JP2021067811A - Resist pattern forming method - Google Patents

Abstract

To provide a resist pattern forming method capable of forming a resist pattern excellent in clarity.SOLUTION: The resist pattern forming method includes the steps of: forming a resist film using a positive resist composition which contains a polymer having a monomer unit (A) represented by general formula (I) and a monomer unit (B) represented by general formula (II) and a solvent; exposing the resist film; and developing the resist film. The development is performed using a developer containing a hydrofluorocarbon.SELECTED DRAWING: None

Description

The present invention relates to a resist pattern forming method.

Conventionally, in fields such as semiconductor manufacturing, ionizing radiation such as electron beams and short-wavelength light such as ultraviolet rays (including extreme ultraviolet rays (EUV)) (hereinafter, ionizing radiation and short-wavelength light are combined to form "ionizing radiation, etc." A polymer whose main chain is cleaved to reduce its molecular weight by irradiation with (may be referred to as) is used as a main chain cleaved positive type resist.

For example, Patent Document 1 contains an α-chloroacrylic acid fluoroester unit having an organic group having 5 or more and 7 or less fluorine atoms as a polymer that can be used as a main chain breaking type positive resist. , Polymers having a weight average molecular weight of 20,000 or more and 50,000 or less are described. In Patent Document 1, a resist film is formed by using a positive resist composition containing the polymer and a solvent, and the obtained resist film is exposed and developed.

International Publication No. 2018/1236667

Here, in the formation of the resist pattern, it is required that the boundary between the portion where the resist film remains after exposure and development and the portion where the resist film is dissolved is clear (that is, excellent in clarity). However, the conventional resist pattern forming method using a polymer has room for improvement in that the clarity of the obtained resist pattern is further enhanced.

Therefore, an object of the present invention is to provide a resist pattern forming method capable of forming a resist pattern having excellent clarity.

The present inventor has conducted diligent studies for the purpose of solving the above problems. Then, the present inventor formed a resist film using a positive resist composition containing a polymer having a predetermined monomer unit and having a weight average molecular weight of a predetermined value or more, and obtained a resist. The present invention has been completed by finding that a highly clear resist pattern can be formed by exposing the film with ionizing radiation or the like and then developing the exposed resist film with a predetermined developer.

〔一般式（Ｉ）中、Ｘは、フッ素原子、塩素原子、臭素原子、ヨウ素原子、またはアスタチン原子であり、Ｒ¹は、フッ素原子を含む有機基である。〕
で表わされる単量体単位（Ａ）と、
下記一般式（ＩＩ）：

〔一般式（ＩＩ）中、Ｒ²は、水素原子、フッ素原子、非置換のアルキル基またはフッ素原子で置換されたアルキル基であり、Ｒ³は、水素原子、非置換のアルキル基またはフッ素原子で置換されたアルキル基であり、ｐおよび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（Ｂ）とを有する重合体、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、前記重合体の重量平均分子量が１００，０００以上であり、前記現像を、ハイドロフルオロカーボン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、単量体単位（Ａ）および単量体単位（Ｂ）を含有し、且つ重量平均分子量が１００，０００以上である重合体を含むレジスト組成物を用いてレジスト膜を形成し、得られたレジスト膜を露光した後、ハイドロフルオロカーボンを含む現像液を用いて、露光されたレジスト膜を現像することで、明瞭性の高い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、重合体の「重量平均分子量」は、ゲル浸透クロマトグラフィーを使用し、ポリスチレン換算値として測定することができる。
また、本発明において、一般式（ＩＩ）中のｐが２以上の場合には、複数あるＲ²は互いに同一でも異なっていてもよく、また、一般式（ＩＩ）中のｑが２以上の場合には、複数あるＲ³は互いに同一でも異なっていてもよい。 That is, the present invention aims to advantageously solve the above problems, and the resist pattern forming method of the present invention is described in the following general formula (I):

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

[In general formula (II), R ² is a hydrogen atom, a fluorine atom, an unsubstituted alkyl group or an alkyl group substituted with a fluorine atom, and R ³ is a hydrogen atom, an unsubstituted alkyl group or a fluorine atom. It is an alkyl group substituted with, and p and q are integers of 0 or more and 5 or less, and p + q = 5. ], A step of forming a resist film using a polymer having a monomer unit (B) and a solvent, a step of exposing the resist film, and a step of exposing the resist film. It is characterized in that the step of developing the resist film is included, the weight average molecular weight of the polymer is 100,000 or more, and the development is carried out using a developing solution containing hydrofluorocarbon. As described above, a resist film is formed by using a resist composition containing a polymer unit (A) and a monomer unit (B) and having a weight average molecular weight of 100,000 or more. After exposing the obtained resist film, the exposed resist film can be developed with a developing solution containing hydrofluorocarbon to form a highly clear resist pattern.
In the present invention, the "weight average molecular weight" of the polymer can be measured as a polystyrene-equivalent value by using gel permeation chromatography.
Further, in the present invention, when p in the general formula (II) is 2 or more, a plurality of R ^2s may be the same or different from each other, and q in the general formula (II) is 2 or more. In some cases, the plurality of R ^3s may be the same or different from each other.

Here, in the resist pattern forming method of the present invention, it is preferable that the developer further contains hydrofluoroether. By using a developer containing hydrofluorocarbon and hydrofluoro ether, the resolution of the obtained resist pattern can be improved and good clarity can be sufficiently ensured.

In the resist pattern forming method of the present invention, the solubility parameter of the hydrofluoroether ^{is preferably 6.6 (cal / cm 3} ) ^1/2 or less. When the solubility parameter of the hydrofluoroether (hereinafter, may be abbreviated as “SP value”) is not more than the above value, the resolution of the obtained resist pattern can be improved and the clarity can be further improved.
In the present invention, the "solubility parameter" of the hydrofluoroether can be calculated by using the method described in Examples.

Further, in the resist pattern forming method of the present invention, the solubility parameter of the hydrofluoroether is preferably less than ^{6.5 (cal / cm 3} ) ^1/2. When the solubility parameter of the hydrofluoroether is less than the above value, the resolution of the obtained resist pattern can be further improved and the clarity can be further improved.

Further, in the resist pattern forming method of the present invention, it is preferable that the _{hydrofluoroether is CF 3} CF ₂ CF (OCH ₃ ) CF (CF ₃ ) _{2. When CF 3} CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ is used as the hydrofluoroether, the resolution of the obtained resist pattern can be improved and the clarity can be further improved.

Here, in the resist pattern forming method of the present invention, the ratio of the hydrofluoroether to the total of the hydrofluorocarbon and the hydrofluoroether in the developer is more than 0% by mass and 90% by mass or less. Is preferable. When the ratio of the hydrofluorocarbon to the hydrofluoro ether is within the above range, the resolution of the obtained resist pattern can be improved and good clarity can be sufficiently ensured. In addition, when the resist film is exposed and developed, sufficient solubility of the exposed portion in the developing solution can be ensured, and a resist pattern can be satisfactorily formed.

In the resist pattern forming method of the present invention, it is preferable that X in the general formula (I) is a chlorine atom. When X in the general formula (I) is a chlorine atom, the breakability of the main chain of the polymer when irradiated with ionizing radiation or the like can be improved. In addition, the polymer can be easily prepared.

Further, in the resist pattern forming method of the present invention, it is preferable that the proportion of components having a molecular weight of less than 10,000 is 0.2% or less in the polymer. When the ratio of the components having a molecular weight of less than 10,000 in the polymer is not more than the above value, the resolution of the obtained resist pattern can be improved.
In the present invention, the "ratio of components having a molecular weight of less than 10,000" uses a chromatogram obtained by gel permeation chromatography, and the molecular weight in the chromatogram with respect to the total area (A) of the peaks in the chromatogram. It can be obtained by calculating the ratio (= (B / A) × 100%) of the total (B) of the peak areas of the components having a value of less than 10,000.

Further, in the resist pattern forming method of the present invention, it is preferable that the _{hydrofluorocarbon is CF 3} CFHCHFCF ₂ CF _{3. If a developer containing CF 3} CFHCHFCF ₂ CF ₃ is used as the hydrofluorocarbon, the resolution of the obtained resist pattern can be improved and the clarity can be further enhanced.

According to the present invention, it is possible to provide a resist pattern forming method capable of forming a resist pattern having excellent clarity.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the resist pattern forming method of the present invention is a main chain cutting type in which the main chain is cut by irradiation with ionizing radiation such as an electron beam or short wavelength light such as ultraviolet rays (including EUV) to reduce the molecular weight. A positive resist is used. The resist pattern forming method of the present invention is not particularly limited, and is suitable for forming a resist pattern in a manufacturing process such as a printed circuit board such as a build-up substrate, a semiconductor, a photomask, and a mold. Can be used.

(Resist pattern forming method)
The resist pattern forming method of the present invention is a step of forming a resist film using a positive resist composition containing a predetermined polymer formed by using a predetermined monomer (resist film forming step), and exposing the resist film. At least a step of developing the exposed resist film (exposure step) and a step of developing the exposed resist film (development step) are included.
The resist pattern forming method of the present invention may include steps other than the resist film forming step, the exposure step, and the developing step described above. For example, the resist pattern forming method of the present invention may optionally further include a step of removing the developer (rinse step) after the developing step.

Then, in the method for forming a resist pattern of the present invention, a resist film is formed using a positive resist composition containing a predetermined polymer in the resist film forming step, and a developing solution containing hydrofluorocarbon is used in the developing step. Since the development is performed using the resist pattern, a resist pattern having excellent clarity can be formed.

<Resist film forming process>
In the resist film forming step, a positive resist composition is applied onto a work piece such as a substrate to be processed using a resist pattern, and the applied positive resist composition is dried to form a resist film. .. Here, the method for applying and drying the positive resist composition is 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 polymer 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 positive resist composition.

〔一般式（Ｉ）中、Ｘは、フッ素原子、塩素原子、臭素原子、ヨウ素原子、またはアスタチン原子であり、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）：

〔一般式（ＩＩ）中、Ｒ²は、水素原子、フッ素原子、非置換のアルキル基またはフッ素原子で置換されたアルキル基であり、Ｒ³は、水素原子、非置換のアルキル基またはフッ素原子で置換されたアルキル基であり、ｐおよび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（Ｂ）とを有し、重量平均分子量が１００，０００以上であることを特徴とする。 [Polymer]
In the polymer used in the resist pattern forming method of the present invention, the main chain is cleaved by irradiation with ionizing radiation such as an electron beam or short wavelength light such as ultraviolet rays (including EUV) to reduce the molecular weight. It is a polymer that can be satisfactorily used as a positive type resist. Then, the polymer has the following general formula (I):

[In the general formula (I), X is a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, or an astatin atom, and R ¹ is an organic group containing a fluorine atom. ] And the monomer unit (A)
The following general formula (II):

[In general formula (II), R ² is a hydrogen atom, a fluorine atom, an unsubstituted alkyl group or an alkyl group substituted with a fluorine atom, and R ³ is a hydrogen atom, an unsubstituted alkyl group or a fluorine atom. It is an alkyl group substituted with, and p and q are integers of 0 or more and 5 or less, and p + q = 5. ], The weight average molecular weight is 100,000 or more.

The above-mentioned polymer may contain any monomer unit other than the monomer unit (A) and the monomer unit (B), but among all the monomer units constituting the polymer. The ratio of the monomer unit (A) and the monomer unit (B) is preferably 90 mol% or more in total, more preferably 100 mol%, and 100 mol% (that is,). , The polymer contains only the monomer unit (A) and the monomer unit (B)).
Then, as long as the above-mentioned polymer has a monomer unit (A) and a monomer unit (B), for example, a random polymer, a block polymer, an alternating polymer (ABAB ...), etc. However, it is preferable that the polymer contains 90% by mass or more of the alternating polymer (upper limit is 100% by mass). Here, it is preferable that the alternating polymers do not form a crosslinked product. ^{Since the polymer contains a fluorine atom in R 1} of the monomer unit (A), it is difficult to form a crosslinked product.

Since the above-mentioned polymer contains a predetermined monomer unit (A) and a monomer unit (B), ionizing radiation or the like (for example, electron beam, KrF laser, ArF laser, EUV laser, etc.) When irradiated with, the main chain is cleaved to reduce the molecular weight.

（一般式（ＩＩＩ）中、ＸおよびＲ¹は、一般式（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) ―
The monomer unit (A) is represented by the following general formula (III):

(In the general formula (III), X and R ¹ are the same as those in the general formula (I).) It is a structural unit derived from the monomer (a) represented by the general formula (I).

The ratio of the monomer unit (A) to all the monomer units constituting the polymer is not particularly limited, and can be, for example, 30 mol% or more and 70 mol% or less, and 40 mol% or more and 60 mol% or more. It is preferably 45 mol% or more and 55 mol% or less, more preferably 45 mol% or more.

Here, X in the general formula (I) and the general formula (III) needs to be a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, or an astatine atom from the viewpoint of absorption efficiency of ionizing radiation and the like. is there. From the viewpoint of improving the breakability of the main chain of the polymer when irradiated with ionizing radiation or the like, X in the general formula (I) and the general formula (III) is preferably a chlorine atom. The monomer (a) in which X in the general formula (III) is a chlorine atom has excellent polymerizable properties, and the monomer unit (A) in which X in the general formula (I) is a chlorine atom. The polymer having the above is also excellent in that it is easy to prepare.

^{Here, R 1} in the general formula (I) and the general formula (III) needs to be an organic group containing a fluorine atom. Unless R ¹ is an organic group containing a fluorine atom, the breakability of the main chain of the polymer when irradiated with ionizing radiation or the like cannot be ensured. ^{R 1} in the general formula (I) and the general formula (III) is preferably an organic group having 3 or more fluorine atoms, and preferably an organic group having 7 or less fluorine atoms. , It is more preferable that the organic group has 5 fluorine atoms. When ^{the number of fluorine atoms in R 1} is 3 or more, the breakability of the main chain of the polymer when irradiated with ionizing radiation or the like can be made sufficient. On the other hand, when ^{the number of fluorine atoms in R 1} is 7 or less, the resolution of the obtained resist pattern can be improved and the clarity can be further improved.
Further, ^{the number of carbon atoms 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 number of carbon atoms of R 1} is 2 or more, the solubility of the polymer after exposure in a developing solution can be sufficiently secured, and when ^{the number of carbon atoms of R 1} is 10 or less, the glass transition point. It is possible to suppress the decrease in the amount of the resist pattern and further enhance the clarity of the obtained resist pattern.

^{Specifically, R 1} in the general formula (I) and the general formula (III) is preferably a fluoroalkyl group, a fluoroalkoxyalkyl group, or a fluoroalkoxyalkenyl group, and more preferably a fluoroalkyl group. preferable. If R ¹ is the above-mentioned group, the breakability of the main chain of the polymer when irradiated with ionizing radiation or the like can be sufficiently improved.

Here, as the fluoroalkyl group, for example, 2,2,2-trifluoroethyl group (the number of fluorine atoms is 3, the number of carbon atoms is 2), 2,2,3,3,3-pentafluoropropyl. Group (5 fluorine atoms, 3 carbon atoms, structural formula X below), 3,3,4,5,4-pentafluorobutyl group (5 fluorine atoms, 4 carbon atoms) , 1H-1- (trifluoromethyl) trifluoroethyl group (6 fluorine atoms, 3 carbon atoms), 1H, 1H, 3H-hexafluorobutyl group (of fluorine atoms) Number 6, carbon atom number 4), 2,2,3,3,4,5,4-heptafluorobutyl group (number of fluorine atom number 7, number of carbon atom number 4), or 1, Examples thereof include 2,2,2-tetrafluoro-1- (trifluoromethyl) ethyl groups (7 fluorine atoms and 3 carbon atoms). Among these, 2,2,3,3,3-pentafluoropropyl groups (the number of fluorine atoms is 5, the number of carbon atoms is 3, and the following structural formula X) are preferable.
Examples of the fluoroalkoxyalkyl group include a fluoroethoxymethyl group and a fluoroethoxyethyl group.
Examples of the fluoroalkoxyalkenyl group include a fluoroethoxyvinyl group.

The monomer (a) represented by the above-mentioned general formula (III) that can form the monomer unit (A) represented by the above-mentioned general formula (I) is particularly limited. Not, for example, α-chloroacrylic acid 2,2,2-trifluoroethyl (number of fluorine atoms is 3), α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl (number of fluorine atoms) 5), α-chloroacrylic acid 3,3,4,5,4-pentafluorobutyl (number of fluorine atoms is 5), α-chloroacrylic acid 1H-1- (trifluoromethyl) trifluoroethyl (fluorine) Number of atoms is 6), α-chloroacrylic acid 1H, 1H, 3H-hexafluorobutyl (number of fluorine atoms is 6), α-chloroacrylic acid 1,2,2,2-tetrafluoro-1- (tri) Α-chloroacrylic acid such as fluoromethyl) ethyl (7 fluorine atoms), α-chloroacrylic acid 2,2,3,3,4,5,4-heptafluorobutyl (7 fluorine atoms) Acid fluoroalkyl ester; α-chloroacrylic acid fluoro, such as α-chloroacrylic acid pentafluoroethoxymethyl ester (number of fluorine atoms is 5) and α-chloroacrylic acid pentafluoroethoxyethyl ester (number of fluorine atoms is 5). Aalkoxyalkyl ester; α-chloroacrylic acid fluoroalkoxyalkenyl ester such as α-chloroacrylic acid pentafluoroethoxyvinyl ester (the number of fluorine atoms is 5); and the like.

The monomer unit (A) is preferably a structural unit derived from α-chloroacrylic acid fluoroalkyl ester. Furthermore, the monomer unit (A) is a structural unit derived from α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl among α-chloroacrylic acid fluoroalkyl esters. Is more preferable. If the monomer unit (A) is a structural unit derived from α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl, the resolution of the resist pattern can be improved and the clarity can be further enhanced. Can be done. In addition, the breakability of the main chain of the polymer when irradiated with ionizing radiation or the like can be sufficiently ensured.

（一般式（ＩＶ）中、Ｒ²〜Ｒ³、ならびに、ｐおよびｑは、一般式（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) ―
Further, the monomer unit (B) is represented by the following general formula (IV):

(In the general formula (IV), R ^{2 to} R ³ , and p and q are the same as those in the general formula (II)), which is a structural unit derived from the monomer (b).

The ratio of the monomer unit (B) to all the monomer units constituting the polymer is not particularly limited, and can be, for example, 30 mol% or more and 70 mol% or less, and 40 mol% or more and 60 mol% or more. It is preferably 45 mol% or more and 55 mol% or less, more preferably 45 mol% or more.

^{Here, the alkyl group substituted with a fluorine atom which can constitute R 2 to} R ³ in the general formula (II) and the general formula (IV) is not particularly limited, and the hydrogen atom in the alkyl group is not particularly limited. Examples thereof include a group having a structure in which a part or all of the above is substituted with a fluorine atom.
^{Further, the unsubstituted alkyl group capable of constituting R 2 to} R ³ in the general formula (II) and the general formula (IV) is not particularly limited, and the number of unsubstituted carbon atoms is 1 or more and 5 The following alkyl groups can be mentioned. Of these, ^{as the unsubstituted alkyl group capable of forming R 2 to} R ³ , a methyl group or an ethyl group is preferable.

^{Further, from the viewpoint of improving the ease of preparation of the polymer, all of R 2} and / or R ³ existing in the general formula (II) and the general formula (IV) are hydrogen atoms or unsubstituted alkyls. It is preferably a group, more preferably an alkyl group having a hydrogen atom or an unsubstituted carbon atom of 1 or more and 5 or less, and further preferably a hydrogen atom.
From the viewpoint of improving the ease of preparation of the polymer, a p in the general formula (II) and the general formula (IV) is 5, q is 0, all 5 There R ² is hydrogen preferably an atom or an unsubstituted alkyl group, more preferably the number of all there are five R ² is a hydrogen atom or an unsubstituted carbon atom is an alkyl group having 1 to 5, there are five R It is more preferable that all of ^{2 are hydrogen atoms.}

The monomer (b) represented by the above-mentioned general formula (IV) that can form the monomer unit (B) represented by the above-mentioned general formula (II) is particularly limited. Not, for example, α-methylstyrene (AMS) such as (b-1) to (b-11) below and derivatives thereof (for example, 4-fluoro-α-methylstyrene (4FAMS) according to the general formula (b-2). )).

From the viewpoint of improving the ease of preparation of the polymer, the monomer unit (B) may not contain a fluorine atom (that is, only the monomer unit (A) contains a fluorine atom). It is preferably a structural unit derived from α-methylstyrene. That is, p and q in the general formula (II) and the general formula (IV), and R ^{2 to} R ³ have p = 5, q = 0, and ^{all five R 2} are hydrogen atoms. Is particularly preferable.

-Percentage of components with a molecular weight of less than 10,000-
The polymer used in the resist pattern forming method of the present invention preferably has a molecular weight of less than 10,000 in a proportion of 0.2% or less, more preferably 0.15% or less. , 0.1% or less is more preferable. When the proportion of the components having a molecular weight of less than 10,000 is 0.2% or less, the resolution of the obtained resist pattern can be improved and the clarity can be further enhanced. The lower limit of the proportion of the components having a molecular weight of less than 10,000 is not particularly limited.

-Percentage of components with a molecular weight of more than 100,000-
Here, in the polymer used in the resist pattern forming method of the present invention, the proportion of components having a molecular weight of more than 100,000 is preferably 45% or more, more preferably 50% or more, and 55%. The above is more preferable, and 63% or more is particularly preferable. When the proportion of the component having a molecular weight of more than 100,000 is 45% or more, the resolution of the obtained resist pattern can be improved and the clarity can be further improved. The upper limit of the proportion of the component having a molecular weight of more than 100,000 is not particularly limited, but from the viewpoint of improving the productivity of the polymer, for example, it can be 95% or less, and can be 85% or less. it can.
In the present invention, the "ratio of components having a molecular weight of more than 100,000" uses a chromatogram obtained by gel permeation chromatography, and the molecular weight in the chromatogram with respect to the total area (A) of peaks in the chromatogram. Can be obtained by calculating the ratio (= (C / A) × 100%) of the total (C) of the peak areas of the components having a value of more than 100,000.

-Weight average molecular weight-
The weight average molecular weight (Mw) of the polymer needs to be 100,000 or more, preferably 125,000 or more, more preferably 150,000 or more, and 300,000 or less. It is preferably 250,000 or less, more preferably 200,000 or less. If the weight average molecular weight (Mw) of the polymer is less than 100,000, the clarity and resolution of the resist pattern cannot be sufficiently ensured. On the other hand, when the weight average molecular weight (Mw) of the polymer is 300,000 or less, the sensitivity in forming the resist pattern can be improved while ensuring the productivity of the polymer.

-Number average molecular weight-
The number average molecular weight (Mn) of the polymer is preferably 90,000 or more, more preferably 110,000 or more, preferably 200,000 or less, and preferably 150,000 or less. Is more preferable. When the number average molecular weight (Mn) of the polymer is 90,000 or more, the resolution of the obtained resist pattern can be improved and the clarity can be further improved. Further, the efficiency of forming the resist pattern can be improved. On the other hand, when the number average molecular weight (Mn) of the polymer is 200,000 or less, the sensitivity in forming the resist pattern can be improved while ensuring the productivity of the polymer.

-Molecular weight distribution-
The molecular weight distribution (Mw / Mn) of the polymer is preferably 1.3 or more, more preferably 1.35 or more, further preferably 1.39 or more, and 1.4 or more. Is particularly preferable, 2.0 or less is preferable, 1.6 or less is more preferable, and 1.5 or less is further preferable. When the molecular weight distribution (Mw / Mn) of the polymer is 1.3 or more, the polymer can be efficiently produced. On the other hand, when the molecular weight distribution (Mw / Mn) of the polymer is 2.0 or less, the resolution of the resist pattern can be improved and the clarity can be further improved.
In the present invention, the "molecular weight distribution" can be obtained by calculating the ratio of the weight average molecular weight to the number average molecular weight (weight average molecular weight / number average molecular weight). Then, in the present invention, the "number average molecular weight" and the "weight average molecular weight" can be measured as standard polystyrene-equivalent values using gel permeation chromatography.

[Method for preparing polymer]
Then, the polymer having the above-mentioned monomer unit (A) and monomer unit (B) polymerizes, for example, a monomer composition containing the monomer (a) and the monomer (b). After that, it can be prepared by purifying the arbitrarily obtained polymer.
The composition of the polymer, the molecular weight distribution, the weight average molecular weight and the number average molecular weight, and the ratio of the components of each molecular weight in the polymer can be adjusted by changing the polymerization conditions and the purification conditions. Specifically, for example, the composition of the polymer can be adjusted by changing the content ratio of each monomer in the monomer composition used for the polymerization.

-Polymerization of monomeric composition-
Here, the monomer composition used for preparing the polymer includes a monomer component containing the monomer (a) and the monomer (b), an optionally usable solvent, and a polymerization initiator. , Mixtures with optionally added additives can be used. Then, the polymerization of the monomer composition can be carried out by using a known method. Above all, when a solvent is used, it is preferable to use cyclopentanone or the like as the solvent. Further, as the polymerization initiator, it is preferable to use a radical polymerization initiator such as azobisisobutyronitrile.

The polymer obtained by polymerizing the monomer composition may be used as it is as a polymer, but is not particularly limited, and a good solvent such as tetrahydrofuran is added to the solution containing the polymer. After that, the solution to which a good solvent is added is dropped into a poor solvent such as methanol to coagulate the polymer, and the polymer can be recovered and purified as follows.

-Purification of polymer-
The purification method used when purifying the obtained polymer to obtain the polymer having the above-mentioned properties is not particularly limited, and a known purification method such as a reprecipitation method or a column chromatography method may be used. Can be done. Above all, it is preferable to use the reprecipitation method as the purification method.
The purification of the polymer may be repeated a plurality of times.

Then, in the purification of the polymer by the reprecipitation method, for example, the obtained polymer is dissolved in a good solvent such as tetrahydrofuran, and then the obtained solution is mixed with a good solvent such as tetrahydrofuran and a poor solvent such as methanol. It is preferable to carry out by dropping into a solvent and precipitating a part of the polymer. In this way, if the polymer solution is dropped into the mixed solvent of the good solvent and the poor solvent to purify the polymer, the weight obtained by changing the types and mixing ratios of the good solvent and the poor solvent can be obtained. The molecular weight distribution of the coalescence, the weight average molecular weight and the number average molecular weight, and the ratio of each molecular weight component in the polymer can be easily adjusted. Specifically, for example, the higher the proportion of the good solvent in the mixed solvent, the larger the molecular weight of the polymer precipitated in the mixed solvent.

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

[solvent]
The solvent is not particularly limited as long as it is a solvent capable of dissolving the above-mentioned polymer, and for example, a known solvent as described in Japanese Patent No. 59383536 can be used. Above all, from the viewpoint of obtaining a positive resist composition having an appropriate viscosity and improving the coatability of the positive resist composition, the solvent is an organic acid ester such as n-pentyl ester or n-hexyl ester. , 2-methoxy-1-methyl ethyl acetate, isoamyl acetate, or a mixture thereof is preferable, 2-methoxy-1-methyl ethyl acetate, isoamyl acetate, or a mixture thereof is more preferable, and isoamyl acetate is further preferable.

<Exposure process>
In the exposure step, the resist film formed in the resist film forming step is irradiated with ionizing radiation or the like 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 with ionizing radiation or the like.

<Development process>
In the developing step, the resist film on which the desired pattern is drawn in the exposure step is subjected to a developing process. Then, the resist film can be developed by, for example, bringing the resist film into contact with a developing solution. The method of bringing the resist film into contact with the developing solution is not particularly limited, and known methods such as immersing the resist film in the developing solution and applying the developing solution to the resist film can be used.

<< Developer >>
Here, the developer used in the developing step of the resist pattern forming method of the present invention needs to contain hydrofluorocarbon, and may optionally further contain hydrofluoroether. The developer may contain a solvent other than hydrofluorocarbon and hydrofluoroether (other solvents), but it may consist of only the above-mentioned hydrofluorocarbon or only the above-mentioned hydrofluorocarbon and hydrofluoroether. Is preferable.
Then, in the resist pattern forming method of the present invention, the resist film formed by using the positive resist composition containing the above-mentioned predetermined polymer is developed with a developing solution containing hydrofluorocarbon. A resist pattern having excellent clarity can be formed.

―SP value―
Here, the solubility parameter (SP value) of the developing solution ^{is preferably less than 6.8 (cal / cm 3} ) ^{1/2, and} more preferably 6.7 (cal / cm ³ ) ^1/2 or less. When the SP value of the developer is ^{less than 6.8 (cal / cm 3} ) ^1/2 , the resolution of the obtained resist pattern can be improved and the clarity can be further improved. Further, the contrast between the exposed portion and the unexposed portion of the positive resist composition can be easily adjusted, and the resist pattern forming efficiency is improved. The SP value of the developing solution can be adjusted, for example, by changing the type of developing solution to be adopted and, when two or more kinds of developing solutions are mixed and used, their mixing ratios. The lower limit of the SP value of the developing solution is not particularly limited, but can be, for example, 6.2 (cal / cm ³ ) ^1/2 or more. In the present invention, the "solubility parameter" of the developer can be calculated by using the method described in Examples.

[Hydrofluorocarbon]
Here, the hydrofluorocarbon contained in the developer used in the resist pattern forming method of the present invention is a compound in which some or all of the hydrogen atoms constituting the hydrocarbon compound (hydrocarbon) are replaced with fluorine atoms.

―SP value―
The hydrofluorocarbon preferably has an SP value of 7.2 (cal / cm ³ ) ^1/2 or less, more preferably 7.0 (cal / cm ³ ) ^1/2 or less, and 6. It is more preferably 9 (cal / cm ³ ) ^1/2 or less, and particularly preferably 6.8 (cal / cm ³ ) ^1/2. When the SP value of the hydrofluoroether is 7.2 (cal / cm ³ ) ^1/2 or less, the resolution of the obtained resist pattern can be improved and the clarity can be further improved. The SP value of the hydrofluorocarbon can be adjusted, for example, by changing the type of hydrofluorocarbon to be adopted and, when two or more types of hydrofluorocarbons are mixed and used, the mixing ratio thereof. Then, as long as the total SP value of the hydrofluorocarbon is 7.2 (cal / cm ³ ) ^1/2 or less, the hydrofluorocarbon having an SP value of more than 7.2 (cal / cm ³ ) ^{1/2 is SP.} It may be mixed with a hydrofluorocarbon having a value of 7.2 (cal / cm ³ ) ^{1/2 or less.}
The lower limit of the SP value of hydrofluorocarbon is not particularly limited, but can be, for example, 6.5 (cal / cm ³ ) ^1/2 or more. In the present invention, the "solubility parameter" of hydrofluorocarbon can be calculated by using the method described in Examples.

Here, the hydrofluorocarbon is not particularly limited, and for example, 1,1,1,2,3,4,5,5,5-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, Examples thereof include 1,3,3-pentafluorobutane and 1,1,1,2,2,3,3,4,4-nonafluorohexane. One of these may be used alone, or two or more of them may be used in combination. Among them, from the viewpoint of improving the resolution of the resist pattern and further enhancing the clarity of the resist pattern, the hydrofluorocarbon is preferably 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 CFHCHFCF 2} CF ₃ , SP value: 6.8 (cal / cm ³ ) ^1/2 ) is more preferable.
The hydrofluorocarbons described above are commercially available, for example, as Bertrel XF (registered trademark) manufactured by Mitsui-Dupont Fluorochemicals.

[Hydrofluoroether]
If a developer containing hydrofluoroether in addition to hydrofluorocarbon is used as the developer used in the resist pattern forming method of the present invention, the resolution of the obtained resist pattern is improved and good clarity is sufficiently ensured. be able to.

―SP value―
Here, the hydrofluoroether preferably has an SP value of 6.6 (cal / cm ³ ) ^1/2 or less, and more preferably less than 6.5 (cal / cm ³ ) ^1/2. When the SP value of the hydrofluoroether is 6.6 (cal / cm ³ ) ^1/2 or less, the resolution of the obtained resist pattern can be improved and the clarity can be further improved. The SP value of the hydrofluoroether can be adjusted, for example, by changing the type of hydrofluoroether to be adopted and, when two or more types of hydrofluoroether are mixed and used, the mixing ratio thereof. it can. Then, as long as the total SP value of the hydrofluoroether is 6.6 (cal / cm ³ ) ^1/2 or less, the hydrofluoroether having an SP value of more than 6.6 (cal / cm ³ ) ^1/2 is used. , It may be mixed with a hydrofluoroether having an SP value of 6.6 (cal / cm ³ ) ^{1/2 or less.}
The lower limit of the SP value of the hydrofluoroether is not particularly limited, but can be, for example, 6.0 (cal / cm ³ ) ^1/2 or more.

The hydrofluoro ether is not particularly limited, and for example, methyl nonafluorobutyl ether, methyl nonafluoroisobutyl ether, ethyl nonafluorobutyl ether, ethyl nonafluoroisobutyl ether, 1,1,1,2,2,3 , 4, 5, 5, 5-decafluoro-3 methoxy-4- (trifluoromethyl) pentane and the like.
The hydrofluoroethers described above are commercially available, for example, as Novec® 7100, Novec 7200, Novec 7300, etc. manufactured by 3M.

Here, one type of the above-mentioned hydrofluoroether may be used alone, or two or more types may be used in combination. _{As the hydrofluoro ether, methyl nonafluorobutyl ether (CF 3} CF ₂ CF ₂ CF ₂ OCH ₃ , SP value: 6.5) from the viewpoint of improving the resolution of the resist pattern and further enhancing the clarity of the resist pattern. (Cal / cm ³ ) ^1/2 ), ethyl nonafluorobutyl ether (CF ₃ CF ₂ CF ₂ CF ₂ OC ₂ H ₅ , SP value: 6.3 (cal / cm ³ ) ^1/2 ), 1, 1, 1,2,2,3,4,5,5,5-decafluoro-3 methoxy-4- (trifluoromethyl) pentane (CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ , SP value: 6.2 (cal / cm ³ ) ^1/2 ) is preferable, and 1,1,1,2,2,3,4,5,5-decafluoro-3methoxy-4- (trifluoromethyl) pentane (CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ ) is more preferable.

-Mass ratio of hydrofluorocarbons and hydrofluoroethers-
Further, the ratio of the hydrofluoroether to the total of the hydrofluorocarbon and the hydrofluoroether in the developing solution is preferably more than 0% by mass, where the total amount of the hydrofluorocarbon and the hydrofluoroether is 100% by mass. It is more preferably 10% by mass or more, further preferably 20% by mass or more, preferably 90% by mass or less, more preferably 80% by mass or less, and 75% by mass or less. Is more preferable. When the ratio of hydrofluoroether to the total of hydrofluorocarbon and hydrofluoroether is more than 0% by mass, good clarity can be sufficiently ensured while improving the resolution of the obtained resist pattern, and 90 mass. When it is less than%, when the resist film is exposed and developed, sufficient solubility of the exposed portion in the developing solution can be ensured, and the resist pattern can be satisfactorily formed.

[Other solvents]
The other solvent that can be arbitrarily contained in the developer used in the resist pattern forming method of the present invention is not particularly limited as long as it is a solvent other than the above-mentioned hydrofluorocarbon and hydrofluoro ether. The developer may contain one kind of other solvent or two or more kinds.
The content ratio of the other solvent in the developing solution is preferably 5% by mass or less, preferably 1% by mass or less, from the viewpoint of improving the resolution of the obtained resist pattern and further enhancing the clarity. It is more preferable, and it is further preferable that it is 0% by mass.

[Development conditions]
The temperature of the developing solution at the time of development is not particularly limited, but can be, for example, 21 ° C. or higher and 25 ° C. or lower. The development time can be, for example, 20 seconds or more and 1 minute or less.

<Rinse process>
In the resist pattern forming method of the present invention, a step of removing the developing solution may be optionally carried out after the developing step. The developer can be removed by using, for example, a rinse solution.
Here, as the rinsing solution, for example, the same developer as the developing solution described in the section of "development process" can be mentioned. Among them, as the rinsing solution, methyl nonafluorobutyl ether (CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ , SP value: 6.5 (cal / cm ³ ) ^1/2 ), ethyl nonafluorobutyl ether (CF ₃ CF ₂ CF) ₂ CF ₂ OC ₂ H ₅ , SP value: 6.3 (cal / cm ³ ) ^1/2 ), 1,1,1,2,2,3,4,5,5,5-decafluoro-3methoxy -4- (Trifluoromethyl) pentane (CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ , SP value: 6.2 (cal / cm ³ ) ^1/2 ) is preferable, 1, 1, 1 , 2,2,3,4,5,5,5-decafluoro-3methoxy-4- (trifluoromethyl) pentane (CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ ) is more preferred. One of these may be used alone, or two or more of them may be used in combination. When selecting the rinsing solution, it is preferable to select a rinsing solution that is more difficult to dissolve the resist film before the exposure step than the developer used in the developing step and is easily mixed with the developing solution.

The method of bringing the developed resist film into contact with the rinsing solution is not particularly limited, and a known method such as immersing the resist film in the rinsing solution or applying the rinsing solution to the resist film is used. be able to. The temperature of the rinsing liquid at the time of rinsing is not particularly limited, but can be, for example, 21 ° C. or higher and 25 ° C. or lower. The rinsing time can be, for example, 5 seconds or more and 1 minute 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 following description, "%" and "part" representing quantities are based on mass unless otherwise specified.
Then, in Examples and Comparative Examples, the weight average molecular weight, the number average molecular weight and the molecular weight distribution of the polymer, the ratio of each molecular weight component in the polymer, and the SP values of the developer, hydrofluorocarbon and hydrofluoro ether are as follows. It was evaluated by the method of.
<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 various polymers obtained in Examples and Comparative Examples were measured by gel permeation chromatography, and the molecular weight distribution (Mw / Mn) was calculated.
Specifically, gel permeation chromatography (manufactured by Tosoh Corporation, HLC-8220) is used, and tetrahydrofuran is used as the developing solvent, and the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polymer are converted into standard polystyrene. Obtained as a value. Then, the molecular weight distribution (Mw / Mn) was calculated.
<Ratio of components of each molecular weight in the polymer>
A GPC chart of the polymer was obtained using gel permeation chromatography (Tosoh, HLC-8220) and tetrahydrofuran as the developing solvent. Then, from the obtained GPC chart, the total area of the peaks (A), the total area of the peaks of the components having a molecular weight of less than 10,000 (B), and the total area of the peaks of the components having a molecular weight of more than 100,000 are totaled. (C) was calculated. Then, the ratio of the components of each molecular weight was calculated using the following formula.
Percentage of components with a molecular weight of less than 10,000 (%) = (B / A) x 100
Percentage of components with a molecular weight over 100,000 (%) = (C / A) x 100
<SP value>
The SP values of the developers, hydrofluorocarbons and hydrofluoroethers used in Examples and Comparative Examples were calculated using Hoy's atomic group contribution method. The developer, hydrofluorocarbon or hydrofluoroether has two types of components (component (I) and component (II)) having an SP value of α and a component (II) having an SP value of β. In the case of a mixture (mixed developer, mixed hydrocarbon or mixed hydrofluoroether) having a ratio ((I) :( II) = x: y), the SP value was measured by the following method.
SP value of the mixture = α × (x / x + y) + β × (y / x + y)

γ値の値が大きいほど、感度曲線の傾きが大きく、明瞭性の高いパターンを良好に形成し得ることを示す。
＜形成効率（Ｅｔｈ）＞
「明瞭性（γ値）」の評価方法と同様にして、上記ポジ型レジスト組成物（濃度：１１％）を用いて、シリコンウェハ上にレジスト膜を形成した。得られたレジスト膜の初期厚みＴ₀を光学式膜厚計（ＳＣＲＥＥＮセミコンダクターソリューションズ社製、ラムダエース）で測定した。また、γ値の算出の際に得られた直線（感度曲線の傾きの近似線）の残膜率が０となる際の、電子線の総照射量Ｅｔｈ（μＣ／ｃｍ²）を求めた。なお、Ｅｔｈの値が小さいほど、レジスト膜の感度が高く、レジストパターンの形成効率が高いことを意味する。
＜解像度＞
スピンコーター（ミカサ社製、ＭＳ−Ａ１５０）を使用し、上記ポジ型レジスト組成物（濃度：２％）を直径４インチのシリコンウェハ上に厚み５０ｎｍとなるように塗布した。そして、塗布したポジ型レジスト組成物を温度１５０℃のホットプレートで３分間加熱して、シリコンウェハ上に厚さ５０ｎｍのポジ型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（Ｅｏｐ）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・ケマーズフロロプロダクツ社製、バートレルＸＦ、ＣＦ₃ＣＦＨＣＦＨＣＦ₂ＣＦ₃、ＳＰ値：６．８（ｃａｌ／ｃｍ³）^1/2）とハイドロフルオロエーテル（３Ｍ社製、Ｎｏｖｅｃ７３００、ＣＦ₃ＣＦ₂ＣＦ（ＯＣＨ₃）ＣＦ（ＣＦ₃）₂、ＳＰ値：６．２（ｃａｌ／ｃｍ³）^1/2）との混合溶液（ＣＦ₃ＣＦＨＣＦＨＣＦ₂ＣＦ₃：ＣＦ₃ＣＦ₂ＣＦ（ＯＣＨ₃）ＣＦ（ＣＦ₃）₂（質量比）＝８０：２０）を用いて温度２３℃で３０秒間の現像処理を行った。その後、リンス液として、ハイドロフルオロエーテルであるＣＦ₃ＣＦ₂ＣＦ（ＯＣＨ₃）ＣＦ（ＣＦ₃）₂（３Ｍ社製、Ｎｏｖｅｃ７３００）を用いて、温度２３℃で１０秒間リンス処理して、レジストパターンを形成した。なお、最適露光量は、それぞれＥｔｈ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１６ｎｍ、１８ｎｍ、２０ｎｍ、３０ｎｍ（即ち、ハ−フピッチ１６ｎｍ、１８ｎｍ、２０ｎｍ、３０ｎｍ）とした。そして、走査型電子顕微鏡（日本電子社製、ＪＳＭ−７８００Ｆ ＰＲＩＭＥ）を用いて倍率１０万倍で観察を行い、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 polymer A (crude)>
[Polymerization of monomeric composition]
3. 3.0 g of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl (ACAPFP) as the monomer (a) and α-methylstyrene (AMS) as the monomer (b). A monomer composition containing 4680 g, 0.0021 g of azobisisobutyronitrile (AIBN) as a polymerization initiator, and 6.4569 g of cyclopentanone (CPN) as a solvent is placed in a glass container and placed in a glass container. Was sealed and replaced with nitrogen, and the mixture was stirred in a constant temperature bath at 53 ° C. for 50 hours under a nitrogen atmosphere. Then, the temperature was returned to room temperature, the inside of the glass container was released to the atmosphere, and then 10 g of tetrahydrofuran (THF) was added to the obtained solution. Then, the solution to which THF was added was added dropwise to 100 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 A; crude). The obtained polymer A (crude) contained 50 mol% each of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit and α-methylstyrene unit.
[Purification of polymer A (crude)]
Next, the obtained polymer A (clude) was dissolved in 100 g of THF, and the obtained solution was dissolved in 1000 g of a mixed solvent of THF and methanol (the mixing ratio of THF and methanol was a mass ratio of THF: methanol =. It was added dropwise to 24:76) to precipitate a white coagulated product (polymer A containing α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit and α-methylstyrene unit). Then, the solution containing the precipitated polymer A was filtered through a Kiriyama funnel to obtain a white polymer A. Then, with respect to the obtained polymer A, the weight average molecular weight, the number average molecular weight and the molecular weight distribution, and the ratio of the components of each molecular weight in the polymer A were measured. The results are shown in Table 1.
<Preparation of positive resist composition>
The obtained polymer was dissolved in isoamyl acetate as a solvent to prepare a positive resist composition having a polymer concentration of 11% and a positive resist composition having a polymer concentration of 2%. Then, using a positive resist composition having a polymer concentration of 11%, the clarity (γ value) and formation efficiency (Eth) of the resist pattern were evaluated according to the following. Further, using a positive resist composition having a polymer concentration of 2%, a resist pattern was formed as follows, and the resolution of the resist pattern was evaluated. The results are all shown in Table 1.
<Clarity (γ value)>
Using a spin coater (MS-A150 manufactured by Mikasa), the positive resist composition (concentration: 11%) 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 150 ° C. for 3 minutes to form a resist film on a silicon wafer (resist film forming step). Then, using an electron beam drawing apparatus (ELS-S50 manufactured by Elionix Inc.), a plurality of patterns (dimensions 500 μm × 500 μm) having different electron beam irradiation amounts are drawn on the resist film (exposure step), and development for resist is performed. As liquids, hydrofluorocarbon (Mitsui / Chemers Fluoroproducts, Bartrel _{XF, CF 3 CFHCFLHCF 2} CF ₃ , SP value: 6.8 (cal / cm ³ ) ^1/2 ) and hydrofluoroether (3M, 3M) Novec 7300, CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ , SP value: 6.2 (cal / cm ³ ) ^1/2 ) mixed solution (CF ₃ CFHCHFCF ₂ CF ₃ : CF ₃ CF ₂₎ Using CF (OCH ₃ ) CF (CF ₃ ) ₂ (mass ratio) = 80:20), development treatment was performed at a temperature of 23 ° C. for 30 seconds (development step), and then hydrofluoroether (3M) was used as a rinse solution. Rinse was performed at a temperature of 23 ° C. for 10 seconds using a Novec 7300 manufactured by the same company (rinse step). 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 part was measured with an optical film thickness meter (Lambda Ace, manufactured by SCREEN Semiconductor Solutions), and the common logarithm of the total irradiation amount of the electron beam and the residual film of the resist film after development were measured. A sensitivity curve showing the relationship with the rate (= film thickness of the resist film after development / film thickness of the resist film formed on the silicon wafer) was created.
Then, regarding the obtained sensitivity curve (horizontal axis: common logarithm of total irradiation amount of electron beam, vertical axis: residual film ratio of resist film (0 ≤ residual film ratio ≤ 1.00)), the following formula is used. The γ value was calculated. In the following formula, E ₀ is a quadratic function obtained by fitting the sensitivity curve to a quadratic function in the range of 0.20 to 0.80 residual film ratio (regular use of residual film ratio and total irradiation amount). It is the logarithm of the total irradiation dose obtained when 0 is substituted for the residual film ratio (function with the logarithm). Further, E ₁ creates a straight line (approximate line of the slope of the sensitivity curve) connecting the obtained point with a residual film ratio of 0 and the point with a residual film ratio of 0.50 on the obtained quadratic function, and the obtained straight line. It is the logarithm of the total irradiation amount 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). The following equation represents the slope of the straight line between the residual film ratio of 0 and 1.00.

The larger the γ value, the larger the slope of the sensitivity curve, indicating that a pattern with high clarity can be formed satisfactorily.
<Formation efficiency (Eth)>
A resist film was formed on a silicon wafer using the positive resist composition (concentration: 11%) in the same manner as in the evaluation method of "clarity (γ value)". The initial thickness T ₀ of the obtained resist film was measured with an optical film thickness meter (Lambda Ace, manufactured by SCREEN Semiconductor Solutions). ^{In addition, the total irradiation amount 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 in the calculation of the γ value becomes 0 was obtained. The smaller the Eth value, the higher the sensitivity of the resist film and the higher the efficiency of forming the resist pattern.
<Resolution>
Using a spin coater (MS-A150 manufactured by Mikasa), the positive resist composition (concentration: 2%) was applied onto a silicon wafer having a diameter of 4 inches so as to have a thickness of 50 nm. Then, the applied positive resist composition was heated on a hot plate at a temperature of 150 ° C. for 3 minutes to form a positive resist film having a thickness of 50 nm on a silicon wafer. Then, the resist film was exposed to the optimum exposure amount (Eop) using an electron beam drawing apparatus (ELS-S50 manufactured by Elionix Inc.), and a pattern was drawn.
After that, as a developer for resist, hydrofluorocarbon (manufactured by Mitsui-Kemers Fluoroproducts, Bartrel _{XF, CF 3 CFHCHFCF 2} CF ₃ , SP value: 6.8 (cal / cm ³ ) ^1/2 ) and hydrofluoroether. (3M, Novec 7300, CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ , SP value: 6.2 (cal / cm ³ ) ^1/2 ) mixed solution (CF ₃ CFHCHFCF ₂ CF ₃₎ : CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ (mass ratio) = 80:20) was used to develop at a temperature of 23 ° C. for 30 seconds. Then, using a hydrofluoroether CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ (3M, Novec7300) as a rinsing solution, the resist pattern was rinsed at a temperature of 23 ° C. for 10 seconds. Was formed. The optimum exposure amount was appropriately set with a value of about twice that of Eth as a guide. The resist pattern lines (unexposed areas) and spaces (exposed areas) were set to 16 nm, 18 nm, 20 nm, and 30 nm (that is, half pitches of 16 nm, 18 nm, 20 nm, and 30 nm, respectively). Then, observation was performed using a scanning electron microscope (JSM-7800F PRIME manufactured by JEOL Ltd.) at a magnification of 100,000 times, and the half pitch formed by the pattern was used as the resolution.

(Examples 2 to 4)
Mixing ratio (mass) _{of CF 3} CFHCFHCF ₂ CF ₃ and CF ₃ CF ₂ CF (OCH ₃ ) CF (CF _{3 ) 2 in} the mixed solution used as the developing solution for resist when forming the resist pattern in various evaluations. The polymer and positive resist composition were prepared and various evaluations were carried out in the same manner as in Example 1 except that the ratio) was changed as follows. The results are shown in Table 1.
Example 2: CF ₃ CFHCFHCF ₂ CF ₃ : CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ = 60:40
Example 3: CF ₃ CFHCFHCF ₂ CF ₃ : CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ = 40:60
Example 4: CF ₃ CFHCFHCF ₂ CF ₃ : CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ = 20:80

(Examples 5 to 8)
The positive resist composition was prepared and various evaluations were carried out in the same manner as in Examples 1 to 4, except that the polymer B prepared as follows was used instead of the polymer A. The results are shown in Table 1.
<Preparation of polymer B (crude)>
[Polymerization of monomeric composition]
3. 3.0 g of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl (ACAPFP) as the monomer (a) and α-methylstyrene (AMS) as the monomer (b). A monomer composition containing 4680 g, 0.0014 g of azobisisobutyronitrile (AIBN) as a polymerization initiator, and 6.4666 g of cyclopentanone (CPN) as a solvent is placed in a glass container and placed in a glass container. Was sealed and replaced with nitrogen, and the mixture was stirred in a constant temperature bath at 40 ° C. for 50 hours under a nitrogen atmosphere. Then, the temperature was returned to room temperature, the inside of the glass container was released to the atmosphere, and then 10 g of tetrahydrofuran (THF) was added to the obtained solution. Then, the solution to which THF was added was added dropwise to 100 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 B; concretion). The obtained polymer B (crude) contained 50 mol% each of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit and α-methylstyrene unit.
[Purification of polymer B (crude)]
Next, the obtained polymer B (clude) was dissolved in 100 g of THF, and the obtained solution was dissolved in 1000 g of a mixed solvent of THF and methanol (the mixing ratio of THF and methanol was a mass ratio of THF: methanol =. It was added dropwise to 25:75) to precipitate a white coagulated product (polymer B containing α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit and α-methylstyrene unit). Then, the solution containing the precipitated polymer B was filtered through a Kiriyama funnel to obtain a white polymer B. Then, with respect to the obtained polymer B, the weight average molecular weight, the number average molecular weight and the molecular weight distribution, and the ratio of the components of each molecular weight in the polymer B were measured. The results are shown in Table 1.

(Example 9)
Instead of the polymer A, the polymer C prepared as follows was used. In addition, when forming a resist pattern in various evaluations, as a developer for resist, a mixed solution of hydrofluorocarbon and hydrofluoroether (CF ₃ CFHCHFCF ₂ CF ₃ : CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃₎ ) ₂ = 80:20), hydrofluorocarbon (CF ₃ CFHCHFCF ₂ CF ₃ ) was used. Other than that, the positive resist composition was prepared and various evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.
<Preparation of polymer C (crude)>
[Polymerization of monomeric composition]
3. 3.0 g of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl (ACAPFP) as the monomer (a) and α-methylstyrene (AMS) as the monomer (b). A monomer composition containing 4680 g, 0.0014 g of azobisisobutyronitrile (AIBN) as a polymerization initiator, and 6.4666 g of cyclopentanone (CPN) as a solvent is placed in a glass container and placed in a glass container. Was sealed and replaced with nitrogen, and the mixture was stirred in a constant temperature bath at 40 ° C. for 50 hours under a nitrogen atmosphere. Then, the temperature was returned to room temperature, the inside of the glass container was released to the atmosphere, and then 10 g of tetrahydrofuran (THF) was added to the obtained solution. Then, the solution to which THF was added was added dropwise to 100 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 C; crude). The obtained polymer C (crude) contained 50 mol% each of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit and α-methylstyrene unit.
[Purification of polymer C (crude)]
Next, the obtained polymer C (clude) was dissolved in 100 g of THF, and the obtained solution was dissolved in 1000 g of a mixed solvent of THF and methanol (the mixing ratio of THF and methanol was a mass ratio of THF: methanol =. Dropped onto 25.5: 74.5) to add a white coagulated product (polymer C containing α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit and α-methylstyrene unit). Precipitated. Then, the solution containing the precipitated polymer C was filtered through a Kiriyama funnel to obtain a white polymer C. Then, with respect to the obtained polymer C, the weight average molecular weight, the number average molecular weight and the molecular weight distribution, and the ratio of the components of each molecular weight in the polymer C were measured. The results are shown in Table 1.

(Examples 10 to 13)
When forming a resist pattern in various evaluations, as a developing solution for resist _{, instead of hydrofluorocarbon (CF 3} CFHCFLHCF ₂ CF ₃ ), hydrofluorocarbon (CF ₃ CFHCFLHCF ₂ CF ₃ ) and hydrofluoroether (manufactured by 3M Co., Ltd.) The polymer and the polymer and the same as in Example 9 except that a mixed solution with Novec 7100, CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ , SP value: 6.5 (cal / cm ³ ) ^{1/2) was used.} The positive resist composition was prepared and various evaluations were carried out. The results are shown in Table 2. The mixing ratio (mass ratio) of _{CF 3} CFHCFHCF ₂ CF ₃ and CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ in the mixed solution used as the developer for resist was as follows.
Example 10: CF ₃ CFHCHFCF ₂ CF ₃ : CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ = 80:20
Example 11: CF ₃ CFHCHFCF ₂ CF ₃ : CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ = 60: 40
Example 12: CF ₃ CFHCFHCF ₂ CF ₃ : CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ = 40: 60
Example 13: CF ₃ CFHCHFCF ₂ CF ₃ : CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ = 20: 80

(Comparative Example 1)
A positive resist composition was prepared and various evaluations were carried out in the same manner as in Example 9 except that the polymer D prepared as follows was used instead of the polymer A. The results are shown in Table 2.
<Preparation of polymer D (crude)>
[Polymerization of monomeric composition]
3. 3.0 g of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl (ACAPFP) as the monomer (a) and α-methylstyrene (AMS) as the monomer (b). A monomer composition containing 4764 g, 0.0055 g of azobisisobutyronitrile (AIBN) as a polymerization initiator, and 1.6205 g of cyclopentanone (CPN) as a solvent is placed in a glass container and placed in a glass container. Was sealed and replaced with nitrogen, and the mixture was stirred in a constant temperature bath at 78 ° C. for 6 hours under a nitrogen atmosphere. Then, the temperature was returned to room temperature, the inside of the glass container was released to the atmosphere, and then 10 g of tetrahydrofuran (THF) was added to the obtained solution. Then, the solution to which THF was added was added dropwise to 100 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 D; concretion). The obtained polymer B (crude) contained 50 mol% each of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit and α-methylstyrene unit.
[Purification of polymer D (crude)]
Next, the obtained polymer D (clude) was dissolved in 100 g of THF, and the obtained solution was dissolved in 1000 g of a mixed solvent of THF and methanol (the mixing ratio of THF and methanol is THF: methanol = It was added dropwise to 15:85) to precipitate a white coagulated product (polymer D containing α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit and α-methylstyrene unit). Then, the solution containing the precipitated polymer D was filtered through a Kiriyama funnel to obtain a white polymer D. Then, with respect to the obtained polymer D, the weight average molecular weight, the number average molecular weight and the molecular weight distribution, and the ratio of the components of each molecular weight in the polymer D were measured. The results are shown in Table 2.

(Comparative Examples 2 to 5)
In forming the resist pattern in various evaluations, as a resist developing solution in place of the hydrofluorocarbons (CF ₃ CFHCFHCF ₂ CF _3), hydrofluorocarbons (CF ₃ CFHCFHCF ₂ CF ₃₎ and hydrofluoroether (CF ₃ CF ₂ A polymer and a positive resist composition were prepared and various evaluations were carried out in the same manner as in Comparative Example 1 except that a mixed solution with CF (OCH ₃ ) CF (CF ₃ ) _{2) was used.} The results are shown in Table 2. The mixing ratio (mass ratio) of _{CF 3} CFHCFHCF ₂ CF ₃ and CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ in the mixed solution used as the developer for resist is as follows. did.
Comparative Example 2: CF ₃ CFHCFHCF ₂ CF ₃ : CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ = 80:20
Comparative Example 3: CF ₃ CFHCFHCF ₂ CF ₃ : CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ = 60:40
Comparative Example 4: CF ₃ CFHCFHCF ₂ CF ₃ : CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ = 40:60
Comparative Example 5: CF ₃ CFHCFHCF ₂ CF ₃ : CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) ₂ = 20:80

In addition, in Table 1 and Table 2 shown below,
"Bertrel XF" represents 1,1,1,2,3,4,5,5,5-decafluoropentane (CF ₃ CFHCHFCF ₂ CF ₃ ).
"Novec7300" is 1,1,1,2,2,3,4,5,5,5-decafluoro-3 methoxy-4- (trifluoromethyl) pentane (CF ₃ CF ₂ CF (OCH ₃ ) CF. (CF ₃ ) ₂ ) is shown,
“Novec 7100” indicates methyl nonafluorobutyl ether (CF ₃ CF ₂ CF ₂ CF ₂ OCH ₃ ).
Further, in Tables 1 and 2, the "SP value of the developing solution" is represented by a value rounded to the second decimal place.

From Tables 1 and 2, a polymer containing a predetermined monomer unit (A) and a monomer unit (B) and having a weight average molecular weight of 100,000 or more was used as the positive resist, and predetermined. It can be seen that in Examples 1 to 13 in which the developing step was carried out using the developing solution of No. 1, a resist pattern having excellent clarity could be formed. Further, it can be seen that the resist patterns of Examples 1 to 13 are also excellent in resolution.
On the other hand, in Comparative Examples 1 to 5 using a polymer having a weight average molecular weight of less than 100,000 as the positive resist, it can be seen that a resist pattern having excellent clarity could not be formed. Further, it can be seen that the resist patterns of Comparative Examples 1 to 5 are also inferior in resolution.

According to the present invention, it is possible to provide a resist pattern forming method capable of forming a resist pattern having excellent clarity.

Claims (9)

The following general formula (I):

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

[In general formula (II), R ² is a hydrogen atom, a fluorine atom, an unsubstituted alkyl group or an alkyl group substituted with a fluorine atom, and R ³ is a hydrogen atom, an unsubstituted alkyl group or a fluorine atom. It is an alkyl group substituted with, and p and q are integers of 0 or more and 5 or less, and p + q = 5. ]
A step of forming a resist film using a polymer having a monomer unit (B) represented by (B) and a positive resist composition containing a solvent.
The step of exposing the resist film and
The step of developing the exposed resist film and
Including
The polymer has a weight average molecular weight of 100,000 or more.
A resist pattern forming method in which the development is carried out using a developing solution containing hydrofluorocarbon. The resist pattern forming method according to claim 1, wherein the developer further contains hydrofluoroether. The resist pattern forming method according to claim 2, wherein the solubility parameter of the hydrofluoroether is 6.6 (cal / cm ³ ) ^{1/2 or less.} The resist pattern forming method according to claim 2, wherein the solubility parameter of the hydrofluoroether ^{is less than 6.5 (cal / cm 3} ) ^1/2. The resist pattern forming method according to claim ₂ , wherein the hydrofluoroether is CF ₃ CF ₂ CF (OCH ₃ ) CF (CF ₃ ) 2. The resist according to any one of claims 2 to 5, wherein the ratio of the hydrofluoroether to the total of the hydrofluorocarbon and the hydrofluoroether in the developer is more than 0% by mass and 90% by mass or less. Pattern formation method. The resist pattern forming method according to any one of claims 1 to 6, wherein X in the general formula (I) is a chlorine atom. The resist pattern forming method according to any one of claims 1 to 7, wherein the polymer has a proportion of components having a molecular weight of less than 10,000 of 0.2% or less. The resist pattern forming method according to any one of claims 1 to 8, wherein the hydrofluorocarbon is CF ₃ CFHCHFCF ₂ CF _3.