JP2023003342A - Resist pattern forming method - Google Patents

Abstract

To provide a resist pattern forming method capable of forming a resist pattern with little loss of a resist pattern top and high contrast.SOLUTION: The resist pattern forming method comprises: forming a resist film using a positive resist composition which contains a main chain scission-type copolymer A containing a fluorine substituent, a main chain scission-type copolymer B containing a fluorine substituent, and a solvent and in which the difference between the surface free energy of the copolymer A and the surface free energy of the copolymer B is 4 mJ/m2 or more; exposing the resist film; and developing the exposed resist film using a developer containing at least a solvent having a solubility parameter of 8 (cal/cm3)1/2 or less.SELECTED DRAWING: None

Description

The present invention relates to a method of forming a resist pattern, and more particularly to a method of forming a resist pattern using a positive resist composition.

Conventionally, in fields such as semiconductor manufacturing, ionizing radiation such as electron beams and short-wavelength light such as ultraviolet rays (hereinafter, ionizing radiation and short-wavelength light may be collectively referred to as "ionizing radiation, etc."). Polymers whose main chains are cleaved by irradiation to increase their solubility in developers have been used as positive resists of the main chain scission type.

For example, in Patent Document 1, α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2 is disclosed as a main chain scission type positive resist excellent in sensitivity to ionizing radiation and heat resistance. A positive resist composition comprising a positive resist comprising a copolymer containing -trifluoroethyl units and α-methylstyrene units is disclosed.

JP 2018-154754 A

However, the resist pattern formed using the conventional positive resist composition has room for improvement in terms of reducing the top loss of the resist pattern and increasing the contrast of the resist pattern. .

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method of forming a resist pattern that can form a high-contrast resist pattern with less decrease in the top of the resist pattern.

The inventor of the present invention has made intensive studies in order to achieve the above object. Then, the present inventors formed a resist film using a positive resist composition containing two kinds of predetermined copolymers as a positive resist, and when developing the exposed resist film, a predetermined development The present inventors have newly found that a resist pattern with a high contrast can be formed with little decrease in the top of the resist pattern by performing development using a liquid, and have completed the present invention.

That is, an object of the present invention is to advantageously solve the above problems, and a resist pattern forming method of the present invention comprises a main chain scission type copolymer A containing a fluorine and a solvent, and the difference between the surface free energy of the copolymer A and the surface free energy of the copolymer B is 4 mJ / m ² or more a resist film forming step of forming a resist film using a certain positive resist composition; an exposure step of ^exposing the resist film ^; and a developing step of developing with a developer containing at least a solvent of ² or less. Thus, after forming a resist film using a positive resist composition containing copolymer A and copolymer B having a surface free energy difference of 4 mJ/m ² or more and exposing the resist film, If the exposed resist film is developed using a developer containing at least a solvent having a solubility parameter of 8 (cal/cm ³ ) ^1/2 or less, the resist pattern top is less reduced and the contrast is high. Patterns can be formed.
In the present invention, the term "main chain scission type" means that when the copolymer is irradiated with ionizing radiation such as an electron beam or extreme ultraviolet (EUV), the copolymer It means having the property that the main chain is cut.
In addition, in the present invention, the "surface free energy" and "solubility parameter" (hereinafter also referred to as "SP value") can be calculated using the methods described in the examples of the present specification.

〔式（Ｉ）中、Ｌは、フッ素原子を有する２価の連結基であり、Ａｒは、置換基を有していてもよい芳香環基である。〕で表される単量体単位（Ｉ）と、
下記式（ＩＩ）：

〔式（ＩＩ）中、Ｒ^１は、アルキル基であり、Ｒ^２は、水素原子、アルキル基、ハロゲン原子、ハロゲン化アルキル基、水酸基、カルボキシル基又はハロゲン化カルボキシル基であり、Ｒ^３は、水素原子、非置換のアルキル基又はフッ素原子で置換されたアルキル基であり、ｐ及びｑは、０以上５以下の整数であり、ｐ＋ｑ＝５である。〕で表される単量体単位（ＩＩ）と、を有することが好ましい。単量体単位（Ｉ）と単量体単位（ＩＩ）とを有する共重合体Ａを用いれば、レジストパターンのコントラストを更に高めることができる。
なお、本発明において、「置換基を有していてもよい」とは、「無置換の、又は、置換基を有する」を意味する。 Here, in the resist pattern forming method of the present invention, the copolymer A is represented by the following formula (I):

[In the formula (I), L is a divalent linking group having a fluorine atom, and Ar is an aromatic ring group optionally having a substituent. ] A monomeric unit (I) represented by
Formula (II) below:

[In formula (II), R ¹ is an alkyl group, R ² 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 ³ is It is a hydrogen atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom, p and q are integers of 0 or more and 5 or less, and p+q=5. ] and a monomer unit (II) represented by The contrast of the resist pattern can be further enhanced by using the copolymer A containing the monomer unit (I) and the monomer unit (II).
In the present invention, "optionally having a substituent" means "unsubstituted or having a substituent".

〔式（ＩＩＩ）中、Ｒ^１は、フッ素原子の数が５以上７以下の有機基である。〕で表される単量体単位（ＩＩＩ）と、
下記式（ＩＶ）：

〔式（ＩＶ）中、Ｒ^１は、アルキル基であり、Ｒ^２は、水素原子、フッ素原子、非置換のアルキル基又はフッ素原子で置換されたアルキル基であり、Ｒ^３は、水素原子、非置換のアルキル基又はフッ素原子で置換されたアルキル基であり、ｐ及びｑは、０以上５以下の整数であり、ｐ＋ｑ＝５である。〕で表される単量体（ＩＶ）と、を有することが好ましい。単量体単位（ＩＩＩ）と単量体単位（ＩＶ）とを有する共重合体Ｂを用いれば、レジストパターンのコントラストを一層高めることができる。 Further, in the resist pattern forming method of the present invention, the copolymer B is represented by the following formula (III):

[In the formula (III), R ¹ is an organic group having 5 or more and 7 or less fluorine atoms. ] A monomeric unit (III) represented by
Formula (IV) below:

[In formula (IV), R ¹ is an alkyl group, R ² is a hydrogen atom, a fluorine atom, an unsubstituted alkyl group or a fluorine atom-substituted alkyl group, R ³ is a hydrogen atom, It is an unsubstituted alkyl group or an alkyl group substituted with a fluorine atom, p and q are integers from 0 to 5, and p+q=5. ] and a monomer (IV) represented by The contrast of the resist pattern can be further enhanced by using the copolymer B having the monomer unit (III) and the monomer unit (IV).

Further, in the method of forming a resist pattern of the present invention, the developing step includes a treatment (1) in which a solvent having a solubility parameter of 8 (cal/cm ³ ) ^1/2 or less is used as a developer (1) for development. , and a process (2) of developing with a developer (2) different from the developer (1), and the processes (1) and (2) are preferably performed in this order. In the development step, as processing (1), development is performed using a solvent having a solubility parameter of 8 (cal/cm ³ ) ^1/2 or less as developer (1), and then as processing (2), developer ( If the developer (2) different from 1) is used for development, it is possible to efficiently form a resist pattern with a higher contrast while reducing the reduction of the top of the resist pattern.

Moreover, in the resist pattern forming method of the present invention, the developer (1) is preferably a hydrocarbon solvent. If a hydrocarbon solvent is used as the developer (1), the contrast of the resist pattern can be further enhanced.

Moreover, in the resist pattern forming method of the present invention, the developer (2) is preferably an alcohol solvent. If an alcohol-based solvent is used as the developer (2), the contrast of the resist pattern can be further enhanced.

According to the present invention, it is possible to form a high-contrast resist pattern with less decrease in the resist pattern top.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail.
The resist pattern forming method of the present invention is a method of forming a resist pattern using ionizing radiation such as an electron beam and EUV. The resist pattern forming method of the present invention is not particularly limited, and can be used, for example, when forming a resist pattern in the manufacturing process of semiconductors, photomasks, molds, and the like.

(Resist pattern forming method)
The method for forming a resist pattern of the present invention includes a step of forming a resist film using a predetermined positive resist composition described in detail below (resist film forming step), a step of exposing the resist film (exposure step), and a step of developing the exposed resist film using a predetermined developer described in detail below (development step).

The resist pattern forming method of the present invention may further include steps other than the resist film forming step, exposure step and developing step described above. Specifically, the resist pattern forming method of the present invention may include, before the resist film forming step, a step of forming an underlayer film on the substrate on which the resist film is to be formed (underlayer film forming step). Moreover, the resist pattern forming method of the present invention may include a step of heating the exposed resist film (post-exposure bake step) between the exposure step and the development step. Moreover, the resist pattern forming method of the present invention may further include a step of removing the developer (rinsing step) after the developing step. After forming the resist pattern by the method of forming a resist pattern of the present invention, the method may further include a step of etching the underlying film and/or the substrate (etching step).

Then, in the method of forming a resist pattern of the present invention, a resist film is formed using a positive resist composition containing a predetermined copolymer, and in the developing step, the resist pattern is formed by developing using a predetermined developer. It is possible to form a resist pattern with little top reduction and high contrast.
Each step in the resist pattern forming method of the present invention will be described below in order.

<Lower layer film forming process>
In the lower layer film forming step that can optionally be performed before the resist film forming step, an lower layer film is formed on the substrate. By providing the underlayer film on the substrate, the surface of the substrate is made hydrophobic. As a result, the affinity between the substrate and the resist film can be enhanced, and the adhesion between the substrate and the resist film can be enhanced. The underlayer film may be an inorganic underlayer film or an organic underlayer film.

-substrate-
Here, the substrate is not particularly limited, and a substrate having an insulating layer and a copper foil provided on the insulating layer, which is used for manufacturing a printed circuit board, and a light shielding layer formed on the substrate. Mask blanks or the like formed by the coating can be used.

Materials for the substrate include, for example, metals (silicon, copper, chromium, iron, aluminum, etc.), glass, titanium oxide, silicon dioxide (SiO ₂ ), silica, inorganic substances such as mica; nitrides such as SiN; Oxynitrides; organic substances such as acryl, polystyrene, cellulose, cellulose acetate, and phenolic resins; Among them, metal is preferable as the material of the substrate. By using a substrate such as a silicon substrate, a silicon dioxide substrate or a copper substrate, preferably a silicon substrate or a silicon dioxide substrate, a structure with a cylindrical structure can be formed.

Also, the size and shape of the substrate are not particularly limited. The surface of the substrate may be smooth, curved, uneven, or flake-shaped.

Furthermore, the surface of the substrate may be surface-treated 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-based coupling agent capable of reacting with hydroxyl groups. As a result, the surface layer of the substrate can be changed from hydrophilic to hydrophobic, and the adhesion between the substrate and the underlying film or between the substrate and the resist layer can be enhanced. At this time, the silane-based coupling agent is not particularly limited, but hexamethyldisilazane is preferable.

The inorganic underlayer film provided on the substrate can be formed, for example, by coating an inorganic material on the substrate and performing baking or the like. Examples of inorganic materials include silicon-based materials.

Further, the organic underlayer film provided on the substrate can be formed, for example, by coating an organic material on the substrate to form a coating film and drying the coating film. The organic materials are not limited to those sensitive to light or electron beams, and for example, resist materials and resin materials commonly used in the fields of semiconductors and liquid crystals can be used. Among them, the organic material is preferably a material capable of forming an organic underlayer film that can be etched, particularly dry-etched. In the case of such an organic material, a pattern formed by processing a resist film is used to etch an organic underlying film, thereby transferring the pattern to the underlying film to form a pattern of the underlying film. be able to. Among them, as the organic material, a material capable of forming an organic underlayer film that can be etched by oxygen plasma etching or the like is preferable. Examples of the organic material used for forming the organic underlayer film include AL412 manufactured by Brewer Science.

The application of the organic material described above can be performed by a conventionally known method using spin coating, a spinner, or the like. Moreover, as a method for drying the coating film, any method can be used as long as the solvent contained in the organic material can be volatilized, and examples thereof include a baking method. At that time, 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, preferably 500 seconds or shorter, more preferably 400 seconds or shorter, and 300 seconds or shorter. More preferably, it is particularly preferably 180 seconds or less. Although the thickness of the underlayer film after drying the coating film is not particularly limited, it is preferably 10 nm or more and 100 nm or less.

<Resist film forming process>
In the resist film forming step, a predetermined positive resist composition used in the method of forming a resist pattern of the present invention is applied onto a substrate to be processed using a resist pattern (on the underlying film when the underlying film is formed). A resist film is formed by coating and drying the coated positive resist composition. The substrate used in the resist film forming step is not particularly limited, and for example, the substrate described in <Lower layer film forming step> can be used.

[Positive resist composition]
Then, the positive resist composition used in the resist film forming step contains a copolymer A, a copolymer B, and a solvent, and optionally further contains known additives that can be incorporated into the positive resist composition. contains.
The positive resist composition preferably does not substantially contain components having a weight average molecular weight (Mw) of less than 1,000. is preferably less than 0.05% by mass, more preferably less than 0.01% by mass, and even more preferably less than 0.001% by mass.

[Copolymer A]
Copolymer A contained in the positive resist composition is a main chain scission type copolymer containing fluorine substituents. In addition, the fluorine substituent is not particularly limited as long as it is a substituent having a fluorine atom.

[Surface free energy of copolymer A]
Here, the surface free energy of copolymer A is preferably 28 mJ/m ² or more, more preferably 29 mJ/m ² or more, still more preferably 30 mJ/m ² or more, and 35 mJ/m 2 or more. It is preferably m ² or less, more preferably 34 mJ/m ² or less, and even more preferably 33 mJ/m ² or less.

〔式（Ｉ）中、Ｌは、フッ素原子を有する２価の連結基であり、Ａｒは、置換基を有していてもよい芳香環基である。〕で表される単量体単位（Ｉ）と、
下記式（ＩＩ）：

〔式（ＩＩ）中、Ｒ^１は、アルキル基であり、Ｒ^２は、水素原子、アルキル基、ハロゲン原子、ハロゲン化アルキル基、水酸基、カルボキシル基又はハロゲン化カルボキシル基であり、Ｒ^３は、水素原子、非置換のアルキル基又はフッ素原子で置換されたアルキル基であり、ｐ及びｑは、０以上５以下の整数であり、ｐ＋ｑ＝５である。〕で表される単量体単位（ＩＩ）と、を有することが好ましい。 From the viewpoint of further increasing the contrast of the resist pattern, the copolymer A has the following formula (I):

[In the formula (I), L is a divalent linking group having a fluorine atom, and Ar is an aromatic ring group optionally having a substituent. ] A monomeric unit (I) represented by
Formula (II) below:

[In formula (II), R ¹ is an alkyl group, R ² 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 ³ is It is a hydrogen atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom, p and q are integers of 0 or more and 5 or less, and p+q=5. ] and a monomer unit (II) represented by

Incidentally, the copolymer A may contain any monomer unit other than the monomer unit (I) and the monomer unit (II), but all the monomers constituting the copolymer A The ratio of the monomer units (I) and the monomer units (II) in the units is preferably 90 mol% or more in total, and is 100 mol% (that is, the copolymer A contains the monomer units (I) and the monomeric unit (II) only) is more preferred.

Since the copolymer A contains the monomer unit (I) and the monomer unit (II), when it is irradiated with an electron beam or the like, the main chain is cut and the molecular weight is reduced.

〔式（ａ）中、Ｌ及びＡｒは、式（Ｉ）と同様である。〕で表される単量体（ａ）に由来する構造単位である。 -Monomer unit (I)-
Here, the monomeric unit (I) is represented by the following formula (a):

[In Formula (a), L and Ar are the same as in Formula (I). ] is a structural unit derived from the monomer (a) represented by

As the divalent linking group having a fluorine atom, which can constitute L in the formula (I) and the formula (a), for example, a divalent chain alkyl group having 1 to 5 carbon atoms and having a fluorine atom etc.

Ar in formula (I) and formula (a) includes an optionally substituted aromatic hydrocarbon ring group and an optionally substituted aromatic heterocyclic group. .

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, and a chrysene ring group. 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 A ring group, a perylene ring group, a pentaphen ring group, a picene ring group, a pyrantrene ring group, and the like can be mentioned.

In addition, 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, and an oxadiazole. ring group, triazole ring group, imidazole ring group, pyrazole ring group, thiazole ring group, indole ring group, benzimidazole ring group, benzothiazole ring group, benzoxazole ring group, quinoxaline ring group, quinazoline ring group, phthalazine ring group, A benzofuran ring group, a dibenzofuran ring group, a benzothiophene ring group, a dibenzothiophene ring group, a carbazole ring group, and the like can be mentioned.

Furthermore, the substituent that Ar may have is not particularly limited, and examples thereof include an alkyl group, a fluorine atom and a fluoroalkyl group. Examples of the alkyl group as the substituent that Ar may have include chain alkyl groups having 1 to 6 carbon atoms such as methyl group, ethyl group, propyl group, n-butyl group and isobutyl group. Further, the fluoroalkyl group as a substituent that Ar may have includes, for example, a fluoroalkyl group having 1 to 5 carbon atoms such as a trifluoromethyl group, a trifluoroethyl group, and a pentafluoropropyl group.

Among them, from the viewpoint of sufficiently improving the sensitivity to electron beams and the like, Ar in the formula (I) and the formula (a) is preferably an aromatic hydrocarbon ring group optionally having a substituent. A substituted aromatic hydrocarbon ring group is more preferred, and a benzene ring group (phenyl group) is even more preferred.

Then, from the viewpoint of sufficiently improving the sensitivity to electron beams, etc., the monomer represented by the above formula (a) that can form the monomer unit (I) represented by the above formula (I) As the body (a), α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) and α-chloroacrylate-1-(4-methoxyphenyl) -1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPhOMe) is preferred, and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl is more preferred . That is, copolymer A contains α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-chloroacrylate-1-(4-methoxyphenyl)- It preferably has at least one of 1-trifluoromethyl-2,2,2-trifluoroethyl units, and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl It is more preferable to have units.

In addition, the ratio of the monomer unit (I) in the total monomer units constituting the copolymer A is not particularly limited, and can be, for example, 30 mol % or more and 70 mol % or less.

〔式（ｂ）中、Ｒ^１～Ｒ^３、並びに、ｐ及びｑは、式（ＩＩ）と同様である。〕で表される単量体（ｂ）に由来する構造単位である。 Further, the monomer unit (II) has the following formula (b):

[In formula (b), R ¹ to R ³ , p and q are the same as in formula (II). ] is a structural unit derived from the monomer (b) represented by

Here, the alkyl group that can constitute R ¹ and R ² in formula (II) and formula (b) is not particularly limited, and examples thereof include unsubstituted alkyl groups having 1 to 5 carbon atoms. . Among them, the alkyl group that can constitute R ¹ and R ² is preferably a methyl group or an ethyl group.

Moreover, the halogen atom that can constitute R ² in the formulas (II) and (b) is not particularly limited, and includes a fluorine atom, a chlorine atom, a bromine atom, an iodine atom and the like. Among them, a fluorine atom is preferable as the halogen atom.

Further, the halogenated alkyl group that can constitute R ² in formula (II) and formula (b) is not particularly limited and includes, for example, a fluoroalkyl group having 1 to 5 carbon atoms. Among them, the halogenated alkyl group is preferably a perfluoroalkyl group having 1 to 5 carbon atoms, more preferably a trifluoromethyl group.

Furthermore, the halogenated carboxyl group that can constitute R ² in the formulas (II) and (b) is not particularly limited, and examples thereof include a chlorinated carboxyl group (-C(=O)-Cl), a fluorinated Carboxyl group (-C(=O)-F), brominated carboxyl group (-C(=O)-Br) and the like.

In addition, the unsubstituted alkyl group that can constitute R ³ in formula (II) and formula (b) is not particularly limited, and an unsubstituted alkyl group having 1 to 5 carbon atoms is mentioned. Among them, the unsubstituted alkyl group that can constitute R ³ is preferably a methyl group or an ethyl group.

The fluorine atom-substituted alkyl group that can constitute R ³ in formula (II) and formula (b) is not particularly limited, and some or all of the hydrogen atoms in the alkyl group may be substituted with fluorine atoms. A group having a structure substituted with is exemplified.

Then, from the viewpoint of improving the ease of preparation of copolymer A and the scission of the main chain when irradiated with an electron beam or the like, R ¹ in formula (II) and formula (b) has 1 carbon atom. An alkyl group of ∼5 is preferred, and a methyl group is more preferred.

In addition, from the viewpoint of improving the ease of preparation of copolymer A and the scission of the main chain when irradiated with an electron beam or the like, p in formula (II) and formula (b) is 0 or 1. is preferred.

Furthermore, when p in formula (II) and formula (b) is any one of 1 to 5, R ² in formula (II) and formula (b) is an alkyl group having 1 to 5 carbon atoms. is preferred, and a methyl group is more preferred.

The monomer (b) represented by the above formula (b), which can form the monomer unit (II) represented by the above formula (II), is not particularly limited, Examples thereof include α-methylstyrene (AMS) such as the following monomers (b-1) to (b-12) and derivatives thereof.

From the viewpoint of ease of preparation of the copolymer A and improvement of the scission of the main chain when irradiated with an electron beam or the like, the above-described formula ( α-Methylstyrene is preferred as the monomer (b) represented by b). That is, the copolymer A preferably has α-methylstyrene units.

The ratio of the monomer units (II) in the total monomer units constituting the copolymer A is not particularly limited, and can be, for example, 30 mol % or more and 70 mol % or less.

-Properties of copolymer A-
= weight average molecular weight (Mw) =
The weight average molecular weight (Mw) of copolymer A is preferably 100,000 or more, more preferably 125,000 or more, still more preferably 150,000 or more, preferably 600,000 or less, and preferably 500,000 or less. It is more preferable to have When the weight-average molecular weight (Mw) of the copolymer A is at least the above lower limit, the reduction of the top of the resist pattern can be further reduced, and a resist pattern with further improved contrast can be formed. Also, if the weight average molecular weight (Mw) of the copolymer A is equal to or less than the above upper limit, it is possible to facilitate adjustment of the positive resist composition.

= number average molecular weight (Mn) =
The number average molecular weight (Mn) of copolymer A is preferably 100,000 or more, more preferably 110,000 or more, preferably 300,000 or less, and more preferably 200,000 or less. When the number average molecular weight of the copolymer A is at least the above lower limit, it is possible to further reduce the decrease in the top of the resist pattern and form a resist pattern with further improved contrast. Moreover, when the number average molecular weight of the copolymer A is equal to or less than the above upper limit, the preparation of the positive resist composition is further facilitated.

= molecular weight distribution (Mw/Mn) =
The molecular weight distribution (Mw/Mn) of the copolymer A is preferably 1.20 or more, more preferably 1.25 or more, further preferably 1.30 or more. 00 or less, more preferably 1.80 or less, and even more preferably 1.60 or less.
In the present invention, the "number average molecular weight" can be measured as a standard polystyrene conversion value using gel permeation chromatography, and the "molecular weight distribution" is the ratio of the weight average molecular weight to the number average molecular weight (weight average molecular weight It can be obtained by calculating the molecular weight/number average molecular weight).

-Method for preparing copolymer A-
Then, the copolymer A having the monomer unit (I) and the monomer unit (II) described above is, for example, a monomer composition containing the monomer (a) and the monomer (b) After polymerizing, the resulting copolymer can be recovered and optionally purified.
The composition, molecular weight distribution, number average molecular weight and weight average molecular weight of copolymer A can be adjusted by changing 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. Also, 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.

=Polymerization of monomer composition=
Here, the monomer composition used for preparing the copolymer A includes a monomer component containing the monomer (a) and the monomer (b), an optionally usable solvent, and optionally Mixtures of the available polymerization initiators and optionally added additives can be used. Polymerization of the monomer composition can then be carried out using known methods. Among them, it is preferable to use cyclopentanone, water, or the like as the solvent.

Further, the polymer obtained by polymerizing the monomer composition is not particularly limited. After adding a good solvent such as tetrahydrofuran to a solution containing the polymer, The polymer can be recovered by dropping it into a poor solvent such as ethanol, 1-propanol, 1-butanol, 1-pentanol, hexane, etc. to solidify the polymer.

= Purification of polymer =
The purification method used for purifying the obtained polymer is not particularly limited, and known purification methods such as reprecipitation and column chromatography can be used. Among them, it is preferable to use a reprecipitation method as the purification method.
Further, the purification of the polymer may be repeated multiple times.

Purification of the polymer by the reprecipitation method is performed, for example, by dissolving the obtained polymer in a good solvent such as tetrahydrofuran, and then dissolving the resulting solution in a good solvent such as tetrahydrofuran with methanol, ethanol, 1-propanol, It is preferable to add dropwise to a mixed solvent with a poor solvent such as 1-butanol, 1-pentanol, hexane, etc. to precipitate a part of the polymer. In this way, if the polymer solution is added dropwise to a mixed solvent of a good solvent and a poor solvent for purification, the copolymer obtained can be obtained by changing the kind and mixing ratio of the good solvent and the poor solvent. Molecular weight distribution, number average molecular weight and weight average molecular weight can be easily adjusted. Specifically, for example, the higher the ratio of the good solvent in the mixed solvent, the greater the molecular weight of the copolymer that precipitates in the mixed solvent.

When the polymer is purified by a reprecipitation method, as the copolymer A, a polymer precipitated in a mixed solvent of a good solvent and a poor solvent may be used as long as the desired properties are satisfied. A polymer that did not precipitate in the solvent (that is, a polymer dissolved in the mixed solvent) may be used. Here, the polymer that has not precipitated in the mixed solvent can be recovered from the mixed solvent using a known technique such as concentration to dryness.

[Copolymer B]
Copolymer B contained in the positive resist composition is a main chain scission type copolymer containing fluorine substituents. Copolymer B is required to have a surface free energy difference of 4 mJ/m ² or more from Copolymer A described above. The fluorine substituent is not particularly limited as long as it is a substituent having a fluorine atom.

[Surface free energy of copolymer B]
Here, the surface free energy of copolymer B is preferably 18 mJ/m ² or more, more preferably 19 mJ/m ² or more, even more preferably 20 mJ/m ² or more, and 27 mJ/m 2 or more. It is preferably m ² or less, more preferably 26 mJ/m ² or less, and even more preferably 25 mJ/m ² or less.

Then, the surface free energy of the copolymer B is the difference between the surface free energy of the copolymer A [that is, the value of (surface free energy of the copolymer A) - (surface free energy of the copolymer B)] should be 4 mJ/ ^m2 or more, and this difference is preferably 5.5 mJ/ ^m2 or more, more preferably 6 mJ/ ^m2 or more, and more preferably 6.5 mJ/ ^m2 or more. is more preferably 12 mJ/m ² or less, more preferably 11 mJ/m ² or less, even more preferably 10 mJ/m ² or less.

〔式（ＩＩＩ）中、Ｒ^１は、フッ素原子の数が５以上７以下の有機基である。〕で表される単量体単位（ＩＩＩ）と、下記式（ＩＶ）：

〔式（ＩＶ）中、Ｒ^１は、アルキル基であり、Ｒ^２は、水素原子、フッ素原子、非置換のアルキル基又はフッ素原子で置換されたアルキル基であり、Ｒ^３は、水素原子、非置換のアルキル基又はフッ素原子で置換されたアルキル基であり、ｐ及びｑは、０以上５以下の整数であり、ｐ＋ｑ＝５である。〕で表される単量体単位（ＩＶ）と、を有することが好ましい。 Then, from the viewpoint of further increasing the contrast of the resist pattern, the copolymer B has the following formula (III):

[In the formula (III), R ¹ is an organic group having 5 or more and 7 or less fluorine atoms. ] and a monomer unit (III) represented by the following formula (IV):

[In formula (IV), R ¹ is an alkyl group, R ² is a hydrogen atom, a fluorine atom, an unsubstituted alkyl group or a fluorine atom-substituted alkyl group, R ³ is a hydrogen atom, It is an unsubstituted alkyl group or an alkyl group substituted with a fluorine atom, p and q are integers from 0 to 5, and p+q=5. ] and a monomer unit (IV) represented by

Incidentally, the copolymer B may contain any monomer unit other than the monomer units (III) and the monomer units (IV), but all the monomers constituting the copolymer B The ratio of the monomer units (III) and the monomer units (IV) in the units is preferably 90 mol% or more in total, and is 100 mol% (that is, the copolymer B is a monomer unit (III) and only the monomer unit (IV)) is more preferred.

Since the copolymer B contains the monomer unit (III) and the monomer unit (IV), when it is irradiated with an electron beam or the like, the main chain is cut and the molecular weight is reduced. In addition, since at least the monomer unit (III) of the copolymer B has a fluorine atom, the surface free energy of the copolymer B can be easily adjusted. It is resistant to leaked light such as light, and the contrast of the pattern can be further increased.

〔式（ｃ）中、Ｒ^１は、式（ＩＩＩ）と同様である。〕で表される単量体（ｃ）に由来する構造単位である。 Here, the monomer unit (III) is represented by the following formula (c):

[In formula (c), R ¹ is the same as in formula (III). ] is a structural unit derived from the monomer (c) represented by

In formulas (III) and (c), the number of carbon atoms in R ¹ is preferably 2 or more and 10 or less, more preferably 5 or less. If the number of carbon atoms is at least the above lower limit, the solubility in the developer can be sufficiently improved. Further, 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.

Specifically, R ¹ in formulas (III) and (c) is preferably a fluoroalkyl group, a fluoroalkoxyalkyl group, or a fluoroalkoxyalkenyl group, more preferably a fluoroalkyl group. If R ¹ is the group described above, the scission of the main chain of copolymer B upon irradiation with an electron beam or the like can be sufficiently improved.

Here, examples of the fluoroalkyl group include a 2,2,3,3,3-pentafluoropropyl group (having 5 fluorine atoms and 3 carbon atoms), 3,3,4,4,4-pentafluoropropyl fluorobutyl group (5 fluorine atoms, 4 carbon atoms), 1H-1-(trifluoromethyl)trifluoroethyl group (6 fluorine atoms, 3 carbon atoms), 1H, 1H, 3H- Hexafluorobutyl group (6 fluorine atoms, 4 carbon atoms), 2,2,3,3,4,4,4-heptafluorobutyl group (7 fluorine atoms, 4 carbon atoms) , and 1,2,2,2-tetrafluoro-1-(trifluoromethyl)ethyl group (having 7 fluorine atoms and 3 carbon atoms). Among them, a 2,2,3,3,3-pentafluoropropyl group (having 5 fluorine atoms and 3 carbon atoms) or 2,2,3,3,4,4,4-heptafluorobutyl A group (having 7 fluorine atoms and 4 carbon atoms) is preferred, and a 2,2,3,3,3-pentafluoropropyl group (having 5 fluorine atoms and 3 carbon atoms) is more preferred.
Further, examples of the fluoroalkoxyalkyl group include a fluoroethoxymethyl group and a fluoroethoxyethyl group.
Furthermore, examples of fluoroalkoxyalkenyl groups include fluoroethoxyvinyl groups.

The monomer (c) represented by the above formula (c), which can form the monomer unit (III) represented by the above formula (III), is not particularly limited, For example, α-chloroacrylate 2,2,3,3,3-pentafluoropropyl, α-chloroacrylate 3,3,4,4,4-pentafluorobutyl, α-chloroacrylate 1H-1-( trifluoromethyl)trifluoroethyl, 1H,1H,3H-hexafluorobutyl α-chloroacrylate, 1,2,2,2-tetrafluoro-1-(trifluoromethyl)ethyl α-chloroacrylate, α- α-Chloroacrylic acid fluoroalkyl esters such as 2,2,3,3,4,4,4-heptafluorobutyl chloroacrylate; α-chloroacrylic acid pentafluoroethoxymethyl ester, α-chloroacrylic acid pentafluoro α-chloroacrylic acid fluoroalkoxyalkyl esters such as ethoxyethyl ester; α-chloroacrylic acid fluoroalkoxyalkenyl esters such as α-chloroacrylic acid pentafluoroethoxyvinyl ester;

From the viewpoint of further improving the scission of the main chain of the copolymer B when irradiated with an electron beam or the like, the monomer unit (III) is a structural unit derived from α-chloroacrylic acid fluoroalkyl ester. is preferably

〔式（ｄ）中、Ｒ^１～Ｒ^３、並びに、ｐ及びｑは、式（ＩＶ）と同様である。）で表される単量体（ｄ）に由来する構造単位である。 Further, the monomer unit (IV) has the following general formula (d):

[In formula (d), R ¹ to R ³ and p and q are the same as in formula (IV). ) is a structural unit derived from the monomer (d) represented by

Here, the alkyl group that can constitute R ¹ in formula (IV) and formula (d) is not particularly limited, and includes an alkyl group having 1 or more and 5 or less carbon atoms. Among them, the alkyl group that can constitute R ¹ is preferably a methyl group or an ethyl group.

In addition, the unsubstituted alkyl group that can constitute R ² and R ³ in formulas (IV) and (d) is not particularly limited, and includes an unsubstituted alkyl group having 1 to 5 carbon atoms. . Among them, the unsubstituted alkyl group that can constitute R ² and R ³ is preferably a methyl group or an ethyl group.

Furthermore, the fluorine atom-substituted alkyl group that can constitute R ² and R ³ in formulas (IV) and (d) is not particularly limited, and some or all of the hydrogen atoms in the alkyl group are A group having a structure substituted with a fluorine atom is included.

And from the viewpoint of improving the ease of preparation of copolymer B, all of R ² and / or R ³ present in plurality in formula (IV) and formula (d) are hydrogen atoms or unsubstituted alkyl is preferably a group, preferably a hydrogen atom or an unsubstituted alkyl group having 1 to 5 carbon atoms, preferably a hydrogen atom.

The monomer (d) represented by the above formula (d), which can form the monomer unit (IV) represented by the above formula (IV), is not particularly limited, Examples thereof include α-methylstyrene (AMS) such as the following monomers (d-1) to (d-11) and derivatives thereof (eg, 4-fluoro-α-methylstyrene: 4FAMS).

From the viewpoint of ease of preparation of the copolymer B and improvement of the scission of the main chain when irradiated with an electron beam or the like, the above-mentioned formula ( Preferred monomers (d) represented by d) are α-methylstyrene and 4-fluoro-α-methylstyrene. That is, copolymer B preferably has α-methylstyrene units or 4-fluoro-α-methylstyrene units.

The ratio of the monomer units (IV) in the total monomer units constituting the copolymer B is not particularly limited, and can be, for example, 30 mol % or more and 70 mol % or less.

-Properties of copolymer B-
= weight average molecular weight (Mw) =
The weight average molecular weight (Mw) of copolymer B is preferably 10,000 or more, more preferably 17,000 or more, still more preferably 25,000 or more, and preferably 250,000 or less, and 180,000 or less. It is more preferably 50,000 or less. When the weight-average molecular weight (Mw) of the copolymer B is at least the above lower limit, it is possible to suppress excessive increase in the solubility of the resist film in the developer at a low irradiation dose. Further, when the weight average molecular weight (Mw) of the copolymer B is equal to or less than the above upper limit, it is easy to prepare a positive resist composition.

= number average molecular weight (Mn) =
The number average molecular weight (Mn) of copolymer B is preferably 7,000 or more, more preferably 10,000 or more, and preferably 150,000 or less. If the number average molecular weight of the copolymer B is at least the above lower limit, it is possible to further suppress the excessive increase in the solubility of the resist film in a developer at a low irradiation dose, and to form a resist pattern with a further improved contrast. can be formed. Moreover, if the number average molecular weight of the copolymer B is equal to or less than the above upper limit, it is easier to prepare a positive resist composition.

= molecular weight distribution (Mw/Mn) =
The molecular weight distribution (Mw/Mn) of copolymer B is preferably 1.10 or more, more preferably 1.20 or more, preferably 1.70 or less, and 1.65. The following are more preferable. If the molecular weight distribution (Mw/Mn) of the copolymer B is at least the above lower limit, the ease of production of the copolymer B can be enhanced. Moreover, if the molecular weight distribution (Mw/Mn) of the copolymer B is equal to or less than the above upper limit, the contrast of the resulting resist pattern can be further enhanced.

-Method for preparing copolymer B-
And the copolymer B having the monomer unit (III) and the monomer unit (IV) described above is not particularly limited, for example, a monomer containing a monomer (c) and a monomer (d) After polymerizing the polymer composition, the resulting copolymer can be recovered and optionally purified. Here, the polymerization method and purification method are not particularly limited, and may be the same as the polymerization method and purification method of copolymer A described above. Moreover, in preparing the copolymer B, it is preferable to use a polymerization initiator, and for example, a polymerization initiator such as azobisisobutyronitrile can be preferably used.

〔solvent〕
The solvent contained in the positive resist composition is not particularly limited as long as it is capable of dissolving the copolymer A and copolymer B described above. Known solvents such as can be used. Among them, anisole, propylene glycol monomethyl ether acetate (PGMEA), cyclopentanone, and cyclohexanone are used as solvents from the viewpoint of obtaining a positive resist composition having an appropriate viscosity and improving the coatability of the positive resist composition. Alternatively, isoamyl acetate is preferably used.

<Preparation of positive resist composition>
A positive resist composition can be prepared by mixing the above-described copolymer A, copolymer B, solvent, and optionally known additives. At that time, the mixing method is not particularly limited, and the mixing may be performed by a known method. Moreover, you may filter and prepare a mixture after mixing each component.

[Filtration]
Here, the method for filtering the mixture is not particularly limited, and for example, it can be filtered using a filter. The filter is not particularly limited, and includes, for example, fluorocarbon-based, cellulose-based, nylon-based, polyester-based, and hydrocarbon-based filtration membranes. Above all, from the viewpoint of effectively preventing impurities such as metals from entering the positive resist composition from metal pipes that may be used in the preparation of copolymer A and copolymer B, the filter is configured. Polyfluorocarbons such as nylon, polyethylene, polypropylene, polytetrafluoroethylene, Teflon (registered trademark), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), nylon, and composite membranes of polyethylene and nylon etc. are preferred. As filters, for example, those disclosed in US Pat. No. 6,103,122 may be used. Also, the filter is commercially available as Zeta Plus (registered trademark) 40Q manufactured by CUNO Incorporated. Additionally, 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. Cation exchange resins include, for example, sulfonated phenol-formaldehyde condensates, sulfonated phenol-benzaldehyde condensates, sulfonated styrene-divinylbenzene copolymers, sulfonated methacrylic acid-divinylbenzene copolymers, and Other types of sulfonic acid or carboxylic acid group-containing polymers and the like are included. The cation exchange resin is provided with H ⁺ counterions, NH ₄ ⁺ counterions or alkali metal counterions such as K ⁺ and Na ⁺ counterions. And the cation exchange resin preferably has a hydrogen counterion. Such cation exchange resins include Microlite® PrCH from Purolite, a sulfonated styrene-divinylbenzene copolymer with H ^{2 +} counterions. Such cation exchange resins are commercially available as AMBERLYST® from Rohm and Haas.

Furthermore, the pore size of the filter is preferably 0.001 μm or more and 1 μm or less. If the pore size of the filter is within the above range, it is possible to sufficiently prevent impurities such as metals from entering the positive resist composition.

[Proportion of Copolymer A and Copolymer B]
The ratio of the copolymer A and the copolymer B in the positive resist composition is not particularly limited, but the ratio of the copolymer B is 100% by mass in total of the copolymer A and the copolymer B. It is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, preferably 30% by mass or less, and 25% by mass or less. It is more preferable that the content is 20 mass % or less. If the proportion of the copolymer B is at least the above lower limit, it is possible to suppress the excessive increase in the solubility of the resist film in the developing solution at a low irradiation dose, and to form a resist pattern with further improved contrast. can be done. Moreover, if the proportion of the copolymer B is equal to or less than the above upper limit, deterioration of the sensitivity of the positive resist can be suppressed.

In the resist film forming step, the method for applying and drying the positive resist composition is not particularly limited, and methods generally used for forming a resist film can be used. Among them, heating (pre-baking) is preferable as the drying method. In addition, 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 copolymer A and copolymer B in the membrane, the temperature is preferably 250° C. or lower, more preferably 220° C. or lower, and preferably 200° C. or lower. More preferred. Furthermore, from the viewpoint of improving the film density of the resist film formed through prebaking, the prebaking time is preferably 10 seconds or longer, more preferably 20 seconds or longer, and further preferably 30 seconds or longer. Preferably, the time is preferably 10 minutes or less, more preferably 5 minutes or less, from the viewpoint of reducing changes in the molecular weights and molecular weight distributions of the copolymer A and the copolymer B in the resist film before and after prebaking. Minutes or less is more preferable.

<Exposure process>
In the exposure step, the resist film formed in the resist film forming step is irradiated with ionizing radiation such as an electron beam and EUV to draw a desired pattern. For electron beam irradiation, a known drawing apparatus such as an electron beam drawing apparatus or an EUV exposure apparatus can be used.

<Post-exposure bake process>
An optional post-exposure bake step heats the resist film exposed in the exposure step. By performing the post-exposure baking process, the surface roughness of the resist pattern can be reduced.

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, and 170° C. or lower. is more preferably 150° C. or lower. If the heating temperature is within the above range, the surface roughness of the resist pattern can be satisfactorily reduced while enhancing the clarity of the resist pattern.

The time (heating time) for heating the resist film in the post-exposure baking step is preferably 10 seconds or longer, more preferably 20 seconds or longer, and even more preferably 30 seconds or longer. If the heating time is 10 seconds or more, the surface roughness of the resist pattern can be sufficiently reduced while enhancing the clarity of the resist pattern. On the other hand, from the viewpoint of production efficiency, the heating time is, for example, preferably 10 minutes or less, more preferably 5 minutes or less, and even more preferably 3 minutes or less.

The method of heating the resist film in the post-exposure baking step is not particularly limited, and examples thereof include a method of heating the resist film with a hot plate, a method of heating the resist film in an oven, and a method of blowing hot air onto the resist film. mentioned.

<Development process>
In the development step, the exposed resist film (the exposed and heated resist film when the post-exposure bake step is performed) is treated with a solubility parameter (SP value) of 8 (cal/cm ³ ) ^1/2 or less. Development is performed using a developer containing at least a solvent.

[Developer]
Here, the SP value of the developer is preferably 7.9 (cal/cm ³ ) ^1/2 or less, more preferably 7.8 (cal/cm ³ ) ^1/2 or less. .0 (cal/cm ³ ) ^1/2 or more is preferable, 6.2 (cal/cm ³ ) ^1/2 or more is more preferable, and 6.4 (cal/cm ³ ) ^1/2 or more is preferable. It is more preferable that it is above. If the SP value of the developer is within the above range, the contrast of the resist pattern can be further enhanced.

As the developer containing at least a solvent having an SP value of 8 (cal/cm ³ ) ^1/2 or less, a solvent having an SP value of 8 (cal/cm ³ ) ^1/2 or less is used alone. can be done. Alternatively, as a developer containing at least a solvent having an SP value of 8 (cal/cm ³ ) ^1/2 or less, a solvent having an SP value of 8 (cal/cm ³ ) ^1/2 or less and a solvent having an SP value of 8 ( cal/cm ³ ) ^1/2 or less, and a mixed solvent containing a different solvent (hereinafter referred to as "another solvent") can be used.

When a solvent having an SP value of 8 (cal/cm ^{3 ) 1/2 or less is used alone as a developer, the SP value is 8 (cal/cm 3 ) 1/2 or less} in the developing process. including processing (1) of developing using a certain solvent as developer (1) and processing (2) of developing using developer (2) different from developer (1), processing (1) and It is preferable to perform processing (2) in this order. In the development step, a process (1) is performed in which a solvent having an SP value of 8 (cal/cm ³ ) ^1/2 or less is used as a developer (1) for development. By performing the process (2) of developing using the developer (2), it is possible to efficiently form a resist pattern with a higher contrast while reducing the reduction of the top of the resist pattern.

The developer (1) is not particularly limited as long as it is a solvent having an SP value of 8 (cal/cm ³ ) ^1/2 or less. ³ ) It is preferable to use a hydrocarbon-based solvent that is ^1/2 or less. Here, as the hydrocarbon-based solvent, for example, a linear or branched aliphatic hydrocarbon having 12 or less carbon atoms can be mentioned. Hydrocarbons are preferred. When the number of carbon atoms is 7 or more, when the resist film is brought into contact with the developer (1) and developed, volatilization of the developer (1) is suppressed and the surface of the resist film is uniformly spread with the developer (1). can be painted on. Also, if the number of carbon atoms is 10 or less, the developer (1) can be easily removed in the rinse step. Preferred hydrocarbon solvents include branched chain alkanes such as heptane, octane, nonane, and decane. One of the hydrocarbon-based solvents may be used alone, or two or more thereof may be used in combination.

The boiling point of the developer (1) is not particularly limited, but is preferably 80° C. or higher, more preferably 90° C. or higher, preferably 230° C. or lower, and 200° C. or lower. is preferred. If the boiling point of the developer (1) is the above lower limit, when the resist film is developed by contacting the developer (1), volatilization of the developer (1) is further suppressed, and the developer (1) The in-plane of the resist film can be coated more uniformly. Moreover, if the boiling point of the developer (1) is equal to or lower than the above upper limit, the developer (1) can be more easily removed in the rinsing step.

The developer (2) is not particularly limited as long as it is different from the developer (1), but the SP value of the developer (2) should be more than 8 (cal/cm ³ ) ^1/2 . is preferably 9 (cal/cm ³ ) ^1/2 or more, and more preferably 10 (cal/cm ³ ) ^1/2 or more. Preferable developer (2) includes, for example, alcohol solvents having 1 to 10 carbon atoms, preferably 5 or less carbon atoms. Alcohols such as propanol (isopropyl alcohol), 1-butanol, 2-butanol, 1-pentanol, 2-pentanol and 3-pentanol can be mentioned. Among these, ethanol, 1-propanol, 2-propanol, and 1-butanol are preferable from the viewpoint of further increasing the contrast of the resist pattern. These alcohols may be used individually by 1 type, and may combine 2 or more types.

Further, as described above, when a mixed solvent containing a solvent having an SP value of 8 (cal/cm ³ ) ^1/2 or less and another solvent is used as the developer, the SP value is 8 (cal /cm ³ ) ^1/2 or less and the other solvent (solvent with SP value of 8 (cal/cm ³ ) ^1/2 or less: other solvent) is 10:90 to 90: It is preferably 10, more preferably 30:70 to 70:30. If the mass ratio of the mixed solvent containing the solvent having an SP value of 8 (cal/cm ³ ) ^1/2 or less and the other solvent is within the above range, the contrast of the resist pattern can be further enhanced.

Here, when a mixed solvent containing a solvent having an SP value of 8 (cal/cm ³ ) ^1/2 or less and another solvent is used as a developer, the SP value is 8 (cal/cm ³ ) ^1/2 The solvent having a molecular weight of ² or less is not particularly limited, and for example, the above-mentioned hydrocarbon solvents can be preferably used. Moreover, the other solvent is not particularly limited, and for example, the above-described alcohol-based solvent can be preferably used.

Then, the development of the resist film can be performed, for example, by bringing the resist film into contact with the developer described above. The method of bringing the resist film into contact with the developer is not particularly limited, and known techniques such as immersion of the resist film in the developer and application of the developer to the resist film can be used.

The temperature of the developer during development is not particularly limited, but can be, for example, 5° C. or higher and 40° C. or lower. Also, the development time can be, for example, 10 seconds or more and 4 minutes or less.

The developer may also be filtered prior to use. As the filtering method, for example, the filtering method using a filter as described in the section "Preparation of positive resist composition" can be mentioned.

<Rinse process>
An optional rinse step removes the developer after the development step. The developer can be removed using, for example, a rinse.
Specific examples of the rinsing liquid include hydrocarbon solvents, alcohol solvents, water, and the like exemplified in the section "developing step". Here, the rinse liquid may contain a surfactant. When selecting the 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.

The temperature of the rinsing liquid during rinsing is not particularly limited, but can be, for example, 5° C. or higher and 40° C. or lower. Also, the rinse time can be, for example, 5 seconds or more and 3 minutes or less.

Also, the rinse solution used in the rinse step may be filtered before use. As the filtering method, for example, the filtering method using a filter as described in the section "Preparation of positive resist composition" can be mentioned.

<Etching process>
In an optional etching step, the underlying film and/or substrate is etched using the resist pattern described above as a mask to form a pattern in the underlying film and/or substrate.
At that time, the number of times of etching is not particularly limited, and may be one or more times. Etching may be either 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 according to the underlying film to be etched, the elemental composition of the substrate, and the like. Examples of etching gas include fluorine-based gases such as CHF ₃ , CF ₄ , C ₂ F ₆ , C ₃ F ₈ and SF ₆ ; chlorine-based gases such as Cl ₂ and BCl ₃ ; O ₂ , O ₃ and H ₂ O and the like. oxygen _- based gases; _H2 , _NH3 , _CO , _CO2 , _CH4 , _{C2H2 , C2H4 , C2H6 , C3H4} , _C3H6 , _C3H8 , _HF , HI, HBr, HCl, NO, NH ₃ , BCl ₃ and other reducing gases; He, N ₂ , Ar and other inert gases. These gases may be used singly or in combination of two or more. An oxygen-based gas is usually used for dry etching of an inorganic underlayer film. For dry etching of substrates, a fluorine-based gas is usually used, and a mixture of a fluorine-based gas and an inert gas is preferably used.

Further, if necessary, the underlayer film remaining on the substrate may be removed before etching the substrate or after etching the substrate. When the underlying film is removed before etching the substrate, the underlying film may be a patterned underlying film or an unpatterned underlying film.

Here, as a method for removing the lower layer film, for example, the above-described dry etching can be used. In the case of an inorganic lower layer film, the lower layer film may be removed by bringing a liquid such as a basic liquid or an acidic liquid, preferably a basic liquid, into contact with the lower layer film. Here, the basic liquid is not particularly limited, and examples thereof include alkaline hydrogen peroxide water and the like. The method for removing the lower layer film by wet stripping using alkaline hydrogen peroxide solution is not particularly limited as long as it is a method that allows the lower layer film and alkaline hydrogen peroxide solution to come into contact with each other for a certain period of time under heating conditions. in a heated alkaline hydrogen peroxide solution, a method of spraying an alkaline hydrogen peroxide solution on the lower layer film in a heated environment, a method of applying a heated alkaline hydrogen peroxide solution to the lower layer film, and the like. After performing one of these methods, the substrate is washed with water and dried to obtain a substrate from which the underlayer film has been removed.

(Etching resistance of resist film)
The resist film obtained by the method for forming a resist pattern of the present invention has excellent etching resistance, particularly excellent dry etching resistance. The resist film tends to be more excellent in dry etching resistance as the ratio of the carbon content per unit volume of the copolymer A and the copolymer B contained in the positive resist composition increases.

Then, according to the method of forming a resist pattern of the present invention, for example, it is possible to obtain a laminate provided with a resist film having a two-layer structure as described below.

(Laminate)
A laminate obtained by the method of forming a resist pattern of the present invention comprises a substrate and a resist film formed on the substrate. Prepared with the upper layer. The lower layer is composed of the copolymer A described above, and the upper layer is composed of the copolymer B described above. The resist film included in the laminate of the present invention can be formed by the method of forming a resist pattern of the present invention.

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.
In the examples and comparative examples, the number average molecular weight, weight average molecular weight and molecular weight distribution of the copolymer, surface free energy, and developer solubility parameter were measured by the following methods.

<Number average molecular weight, weight average molecular weight and molecular weight distribution>
The number average molecular weight (Mn) and weight average molecular weight (Mw) of the obtained copolymer A and copolymer B were measured using gel permeation chromatography, and the molecular weight distribution (Mw/Mn) was calculated.
Specifically, using a gel permeation chromatograph (manufactured by Tosoh, HLC-8220), using tetrahydrofuran as a developing solvent, the number average molecular weight (Mn) and weight average molecular weight (Mn) of copolymer A and copolymer B Mw) was obtained as a standard polystyrene conversion value. Then, the molecular weight distribution (Mw/Mn) was calculated. It was confirmed that each of the obtained copolymers A and B substantially did not contain components having a weight-average molecular weight (Mw) of less than 1,000.

<Surface free energy>
<<Surface free energy of copolymer A>>
The copolymer A1 as the copolymer A prepared in Preparation Example 1 was dissolved in isoamyl acetate to prepare a composition (A) for surface free energy measurement with a concentration of 3% by mass. Using the obtained composition (A), a film was produced by the following method.
<<Method for producing film>>
Using a spin coater (manufactured by Mikasa, MS-A150), the composition (A) prepared as described above was applied to a silicon wafer having a diameter of 4 inches to a thickness of 50 nm. Then, the applied composition (A) was heated on a hot plate at a temperature of 170° C. for 1 minute to form a resist film on the silicon wafer.
Next, the resulting film (membrane) was measured using a contact angle meter (Drop Master 700, manufactured by Kyowa Interface Science Co., Ltd.) to determine the surface tension, polar term (p) and dispersion force term (d) of two types with known The contact angle of the solvent (water and diiodomethane) was measured under the following conditions, the surface free energy was evaluated by the Owens-Wendt (extended Fowkes formula) method, and the surface free energy of the film was calculated. The surface free energy of the obtained film (membrane) was used as the surface free energy of the copolymer A.
<<Measurement conditions for contact angle measurement>>
Needle: metal needle 22G (water), Teflon (registered trademark) coating 22G (diiodomethane)
Standby time: 1000ms
Liquid volume: 1.8 μL
Liquid contact recognition: water 50 dat, diiodomethane 100 dat
Temperature: 23°C
<<Surface free energy of copolymer B>>
The surface free energy of copolymer B was calculated in the same manner as in the calculation of the surface free energy of copolymer A described above, except that copolymer B prepared in Preparation Examples 2 to 7 was used instead of copolymer A. asked for

<Solubility parameter (SP value) of developer>
Literature values calculated by the Hansen method were used as the solubility parameters (SP values) of the developers used in Examples and Comparative Examples.

<Preparation of copolymer A>
<<Preparation Example 1: Preparation of Copolymer A1>>
[Preparation of aqueous solution of semi-hardened beef tallow fatty acid potash soap with a solid content of 18%]
100 g of ion-exchanged water was prepared, heated to 70° C. with stirring, and 8.40 g of potassium hydroxide (49% aqueous solution) was added. Next, 19.6 g of beef tallow 45° hardened fatty acid HFA (manufactured by NOF Corporation) was added at an addition rate of 1.28 g/min, and then 0.126 g of potassium silicate was added. Then, the mixture was stirred at 80° C. for 2 hours or more to obtain an aqueous solution of semi-hardened beef tallow fatty acid potash soap having a solid content of 18%.
[Synthesis of polymer]
3 g of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as the monomer (a) was placed in a glass ampoule containing a stirring bar; 1.066 g of α-methylstyrene as monomer (b) was added. Further, in the same ampoule, 6.771 g of ion-exchanged water is added to 0.5463 g of the above-prepared 18% solids aqueous solution of the semi-cured beef tallow fatty acid potash soap to obtain a monomer composition, and then the ampoule is filled. It was sealed, and pressurization and depressurization with nitrogen gas were repeated 10 times to remove oxygen in the system.
Then, the inside of the system was heated to 75° C., and the polymerization reaction was carried out for 1 hour. Next, 10 g of tetrahydrofuran (THF) was added to the system, and the obtained solution was dropped into 100 g of MeOH to precipitate a polymer. After that, the precipitated polymer was collected by filtration. The obtained polymer was a copolymer containing 54 mol % of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and 46 mol % of α-methylstyrene units. was a coalescence.
After that, the obtained copolymer (copolymer A1 before purification) was measured for number average molecular weight, weight average molecular weight and molecular weight distribution. Table 1 shows the results.
[Purification of polymer]
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) to obtain a white coagulum (α- A copolymer containing 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl chloroacrylate units and α-methylstyrene units) was precipitated. Thereafter, the solution containing the precipitated copolymer was filtered through a Kiriyama funnel, and the white copolymer (α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units 54 mol % and 46 mol % of α-methylstyrene units).
After that, the obtained copolymer (copolymer A1 after purification) was measured for number average molecular weight, weight average molecular weight, molecular weight distribution, and surface free energy. Table 1 shows the results.

<Preparation Example 2: Preparation of copolymer B1>
[Synthesis of polymer]
3 g of α-chloroacrylate 2,2,3,3,3-pentafluoropropyl (ACAPFP) as monomer (c) and 3.476 g of α-methylstyrene as monomer (d); A monomer composition containing 0.0551 g of azobisisobutyronitrile as a polymerization initiator and 1.6205 g of cyclopentanone as a solvent is placed in a glass container, and the glass container is sealed and replaced with nitrogen. The mixture was stirred for 6 hours in a constant temperature bath at 78°C under atmosphere.
Thereafter, the temperature was returned to room temperature, and after the inside of the glass container was exposed to the atmosphere, 10 g of THF was added to the obtained solution. Then, the solution containing THF was dropped into 100 g of MeOH as a solvent to precipitate a polymer. After that, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white coagulate (polymer). The obtained polymer was a copolymer containing 50 mol % of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and 50 mol % of α-methylstyrene units.
After that, various measurements were performed in the same manner as in Preparation Example 1 for the obtained copolymer (copolymer B1 before purification). Table 1 shows the results.
[Purification of polymer]
Next, the obtained polymer is dissolved in 100 g of THF, and the obtained solution is added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 6:94) to form a white solid (α - a copolymer containing 2,2,3,3,3-pentafluoropropyl chloroacrylate units and α-methylstyrene units) was precipitated. Thereafter, the solution containing the precipitated coagulum was filtered through a Kiriyama funnel, and the white polymer (α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit 50 mol% and α-methylstyrene unit 50 mol% A copolymer containing and was obtained.
After that, various measurements were performed in the same manner as in Preparation Example 1 for the obtained copolymer (copolymer B1 after purification). Table 1 shows the results.

<<Preparation Example 3: Preparation of Copolymer B2>>
[Synthesis of polymer]
Except that the amount of azobisisobutyronitrile as a polymerization initiator was changed to 0.02755 g and that the obtained polymer was not purified, the same operation as in Preparation Example 2 was performed to obtain a white A copolymer containing 50 mol % of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and 50 mol % of α-methylstyrene units was obtained as a coagulate (polymer).
The obtained copolymer was designated as copolymer B2, and various measurements were carried out in the same manner as in Preparation Example 1 for copolymer B2. Table 1 shows the results.

<<Preparation Example 4: Preparation of Copolymer B3>>
[Synthesis of polymer]
A white coagulate (polymer) was obtained in the same manner as in Preparation Example 2, except that the amount of azobisisobutyronitrile as a polymerization initiator was changed to 0.00551 g. The obtained polymer was a copolymer containing 50 mol % of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and 50 mol % of α-methylstyrene units.
After that, various measurements were performed in the same manner as in Preparation Example 1 for the obtained copolymer (copolymer B3 before purification). Table 1 shows the results.
[Purification of polymer]
Then, the obtained polymer was dissolved in 100 g of THF, and the obtained solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 15:85) to form a white solid (α - a copolymer containing 2,2,3,3,3-pentafluoropropyl chloroacrylate units and α-methylstyrene units) was precipitated. Thereafter, the solution containing the precipitated coagulum was filtered through a Kiriyama funnel, and the white polymer (α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit 50 mol% and α-methylstyrene unit 50 mol% A copolymer containing and was obtained.
After that, various measurements were performed in the same manner as in Preparation Example 1 for the obtained copolymer (copolymer B3 after purification). Table 1 shows the results.

<<Preparation Example 5: Preparation of Copolymer B4>>
[Synthesis of polymer]
Except for changing the amount of azobisisobutyronitrile as a polymerization initiator to 0.02755 g, the same operation as in Preparation Example 2 was performed to obtain a white coagulate (polymer). The obtained polymer was a copolymer containing 50 mol % of α-chloroacrylic acid 2,2,2,3,3,3-pentafluoropropyl units and 50 mol % of α-methylstyrene units.
After that, various measurements were performed in the same manner as in Preparation Example 1 for the obtained copolymer (copolymer B4 before purification). Table 1 shows the results.
[Purification of polymer]
Next, the resulting polymer is dissolved in 100 g of THF, and the resulting solution is added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 9:91) to form a white solid (α - a copolymer containing 2,2,3,3,3-pentafluoropropyl chloroacrylate units and α-methylstyrene units) was precipitated. Thereafter, the solution containing the precipitated coagulum was filtered through a Kiriyama funnel, and the white polymer (α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit 50 mol% and α-methylstyrene unit 50 mol% A copolymer containing and was obtained.
After that, various measurements were performed in the same manner as in Preparation Example 1 for the obtained copolymer (copolymer B4 after purification). Table 1 shows the results.

<<Preparation Example 6: Preparation of copolymer B5>>
[Synthesis of polymer]
Except for changing the amount of azobisisobutyronitrile as a polymerization initiator to 0.1102 g, the same operation as in Preparation Example 2 was performed to obtain a white coagulate (polymer). The obtained polymer was a copolymer containing 50 mol % of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl units and 50 mol % of α-methylstyrene units.
After that, the obtained copolymer (copolymer B5 before purification) was subjected to various measurements in the same manner as in Preparation Example 1. Table 1 shows the results.
[Purification of polymer]
Then, the resulting polymer is dissolved in 100 g of THF, and the resulting solution is added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) 5:95) to form a white solid (α - a copolymer containing 2,2,3,3,3-pentafluoropropyl chloroacrylate units and α-methylstyrene units) was precipitated. Thereafter, the solution containing the precipitated coagulum was filtered through a Kiriyama funnel, and the white polymer (α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit 50 mol% and α-methylstyrene unit 50 mol% A copolymer containing and was obtained.
After that, various measurements were performed in the same manner as in Preparation Example 1 for the obtained copolymer (copolymer B5 after purification). Table 1 shows the results.

<<Preparation Example 7: Preparation of copolymer B6>>
[Synthesis of polymer]
Except that the amount of azobisisobutyronitrile as a polymerization initiator was changed to 0.551 g and that the obtained polymer was not purified, the same operation as in Preparation Example 2 was performed to obtain a white A polymer (a copolymer containing 50 mol % of 2,2,3,3,3-pentafluoropropyl α-chloroacrylate and 50 mol % of α-methylstyrene) was obtained.
The obtained copolymer was designated as copolymer B6, and various measurements were performed in the same manner as in Preparation Example 1 for copolymer B6. Table 1 shows the results.

In Table 1,
"ACAFPh" represents α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl,
"ACAPFP" stands for 2,2,3,3,3-pentafluoropropyl α-chloroacrylate;
"KORR (18%) soap" refers to an 18% solids aqueous solution of semi-hardened tallow fatty acid potash soap;
"THF" stands for tetrahydrofuran;
"MeOH" represents methanol.

(Example 1)
<Preparation of positive resist composition>
As the copolymer A, the copolymer A1 prepared in Preparation Example 1 and as the copolymer B, the copolymer B1 prepared in Preparation Example 2 were used. Then, the copolymer A and the copolymer B were dissolved in isoamyl acetate as a solvent so that the mass ratio (copolymer A:copolymer B) was 90:10. Then, a positive resist composition containing the copolymer A and the copolymer B and having a concentration of 3% by mass was prepared.

<Formation of resist pattern>
<<Resist film formation process>>
Using a spin coater (Mikasa, MS-A150), the positive resist composition obtained as described above was applied to a silicon wafer having a diameter of 4 inches to a thickness of 50 nm. Then, the applied positive resist composition was heated on a hot plate at a temperature of 170° C. for 1 minute to form a resist film on the silicon wafer.
<<Exposure process>>
The formed resist film was exposed. Specifically, using an electron beam drawing apparatus (ELS-S50, manufactured by Elionix), a plurality of patterns (dimensions of 500 μm×500 μm) with different electron beam doses were drawn on the resist film. The dose of the electron beam was varied by 4 μC/cm ² within the range of 4 μC/cm ² to 200 μC/cm ² .
<<Post-exposure baking process>>
The exposed resist film was heated with a hot plate at 100° C. for 1 minute.
<<development process>>
The exposed resist film was developed using a developer. Specifically, heptane (SP value: 7.4 (cal/cm ³ ) ^1/2 , boiling point: 98°C) was used as developer (1), and development processing was performed at a temperature of 23°C for 1 minute ( process (1)). After that, the developer (1) was removed by nitrogen blow. Subsequently, using ethanol (SP value: 12.7 (cal/cm ³ ) ^1/2 , boiling point: 78°C) as developer (2), development processing was performed at a temperature of 23°C for 1 minute (processing ( 2)). After that, the developer (2) was removed by nitrogen blow.

<γ value>
The thickness of the resist film in the portion where the pattern was drawn as described above was measured with an optical film thickness meter (Lambda Ace, manufactured by SCREEN Semiconductor Solutions Co., Ltd.). A sensitivity curve showing the relationship between the residual film ratio (=thickness of the resist film after development/thickness of the resist film formed on the silicon wafer) was prepared.
Then, the resulting sensitivity curve (horizontal axis: common logarithm of the total electron beam dose, vertical axis: residual film ratio of the resist film (0≦remaining film ratio≦1.00)), the residual film ratio is 0.20. The sensitivity curve is fitted to a quadratic function in the range of ~0.80, and the point of the residual film rate of 0 and the residual film rate on the obtained quadratic function (function of the residual film rate and the common logarithm of the total irradiation dose) A straight line (approximation line of the slope of the sensitivity curve) connecting the 0.50 points was created.
Also, the γ value was obtained using the following formula. Table 2 shows the results. In the following formula, E ₀ is the quadratic function obtained by fitting the sensitivity curve to a quadratic function in the range of the residual film rate of 0.20 to 0.80 (commonly used for the residual film rate and total irradiation dose is the logarithm of the total dose obtained when the remaining film rate of 0 is substituted for the function of the logarithm. In addition, E1 is _a straight line (approximation line of the slope of the sensitivity curve) connecting the point of the residual film rate of 0 and the point of the residual film rate of 0.50 on the obtained quadratic function, and the obtained straight line It is the logarithm of the total irradiation dose obtained when the residual film ratio of 1.00 is substituted for (the function of the residual film ratio and the common logarithm of the total irradiation dose). The following formula represents the slope of the straight line between the residual film ratios of 0 and 1.00. If the γ value exceeds 9.8, the slope of the sensitivity curve is large, indicating that a high-contrast resist pattern can be satisfactorily formed.

<Eth>
The initial thickness _T0 of the resist film obtained above was measured with an optical film thickness meter (Lambda Ace manufactured by SCREEN Semiconductor Solution Co., Ltd.). In addition, the total dose Eth (μC/cm ² ) of the electron beam when the residual film ratio of the straight line (approximate line of the slope of the sensitivity curve) obtained when calculating the γ value was 0 was determined. Table 2 shows the results. The smaller the Eth value, the higher the sensitivity of the resist film and the higher the resist pattern formation efficiency.

(Examples 2-3)
<Preparation of positive resist composition>
Copolymer B2 was used as copolymer B in preparing the positive resist composition. Then, except that the mass ratio of copolymer A and copolymer B (copolymer A: copolymer B) was set to 80:20 (Example 2) and 70:30 (Example 3). prepared a positive resist composition in the same manner as in Example 1.
<Formation of resist pattern>
A resist pattern was formed in the same manner as in Example 1 except that the positive resist composition prepared as described above was used, and various measurements were performed. Table 2 shows the results.

(Examples 4 to 11)
<Preparation of positive resist composition>
Copolymer B1 (Example 6), Copolymer B3 (Examples 4 and 10), Copolymer B4 (Examples 5, 7, 11) and copolymer B5 (Examples 8 and 9) were used. Then, the mass ratio of copolymer A and copolymer B (copolymer A: copolymer B) was 80: 20 (Examples 4, 6, 8, 11), 70: 30 (Examples 5, 9 ) and 90:10 (Examples 7 and 10), positive resist compositions were prepared in the same manner as in Example 1.
<Formation of resist pattern>
In the development step, the developer (2) was isopropyl alcohol (SP value: 11.5 (cal/cm ³ ) ^1/2 , boiling point: 83°C, Examples 4 to 6), 1-propanol (SP value: 11 .9 (cal/cm ³ ) ^1/2 , boiling point: 97°C, Examples 7-9), 1-butanol (SP value: 11.4 (cal/cm ³ ) ^1/2 , boiling point: 117°C, Treatment (2) was carried out using Examples 10, 11). Other than that, a resist pattern was formed in the same manner as in Example 1, and various measurements were performed. Table 2 shows the results.

(Examples 12-18)
<Preparation of positive resist composition>
As copolymer B, copolymer B1 (Examples 12, 16 and 18) and copolymer B4 (Examples 13 to 15 and 17) were used. And the mass ratio of copolymer A and copolymer B (copolymer A: copolymer B) is 90: 10 (Examples 12, 15), 80: 20 (Examples 13, 16, 17), 70 A positive resist composition was prepared in the same manner as in Example 1, except that it was adjusted to : 30 (Examples 14 and 18).
<Formation of resist pattern>
In the development step, Octane (SP value: 7.5 cal/cm ³ ) ^1/2 , boiling point: 125° C.) was used as developer (1), and processing (1) was carried out. Further, as the developer (2), the above ethanol (Example 12), the above isopropyl alcohol (Examples 13 and 14), the above 1-propanol (Examples 15 and 16), the above 1-butanol (Example 17, 18) were used to carry out treatment (2). Other than that, a resist pattern was formed in the same manner as in Example 1, and various measurements were performed. Table 3 shows the results.

(Examples 19-22)
<Preparation of positive resist composition>
As copolymer B, copolymer B1 (Examples 21 and 22) and copolymer B4 (Examples 19 and 20) were used. Then, the mass ratio of the copolymer A and the copolymer (copolymer A: copolymer B) was 90:10 (Example 19), 80:20 (Examples 20 and 21), 70:30 (implementation Example 22) A positive resist composition was prepared in the same manner as in Example 1, except that 2) was used.
<Formation of resist pattern>
In the development step, processing (1) was performed using nonane (SP value: 7.7 cal ³ /cm) ^1/2 , boiling point: 150° C.) as developer (1). In addition, processing (2) using the above isopropyl alcohol (Examples 19 and 20), the above 1-propanol (Example 21), and the above 1-butanol (Example 22) as the developer (2) did Other than that, a resist pattern was formed in the same manner as in Example 1, and various measurements were performed. Table 3 shows the results.

(Examples 23-31)
<Preparation of positive resist composition>
Examples of copolymer B include copolymer B1 (Examples 26 and 30), copolymer B2 (Example 29), copolymer B3 (Example 24), copolymer B4 (Examples 25 and 28), Copolymer B5 (Examples 27 and 31) and copolymer B6 (Example 23) were used. Then, the mass ratio of copolymer A and copolymer B (copolymer A: copolymer B) was 80:20 (Examples 23, 25, 30, 31), 90:10 (Examples 24, 28 ) and 70:30 (Examples 26, 27, 29), positive resist compositions were prepared in the same manner as in Example 1.
<Formation of resist pattern>
In the development step, processing (1) was performed using decane (SP value: 7.7) cal/cm ³ ) ^1/2 , boiling point: 174°C as developer (1). Further, as the developer (2), the above ethanol (Example 23), the above isopropyl alcohol (Examples 24 to 27), the above 1-propanol (Examples 28 and 29), the above 1-butanol ( Treatment (2) was carried out using Examples 30, 31). Other than that, a resist pattern was formed in the same manner as in Example 1, and various measurements were performed. Table 4 shows the results.

(Example 32)
<Preparation of positive resist composition>
As copolymer B, copolymer B3 was used. Then, a positive resist composition was prepared in the same manner as in Example 1, except that the mass ratio of copolymer A and copolymer B (copolymer A:copolymer B) was set to 80:20. prepared.
<Formation of resist pattern>
In the development step, the exposed resist film was developed using a mixed solvent containing the above-described heptane and the above-described isopropyl alcohol as a developer at a mass ratio (heptane:isopropyl alcohol) of 50:50. Other than that, a resist pattern was formed in the same manner as in Example 1, and various measurements were performed. Table 5 shows the results.

(Examples 33-35)
<Preparation of positive resist composition>
As copolymer B, copolymer B4 was used. Then, a positive resist composition was prepared in the same manner as in Example 1, except that the mass ratio of copolymer A and copolymer B (copolymer A:copolymer B) was set to 80:20. prepared.
<Formation of resist pattern>
In the development step, the exposed resist film was treated with a mixed solvent (Example 33) containing the above-described octane and the above-described isopropyl alcohol as a developer at a mass ratio (octane:isopropyl alcohol) of 50:50, and the above-described nonane. A mixed solvent (Example 34) containing the above isopropyl alcohol at a mass ratio (nonane:isopropyl alcohol) of 50:50, and a mixed solvent containing the above decane and the above isopropyl alcohol at a mass ratio (decane:isopropyl alcohol) of 50:50 A mixed solvent (Example 35) was used. Other than that, a resist pattern was formed in the same manner as in Example 32, and various measurements were performed. Table 5 shows the results.

(Comparative example 1)
<Preparation of positive resist composition>
Copolymer B was not used, and only copolymer A1 was used as copolymer A. Then, the copolymer A1 was dissolved in isoamyl acetate as a solvent to prepare a positive resist composition having a concentration of 3% by mass.
<Formation of resist pattern>
In the development process, only the processing (1) was performed using the above ethanol as the developer (1), and the processing (2) using the developer (2) was not performed. Other than that, a resist pattern was formed in the same manner as in Example 1, and various measurements were performed. Table 6 shows the results.

(Comparative Examples 2-4)
<Preparation of positive resist composition>
A positive resist composition was prepared in the same manner as in Comparative Example 1.
<Formation of resist pattern>
Comparative Example 1 except that the above isopropyl alcohol (Comparative Example 2), the above 1-propanol (Comparative Example 3), and the above 1-butanol (Comparative Example 4) were used as the developer (1) in the development step. A resist pattern was formed in the same manner as in , and various measurements were performed. Table 6 shows the results.

From Tables 2 to 5, a resist film was formed using a positive resist composition containing predetermined copolymer A and copolymer B, and after exposure of the obtained resist film, the SP value was 8 (cal/ cm ³ ) ^1/2 or less, in Examples 1 to 35 in which development was performed using a developer containing at least a solvent of 1/2 or less, the sensitivity of the resist film was high and the efficiency of resist pattern formation was high from the values of Eth and γ values. Therefore, it can be seen that the decrease of the resist pattern top is small. Moreover, in Examples 1 to 35, the γ value exceeds 9.8, which indicates that a high-contrast resist pattern can be formed.
On the other hand, from Table 6, a resist film was formed using a positive resist composition containing only a predetermined copolymer A, and after exposure of the obtained resist film, the SP value was 8 (cal/cm ³ ) ¹ . In Comparative Examples 1 to 4 in which development was performed using a developer exceeding ^/2 , the γ value was 9.8 or less, so in Comparative Examples 1 to 4, the decrease in the resist pattern top was small, and , it can be seen that a resist pattern with high contrast could not be formed.

According to the resist pattern forming method of the present invention, it is possible to form a high-contrast resist pattern with little decrease in the resist pattern top.

Claims (6)

A main chain scission type copolymer A containing a fluorine substituent, a main chain scission type copolymer B containing a fluorine substituent, and a solvent, and the surface free energy of the copolymer A, a resist film forming step of forming a resist film using a positive resist composition having a free energy difference of 4 mJ/m ² or more on the surface of the copolymer B;
an exposure step of exposing the resist film;
a developing step of developing the exposed resist film using a developer containing at least a solvent having a solubility parameter of 8 (cal/cm ³ ) ^1/2 or less. The copolymer A has the following formula (I):

[In the formula (I), L is a divalent linking group having a fluorine atom, and Ar is an aromatic ring group optionally having a substituent. ] A monomeric unit (I) represented by
Formula (II) below:

[In formula (II), R ¹ is an alkyl group, R ² 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 ³ is It is a hydrogen atom, an unsubstituted alkyl group, or an alkyl group substituted with a fluorine atom, p and q are integers of 0 or more and 5 or less, and p+q=5. ]
2. The method of forming a resist pattern according to claim 1, comprising a monomer unit (II) represented by The copolymer B is represented by the following formula (III):

[In the formula (III), R ¹ is an organic group having 5 or more and 7 or less fluorine atoms. ]
A monomeric unit (III) represented by
Formula (IV) below:

[In formula (IV), R ¹ is an alkyl group, R ² is a hydrogen atom, a fluorine atom, an unsubstituted alkyl group or a fluorine atom-substituted alkyl group, R ³ is a hydrogen atom, It is an unsubstituted alkyl group or an alkyl group substituted with a fluorine atom, p and q are integers from 0 to 5, and p+q=5. ]
3. The method of forming a resist pattern according to claim 1, comprising the monomer (IV) represented by: The developing step includes a process (1) in which a solvent having a solubility parameter of 8 (cal/cm ³ ) ^1/2 or less is used as a developer (1) for development, and a developer different from the developer (1). including processing (2) for development using liquid (2),
4. The method of forming a resist pattern according to claim 1, wherein said treatment (1) and said treatment (2) are performed in this order. 5. The method of forming a resist pattern according to claim 4, wherein said developer (1) is a hydrocarbon solvent. 6. The method of forming a resist pattern according to claim 4, wherein said developer (2) is an alcoholic solvent.