymer mixture can enhance resistance to pattern collapse while ensuring the clarity of the resist pattern.

[0015] Another object of the present invention is to advantageously solve the above-mentioned problems, and [7] the present invention provides a positive resist composition comprising any one of the following (A) to (C) and a solvent: (A) a copolymer according to any one of the above [1] to [4]; (B) a copolymer A and a copolymer B, wherein the copolymer A is any one of the above [1] to [4], and the difference in surface free energy between the copolymer B and the copolymer A is 3 mJ / m ２ (C) A copolymer mixture comprising a copolymer A and a copolymer B, wherein the copolymer A is any one of the copolymers [1] to [4] above, and the copolymer B is a copolymer represented by the following formula (IV): [In formula (IV), L ２ is a divalent linking group having a fluorine atom, and Ar ２ represents an aromatic ring group which may have a substituent, and X ３ 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, and a monomer unit (IV) represented by the following formula (V): [In formula (V), R ５ is an alkyl group, and R ６ 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, and R ７ represents a hydrogen atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom, and r and s are integers of 0 or greater and 5 or less, and r+s=5.] The above positive resist composition can form a resist pattern that is highly resistant to pattern collapse while ensuring clarity.

[0016] [8] In the positive resist composition of [7] above, it is preferable that the composition is substantially free of components having a weight-average molecular weight of less than 1000. The clarity of the resist pattern can be improved if the composition is substantially free of components having a weight-average molecular weight of less than 1000. In this specification, the proportion (presence) of "components having a weight-average molecular weight of less than 1000" can be measured using the method described in the Examples. In this specification, "substantially free" means that the components are not actively blended in, except in cases where they are inevitably mixed in. Specifically, this means that the proportion of components having a weight-average molecular weight of less than 1000 in the positive resist composition is less than 0.05% by mass.

[0017] According to the present invention, it is possible to provide a copolymer that can enhance resistance to pattern collapse while ensuring the clarity of the resist pattern. Furthermore, according to the present invention, it is possible to provide a copolymer mixture that can enhance resistance to pattern collapse while ensuring the clarity of the resist pattern. Furthermore, according to the present invention, it is possible to provide a positive resist composition that can form a resist pattern that has high resistance to pattern collapse while ensuring clarity.

[0018] Hereinafter, embodiments of the present invention will be described in detail. The copolymer of the present invention can be suitably used in main chain scission type positive resist compositions in which the main chain is scissed by ionizing radiation or the like, resulting in a lower molecular weight. Furthermore, the copolymer mixture of the present invention contains the copolymer of the present invention, and can also be suitably used in main chain scission type positive resist compositions. Furthermore, the positive resist composition of the present invention contains the copolymer of the present invention or the copolymer mixture of the present invention, and can be used, for example, when forming a resist pattern in the production process of printed circuit boards such as build-up boards.

[0019] (Copolymer) The copolymer of the present invention is represented by the following formula (I): [In formula (I), L １ is a divalent linking group having a fluorine atom, and Ar １ represents an aromatic ring group which may have a substituent, and X １is 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, and a monomer unit (I) represented by the following formula (II): [In formula (II), R １ is an organic group having 3 to 10 fluorine atoms, and X ２ 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, and a monomer unit (II) represented by the following formula (III): [In formula (III), R ２ is an alkyl group, and R ３ is a hydrogen atom, a fluorine atom, an unsubstituted alkyl group or an alkyl group substituted with a fluorine atom, and R ４ is a hydrogen atom, an unsubstituted alkyl group or an alkyl group substituted with a fluorine atom, and p and q are integers of 0 to 5, and p+q=5.

[0020] The copolymer of the present invention may contain any monomer unit other than the monomer unit (I), the monomer unit (II), and the monomer unit (III). However, the total proportion of the monomer units (I), (II), and (III) in the total monomer units constituting the copolymer is preferably 90 mol% or more, more preferably 100 mol% (i.e., the copolymer contains only the monomer units (I), (II), and (III)). Here, the copolymer of the present invention may be, for example, a random copolymer, a block copolymer, a ternary alternating copolymer, etc., as long as it contains the monomer units (I), (II), and (III). However, a ternary alternating copolymer is preferred. In this specification, a ternary alternating copolymer is an alternating copolymer in which the monomer unit (I) or the monomer unit (II) is copolymerized between the monomer units (III). That is, in a schematic representation, the individual monomer units are bonded in the following manner: "-(III)-(I)-(III)-(II)-(III)-".

[0021] The copolymer of the present invention has a predetermined monomer unit (I), a monomer unit (II), and a monomer unit (III), and when the irradiation dose of ionizing radiation or the like reaches a specific amount, the main chain of the copolymer only in the irradiated portion is effectively cleaved and the molecular weight is reduced. Then, the reduced molecular weight component is well dissolved in the developer. This ensures the clarity of the resist pattern (i.e., the γ value is high). Although the reason for this is unclear, it is thought that the L of the monomer unit (I) １ and R of the monomer unit (II) １ It is presumed that the electron-withdrawing ability of the fluorine atom in the copolymer improves the sensitivity to ionizing radiation and the like, and the ease of generating radicals when irradiated with ionizing radiation and the like. Furthermore, the copolymer of the present invention can improve the pattern collapse resistance by having the predetermined monomer unit (I), monomer unit (II) and monomer unit (III). Although the reason for this is not clear, it is believed that the L １ and R of the monomer unit (II) １ It is presumed that the fluorine atoms in (I) improve the liquid repellency of the copolymer, thereby suppressing the occurrence of pulling between patterns when removing a developer or rinse solution during the process of forming a resist pattern. Furthermore, the copolymer of the present invention can suppress the occurrence of resist residues by having the predetermined monomer units (I), (II), and (III). Although the reason for this is not clear, it is presumed that the aromatic ring groups in the monomer units (I) and (III) improve the solubility in a developer.

[0022] <Monomer Unit (I)> Here, the monomer unit (I) is a monomer unit represented by the following formula (a): [In formula (a), L １ , Ar １ and X １ is the same as in formula (I).

[0023] L in formula (I) and formula (a) １Examples of the divalent linking group having a fluorine atom that can constitute the above formula include a divalent chain alkyl group having 1 to 5 carbon atoms and having a fluorine atom. Specific examples of the divalent linking group having a fluorine atom include a trifluoromethylmethylene group, a pentafluoroethylmethylene group, and a bis(trifluoromethyl)methylene group. Among these, the pentafluoroethylmethylene group and the bis(trifluoromethyl)methylene group are preferred, and the bis(trifluoromethyl)methylene group is more preferred.

[0024] L １ The number of fluorine atoms in (a divalent linking group having a fluorine atom) is preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more, and is preferably 10 or less, and more preferably 7 or less. １ When the number of fluorine atoms in is equal to or greater than the above lower limit, the sensitivity to ionizing radiation and the clarity of the resist pattern can be improved. １ When the number of fluorine atoms is equal to or less than the upper limit, the production efficiency of the copolymer can be improved.

[0025] Ar in formula (I) and formula (a) １ Examples of the aromatic ring group which may have a substituent and which can constitute the above formula include an aromatic hydrocarbon ring group which may have a substituent and an aromatic heterocyclic group which may have a substituent.

[0026] The aromatic hydrocarbon ring group is not particularly limited, and examples thereof include a benzene ring group, a biphenyl ring group, a naphthalene ring group, an azulene ring group, an anthracene ring group, a phenanthrene ring group, a pyrene ring group, a chrysene ring group, a naphthacene ring group, a triphenylene ring group, an o-terphenyl ring group, an m-terphenyl ring group, a p-terphenyl ring group, an acenaphthene ring group, a coronene ring group, a fluorene ring group, a fluoranthrene ring group, a pentacene ring group, a perylene ring group, a pentaphene ring group, a picene ring group, and a pyranthrene ring group.

[0027] The aromatic heterocyclic group is not particularly limited, and examples thereof include a furan ring group, a thiophene ring group, a pyridine ring group, a pyridazine ring group, a pyrimidine ring group, a pyrazine ring group, a triazine ring group, an oxadiazole ring group, a triazole ring group, an imidazole ring group, a pyrazole ring group, a thiazole ring group, an indole ring group, a benzimidazole ring group, a benzothiazole group, a benzoxazole ring group, a quinoxaline ring group, a quinazoline ring group, a phthalazine ring group, a benzofuran ring group, a dibenzofuran ring group, a benzothiophene ring group, a dibenzothiophene ring group, and a carbazole ring group.

[0028] Ar １ The substituent that Ar may have is not particularly limited, and examples thereof include an alkyl group, a fluorine atom, a fluoroalkyl group, etc. １ Examples of the alkyl group as a substituent that Ar may have include chain alkyl groups having 1 to 6 carbon atoms, such as a methyl group, an ethyl group, a propyl group, an n-butyl group, and an isobutyl group. １ Examples of the fluoroalkyl group as a substituent that may be possessed by include fluoroalkyl groups having 1 to 5 carbon atoms, such as a trifluoromethyl group, a trifluoroethyl group, and a pentafluoropropyl group.

[0029] Among these, from the viewpoint of improving the ease of production of the copolymer, Ar １ As the alkyl group, an aromatic hydrocarbon ring group which may have a substituent is preferable, an unsubstituted aromatic hydrocarbon ring group is more preferable, and a benzene ring group (phenyl group) is even more preferable.

[0030] X in formula (I) and formula (a) １ Examples of halogen atoms that can constitute the above include a chlorine atom, a fluorine atom, a bromine atom, an iodine atom, and an astatine atom.

[0031] X in formula (I) and formula (a) １ Examples of alkylsulfonyl groups that can constitute the above include a methylsulfonyl group and an ethylsulfonyl group.

[0032] X in formula (I) and formula (a) １Examples of the alkoxy group that can constitute the above group include a methoxy group, an ethoxy group, and a propoxy group.

[0033] X in formula (I) and formula (a) １ Examples of the acyl group that can constitute the above include a formyl group, an acetyl group, and a propionyl group.

[0034] X in formula (I) and formula (a) １ Examples of the alkyl ester group that can constitute the above formula include a methyl ester group and an ethyl ester group.

[0035] X in formula (I) and formula (a) １ Examples of halogenated alkyl groups that can constitute the above include halogenated methyl groups having 1 or more and 3 or less halogen atoms.

[0036] Among the above, X １ is preferably a halogen atom, more preferably a chlorine atom.

[0037] From the viewpoint of sufficiently improving sensitivity to ionizing radiation and the like, the monomer (a) represented by formula (a) is preferably at least one monomer selected from the group consisting of 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl α-chloroacrylate (ACAFPh), 1-phenyl-2,2,2-trifluoroethyl α-chloroacrylate (ACAHFPh), and 1-(4-methoxyphenyl)-1-trifluoromethyl-2,2,2-trifluoroethyl α-chloroacrylate (ACAFPhOMe), and more preferably 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl α-chloroacrylate. That is, the copolymer preferably has at least one monomer unit selected from the group consisting of an α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl unit, an α-chloroacrylate-1-phenyl-2,2,2-trifluoroethyl unit, and an α-chloroacrylate-1-(4-methoxyphenyl)-1-trifluoromethyl-2,2,2-trifluoroethyl unit, and more preferably has an α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl unit.

[0038] The proportion of the monomer unit (I) in the copolymer is preferably 1 mol% or more, more preferably 3 mol% or more, even more preferably 5 mol% or more, even more preferably 8 mol% or more, and preferably 40 mol% or less, more preferably 30 mol% or less, even more preferably 20 mol% or less, and even more preferably 15 mol% or less, when the total amount of all monomer units in the copolymer is taken as 100 mol%. When the proportion of the monomer unit (I) in the copolymer is equal to or greater than the lower limit specified above, the pattern collapse resistance of the resist pattern can be improved. Furthermore, the amount of resist residue can be reduced. On the other hand, when the proportion of the monomer unit (I) in the copolymer is equal to or less than the upper limit specified above, the sensitivity to ionizing radiation and the clarity of the resist pattern can be improved.

[0039] <Monomer unit (II)> Here, the monomer unit (II) different from the monomer unit (I) is a monomer unit represented by the following formula (b) which is different from the monomer (a): [In formula (b), R １ and X ２ is the same as in formula (II).

[0040] R in formula (II) and formula (b) １ is an organic group having 3 to 10 fluorine atoms. １ The number of fluorine atoms in R is preferably 5 or more, more preferably 6 or more, even more preferably 7 or more, still more preferably 8 or more, and preferably 9 or less. １ When the number of fluorine atoms in R is equal to or greater than the lower limit, the sensitivity to ionizing radiation and the clarity of the resist pattern can be improved. １ If the number of fluorine atoms in R is 8 or more, the production efficiency of the copolymer can be improved. １ Even if the number of fluorine atoms in R is equal to or less than the upper limit, the production efficiency of the copolymer can be improved. １ If the number of fluorine atoms is equal to or less than the upper limit, the sensitivity to ionizing radiation and the like can be improved.

[0041] R in formula (II) and formula (b) １ The number of carbon atoms is preferably 2 or more and 10 or less, and more preferably 5 or less. When the number of carbon atoms is equal to or more than the above lower limit, the solubility in a developer can be sufficiently improved. On the other hand, when the number of carbon atoms is equal to or less than the above upper limit, the clarity of the resist pattern can be sufficiently ensured.

[0042] R １ The organic group in the formula (I) preferably does not have an aromatic ring, and is more preferably a chain. Examples of such an organic group include fluoroalkyl groups such as (b-1) to (b-31) below, fluoroalkoxyalkyl groups such as (b-32) to (b-55) below, and fluoroalkoxyalkenyl groups such as fluoroethoxyvinyl groups.

[0043]

[0044]

[0045] Among the above, R １ The organic group in (b-13) is preferably a fluoroalkyl group, and more preferably a fluoroalkyl group in (b-20) (2,2,3,3,3-pentafluoropropyl group), a fluoroalkyl group in (b-25) (2,2,3,3,4,4,4-heptafluorobutyl group), or a fluoroalkyl group in (b-31) (2,2,3,3,4,4,5,5,5-nonafluoropentyl group). More preferably, it is a 2,2,3,3,3-pentafluoropropyl group, a 2,2,3,3,4,4,4-heptafluorobutyl group, or a 2,2,3,3,4,4,5,5,5-nonafluoropentyl group, even more preferably a 2,2,3,3,4,4,4-heptafluorobutyl group or a 2,2,3,3,4,4,5,5,5-nonafluoropentyl group, and even more preferably a 2,2,3,3,4,4,5,5,5-nonafluoropentyl group.

[0046] X in formula (II) and formula (b) ２ Examples of halogen atoms that can constitute the above include a chlorine atom, a fluorine atom, a bromine atom, an iodine atom, and an astatine atom.

[0047] X in formula (II) and formula (b) ２ Examples of alkylsulfonyl groups that can constitute the above include a methylsulfonyl group and an ethylsulfonyl group.

[0048] X in formula (II) and formula (b) ２ Examples of the alkoxy group that can constitute the above group include a methoxy group, an ethoxy group, and a propoxy group.

[0049] X in formula (II) and formula (b) ２ Examples of the acyl group that can constitute the above include a formyl group, an acetyl group, and a propionyl group.

[0050] X in formula (II) and formula (b) ２Examples of the alkyl ester group that can constitute the above formula include a methyl ester group and an ethyl ester group.

[0051] X in formula (II) and formula (b) ２ Examples of halogenated alkyl groups that can constitute the above include halogenated methyl groups having 1 or more and 3 or less halogen atoms.

[0052] Among the above, X ２ is preferably a halogen atom, more preferably a chlorine atom, and X １ It is more preferable that the value is the same as

[0053] More specifically, examples of the monomer (b) represented by formula (b) include 2,2,2-trifluoroethyl α-chloroacrylate (ACATFE), 2,2,3,3,3-pentafluoropropyl α-chloroacrylate (ACAPFP), 3,3,4,4,4-pentafluorobutyl α-chloroacrylate, 2,2,3,3,4,4,5,5,5-nonafluoropentyl α-chloroacrylate, 1H-1-(trifluoromethyl)trifluoroethyl α-chloroacrylate, 1H,1H,3H-hexafluorobutyl α-chloroacrylate, and 1H-chloroacrylic acid ester. α-chloroacrylic acid fluoroalkyl esters such as α-chloroacrylic acid pentafluoroethoxymethyl ester and α-chloroacrylic acid pentafluoroethoxyethyl ester; α-chloroacrylic acid fluoroalkoxyalkyl esters such as α-chloroacrylic acid pentafluoroethoxyvinyl ester; and the like. Among these, α-chloroacrylic acid fluoroalkyl esters are preferred because they can improve sensitivity to ionizing radiation and the like, and 2,2,2-trifluoroethyl α-chloroacrylate, 2,2,3,3,3-pentafluoropropyl α-chloroacrylate, 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylate, and 2,2,3,3,4,4,5,5,5-nonafluoropentyl α-chloroacrylate are more preferred, and α-chloroacrylic acid fluoroalkyl esters are more preferred. 2,2,3,3,3-pentafluoropropyl α-chloroacrylate and 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylate are more preferred, 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylate and 2,2,3,3,4,4,5,5,5-nonafluoropentyl α-chloroacrylate are even more preferred, and 2,2,3,3,4,4,5,5,5-nonafluoropentyl α-chloroacrylate is even more preferred.That is, the copolymer preferably has an α-chloroacrylic acid fluoroalkyl ester unit, and more preferably has at least one monomer unit selected from the group consisting of an α-chloroacrylic acid 2,2,2-trifluoroethyl unit, an α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit, an α-chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl unit, and an α-chloroacrylic acid 2,2,3,3,4,4,5,5,5-nonafluoropentyl unit, and It is more preferable that the copolymer has at least one monomer unit selected from the group consisting of a 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylate unit and a 2,2,3,3,4,4,5,5,5-nonafluoropentyl α-chloroacrylate unit, even more preferable that the copolymer has at least one monomer unit selected from the group consisting of a 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylate unit and a 2,2,3,3,4,4,5,5,5-nonafluoropentyl α-chloroacrylate unit, and even more preferable that the copolymer has a 2,2,3,3,4,4,5,5,5-nonafluoropentyl α-chloroacrylate unit.

[0054] The proportion of the monomer unit (II) in the copolymer is preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 30 mol% or more, even more preferably 35 mol% or more, and preferably 70 mol% or less, more preferably 60 mol% or less, even more preferably 50 mol% or less, and even more preferably 45 mol% or less, when the total monomer units in the copolymer is taken as 100 mol%. If the proportion of the monomer unit (II) in the copolymer is equal to or greater than the lower limit above, when the total monomer units in the copolymer is taken as 100 mol%, the sensitivity to ionizing radiation and the clarity of the resist pattern can be improved. On the other hand, if the proportion of the monomer unit (II) in the copolymer is equal to or less than the upper limit above, when the total monomer units in the copolymer is taken as 100 mol%, the pattern collapse resistance of the resist pattern can be improved. In addition, the amount of resist residue can be reduced.

[0055] The total proportion of the monomer units (I) and (II) in the copolymer is preferably 45 mol% or more, more preferably 47 mol% or more, and preferably 70 mol% or less, more preferably 60 mol% or less, and even more preferably 55 mol% or less, when the total monomer units in the copolymer is taken as 100 mol%. When the total proportion of the monomer units (I) and (II) in the copolymer is equal to or greater than the lower limit, when the total monomer units in the copolymer is taken as 100 mol%, the clarity of the resist pattern can be improved. On the other hand, when the total proportion of the monomer units (I) and (II) in the copolymer is equal to or less than the upper limit, when the total monomer units in the copolymer is taken as 100 mol%, the pattern collapse resistance can be improved. Furthermore, the amount of resist residue can be reduced.

[0056] <Monomer Unit (III)> Here, the monomer unit (III) is a monomer unit represented by the following formula (c): [In formula (c), R ２ ~R ４ and p and q are the same as in formula (III).

[0057] R in formula (III) and formula (c) ２ The alkyl group that can constitute R is not particularly limited, and examples thereof include alkyl groups having 1 to 5 carbon atoms. ２ The alkyl group that can constitute the above is preferably a methyl group or an ethyl group.

[0058] R in formula (III) and formula (c) ３ , R ４ The unsubstituted alkyl group that can constitute R is not particularly limited, and examples thereof include unsubstituted alkyl groups having 1 to 5 carbon atoms. ３ , R ４ The unsubstituted alkyl group that can constitute the above is preferably a methyl group or an ethyl group.

[0059] R in formula (III) and formula (c) ３ , R ４The alkyl group substituted with fluorine atoms that can constitute the above group is not particularly limited, and examples thereof include groups having a structure in which some or all of the hydrogen atoms in the alkyl group have been substituted with fluorine atoms.

[0060] In formula (III) and formula (c), when p is 2 or more, each R ３ may be the same or different from each other. When q is 2 or more, each R ４ may be the same or different. In formula (III) and formula (c), p=5 (i.e., q=0) is preferred.

[0061] From the viewpoint of improving the ease of preparation of the copolymer, it is preferable that a plurality of R ３ and / or R ４ are preferably all hydrogen atoms or unsubstituted alkyl groups, more preferably hydrogen atoms or unsubstituted alkyl groups having 1 to 5 carbon atoms, and even more preferably hydrogen atoms.

[0062] The monomer (c) represented by formula (c) is not particularly limited, and examples thereof include α-methylstyrene (AMS) and its derivatives (e.g., 4-fluoro-α-methylstyrene: 4FAMS), such as the following monomers (c-1) to (c-11).

[0063]

[0064] From the viewpoints of ease of preparation of the copolymer and improving the severability of the main chain when irradiated with an electron beam or the like, the monomer (c) represented by formula (c) is preferably α-methylstyrene (c-1) or 4-fluoro-α-methylstyrene (c-2), and more preferably α-methylstyrene. That is, the copolymer preferably has an α-methylstyrene unit or a 4-fluoro-α-methylstyrene unit, and more preferably has an α-methylstyrene unit.

[0065] The proportion of the monomer unit (III) in the copolymer is not particularly limited, and when the total monomer units in the copolymer is taken as 100 mol%, it can be, for example, 30 mol% or more, preferably 40 mol% or more, and more preferably 45 mol% or more. It can be, for example, 70 mol% or less, preferably 60 mol% or less, more preferably 55 mol% or less, and even more preferably 53 mol% or less.

[0066] <Properties of the Copolymer> [Weight-Average Molecular Weight (Mw)] The weight-average molecular weight (Mw) of the copolymer is preferably 10,000 or more, more preferably 17,000 or more, even more preferably 25,000 or more, and preferably 250,000 or less, more preferably 180,000 or less, even more preferably 80,000 or less, and even more preferably 50,000 or less. If the weight-average molecular weight (Mw) of the copolymer is equal to or greater than the above-mentioned lower limit, it is possible to prevent the solubility of the resist film in the developer from excessively increasing at a low irradiation dose. On the other hand, if the weight-average molecular weight (Mw) of the copolymer is equal to or less than the above-mentioned upper limit, it is possible to easily prepare a positive resist composition. In this specification, the "weight-average molecular weight" can be measured using the method described in the examples.

[0067] [Number Average Molecular Weight (Mn)] The number average molecular weight (Mn) of the copolymer is preferably 7,000 or more, more preferably 10,000 or more, even more preferably 20,000 or more, and preferably 150,000 or less, more preferably 100,000 or less, even more preferably 70,000 or less, and even more preferably 40,000 or less. If the number average molecular weight (Mn) of the copolymer is equal to or greater than the above-mentioned lower limit, excessive increase in the solubility of the resist film in the developer at a low irradiation dose can be further suppressed, and a resist pattern with further improved clarity can be formed. On the other hand, if the number average molecular weight (Mn) of the copolymer is equal to or less than the above-mentioned upper limit, a positive resist composition can be more easily prepared. In this specification, the "number average molecular weight" can be measured using gel permeation chromatography as a standard polystyrene equivalent value.

[0068] [Molecular Weight Distribution (Mw / Mn)] The molecular weight distribution (Mw / Mn) of the copolymer is preferably 1.10 or more, more preferably 1.20 or more, and even more preferably 1.45 or more, and is preferably 1.80 or less, more preferably 1.70 or less, and even more preferably 1.65 or less. If the molecular weight distribution (Mw / Mn) of the copolymer is equal to or greater than the lower limit, the ease of production of the copolymer can be improved. On the other hand, if the molecular weight distribution (Mw / Mn) of the copolymer is equal to or less than the upper limit, the clarity of the obtained resist pattern can be further improved. In this specification, 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).

[0069] [Surface free energy] The surface free energy of the copolymer is 18 mJ / m ２ It is preferable that the concentration is 19 mJ / m or more. ２ More preferably, it is 20 mJ / m or more. ２ More preferably, it is 27 mJ / m or more. ２ Preferably, it is 26 mJ / m or less. ２ More preferably, it is 25 mJ / m or less. ２ More preferably, it is 24 mJ / m or less. ２ Even more preferably, it is 22 mJ / m or less. ２ It is even more preferable that the surface free energy is below 0.05 wt %. The surface free energy can be adjusted by the types and proportions of the monomer units constituting the copolymer.

[0070] <Method for Preparing Copolymer> The method for preparing the copolymer is not particularly limited. For example, a copolymer having monomer units (I), (II), and (III) can be prepared by polymerizing a monomer composition containing monomers (a), (b), and (c), and any monomer copolymerizable with these monomers, recovering the resulting copolymer, and optionally purifying it. The composition, molecular weight distribution, number average molecular weight, and weight average molecular weight of the copolymer can be adjusted by changing the polymerization conditions and purification conditions. Specifically, for example, the number average molecular weight and weight average molecular weight can be increased by lowering the polymerization temperature. The number average molecular weight and weight average molecular weight can be increased by shortening the polymerization time. Furthermore, purification can narrow the molecular weight distribution.

[0071] [Polymerization of Monomer Composition] The monomer composition used to prepare the copolymer may be, for example, a mixture of monomer components including monomer (a), monomer (b), monomer (c), and any monomer copolymerizable with these monomers, an optionally usable solvent, an optionally usable polymerization initiator, and any additives. The polymerization of the monomer composition can be carried out using a known method. Among these, cyclopentanone, water, or the like is preferably used as the solvent. Furthermore, azobisisobutyronitrile, for example, is preferably used as the polymerization initiator.

[0072] The polymer obtained by polymerizing the monomer composition can be recovered by adding a good solvent such as tetrahydrofuran to a solution containing the polymer, and then dropping the solution to which the good solvent has been added into a poor solvent such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, or hexane to coagulate the polymer, without any particular limitation.

[0073] [Purification of Polymer] The purification method used to purify the obtained polymer is not particularly limited, and known purification methods such as reprecipitation and column chromatography can be used. Among them, the reprecipitation method is preferred as the purification method. The purification of the polymer may be repeated multiple times.

[0074] Purification of a polymer by the reprecipitation method is preferably carried out, for example, by dissolving the obtained polymer in a good solvent such as tetrahydrofuran, and then dropping the obtained solution 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 to precipitate a portion of the polymer. In this way, by dropping a solution of the polymer into a mixed solvent of a good solvent and a poor solvent to perform purification, the molecular weight distribution, number average molecular weight, and weight average molecular weight of the resulting copolymer can be easily adjusted by changing the types and mixing ratios of the good solvent and poor solvent. Specifically, for example, the molecular weight of the copolymer precipitated in the mixed solvent can be increased by increasing the proportion of the good solvent in the mixed solvent.

[0075] When purifying a polymer by the reprecipitation method, a polymer precipitated in a mixed solvent of a good solvent and a poor solvent may be used as the copolymer, as long as the copolymer has the desired properties. Alternatively, a polymer not precipitated in the mixed solvent (i.e., a polymer dissolved in the mixed solvent) may be used. Here, the polymer not precipitated in the mixed solvent can be recovered from the mixed solvent by a known method such as concentration to dryness.

[0076] (Copolymer Mixture) The copolymer mixture of the present invention contains copolymer A and copolymer B, and optionally further contains a polymer other than copolymer A and copolymer B. In the copolymer mixture of the present invention, copolymer A is the copolymer of the present invention. The copolymer of the present invention can enhance resistance to pattern collapse while ensuring the clarity of the resist pattern, so the copolymer mixture of the present invention containing this copolymer can also enhance resistance to pattern collapse while ensuring the clarity of the resist pattern. Note that the copolymer mixture does not usually contain a solvent.

[0077] <Copolymer A> The copolymer of the present invention is used as the copolymer A. Details of the copolymer of the present invention have been explained above, and therefore further explanation will be omitted here.

[0078] [Proportion of Copolymer A] The content of copolymer A in the copolymer mixture is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, even more preferably 15% by mass or more, and preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less, when the total of all components of the copolymer mixture is taken as 100% by mass. If the proportion of copolymer A in the copolymer mixture is not less than the above lower limit, when the total of all components of the copolymer mixture is taken as 100% by mass, the clarity of the resist pattern can be improved. On the other hand, if the proportion of copolymer A in the copolymer mixture is not more than the above upper limit, when the total of all components of the copolymer mixture is taken as 100% by mass, the sensitivity to ionizing radiation and the like can be improved.

[0079] <Copolymer B> Copolymer B is not particularly limited and any copolymer can be used as long as it does not fall under the copolymer of the present invention and is a polymer whose main chain is cleaved by irradiation with ultraviolet light or the like. Examples of copolymers whose main chain is cleaved include copolymers described in JP-A-2022-65445. Among them, copolymer B is a copolymer having a surface free energy difference of 3 mJ / m from copolymer A. ２ It is preferable to use the above copolymers or (2) a copolymer having a monomer unit (IV) and a monomer unit (V) described later. ２ It is more preferable to use a copolymer having the above and the monomer unit (IV) and the monomer unit (V).

[0080] In the above embodiment (1), the difference between the surface free energy of copolymer B and the surface free energy of copolymer A is 3 mJ / m ２ The difference in surface free energy between copolymer B and copolymer A is 3 mJ / m ２ If the difference in surface free energy between copolymer B and copolymer A is 4 mJ / m or more, it is possible to improve the resistance to pattern collapse while ensuring the clarity of the resist pattern.２ It is preferable that the concentration is 5.5 mJ / m or more. ２ More preferably, it is 6 mJ / m or more. ２ More preferably, it is 6.5 mJ / m or more. ２ It is even more preferable that the concentration is 8 mJ / m or more. ２ More preferably, it is 9 mJ / m or more. ２ It is even more preferable that the concentration is 10 mJ / m or more. ２ It is particularly preferable that the difference between the surface free energy of copolymer B and the surface free energy of copolymer A is equal to or greater than the above lower limit, the clarity of the resist pattern can be improved. On the other hand, the difference between the surface free energy of copolymer B and the surface free energy of copolymer A is, for example, 14 mJ / m ２ less than 13 mJ / m ２ It may be less than 12 mJ / m ２ It may be less than 11 mJ / m ２ Here, the surface free energy of copolymer B may be larger or smaller than the surface free energy of copolymer A. However, since the difference between the surface free energies of copolymer B and copolymer A can be easily adjusted, it is preferable that the surface free energy of copolymer B is larger than the surface free energy of copolymer A (i.e., "surface free energy of copolymer B" > "surface free energy of copolymer A"). The surface free energy of copolymer B is 28 mJ / m ２ It is preferable that the concentration is 29 mJ / m or more. ２ More preferably, it is 30 mJ / m or more. ２ More preferably, it is 35 mJ / m or more. ２ Preferably, it is 34 mJ / m or less. ２ More preferably, it is 33 mJ / m or less. ２ It is more preferable that:

[0081] In the above embodiment (2), the copolymer B is represented by the following formula (IV): [In formula (IV), L ２ is a divalent linking group having a fluorine atom, and Ar ２represents an aromatic ring group which may have a substituent, and X ３ 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, and a monomer unit (IV) represented by the following formula (V): [In formula (V), R ５ is an alkyl group, and R ６ 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, and R ７ is a hydrogen atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom, and r and s are integers of 0 to 5, with r+s=5. When copolymer B contains monomer unit (IV) and monomer unit (V), it is possible to improve resistance to pattern collapse while ensuring the clarity of the resist pattern. Copolymer B may contain any monomer unit other than monomer unit (IV) and monomer unit (V) (excluding monomer unit (II)). However, the total proportion of monomer unit (IV) and monomer unit (V) among all monomer units constituting copolymer B is preferably 90 mol% or more, and more preferably 100 mol% (i.e., copolymer B contains only monomer unit (IV) and monomer unit (V)). Here, copolymer B may be, for example, any of a random copolymer, a block copolymer, and a ternary alternating copolymer, but is preferably a ternary alternating copolymer.

[0082] [Monomer Unit (IV)] Here, the monomer unit (IV) is a monomer unit represented by the following formula (d): [In formula (d), L ２ , Ar ２ and X ３ is the same as in formula (IV).

[0083] L in formula (IV) and formula (d) ２ Examples of the divalent linking group having a fluorine atom that can constitute the formula (I) and the formula (a) include L １ Examples of the divalent linking group include the same groups as the divalent linking group having a fluorine atom that can constitute the following group.

[0084] Ar in formula (IV) and formula (d) ２ The aromatic ring group which may have a substituent and can constitute the above formula (I) and formula (a) includes Ar １ Examples of the aromatic ring group include the same groups as the aromatic ring group which may have a substituent and can constitute the following group.

[0085] X in formula (IV) and formula (d) ３ The halogen atoms that can constitute the formula (I) and the formula (a) include X １ The halogen atoms which can constitute the above-mentioned groups are also included.

[0086] X in formula (IV) and formula (d) ３ Examples of alkylsulfonyl groups that can constitute the above include X in formula (I) and formula (a). １ Examples include groups similar to the alkylsulfonyl group which can constitute the following.

[0087] X in formula (IV) and formula (d) ３ The alkoxy group that can constitute the formula (I) and the formula (a) includes X １ Examples include the same groups as the alkoxy groups which can constitute the above.

[0088] X in formula (IV) and formula (d) ３ Examples of the acyl group that can constitute the formula (I) and the formula (a) include X １ Examples include the same groups as the acyl group which can constitute the above.

[0089] X in formula (IV) and formula (d) ３ Examples of alkyl ester groups that can constitute the above include X in formula (I) and formula (a). １ Examples include the same groups as the alkyl ester groups which can constitute the above.

[0090] X in formula (IV) and formula (d) ３ Examples of halogenated alkyl groups that can constitute the above include X in formula (I) and formula (a). １ Examples include the same groups as the halogenated alkyl groups that can constitute the above.

[0091] Among the above, X ３ is preferably a halogen atom, more preferably a chlorine atom, and X １It is more preferable that the value is the same as

[0092] The proportion of the monomer unit (IV) in copolymer B is not particularly limited, and when the total amount of all monomer units in copolymer B is taken as 100 mol%, it can be, for example, 30 mol% or more, preferably 40 mol% or more, and more preferably 45 mol% or more, and can be, for example, 70 mol% or less, preferably 60 mol% or less, and more preferably 55 mol% or less.

[0093] [Monomer Unit (V)] Here, the monomer unit (V) is a monomer unit represented by the following formula (e): [In formula (e), R ５ ~R ７ and r and s are the same as in formula (V).

[0094] R in formula (V) and formula (e) ５ , R ６ The alkyl group that can constitute R is not particularly limited, and examples thereof include unsubstituted alkyl groups having 1 to 5 carbon atoms. ５ , R ６ The alkyl group that can constitute the above is preferably a methyl group or an ethyl group.

[0095] R in formula (V) and formula (e) ６ The halogen atom that can constitute the group is not particularly limited, and examples thereof include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc. Among these, a fluorine atom is preferred as the halogen atom.

[0096] R in formula (V) and formula (e) ６ The halogenated alkyl group that can constitute the above is not particularly limited, and examples thereof include fluoroalkyl groups having 1 to 5 carbon atoms. Among these, the halogenated alkyl group is preferably a perfluoroalkyl group having 1 to 5 carbon atoms, and more preferably a trifluoromethyl group.

[0097] R in formula (V) and formula (e) ６The halogenated carboxyl group that can constitute the above group is not particularly limited, and examples thereof include a chlorocarboxyl group (-C(=O)-Cl), a fluorinated carboxyl group (-C(=O)-F), a brominated carboxyl group (-C(=O)-Br), etc.

[0098] R in formula (V) and formula (e) ７ The unsubstituted alkyl group that can constitute R is not particularly limited, and examples thereof include unsubstituted alkyl groups having 1 to 5 carbon atoms. ７ The unsubstituted alkyl group that can constitute the above is preferably a methyl group or an ethyl group.

[0099] R in formula (V) and formula (e) ７ The alkyl group substituted with fluorine atoms that can constitute the above group is not particularly limited, and examples thereof include groups having a structure in which some or all of the hydrogen atoms in the alkyl group have been substituted with fluorine atoms.

[0100] In formula (V) and formula (e), when r is 2 or more, each R ６ may be the same or different from each other. ７ may be the same or different. In formula (V) and formula (e), r=5 (i.e., s=0) is preferred.

[0101] A plurality of R's present in formula (V) and formula (e) ６ and / or R ７ are preferably all hydrogen atoms.

[0102] The monomer (e) represented by formula (e) is not particularly limited, and examples thereof include α-methylstyrene (AMS) and its derivatives such as the following monomers (e-1) to (e-12).

[0103]

[0104] From the viewpoints of easiness in preparing the copolymer B and improving the scission property of the main chain when irradiated with an electron beam or the like, the monomer (e) represented by formula (e) is preferably α-methylstyrene (e-1). That is, the copolymer B preferably has an α-methylstyrene unit.

[0105] The proportion of the monomer units (V) in copolymer B is not particularly limited, and when the total amount of all monomer units in copolymer B is taken as 100 mol%, it can be, for example, 30 mol% or more, preferably 40 mol% or more, and more preferably 45 mol% or more, and can be, for example, 70 mol% or less, preferably 60 mol% or less, and more preferably 55 mol% or less.

[0106] [Properties of Copolymer B] —Weight Average Molecular Weight (Mw)— The weight average molecular weight (Mw) of Copolymer B is preferably 100,000 or more, more preferably 125,000 or more, and even more preferably 150,000 or more; and is preferably 600,000 or less, more preferably 500,000 or less, and even more preferably 300,000 or less.

[0107] —Number Average Molecular Weight (Mn)— The number average molecular weight (Mn) of copolymer B is preferably 100,000 or more, more preferably 110,000 or more, and is preferably 300,000 or less, more preferably 200,000 or less, and even more preferably 150,000 or less.

[0108] —Molecular Weight Distribution (Mw / Mn)— The molecular weight distribution (Mw / Mn) of Copolymer B is preferably 1.20 or more, more preferably 1.25 or more, and even more preferably 1.30 or more; and is preferably 2.00 or less, more preferably 1.80 or less, and even more preferably 1.60 or less.

[0109] [Proportion of Copolymer B] The content of copolymer B in the copolymer mixture is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 75% by mass or more, and is preferably 99% by mass or less, more preferably 95% by mass or less, even more preferably 90% by mass or less, and even more preferably 85% by mass or less, when the total of all components of the copolymer mixture is taken as 100% by mass. If the proportion of copolymer B in the copolymer mixture is not less than the above lower limit, when the total of all components of the copolymer mixture is taken as 100% by mass, the sensitivity to ionizing radiation and the like can be improved. On the other hand, if the proportion of copolymer B in the copolymer mixture is not more than the above upper limit, when the total of all components of the copolymer mixture is taken as 100% by mass, the clarity of the resist pattern can be improved.

[0110] [Method for preparing copolymer B] The method for preparing copolymer B is not particularly limited. For example, copolymer B having the above-mentioned monomer unit (IV) and monomer unit (V) can be prepared by polymerizing a monomer composition containing monomer (d), monomer (e), and any monomer copolymerizable with these monomers, and then 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 the method described in the above section "Method for preparing copolymer." Furthermore, conventionally known methods such as suspension polymerization and solution polymerization can also be used as the polymerization method and purification method. Note that a polymerization initiator may be used when preparing copolymer B.

[0111] (Positive Resist Composition) The positive resist composition of the present invention comprises the copolymer of the present invention or the copolymer mixture of the present invention, and a solvent, and optionally further comprises known additives that can be incorporated into resist compositions. Specifically, the positive resist composition of the present invention comprises, for example, any one of the following (A) to (C), and a solvent: (A) the copolymer of the present invention; (B) a resist composition comprising copolymer A and copolymer B, wherein copolymer A is the copolymer of the present invention, and the difference in surface free energy between copolymer B and copolymer A is 3 mJ / m ２(C) A copolymer mixture comprising copolymer A and copolymer B, wherein copolymer A is the copolymer of the present invention, and copolymer B is a copolymer represented by the following formula (IV): [In formula (IV), L ２ is a divalent linking group having a fluorine atom, and Ar ２ represents an aromatic ring group which may have a substituent, and X ３ 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, and a monomer unit (IV) represented by the following formula (V): [In formula (V), R ５ is an alkyl group, and R ６ 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, and R ７ is a hydrogen atom, an unsubstituted alkyl group or an alkyl group substituted with a fluorine atom, r and s are integers of 0 or more and 5 or less, and r+s=5.

[0112] The copolymer of the present invention and the copolymer mixture of the present invention are able to enhance resistance to pattern collapse while ensuring the clarity of the resist pattern. Therefore, a positive resist composition of the present invention that contains this copolymer or this copolymer mixture can form a resist pattern that ensures clarity while exhibiting high resistance to pattern collapse.

[0113] It is preferable that the positive resist composition of the present invention is substantially free of components having a weight-average molecular weight of less than 1000. Specifically, the content of components having a weight-average molecular weight of less than 1000 in the positive resist composition is less than 0.05% by mass, preferably less than 0.01% by mass, and more preferably less than 0.001% by mass. If the positive resist composition is substantially free of components having a weight-average molecular weight of less than 1000, the clarity of the resist pattern can be improved.

[0114] <Copolymer and Copolymer Mixture> The copolymer of the present invention and the copolymer mixture of the present invention (copolymer A and copolymer B) have been described in detail above, and therefore further description will be omitted here.

[0115] [Proportion of Copolymer in Embodiment (A)] When the total of all components of the positive resist composition is taken as 100 mass %, the content of the copolymer in the positive resist composition is preferably 0.5 mass % or more, more preferably 1 mass % or more, and even more preferably 1.5 mass % or more, and is preferably 15 mass % or less, more preferably 10 mass % or less, and even more preferably 5 mass % or less.

[0116] [Proportion of the Copolymer Mixture in Embodiments (B) and (C)] When the positive resist composition contains a copolymer mixture (that is, when the positive resist composition contains Copolymer A and Copolymer B), the content of the copolymer mixture in the positive resist composition, relative to the total of all components of the positive resist composition being 100 mass %, is preferably 0.5 mass % or more, more preferably 1 mass % or more, and even more preferably 1.5 mass % or more, and is preferably 15 mass % or less, more preferably 10 mass % or less, and even more preferably 5 mass % or less.

[0117] <Solvent> There are no particular restrictions on the solvent, so long as it is a solvent that is able to dissolve the copolymer of the present invention, and copolymer A and copolymer B in the copolymer mixture, and it is possible to use known solvents such as those described in Japanese Patent No. 5938536. Of these, from the perspective of obtaining a positive resist composition with an appropriate viscosity and improving the coatability of the positive resist composition, it is preferable to use anisole, propylene glycol monomethyl ether acetate (PGMEA), cyclopentanone, cyclohexanone, or isoamyl acetate as the solvent.

[0118] <Preparation of Positive Resist Composition> The positive resist composition can be prepared by mixing the copolymer or copolymer mixture of the present invention (copolymer A and copolymer B), a solvent, and any known additives that can be used. There are no particular limitations on the mixing method, and mixing can be carried out by a known method. Alternatively, the positive resist composition can be prepared by mixing the components and then filtering the mixture.

[0119] [Filtration] The method for filtering the mixture is not particularly limited, and for example, it can be performed using a filter. The filter is not particularly limited, and examples include fluorocarbon, cellulose, nylon, polyester, and hydrocarbon-based filter membranes. Among these, from the viewpoint of effectively preventing impurities such as metals from being mixed into the positive resist composition from metal piping, etc., which may be used during the preparation of the copolymer of the present invention and copolymer A and copolymer B in the copolymer mixture, preferred materials for the filter include polyfluorocarbons such as polyethylene, polypropylene, polytetrafluoroethylene, and Teflon (registered trademark), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers (PFA), nylon, and composite membranes of polyethylene and nylon. Filters such as those disclosed in U.S. Pat. No. 6,103,122 may be used. Alternatively, commercially available filters such as Zeta Plus (registered trademark) 40Q manufactured by CUNO Incorporated may be used. Furthermore, the filter may contain a strong or weak cationic ion exchange resin. 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 methacrylic acid-divinylbenzene copolymers, and other types of polymers containing sulfonic or carboxylic acid groups. ＋ Counterion, NH ４ ＋ counter ions or alkali metal counter ions, e.g., K ＋ and Na ＋ Counterions are provided. The cation exchange resin preferably has hydrogen counterions. Examples of such cation exchange resins include H ＋Sulfonated styrene-divinylbenzene copolymers with counterions, such as Microlite® PrCH from Purolite Corp. Such cation exchange resins are commercially available as AMBERLYST® from Rohm and Haas.

[0120] The pore size of the filter is preferably from 0.001 μm to 1 μm, inclusive. If the pore size of the filter is within this range, it is possible to sufficiently prevent impurities such as metals from being mixed into the positive resist composition.

[0121] (Method of Forming Resist Pattern) The positive resist composition of the present invention described above can be suitably used for forming a resist pattern. The method of forming a resist pattern includes at least the following steps: forming a resist film using the positive resist composition of the present invention (resist film formation step), exposing the resist film (exposure step), and developing the exposed resist film (development step). The method of forming a resist pattern may include further steps in addition to the resist film formation step, exposure step, and development step. Specifically, the method of forming a resist pattern may include a step of forming an underlayer film on the substrate on which the resist film will be formed (underlayer film formation step) before the resist film formation step. The method of forming a resist pattern may also include a step of heating the exposed resist film (post-exposure bake (PEB) step) between the exposure step and the development step. The method of forming a resist pattern may also include a step of removing a developer after the development step (developer removal step). After forming a resist pattern by the method of forming a resist pattern, the method of forming a resist pattern may also include a step of etching the underlayer film and / or the substrate (etching step). In this method of forming a resist pattern, a positive resist composition of the present invention is used as the positive resist composition, so it is possible to form a resist pattern that is highly resistant to pattern collapse while ensuring clarity.

[0122] <Underlayer Film Formation Step> In the underlayer film formation step, which can be optionally performed before the resist film formation step, an underlayer film is formed on a substrate. By providing the underlayer film on the substrate, the surface of the substrate is made 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.

[0123] The inorganic underlayer film can be formed by applying an inorganic material onto a substrate and then baking it, etc. Examples of inorganic materials include silicon-based materials.

[0124] The organic underlayer film can be formed by applying an organic material to a substrate to form a coating film and drying it. The organic material is not limited to those sensitive to light or electron beams, and can be, for example, a resist material or resin material commonly used in the semiconductor and liquid crystal fields. Among these, the organic material is preferably a material capable of forming an organic underlayer film that can be etched, particularly dry etched. With such an organic material, the organic underlayer film can be etched using a pattern formed by processing a resist film, thereby transferring the pattern to the underlayer film and forming a pattern in the underlayer film. Among these, the organic material is preferably a material capable of forming an organic underlayer film that can be etched by oxygen plasma etching or the like. Examples of organic materials used to form the organic underlayer film include AL412 from Brewer Science.

[0125] The organic material can be applied by a conventional method using spin coating or a spinner. The method for drying the coating film may be any method capable of volatilizing the solvent contained in the organic material, such as baking. The baking conditions are not particularly limited, but the baking temperature is preferably 80°C or higher and 300°C or lower, and more preferably 200°C or higher and 300°C or lower. The baking time is preferably 30 seconds or longer, more preferably 60 seconds or longer, and preferably 500 seconds or shorter, more preferably 400 seconds or shorter, even more preferably 300 seconds or shorter, and particularly preferably 180 seconds or shorter. The thickness of the underlayer film after drying the coating film is not particularly limited, but is preferably 10 nm or higher and 100 nm or lower.

[0126] [Substrate] Here, the substrate on which the underlayer film or resist film can be formed in the resist pattern forming method is not particularly limited, and examples that can be used include a substrate having an insulating layer and copper foil provided on the insulating layer, which is used in the manufacture of printed circuit boards, etc.; and a mask blank having a light-shielding layer formed on a substrate.

[0127] The substrate material may be, for example, metal (silicon, copper, chromium, iron, aluminum, etc.), glass, titanium oxide, silicon dioxide (SiO ２ Examples of suitable substrates include inorganic materials such as silica and mica; nitrides such as SiN; oxynitrides 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, as the substrate, a cylindrical structure can be formed.

[0128] The size and shape of the substrate are not particularly limited. The surface of the substrate may be smooth, curved, or uneven, and may be a thin plate-shaped substrate.

[0129] The surface of the substrate may be subjected to a surface treatment as necessary. For example, in the case of a substrate having hydroxyl groups on its surface layer, the surface of the substrate can be treated using a silane coupling agent capable of reacting with the hydroxyl groups. This changes the surface layer of the substrate from hydrophilic to hydrophobic, thereby improving the adhesion between the substrate and the underlayer film or between the substrate and the resist layer. In this case, the silane coupling agent is not particularly limited, but hexamethyldisilazane is preferred.

[0130] <Resist film forming step> In the resist film forming step, the positive resist composition of the present invention is applied onto a workpiece such as a substrate to be processed using the resist pattern (or onto an underlayer film if an underlayer film is formed), and the applied positive resist composition is dried to form a resist film.

[0131] The coating method and drying method for the positive resist composition are not particularly limited, and methods commonly used in forming resist films can be used. Among these, heating (prebaking) is preferred as the drying method. From the viewpoint of improving the film density of the resist film, the prebaking 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 reducing changes in the molecular weight and molecular weight distribution of the copolymer of the present invention and copolymer A and copolymer B in the copolymer mixture of the present invention in the resist film before and after prebaking, the prebaking 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 improving the film density of the resist film formed after prebaking, the prebaking time is preferably 10 seconds or longer, more preferably 20 seconds or longer, and even more preferably 30 seconds or longer. From the viewpoint of further reducing changes in the molecular weight and molecular weight distribution of the copolymer of the present invention, and of the copolymer A and the copolymer B in the copolymer mixture of the present invention, in the resist film before and after prebaking, the prebaking time is preferably 10 minutes or less, more preferably 5 minutes or less, and even more preferably 3 minutes or less.

[0132] In the exposure process, the resist film formed in the resist film formation process is irradiated with ionizing radiation or the like to write a desired pattern. Note that the electron beam irradiation can be performed using a known writing device such as an electron beam writing device or an EUV exposure device.

[0133] <Post-exposure bake step> In the post-exposure bake step, which may be optionally performed, the resist film exposed in the exposure step is heated. By performing the post-exposure bake step, the surface roughness of the resist pattern can be reduced.

[0134] Here, the heating temperature is preferably 70° C. or higher, more preferably 80° C. or higher, and even more preferably 90° C. or higher, and is preferably 200° C. or lower, more preferably 170° C. or lower, and even more preferably 150° C. or lower. When 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.

[0135] The time for heating the resist film in the post-exposure bake step (heating time) is preferably 10 seconds or longer, more preferably 20 seconds or longer, and even more preferably 30 seconds or longer. A heating time of 10 seconds or longer can further improve the clarity of the resist pattern while sufficiently reducing the surface roughness of the resist pattern. On the other hand, from the viewpoint of production efficiency, the heating time is, for example, preferably 10 minutes or shorter, more preferably 5 minutes or shorter, and even more preferably 3 minutes or shorter.

[0136] The method for heating the resist film in the post-exposure bake step is not particularly limited, and examples thereof include a method of heating the resist film on a hot plate, a method of heating the resist film in an oven, and a method of blowing hot air onto the resist film.

[0137] <Developing Step> In the developing step, the exposed resist film (or the exposed and heated resist film if a post-exposure bake step has been performed) is developed to form a developed film on the workpiece. Here, the resist film can be developed, for example, by contacting the resist film with a developer. The method for contacting the resist film 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.

[0138] [Developer] The developer can be appropriately selected depending on the properties of the copolymer of the present invention and the copolymer A and copolymer B in the copolymer mixture of the present invention. Specifically, when selecting the developer, it is preferable to select a developer that does not dissolve the resist film before the exposure step, but can dissolve the exposed portion of the resist film after the exposure step. The developer may be used alone or in a mixture of two or more types in any ratio. The developer may be, for example, 1,1,1,2,3,4,4,5,5,5-decafluoropentane (CF ３ CFHCFHCF ２ CF ３ ), 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, and other hydrofluorocarbons; 2,2-dichloro-1,1,1-trifluoroethane, 1,1-dichloro-1-fluoroethane, 1,1-dichloro-2,2,3,3,3-pentafluoropropane (CF ３ CF ２ CHCl ２ ), 1,3-dichloro-1,1,2,2,3-pentafluoropropane (CClF ２ CF ２ CHClF), methyl nonafluorobutyl ether (CF ３ CF ２ CF ２ CF ２ OCH ３), methyl nonafluoroisobutyl ether, ethyl nonafluorobutyl ether (CF ３ CF ２ CF ２ CF ２ O.C. ２ H ５ ), ethyl nonafluoroisobutyl ether, perfluorohexyl methyl ether (CF ３ CF ２ CF (OCH ３ ) C ３ F ７ ) and hydrofluoroethers such as CF ４ , C ２ F ６ , C ３ F ８ , C ４ F ８ , C ４ F １０ , C ５ F １２ , C ６ F １２ , C ６ F １４ , C ７ F １４ , C ７ F １６ , C ８ F １８ , C ９ F ２０ Examples of solvents that can be used include perfluorocarbons such as fluorine-based solvents, alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, and 3-pentanol, alkyl acetates such as amyl acetate and hexyl acetate, mixtures of fluorine-based solvents and alcohols, mixtures of fluorine-based solvents and alkyl acetates, mixtures of alcohols and alkyl acetates, and mixtures of fluorine-based solvents, alcohols, and alkyl acetates. Of these, from the viewpoint of further enhancing the clarity of the resist pattern, it is preferable to use an alcohol such as 2-butanol or isopropyl alcohol for development.

[0139] The temperature of the developer during development is not particularly limited, but may be, for example, 5° C. to 40° C. The development time may be, for example, 10 seconds to 4 minutes.

[0140] <Developer Removal Step> In the developer removal step optionally included in the resist pattern formation method, the developer is removed from the developed resist film to form a resist pattern on the workpiece. The developer can be removed by air blowing using a gas such as nitrogen, or by rinsing using a rinse solution. Here, the method for contacting the developed resist film with the rinse solution in the rinse process is not particularly limited, and known techniques such as immersing the resist film in the rinse solution or applying the rinse solution to the resist film can be used. Specific examples of rinse solutions include the same developers as those exemplified in the "Development Step" section, as well as hydrocarbon solvents such as octane and heptane, and water. Here, the rinse solution may contain a surfactant. When selecting a rinse solution, it is preferable to select a rinse solution that is less likely to dissolve the resist film before the exposure step than the developer used in the development step and that is easily mixed with the developer.

[0141] The temperature of the rinse solution during rinsing is not particularly limited, but may be, for example, 5° C. to 40° C. The rinse time may be, for example, 5 seconds to 3 minutes.

[0142] The developer and rinse may be filtered before use, for example, by the filter method described above in the section "Preparation of a Positive Resist Composition."

[0143] <Etching Step> In the etching step, which can be optionally performed, the underlayer film and / or the substrate are etched using the above-mentioned resist pattern as a mask to form a pattern on the underlayer film and / or the substrate. In this case, the number of etchings is not particularly limited, and may be one or more times. Furthermore, the etching may be dry etching or wet etching, but dry etching is preferred. Dry etching can be performed using a known dry etching device. The etching gas used in dry etching can be appropriately selected depending on the elemental composition of the underlayer film and the substrate to be etched, etc. Examples of the etching gas include CHF ３ , C.F. ４ , C ２ F ６ , C ３ F ８ , SF ６ fluorine-based gases such as Cl ２ , BCl ３ Chlorine-based gases such as O ２ , O ３ , H ２ Oxygen-based gases such as O; ２ , N.H. ３ , CO, CO ２ , C.H. ４ , C ２ H ２ , C ２ H ４ , C ２ H ６ , C ３ H ４ , C ３ H ６ , C ３ H ８ , HF, HI, HBr, HCl, NO, BCl ３ reducing gases such as He, N ２ , and inert gases such as Ar. These gases may be used alone or in combination of two or more. For dry etching of an inorganic underlayer film, an oxygen-based gas is usually used. For dry etching of a substrate, a fluorine-based gas is usually used, and a mixture of a fluorine-based gas and an inert gas is preferably used.

[0144] Furthermore, if necessary, the underlayer film remaining on the substrate may be removed before or after etching the substrate. When the underlayer film is removed before etching the substrate, the underlayer film may be a patterned or unpatterned underlayer film.

[0145] Here, examples of methods for removing the underlayer film include the above-mentioned dry etching. In the case of an inorganic underlayer film, the underlayer film may be removed by contacting the underlayer film with a liquid such as a basic or acidic liquid, preferably a basic liquid. The basic liquid is not particularly limited, and examples thereof include alkaline hydrogen peroxide. The method for removing the underlayer film by wet stripping using alkaline hydrogen peroxide is not particularly limited as long as it allows the underlayer film and alkaline hydrogen peroxide to come into contact with each other for a certain period of time under heated conditions. Examples include a method of immersing the underlayer film in heated alkaline hydrogen peroxide, a method of spraying alkaline hydrogen peroxide onto the underlayer film in a heated environment, and a method of coating the underlayer film with heated alkaline hydrogen peroxide. After performing any of these methods, the substrate is washed with water and dried to obtain a substrate from which the underlayer film has been removed.

[0146] Below, an example of a method for forming a resist pattern using the positive resist composition of the present invention and a method for etching an underlayer film and a substrate using the formed resist pattern will be described. However, since the substrate used in the following example and the conditions in each step can be the same as the substrate and conditions in each step described above, explanations will be omitted below. It should be noted that the method for forming a resist pattern is not limited to the method shown in the following example.

[0147] An example of the resist pattern forming method is a resist pattern forming method using an electron beam or EUV, which includes the above-mentioned underlayer film forming step, resist film forming step, exposure step, developing step, and developer removing step.An example of the etching method is a method in which the resist pattern formed by the resist pattern forming method is used as a mask, and includes an etching step.

[0148] Specifically, in the underlayer film formation step, an inorganic material is applied to a substrate and baked to form an inorganic underlayer film. Next, in the resist film formation step, a positive resist composition of the present invention is applied to the inorganic underlayer film formed in the underlayer film formation step, and the composition is dried to form a resist film. Then, in the exposure step, the resist film formed in the resist film formation step is irradiated with EUV light to write a desired pattern. Furthermore, in the development step, the resist film exposed in the exposure step is brought into contact with a developer to develop the resist film, thereby forming a resist pattern on the underlayer film. Then, in the developer removal step, the resist film developed in the development step is brought into contact with a rinse solution to rinse the developed resist film. Then, in the etching step, the underlayer film is etched using the resist pattern as a mask to form a pattern in the underlayer film. Next, the substrate is etched using the patterned underlayer film as a mask to form a pattern on the substrate.

[0149] <Etching Resistance of Resist Film> The resist film obtained by the above-described method for forming a resist pattern has excellent etching resistance, and in particular, excellent dry etching resistance. Note that the higher the proportion of carbon content per unit volume of the copolymer of the present invention, or of Copolymer A and Copolymer B in the copolymer mixture of the present invention, contained in the positive resist composition, the more excellent the dry etching resistance of the resist film tends to be.

[0150] <Laminate> The laminate obtained by the above-described method for forming a resist pattern includes a substrate and a resist film formed on the substrate. Such a laminate can be suitably used as a printed circuit board.

[0151] 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, comparative examples, and preparation examples, the proportion of monomer units in the copolymer, the number average molecular weight, weight average molecular weight, molecular weight distribution, and surface free energy of the copolymer were measured by the following methods. Here, the surface free energy was measured only for Examples 1, 2, 5, 10, and 11, and Preparation Examples 1 and 2. In the examples and comparative examples, the γ value, Eth, pattern collapse resistance, and resist residue were measured or evaluated by the following methods.

[0152] <Proportion of Monomer Units in Copolymer> For the copolymer obtained in the preparation example, １ The proportion of the monomer unit in the copolymer was calculated using H-NMR. Specifically, the copolymer obtained in the preparation example was dissolved in chloroform-d, 99.8% (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to a concentration of 10% by mass, and the solution was measured using a nuclear magnetic resonance spectrometer (manufactured by JEOL Ltd., 400 mHz). The proportion of the monomer unit in the copolymer was calculated from the measurement results.

[0153] <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 copolymers A and B obtained in the Examples, Comparative Examples, and Preparation Examples were measured using gel permeation chromatography, and the molecular weight distribution (Mw / Mn) was calculated. Specifically, a gel permeation chromatograph (HLC-8220, manufactured by Tosoh Corporation) was used with tetrahydrofuran as a developing solvent to determine the number average molecular weight (Mn) and weight average molecular weight (Mw) of the copolymers in terms of standard polystyrene. The molecular weight distribution (Mw / Mn) was then calculated. It was confirmed that each of copolymers A and B contained substantially no components having a weight average molecular weight of less than 1,000 (less than 0.05% by mass).

[0154] <Surface Free Energy> Surface free energy was measured using the copolymers obtained in Examples 1, 2, 5, 10, and 11, and Preparation Examples 1 and 2. Specifically, the copolymer was first dissolved in isoamyl acetate as a solvent to prepare a positive resist composition with a concentration of 2% by mass. Next, using a spin coater (MS-A150, manufactured by Mikasa Co., Ltd.), the positive resist composition was applied to a silicon wafer with a diameter of 4 inches to a thickness of 50 nm. The applied positive resist composition was then heated on a hot plate at 170°C for 1 minute to form a film (resist film) on the silicon wafer. For the obtained film (resist film), the contact angles of two solvents (water and diiodomethane) with known surface tensions, polarity terms (p), and dispersion terms (d) were measured using a contact angle meter (Drop Master 700, manufactured by Kyowa Interface Science) under the following conditions, and the surface free energy was evaluated using the Owens-Wendt (extended Fowkes equation) method, and the surface free energy of the film (resist film) was calculated. <<Contact angle measurement conditions>> Needle: metal needle 22G (water), Teflon (registered trademark) coated 22G (diiodomethane) Waiting time: 1000 ms Liquid volume: 1.8 μL Liquid contact recognition: water 50 dat, diiodomethane 100 dat Temperature: 23°C

[0155] <γ Value> The γ value was measured using the positive resist compositions obtained in the examples and comparative examples. Specifically, first, using a spin coater (MS-A150, manufactured by Mikasa Co., Ltd.), the positive resist composition was applied to a silicon wafer with a diameter of 4 inches to a thickness of 50 nm. Next, the applied positive resist composition was heated on a hot plate at 170°C for 1 minute to form a resist film on the silicon wafer (resist film formation process). Then, using an electron beam lithography device (ELS-S50, manufactured by Elionix Co., Ltd.), multiple patterns (dimensions: 500 μm × 500 μm) with different electron beam irradiation doses were written on the resist film (exposure process). Furthermore, the exposed resist film was heated on a hot plate at 100°C for 1 minute (post-exposure bake process). The heated resist film was subjected to a development process using isopropyl alcohol (IPA) as a developer at 23°C for 1 minute (development process). Thereafter, the developer was removed by nitrogen blowing (developer removal process). The electron beam irradiation dose was 4 μC / cm ２ to 200 μC / cm ２ Within the range of 4 μC / cm ２ Next, the thickness of the resist film in the written portion was measured using an optical film thickness meter (Lambda Ace, manufactured by SCREEN Semiconductor Solutions), and a sensitivity curve was created showing the relationship between the common logarithm of the total dose of 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). The γ value was calculated using the following formula. The results are shown in Tables 2 and 3. In the following formula, E ０ is the logarithm of the total irradiation dose obtained by fitting the sensitivity curve to a quadratic function in the range of the residual film ratio of 0.20 to 0.80 and substituting the residual film ratio of 0 for the obtained quadratic function (a function of the residual film ratio and the common logarithm of the total irradiation dose). １is the logarithm of the total irradiation dose obtained when a line (an approximation line of the slope of the sensitivity curve) connecting the point of the residual film ratio 0 and the point of the residual film ratio 0.50 on the obtained quadratic function is created and a residual film ratio of 1.00 is substituted for the obtained line (a function of the residual film ratio and the common logarithm of the total irradiation dose).The following formula represents the slope of the line between the residual film ratio 0 and the residual film ratio 1.00.Note that the larger the γ value, the greater the slope of the sensitivity curve, indicating that a clear pattern can be formed well.Here, if the γ value is 10 or more, it can be said that the clarity of the resist pattern is ensured.

[0156] <Eth> A resist film was formed on a silicon wafer in the same manner as in the evaluation method for the "γ value." The initial thickness T ０ was measured using an optical film thickness meter (Lambda Ace, manufactured by SCREEN Semiconductor Solutions). The total electron beam irradiation dose Eth (μC / cm) was calculated when the residual film ratio of the straight line (approximation line of the slope of the sensitivity curve) obtained in calculating the γ value became 0. ２ The results are shown in Tables 2 and 3. The smaller the Eth value, the higher the sensitivity of the resist film and the higher the efficiency of forming a resist pattern.

[0157] <Resistance to Pattern Collapse> Resistance to pattern collapse was evaluated using the positive resist compositions obtained in the examples and comparative examples. Specifically, first, using a spin coater (MS-A150 manufactured by Mikasa), the positive resist composition was applied to a silicon wafer with a diameter of 4 inches to a thickness of 50 nm. Next, the applied positive resist composition was heated on a hot plate at a temperature of 120°C for 1 minute to form a resist film on the silicon wafer (resist film formation step). The resist film had a thickness of 50 nm. Then, using an electron beam lithography system (ELS-S50 manufactured by Elionix), the resist film was exposed at an optimum exposure dose (Eop) to write a pattern (exposure step). The exposed resist film was heated on a hot plate at 90°C for 1 minute (post-exposure bake step). The resist film after the post-exposure bake step was subjected to a development treatment using isopropyl alcohol (IPA) as a developer at a temperature of 23°C for 1 minute (development step). The developer was then removed by nitrogen blowing to form a resist pattern (developer removal step). The formed resist patterns were then observed for the presence or absence of pattern collapse. The optimum exposure dose (Eop) was appropriately set, with a value approximately twice the Eth as a guide. The lines (unexposed areas) and spaces (exposed areas) of the resist pattern were each set to 20 nm. The suppression of pattern collapse was evaluated according to the following criteria. The results are shown in Tables 2 and 3. A: No pattern collapse B: Pattern collapse occurred in 1 to 3 locations C: Pattern collapse occurred in 4 or more locations

[0158] <Resist Residue> The positive resist compositions obtained in the examples and comparative examples were used to evaluate resist residue. Specifically, first, a spin coater (MS-A150, manufactured by Mikasa Co., Ltd.) was used to apply the positive resist composition to a silicon wafer with a diameter of 4 inches. Next, the applied positive resist composition was heated on a hot plate at a temperature of 180°C for 3 minutes to form a resist film with a thickness of 40 nm on the silicon wafer (resist film formation step). Then, an electron beam lithography system (ELS-S50, manufactured by Elionix Co., Ltd.) was used to expose the resist film at an optimum exposure dose (Eop) to write a pattern (exposure step). Thereafter, a development process was carried out for 1 minute at a temperature of 23°C using isopropyl alcohol (IPA) as the developer (development step). The resist pattern was then rinsed for 10 seconds using a fluorine-based solvent (3M Corporation, Novec (registered trademark) 7100, methyl nonafluorobutyl ether, freezing point: -135°C, boiling point: 61°C) with a surface tension of 13.6 mN / m as a rinse solution (developer removal step). The resist pattern was then observed at a magnification of 100,000 times using a scanning electron microscope (SEM), and the extent of residue remaining in the resist pattern was evaluated according to the following criteria. Residue remaining in the resist pattern can be confirmed in the SEM image as bright "dots" or the like compared to line pattern areas where no residue is present. The results are shown in Tables 2 and 3. A: No residue was confirmed in the hp25nm resist pattern. B: Very little residue was confirmed in the hp25nm resist pattern, but within the acceptable range. C: A large amount of residue was confirmed in the hp25nm resist pattern, outside the acceptable range.

[0159] Example 1 Preparation of Copolymer A monomer composition A1 containing 0.7207 g of 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl α-chloroacrylate (ACAFPh) as the monomer (a), 2.5004 g of 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylate (ACAHFB) as the monomer (b), 3.0000 g of α-methylstyrene as the monomer (c) (corresponding to approximately 2.34 equivalents when the total of ACAFPh and ACAHFB is taken as 1 equivalent), 0.0048 g of azobisisobutyronitrile as a polymerization initiator, and 1.5565 g of cyclopentanone as a solvent was placed in a glass container, the glass container was sealed and purged with nitrogen, and the mixture was stirred in a constant temperature bath at 78°C under a nitrogen atmosphere for 6 hours. After that, the temperature was returned to room temperature, and the glass container was opened to the atmosphere. Then, 10 g of THF was added to the obtained solution. Then, the solution to which THF had been added was dropped into 100 g of MeOH as a solvent to precipitate a polymer. Thereafter, the solution containing the precipitated polymer was filtered using a Kiriyama funnel to obtain a white coagulated product (copolymer A1). The ratio of the monomer units in the obtained copolymer A1 was １ Calculations using H-NMR revealed that copolymer A1 was a copolymer containing 10 mol% of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units, 40 mol% of α-chloroacrylate-2,2,3,3,4,4,4-heptafluorobutyl units, and 50 mol% of α-methylstyrene units. The number average molecular weight, weight average molecular weight, molecular weight distribution, and surface free energy of the resulting copolymer A1 were then measured. The results are shown in Table 1.

[0160] <Preparation of Positive Resist Composition> The copolymer A1 prepared as described above was dissolved in isoamyl acetate as a solvent to prepare a positive resist composition with a concentration of 2 mass%. The γ value, Eth, pattern collapse resistance, and resist residue of the obtained positive resist composition were measured or evaluated. The results are shown in Table 2.

[0161] Example 2 In the preparation of the copolymer, instead of the monomer composition A1, 1.4413 g of α-chloroacrylic acid-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as the monomer (a), 1.8753 g of α-chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl (ACAHFB) as the monomer (b), 3.0000 g of α-methylstyrene as the monomer (c) (corresponding to approximately 2.34 equivalents when the total of ACAFPh and ACAHFB is 1 equivalent), 0.0048 g of azobisisobutyronitrile as the polymerization initiator, and 1.5803 g of cyclopentanone as the solvent were used to prepare copolymer A2. Various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0162] (Example 3) In the preparation of the copolymer, instead of the monomer composition A1, 2.1620 g of α-chloroacrylic acid-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as monomer (a), 1.2502 g of α-chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl (ACAHFB) as monomer (b), 3.0000 g of α-methylstyrene as monomer (c) (equivalent to approximately 2.34 equivalents when the total of ACAFPh and ACAHFB is 1 equivalent), 0.0048 g of azobisisobutyronitrile as a polymerization initiator, and 1.6042 g of cyclopentanone as a solvent were used to prepare copolymer A3. Various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0163] Example 4 In the preparation of the copolymer, instead of the monomer composition A1, 2.8826 g of α-chloroacrylic acid-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as the monomer (a), 0.6251 g of α-chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl (ACAHFB) as the monomer (b), 3.0000 g of α-methylstyrene as the monomer (c) (corresponding to approximately 2.34 equivalents when the total of ACAFPh and ACAHFB is 1 equivalent), 0.0048 g of azobisisobutyronitrile as the polymerization initiator, and 1.6281 g of cyclopentanone as the solvent were used to prepare copolymer A4. Various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0164] Example 5 In the preparation of the copolymer, instead of the monomer composition A1, 0.7207 g of α-chloroacrylic acid-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as the monomer (a), 2.0711 g of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl (ACAPFP) as the monomer (b), 3.0000 g of α-methylstyrene as the monomer (c) (corresponding to approximately 2.34 equivalents when the total of ACAFPh and ACAPFP is 1 equivalent), 0.0048 g of azobisisobutyronitrile as a polymerization initiator, and 1.4491 g of cyclopentanone as a solvent were used to prepare copolymer A5. Various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0165] (Example 6) In the preparation of the copolymer, instead of the monomer composition A1, 1.4413 g of α-chloroacrylic acid-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as the monomer (a), 1.5534 g of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl (ACAPFP) as the monomer (b), 3.0000 g of α-methylstyrene as the monomer (c) (corresponding to approximately 2.34 equivalents when the total of ACAFPh and ACAPFP is 1 equivalent), 0.0048 g of azobisisobutyronitrile as a polymerization initiator, and 1.4999 g of cyclopentanone as a solvent were used to prepare copolymer A6, except that various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0166] (Example 7) In the preparation of the copolymer, instead of the monomer composition A1, 2.1620 g of α-chloroacrylic acid-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as the monomer (a), 1.0356 g of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl (ACAPFP) as the monomer (b), 3.0000 g of α-methylstyrene as the monomer (c) (equivalent to approximately 2.34 equivalents when the total of ACAFPh and ACAPFP is 1 equivalent), 0.0048 g of azobisisobutyronitrile as a polymerization initiator, and 1.5506 g of cyclopentanone as a solvent were used to prepare copolymer A7, except that various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0167] (Example 8) In the preparation of the copolymer, instead of the monomer composition A1, 2.8826 g of α-chloroacrylic acid-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as the monomer (a), 0.5178 g of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl (ACAPFP) as the monomer (b), 3.0000 g of α-methylstyrene as the monomer (c) (equivalent to approximately 2.34 equivalents when the total of ACAFPh and ACAPFP is 1 equivalent), 0.0048 g of azobisisobutyronitrile as a polymerization initiator, and 1.6013 g of cyclopentanone as a solvent were used to prepare copolymer A8, except that various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0168] (Example 9) In the preparation of the copolymer, instead of the monomer composition A1, 0.7207 g of α-chloroacrylic acid-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as the monomer (a), 1.6361 g of α-chloroacrylic acid 2,2,2-trifluoroethyl (ACATFE) as the monomer (b), 3.0000 g of α-methylstyrene as the monomer (c) (corresponding to approximately 2.34 equivalents when the total of ACAFPh and ACATFE is 1 equivalent), 0.0048 g of azobisisobutyronitrile as a polymerization initiator, and 1.4021 g of cyclopentanone as a solvent were used to prepare copolymer A9. Various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0169] Example 10 In the preparation of the copolymer, instead of the monomer composition A1, 0.5731 g of α-chloroacrylic acid-1-phenyl-2,2,2-trifluoroethyl (ACAHFPh) as the monomer (a), 2.5004 g of α-chloroacrylic acid 2,2,2-trifluoroethyl (ACAHFB) as the monomer (b), 3.0000 g of α-methylstyrene as the monomer (c) (corresponding to approximately 2.34 equivalents when the total of ACAHFPh and ACAHFB is 1 equivalent), 0.0048 g of azobisisobutyronitrile as the polymerization initiator, and 1.5196 g of cyclopentanone as the solvent were used to prepare copolymer A10. Various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0170] (Example 11) In the preparation of the copolymer, instead of the monomer composition A1, 0.5731 g of α-chloroacrylic acid-1-phenyl-2,2,2-trifluoroethyl (ACAHFPh) as the monomer (a), 2.0711 g of α-chloroacrylic acid 2,2,2-trifluoroethyl (ACAPFP) as the monomer (b), 3.0000 g of α-methylstyrene as the monomer (c) (corresponding to approximately 2.34 equivalents when the total of ACAHFPh and ACAPFP is 1 equivalent), 0.0048 g of azobisisobutyronitrile as the polymerization initiator, and 1.4122 g of cyclopentanone as the solvent were used to prepare the copolymer A11. Various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0171] Example 12 In the preparation of the copolymer, instead of the monomer composition A1, 0.5731 g of α-chloroacrylic acid-1-phenyl-2,2,2-trifluoroethyl (ACAHFPh) as the monomer (a), 1.6361 g of α-chloroacrylic acid 2,2,2-trifluoroethyl (ACATFE) as the monomer (b), 3.0000 g of α-methylstyrene as the monomer (c) (corresponding to approximately 2.34 equivalents when the total of ACAHFPh and ACATFE is 1 equivalent), 0.0048 g of azobisisobutyronitrile as the polymerization initiator, and 1.3781 g of cyclopentanone as the solvent were used to prepare copolymer A12. Various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0172] (Example 13) In the preparation of the copolymer, instead of the monomer composition A1, 0.7221 g of α-chloroacrylic acid-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as the monomer (a), 2.9394 g of α-chloroacrylic acid 2,2,3,3,4,4,5,5,5-nonafluoropentyl (ACANFP) as the monomer (b), 3.0000 g of α-methylstyrene as the monomer (c) (corresponding to approximately 2.34 equivalents when the total of ACAFPh and ACANFP is 1 equivalent), 0.0067 g of azobisisobutyronitrile as a polymerization initiator, and 1.6587 g of cyclopentanone as a solvent were used to prepare copolymer A13. Various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0173] Example 14 In the preparation of the copolymer, instead of the monomer composition A1, 1.4442 g of α-chloroacrylic acid-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as the monomer (a), 2.3990 g of α-chloroacrylic acid 2,2,3,3,4,4,5,5,5-nonafluoropentyl (ACANFP) as the monomer (b), 3.0000 g of α-methylstyrene as the monomer (c) (corresponding to approximately 2.34 equivalents when the total of ACAFPh and ACANFP is 1 equivalent), 0.0066 g of azobisisobutyronitrile as the polymerization initiator, and 1.6556 g of cyclopentanone as the solvent were used to prepare copolymer A14. Various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0174] Comparative Example 1 In the preparation of the copolymer, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in place of the monomer composition A1, a monomer composition A15 containing 3.0000 g of 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl α-chloroacrylate (ACAFPh) as the monomer (a), 0.0396 g of azobisisobutyronitrile as a polymerization initiator, and 7.0924 g of cyclopentanone as a solvent was used to prepare copolymer A15. The results are shown in Tables 1 and 2.

[0175] Comparative Example 2 In the preparation of the copolymer, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in place of the monomer composition A1, a monomer composition A16 containing 3.0000 g of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as the monomer (a), 2.4930 g of α-methylstyrene as the monomer (c) (corresponding to approximately 2.34 equivalents when ACAFPh is taken as 1 equivalent), and 0.0040 g of azobisisobutyronitrile as a polymerization initiator was used to prepare copolymer A16. The results are shown in Tables 1 and 2.

[0176] (Comparative Example 3) In the preparation of the copolymer, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in place of the monomer composition A1, a monomer composition A17 containing 3.0000 g of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as the monomer (a), 0.5389 g of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl (ACAPFP) as the monomer (b), 0.1980 g of azobisisobutyronitrile as a polymerization initiator, and 8.9801 g of cyclopentanone as a solvent was used to prepare copolymer A17. The results are shown in Tables 1 and 2.

[0177] Comparative Example 4 In the preparation of the copolymer, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in place of the monomer composition A1, a monomer composition A18 containing 3.0000 g of 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl α-chloroacrylate (ACAFPh) as the monomer (a), 0.6506 g of 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylate (ACAHFB) as the monomer (b), 0.1980 g of azobisisobutyronitrile as a polymerization initiator, and 8.9801 g of cyclopentanone as a solvent was used to prepare copolymer A18. The results are shown in Tables 1 and 2.

[0178] Comparative Example 5 In the preparation of the copolymer, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in place of the monomer composition A1, a monomer composition A19 containing 3.0000 g of 2,2,3,3,3-pentafluoropropyl α-chloroacrylate (ACAPFP) as the monomer (b), 3.4764 g of α-methylstyrene as the monomer (c) (corresponding to approximately 2.34 equivalents when ACAPFP is taken as 1 equivalent), 0.0055 g of azobisisobutyronitrile as a polymerization initiator, and 1.6205 g of cyclopentanone as a solvent was used to prepare copolymer A19. The results are shown in Tables 1 and 2.

[0179] (Preparation Example 1) <Preparation of Copolymer> A monomer composition B1 containing 3.0000 g of α-chloroacrylic acid-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as the monomer (d), 1.0659 g of α-methylstyrene as the monomer (e), and 1.8000 g of ion-exchanged water as a solvent was added to a glass ampoule containing a stirrer, and the ampoule was sealed. The system was pressurized and depressurized with nitrogen gas 10 times to remove oxygen. Next, the system was heated to 60°C, and the reaction was carried out for 8 hours to obtain a reaction solution in which a polymer was suspended. The polymer in the reaction solution was then recovered by filtration. Next, 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) 33:67), causing precipitation of a white coagulum. This coagulated material was recovered again by filtration, and the polymer recovered by filtration was dissolved in 10 g of THF. The resulting solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 33:67) to precipitate a white coagulated material (copolymer B1). Thereafter, the solution containing the precipitated copolymer B1 was filtered using a Kiriyama funnel to obtain a white copolymer B1. The proportion of the monomer units in the resulting copolymer B1 was １ Calculation using H-NMR revealed that copolymer B1 contained 55 mol% of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and 45 mol% of α-methylstyrene units. The number average molecular weight, weight average molecular weight, molecular weight distribution, and surface free energy of the resulting copolymer B1 were then measured. The results are shown in Table 1.

[0180] (Preparation Example 2) In the preparation of the copolymer, various operations and measurements were carried out in the same manner as in Preparation Example 2, except that in place of the monomer composition B1, a monomer composition B2 containing 2.3855 g of 1-phenyl-2,2,2-trifluoroethyl α-chloroacrylate (ACAHFPh) as the monomer (d), 1.0659 g of α-methylstyrene as the monomer (e), and 1.8000 g of ion-exchanged water as a solvent was used to prepare copolymer B2. The results are shown in Table 1.

[0181] Example 15 Preparation of Positive Resist Composition The copolymer A1 prepared as described above and the copolymer B1 prepared as described above were dissolved in isoamyl acetate as a solvent so that the mass ratio of copolymer A1 to copolymer B1 was 5:95 (copolymer A:copolymer B), thereby preparing a positive resist composition with a concentration of 2 mass%. The γ value, Eth, pattern collapse resistance, and resist residue of the obtained positive resist composition were measured or evaluated. The results are shown in Table 3.

[0182] (Example 16) In preparing a positive resist composition, the mass ratio of copolymer A1 to copolymer B1 was changed to 10:90 (copolymer A:copolymer B), except that the procedures, measurements, and evaluations were carried out in the same manner as in Example 15. The results are shown in Table 3.

[0183] Example 17 In preparing a positive resist composition, the mass ratio of copolymer A1 to copolymer B1 was changed to 20:80 (copolymer A:copolymer B), and the other operations, measurements, and evaluations were carried out in the same manner as in Example 15. The results are shown in Table 3.

[0184] (Example 18) In preparing a positive resist composition, the mass ratio of copolymer A1 to copolymer B1 was changed to 30:70 (copolymer A:copolymer B), and the other operations, measurements, and evaluations were carried out in the same manner as in Example 15. The results are shown in Table 3.

[0185] Example 19 In the preparation of a positive resist composition, various operations, measurements and evaluations were carried out in the same manner as in Example 17, except that Copolymer A2 was used instead of Copolymer A1. The results are shown in Table 3.

[0186] Example 20 In the preparation of a positive resist composition, various operations, measurements and evaluations were carried out in the same manner as in Example 17, except that Copolymer A5 was used instead of Copolymer A1. The results are shown in Table 3.

[0187] Example 21 In the preparation of a positive resist composition, various operations, measurements and evaluations were carried out in the same manner as in Example 17, except that copolymer A10 was used instead of copolymer A1. The results are shown in Table 3.

[0188] Example 22 In the preparation of a positive resist composition, various operations, measurements and evaluations were carried out in the same manner as in Example 17, except that copolymer A11 was used instead of copolymer A1. The results are shown in Table 3.

[0189] Example 23 In the preparation of a positive resist composition, various operations, measurements and evaluations were carried out in the same manner as in Example 17, except that copolymer A13 was used instead of copolymer A1. The results are shown in Table 3.

[0190] Example 24 In the preparation of a positive resist composition, various operations, measurements and evaluations were carried out in the same manner as in Example 17, except that copolymer A14 was used instead of copolymer A1. The results are shown in Table 3.

[0191] Example 25 In the preparation of a positive resist composition, various operations, measurements and evaluations were carried out in the same manner as in Example 17, except that copolymer B2 was used instead of copolymer B1. The results are shown in Table 3.

[0192] In the tables, "solution" refers to solution polymerization, "bulk" refers to bulk polymerization, "suspension" refers to suspension polymerization, "ACAFPh" refers to 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl α-chloroacrylate, "ACAHFPh" refers to 1-phenyl-2,2,2-trifluoroethyl α-chloroacrylate, "ACANFP" refers to 2,2,3,3,4,4,5,5,5-nonafluoropentyl α-chloroacrylate, "ACAHFB" refers to 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylate, "ACAPFP" refers to 2,2,3,3,3-pentafluoropropyl α-chloroacrylate, "ACATFE" refers to 2,2,2-trifluoroethyl α-chloroacrylate, and "IPA" refers to isopropyl alcohol.

[0193]

[0194]

[0195]

[0196] As is clear from Tables 2 and 3, Examples 1 to 25 ensured the clarity of the resist pattern (γ value of 10 or more) and also exhibited high resistance to pattern collapse.

[0197] According to the present invention, it is possible to provide a copolymer that can enhance resistance to pattern collapse while ensuring the clarity of the resist pattern. Furthermore, according to the present invention, it is possible to provide a copolymer mixture that can enhance resistance to pattern collapse while ensuring the clarity of the resist pattern. Furthermore, according to the present invention, it is possible to provide a positive resist composition that can form a resist pattern that has high resistance to pattern collapse while ensuring clarity.

Claims

1. Formula (I) below: 【Chemistry 1】 [In formula (I), L １ It is a divalent linking group having a fluorine atom, and Ar １ X is an aromatic ring group which may have substituents, １ This 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. A monomer unit (I) represented by, The following formula (II) is different from the monomer unit (I) mentioned above: 【Chemistry 2】 [In formula (II), R １ X is an organic group having 3 to 10 fluorine atoms. ２ This 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. The monomer unit (II) represented by, Formula (III): 【Transformation 3】 [In formula (III), R ２ is an alkyl group, R ３ R is a hydrogen atom, a fluorine atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom. ４ [where p 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 copolymer having monomer units (III) represented by .

2. The above-mentioned R １ The copolymer according to claim 1, wherein the number of fluorine atoms of the above is 5 or more.

3. Said L １ The copolymer according to claim 1, wherein the number of fluorine atoms is 4 or more.

4. The copolymer according to claim 1, wherein the total ratio of monomer unit (I) and monomer unit (II) is 45 mol% or more and 70 mol% or less, when the total monomer units in the copolymer are considered to be 100 mol%.

5. It comprises copolymer A and copolymer B, The copolymer A is the copolymer according to any one of claims 1 to 4. The difference between the surface free energy of copolymer B and the surface free energy of copolymer A is 3 mJ / m ２ The copolymer mixture is as described above.

6. It comprises copolymer A and copolymer B, The copolymer A is the copolymer according to any one of claims 1 to 4. The copolymer B is of the following formula (IV): 【Chemistry 4】 [In formula (IV), L ２ It is a divalent linking group having a fluorine atom, and Ar ２ X is an aromatic ring group which may have substituents, ３ This 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. A monomer unit (IV) represented by, The following equation (V): 【Transformation 5】 [In formula (V), R ５ is an alkyl group, R ６ R is a hydrogen atom, alkyl group, halogen atom, halogenated alkyl group, hydroxyl group, carboxyl group or halogenated carboxyl group, ７ [where r is a hydrogen atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom, and r and s are integers between 0 and 5, with r + s = 5.] A copolymer mixture having monomer units (V) represented by .

7. A positive-type resist composition comprising one of the following (A) to (C) and a solvent. (A) The copolymer according to any one of claims 1 to 4. (B) comprising copolymer A and copolymer B, The copolymer A is the copolymer according to any one of claims 1 to 4. The difference between the surface free energy of copolymer B and the surface free energy of copolymer A is 3 mJ / m ２ The copolymer mixture is as described above. (C) comprising copolymer A and copolymer B, The copolymer A is the copolymer according to any one of claims 1 to 4. The copolymer B is of the following formula (IV): 【Transformation 6】 [In formula (IV), L ２ It is a divalent linking group having a fluorine atom, and Ar ２ X is an aromatic ring group which may have substituents, ３ This 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. A monomer unit (IV) represented by, The following equation (V): 【Transformation 7】 [In formula (V), R ５ is an alkyl group, R ６ R is a hydrogen atom, alkyl group, halogen atom, halogenated alkyl group, hydroxyl group, carboxyl group or halogenated carboxyl group, ７ [where r is a hydrogen atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom, and r and s are integers between 0 and 5, with r + s = 5.] A copolymer mixture having monomer units (V) represented by ,

8. The positive-type resist composition according to claim 7, which does not contain any component having a weight-average molecular weight of less than 1000.

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