JP2020067535A - Method for forming resist pattern - Google Patents

Abstract

To provide a method for forming a resist pattern excellent in resolution.SOLUTION: A method for forming a resist pattern includes the steps of: forming a resist film using a positive resist composition which contains a copolymer having a monomer unit (A) represented by a formula (I) and a monomer unit (B) represented by a formula (II) and a solvent; exposing the resist film; and developing the exposed resist film. The development is performed using a developer containing a hydrofluorocarbon and a fluorine-based solvent whose boiling point is different from that of the hydrofluorocarbon by 25°C or lower in absolute value. In the formula, Rrepresents an organic group containing a fluorine atom.SELECTED DRAWING: None

Description

  The present invention relates to a resist pattern forming method, and more particularly to a resist pattern forming method using a positive resist composition containing a copolymer that can be preferably used as a positive resist.

  Conventionally, in the field of semiconductor manufacturing and the like, short-wavelength light such as ionizing radiation such as electron beams and ultraviolet rays (hereinafter, ionizing radiation and short-wavelength light may be collectively referred to as “ionizing radiation and the like”). A polymer whose main chain is cleaved by irradiation to increase its solubility in a developing solution is used as a main chain cleaving positive resist.

  Specifically, for example, in Patent Documents 1 and 2, an α-methylstyrene unit and an α-chloroacrylic acid 2 are described as a main chain cleavage type positive type resist capable of suppressing the occurrence of collapse of a resist pattern during development. A positive resist made of a predetermined copolymer containing a fluorine atom, such as a copolymer containing a 2,3,3,3-pentafluoropropyl unit is disclosed.

In Patent Documents 1 and 2, after exposing a resist film formed by using a positive resist made of a fluorine atom-containing copolymer, a hydrofluorocarbon such as CF ₃ CFHCFHCF ₂ CF ₃ is used as a developer. By developing the resist pattern, a resist pattern is formed.

JP, 2008-106065, A JP, 2008-106066, A

  Here, in recent years, along with the demand for further miniaturization of the pattern, in forming the resist pattern using a positive resist, it is required to enable formation of a resist pattern having excellent resolution. However, the conventional method of forming a resist pattern using hydrofluorocarbon as a developing solution has room for improvement in that a resist pattern having a further improved resolution is formed.

  Therefore, it is an object of the present invention to provide a method for forming a resist pattern having excellent resolution by using a fluorine atom-containing copolymer as a positive resist.

  The present inventor has conducted extensive studies to achieve the above object. Then, the present inventor, when forming a resist pattern using a copolymer containing a fluorine atom as a positive resist, performs development using a developing solution containing hydrofluorocarbon and a predetermined fluorine-based solvent. Then, they found that a resist pattern having excellent resolution can be formed, and completed the present invention.

〔一般式（Ｉ）中、Ｒ¹は、フッ素原子を含む有機基である。〕
で表される単量体単位（Ａ）と、下記一般式（ＩＩ）：

〔式（ＩＩ）中、Ｒ²は、アルキル基であり、Ｒ³は、アルキル基、ハロゲン原子またはハロゲン化アルキル基であり、ｐは、０以上５以下の整数であり、Ｒ³が複数存在する場合、それらは互いに同一でも異なっていてもよい。〕
で表される単量体単位（Ｂ）とを有する共重合体、および、溶剤を含むポジ型レジスト組成物を用いてレジスト膜を形成する工程と、前記レジスト膜を露光する工程と、露光された前記レジスト膜を現像する工程とを含み、前記現像を、ハイドロフルオロカーボンと、前記ハイドロフルオロカーボンとの沸点の差が絶対値で２５℃以下であるフッ素系溶剤とを含む現像液を用いて行うことを特徴とする。このように、ハイドロフルオロカーボンと、ハイドロフルオロカーボンとの沸点の差が絶対値で２５℃以下であるフッ素系溶剤とを含む現像液を使用すれば、上記単量体単位（Ａ）および単量体単位（Ｂ）を有する共重合体をポジ型レジストとして使用して解像度に優れるレジストパターンを形成することができる。
なお、本発明において、「沸点」は、圧力（絶対圧）１ａｔｍの環境下、蒸留法で測定することができる。 That is, the present invention has an object to advantageously solve the above problems, and a method for forming a resist pattern according to the present invention comprises the following general formula (I):

[In the general formula (I), R ¹ is an organic group containing a fluorine atom. ]
And a monomer unit (A) represented by the following general formula (II):

[In the formula (II), R ² is an alkyl group, R ³ is an alkyl group, a halogen atom or a halogenated alkyl group, p is an integer of 0 or more and 5 or less, and R ³ is present in plural. If so, they may be the same or different from each other. ]
A step of forming a resist film using a positive resist composition containing a copolymer having a monomer unit (B) represented by and a solvent; a step of exposing the resist film; And a step of developing the resist film, wherein the developing is performed using a developing solution containing hydrofluorocarbon and a fluorine-based solvent having a difference in boiling point between the hydrofluorocarbon and the absolute value of 25 ° C. or less. Is characterized by. Thus, when a developing solution containing hydrofluorocarbon and a fluorine-based solvent having a difference in boiling point between hydrofluorocarbon and absolute value of 25 ° C. or less is used, the monomer unit (A) and the monomer unit are The copolymer having (B) can be used as a positive resist to form a resist pattern having excellent resolution.
In the present invention, the "boiling point" can be measured by a distillation method under an environment of a pressure (absolute pressure) of 1 atm.

Here, in the resist pattern forming method of the present invention, the hydrofluorocarbon is preferably CF ₃ CFHCFHCF ₂ CF ₃ . By using a developing solution containing CF ₃ CFHCFHCF ₂ CF ₃ as the hydrofluorocarbon, the resolution of the resist pattern can be further improved.

  Further, in the resist pattern forming method of the present invention, it is preferable that the fluorine-based solvent is at least one selected from the group consisting of hydrochlorofluorocarbon, hydrofluoroether and perfluorocarbon. If a developing solution containing at least one selected from the group consisting of hydrochlorofluorocarbons, hydrofluoroethers and perfluorocarbons is used as the fluorine-based solvent, the resolution of the resist pattern can be further improved.

Further, in the resist pattern forming method of the present invention, the fluorine-based solvent is CF ₃ CF ₂ CHCl ₂ , CClF ₂ CF ₂ CHClF, CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ , CF ₃ CF ₂ CF ₂ CF ₂ OC. It is preferably at least one selected from the group consisting of ₂ H ₅ and C ₈ F ₁₈ . Fluorine-based solvent selected from the group consisting of CF ₃ CF ₂ CHCl ₂ , CClF ₂ CF ₂ CHClF, CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ , CF ₃ CF ₂ CF ₂ CF ₂ OC ₂ H ₅ and C ₈ F _18. If a developing solution containing at least one of the above is used, the resolution of the resist pattern can be further improved.

  Further, in the resist pattern forming method of the present invention, in the developer, the content ratio of the hydrofluorocarbon and the fluorine-based solvent (hydrofluorocarbon: fluorine-based solvent) is 40:60 to 60:40 on a mass basis. Preferably there is. When the content ratio of the hydrofluorocarbon and the fluorine-based solvent is within the above range, a clearer pattern can be efficiently formed.

  In the resist pattern forming method of the present invention, the monomer unit (A) is an α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit, and the monomer unit (B ) Is preferably an α-methylstyrene unit or a 4-fluoro-α-methylstyrene unit. If the copolymer has the above-mentioned monomer unit, a clearer pattern can be efficiently formed.

  According to the present invention, a copolymer having a fluorine atom can be used as a positive resist to form a resist pattern having excellent resolution.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the resist pattern forming method of the present invention uses a main chain-cutting type positive resist, in which the main chain is cut to have a low molecular weight by irradiation with short-wavelength light such as ionizing radiation such as an electron beam or ultraviolet light. It is a thing. 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 a manufacturing process of a semiconductor, a photomask, a mold or the like.

(Method of forming resist pattern)
The resist pattern forming method of the present invention uses a positive resist composition described in detail below. Specifically, the resist pattern forming method of the present invention forms a resist film using a predetermined positive resist composition containing a copolymer containing a fluorine atom, which is formed using a predetermined monomer. A step (resist film forming step), a step of exposing the resist film (exposure step), and a step of developing the exposed resist film (developing step), and optionally a step of rinsing the developed resist film (Rinse step) is further included. Furthermore, in the resist pattern forming method of the present invention, the developing step is performed using a developing solution containing a hydrofluorocarbon and a fluorine-based solvent having a boiling point difference between the hydrofluorocarbon and the absolute value of 25 ° C. or less. Characterize.

<Resist film forming step>
In the resist film forming step, a positive resist composition is applied onto a work piece such as a substrate processed using a resist pattern, and the applied positive resist composition is dried to form a resist film. .
Here, the method of applying the positive resist composition and the method of drying the positive resist composition are not particularly limited, and a method generally used for forming a resist film can be used. Then, in the pattern forming method of the present invention, the following positive resist composition is used.

[Positive resist composition]
The positive resist composition contains a predetermined copolymer containing a fluorine atom, which will be described in detail below, and a solvent, and optionally further contains a known additive that can be incorporated into the resist composition.

〔式（Ｉ）中、Ｒ¹は、フッ素原子を含む有機基である。〕
で表される単量体単位（Ａ）と、
下記式（ＩＩ）：

〔式（ＩＩ）中、Ｒ²は、アルキル基であり、Ｒ³は、アルキル基、ハロゲン原子またはハロゲン化アルキル基であり、ｐは、０以上５以下の整数であり、Ｒ³が複数存在する場合、それらは互いに同一でも異なっていてもよい。〕
で表される単量体単位（Ｂ）とを有する。 [Copolymer]
The copolymer contained in the positive resist composition used in the resist pattern forming method of the present invention has the following formula (I):

[In the formula (I), R ¹ is an organic group containing a fluorine atom. ]
A monomer unit (A) represented by
Formula (II) below:

[In the formula (II), R ² is an alkyl group, R ³ is an alkyl group, a halogen atom or a halogenated alkyl group, p is an integer of 0 or more and 5 or less, and R ³ is present in plural. If so, they may be the same or different from each other. ]
And a monomer unit (B) represented by

  The copolymer may contain any monomer unit other than the monomer unit (A) and the monomer unit (B), but among all the monomer units constituting the copolymer. The total proportion of the monomer unit (A) and the monomer unit (B) is preferably 90 mol% or more, and 100 mol% (that is, the copolymer is the monomer unit (A)). And containing only the monomer unit (B)).

  Since the copolymer contains the predetermined monomer unit (A) and monomer unit (B), ionizing radiation (eg, electron beam, KrF laser, ArF laser, EUV laser, etc.) Upon irradiation, the main chain is cleaved to lower the molecular weight. Further, since at least the monomer unit (A) of the copolymer has a fluorine atom, it is possible to suppress the occurrence of collapse of the resist pattern during development when used as a resist.

〔式（ＩＩＩ）中、Ｒ¹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 (A)-
Here, the monomer unit (A) has the following formula (III):

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

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

Here, from the viewpoint of improving the cutting property of the main chain of the copolymer upon irradiation with ionizing radiation or the like, so that the resist pattern can be formed more efficiently, formula (I) and formula (III) The number of fluorine atoms contained in R ¹ therein is preferably 4 or more, and more preferably 5 or more. Further, from the viewpoint of improving the clarity of the resist pattern obtained when used as a positive resist, the number of fluorine atoms contained in R ¹ in formulas (I) and (III) is 7 or less. It is preferably 6 or less, and more preferably 6 or less.

Further, the carbon number of R ¹ is preferably 2 or more and 10 or less, more preferably 3 or more and 4 or less, and further preferably 3. When the carbon number is at least the above lower limit, the solubility in the developing solution can be sufficiently improved. Further, when the number of carbon atoms is not more than the above upper limit value, it is possible to suppress the decrease of the glass transition point and sufficiently secure the clarity of the obtained resist pattern.

Specifically, R ¹ in the formula (I) and the formula (III) is preferably a fluoroalkyl group, a fluoroalkoxyalkyl group or a fluoroalkoxyalkenyl group, and more preferably a fluoroalkyl group. When R ¹ is the above-mentioned group, the main chain cutting property of the copolymer upon irradiation with ionizing radiation or the like can be sufficiently improved.

Here, examples of the fluoroalkyl group include a 2,2,2-trifluoroethyl group (having 3 fluorine atoms and 2 carbon atoms), a 2,2,3,3,3-pentafluoropropyl group ( Number of fluorine atoms is 5 and carbon number is 3), 3,3,4,4,4-pentafluorobutyl group (number of fluorine atoms is 5 and carbon number is 4), 1H-1- (trifluoromethyl) Trifluoroethyl group (having 6 fluorine atoms and 3 carbon atoms), 1H, 1H, 3H-hexafluorobutyl group (having 6 fluorine atoms and 4 carbon atoms), 2, 2, 3, 3, 4,4,4-Heptafluorobutyl group (having 7 fluorine atoms and 4 carbon atoms), and 1,2,2,2-tetrafluoro-1- (trifluoromethyl) ethyl group (fluorine atom And the number of carbon atoms is 3). Of these, a 2,2,3,3,3-pentafluoropropyl group (having 5 fluorine atoms and 3 carbon atoms) is preferable.
Further, examples of the fluoroalkoxyalkyl group include a fluoroethoxymethyl group and a fluoroethoxyethyl group.
Further, examples of the fluoroalkoxyalkenyl group include a fluoroethoxyvinyl group and the like.

  The monomer (a) represented by the above formula (III), which can form the monomer unit (A) represented by the above formula (I), is not particularly limited, For example, α, 2-chloroacrylic acid 2,2,2-trifluoroethyl, α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl, α-chloroacrylic acid 3,3,4,4,4 -Pentafluorobutyl, α-chloroacrylic acid 1H-1- (trifluoromethyl) trifluoroethyl, α-chloroacrylic acid 1H, 1H, 3H-hexafluorobutyl, α-chloroacrylic acid 1,2,2,2 Α-chloroacrylic acid fluoroalkyl ester such as tetrafluoro-1- (trifluoromethyl) ethyl, α-chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl; α-chloro Α-chloroacrylic acid fluoroalkoxyalkyl esters such as acrylic acid pentafluoroethoxymethyl ester and α-chloroacrylic acid pentafluoroethoxyethyl ester; α-chloroacrylic acid fluoroalkoxyalkenyls such as α-chloroacrylic acid pentafluoroethoxyvinyl ester Ester; and the like.

  From the viewpoint of further improving the cutting property of the main chain of the copolymer upon irradiation with ionizing radiation, the monomer unit (A) is a structural unit derived from α-chloroacrylic acid fluoroalkyl ester. Preferably there is. More specifically, the monomer unit (A) is derived from α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl among the structural units derived from α-chloroacrylic acid fluoroalkyl ester. It is more preferably a structural unit. When the monomer unit (A) is a structural unit derived from 2,2,3,3,3-pentafluoropropyl α-chloroacrylic acid, the main chain of the copolymer can be easily cut, and the resist pattern Can be formed more efficiently, and the clarity of the obtained resist pattern can be improved.

〔式（ＩＶ）中、Ｒ²およびＲ³、並びに、ｐ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。 -Monomer unit (B)-
The monomer unit (B) has the following formula (IV):

[In the formula (IV), R ² and R ³ , and p are the same as those in the formula (II). ] It is a structural unit derived from the monomer (b) represented by this.

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

Here, the alkyl group that can form R ^{2 to} R ³ in formulas (II) and (IV) is not particularly limited, and examples thereof include an unsubstituted alkyl group having 1 to 5 carbon atoms. . Of these, a methyl group or an ethyl group is preferable as the alkyl group that can form R ^{2 to} R ³ .

Further, the halogen atom which can constitute R ³ in the formulas (II) and (IV) is not particularly limited, and examples thereof include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. Among them, the halogen atom is preferably a fluorine atom.

Furthermore, the halogenated alkyl group that can constitute R ³ in formulas (II) and (IV) is not particularly limited, and examples thereof include a fluoroalkyl group having 1 to 5 carbon atoms. Above all, as the halogenated alkyl group, a perfluoroalkyl group having 1 to 5 carbon atoms is preferable, and a trifluoromethyl group is more preferable.

Then, from the viewpoint of improving the ease of preparation of the copolymer and the cutting property of the main chain upon irradiation with ionizing radiation or the like, R ² in the formula (II) and the formula (IV) has 1 to 1 carbon atoms. It is preferably an alkyl group of 5 and more preferably a methyl group.

  Further, from the viewpoint of ease of preparation of the copolymer and improvement of the scission of the main chain upon irradiation with ionizing radiation or the like, p in the formulas (II) and (IV) is 0 or 1. It is preferable.

Among them, from the viewpoint of improving the formation efficiency of the resist pattern, p in the formulas (II) and (IV) is 1, and R ³ is a fluorine atom or a fluoroalkyl group having 1 to 5 carbon atoms. It is more preferable that p is 1, R ³ is a fluorine atom or a perfluoroalkyl group having 1 to 5 carbon atoms, and it is further preferable that p is 1 and R ³ is a fluorine atom.

The monomer (b) represented by the above formula (IV) capable of forming the monomer unit (B) represented by the above formula (II) is not particularly limited, For example, α-methylstyrene and derivatives thereof such as the following (b-1) to (b-12) can be mentioned.

  From the viewpoint of improving the ease of preparation of the copolymer and enabling the resist pattern to be formed more efficiently, the monomer unit (B) is α-methylstyrene or 4-fluoro-α. A structural unit derived from -methylstyrene is preferable, and a structural unit derived from 4-fluoro-α-methylstyrene is more preferable. That is, the copolymer preferably has an α-methylstyrene unit or a 4-fluoro-α-methylstyrene unit, more preferably a 4-fluoro-α-methylstyrene unit.

-Properties of copolymer-
The weight average molecular weight (Mw) of the copolymer is preferably 20,000 or more, more preferably 30,000 or more, further preferably 45,000 or more, and preferably 100,000 or less, 60,000. It is more preferably not more than 50,000, and even more preferably not more than 50,000. When the weight average molecular weight (Mw) of the copolymer is at least the above lower limit, the elasticity of the positive resist formed using the copolymer can be improved, so that the occurrence of collapse of the resist pattern is further suppressed. It is possible. Further, if the weight average molecular weight (Mw) of the copolymer is not more than the above upper limit value, the sensitivity can be improved.
The "weight average molecular weight (Mw)" of the copolymer can be measured as a standard polystyrene conversion value using gel permeation chromatography.

The number average molecular weight (Mn) of the copolymer is preferably 10,000 or more, more preferably 30,000 or more, further preferably 35,000 or more, and preferably 100,000 or less, 50,000. It is more preferably at most 40,000, still more preferably at most 40,000. When the number average molecular weight (Mn) of the copolymer is at least the above lower limit value, the elasticity of the positive resist formed using the copolymer can be improved, so that the occurrence of collapse of the resist pattern is further suppressed. It is possible. Further, if the number average molecular weight (Mn) of the copolymer is not more than the above upper limit value, the sensitivity can be improved.
The "number average molecular weight (Mn)" of the copolymer can be measured as a standard polystyrene conversion value by using gel permeation chromatography as in the case of the "weight average molecular weight (Mw)" described above.

The molecular weight distribution (Mw / Mn) of the copolymer is preferably 1.20 or more, more preferably 1.30 or more, preferably 2.00 or less, and 1.40 or less. Is more preferable. When the molecular weight distribution (Mw / Mn) of the copolymer is at least the above lower limit, the ease of manufacturing the copolymer can be increased. If the molecular weight distribution (Mw / Mn) of the copolymer is not more than the above upper limit value, the clarity of the obtained resist pattern can be increased.
In the present invention, the “molecular weight distribution (Mw / Mn)” refers to the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn).

-Method for preparing copolymer-
And the above-mentioned copolymer having the monomer unit (A) and the monomer unit (B) is, for example, a monomer composition containing the monomer (a) and the monomer (b). After the polymerization, the obtained copolymer can be recovered and optionally purified.
The composition, molecular weight distribution, weight average molecular weight and number average molecular weight of the copolymer can be adjusted by changing the polymerization conditions and the purification conditions. Specifically, for example, the composition of the copolymer can be adjusted by changing the content ratio of each monomer in the monomer composition used for the polymerization. The weight average molecular weight and the number average molecular weight can be reduced by increasing the polymerization temperature. Furthermore, the weight average molecular weight and the number average molecular weight can be reduced by shortening the polymerization time. Moreover, the molecular weight distribution can be narrowed by performing purification.

  Here, the monomer composition used for preparing the copolymer includes a monomer component containing the monomer (a) and the monomer (b), an optionally usable solvent, and a polymerization initiator. And a mixture with an optionally added additive can be used. Then, the polymerization of the monomer composition can be performed using a known method. Among them, when a solvent is used, it is preferable to use cyclopentanone or the like as the solvent. As the polymerization initiator, it is preferable to use a radical polymerization initiator such as azobisisobutyronitrile.

  The polymer obtained by polymerizing the monomer composition is not particularly limited, and after adding a good solvent such as tetrahydrofuran to the solution containing the polymer, the solution obtained by adding the good solvent to methanol or the like. It is possible to collect the polymer by dropping it into the poor solvent and coagulating the polymer.

The purification method used when purifying the obtained polymer is not particularly limited, and known purification methods such as a reprecipitation method and a column chromatography method can be mentioned. Among them, the reprecipitation method is preferably used as the purification method.
The purification of the polymer may be repeated multiple times.

  And, the purification of the polymer by the reprecipitation method, for example, after dissolving the obtained polymer in a good solvent such as tetrahydrofuran, the resulting solution is mixed with a good solvent such as tetrahydrofuran and a poor solvent such as methanol. It is preferable to carry out the reaction by dropping it in a solvent and precipitating a part of the polymer. In this way, if the solution of the polymer is added dropwise to the mixed solvent of the good solvent and the poor solvent for purification, by changing the kind and the mixing ratio of the good solvent and the poor solvent, the obtained copolymer The molecular weight distribution, weight average molecular weight and number average molecular weight can be easily adjusted. Specifically, for example, the higher the ratio of the good solvent in the mixed solvent, the larger the molecular weight of the copolymer precipitated in the mixed solvent.

  When the polymer is purified by the reprecipitation method, the copolymer used in the present invention may be a polymer precipitated in a mixed solvent of a good solvent and a poor solvent, or precipitated in the mixed solvent. Polymers that have not been formed (that is, polymers that are dissolved in a mixed solvent) may be used. Here, the polymer not precipitated in the mixed solvent can be recovered from the mixed solvent by a known method such as concentration to dryness.

〔solvent〕
The solvent is not particularly limited as long as it is a solvent capable of dissolving the above-mentioned copolymer, and known solvents such as the solvent described in Japanese Patent No. 5938536 can be used. Among them, anisole, propylene glycol monomethyl ether acetate (PGMEA), cyclopentanone, and cyclohexanone are used as the solvent from the viewpoint of obtaining a positive resist composition having an appropriate viscosity and improving the coatability of the positive resist composition. Preferably, hexyl acetate or isoamyl acetate is used.

<Exposure process>
In the exposure step, the resist film formed in the resist film forming step is irradiated with ionizing radiation or light to draw a desired pattern.
A known drawing device such as an electron beam drawing device or a laser drawing device can be used for irradiation of ionizing radiation or light.

<Developing process>
In the developing step, the resist film exposed in the exposing step is brought into contact with a developing solution to develop the resist film and form a resist pattern on the workpiece.
Here, the method of bringing the resist film and the developing solution into contact with each other is not particularly limited, and a known method such as dipping the resist film in the developing solution or coating the developing solution on the resist film may be used. it can.

[Developer]
The developing solution used in the resist pattern forming method of the present invention needs to contain hydrofluorocarbon and a fluorine-based solvent having a difference in boiling point between the hydrofluorocarbon and the absolute value of 25 ° C. or less. The developer may contain a solvent other than the hydrofluorocarbon and the fluorinated solvent as long as the desired effect can be obtained, but it is preferable that the developer is composed of only the hydrofluorocarbon and the fluorinated solvent.

  Then, in the resist pattern forming method of the present invention, with respect to the resist film formed by using the positive resist composition containing the above-described predetermined copolymer, the difference between the boiling points of hydrofluorocarbon and the hydrofluorocarbon is an absolute value. Since a developing solution containing a fluorine-based solvent having a temperature of 25 ° C. or lower is used, a resist pattern having excellent resolution can be formed.

-Hydrofluorocarbon-
Here, the hydrofluorocarbon is not particularly limited and, for example, 1,1,1,2,3,4,4,5,5,5-decafluoropentane, 1,1,1,2,2 , 3,3,4,4,5,5,6,6-tridecafluorohexane, 1,1,1,2,2,3,4,5,5,5-decafluoropentane, 1,1, 1,3,3-pentafluorobutane, 1,1,1,2,2,3,3,4,4-nonafluorohexane and the like can be mentioned. Among them, from the viewpoint of further improving the resolution of the obtained resist pattern, the hydrofluorocarbon is preferably a hydrofluorocarbon having 5 or more and 6 or less carbon atoms, and 1,1,1,2,3,4,4,5,5. , 5-decafluoropentane (CF ₃ CFHCFHCF ₂ CF ₃ ) is more preferable.
The hydrofluorocarbon as described above is commercially available, for example, as Bertrel XF (registered trademark) manufactured by Mitsui DuPont Fluorochemicals.

  In addition, the boiling point of the hydrofluorocarbon is preferably 40 ° C. or higher, more preferably 50 ° C. or higher, preferably 70 ° C. or lower, and more preferably 60 ° C. or lower. When the boiling point is within the above range, the resolution of the obtained resist pattern can be further improved. Further, when the boiling point is at least the above lower limit, handling of the developer is easy.

-Fluorine-based solvent-
As the fluorine-based solvent, any fluorine-based solvent having an absolute value of the boiling point difference with hydrofluorocarbon of 25 ° C. or less can be used. Among them, from the viewpoint of further improving the resolution of the obtained resist pattern, as the fluorine-based solvent, it is preferable to use at least one selected from the group consisting of hydrochlorofluorocarbons, hydrofluoroethers and perfluorocarbons, and hydrofluoroethers. Is more preferably used.

Here, the hydrochlorofluorocarbon is not particularly limited, and examples thereof include 2,2-dichloro-1,1,1-trifluoroethane, 1,1-dichloro-1-fluoroethane, and 1,1-dichloro. -2,2,3,3,3-pentafluoropropane, 1,3-dichloro-1,1,2,2,3-pentafluoropropane and the like can be mentioned. Among them, from the viewpoint of further improving the resolution of the obtained resist pattern, the hydrochlorofluorocarbon is preferably a hydrochlorofluorocarbon having a carbon number of 3 or less, and 1,1-dichloro-2,2,3,3,3- More preferred are pentafluoropropane (CF ₃ CF ₂ CHCl ₂ ) and 1,3-dichloro-1,1,2,2,3-pentafluoropropane (CClF ₂ CF ₂ CHClF).
The hydrochlorofluorocarbon as described above is commercially available, for example, as Asahiclin AK-225 manufactured by AGC.

The hydrofluoroether is not particularly limited, and examples thereof include methylnonafluorobutyl ether, methylnonafluoroisobutyl ether, ethylnonafluorobutyl ether, and ethylnonafluoroisobutylether. Among them, as the hydrofluoroether, methylnonafluorobutyl ether (CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ ) and ethylnonafluorobutyl ether (CF ₃ CF) are used from the viewpoint of further improving the resolution and clarity of the obtained resist pattern. _{2 CF 2 CF 2 OC 2 H} 5) are preferred, methyl nonafluorobutyl ether _{(CF 3 CF 2 CF 2 CF} 2 OCH 3) is more preferable.
The hydrofluoroethers described above are commercially available, for example, as Novec (registered trademark) 7100 and Novec (registered trademark) 7200 manufactured by 3M.

Further, the perfluorocarbon is not particularly limited, and examples thereof include CF ₄ , C ₂ F ₆ , C ₃ F ₈ , C ₄ F ₈ , C ₄ F ₁₀ , C ₅ F ₁₂ , C ₆ F ₁₂ , C. _{6 F 14, C 7 F 14} , C 7 F 16, C 8 F 18, C 9 F 20 , and the like. Among them, from the viewpoint of further improving the resolution of the obtained resist pattern, the perfluorocarbon is preferably a perfluorocarbon having 6 or more and 10 or less carbon atoms, and more preferably C ₈ F ₁₈ .
The perfluorocarbon as described above is commercially available as, for example, PF-5052 manufactured by 3M Company.

Among the above, from the viewpoint of easy availability and further improvement of the resolution of the resist pattern, as the fluorine-based solvent, CF ₃ CF ₂ CHCl ₂ , CClF ₂ CF ₂ CHClF, CF ₃ CF ₂ CF ₂ CF _{2 are used.} It is preferable to use at least one selected from the group consisting of OCH ₃ , CF ₃ CF ₂ CF ₂ CF ₂ OC ₂ H ₅ and C ₈ F ₁₈ . From the viewpoint of further improving the resolution and clarity of the obtained resist pattern, it is particularly preferable to use CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ as the fluorine-based solvent.

  The boiling point of the fluorine-based solvent is preferably 40 ° C. or higher, more preferably 50 ° C. or higher, further preferably 60 ° C. or higher, more preferably 90 ° C. or lower, 80 ° C. The temperature is more preferably below, and further preferably 70 ° C or below. When the boiling point is within the above range, the resolution of the obtained resist pattern can be further improved. Further, when the boiling point is at least the above lower limit, handling of the developer is easy.

The absolute value (= | α-β |) of the difference between the boiling point α of the hydrofluorocarbon and the boiling point β of the fluorine-based solvent needs to be 0 ° C. or higher and 25 ° C. or lower and is 3 ° C. or higher. Is preferable, 5 ° C or higher is more preferable, 15 ° C or lower is preferable, and 10 ° C or lower is more preferable. When | α-β | is within the above range, the resolution of the obtained resist pattern can be sufficiently improved.
From the viewpoint of further improving the resolution of the obtained resist pattern, the boiling point β of the fluorine-based solvent is preferably larger than the boiling point α of the hydrofluorocarbon.

-Content ratio-
The content ratio of the hydrofluorocarbon and the fluorine-based solvent (hydrofluorocarbon: fluorine-based solvent) in the developer is preferably 10:90 to 90:10 on a mass basis, and 40:60 to 60: It is more preferably 40. When the content ratio of the hydrofluorocarbon and the fluorine-based solvent is within the above range, a clearer pattern can be efficiently formed.

[Development conditions]
The temperature of the developing solution at the time of development is not particularly limited, but may be, for example, 21 ° C. or higher and 25 ° C. or lower. Further, the development time can be, for example, 30 seconds or more and 4 minutes or less.

<Rinse process>
In the optional rinsing step, the resist film developed in the developing step is brought into contact with a rinsing liquid to rinse the developed resist film and form a resist pattern on the workpiece. If the rinse step is performed after the developing step, the residue of the resist attached to the developed resist film can be effectively removed.
Here, the method of contacting the developed resist film and the rinse liquid is not particularly limited, and a known method such as dipping the resist film in the rinse liquid or coating the rinse liquid on the resist film can be used. Can be used.

[Rinse liquid]
The rinse liquid is not particularly limited as long as it can remove the resist residue attached to the developed resist film, and any rinse liquid can be used.
Specifically, as the rinse liquid, for example, a rinse liquid having a surface tension of 17 mN / m or less measured by a ring method at a temperature of 25 ° C. can be used. And as the rinse liquid having a surface tension of 17 mN / m or less, for example, CF ₃ CFHCFHCF ₂ CF ₃ (surface tension: 14.1 mN / m), CF ₃ CF ₂ CHCl ₂ (surface tension 16.2 mN / m) , CClF ₂ CF ₂ CHClF (surface tension 16.2 mN / m), CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ (surface tension 13.6 mN / m), C ₈ F ₁₈ (surface tension 13.6 mN / m), Fluorine-based solvents such as C ₄ F ₉ OC ₂ H ₅ (surface tension 13.6 mN / m), C ₂ F ₅ CF (OCH ₃ ) C ₃ F ₇ (surface tension 15.1 mN / m) and mixtures thereof Can be mentioned. Among them, CF ₃ CFHCFHCF ₂ CF ₃ or CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ (methylnonafluorobutyl ether) is preferable as the rinse liquid, and CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ is more preferable.

[Rinse condition]
The temperature of the rinse liquid at the time of rinsing is not particularly limited, but may be, for example, 21 ° C. or higher and 25 ° C. or lower. In addition, the rinse time can be, for example, 5 seconds or more and 3 minutes or less.

Hereinafter, the present invention will be specifically described based on Examples, but the present invention is not limited to these Examples.
In the examples and comparative examples, the weight average molecular weight, number average molecular weight and molecular weight distribution of the copolymer were evaluated by the following methods.

<Weight average molecular weight, number average molecular weight and molecular weight distribution>
The weight average molecular weight (Mw) and the number average molecular weight (Mn) of the obtained copolymer were measured by gel permeation chromatography, and the molecular weight distribution (Mw / Mn) was calculated.
Specifically, using a gel permeation chromatograph (HLC-8220 manufactured by Tosoh Corporation) and tetrahydrofuran as a developing solvent, the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the copolymer are converted into standard polystyrene. It was calculated as a value. Then, the molecular weight distribution (Mw / Mn) was calculated.

［レジストパターンの解像度］
スピンコーター(ミカサ社製、ＭＳ−Ａ１５０)を使用し、濃度２質量％のポジ型レジスト組成物を直径４インチのシリコンウェハ上に塗布した。次いで、塗布したポジ型レジスト組成物を温度１６０℃のホットプレートで５分間加熱して、シリコンウェハ上に厚さ５０ｎｍのレジスト膜を形成した。そして、電子線描画装置（エリオニクス社製、ＥＬＳ−Ｓ５０）を用いて、レジスト膜を最適露光量（Ｅ_op）で露光して、パターンを描画した。その後、レジスト用現像液として、ハイドロフルオロカーボン（三井・デュポンフロロケミカル社製、バートレルＸＦ（登録商標）、ＣＦ₃ＣＦＨＣＦＨＣＦ₂ＣＦ₃、沸点：５５℃）とハイドロフルオロエーテル（３Ｍ社製、Ｎｏｖｅｃ（登録商標）７１００、ＣＦ₃ＣＦ₂ＣＦ₂ＣＦ₂ＯＣＨ₃、沸点：６１℃）との混合溶液（ＣＦ₃ＣＦＨＣＦＨＣＦ₂ＣＦ₃：ＣＦ₃ＣＦ₂ＣＦ₂ＣＦ₂ＯＣＨ₃（質量比）＝８０：２０）を用いて温度２３℃で１分間の現像処理を行った。その後、リンス液としてメチルノナフルオロブチルエーテル（３Ｍ社製、Ｎｏｖｅｃ（登録商標）７１００、表面張力：１３．６ｍＮ／ｍ）を用いて１０秒間リンスしてレジストパターンを形成した。なお、最適露光量（Ｅ_op）は、それぞれ、上記で測定したＥ_thの約２倍の値を目安として、適宜設定した。また、レジストパターンのライン（未露光領域）とスペース（露光領域）は、それぞれ１８ｎｍ、２０ｎｍ、２５ｎｍ、３０ｎｍ（即ち、ハーフピッチ１８ｎｍ、２０ｎｍ、２５ｎｍ、３０ｎｍ）とした。
そして、走査型電子顕微鏡（Scanning Electron Microscope：ＳＥＭ）を用いて倍率１００，０００倍で観察し、パターンが形成しているハーフピッチを解像度とした。 (Example 1)
<Preparation of copolymer>
[Synthesis of polymer]
2. 3.0 g of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl (ACAPFP) as monomer (a) and α-methylstyrene (AMS) as monomer (b) 3. A monomer composition containing 476 g, 0.00551 g of azobisisobutyronitrile as a polymerization initiator, and 1.620 g of cyclopentanone as a solvent was placed in a glass container, and the glass container was sealed and replaced with nitrogen. Then, the mixture was stirred under a nitrogen atmosphere in a constant temperature bath at 78 ° C. for 6 hours. Then, the temperature was returned to room temperature, the inside of the glass container was opened to the atmosphere, and 10 g of tetrahydrofuran (THF) was added to the obtained solution. Then, the solution to which THF was added was dropped into 300 g of methanol to precipitate a polymer. Then, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white coagulated product (polymer). The weight average molecular weight (Mw) of the obtained polymer was 46772, the number average molecular weight (Mn) was 29853, and the molecular weight distribution (Mw / Mn) was 1.567. Further, the obtained polymer contained 50 mol% of α, 2-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit and 50 mol% of α-methylstyrene unit.
[Purification of polymer]
Next, the obtained polymer was dissolved in 100 g of THF, the obtained solution was added dropwise to a mixed solvent of 150 g of THF and 850 g of methanol (MeOH), and a white coagulated substance (α-methylstyrene unit and α-chloroacryl unit) was added. Acid 2,2,3,3,3-pentafluoropropyl unit containing copolymer) was deposited. Then, the solution containing the precipitated copolymer was filtered through a Kiriyama funnel to obtain a white copolymer. Then, the weight average molecular weight, the number average molecular weight, and the molecular weight distribution of the obtained copolymer were measured. As a result, the weight average molecular weight was 49486, the number average molecular weight was 36136, and the molecular weight distribution was 1.369.
The resulting copolymer contained 50 mol% each of 2,2,3,3,3-pentafluoropropyl α-chloroacrylic acid unit and α-methylstyrene unit.
<Preparation of positive resist composition>
The obtained copolymer was dissolved in isoamyl acetate as a solvent to prepare resist solutions (positive resist composition) having a copolymer concentration of 11% by mass and 2% by mass, respectively.
Then, using a positive resist composition comprising a resist solution having a copolymer concentration of 11% by mass, a resist pattern was formed as follows, and the E _th and γ values of the copolymer were evaluated. . Further, using a positive resist composition comprising a resist solution having a copolymer concentration of 2% by mass, a resist pattern was formed as follows, and the resolution of the resist pattern was evaluated. The results are shown in Table 1.
<Formation and evaluation of resist pattern>
[E _th and γ values]
Using a spin coater (MS-A150, manufactured by Mikasa), a positive resist composition having a concentration of 11 mass% was applied onto a silicon wafer having a diameter of 4 inches so as to have a thickness of 500 nm. Then, the applied positive resist composition was heated on a hot plate at a temperature of 160 ° C. for 5 minutes to form a resist film on the silicon wafer. Then, using an electron beam drawing apparatus (ELS-S50 manufactured by Elionix Co., Ltd.), a plurality of patterns (dimensions 500 μm × 500 μm) having different irradiation doses of electron beams are drawn on the resist film, and as a resist developing solution, hydro Fluorocarbon (Mitsui DuPont Fluorochemicals, Bertrel XF (registered trademark), CF ₃ CFHCFHCF ₂ CF ₃ , boiling point: 55 ° C.) and hydrofluoroether (3M, Novec (registered trademark) 7100, CF ₃ CF ₂ CF) 1) at a temperature of 23 ° C. using a mixed solution (CF ₃ CFHCFHCF ₂ CF ₃ : CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ (mass ratio) = 80: 20) with ₂ CF ₂ OCH ₃ , boiling point: 61 ° C. After performing a development process for 1 minute, methyl nonafluorobutyl ether (manufactured by 3M, Novec (registered trademark)) is used as a rinse liquid. 100, surface tension: 13.6mN / m) and rinsed for 10 seconds using a. The irradiation amount of the electron beam was varied in the range of 4μC / cm ² of 200μC / cm ² by 4μC / cm ^2. Next, the thickness of the resist film in the drawn portion was measured with an optical film thickness meter (Lambda Ace manufactured by SCREEN Semiconductor Solutions Co., Ltd.), and the common logarithm of the total electron beam irradiation amount and the residual film of the resist film after development were measured. A sensitivity curve showing a relationship with the ratio (= thickness of resist film after development / thickness of resist film formed on silicon wafer) was prepared.
The obtained sensitivity curve (horizontal axis: common logarithm of total irradiation amount of electron beam, vertical axis: residual film rate of resist film (0 ≦ remaining film rate ≦ 1.00)) was 0.20. The sensitivity curve was fitted to a quadratic function in the range of to 0.80, and the point of residual film rate 0 and the residual film ratio on the obtained quadratic function (function of residual film rate and common logarithm of total irradiation) A straight line (an approximate line of the slope of the sensitivity curve) connecting the point of 0.50 was created. Further, the total irradiation dose E _th (μC / cm ² ) of the electron beam when the residual film ratio of the obtained straight line (function of the residual film ratio and the common logarithm of the total irradiation amount) was 0 was obtained. It should be _noted that the smaller the value of E _th , the better the ability of the copolymer as a positive resist to be cut and dissolved in a developing solution with a small irradiation amount (that is, a resist pattern can be formed efficiently). Indicates.
Further, the γ value was calculated using the following formula. In the formula below, E ₀ is a quadratic function obtained by fitting the sensitivity curve to a quadratic function in the range of the residual film ratio of 0.20 to 0.80 (the residual film ratio and the total dose are the usual values). It is the logarithm of the total irradiation amount obtained when the residual film rate 0 is substituted for the function of (logarithm). Further, E ₁ is a straight line obtained by creating a straight line (an approximate line of the slope of the sensitivity curve) that connects the point of the remaining film rate 0 and the point of the remaining film rate of 0.50 on the obtained quadratic function. It is the logarithm of the total irradiation dose obtained when the residual film ratio 1.00 is substituted for (the function of the residual film ratio and the common logarithm of the total irradiation amount). Then, the following equation represents the slope of the above straight line between the remaining film ratios of 0 and 1.00. It should be noted that the larger the value of γ, the larger the slope of the sensitivity curve, indicating that a clear pattern can be formed well.

[Resist pattern resolution]
Using a spin coater (MS-A150, manufactured by Mikasa Co., Ltd.), a positive resist composition having a concentration of 2 mass% was applied on a silicon wafer having a diameter of 4 inches. Then, the applied positive resist composition was heated on a hot plate at a temperature of 160 ° C. for 5 minutes to form a resist film having a thickness of 50 nm on the silicon wafer. Then, the resist film was exposed with an optimum exposure amount (E _op ) using an electron beam drawing apparatus (ELS-S50 manufactured by Elionix Co., Ltd.) to draw a pattern. After that, as a resist developing solution, hydrofluorocarbon (manufactured by Mitsui DuPont Fluorochemical Co., Bertrel XF (registered trademark), CF ₃ CFHCFHCF ₂ CF ₃ , boiling point: 55 ° C.) and hydrofluoroether (manufactured by 3M, Novec (registered) Trademark) 7100, CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ , boiling point: 61 ° C.) (CF ₃ CFHCFHCF ₂ CF ₃ : CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ (mass ratio) = 80: 20) Was used for 1 minute at 23 ° C. After that, a resist pattern was formed by rinsing for 10 seconds using methyl nonafluorobutyl ether (3M, Novec (registered trademark) 7100, surface tension: 13.6 mN / m) as a rinse liquid. The optimum exposure dose (E _op ) was appropriately set with a value of about twice the E _th measured above as a guide. The line (unexposed region) and the space (exposed region) of the resist pattern were 18 nm, 20 nm, 25 nm, and 30 nm (that is, half pitch 18 nm, 20 nm, 25 nm, and 30 nm).
Then, it was observed with a scanning electron microscope (SEM) at a magnification of 100,000, and the half pitch formed by the pattern was taken as the resolution.

(Examples 2 to 4)
When forming and evaluating the resist pattern, a mixed solution of CF ₃ CFHCFHCF ₂ CF ₃ : CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ (mass ratio) of 60:40 was used as a resist developing solution (Example 2). , 40:60 mixed solution (Example 3) and 20:80 mixed solution (Example 4) were used in the same manner as in Example 1 to prepare a copolymer and a positive resist composition. , And formation and evaluation of resist patterns were performed. The results are shown in Table 1.

(Examples 5 to 8)
When forming and evaluating a resist pattern, Novec (registered trademark) 7200 was used as a hydrofluoroether instead of Novec (registered trademark) 7200 (3M, CF ₃ CF ₂ CF ₂ CF ₂ OC ₂ H ₅ , boiling point: 76). Was prepared in the same manner as in Examples 1 to 4 except that (C) was used, and a copolymer and a positive resist composition were prepared, and a resist pattern was formed and evaluated. The results are shown in Table 1.

(Comparative Example 1)
When forming and evaluating the resist pattern, hydrofluorocarbon (Bertrel XF (registered trademark), CF ₃ CFHCFHCF ₂ CF ₃ , CF ₃ CFHCFHCF ₂ CF ₃ , boiling point: 55 ° C.) manufactured by Mitsui DuPont Fluorochemicals alone is used as a resist developer. Except for the above, in the same manner as in Example 1, the copolymer and the positive resist composition were prepared, and the resist pattern was formed and evaluated. The results are shown in Table 1.

(Comparative example 2)
When forming and evaluating a resist pattern, hydrofluoroether (Novec (registered trademark) 7100, CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ , manufactured by 3M, boiling point: 61 ° C.) is used alone as a resist developing solution. Except for the above, in the same manner as in Example 1, the copolymer and the positive resist composition were prepared, and the resist pattern was formed and evaluated. The results are shown in Table 1.

(Comparative example 3)
When forming and evaluating the resist pattern, hydrofluoroether (3M, Novec (registered trademark) 7200, CF ₃ CF ₂ CF ₂ CF ₂ OC ₂ H ₅ , boiling point: 76 ° C.) was used alone as a resist developing solution. The copolymer and the positive resist composition were prepared, and the resist pattern was formed and evaluated in the same manner as in Example 1 except that the above was used. The results are shown in Table 1.

(Comparative example 4)
When forming and evaluating the resist pattern, Novec (registered trademark) 7300 was used as the hydrofluoroether instead of Novec (registered trademark) 7300 (3M, CF ₃ CF ₂ CF (OCH ₃ ) C ₃ F ₇ , boiling point: It was tried to prepare a copolymer and a positive resist composition and to form and evaluate a resist pattern in the same manner as in Comparative Example 2 except that (98 ° C.) was used. It was not dissolved, and the resist pattern could not be formed and evaluated. The results are shown in Table 1.

(Comparative Examples 5-8)
When forming and evaluating the resist pattern, Novec (registered trademark) 7300 was used as the hydrofluoroether instead of Novec (registered trademark) 7300 (3M, CF ₃ CF ₂ CF (OCH ₃ ) C ₃ F ₇ , boiling point: Preparation of a copolymer and a positive resist composition, and formation and evaluation of a resist pattern were performed in the same manner as in Examples 1 to 4 except that (98 ° C.) was used. The results are shown in Table 1.
In Comparative Example 8, the electron beam-irradiated portion was not dissolved in the developing solution, and the resist pattern could not be formed and evaluated.

(Examples 9 to 16 and Comparative Examples 9 to 16)
Preparation of a copolymer and a positive resist composition, and a resist pattern in the same manner as in Examples 1 to 8 and Comparative Examples 1 to 8 except that the copolymer prepared as described below was used. Formed and evaluated. The results are shown in Table 2.
In Comparative Example 12 and Comparative Example 16, the electron beam-irradiated portion was not dissolved in the developing solution, and the resist pattern could not be formed and evaluated.
<Preparation of copolymer>
[Synthesis of polymer]
3.0 g of 2,2,3,3,3-pentafluoropropyl α-chloroacrylic acid (ACAPFP) as the monomer (a) and 4-fluoro-α-methylstyrene (as the monomer (b) ( 4FAMS) 3.235 g and azobisisobutyronitrile 0.00521 g as a polymerization initiator were placed in a glass container, and the glass container was sealed and purged with nitrogen. The mixture was stirred for 6 hours in a constant temperature bath at ℃. Then, the temperature was returned to room temperature, the inside of the glass container was opened to the atmosphere, and 10 g of tetrahydrofuran (THF) was added to the obtained solution. Then, the solution to which THF was added was dropped into 300 g of methanol to precipitate a polymer. Then, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white coagulated product (polymer). The weight average molecular weight (Mw) of the obtained polymer was 38837, the number average molecular weight (Mn) was 22658, and the molecular weight distribution (Mw / Mn) was 1.714. Further, the obtained polymer contained 50 mol% of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit and 50 mol% of 4-fluoro-α-methylstyrene unit.
[Purification of polymer]
Next, the obtained polymer was dissolved in 100 g of THF, the obtained solution was added dropwise to a mixed solvent of 50 g of THF and 950 g of methanol (MeOH), and a white coagulated product (4-fluoro-α-methylstyrene unit and A copolymer containing α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit) was deposited. Then, the solution containing the precipitated copolymer was filtered through a Kiriyama funnel to obtain a white copolymer. Then, the weight average molecular weight, the number average molecular weight, and the molecular weight distribution of the obtained copolymer were measured. As a result, the weight average molecular weight was 47603, the number average molecular weight was 36477, and the molecular weight distribution was 1.305.
The obtained copolymer contained 50 mol% each of 2,2,3,3,3-pentafluoropropyl α-chloroacrylic acid unit and 4-fluoro-α-methylstyrene unit.

From Table 1, it can be seen that in Examples 1 to 8 using a predetermined developing solution, a resist pattern having excellent resolution can be formed as compared with Comparative Examples 1 to 8.
Further, from Table 2, it can be seen that in Examples 9 to 16 using a predetermined developing solution, a resist pattern having excellent resolution can be formed as compared with Comparative Examples 9 to 16.

  According to the present invention, a copolymer having a fluorine atom can be used as a positive resist to form a resist pattern having excellent resolution.

Claims (6)

The following general formula (I):

[In the general formula (I), R ¹ is an organic group containing a fluorine atom. ]
A monomer unit (A) represented by
The following general formula (II):

[In the formula (II), R ² is an alkyl group, R ³ is an alkyl group, a halogen atom or a halogenated alkyl group, p is an integer of 0 or more and 5 or less, and R ³ is present in plural. If so, they may be the same or different from each other. ]
A step of forming a resist film using a positive resist composition containing a copolymer having a monomer unit (B) represented by
Exposing the resist film,
Developing the exposed resist film,
Including,
A method for forming a resist pattern, wherein the development is performed using a developing solution containing a hydrofluorocarbon and a fluorine-based solvent having a boiling point difference between the hydrofluorocarbon and the absolute value of 25 ° C. or less. The resist pattern forming method according to claim 1, wherein the hydrofluorocarbon is CF ₃ CFHCFHCF ₂ CF ₃ .   The resist pattern forming method according to claim 1, wherein the fluorine-based solvent is at least one selected from the group consisting of hydrochlorofluorocarbons, hydrofluoroethers, and perfluorocarbons. The fluorine-based solvent is a group consisting of CF ₃ CF ₂ CHCl ₂ , CClF ₂ CF ₂ CHClF, CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ , CF ₃ CF ₂ CF ₂ CF ₂ OC ₂ H ₅ and C ₈ F _18. The resist pattern forming method according to claim 1, wherein the resist pattern forming method is at least one selected from the above.   5. The developing solution according to claim 1, wherein a content ratio of the hydrofluorocarbon and the fluorine-based solvent (hydrofluorocarbon: fluorine-based solvent) is 40:60 to 60:40 on a mass basis. A method for forming a resist pattern as described. The monomer unit (A) is a 2,2,3,3,3-pentafluoropropyl unit of α-chloroacrylic acid,
The resist pattern forming method according to claim 1, wherein the monomer unit (B) is an α-methylstyrene unit or a 4-fluoro-α-methylstyrene unit.