JP2020084007A - Polymer and positive resist composition - Google Patents

Abstract

〔式（Ｉ）中、Ｒ^１は、フッ素原子の数が４の有機基である。〕
【選択図】なしPROBLEM TO BE SOLVED: To provide a polymer capable of forming a resist pattern having sufficiently high resolution and clarity when it is used as a main chain cleavage type positive resist.
A polymer having a monomer unit (A) represented by the general formula (I) and a monomer unit (B) represented by the general formula (II).

[In the formula (I), R ¹ is an organic group having 4 fluorine atoms. ]
[Selection diagram] None

Description

The present invention relates to a polymer and a positive resist composition, and more particularly to a polymer that can be preferably used as a positive resist and a positive resist composition containing the polymer.

Conventionally, in the field of semiconductor manufacturing, etc., ionizing radiation such as extreme ultraviolet (EUV) and electron beams, and short-wavelength light such as ultraviolet rays (hereinafter, "ionizing radiation and short-wavelength light are collectively referred to as "ionizing radiation"). The polymer whose main chain is cleaved by the irradiation of ", etc." to increase the solubility in a developing solution is used as a main chain cleaving positive resist.

And, for example, in Patent Document 1, an α-methylstyrene/α-chloro containing α-methylstyrene (AMS) unit and an α-chloromethyl acrylate unit as a high-sensitivity main chain cleavage type positive resist. A positive resist made of a methyl acrylate copolymer is disclosed.

Japanese Patent Publication No. 8-3636

In recent years, due to the demand for higher integration of semiconductor integrated circuits, it has been required to miniaturize a resist pattern obtained using a resist composition to improve the resolution. Further, in the main chain cleavage type positive type resist, the efficiency at the time of patterning is improved, and the obtained resist pattern is clear, that is, as a result of patterning, the portion where the resist film remains is dissolved. It is required that the boundary with the existing part is clear. Specifically, from the viewpoint of enabling formation of a resist pattern with higher clarity, the resist does not dissolve in the developer unless the irradiation amount reaches a specific amount, and the resist is rapidly dissolved when the specific amount is reached. It has a characteristic that the main chain is cleaved and dissolved in a developing solution, that is, it represents the magnitude of the slope of a sensitivity curve showing the relationship between the common logarithm of the dose of ionizing radiation and the residual film thickness of resist after development. It is required to increase the γ value. However, the positive resist composed of the α-methylstyrene/α-methyl chloroacrylate copolymer described in Patent Document 1 could not form a resist pattern having sufficiently high resolution and clarity.

Therefore, an object of the present invention is to provide a polymer capable of forming a resist pattern having sufficiently high resolution and clarity, which can be favorably used as a resist, and a positive resist composition containing the polymer. And

The present inventor has conducted extensive studies to achieve the above object. Then, the present inventors have found that a resist formed using a positive resist composition containing a predetermined polymer containing an α-chloroacrylic acid fluoroester unit having an organic group having 4 fluorine atoms has a main chain The present invention has been newly found that a resist pattern having sufficiently high resolution and clarity can be favorably formed when it is used as a cutting-type positive resist, and the present invention has been completed.

〔式（Ｉ）中、Ｒ^１は、フッ素原子の数が４の有機基である。〕
で表される単量体単位（Ａ）と、
下記一般式（ＩＩ）：

〔式（ＩＩ）中、Ｒ^２は、水素原子、フッ素原子、非置換のアルキル基又はフッ素原子で置換されたアルキル基であり、Ｒ^３は、水素原子、非置換のアルキル基又はフッ素原子で置換されたアルキル基であり、ｐ及びｑは、０以上５以下の整数であり、ｐ＋ｑ＝５である。〕で表される単量体単位（Ｂ）と、を有する、ことを特徴とする。重合体にフッ素原子の数が４の有機基を有するα−クロロアクリル酸フルオロエステル単位を含有させれば、当該重合体をポジ型レジストとして使用した際に、解像度及び明瞭性の充分に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、式（ＩＩ）中のｐが２以上の場合には、複数あるＲ^２は互いに同一でも異なっていてもよく、また、式（ＩＩ）中のｑが２以上の場合には、複数あるＲ^３は互いに同一でも異なっていてもよい。 That is, the present invention is intended to advantageously solve the above-mentioned problems, and the polymer of the present invention has the following general formula (I):

[In the formula (I), R ¹ is an organic group having 4 fluorine atoms. ]
A monomer unit (A) represented by
The following general formula (II):

[In the 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 a substituted alkyl group, p and q are integers of 0 or more and 5 or less, and p+q=5. ] It has a monomer unit (B) represented by these, It is characterized by the above-mentioned. If the polymer contains an α-chloroacrylic acid fluoroester unit having an organic group having 4 fluorine atoms, the resist has sufficiently high resolution and clarity when the polymer is used as a positive resist. A pattern can be formed.
In the present invention, when p in the formula (II) is 2 or more, a plurality of R ^{2 s} may be the same or different, and when q in the formula (II) is 2 or more. , A plurality of R ^{3 s} may be the same or different.

Here, in the polymer of the present invention, R ¹ is preferably a tetrafluoroalkyl group. When R ¹ of the monomer unit (A) is a tetrafluoroalkyl group, the resolution and clarity of the resulting resist pattern can be further improved.

Further, in the polymer of the present invention, it is preferable that R ¹ is a 2,2,3,3-tetrafluoropropyl group. When R ¹ of the monomer unit (A) is a 2,2,3,3-tetrafluoropropyl group, the resolution and clarity of the resulting resist pattern can be further improved.

Furthermore, the polymer of the present invention preferably has a weight average molecular weight (Mw) of 30,000 or more and 160000 or less. When the weight average molecular weight (Mw) of the polymer is within the above range, the resolution and clarity when used as a positive resist can be improved.

Furthermore, the polymer of the present invention preferably has a molecular weight distribution (Mw/Mn) of 1.8 or less. When the molecular weight distribution (Mw/Mn) of the polymer is 1.8 or less, the clarity of the obtained resist pattern can be further enhanced.

Further, in the polymer of the present invention, the monomer unit (B) is preferably a 4-fluoro-α-methylstyrene unit. When the monomer unit (B) is a 4-fluoro-α-methylstyrene unit, the sensitivity when used as a positive resist can be improved.

Moreover, this invention aims at solving the said subject advantageously, and the positive resist composition of this invention is characterized by including any of the above-mentioned polymers, and a solvent. When the positive resist composition contains the above-mentioned polymer, a resist pattern having sufficiently high resolution and clarity can be formed by using the positive resist composition.

According to the polymer of the present invention, it is possible to provide a main chain scission-type positive resist capable of forming a resist pattern having sufficiently high resolution and clarity.
According to the positive resist composition of the present invention, a resist pattern having sufficiently high resolution and clarity can be efficiently formed.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the polymer of the present invention is a main chain cutting type positive resist in which the main chain is cut by irradiation of ionizing radiation such as EUV and electron beam, and light of a short wavelength such as ultraviolet ray to lower the molecular weight. Can be used satisfactorily. Then, the positive resist composition of the present invention contains the polymer of the present invention as a positive resist, for example, in a manufacturing process of a printed board such as a build-up board, a semiconductor, a photomask, and a mold. It can be preferably used when forming a resist pattern.

〔式（Ｉ）中、Ｒ^１は、フッ素原子の数が４の有機基である。〕で表される単量体単位（Ａ）と、
下記一般式（ＩＩ）：

〔式（ＩＩ）中、Ｒ^２は、水素原子、フッ素原子、非置換のアルキル基又はフッ素原子で置換されたアルキル基であり、Ｒ^３は、水素原子、非置換のアルキル基又はフッ素原子で置換されたアルキル基であり、ｐ及びｑは、０以上５以下の整数であり、ｐ＋ｑ＝５である。〕で表される単量体単位（Ｂ）と、を有する。 (Polymer)
The polymer of the present invention has the following general formula (I):

[In the formula (I), R ¹ is an organic group having 4 fluorine atoms. ] The monomer unit (A) represented by
The following general formula (II):

[In the 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 a substituted alkyl group, p and q are integers of 0 or more and 5 or less, and p+q=5. ] And the monomer unit (B) represented by these.

The polymer of the present invention may contain any monomer unit other than the monomer unit (A) and the monomer unit (B), but all the monomer units constituting the polymer. The total proportion of the monomer unit (A) and the monomer unit (B) is preferably 90 mol% or more in total, more preferably substantially 100 mol%, and 100 mol% ( That is, it is more preferable that the polymer contains only the monomer unit (A) and the monomer unit (B).

The polymer of the present invention is, for example, a random polymer, a block polymer, an alternating polymer (ABAB...) As long as it has a monomer unit (A) and a monomer unit (B). It may be either, but it is preferably a polymer containing 90% by mass or more of the alternating polymer (the upper limit is 100% by mass). Here, it is preferable that the alternating polymers do not form a crosslinked body. When R ¹ of the monomer unit (A) contains a fluorine atom, a crosslinked body is not formed.

Since the polymer of the present invention contains the predetermined monomer unit (A) and monomer unit (B), ionizing radiation (eg, electron beam, KrF laser, ArF laser, EUV laser, etc.) ) Is irradiated, the main chain is cleaved to lower the molecular weight. Further, since the polymer of the present invention contains a monomer unit (A) having an organic group having 4 fluorine atoms, when used as a positive resist, a resist pattern having sufficiently high resolution and clarity is obtained. Can be formed. Furthermore, in the polymer of the present invention, since at least the monomer unit (A) contains a fluorine atom, it is possible to sufficiently suppress the occurrence of collapse of the resist pattern when the polymer is used as a positive resist. is there.

（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 general formula (III):

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

The proportion of the monomer unit (A) in 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.

Here, from the viewpoint of increasing the resolution of the obtained resist pattern, R ¹ in the formulas (I) and (III) needs to be an organic group having 4 fluorine atoms.
For example, R ¹ in formulas (I) and (III) includes a tetrafluoroalkyl group, a tetrafluoroalkoxyalkyl group, or a tetrafluoroalkoxyalkenyl group. Above all, R ¹ is preferably a tetrafluoroalkyl group from the viewpoint of being able to form a resist pattern having higher resolution and clarity. Examples of such a tetrafluoroalkyl group include a 2,2,3,3-tetrafluoropropyl group and a 3,3,4,4-tetrafluorobutyl group. Among them, it is particularly preferable that R ¹ is a 2,2,3,3-tetrafluoropropyl group from the viewpoint that a resist pattern having higher resolution and higher clarity can be formed.

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-chloroacrylic acid fluoroalkyl esters such as α-chloroacrylic acid 2,2,3,3-tetrafluoropropyl and α-chloroacrylic acid 3,3,4,4-tetrafluorobutyl; α-chloro Α-chloroacrylic acid fluoroalkoxyalkyl esters such as acrylic acid tetrafluoroethoxymethyl ester and α-chloroacrylic acid tetrafluoroethoxyethyl ester; α-chloroacrylic acid fluoroalkoxyalkenyls such as α-chloroacrylic acid tetrafluoroethoxyvinyl ester Ester; and the like.

（式（ＩＶ）中、Ｒ^２〜Ｒ^３、並びに、ｐ及びｑは、式（ＩＩ）と同様である。）で表される単量体（ｂ）に由来する構造単位である。 <Monomer unit (B)>
The monomer unit (B) has the following general formula (IV):

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

The proportion of the monomer unit (B) in 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.

Here, the alkyl group substituted by a fluorine atom which may constitute R ^{2 to} R ³ in the formulas (II) and (IV) is not particularly limited, and one of hydrogen atoms in the alkyl group is not particularly limited. Examples thereof include groups having a structure in which a part or all of them are substituted with a fluorine atom.
In addition, the unsubstituted alkyl group that can form R ^{2 to} R ³ in the formulas (II) and (IV) is not particularly limited, and an unsubstituted alkyl group having 1 to 5 carbon atoms can be used. Can be mentioned. Of these, a methyl group or an ethyl group is preferable as the unsubstituted alkyl group that can form R ^{2 to} R ³ .

From the viewpoint of increasing the sensitivity when the polymer is used for forming a resist pattern, at least one of R ² and/or R ³ present in the formulas (II) and (IV) has a fluorine atom. It is preferable that p is 5 in formulas (II) and (IV), q is 0, and R ² at the 4-position of the 5 R ² is a fluorine atom. More preferably, four R ² are hydrogen atoms.

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, Examples thereof include α-methylstyrene (AMS) such as the following (b-1) to (b-11) and derivatives thereof (for example, 4-fluoro-α-methylstyrene: 4FAMS).

The monomer unit (B) is represented by the above formula (b-2) from the viewpoint of enhancing the solubility in a developing solution and enhancing the sensitivity when the polymer is used for forming a resist pattern. It is preferably a unit derived from 4-fluoro-α-methylstyrene (4FAMS).

(Properties of polymer)
<Weight average molecular weight>
Here, the weight average molecular weight (Mw) of the polymer of the present invention is preferably 160,000 or less, preferably 30,000 or more, more preferably 60,000 or more, further preferably 65,000 or more. , 75000 or more is particularly preferable. When the weight average molecular weight (Mw) of the polymer is within the above range, the resolution and clarity of the resist pattern formed using the polymer can be sufficiently improved.

<Number average molecular weight>
Further, the number average molecular weight (Mn) of the polymer of the present invention is preferably 19000 or more, more preferably 38000 or more, and preferably 100000 or less. When the number average molecular weight (Mn) of the polymer is 19000 or more, it is possible to prevent the solubility of the resist film in a developing solution from increasing at an excessively low irradiation amount, and the resulting resist pattern becomes unclear. It is possible to suppress the decrease.

<Molecular weight distribution>
The molecular weight distribution (Mw/Mn) of the polymer of the present invention is preferably 1.8 or less, more preferably 1.6 or less. When the molecular weight distribution (Mw/Mn) of the polymer is at most the upper limit value, the clarity of the obtained resist pattern can be effectively enhanced. The molecular weight distribution of the polymer is not particularly limited and may be, for example, 1.25 or more. When the molecular weight distribution (Mw/Mn) of the polymer is 1.25 or more, the easiness of producing the polymer can be improved.

(Method for preparing polymer)
And the polymer which has the above-mentioned monomer unit (A) and monomer unit (B) polymerizes the monomer composition containing a monomer (a) and a monomer (b), for example. After that, it can be prepared by optionally purifying the obtained polymer.
The composition, molecular weight distribution, weight average molecular weight and number average molecular weight of 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. 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 adjusted by appropriately changing the mixing ratio in the case of the type of solvent used during purification and the mixed solvent. Furthermore, the weight average molecular weight and the number average molecular weight can be increased by setting the polymerization time within an appropriate range.

<Polymerization of monomer composition>
Here, as the monomer composition used for preparing the polymer of the present invention, a monomer component containing the monomer (a) and the monomer (b), an optionally usable solvent, and a polymerization Mixtures of initiators and optionally added additives can be used. Then, the polymerization of the monomer composition can be performed using a known method. Especially, when using a solvent, it is preferable to use cyclopentanone etc. as a solvent. Further, it is preferable to use a radical polymerization initiator such as azobisisobutyronitrile as the polymerization initiator. The weight average molecular weight and the number average molecular weight of the polymer can also be adjusted by changing the blending amount of the polymerization initiator. Specifically, the weight average molecular weight and the number average molecular weight can be increased by decreasing the compounding amount of the polymerization initiator, and can be decreased by increasing the compounding amount of the polymerization initiator. ..

The polymer obtained by polymerizing the monomer composition may be used as it is as a polymer. Further, a polymerization solution containing a polymer may be dropped into a poor solvent such as hexane to cause precipitation, and the obtained precipitate may be used as a polymer. Furthermore, without particular limitation, after adding a good solvent such as tetrahydrofuran to a solution containing the polymer, the solution containing the good solvent is dropped into a poor solvent such as methanol or hexane to coagulate the polymer. It can also be recovered and purified as follows.

<Purification of 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.

Then, 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, a good solvent such as tetrahydrofuran and a poor solvent such as hexane. It is preferable to carry out dropwise addition to the mixed solvent of 1 or a solvent consisting of one or more poor solvents to precipitate a part of the polymer (that is, reprecipitation). The molecular weight distribution, weight average molecular weight and number average molecular weight of the resulting polymer can be adjusted by changing the type or composition of the solvent in which the polymer solution is dropped. Among them, when the solution of the polymer is added dropwise to the mixed solvent of the good solvent and the poor solvent to purify the polymer, the types and mixing ratios of the good solvent and the poor solvent, and the mixed solvent and the polymer. The molecular weight distribution, weight average molecular weight, and number average molecular weight of the polymer obtained can be easily adjusted by changing the weight ratio and the like. Specifically, for example, the higher the ratio of the good solvent in the mixed solvent, the larger the molecular weight of the polymer precipitated in the mixed solvent. Further, for example, by preventing the ratio of the amount of the polymer to the mixed solvent from becoming excessively small, the molecular weight of the polymer precipitated in the mixed solvent can be increased.

When the polymer is purified by the reprecipitation method, a reprecipitated polymer may be used as the polymer of the present invention, or a polymer not reprecipitated (that is, dissolved in a solvent). Polymers) may be used. Here, the polymer not precipitated in the solvent can be recovered from the solvent by using a known method such as concentration to dryness.

(Positive resist composition)
The positive resist composition of the present invention contains the above-mentioned polymer and a solvent, and optionally further contains a known additive that can be incorporated into the resist composition. Since the positive resist composition of the present invention contains the above-mentioned polymer as a positive resist, it is necessary to form a resist pattern having sufficiently high resolution and clarity when used for forming a resist pattern. You can

<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 described in Japanese Patent No. 5938536 can be used. Among them, 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 such as n-pentyl ester, n-hexyl ester, and acetic acid. 2-Methoxy-1-methylethyl, isoamyl acetate, or a mixture thereof is preferable, 2-methoxy-1-methylethyl acetate, isoamyl acetate, or a mixture thereof is more preferable, and isoamyl acetate is further preferable.

(Method of forming resist pattern)
The resist pattern forming method using the resist composition of the present invention comprises (1) a step of forming a resist film using the positive resist composition of the present invention (resist film forming step), and (2) exposing the resist film. It is preferable to include a step of performing (exposure step) and a step (3) of developing the exposed resist film (developing step). Further, it may optionally further include a rinse step of removing the developing solution after the developing step.

<Resist film forming step>
In the step (1), the positive resist composition of the present invention 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. Form a film. The coating method and drying method are not particularly limited, and known coating methods and drying methods can be used.

<Exposure process>
In the step (2), the resist film 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 step (3), the resist film exposed in the exposure 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 into contact with the developing solution 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 can be used. ..

[Developer]
The developer used in the method for forming a resist pattern of the present invention is not particularly limited, and a fluorine-based developer such as CF ₃ CFHCFHCF ₂ CF ₃ , CF ₃ CF ₂ CHCl ₂ , CClF ₂ CF ₂ CHClF, and C ₈ F _{18 is} used. solvent (fluorine-containing solvents other than the hydrofluoroether _{solvents); C 3 F 7 OCH 3} , C 4 F 9 OCH 3, C 4 F 9 OC 2 H 5, C 2 F 5 CF (OCH 3) C 3 F 7 , etc. Hydrofluoroether solvent; alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol); acetic acid esters having alkyl groups such as amyl acetate and hexyl acetate; mixtures of fluorine-based solvents and alcohols; fluorine-based A mixture of a solvent and an acetic acid ester having an alkyl group; a mixture of an alcohol and an acetic acid ester having an alkyl group; a mixture of a fluorine-based solvent, an alcohol and an acetic acid ester having an alkyl group; and the like can be used. Above all, it is preferable to use a fluorine-based solvent from the viewpoint of further improving the resolution and clarity of the obtained resist pattern. When a mixture containing a fluorinated solvent is used as the developing solution, the proportion of the fluorinated solvent in the entire developing solution is preferably more than 50% by volume, more preferably more than 75% by volume, It is more preferably at least vol%, particularly preferably at least 95 vol%.

Then, the developing conditions such as the developing time and the developing temperature in the developing step can be appropriately set so as to obtain a resist pattern of desired quality. For example, the development time can be 1 minute or more and 4 minutes or less. Further, for example, the temperature of the developer can be set to 21° C. or higher and 25° C. or lower.

<Rinse process>
In the rinse step that can be optionally performed after the developing step, the developing solution remaining in the resist pattern on the workpiece, the dissolution residue of the resist film, and the like can be removed using the rinse solution. By performing such a rinse step, the clarity of the obtained resist pattern can be improved.

The rinse liquid that can be used in the rinse step is not particularly limited, and a known solvent can be used. For example, the various solvents listed above as the solvent usable as the developing solution can be used as the rinse solution. The solvent used as the rinse liquid can be appropriately selected according to the type of the developing solution used. Specifically, in selecting the rinse liquid, it is preferable to select a rinse liquid that is easily mixed with the developer so that the rinse liquid can be easily replaced. Among them, from the viewpoint of forming a high-resolution resist pattern, when a fluorine-based solvent other than hydrofluoroether such as CF ₃ CFHCFHCF ₂ CF ₃ is used as the developing solution, C ₄ F ₉ is used as the rinse solution. It is preferred to use a hydrofluoroether solvent such as OCH ₃ .

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 "parts" representing amounts are based on mass unless otherwise specified.
In Examples and Comparative Examples, the weight average molecular weight of the polymer, the number average molecular weight and the molecular weight distribution, and the pattern collapse resistance, Eth, γ value (clarity), and resolution of the positive resist made of the polymer are The following methods were used for measurement and evaluation.

<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 various polymers obtained in Examples and Comparative Examples were measured by gel permeation chromatography to calculate the molecular weight distribution (Mw/Mn). Specifically, using a gel permeation chromatograph (HLC-8220, manufactured by Tosoh Corporation) and using tetrahydrofuran as a developing solvent, the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polymer are converted into standard polystyrene. It was calculated as a value. Then, the molecular weight distribution (Mw/Mn) was calculated.

<Pattern collapse resistance of resist film>
Using a spin coater (MS-A150, manufactured by Mikasa Co., Ltd.), the positive resist compositions prepared in Examples and Comparative Examples were coated on a silicon wafer having a diameter of 4 inches. Next, the applied positive resist composition was heated on a hot plate having a temperature of 180° C. for 3 minutes to form a resist film having a thickness of 50 nm on the silicon wafer. Then, the resist film was exposed at an optimum exposure amount (Eop) using an electron beam drawing apparatus (ELS-S50 manufactured by Elionix Co., Ltd.) to draw a pattern. After that, a fluorine-based solvent (Bartrel XF (registered trademark), CF ₃ CFHCFHCF ₂ CF ₃ manufactured by Mitsui DuPont Fluorochemical Co., Ltd.) was used as a resist developing solution, and development processing was performed at a temperature of 23° C. for 1 minute. After that, a hydrofluoric ether solvent, C ₄ F ₉ OCH ₃ (“Novec (registered trademark) 7100” manufactured by 3M Co., Ltd.), which is a hydrofluoroether solvent, was used to perform a rinsing treatment at a temperature of 23° C. for 10 seconds to form a resist pattern. Formed. Then, the presence or absence of pattern collapse of the formed resist pattern was observed. The optimum exposure dose (Eop) was appropriately set with a value of about twice each Eth as a standard. The line (unexposed region) and space (exposed region) of the resist pattern were 20 nm (Examples 1 to 18 and Comparative Examples 1 and 2) or 25 nm (Comparative Examples 3 and 4), respectively.
Then, the pattern collapse resistance was evaluated according to the following criteria.
A: No pattern collapse B: Pattern collapse

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。 <γ value of resist film>
Using a spin coater (MS-A150, manufactured by Mikasa Co., Ltd.), the positive resist composition prepared in Examples and Comparative Examples 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 180° C. for 3 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 fluorine is used as a resist developer. Development processing was performed at a temperature of 23° C. for 1 minute using a system solvent (Bertrel XF (registered trademark), CF ₃ CFHCFHCF ₂ CF ₃ manufactured by Mitsui DuPont Fluorochemical Co., Ltd.). 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 the 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: electron beam Regarding the common logarithm of the total irradiation amount, the vertical axis: the residual film ratio of the resist film (0≦remaining film ratio≦1.00), the γ value was calculated using the following formula: In the following formula, E ₀ is a quadratic function obtained by fitting the sensitivity curve to a quadratic function in the range of residual film ratio of 0.20 to 0.80, and the obtained quadratic function (function of residual film ratio and common logarithm of total irradiation) It is a logarithm of the total irradiation amount obtained when the residual film rate is 0. Further, E ₁ is the obtained point of the residual film rate 0 and the residual film rate of 0.50 on the quadratic function. It is obtained by creating a connecting straight line (an approximate line of the slope of the sensitivity curve) and substituting the residual film ratio 1.00 into the obtained straight line (a function of the residual film ratio and the common logarithm of the total irradiation). It is a logarithm of the total irradiation amount, and the following formula represents the slope of the above straight line between the remaining film ratios of 0 and 1.00.

It is shown that the larger the γ value, the larger the slope of the sensitivity curve, and the better the pattern with high clarity can be formed.

<Eth>
A resist film was formed on a silicon wafer by using the positive resist compositions prepared in Examples and Comparative Examples in the same manner as in the evaluation method of “γ value of resist film”. 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 Co., Ltd.). Further, the total irradiation dose Eth (μC/cm ² ) of the electron beam when the residual film rate of the straight line (approximate line of the slope of the sensitivity curve) obtained when calculating the γ value was 0 was obtained. Note that the smaller the value of Eth, the higher the sensitivity of the resist film and the higher the efficiency of forming the resist pattern.

<Resist pattern resolution>
Using a spin coater (MS-A150, manufactured by Mikasa), the positive resist composition prepared in Examples and Comparative Examples was applied on a 4-inch silicon wafer so as to have a thickness of 40 nm. Then, the applied positive resist composition was heated on a hot plate at a temperature of 180° C. for 3 minutes to form a positive resist film on the silicon wafer. Then, using an electron beam drawing apparatus (ELS-5700, manufactured by Elionix Co., Ltd.), a line and space 1:1 pattern having a line width of 18 nm, 20 nm, 22 nm, and 25 nm was formed into an optimum exposure amount in each of Examples and Comparative Examples ( Eop), and electron beam drawing was carried out to obtain electron beam drawn wafers.
A line-and-space pattern was formed by immersing the electron beam-drawn wafer at 23° C. for 1 minute in the same developer as used in the evaluation of <pattern collapse resistance of resist film> and for 10 seconds in a rinse solution. It was observed with a scanning electron microscope (SEM) at a magnification of 50,000 times, and the minimum line-and-space width at which the pattern was separated and resolved was examined.

(Example 1)
<Preparation of polymer>
3.0 g of 2,2,3,3-tetrafluoropropyl α-chloroacrylic acid (ACATFP) as the monomer (a) and 3.7508955 g of α-methylstyrene (AMS) as the monomer (b) , A monomer composition containing 0.0059564 g of azobisisobutyronitrile as a polymerization initiator and 1.6818 g of cyclopentanone as a solvent was placed in a glass container, and the glass container was sealed and replaced with nitrogen, The mixture was stirred under a nitrogen atmosphere in a constant temperature bath at 76° 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 polymerization 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; crude).
The resulting polymer (crude) contained 50 mol% of 2,2,3,3-tetrafluoropropyl α-chloroacrylate (ACATFP) units and 50 mol% of α-methylstyrene (AMS) units.

[Purification of polymer (crude)]
Next, 2 g of the obtained polymer (crude) was dissolved in 18 g of THF (tetrahydrofuran) (10% by mass), the obtained polymer solution was added dropwise to 200 g of methanol (MeOH), and a white coagulated product (α- A polymer containing a methylstyrene unit and an α-chloroacrylic acid 2,2,3,3-tetrafluoropropyl unit) was deposited. Then, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white polymer. Then, the weight average molecular weight, the number average molecular weight and the molecular weight distribution of the obtained polymer (polymer once purified) were measured. The results are shown in Table 1.

<Preparation of positive resist composition>
The obtained once-purified polymer was dissolved in isoamyl acetate as a solvent to prepare a resist solution (positive resist composition) having a polymer concentration of 2% by mass. Then, the pattern collapse resistance, γ value, and Eth of the positive resist film made of a polymer, and the resolution of the resist pattern obtained by using the positive resist film were evaluated as described above. The results are shown in Table 1.

(Example 2)
In Example 1, except that the stirring time at the time of preparing the polymer was changed from 6 hours to 2 hours, purification of the polymer (crude) and preparation of the positive resist composition were performed in the same manner as in Example 1. Then, various measurements and evaluations were performed. The results are shown in Table 1.

(Example 3)
The once-purified polymer obtained in Example 2 was further purified as follows (second purification) to obtain a twice-purified polymer. A positive resist composition was prepared in the same manner as in Example 1 except that such a twice-purified polymer was used, and various measurements and evaluations were performed. The results are shown in Table 1.

[Purification of polymer (second purification)]
1 g of the once-purified polymer obtained in Example 2 was dissolved in 9 g of THF (tetrahydrofuran) (10% by mass), and the obtained polymer solution was mixed with a mixed solvent of 6 g of THF and 204 g of methanol (MeOH). The mixture was added dropwise to deposit a white coagulated product (a polymer containing α-methylstyrene units and α,2-chloroacrylic acid 2,2,3,3-tetrafluoropropyl units). Then, the solution containing the precipitated polymer was filtered with a Kiriyama funnel to obtain a white polymer (polymer purified twice). And about the obtained polymer, the weight average molecular weight, the number average molecular weight, and the molecular weight distribution were measured. The results are shown in Table 1.

(Example 4)
In purifying the once-purified polymer obtained in Example 2, except that the polymer solution was added dropwise to 100 g of methanol (MeOH) instead of being added dropwise to the mixed solvent of 6 g of THF and 204 g of methanol (MeOH). Was obtained in the same manner as described in [Purification of polymer (second purification)] in Example 3 to obtain a twice-purified polymer. A positive resist composition was prepared in the same manner as in Example 1 except that the twice-purified polymer was used. The obtained twice-purified polymer and positive resist composition were subjected to various measurements and evaluations as described above. The results are shown in Table 1.

(Example 5)
In purifying the once-purified polymer obtained in Example 2, instead of dropping the polymer solution into a mixed solvent of 6 g of THF and 204 g of methanol (MeOH), a mixture of 3 g of THF and 97 g of methanol (MeOH) was mixed. A twice-purified polymer was obtained in the same manner as described in [Purification of polymer (second purification)] in Example 3 except that the polymer was added dropwise. A positive resist composition was prepared in the same manner as in Example 1 except that the twice-purified polymer was used. The obtained twice-purified polymer and positive resist composition were subjected to various measurements and evaluations as described above. The results are shown in Table 1.

(Example 6)
In purifying the once-purified polymer obtained in Example 2, except that the polymer solution was dropped in 100 g of hexane instead of being dropped in a mixed solvent of 6 g of THF and 204 g of methanol (MeOH). A twice-purified polymer was obtained in the same manner as described in [Purification of polymer (second purification)] in Example 3. A positive resist composition was prepared in the same manner as in Example 1 except that the twice-purified polymer was used. The obtained twice-purified polymer and positive resist composition were subjected to various measurements and evaluations as described above. The results are shown in Table 1.

(Example 7)
Upon purifying the once-purified polymer obtained in Example 2, the polymer solution was added dropwise to a mixed solvent of 20 g of THF and 80 g of hexane instead of being added dropwise to the mixed solvent of 6 g of THF and 204 g of methanol (MeOH). A two-time purified polymer was obtained in the same manner as described in [Polymer purification (second purification)] in Example 3 except for the above. A positive resist composition was prepared in the same manner as in Example 1 except that the twice-purified polymer was used. The obtained twice-purified polymer and positive resist composition were subjected to various measurements and evaluations as described above. The results are shown in Table 1.

(Example 8)
A polymer was obtained in the same manner as in <Preparation of polymer> in Example 1 except for the following points.
In preparing the polymer, the addition amount of azobisisobutyronitrile as a polymerization initiator was changed from 0.0059564 g to 0.0119128 g, and the addition amount of cyclopentanone as a solvent was changed from 1.6818 g to 6.7400 g. Changed to. Further, the polymerization solution was directly added dropwise to hexane without adding THF to the obtained polymerization solution to precipitate a polymer. And about the obtained polymer, the weight average molecular weight, the number average molecular weight, and the molecular weight distribution were measured. The results are shown in Table 1.

Then, a positive resist composition was prepared in the same manner as in Example 1 except that the polymer obtained as described above was used, and various measurements and evaluations were performed according to the above. The results are shown in Table 1.

(Example 9)
In preparing the polymer, a polymer was obtained in the same manner as in Example 8 except that the amount of azobisisobutyronitrile as a polymerization initiator added was changed from 0.0119128 g to 0.0238255 g. A positive resist composition was prepared in the same manner as in Example 1 except that the polymer thus obtained was used. Various measurements and evaluations were performed on the obtained polymer and positive resist composition as described above. The results are shown in Table 1.

(Example 10)
A polymer (one-time-purified polymer) was obtained in the same manner as in Example 1 except that the polymer (crude) was prepared as follows. A positive resist composition was prepared in the same manner as in Example 1 except that this polymer was used. Various measurements and evaluations were performed on the obtained polymer (polymer once purified) and the positive resist composition as described above. The results are shown in Table 2.

<Preparation of polymer (crude)>
Polymerization with 3.0 g of 2,2,3,3-tetrafluoropropyl α-chloroacrylic acid as the monomer (a) and 4.3332686 g of 4-fluoro-α-methylstyrene as the monomer (b). A monomer composition containing 0.0059624 g of azobisisobutyronitrile as an initiator and 1.9361 g of cyclopentanone as a solvent was placed in a glass container, and the glass container was closed and replaced with nitrogen to obtain a nitrogen atmosphere. The mixture was stirred for 6 hours in a constant temperature bath at 76°C. 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 polymerization 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; crude). Then, the weight average molecular weight, the number average molecular weight and the molecular weight distribution of the obtained polymer (crude) were measured.
The obtained polymer (crude) contained 50 mol% of α-chloroacrylic acid 2,2,3,3-tetrafluoropropyl (ACATFP) unit and 50 mol% of 4-fluoro-α-methylstyrene (4FAMS) unit. I was out.

(Example 11)
A polymer (one-time-purified polymer) was obtained in the same manner as in Example 10 except that the stirring time at the time of preparing the polymer (crude) was changed from 6 hours to 2 hours. A positive resist composition was prepared in the same manner as in Example 1 except that this polymer was used. Various measurements and evaluations were performed on the obtained polymer (polymer once purified) and the positive resist composition as described above. The results are shown in Table 2.

(Example 12)
The polymer obtained in Example 11 (polymer purified once) was further purified (second purification) to obtain a polymer purified twice. A positive resist composition was prepared in the same manner as in Example 1 except that the twice-purified polymer was used, and various measurements and evaluations were performed as described above. The results are shown in Table 2.

[Purification of polymer (second purification)]
1 g of the once-purified polymer obtained in Example 11 was dissolved in 9 g of THF (tetrahydrofuran) (10% by mass), and the obtained polymer solution was mixed with a mixed solvent of 6 g of THF and 204 g of methanol (MeOH). The mixture was added dropwise to deposit a white coagulated product (a polymer containing α-methylstyrene units and α,2-chloroacrylic acid 2,2,3,3-tetrafluoropropyl units). Then, the solution containing the precipitated polymer was filtered with a Kiriyama funnel to obtain a white polymer (polymer purified twice). And about the obtained polymer, the weight average molecular weight, the number average molecular weight, and the molecular weight distribution were measured. The results are shown in Table 2.

(Example 13)
In purifying the once-purified polymer obtained in Example 11, except that the polymer solution was added dropwise to 100 g of methanol (MeOH) instead of being added dropwise to the mixed solvent of 6 g of THF and 204 g of methanol (MeOH). Was obtained in the same manner as in [Polymer purification (second purification)] in Example 12 to obtain a twice-purified polymer. A positive resist composition was prepared in the same manner as in Example 1 except that the twice-purified polymer was used. The obtained twice-purified polymer and positive resist composition were subjected to various measurements and evaluations as described above. The results are shown in Table 2.

(Example 14)
Upon purifying the once-purified polymer obtained in Example 11, instead of dropping the polymer solution into a mixed solvent of 6 g of THF and 204 g of methanol (MeOH), a mixture of 3 g of THF and 97 g of methanol (MeOH) was mixed. A twice-purified polymer was obtained in the same manner as in [Polymer purification (second purification)] in Example 12 except that the polymer was added dropwise. A positive resist composition was prepared in the same manner as in Example 1 except that the twice-purified polymer was used. The obtained twice-purified polymer and positive resist composition were subjected to various measurements and evaluations as described above. The results are shown in Table 2.

(Example 15)
In purifying the once-purified polymer obtained in Example 11, except that the polymer solution was dropped into 100 g of hexane instead of being dropped into a mixed solvent of 6 g of THF and 204 g of methanol (MeOH). A twice-purified polymer was obtained in the same manner as in [Polymer purification (second purification)] in Example 12. A positive resist composition was prepared in the same manner as in Example 1 except that the twice-purified polymer was used. The obtained twice-purified polymer and positive resist composition were subjected to various measurements and evaluations as described above. The results are shown in Table 2.

(Example 16)
In purifying the once-purified polymer obtained in Example 11, the polymer solution was added dropwise to a mixed solvent of 20 g of THF and 80 g of hexane instead of dropping to the mixed solvent of 6 g of THF and 204 g of methanol (MeOH). A two-time purified polymer was obtained in the same manner as described in [Purification of polymer (second purification)] in Example 12 except for the above. A positive resist composition was prepared in the same manner as in Example 1 except that the twice-purified polymer was used. The obtained twice-purified polymer and positive resist composition were subjected to various measurements and evaluations as described above. The results are shown in Table 2.

(Example 17)
In preparing the polymer (crude), the addition amount of azobisisobutyronitrile as a polymerization initiator was changed from 0.0059624 g to 0.0119128 g, and the addition amount of cyclopentanone as a solvent was changed from 1.9361 g. It was changed to 7.7409 g. Further, the polymerization solution was directly added dropwise to hexane without adding THF to the obtained polymerization solution to precipitate a polymer. Except for these points, a polymer (crude) was prepared in the same manner as in Example 10, and the obtained polymer (Crude) was further treated in the same manner as in Example 1 (polymer once purified Coalesced). A positive resist composition was prepared in the same manner as in Example 1 except that this polymer was used. Various measurements and evaluations were performed on the obtained polymer and positive resist composition as described above. The results are shown in Table 2.

(Example 18)
In preparing the polymer, a polymer was obtained in the same manner as in Example 17, except that the amount of azobisisobutyronitrile as a polymerization initiator added was changed from 0.0119128 g to 0.0238255 g. A positive resist composition was prepared in the same manner as in Example 1 except that the polymer thus obtained was used. Various measurements and evaluations were performed on the obtained polymer and positive resist composition as described above. The results are shown in Table 2.

(Comparative Example 1)
In Example 1, instead of using the prepared polymer (crude), 2,2,3,3,3-pentafluoropropyl α-chloroacrylate (ACAPFP) and α-methylstyrene prepared by the following method were used. A positive resist composition was prepared and various measurements and evaluations were performed in the same manner as in Example 1 except that the polymer of 1. was used. The results are shown in Table 3.
<Preparation of polymer (Crude)>
2. g of 2,2,3,3,3-pentafluoropropyl α-chloroacrylic acid (ACAPFP) as monomer (a) and α-methylstyrene (AMS) as monomer (b)3. A monomer composition containing 4763522 g, azobisisobutyronitrile 0.0055128 g as a polymerization initiator, and cyclopentanone 1.6204662 g as a solvent was placed in a glass container, and the glass container was sealed and replaced with nitrogen. 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: Crude). The obtained polymer contained 50 mol% of α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl unit and 50 mol% of α-methylstyrene unit.
<Purification of Polymer (Crude)>
Next, the polymer (Crude) obtained above was dissolved in 100 g of THF, and the resulting solution was added dropwise to a mixed solvent of 150 g of THF and 850 g of methanol (MeOH) to give a white coagulated product (α-methylstyrene unit). And a polymer containing 2,2,3,3,3-pentafluoropropyl units of α-chloroacrylic acid) were precipitated. Then, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white polymer. And about the obtained polymer, the weight average molecular weight, the number average molecular weight, and the molecular weight distribution were measured. The results are shown in Table 3.

(Comparative example 2)
A positive resist composition was prepared in the same manner as in Example 1 except that the polymer prepared as described below was used instead of the polymer prepared in Example 1. Evaluation and measurement were performed. The results are shown in Table 3.

<Preparation of polymer (crude)>
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) 3.234826 g and azobisisobutyronitrile 0.0052065 g as a polymerization initiator were placed in a glass container, and the glass container was sealed and replaced with nitrogen to obtain a nitrogen atmosphere. 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; crude). The obtained polymer (crude) contained 50 mol% of 2,2,3,3,3-pentafluoropropyl units of α-chloroacrylic acid and 50 mol% of 4-fluoro-α-methylstyrene units.
<Purification of polymer (crude)>
Next, the obtained polymer (crude) was dissolved in 100 g of THF, and the obtained solution was added dropwise to a mixed solvent of 50 g of THF and 950 g of methanol (MeOH) to give a white coagulated product (4-fluoro-α-methyl). A polymer containing styrene units and 2,2,3,3,3-pentafluoropropyl units of α-chloroacrylic acid) was deposited. Then, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white polymer. And about the obtained polymer, the weight average molecular weight, the number average molecular weight, and the molecular weight distribution were measured. The results are shown in Table 3.

(Comparative example 3)
A positive resist composition was prepared in the same manner as in Example 1 except that the polymer prepared as described below was used instead of the polymer prepared in Example 1 and various evaluations were performed. And the measurement was performed. The results are shown in Table 3.

<Preparation of polymer (crude)>
3.0 g of 2,2,3,3,4,4,4-heptafluorobutyl α-chloroacrylic acid as the monomer (a) and 2.8738 g of α-methylstyrene as the monomer (b). A monomer composition containing 0.0046 g of azobisisobutyronitrile as a polymerization initiator and 1.4696 g of cyclopentanone as a solvent was placed in a glass container, and the glass container was sealed and replaced with nitrogen to obtain nitrogen. Under an atmosphere, the mixture was stirred 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; crude). The obtained polymer (crude) contained 50 mol% of α-chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl unit and 50 mol% of α-methylstyrene unit.
<Purification of polymer (crude)>
Then, the obtained polymer (crude) was dissolved in 100 g of THF, and the obtained solution was added dropwise to a mixed solvent of 100 g of THF and 900 g of methanol (MeOH) to give a white coagulated product (α-methylstyrene unit and α). -Chloroacrylic acid 2,2,3,3,4,4,4-heptafluorobutyl unit-containing polymer) was deposited. Then, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white polymer. And about the obtained polymer, the weight average molecular weight, the number average molecular weight, and the molecular weight distribution were measured. The results are shown in Table 3.

(Comparative example 4)
Instead of using the polymer prepared in Example 1, the polymer prepared as described below was used, and propylene glycol methyl was used instead of isoamyl acetate as a solvent in the preparation of the positive resist composition. A positive resist composition was prepared and various evaluations and measurements were performed in the same manner as in Example 1 except that ether acetate (PGMEA) was used. The results are shown in Table 3.

<Preparation of polymer (crude)>
3.0 g of α-chloroacrylic acid trifluoroethyl (ACATFE) as a monomer (a), 4.398992 g of α-methylstyrene as a monomer (b), and azobisisobutyro as a polymerization initiator A monomer composition containing 0.0069751 g of nitrile and 1.8513686 g of cyclopentanone as a solvent was placed in a glass container, and the glass container was sealed and replaced with nitrogen. Under a nitrogen atmosphere, a constant temperature bath at 78° C. Stir for 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; crude). The obtained polymer (crude) contained 50 mol% of α-chloroacrylate trifluoroethyl unit and 50 mol% of α-methylstyrene unit.
<Purification of polymer (crude)>
Then, the obtained polymer (crude) was dissolved in 100 g of THF, and the obtained solution was added dropwise to a mixed solvent of 150 g of THF and 850 g of methanol (MeOH) to give a white coagulated product (α-methylstyrene unit and α). -A polymer containing trifluoroethyl chloroacrylate units) was deposited. Then, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white polymer. And about the obtained polymer, the weight average molecular weight, the number average molecular weight, and the molecular weight distribution were measured. The results are shown in Table 3.

In addition, in Tables 1-3,
“ACATFP” represents 2,2,3,3-tetrafluoropropyl α-chloroacrylate,
“ACAPFP” represents α-chloroacrylic acid 2,2,3,3,3-pentafluoropropyl,
“ACATFE” represents trifluoroethyl α-chloroacrylate,
“AMS” refers to α-methylstyrene,
“4FAMS” refers to 4-fluoro-α-methylstyrene,
“PGMEA” indicates propylene glycol methyl ether acetate.

From Tables 1 to 3, when a predetermined polymer containing a monomer unit having an organic group having 4 fluorine atoms is used as a positive resist, a resist pattern having sufficiently high resolution and clarity is formed. You can see what you can do. On the other hand, it can be seen that the positive resists of Comparative Examples 1 to 4 which did not use the predetermined polymer could not form a resist pattern having sufficiently high resolution and clarity.
Moreover, the monomer units (B) contained in the polymer were converted into 4-fluoro-α-methylstyrene units by associating Examples 1 to 9 and Examples 10 to 18 in ascending order. It is understood that the sensitivity as a positive resist is increased when
And from Examples 2-5 and Examples 11-14, when the molecular weight distribution (Mw/Mn) of the polymer is 1.6 or less and the weight average molecular weight (Mw) is 65000 or more, the γ value It can be seen that is particularly high, and the clarity of the obtained resist pattern can be improved.
Furthermore, from Examples 3 to 5 and Examples 12 to 14, it is understood that when the weight average molecular weight (Mw) is 75,000 or more, the clarity (γ value) and resolution of the resist pattern can be further enhanced.

According to the polymer of the present invention, it is possible to provide a main chain scission-type positive resist capable of forming a resist pattern having sufficiently high resolution and clarity.
Further, according to the positive resist composition of the present invention, a resist pattern having sufficiently high resolution and clarity can be efficiently formed.

Claims (7)

The following general formula (I):

[In the formula (I), R ¹ is an organic group having 4 fluorine atoms. ]
A monomer unit (A) represented by
The following general formula (II):

[In the 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 a substituted alkyl group, p and q are integers of 0 or more and 5 or less, and p+q=5. ]
A monomer unit (B) represented by
Having a polymer. The polymer according to claim 1, wherein R ¹ is a tetrafluoroalkyl group. The polymer according to claim 2, wherein R ¹ is a 2,2,3,3-tetrafluoropropyl group. The polymer according to any one of claims 1 to 3, which has a weight average molecular weight (Mw) of 30,000 or more and 160000 or less. The polymer according to any one of claims 1 to 4, which has a molecular weight distribution (Mw/Mn) of 1.8 or less. The polymer according to claim 1, wherein the monomer unit (B) is a 4-fluoro-α-methylstyrene unit. A positive resist composition containing the polymer according to claim 1 and a solvent.