Positive-type resist composition for extreme ultraviolet lithography and resist pattern formation kit for extreme ultraviolet lithography

Abstract

The purpose of the present invention is to provide a positive resist composition able to be used to efficiently form an ultrafine resist pattern at high resolution in an EUV lithography system. This positive resist composition for extreme ultraviolet lithography contains a copolymer which has a weight average molecular weight of more than 100,000 and has a monomer unit (A) represented by formula (I) and a monomer unit (B) represented by formula (II). In formula (I), X is a halogen atom or the like, L is a single bond or a divalent linking group, and Ar is an optionally substituted aromatic ring group. In formula (II), R1 is an alkyl group, R2 is an alkyl group, a halogen atom, a halogenated alkyl group, a hydroxyl group, a carboxyl group or a halogenated carboxyl group, p is an integer between 0 and 5, and in a case where a plurality of R2 groups are present, these may be the same as, or different from, each other.

Description

[Technical Field]

[0001] The present invention relates to a positive-type resist composition for extreme ultraviolet lithography and a resist pattern formation kit for extreme ultraviolet lithography. [Background technology]

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

[0003] Specifically, for example, Patent Document 1 discloses a positive-type resist made of a copolymer containing α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-methylstyrene units, which is a main-chain cleavage type positive-type resist with excellent sensitivity to ionizing radiation and heat resistance. [Prior art documents] [Patent Documents]

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

[0005] In recent years, EUV lithography, which uses extreme ultraviolet (EUV) light, has attracted attention as a technique that reduces the proximity effect during exposure compared to electron beams and other methods, and enables the formation of fine patterns. On the other hand, the conventional techniques described above had room for improvement in terms of efficiently forming fine resist patterns with high resolution when using extreme ultraviolet light as the light source for exposure.

[0006] Therefore, the present invention aims to provide a positive-type resist composition and a resist pattern formation kit that can be used to efficiently form fine resist patterns with high resolution in EUV lithography technology. In this invention, "high resolution" means that surface roughness and the occurrence of missing contact holes on the exposed surface after development are suppressed, and that evaluation results such as CD value (Critical Dimension value: a value representing the critical dimension of the line width of the resist pattern), LWR value (Line Width Roughness value: a value representing line width roughness), LER value (Line Edge Roughness value: a value representing line edge roughness), and LCDU value (Local Critical Dimension Uniformity value: local critical dimension uniformity) are good. [Means for solving the problem]

[0007] The inventors diligently conducted research to achieve the above objectives. They discovered that by using a copolymer formed using a predetermined monomer, wherein the weight-average molecular weight is within a predetermined range, fine resist patterns can be efficiently formed with high resolution using EUV lithography technology, thus completing the present invention.

[0008] In other words, the present invention aims to advantageously solve the above problems, and the positive resist composition for extreme ultraviolet lithography of the present invention is the following formula (I): [ka] [In formula (I), X is a halogen atom, a cyano group, an alkylsulfonyl group, an alkoxy group, a nitro group, an acyl group, an alkyl ester group, or a halogenated alkyl group; L is a single bond or a divalent linking group; and Ar is an aromatic ring group which may have substituents.] A monomer unit (A) is represented by the following formula (II): [ka] (In formula (II), R 1 is an alkyl group, and R 2 is an alkyl group, a halogen atom, a halogenated alkyl group, a hydroxyl group, a carboxyl group, or a halogenated carboxyl group, p is an integer of 0 or more and 5 or less, and when there are a plurality of R 2 , they may be the same as or different from each other.) It is characterized by containing a copolymer having a monomer unit (B) represented by and having a weight average molecular weight exceeding 100,000. The copolymer having the monomer unit (A) and the monomer unit (B) can be preferably used as a main chain cleavage type positive resist. Further, if the weight average molecular weight of the copolymer having the monomer unit (A) and the monomer unit (B) exceeds 100,000, when used in EUV lithography, a fine resist pattern can be efficiently formed with high resolution. In the present invention, the "weight average molecular weight" can be measured as a standard polystyrene conversion value using gel permeation chromatography.

[0009] Here, in the positive resist composition for extreme ultraviolet lithography of the present invention, it is preferable that the monomer unit (A) is an α-chloroacrylic acid-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl unit, and the monomer unit (B) is an α-methylstyrene unit or a 4-methyl-α-methylstyrene unit. If the copolymer has the above-mentioned monomer units, the sensitivity to EUV can be sufficiently improved, and a fine resist pattern can be formed better.

[0010] Further, in the positive resist composition for extreme ultraviolet lithography of the present invention, it is preferable that the content ratio of the monomer unit (A) in the copolymer is more than 50 mol% and 60 mol% or less, and the content ratio of the monomer unit (B) is 40 mol% or more and less than 50 mol%. If the ratio of the monomer unit (A) and the monomer unit (B) in the copolymer is within the above range, when used in EUV lithography, a fine resist pattern can be formed more efficiently with high resolution.

[0011] In the positive resist composition for extreme ultraviolet lithography of the present invention, it is preferable that the copolymer has a molecular weight distribution (Mw / Mn) of 1.20 or more and 1.60 or less. Here, in the present invention, the "molecular weight distribution" can be obtained by calculating the ratio of the weight average molecular weight to the number average molecular weight (weight average molecular weight / number average molecular weight), and the "number average molecular weight" can be measured as a standard polystyrene conversion value using gel permeation chromatography.

[0012] Furthermore, in the positive resist composition for extreme ultraviolet lithography of the present invention, it is preferable that the proportion of components having a molecular weight of less than 10,000 in the copolymer is less than 1.5%. If the proportion of components having a molecular weight of less than 10,000 is within the above range, when used in EUV lithography, a fine resist pattern can be formed more efficiently with high resolution. In the present invention, the "proportion of components having a molecular weight of less than 10,000" can be obtained by using the chromatogram obtained by gel permeation chromatography and calculating the ratio (= (B / A) × 100%) of the total area of the peaks in the chromatogram (A) to the total area of the peaks of the components having a molecular weight of less than 10,000 in the chromatogram (B).

[0013] Also, in the positive resist composition for extreme ultraviolet lithography of the present invention, it is preferable that the proportion of components having a molecular weight of less than 50,000 in the copolymer is less than 30%. If the proportion of components having a molecular weight of less than 50,000 is within the above range, when used in EUV lithography, a fine resist pattern can be formed more efficiently with high resolution. In the present invention, the "proportion of components having a molecular weight of less than 50,000" can be obtained by using the chromatogram obtained by gel permeation chromatography and calculating the ratio (= (C / A) × 100%) of the total area of the peaks in the chromatogram (A) to the total area of the peaks of the components having a molecular weight of less than 50,000 in the chromatogram (C).

[0014] Furthermore, in the positive-type resist composition for extreme ultraviolet lithography of the present invention, it is preferable that the copolymer contains less than 70% of components with a molecular weight of less than 100,000. If the proportion of components with a molecular weight of less than 100,000 is within the above range, fine resist patterns can be formed more efficiently and with high resolution when used in EUV lithography. In this invention, the "proportion of components with a molecular weight of less than 100,000" can be determined by using a chromatogram obtained by gel permeation chromatography and calculating the ratio (= (D / A) × 100%) of the total area of ​​peaks (A) of components with a molecular weight of less than 100,000 in the chromatogram.

[0015] Furthermore, in the positive-type resist composition for extreme ultraviolet lithography of the present invention, it is preferable that the copolymer contains more than 8.0% of a component with a molecular weight exceeding 200,000. If the proportion of the component with a molecular weight exceeding 200,000 is within the above range, a fine resist pattern can be formed more efficiently and with high resolution when used in EUV lithography. In this invention, the "proportion of components with a molecular weight exceeding 200,000" can be determined by using a chromatogram obtained by gel permeation chromatography and calculating the ratio (= (E / A) × 100%) of the total area of ​​peaks (A) in the chromatogram to the total area of ​​peaks (E) of components with a molecular weight exceeding 200,000 in the chromatogram.

[0016] Furthermore, this invention aims to advantageously solve the above-mentioned problems, and the resist pattern formation kit for extreme ultraviolet lithography of the present invention is characterized by comprising any of the above-mentioned positive-type resist compositions for extreme ultraviolet lithography and a developer. By using the resist pattern formation kit comprising the above-mentioned positive-type resist composition for extreme ultraviolet lithography and a developer in EUV lithography, fine resist patterns can be efficiently formed with high resolution.

[0017] In this invention, the resist pattern formation kit for extreme ultraviolet lithography preferably uses an alcohol as the developer, and more preferably an alcohol with 2 to 6 carbon atoms. By using an alcohol, preferably an alcohol with 2 to 6 carbon atoms, as the developer, fine resist patterns can be formed more efficiently and with high resolution by EUV lithography. [Effects of the Invention]

[0018] According to the present invention, it is possible to efficiently form fine resist patterns with high resolution using EUV lithography technology. [Modes for carrying out the invention]

[0019] Embodiments of the present invention will be described in detail below. In this invention, "may have substituents" means "unsubstituted or substituted."

[0020] Here, the positive-type resist composition for EUV lithography of the present invention is used to form a resist film when forming a resist pattern using extreme ultraviolet light, which has less proximity effect during exposure compared to electron beams and the like, and enables the formation of fine patterns. The EUV lithography resist pattern formation kit of the present invention contains the positive-type resist composition for EUV lithography of the present invention and can be suitably used, for example, when forming a resist pattern using extreme ultraviolet light in the manufacturing process of printed circuit boards such as build-up substrates.

[0021] (Positive-type resist composition for EUV lithography) The positive resist composition for EUV lithography of the present invention comprises a predetermined copolymer as detailed below, and usually further contains a solvent. The positive resist composition for EUV lithography also optionally further contains known additives that can be incorporated into the resist composition. Furthermore, since the positive-type resist composition for EUV lithography of the present invention contains a predetermined copolymer as a positive-type resist, by using a resist film obtained by coating and drying the positive-type resist composition on a substrate, fine resist patterns can be efficiently formed with high resolution. The positive resist composition for EUV lithography of the present invention may contain polymers other than the predetermined copolymer as the positive resist, but typically it contains only the predetermined copolymer as the positive resist.

[0022] <Copolymer> The copolymer contained in the positive-type resist composition of the present invention is required to have predetermined monomer units (A) and monomer units (B) and to have a weight-average molecular weight greater than 100,000. The copolymer of the present invention may contain any monomer units other than monomer unit (A) and monomer unit (B), but the proportion of monomer unit (A) and monomer unit (B) in the total monomer units constituting the copolymer is preferably 90 mol% or more, and more preferably 100 mol% (i.e., the copolymer contains only monomer unit (A) and monomer unit (B)).

[0023] [Monomeric Unit (A)] Here, the monomer unit (A) is given by the following formula (I): [ka] [In formula (I), X is a halogen atom, a cyano group, an alkylsulfonyl group, an alkoxy group, a nitro group, an acyl group, an alkyl ester group, or a halogenated alkyl group; L is a single bond or a divalent linking group; and Ar is an aromatic ring group which may have substituents.] It is expressed as follows, and equation (III): [ka] It is a structural unit derived from monomer (a) represented by [Equation (III) where X, L, and Ar are the same as in Equation (I)].

[0024] Here, examples of halogen atoms that can constitute X in formulas (I) and (III) include chlorine, fluorine, bromine, iodine, or astatine atoms. Examples of alkylsulfonyl groups that can constitute X in formulas (I) and (III) include methylsulfonyl or ethylsulfonyl groups. Examples of alkoxy groups that can constitute X in formulas (I) and (III) include methoxy, ethoxy, or propoxy groups. Examples of acyl groups that can constitute X in formulas (I) and (III) include formyl, acetyl, or propionyl groups. Examples of alkyl ester groups that can constitute X in formulas (I) and (III) include methyl or ethyl ester groups. Examples of halogenated alkyl groups that can constitute X in formulas (I) and (III) include methyl halides with one to three halogen atoms. In particular, from the viewpoint of efficiently obtaining copolymers useful as main-chain cleavage type positive resists, X is preferably a halogen atom, and more preferably a chlorine atom.

[0025] Furthermore, the divalent linking group that can constitute L in formulas (I) and (III) is not particularly limited and may include, for example, an alkylene group which may have substituents, or an alkenylene group which may have substituents.

[0026] Furthermore, the alkylene group, which may have substituents, is not particularly limited and includes, for example, linear alkylene groups such as methylene, ethylene, propylene, n-butylene, and isobutylene groups, and cyclic alkylene groups such as 1,4-cyclohexylene groups. Among these, linear alkylene groups having 1 to 6 carbon atoms, such as methylene, ethylene, propylene, n-butylene, and isobutylene groups, are preferred as alkylene groups; linear alkylene groups having 1 to 6 carbon atoms, such as methylene, ethylene, propylene, and n-butylene groups, are more preferred; and linear alkylene groups having 1 to 3 carbon atoms, such as methylene, ethylene, and propylene groups, are even more preferred. Furthermore, the alkenylene group, which may have substituents, is not particularly limited and includes, for example, linear alkenylene groups such as etenylene, 2-propenylene, 2-butenylene, and 3-butenylene, and cyclic alkenylene groups such as cyclohexenylene. Among these, linear alkenylene groups having 2 to 6 carbon atoms, such as etenylene, 2-propenylene, 2-butenylene, and 3-butenylene, are preferred as the alkenylene group.

[0027] Among the above, from the viewpoint of sufficiently improving sensitivity to EUV, a divalent linking group is preferably an alkylene group which may have substituents, more preferably a linear alkylene group having 1 to 6 carbon atoms which may have substituents, even more preferably a linear alkylene group having 1 to 6 carbon atoms which may have substituents, and particularly preferably a linear alkylene group having 1 to 3 carbon atoms which may have substituents.

[0028] Furthermore, from the viewpoint of further improving sensitivity to EUV, it is preferable that the divalent linking group that can constitute L in formulas (I) and (III) has one or more electron-withdrawing groups. In particular, when the divalent linking group is an alkylene group having an electron-withdrawing group as a substituent or an alkenylene group having an electron-withdrawing group as a substituent, it is preferable that the electron-withdrawing group is bonded to the carbon adjacent to the carbonyl carbon in formulas (I) and (III) that is bonded to O.

[0029] Furthermore, the electron-withdrawing group that can sufficiently improve sensitivity to EUV is not particularly limited, but includes, for example, at least one selected from the group consisting of a fluorine atom, a fluoroalkyl group, a cyano group, and a nitro group. The fluoroalkyl group is not particularly limited, but includes, for example, a fluoroalkyl group having 1 to 5 carbon atoms. Among these, a perfluoroalkyl group having 1 to 5 carbon atoms is preferred, and a trifluoromethyl group is more preferred.

[0030] Furthermore, from the viewpoint of sufficiently improving sensitivity to EUV, L in formulas (I) and (III) is preferably a methylene group, a cyanomethylene group, a trifluoromethylmethylene group, or a bis(trifluoromethyl)methylene group, with the bis(trifluoromethyl)methylene group being more preferred.

[0031] Furthermore, the Ar in formulas (I) and (III) may include an aromatic hydrocarbon ring group that may have substituents and an aromatic heterocyclic group that may have substituents.

[0032] Furthermore, the aromatic hydrocarbon ring group is not particularly limited, but examples include benzene ring group, biphenyl ring group, naphthalene ring group, azulene ring group, anthracene ring group, phenanthrene ring group, pyrene ring group, chrysene ring group, naphthacene ring group, triphenylene ring group, o-terphenyl ring group, m-terphenyl ring group, p-terphenyl ring group, acenaphthene ring group, coronene ring group, fluorene ring group, fluoranthrene ring group, pentacene ring group, perylene ring group, pentaphene ring group, picene ring group, pyranthrene ring group, and the like.

[0033] Furthermore, aromatic heterocyclic groups are not particularly limited, but include, for example, furan rings, thiophene rings, pyridine rings, pyridazine rings, pyrimidine rings, pyrazine rings, triazine rings, oxadiazole rings, triazole rings, imidazole rings, pyrazole rings, thiazole rings, indole rings, benzimidazole rings, benzothiazole rings, benzoxazole rings, quinoxaline rings, quinazoline rings, phthalazine rings, benzofuran rings, dibenzofuran rings, benzothiophene rings, dibenzothiophene rings, and carbazole rings.

[0034] Furthermore, the substituents that Ar may have are not particularly limited, but include, for example, alkyl groups, fluorine atoms, and fluoroalkyl groups. Examples of alkyl groups as substituents that Ar may have include chain alkyl groups having 1 to 6 carbon atoms, such as methyl groups, ethyl groups, propyl groups, n-butyl groups, and isobutyl groups. Examples of fluoroalkyl groups as substituents that Ar may have include fluoroalkyl groups having 1 to 5 carbon atoms, such as trifluoromethyl groups, trifluoroethyl groups, and pentafluoropropyl groups.

[0035] In particular, from the viewpoint of sufficiently improving sensitivity to EUV, the Ar in formulas (I) and (III) is preferably an aromatic hydrocarbon ring group which may have substituents, more preferably an unsubstituted aromatic hydrocarbon ring group, and even more preferably a benzene ring group (phenyl group).

[0036] Furthermore, from the viewpoint of sufficiently improving sensitivity to EUV, the monomer (a) represented by formula (III) above, which can form the monomer unit (A) represented by formula (I) above, is preferably benzyl α-chloroacrylate and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl, and more preferably α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl. That is, the copolymer preferably has at least one of the α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl unit and the α-chloroacrylate benzyl unit, and more preferably has the α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl unit.

[0037] The proportion of monomer unit (A) in the total monomer units constituting the copolymer is not particularly limited and can be, for example, 30 mol% or more and 70 mol% or less. In particular, the proportion of monomer unit (A) is preferably 50 mol% or more, more preferably more than 50 mol%, even more preferably 52 mol% or more, preferably 60 mol% or less, even more preferably 55 mol% or less, and even more preferably 54 mol% or less. If the proportion of monomer unit (A) is within the above range, when used in EUV lithography, fine resist patterns can be formed more efficiently with high resolution.

[0038] [Monomeric Unit (B)] The monomer unit (B) is given by the following formula (II): [ka] [In formula (II), R 1 R is an alkyl group, 2 is an alkyl group, halogen atom, halogenated alkyl group, hydroxyl group, carboxyl group or halogenated carboxyl group (-C(=O)-X; X is a halogen atom), p is an integer between 0 and 5, and R 2When there are a plurality of them, they may be the same as or different from each other. is represented by the following formula (IV):

Chemical formula

[0039] Here, the alkyl groups that can constitute R 1 ~R 2 in formula (II) and formula (IV) are not particularly limited, and examples thereof include unsubstituted alkyl groups having 1 to 5 carbon atoms. Among them, as the alkyl groups that can constitute R 1 ~R 2 , a methyl group or an ethyl group is preferable.

[0040] Also, the halogen atoms that can constitute R 2 in formula (II) and formula (IV) are not particularly limited, and examples thereof include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc. Among them, as the halogen atom, a fluorine atom is preferable.

[0041] Furthermore, the halogenated alkyl groups that can constitute R 2 in formula (II) and formula (IV) are not particularly limited, and examples thereof include fluoroalkyl groups having 1 to 5 carbon atoms. Among them, as the halogenated alkyl group, a perfluoroalkyl group having 1 to 5 carbon atoms is preferable, and a trifluoromethyl group is more preferable.

[0042] Also, the halogenated carboxyl groups that can constitute R 2 in formula (II) and formula (IV) are not particularly limited, and examples thereof include a carboxyl chloride group (-C(=O)-Cl), a carboxyl fluoride group (-C(=O)-F), a carboxyl bromide group (-C(=O)-Br), etc.

[0043] Furthermore, from the viewpoint of improving the ease of preparation of the copolymer and the cleavage of the main chain when irradiated with EUV, R in formulas (II) and (IV) 1 It is preferably an alkyl group having 1 to 5 carbon atoms, and more preferably a methyl group.

[0044] Furthermore, from the viewpoint of ease of preparation of the copolymer and improvement of the main chain cleavage when irradiated with EUV, it is preferable that p in formulas (II) and (IV) is 0 or 1.

[0045] Furthermore, if p in equations (II) and (IV) is any of 1 to 5, then R in equations (II) and (IV) 2 It is preferably an alkyl group having 1 to 5 carbon atoms, and more preferably a methyl group.

[0046] Furthermore, the monomer (b) represented by formula (IV) above, which can form the monomer unit (B) represented by formula (II) above, is not particularly limited, but includes, for example, α-methylstyrene and its derivatives such as (b-1) to (b-12) below. [ka]

[0047] Furthermore, from the viewpoint of ease of preparation of the copolymer and improvement of the main chain cleavage when irradiated with EUV, it is preferable that the monomer unit (B) is a structural unit derived from α-methylstyrene or 4-methyl-α-methylstyrene. That is, it is preferable that the copolymer has α-methylstyrene units or 4-methyl-α-methylstyrene units.

[0048] Furthermore, the proportion of monomer unit (B) in the total monomer units constituting the copolymer is not particularly limited and can be, for example, 30 mol% or more and 70 mol% or less. In particular, the proportion of monomer unit (B) is preferably 40 mol% or more, more preferably 45 mol% or more, even more preferably 46 mol% or more, preferably 50 mol% or less, more preferably less than 50 mol%, and even more preferably 48 mol% or less. If the proportion of monomer unit (B) is within the above range, when used in EUV lithography, fine resist patterns can be formed more efficiently with high resolution.

[0049] [Properties of copolymers] Furthermore, the copolymer must have a weight-average molecular weight (Mw) greater than 100,000, preferably 110,000 or more, more preferably 150,000 or more, and even more preferably 200,000 or more. If the weight-average molecular weight of the copolymer is within the above range, a fine resist pattern can be efficiently formed with high resolution when used in EUV lithography. While there is no particular upper limit to the weight-average molecular weight of the copolymer, it is preferably 500,000 or less, and more preferably 210,000 or less, from the viewpoint of preventing difficulties in filtration when preparing the positive-type resist composition.

[0050] Furthermore, the number-average molecular weight (Mn) of the copolymer is preferably 70,000 or more, more preferably 110,000 or more, even more preferably 130,000 or more, preferably 400,000 or less, more preferably 300,000 or less, and even more preferably 140,000 or less. If the number-average molecular weight of the copolymer is above the lower limit, fine resist patterns can be efficiently formed with high resolution when used in EUV lithography. Also, if the number-average molecular weight of the copolymer is below the upper limit, the preparation of positive-type resist compositions is easy.

[0051] Furthermore, the molecular weight distribution (Mw / Mn) of the copolymer is preferably 1.20 or higher, more preferably 1.25 or higher, even more preferably 1.30 or higher, preferably 2.00 or lower, more preferably 1.90 or lower, even more preferably 1.60 or lower, even more preferably 1.50 or lower, and particularly preferably 1.40 or lower.

[0052] Furthermore, from the viewpoint of forming fine resist patterns with high resolution and more efficiently when a positive-type resist composition is used in EUV lithography, it is preferable that the copolymer satisfies at least one of the following (1) to (4), and more preferably satisfies all of (1) to (4). (1) The proportion of components with a molecular weight of less than 10,000 is less than 1.5%, preferably 1.3% or less, more preferably 0.5% or less, even more preferably 0.25% or less, even more preferably 0.15% or less, and particularly preferably 0.08% or less. On the other hand, the proportion of components with a molecular weight of less than 10,000 is not particularly limited, but may be, for example, 0.0001% or more, or 0.0003% or more. (2) The proportion of components with a molecular weight of less than 50,000 is less than 30%, preferably 20% or less, more preferably 5% or less, even more preferably 1% or less, and particularly preferably 0.4% or less. On the other hand, the proportion of components with a molecular weight of less than 50,000 is not particularly limited, but may be, for example, 0.01% or more, and may also be 0.05% or more. (3) The proportion of components with a molecular weight of less than 100,000 is less than 70%, preferably 65% ​​or less, more preferably 30% or less, even more preferably 10% or less, even more preferably 5% or less, and particularly preferably 2% or less. On the other hand, the proportion of components with a molecular weight of less than 100,000 is not particularly limited, but may be, for example, 0.1% or more, and may also be 0.5% or more. (4) The proportion of components with a molecular weight exceeding 200,000 is more than 8.0%, preferably 30% or more, more preferably 50% or more, even more preferably 60% or more, and particularly preferably 85% or more. On the other hand, the proportion of components with a molecular weight exceeding 200,000 is not particularly limited, but may be 99% or less, or 95% or less.

[0053] [Method for preparing copolymers] Furthermore, copolymers having the monomer units (A) and (B) described above can be prepared, for example, by polymerizing a monomer composition containing monomer (a) and monomer (b), recovering the resulting copolymer, and optionally purifying it. Furthermore, the composition, molecular weight distribution, weight-average molecular weight, and number-average molecular weight of the copolymer can be adjusted by changing the polymerization method, polymerization conditions (e.g., polymerization temperature, polymerization time, and type and amount of polymerization initiator), and purification conditions. Specifically, for example, the weight-average molecular weight and number-average molecular weight can be increased by lowering the polymerization temperature. Also, the weight-average molecular weight and number-average molecular weight can be increased by shortening the polymerization time. Furthermore, the molecular weight distribution can be reduced by purification.

[0054] Here, the monomer composition used to prepare the copolymer can be a mixture of monomer components containing monomer (a) and monomer (b), an optional solvent, an optional polymerization initiator, and an optional additive. The polymerization of the monomer composition can be carried out using known methods such as solution polymerization or emulsion polymerization. Among these, cyclopentanone and water are preferred as the solvent. Furthermore, it is preferable that the amount of polymerization initiator added is 0 (zero).

[0055] Furthermore, the polymer obtained by polymerizing the monomer composition may be used as a copolymer as is, but it is not particularly limited to being recovered by adding a good solvent such as tetrahydrofuran to a solution containing the polymer, and then dropping the solution with the good solvent added into a poor solvent such as methanol to solidify the polymer.

[0056] The purification method used to purify the obtained polymer is not particularly limited and includes known purification methods such as reprecipitation and column chromatography. Among these, the reprecipitation method is preferred. Note that the purification of the polymer may be carried out repeatedly a plurality of times.

[0057] Then, the purification of the 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 to precipitate a part of the polymer. In this way, if the purification is carried out by dropping the polymer solution into the mixed solvent of the good solvent and the poor solvent, the molecular weight distribution, weight average molecular weight, and number average molecular weight of the obtained copolymer can be easily adjusted by changing the types and mixing ratios of the good solvent and the poor solvent. Specifically, for example, the higher the proportion of the good solvent in the mixed solvent, the larger the molecular weight of the copolymer precipitated in the mixed solvent.

[0058] Note that when purifying the polymer by the reprecipitation method, as the copolymer, as long as it satisfies the desired properties, the polymer precipitated in the mixed solvent of the good solvent and the poor solvent may be used, or the polymer that did not precipitate in the mixed solvent (that is, the polymer dissolved in the mixed solvent) may be used. Here, the polymer that did not precipitate in the mixed solvent can be recovered from the mixed solvent using a known method such as concentration to dryness.

[0059] <Solvent> The solvent contained in the positive resist composition for EUV lithography is not particularly limited as long as it can dissolve the copolymer described above, and known solvents such as those described in Japanese Patent No. 5938536 can be used. Among them, from the viewpoint of obtaining a positive resist composition with an appropriate viscosity and improving the coating property 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.

[0060] <Preparation of Positive Resist Composition for EUV Lithography> Positive resist compositions for EUV lithography can be prepared by mixing the copolymer, solvent, and any known additives that may be used. The mixing method is not particularly limited and can be done by any known method. Alternatively, the mixture may be prepared by filtering after mixing each component.

[0061] [filtration] Here, the method of filtering the mixture is not particularly limited, and for example, it can be filtered using a filter. The filter is not particularly limited, and examples include filtration membranes made of fluorocarbon, cellulose, nylon, polyester, hydrocarbon, etc. Among these, from the viewpoint of effectively preventing impurities such as metals from being mixed into the positive-type resist composition from metal piping, etc., which may be used when preparing the copolymer, the materials constituting the filter are preferably nylon, polyethylene, polypropylene, polytetrafluoroethylene, polyfluorocarbons such as Teflon®, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), nylon, and composite membranes of polyethylene and nylon. As a filter, for example, one disclosed in U.S. Patent No. 6,103,122 may be used. Filters are also commercially available, such as Zeta Plus® 40Q manufactured by CUNO Incorporated. Furthermore, the filter may contain a strongly cationic or weakly cationic ion exchange resin. Here, the average particle size of the ion exchange resin is not particularly limited, but is preferably 2 μm or more and 10 μm or less. Examples of cation exchange resins include sulfonated phenol-formaldehyde condensates, sulfonated phenol-benzaldehyde condensates, sulfonated styrene-divinylbenzene copolymers, sulfonated methacrylate-divinylbenzene copolymers, and other types of sulfonic acid or carboxylic acid group-containing polymers. + Counter-ion, NH4 + Counterions or alkali metal counterions, for example, K + and Na +A counterion is provided. The cation exchange resin preferably has a hydrogen counterion. Such a cation exchange resin may be H + Examples include counterion-containing sulfonated styrene-divinylbenzene copolymers, such as Microlite® PrCH from Purolite. Such cation exchange resins are commercially available as AMBERLYST® from Rohm and Haas.

[0062] Furthermore, the pore size of the filter is preferably 0.001 μm or larger, more preferably 0.005 μm or larger, and preferably 1 μm or smaller. If the pore size of the filter is within the above range, it is possible to sufficiently prevent impurities such as metals from being mixed into the positive-type resist composition.

[0063] (EUV lithography resist pattern formation kit) The EUV lithography resist pattern formation kit of the present invention comprises the above-described positive-type resist composition for EUV lithography and a developer, and can be used when forming a resist pattern using EUV lithography technology. Because the EUV lithography resist pattern formation kit of the present invention contains the above-described positive-type resist composition, it can efficiently form fine resist patterns with high resolution when used in EUV lithography.

[0064] <Developer> The developer used in the EUV lithography resist pattern formation kit of the present invention is not particularly limited and can be appropriately selected according to the properties of the copolymer contained in the positive-type resist composition described above. Specifically, when selecting the developer, it is preferable to select a developer that does not dissolve the resist film before EUV exposure, but can dissolve the exposed areas of the resist film after exposure. Furthermore, one type of developer may be used alone, or two or more types may be mixed in any ratio. As for the developer, for example, hydrofluorocarbons such as 1,1,1,2,3,4,4,5,5,5-decafluoropentane (CF3CFHCFHCF2CF3), 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane, 1,1,1,2,2,3,4,5,5,5-decafluoropentane, 1,1,1,3,3-pentafluorobutane, 1,1,1,2,2,3,3,4,4-nonafluorohexane, 2,2-dichloro-1,1,1-trifluoroethane, 1,1-dichloro-1-fluoroethane, and 1,1-dichloro-2,2,3,3,3-pentafluoro Hydrochlorofluorocarbons such as propane (CF3CF2CHCl2) and 1,3-dichloro-1,1,2,2,3-pentafluoropropane (CClF2CF2CHClF), hydrofluoroethers such as methyl nonafluorobutyl ether (CF3CF2CF2CF2OCH3), methyl nonafluoroisobutyl ether, ethyl nonafluorobutyl ether (CF3CF2CF2CF2OC2H5), ethyl nonafluoroisobutyl ether, and perfluorohexyl methyl ether (CF3CF2CF(OCH3)C3F7), and CF4, C2F6, C3F8, C4F8, C4F 10 , C5F 12 , C6F 12 , C6F 14 , C7F 14 , C7F 16 , C8F 18 , C9F 20Fluorine-based solvents such as perfluorocarbons; alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol, and 1-hexanol; acetate esters having alkyl groups such as amyl acetate and hexyl acetate; mixtures of fluorine-based solvents and alcohols; mixtures of fluorine-based solvents and acetate esters having alkyl groups; mixtures of alcohols and acetate esters having alkyl groups; mixtures of fluorine-based solvents, alcohols and acetate esters having alkyl groups; etc. can be used. Among these, from the viewpoint of forming fine resist patterns with high resolution and more efficiently by EUV lithography, alcohols are preferred, alcohols with 2 to 6 carbon atoms are more preferred, ethanol, isopropyl alcohol, 1-butanol, 2-butanol, 1-pentanol, and 1-hexanol are even more preferred, and isopropyl alcohol is particularly preferred.

[0065] <Method for forming resist patterns using a resist pattern formation kit> The resist pattern formation method using the EUV lithography resist pattern formation kit of the present invention is not particularly limited, and may include, for example, the following steps.

[0066] [Method for forming a resist pattern] A resist pattern formation method using a resist pattern formation kit includes, for example, at least the steps of: forming a resist film on a workpiece such as a substrate using a positive-type resist composition contained in the resist pattern formation kit (resist film formation step); exposing the resist film with EUV light (exposure step); and developing the exposed resist film using a developer solution contained in the resist pattern formation kit (development step). Furthermore, the resist pattern formation method using the resist pattern formation kit may include steps other than the resist film formation step, exposure step, and development step described above. Specifically, the resist pattern formation method 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 resist pattern formation method may further include a step of heating the exposed resist film (post-exposure bake step) between the exposure step and the development step. Furthermore, the resist pattern formation method may further include a step of removing the developer solution after the development step (rinse step). After the resist pattern is formed by the resist pattern formation method, a step of etching the underlayer film and / or the substrate (etching step) may be performed.

[0067] -substrate- Here, the substrate on which a resist film can be formed in the resist pattern formation method is not particularly limited, and substrates having an insulating layer and copper foil provided on the insulating layer, which are used in the manufacture of printed circuit boards, etc., and mask blanks having a light-shielding layer formed on the substrate can be used.

[0068] Examples of substrate materials include metals (silicon, copper, chromium, iron, aluminum, etc.), glass, titanium dioxide, silicon dioxide (SiO2), silica, mica, and other inorganic materials; nitrides such as SiN; oxidized nitrides such as SiON; and organic materials such as acrylic, polystyrene, cellulose, cellulose acetate, and phenolic resin. Among these, metal is preferred as the substrate material. By using, for example, a silicon substrate, a silicon dioxide substrate, or a copper substrate, preferably a silicon substrate or a silicon dioxide substrate, a cylindrical structure can be formed.

[0069] Furthermore, the size and shape of the substrate are not particularly limited. The surface of the substrate may be smooth, curved, or have an uneven shape, or it may be in the form of a thin sheet.

[0070] Furthermore, the surface of the substrate may be surface-treated as needed. For example, in the case of a substrate having hydroxyl groups on its surface, the surface of the substrate can be treated using a silane-based coupling agent that can react with hydroxyl groups. This changes the surface of the substrate from hydrophilic to hydrophobic, thereby improving the adhesion between the substrate and the underlying film, or between the substrate and the resist layer. In this case, the silane-based coupling agent is not particularly limited, but hexamethyldisilazane is preferred.

[0071] -Lower film formation process- In the underlayer formation process, an underlayer is formed on the substrate. By forming an underlayer on the substrate, the surface of the substrate becomes hydrophobic. This increases the affinity between the substrate and the resist film, thereby improving the adhesion between the substrate and the resist film. The underlayer may be an inorganic underlayer or an organic underlayer.

[0072] An inorganic underlayer film can be formed by coating an inorganic material onto a substrate and then firing it. Examples of inorganic materials include silicon-based materials.

[0073] An organic underlayer film can be formed by coating an organic material onto a substrate to form a coating film and then drying it. The organic material is not limited to those sensitive to light or electron beams; for example, resist materials and resin materials commonly used in the semiconductor and liquid crystal fields can be used. In particular, the organic material is preferably one that can form an etchable, especially dry-etchable, organic underlayer film. With such an organic material, the pattern can be transferred to the underlayer film by etching the organic underlayer film using a pattern formed by processing the resist film, thereby forming a pattern on the underlayer film. In particular, the organic material is preferably one that can form an etchable organic underlayer film, such as by oxygen plasma etching. An example of an organic material used for forming an organic underlayer film is AL412 from Brewer Science.

[0074] The application of the above-mentioned organic material can be carried out by conventionally known methods such as spin coating or using a spinner. The drying method for the coating film can be any method that can volatilize the solvent contained in the organic material, such as baking. While the baking conditions are not particularly limited, the baking temperature is preferably 80°C to 300°C, and more preferably 200°C to 300°C. The baking time is preferably 30 seconds or more, more preferably 60 seconds or more, preferably 500 seconds or less, more preferably 400 seconds or less, even more preferably 300 seconds or less, and particularly preferably 180 seconds or less. The thickness of the underlayer film after drying is not particularly limited, but is preferably 10 nm to 100 nm.

[0075] -Resist film formation process- In the resist film formation process, the positive-type resist composition included in the resist pattern formation kit of the present invention is used.

[0076] In the resist film formation process, a positive-type resist composition is applied to a workpiece such as a substrate that will be processed using the resist pattern (or on top of the underlying film if an underlying film is formed), and the applied positive-type resist composition is dried to form a resist film.

[0077] Furthermore, the method for coating and drying the positive-type resist composition is not particularly limited, and methods commonly used for forming resist films can be used. Among these, heating (pre-baking) is preferred as the drying method. The pre-baking temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 140°C or higher, from the viewpoint of improving the film density of the resist film. From the viewpoint of reducing changes in the molecular weight and molecular weight distribution of the copolymer in the resist film before and after pre-baking, it is preferably 250°C or lower, more preferably 220°C or lower, and even more preferably 200°C or lower. Furthermore, the pre-baking time is preferably 10 seconds or more, more preferably 20 seconds or more, and even more preferably 30 seconds or more, from the viewpoint of improving the film density of the resist film formed after pre-baking. From the viewpoint of reducing changes in the molecular weight and molecular weight distribution of the copolymer in the resist film before and after pre-baking, it is preferably 10 minutes or less, more preferably 5 minutes or less, and even more preferably 3 minutes or less.

[0078] -Exposure process- In the exposure process, the resist film formed in the resist film formation process is irradiated with EUV light to create the desired pattern. The wavelength of the EUV light used for irradiation is not particularly limited and can be, for example, 1 nm to 30 nm, preferably 13.5 nm. Furthermore, for EUV irradiation, known exposure equipment such as the EQ-10M (manufactured by ENERGETIQ) and NXE (manufactured by ASML) can be used.

[0079] -Post-exposure baking process- In an optional post-exposure bake process, the resist film exposed in the exposure process is heated. Performing a post-exposure bake process can reduce the surface roughness of the resist pattern.

[0080] Here, the heating temperature is preferably 70°C or higher, more preferably 80°C or higher, even more preferably 90°C or higher, preferably 200°C or lower, more preferably 170°C or lower, and even more preferably 150°C or lower. If the heating temperature is within the above range, the clarity of the resist pattern can be improved while the surface roughness of the resist pattern can be effectively reduced.

[0081] Furthermore, the heating time for the resist film in the post-exposure bake process is preferably 10 seconds or more, more preferably 20 seconds or more, and even more preferably 30 seconds or more. If the heating time is 10 seconds or more, the clarity of the resist pattern can be improved while sufficiently reducing the surface roughness of the resist pattern. On the other hand, from the viewpoint of production efficiency, the heating time is preferably, for example, 10 minutes or less, more preferably 5 minutes or less, and even more preferably 3 minutes or less.

[0082] Furthermore, the method of heating the resist film in the post-exposure baking process is not particularly limited, and examples include heating the resist film on a hot plate, heating the resist film in an oven, or blowing hot air onto the resist film.

[0083] -Developing process- In the development process, the resist film exposed in the exposure process (or the exposed and heated resist film if a post-exposure bake process is performed) is brought into contact with the developer solution contained in the resist pattern formation kit to develop the resist film and form a resist pattern on the workpiece. Here, the method of bringing the resist film and the developer into contact 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. The temperature of the developing solution during development is not particularly limited, but can be, for example, between 21°C and 25°C. The development time can also be, for example, between 15 seconds and 4 minutes.

[0084] By developing with the developer included in the resist pattern formation kit of the present invention, fine resist patterns can be efficiently formed with high resolution.

[0085] -Rinsing process- In the rinsing process, the resist film developed in the developing process is brought into contact with a rinsing solution to rinse the developed resist film and form a resist pattern on the workpiece. Here, the method for bringing the developed resist film into contact with the rinsing solution is not particularly limited, and known methods such as immersing the resist film in the rinsing solution or applying the rinsing solution to the resist film can be used.

[0086] Any rinsing solution can be used as the rinsing solution, as long as it is capable of removing developer and resist residue adhering to the developed resist film; there are no particular limitations on the rinsing solution.

[0087] The temperature of the rinsing solution during rinsing is not particularly limited, but can be, for example, between 21°C and 25°C. The rinsing time can be, for example, between 5 seconds and 3 minutes.

[0088] The developer and rinse solutions described above may be filtered before use. One example of a filtration method is the filter-based filtration method described in the section "Preparation of Positive-Type Resist Composition" above.

[0089] -Etching process- In the etching process, the underlying film and / or substrate are etched using the resist pattern described above as a mask, thereby forming a pattern on the underlying film and / or substrate. In this process, there is no specific number of etching steps; it may be performed once or multiple times. Etching may be performed by dry etching or wet etching, but dry etching is preferred. Dry etching can be performed using a known dry etching apparatus. The etching gas used for dry etching can be appropriately selected depending on the elemental composition of the underlying film or substrate to be etched. Examples of etching gases include fluorine-based gases such as CHF3, CF4, C2F6, C3F8, and SF6; chlorine-based gases such as Cl2 and BCl3; oxygen-based gases such as O2, O3, and H2O; reducing gases such as H2, NH3, CO, CO2, CH4, C2H2, C2H4, C2H6, C3H4, C3H6, C3H8, HF, HI, HBr, HCl, NO, NH3, and BCl3; and inert gases such as He, N2, and Ar. These gases may be used individually or in mixtures of two or more. For dry etching of inorganic underlying films, oxygen-based gases are typically used. Furthermore, fluorine-based gases are typically used for dry etching of substrates, and a mixture of fluorine-based gas and an inert gas is preferably used.

[0090] Furthermore, if necessary, any remaining underlayer film on the substrate may be removed before or after etching the substrate. If the underlayer film is removed before etching the substrate, the underlayer film may be a patterned underlayer film or an underlayer film without a pattern.

[0091] Here, methods for removing the underlying film include, for example, the dry etching method described above. In the case of an inorganic underlying film, the underlying film may be removed by bringing it into contact with a liquid such as a basic solution or an acidic solution, preferably a basic liquid. Here, the basic solution is not particularly limited, and examples include alkaline hydrogen peroxide. Methods for removing the underlying film by wet peeling using alkaline hydrogen peroxide are not particularly limited as long as the underlying film and the alkaline hydrogen peroxide can be in contact for a certain period of time under heated conditions, and examples include immersing the underlying film in heated alkaline hydrogen peroxide, spraying alkaline hydrogen peroxide onto the underlying film in a heated environment, and coating the underlying film with heated alkaline hydrogen peroxide. After performing any of these methods, the substrate can be washed with water and dried to obtain a substrate from which the underlying film has been removed.

[0092] The following describes an example of a resist pattern formation method using the resist pattern formation kit of the present invention, and an example of an etching method for the underlying film and substrate using the formed resist pattern. However, the substrate used in the following example and the conditions in each step can be the same as those described above, so the explanation is omitted below. Note that the resist pattern formation method using the resist pattern formation kit of the present invention is not limited to the method shown in the following example.

[0093] One example of a resist pattern formation method is a resist pattern formation method using EUV, which includes the above-described underlayer film formation step, resist film formation step, exposure step, development step, and rinsing step. Another example of an etching method is one which uses the resist pattern formed by the resist pattern formation method as a mask, and includes an etching step.

[0094] Specifically, in the underlayer film formation process, an inorganic material is applied to the substrate and then fired to form an inorganic underlayer film. Next, in the resist film formation step, the resist composition contained in the resist pattern formation kit of the present invention is applied to the inorganic underlayer film formed in the underlayer film formation step and dried to form a resist film. Then, in the exposure process, the resist film formed in the resist film formation process is irradiated with EUV light to create the desired pattern. Furthermore, in the development process, the resist film exposed in the exposure process is brought into contact with the developer solution contained in the resist pattern formation kit of the present invention to develop the resist film and form a resist pattern on the underlying film. Then, in the rinsing process, the resist film developed in the developing process is brought into contact with the rinsing solution to rinse the developed resist film.

[0095] Then, in the etching process, the underlying film is etched using the above-mentioned resist pattern as a mask, and a pattern is formed on the underlying film. Next, the substrate is etched using the patterned underlayer film as a mask to form a pattern on the substrate. [Examples]

[0096] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the following description, "%" representing quantities refers to mass unless otherwise specified. Furthermore, in the examples and comparative examples, the weight-average molecular weight, number-average molecular weight, and molecular weight distribution of the copolymer, the proportion of each molecular weight component in the copolymer, the optimal exposure dose, CD value, LWR value, LER value, and LCDU value were measured by the following methods.

[0097] <Weight-average molecular weight, number-average molecular weight, and molecular weight distribution> For the copolymers obtained in the examples and comparative examples, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) were measured using gel permeation chromatography, and the molecular weight distribution (Mw / Mn) was calculated. Specifically, a gel permeation chromatograph (manufactured by Tosoh Corporation, HLC-8220) was used, and tetrahydrofuran was used as the developing solvent to determine the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the polymer as values in terms of standard polystyrene. Then, the molecular weight distribution (Mw / Mn) was calculated. <Ratio of components of each molecular weight in the copolymer> Using gel permeation chromatography (manufactured by Tosoh Corporation, HLC-8220) and tetrahydrofuran as the developing solvent, a chromatogram of the copolymer was obtained. Then, from the obtained chromatogram, the total peak area (A), the total area of the peaks of components with a molecular weight of less than 10,000 (B), the total area of the peaks of components with a molecular weight of less than 50,000 (C), the total area of the peaks of components with a molecular weight of less than 100,000 (D), and the total area of the peaks of components with a molecular weight of more than 200,000 (E) were determined. And the ratio of the components of each molecular weight was calculated using the following formula. Ratio of components with a molecular weight of less than 10,000 (%) = (B / A) × 100 Ratio of components with a molecular weight of less than 50,000 (%) = (C / A) × 100 Ratio of components with a molecular weight of less than 100,000 (%) = (D / A) × 100 Ratio of components with a molecular weight of more than 200,000 (%) = (E / A) × 100 <Optimal exposure dose (E op ) The optimal exposure dose (E op ) was determined as the most excellent point from the CD value, LER value, and LWR value by varying the exposure dose and focus. <CD value, LWR value, LER value, LCDU value> The CD value, LWR value, LER value, and LCDU value of the resist patterns formed in the examples and comparative examples were measured and calculated using a high-resolution FEB length measurement device (manufactured by Hitachi High-Technologies Corporation, CG5000) and analysis software (manufactured by Hitachi High-Technologies Corporation, Design Metrology System). A CD value within the range of half-pitch (hp) or contact hole ±5nm, along with lower LWR, LER, and LCDU values, indicates higher resolution of the resist pattern.

[0098] (Example 1) <Preparation of copolymer> [Synthesis of polymers] A monomer composition containing 3.00 g of monomer (a) α-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl chloroacrylate, 2.493 g of monomer (b) α-methylstyrene, and 2.833 g of cyclopentanone as a solvent was added to a glass ampoule containing a stirring bar, sealed, and oxygen was removed from the system by repeatedly pressurizing and depressurizing with nitrogen gas 10 times. The system was then heated to 50°C and the reaction was carried out for 25 hours. Next, 10 g of tetrahydrofuran was added to the system, and the resulting solution was added dropwise to 300 mL of methanol to precipitate the polymer. The precipitated polymer was then recovered by filtration. The obtained polymer was a copolymer containing 50 mol% each of α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units. [Purification of polymers] Subsequently, the polymer recovered by filtration was dissolved in 10 g of tetrahydrofuran (THF), and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and methanol (MeOH) (THF:MeOH (mass ratio) = 27:73) to precipitate a white solidified product (a copolymer containing α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units). Then, the solution containing the precipitated copolymer was filtered using a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of α-methylstyrene units (AMS units) and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units (ACAFPh units)). The weight-average molecular weight, number-average molecular weight, and molecular weight distribution of the obtained copolymer were measured. The results are shown in Table 1. <Preparation of positive-type resist composition> The obtained copolymer was dissolved in isoamyl acetate as a solvent to prepare a resist solution (positive-type resist composition) with a copolymer concentration of 11% by mass. <Resist pattern formation> Using a spin coater (Mikasa, MS-A150), AL412 (Brewer Science) was applied as an underlayer to a 4-inch diameter silicon wafer. The applied AL412 was then heated on a hot plate at 205°C for 1 minute to form a 20 nm thick underlayer on the silicon wafer. Subsequently, the resulting positive-type resist composition was applied on top of the underlayer. The applied positive-type resist composition was then heated on a hot plate at 150°C for 3 minutes to form a 33 nm or 50 nm thick resist film on the silicon wafer. Finally, the resist film was etched using an EUV lithography system (ASML, TWINSCAN NXE:3400B) to achieve the optimal exposure (E op The image was exposed to light to draw a pattern. Then, a development process was performed using isopropyl alcohol (IPA) as the developer at a temperature of 23°C for 30 seconds to form a resist pattern. At that time, the lines (unexposed areas) and spaces (exposed areas) of the resist pattern were set to line and space with a half-pitch (hp) of 16 nm each. The obtained resist patterns were used to measure the CD value, LWR value, and LER value. The results are shown in Table 1.

[0099] (Example 2) The copolymer was prepared, the positive resist composition was prepared, and the resist pattern was formed in the same manner as in Example 1, except that the reaction was carried out at a temperature of 30°C for 80 hours during the synthesis of the polymer and the composition of the mixed solvent used during the purification of the polymer (THF:MeOH (mass ratio)) was set to 29:71. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0100] (Example 3) The copolymer was prepared, the positive-type resist composition was prepared, and the resist pattern was formed in the same manner as in Example 1, except that the copolymer was prepared as described below. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1. <Preparation of copolymer> [Preparation of an aqueous solution of semi-hardened beef tallow fatty acid potassium soap with a solid content of 18%] 100g of deionized water was prepared and heated to 70°C while stirring, and 8.40g of potassium hydroxide (49% aqueous solution) was added. Next, 19.6g of 45° hardened beef tallow fatty acid HFA (manufactured by NOF Corporation) was added at an addition rate of 1.28g / min, and then 0.126g of potassium silicate was added. The mixture was then stirred at 80°C for more than 2 hours to obtain an aqueous solution of semi-hardened beef tallow fatty acid potassium soap with a solid content of 18%. [Synthesis of polymers] 3.00 g of monomer (a) α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl and 2.712 g of monomer (b) α-methylstyrene were added to a glass ampoule containing a stirring bar. Furthermore, to the same ampoule, 0.5463 g of an 18% solids aqueous solution of the semi-hardened beef tallow fatty acid potassium soap prepared above, mixed with 6.771 g of deionized water, was added to form a monomer composition. The ampoule was then sealed, and oxygen in the system was removed by repeatedly pressurizing and depressurizing with nitrogen gas 10 times. The system was then heated to 40°C, and the polymerization reaction was carried out for 11 hours. Next, 10 g of tetrahydrofuran was added to the system, and the resulting solution was added dropwise to 300 mL of methanol to precipitate the polymer. The precipitated polymer was then recovered by filtration. The obtained polymer was a copolymer containing 50 mol% each of α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units. [Purification of polymers] The polymer recovered by filtration was dissolved in 10 g of tetrahydrofuran (THF), and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and methanol (MeOH) (THF:MeOH (mass ratio) = 35:65) to precipitate a white solidified product (a copolymer containing α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units). Subsequently, the solution containing the precipitated copolymer was filtered using a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units). The weight-average molecular weight, number-average molecular weight, and molecular weight distribution of the obtained copolymer were measured. The results are shown in Table 1.

[0101] (Example 4) The copolymer was prepared, the positive-type resist composition was prepared, and the resist pattern was formed in the same manner as in Example 3, except that ethanol (EtOH) was used as the developer when forming the resist pattern. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0102] (Example 5) The copolymer was prepared, a positive-type resist composition was prepared, and a resist pattern was formed in the same manner as in Example 3, except that 3.034 g of 4-methyl-α-methylstyrene (4-isopropenyltoluene) was used instead of α-methylstyrene during the synthesis of the polymer, and the reaction was carried out at a temperature of 50°C for 6 hours, and the composition of the mixed solvent used during the purification of the polymer (THF:MeOH (mass ratio)) was set to 30:70. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0103] (Example 6) The copolymer was prepared, the positive-type resist composition was prepared, and the resist pattern was formed in the same manner as in Example 3, except that 3.034 g of 4-methyl-α-methylstyrene (4-isopropenyltoluene) was used instead of α-methylstyrene during the synthesis of the polymer, and the composition of the mixed solvent used during the purification of the polymer (THF:MeOH (mass ratio)) was set to 33:67. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0104] (Examples 7-9) During the synthesis of the polymers, the amounts of α-methylstyrene were set to 2.132 g (Example 7), 1.599 g (Example 8), and 1.066 g (Example 9), respectively, and the amounts of cyclopentanone were set to 2.199 g (Example 7), 1.971 g (Example 8), and 1.743 g (Example 9), respectively. The reaction was carried out at a temperature of 30°C for 50 hours, and the composition of the mixed solvent used for purifying the polymers (THF:MeOH (mass ratio)) was set to 30:70. Except for these differences, the copolymers, positive-type resist compositions, and resist patterns were prepared in the same manner as in Example 1, and various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0105] (Example 10) The copolymer was prepared, the positive-type resist composition was prepared, and the resist pattern was formed in the same manner as in Example 9, except that ethanol was used as the developer when forming the resist pattern. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0106] (Example 11) The copolymer was prepared, a positive-type resist composition was prepared, and a resist pattern was formed in the same manner as in Example 1, except that the amount of α-methylstyrene was set to 0.5329 g and the amount of cyclopentanone to 1.514 g during the synthesis of the polymer, and the reaction was carried out at a temperature of 30°C for 50 hours, and the composition of the mixed solvent used for the purification of the polymer (THF:MeOH (mass ratio)) was set to 30:70. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0107] (Examples 12-15) In addition to using 1.066 g of α-methylstyrene during polymer synthesis, and setting the polymerization reaction temperature and time to 70°C for 6 hours (Example 12), 60°C for 6 hours (Example 13), 50°C for 6 hours (Example 14), and 40°C for 11 hours (Example 15), respectively, the copolymer was prepared, a positive-type resist composition was prepared, and a resist pattern was formed in the same manner as in Example 3. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0108] (Example 16) The copolymer was prepared, the positive-type resist composition was prepared, and the resist pattern was formed in the same manner as in Example 15, except that ethanol was used as the developer when forming the resist pattern. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0109] (Example 17) The copolymer was prepared, the positive-type resist composition was prepared, and the resist pattern was formed in the same manner as in Example 3, except that 2-butanol (2-BtOH) was used as the developer when forming the resist pattern. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0110] (Example 18) The copolymer was prepared, the positive-type resist composition was prepared, and the resist pattern was formed in the same manner as in Example 9, except that 2-butanol was used as the developer when forming the resist pattern. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0111] (Example 19) The copolymer was prepared, the positive-type resist composition was prepared, and the resist pattern was formed in the same manner as in Example 15, except that 2-butanol was used as the developer when forming the resist pattern. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0112] (Example 20) The copolymer was prepared, the positive resist composition was prepared, and the resist pattern was formed in the same manner as in Example 3, except that the polymerization reaction temperature and time were set to 75°C for 1 hour during polymer synthesis, and the composition of the mixed solvent used during polymer purification (THF:MeOH (mass ratio)) was set to 30:70. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

[0113] (Example 21) The copolymer was prepared, the positive-type resist composition was prepared, and the resist pattern was formed in the same manner as in Example 20, except that the polymer was purified as described below. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 2. [Purification of polymers] The polymer recovered by filtration was dissolved in 10 g of tetrahydrofuran (THF), and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and methanol (MeOH) (THF:MeOH (mass ratio) = 30:70) to precipitate a white solid. Next, the solution containing the precipitated solid was filtered using a Kiriyama funnel, and the resulting white solid was dissolved again in 10 g of tetrahydrofuran (THF). The resulting solution was added dropwise to 100 g of a mixed solvent for repurification (THF:MeOH (mass ratio) = 30:70) to precipitate a white re-solidified product (a copolymer containing α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units) (repurification). Subsequently, the solution containing the precipitated copolymer was filtered using a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units).

[0114] (Examples 22-25) The copolymer, positive-type resist composition, and resist pattern were prepared in the same manner as in Example 21, except that the composition of the mixed solvent used for repurification during the purification of the polymer (THF:MeOH (mass ratio)) was 31:39 (Example 22), 32:68 (Example 23), 33:67 (Example 24), and 34:66 (Example 25), respectively. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

[0115] (Example 26) The copolymer was prepared, the positive-type resist composition was prepared, and the resist pattern was formed in the same manner as in Example 20, except that the polymer was purified as described below. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 2. [Purification of polymers] The polymer recovered by filtration was dissolved in 10 g of tetrahydrofuran (THF), and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and methanol (MeOH) (THF:MeOH (mass ratio) = 30:70) to precipitate a white solid. Next, the solution containing the precipitated solid was filtered using a Kiriyama funnel, and the resulting white solid was dissolved again in 10 g of tetrahydrofuran (THF). The resulting solution was added dropwise to 100 g of a mixed solvent for re-purification (THF:MeOH (mass ratio) = 33:67), and a white re-solidified substance was precipitated (re-purification). Furthermore, the solution containing the precipitated re-solidified substance was filtered using a Kiriyama funnel, and the resulting white re-solidified substance was dissolved again in 10 g of tetrahydrofuran (THF). The obtained solution was added dropwise to 100 g of a mixed solvent for further purification (THF:MeOH (mass ratio) = 33:67), and a white, further solidified product (a copolymer containing α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units) was precipitated (further purification). Subsequently, the solution containing the precipitated copolymer was filtered through a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units).

[0116] (Examples 27-33) Except for using 1.066 g of α-methylstyrene during polymer synthesis, copolymer preparation, positive-type resist composition preparation, and resist pattern formation were carried out in the same manner as in Examples 20-26, and various evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

[0117] (Comparative Example 1) During the synthesis of the polymer, 0.003953 g of azobisisobutyronitrile was added to the monomer composition as a polymerization initiator. The reaction was carried out at 78°C for 3.5 hours without using cyclopentanone, and the polymer was not purified. Except for these differences, the copolymer was prepared, a positive-type resist composition was prepared, and a resist pattern was formed in the same manner as in Example 1. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 3.

[0118] (Comparative Example 2) During the synthesis of the polymer, 0.003953 g of azobisisobutyronitrile was added to the monomer composition as a polymerization initiator, and the reaction was carried out at 78°C for 3.5 hours without using cyclopentanone. The composition of the mixed solvent used during the purification of the polymer (THF:MeOH (mass ratio)) was set to 20:80. Except for these differences, the copolymer was prepared, a positive-type resist composition was prepared, and a resist pattern was formed in the same manner as in Example 1. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 3.

[0119] (Comparative Example 3) The copolymer was prepared, the positive-type resist composition was prepared, and the resist pattern was formed in the same manner as in Example 1, except that the copolymer was prepared and the resist pattern was formed as described below. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 3. <Preparation of copolymer> [Synthesis of polymers] A monomer composition containing 3.00 g of α-pentafluoropropyl chloroacrylate as monomer, 3.476 g of α-methylstyrene as monomer (b), 0.005513 g of azobisisobutyronitrile as polymerization initiator, and 1.620 g of cyclopentanone as solvent was added to a glass ampoule containing a stirring bar, sealed, and oxygen in the system was removed by repeatedly pressurizing and depressurizing with nitrogen gas 10 times. The system was then heated to 78°C and the reaction was carried out for 6 hours. Next, 10 g of tetrahydrofuran was added to the system, and the resulting solution was added dropwise to 300 mL of methanol to precipitate the polymer. The precipitated polymer was then collected by filtration. The obtained polymer was a copolymer containing 50 mol% each of α-methylstyrene units and α-pentafluoropropyl chloroacrylate units. [Purification of polymers] Subsequently, the polymer recovered by filtration was dissolved in 10 g of tetrahydrofuran (THF), and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and methanol (MeOH) (THF:MeOH (mass ratio) = 15:85) to precipitate a white solidified product (a copolymer containing α-methylstyrene units and α-chloroacrylate pentafluoropropyl units). Then, the solution containing the precipitated copolymer was filtered using a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of α-methylstyrene units and α-chloroacrylate pentafluoropropyl units (ACAPFP units)). <Resist pattern formation> Using a spin coater (Mikasa, MS-A150), AL412 (Brewer Science) was applied as an underlayer to a 4-inch diameter silicon wafer. The applied AL412 was then heated on a hot plate at 205°C for 1 minute to form a 20 nm thick underlayer on the silicon wafer. Subsequently, the resulting positive-type resist composition was applied on top of the underlayer. The applied positive-type resist composition was then heated on a hot plate at 150°C for 3 minutes to form a 33 nm or 50 nm thick resist film on the silicon wafer. Then, using an EUV lithography system (ASML, TWINSCAN NXE:3400B), the resist film was exposed at the optimal exposure level (Eop) to draw a pattern. After that, development was performed using hydrofluorocarbon (HFC: Mitsui DuPont Fluorochemicals Co., Ltd., Bartrell XF (CF3CFHCFHCF2CF3)) as the developer at 23°C for 30 seconds. Next, a hydrofluoroether (HFE: Novec® 7100 (C4F9OCH3) manufactured by 3M Corporation) was used as a rinsing solution, and the resist pattern was formed by rinsing at a temperature of 23°C for 10 seconds. In this process, the lines (unexposed areas) and spaces (exposed areas) of the resist pattern were each 16 nm (i.e., half-pitch (hp) 16 nm).

[0120] (Comparative Examples 4-6) During the synthesis of the polymers, the amounts of α-methylstyrene were set to 3.283 g (Comparative Example 4), 3.468 g (Comparative Example 5), and 3.468 g (Comparative Example 6), respectively; the amounts of azobisisobutyronitrile were set to 0.0005207 g (Comparative Example 4), 0.002065 g (Comparative Example 5), and 0.001377 g (Comparative Example 6), respectively; and the amounts of cyclopentanone were set to 1.571 g (Comparative Example 4), 6.466 g (Comparative Example 5), and 6.467 g (Comparative Example 6), respectively. The polymerization reaction temperature and time were also adjusted. The copolymers were prepared, the positive resist compositions were prepared, and the resist patterns were formed in the same manner as in Example 3, except that the preparation times were 78°C for 2 hours (Comparative Example 4), 53°C for 50 hours (Comparative Example 5), and 40°C for 50 hours (Comparative Example 6), respectively, and the composition of the mixed solvent used during the purification of the polymer (THF:MeOH (mass ratio)) was 21:79 (Comparative Example 4), 24:76 (Comparative Example 5), and 26:74 (Comparative Example 6). Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 3.

[0121] (Comparative Example 7) During the synthesis of the polymer, 0.003953 g of azobisisobutyronitrile was added to the monomer composition as a polymerization initiator, and the amount of cyclopentanone was set to 1.380 g. The reaction was carried out at 78°C for 6 hours, and the polymer was not purified. Except for these steps, the copolymer was prepared, the positive-type resist composition was prepared, and the resist pattern was formed in the same manner as in Example 1. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 3.

[0122] [Table 1]

[0123] [Table 2]

[0124] [Table 3]

[0125] Tables 1-3 show that, compared to Comparative Examples 1-7, Examples 1-33 enable the efficient formation of fine resist patterns with high resolution. [Industrial applicability]

[0126] According to the present invention, it is possible to efficiently form fine resist patterns with high resolution using EUV lithography technology.

Claims

1. The following formula (I): 【Chemistry 1】 [In formula (I), X is a halogen atom, a cyano group, an alkylsulfonyl group, an alkoxy group, a nitro group, an acyl group, an alkyl ester group, or a halogenated alkyl group; L is a single bond or a divalent linking group; and Ar is an aromatic ring group which may have substituents.] A monomer unit (A) is represented by the following formula (II): 【Chemistry 2】 [In formula (II), R １ is an alkyl group, R ２ is an alkyl group, halogen atom, halogenated alkyl group, hydroxyl group, carboxyl group, or halogenated carboxyl group, and p is an integer between 0 and 5, R ２ If multiple instances exist, they may be identical or different from one another. The copolymer comprises monomer units (B) represented by and has a weight-average molecular weight greater than 100,000. The copolymer is a positive-type resist composition for extreme ultraviolet lithography, wherein the proportion of components with a molecular weight exceeding 200,000 is greater than 8.0%, and the content of the monomer unit (B) is 30 mol% or more.

2. The monomer unit (A) is an α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl unit, The positive-type resist composition for extreme ultraviolet lithography according to claim 1, wherein the monomer unit (B) is an α-methylstyrene unit or a 4-methyl-α-methylstyrene unit.

3. The copolymer has a content of monomer unit (A) that is greater than 50 mol% and less than or equal to 60 mol%, and a content of monomer unit (B) that is 40 mol% or more and less than 50 mol%, as described in claim 1 or 2.

4. The positive-type resist composition for extreme ultraviolet lithography according to any one of claims 1 to 3, wherein the molecular weight distribution (Mw / Mn) of the copolymer is 1.20 or more and 1.60 or less.

5. The copolymer is a positive-type resist composition for extreme ultraviolet lithography according to any one of claims 1 to 4, wherein the proportion of components with a molecular weight of less than 10,000 is less than 1.5%.

6. The copolymer is a positive-type resist composition for extreme ultraviolet lithography according to any one of claims 1 to 5, wherein the proportion of components with a molecular weight of less than 50,000 is less than 30%.

7. The copolymer is a positive-type resist composition for extreme ultraviolet lithography according to any one of claims 1 to 6, wherein the proportion of components with a molecular weight of less than 100,000 is less than 70%.

8. A resist pattern forming kit for extreme ultraviolet lithography, comprising a positive-type resist composition for extreme ultraviolet lithography according to any one of claims 1 to 7, and a developer.

9. The resist pattern forming kit for extreme ultraviolet lithography according to claim 8, wherein the developing solution is alcohol.

10. The resist pattern forming kit for extreme ultraviolet lithography according to claim 9, wherein the number of carbon atoms in the alcohol is 2 or more and 6 or less.

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