JP2020086063A - Method for forming resist pattern - Google Patents

Abstract

To provide a method for forming a resist pattern, by which a fine resist pattern can be formed with high resolution by using extreme ultraviolet rays.SOLUTION: The method for forming a resist pattern includes: a resist film formation step of forming a resist film by using a positive resist composition comprising a copolymer and a solvent; an exposure step of exposing the resist film to extreme ultraviolet rays; and a development step of developing the exposed resist film with a developer. The copolymer comprises an α-alkylstyrene unit and an α-chloroacrylate unit, in which the percentage of a component having a molecular weight of more than 70000 is 90% or more. The developer comprises alkylketone represented by general formula (I): R-C(=O)-R. In formula (I), Rand Reach independently represent an alkyl group which may have a substituent.SELECTED DRAWING: None

Description

The present invention relates to a resist pattern forming method, and more particularly to a resist pattern forming method using extreme ultraviolet rays.

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

Then, for example, in Patent Document 1, α-methylstyrene/α-chloromethyl acrylate containing α-methyl styrene units and α-methyl chloroacrylate units as a high-sensitivity main chain cleavage type positive resist. A positive resist made of a copolymer is disclosed.

In addition, the formation of a resist pattern using a resist film formed by using a positive type resist made of α-methylstyrene/α-methyl chloroacrylate copolymer is performed in an exposed portion irradiated with ionizing radiation or the like and an ionizing radiation or the like. It is carried out by utilizing the difference in the dissolution rate with respect to the developing solution from the unexposed area not irradiated with. As the developing solution, for example, a carboxylic acid ester solvent having an alkyl group such as amyl acetate or hexyl acetate is widely used (for example, see Patent Document 2).

Further, in recent years, EUV lithography technology using extreme ultraviolet rays (EUV) has attracted attention as a technology that has a smaller proximity effect at the time of exposure than electron beams and enables fine pattern formation. There is. Then, in Non-Patent Document 1, for example, it is formed using a positive resist containing an α-methylstyrene/α-methyl chloroacrylate copolymer containing an α-methylstyrene unit and an α-methyl chloroacrylate unit. The patterning performance of the resist film when exposed to extreme ultraviolet rays is evaluated.

Japanese Patent Publication No. 8-3636 International Publication No. 2013/145695

Roberto Fallica, 6 others, "Lithographic performance of ZEP520A and mr-PosEBR resists exposed by electron beam and extreme ultraviolet lithography", Journal of Vacuum Science & Technology B, October 2017.

However, when the inventors of the present invention tried to form a fine resist pattern by using the EUV lithography technique, the positive resist composed of the conventional α-methylstyrene/α-methyl chloroacrylate copolymer and the conventional positive resist It has been revealed that it is difficult to form a resist pattern with high resolution by using a developing solution.

Therefore, an object of the present invention is to provide a resist pattern forming method using extreme ultraviolet rays, which is capable of forming a fine resist pattern with high resolution.

The present inventors have earnestly studied to achieve the above object. Then, the present inventors formed a resist film using a positive resist composition containing a predetermined copolymer, exposed the resulting resist film with extreme ultraviolet rays, and then exposed the exposed resist film to a predetermined amount. The inventors have found that a fine resist pattern can be formed with high resolution by developing using a developing solution, and completed the present invention.

That is, the present invention has an object to advantageously solve the above problems, and the method for forming a resist pattern of the present invention forms a resist film using a positive resist composition containing a copolymer and a solvent. A resist film forming step, an exposing step of exposing the resist film with extreme ultraviolet rays, and a developing step of developing the exposed resist film with a developing solution, wherein the copolymer is an α-alkylstyrene unit. , The proportion of the component having an α-chloroacrylic acid ester unit and a molecular weight of more than 70,000 is 90% or more, and the developer has the following general formula (I):
^{R 1 -C (= O) -R} 2 ··· (I)
(In the formula (I), R ¹ and R ² each independently represent an alkyl group which may have a substituent). Thus, a resist film using a resist composition containing a copolymer containing an α-alkylstyrene unit and an α-chloroacrylic acid ester unit and having a ratio of components having a molecular weight of more than 70,000 of 90% or more is used. And exposing the resulting resist film with extreme ultraviolet rays, and developing the exposed resist film with a developer containing an alkylketone of formula (I) to form a fine resist pattern. It can be formed with high resolution.

In the present invention, the "ratio of components having a molecular weight of more than 70,000" 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 is 70,000. It can be obtained by calculating the ratio (=(B/A)×100%) of the total (B) of the peak areas of the super component. Further, in the present invention, the “ratio of components having a molecular weight of more than 80,000” described below 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 over 80,000.

Here, in the resist pattern forming method of the present invention, it is preferable that at least one of R ¹ and R ^{2 in} the alkyl ketones represented by the formula (I) is a branched alkyl group. In the formula (I), if at least one of R ¹ and R ² is an alkylketone having a branched alkyl group, the solubility of the resist film in a developing solution is improved and the resolution of the obtained resist pattern is increased. be able to.

Further, in the resist pattern forming method of the present invention, it is preferable that the alkyl ketones include diisobutyl ketone. When a developing solution containing diisobutyl ketone is used, the solubility of the resist film in the developing solution can be further improved and the resolution of the obtained resist pattern can be further increased.

In the resist pattern forming method of the present invention, it is preferable that the ratio of the component having a molecular weight of more than 80,000 in the copolymer is 80% or more. When the proportion of the component having a molecular weight of more than 80,000 in the copolymer is 80% or more, it is possible to sufficiently suppress lowering of the molecular weight of the copolymer when the positive resist composition is dried by heating or the like in the resist film forming step. Thus, a pattern having a desired shape can be satisfactorily formed.

According to the present invention, a fine resist pattern can be efficiently formed with high resolution.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the resist pattern forming method of the present invention is a method of forming a resist pattern using a main chain cleavage type positive resist, in which the main chain is cut by irradiation of extreme ultraviolet rays to lower the molecular weight, and for example, build It can be suitably used when forming a resist pattern in a manufacturing process of a printed circuit board such as an up board, a semiconductor, a photomask, and a mold.

(Method of forming resist pattern)
Then, the resist pattern forming method of the present invention comprises a step of forming a resist film using a positive resist composition containing a predetermined copolymer and a solvent (resist film forming step), and exposing the resist film to extreme ultraviolet rays. It includes at least a step (exposure step) and a step of developing the exposed resist film with a predetermined developing solution (developing step). The resist pattern forming method of the present invention may optionally further include a rinse step of removing the developing solution after the developing step.

In the resist pattern forming method of the present invention, a predetermined polymer, extreme ultraviolet rays, and a predetermined developing solution are used in combination, so that a fine resist pattern can be formed with high resolution.
In the method of forming a resist pattern, it is difficult to form a fine resist pattern unless extreme ultraviolet rays are used. Further, in miniaturizing a resist pattern using extreme ultraviolet rays, a fine resist pattern cannot be formed with high resolution unless a predetermined polymer and a predetermined developing solution are used in combination.

<Resist film forming step>
In the resist film forming step, a positive resist composition is applied onto a work piece such as a substrate processed using a resist pattern (application step), and the applied positive resist composition is dried to form a resist. Form a film (drying step).

<< coating process >>
The work piece to be coated with the positive resist composition in the coating step is not particularly limited, and is a substrate having an insulating layer and a copper foil provided on the insulating layer, which is used for manufacturing a printed circuit board or the like. And a mask blank or the like in which a light shielding layer is formed on a substrate can be used. The coating method of the positive resist composition is not particularly limited, and known coating methods can be used.
Then, the following positive resist composition is used as the positive resist composition applied on the workpiece.

[Positive resist composition]
The positive resist composition used in the resist pattern forming method of the present invention contains a predetermined copolymer and a solvent described in detail below, and optionally further contains a known additive that can be blended in the resist composition. To do.

-Copolymer-
The copolymer contained in the positive resist composition is an α-alkylstyrene/α-chloroacrylic acid ester copolymer containing an α-alkylstyrene unit and an α-chloroacrylic acid ester unit, and has a molecular weight of It is necessary that the ratio of the component having a value of more than 70,000 is equal to or higher than a predetermined value.

Since the copolymer contains a structural unit (α-chloroacrylic acid ester unit) derived from α-chloroacrylic acid ester having a chloro group (-Cl) at the α-position, it is exposed to extreme ultraviolet rays. Then, the main chain is easily cleaved to reduce the molecular weight. Further, since the ratio of the component having a molecular weight of more than 70,000 is equal to or more than a predetermined value in the copolymer, it is possible to form a fine resist pattern with high resolution.

[Α-alkylstyrene unit]
The α-alkylstyrene unit contained in the copolymer is a structural unit derived from α-alkylstyrene. Since the copolymer used for the positive resist composition has an α-alkylstyrene unit, it exhibits excellent dry etching resistance due to the protection stability of the benzene ring when used as a positive resist. To do.
As the α-alkylstyrene unit, for example, a linear alkyl group having 4 or less carbon atoms such as α-methylstyrene unit, α-ethylstyrene unit, α-propylstyrene unit, α-butylstyrene unit, etc. Included are attached α-alkyl styrene units. Among them, the α-alkylstyrene unit is preferably an α-methylstyrene unit from the viewpoint of improving dry etching resistance when the copolymer is used as a positive resist.
Here, the copolymer may have only one type of the above-mentioned unit as the α-alkylstyrene unit, or may have two or more types.

The copolymer preferably contains the α-alkylstyrene unit in a proportion of 30 mol% or more and 70 mol% or less.

[Α-chloroacrylic acid ester unit]
The α-chloroacrylic acid ester unit contained in the copolymer is a structural unit derived from α-chloroacrylic acid ester. Since the copolymer used for the positive resist composition has an α-chloroacrylic acid ester unit, when exposed to extreme ultraviolet rays, the chlorine atom is eliminated and the main chain is easily separated by the β-cleavage reaction. To be disconnected.
Examples of the α-chloroacrylic acid ester unit include α-chloroacrylic acid alkyl ester units such as α-chloroacrylic acid methyl unit and α-chloroacrylic acid ethyl unit. Among them, the α-chloroacrylic acid ester unit is preferably an α-chloromethyl acrylate unit from the viewpoint of enhancing the sensitivity of the resist film formed using the positive resist composition.
Here, the copolymer may have only one type of the above-mentioned unit as the α-chloroacrylic acid ester unit, or may have two or more types.

The copolymer preferably contains α-chloroacrylic acid ester units in a proportion of 30 mol% or more and 70 mol% or less.

[Ratio of components having a molecular weight of more than 70,000]
In the above-mentioned copolymer, the proportion of components having a molecular weight of more than 70,000 needs to be 90% or more, and preferably 93% or more. If the proportion of the component having a molecular weight of more than 70,000 is 90% or more, a fine resist pattern can be formed with high resolution. Further, when the proportion of the component having a molecular weight of more than 70,000 is 90% or more, when the resist film formed by using the positive resist composition containing such a copolymer is dried by heating or the like in the drying step, A decrease in the molecular weight can be suppressed, and a pattern having a desired shape can be satisfactorily formed. The proportion of the component having a molecular weight of more than 70,000 in the copolymer may be 100%.

[Ratio of components having a molecular weight of more than 80,000]
In the above-mentioned copolymer, the ratio of the component having a molecular weight of more than 80,000 is preferably 80% or more, and more preferably 87% or more. When the proportion of the component having a molecular weight of more than 80,000 is 80% or more, the molecular weight is lowered when the resist film formed using the positive resist composition containing such a copolymer is dried by heating or the like in the drying step. This can be sufficiently suppressed, and a pattern having a desired shape can be formed even better. The proportion of the component having a molecular weight of more than 80,000 in the copolymer may be 100%.

(Weight average molecular weight)
The weight average molecular weight (Mw) of the above-mentioned copolymer is, for example, 10,000 or more and 3,000,000 or less, preferably 20,000 or more and 2,000,000 or less, more preferably 30,000 or more and 1,000. It can be 2,000 or less, and more preferably 300,000 or more and 700,000 or less. When the weight average molecular weight (Mw) of the copolymer is not more than the above upper limit value, the coatability of the positive resist composition can be improved. On the other hand, when the weight average molecular weight (Mw) of the copolymer is at least the above lower limit, it is possible to prevent the solubility of the resist film in a developing solution from increasing at an excessively low irradiation amount, and to obtain a resist pattern of It is possible to prevent the resolution from being excessively lowered.
In addition, in this invention, "weight average molecular weight" and "number average molecular weight" mentioned later can be measured as a standard polystyrene conversion value using gel permeation chromatography.

[Molecular weight distribution]
The molecular weight distribution (ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn)) of the above-mentioned copolymer can be, for example, 2.50 or less. Further, the molecular weight distribution (Mw/Mn) of the polymer is preferably 1.20 or more, more preferably 1.30 or more, and preferably 2.10 or less. When the molecular weight distribution (Mw/Mn) of the copolymer is at least the above lower limit, the ease of manufacturing the copolymer can be increased. On the other hand, when the molecular weight distribution (Mw/Mn) of the copolymer is not more than the above upper limit, the resolution of the obtained resist pattern can be increased.

[Method for preparing copolymer]
And the above-mentioned copolymer is prepared by, for example, polymerizing a monomer composition containing α-alkylstyrene and α-chloroacrylic acid ester, and then purifying the obtained polymer. be able to.
The composition, molecular weight distribution, weight average molecular weight and number average molecular weight of the copolymer can be adjusted by changing the polymerization conditions and the purification conditions. Specifically, for example, the composition of the copolymer can be adjusted by changing the content ratio of each monomer in the monomer composition used for the polymerization. The weight average molecular weight and the number average molecular weight can be reduced by increasing the polymerization temperature. Furthermore, the weight average molecular weight and the number average molecular weight can be reduced by shortening the polymerization time.

[[Polymerization of Monomer Composition]]
Here, as the monomer composition used for preparing the above-mentioned copolymer, a monomer component containing α-alkylstyrene and α-chloroacrylic acid ester, an arbitrary solvent, a polymerization initiator, and an optional Mixtures with additives added to can be used. Then, the polymerization of the monomer composition can be performed using a known method. Among these, for example, it is preferable to use the radical polymerization method as disclosed in WO 99/62964, and it is more preferable to use the emulsion polymerization method.

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

[[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 poor solvent such as methanol, or a good solvent such as tetrahydrofuran It is preferable to add the mixture dropwise to a mixed solvent with a poor solvent such as methanol to precipitate a part of the polymer. Among them, from the viewpoint of easily obtaining a product having a desired property, it is preferable to dissolve it in a good solvent and then drop it into a mixed solvent of a good solvent and a poor solvent to precipitate a polymer. In this way, if the solution of the polymer is added dropwise to the mixed solvent of the good solvent and the poor solvent to purify the polymer, by changing the kind and the mixing ratio of the good solvent and the poor solvent, the obtained copolymer can be obtained. The molecular weight distribution, weight average molecular weight and number average molecular weight of the polymer can be easily adjusted. Specifically, for example, the higher the ratio of the good solvent in the mixed solvent, the larger the molecular weight of the copolymer precipitated in the mixed solvent.

When the polymer is purified by the reprecipitation method, the polymer may be a polymer precipitated in a mixed solvent of a good solvent and a poor solvent, or a polymer not precipitated in the mixed solvent. A polymer (that is, a polymer dissolved in a mixed solvent) may be used. Here, the polymer not precipitated in the mixed solvent can be recovered from the mixed solvent by a known method such as concentration to dryness.

Furthermore, the recovered polymer or the purified polymer optionally purified after recovery may be washed with acidic water prepared using an acid such as hydrochloric acid. The pH of the acidic water can be less than pH 6, for example. The washing method with acidic water is not particularly limited, and for example, the method disclosed in WO 99/62964 can be followed.

-solvent-
As the solvent contained in the positive resist composition used in the resist pattern forming method of the present invention, known solvents can be used as long as they can dissolve the above-mentioned copolymer. Among them, the solvents are cyclopentanone, methyl 3-methoxypropionate, methyl crotonic acid, and anisole from the viewpoint of obtaining a positive resist composition having an appropriate viscosity and improving the coatability of the positive resist composition. It is preferable to contain at least one selected from the group consisting of, and it is more preferable to contain anisole. As the solvent, one kind of these components may be used alone, or two or more kinds thereof may be used in combination at an arbitrary ratio.
Further, as described above, the solvent may be a mixture, but from the viewpoint of easy recovery and reuse of the solvent, it is preferably a single solvent composed of a single substance.

<<Drying process>>
The method for drying the positive resist composition is not particularly limited, and a method generally used for forming a resist film can be used, but the positive resist composition is heated (prebaked). It is preferable to form a resist film.
Here, the temperature at which the positive resist composition is dried (drying temperature) is preferably 100° C. or higher, and 110° C. from the viewpoint of the adhesion between the resist film formed through the drying step and the workpiece. More preferably, it is preferably 180° C. or lower, and more preferably 150° C. or lower, from the viewpoint of reducing the thermal effect on the work piece and the resist film. The time for drying the positive resist composition (drying time) is from the viewpoint of sufficiently improving the adhesion between the resist film formed by performing the drying step in the lower temperature range and the workpiece. It is preferably more than 1 minute, more preferably 2 minutes or more, further preferably 3 minutes or more, from the viewpoint of reducing the change in the molecular weight of the copolymer in the resist film before and after the drying step, It is preferably 30 minutes or less, more preferably 10 minutes or less.

The thickness of the resist film may be appropriately adjusted according to the exposure conditions and the like, and can be, for example, 10 nm or more and 100 nm or less, preferably 70 nm or less, more preferably 60 nm or less, and further preferably 40 nm or less. can do.
Further, from the viewpoint of further improving the sensitivity to extreme ultraviolet rays, the density of the resist film formed in the resist film forming step is preferably 1.35 g/cm ³ or more, and 1.40 g/cm ³ or more. Is more preferable. Here, the density of the resist film can be adjusted by changing the composition of the copolymer and the conditions for forming the resist film.

<Exposure process>
In the exposure step, the resist film formed in the resist film forming step is exposed to extreme ultraviolet rays to draw a desired pattern.

The wavelength of the extreme ultraviolet rays to be irradiated is not particularly limited and can be, for example, 1 nm or more and 30 nm or less, and preferably 13.5 nm.
Further, a known exposure device such as EQ-10M (manufactured by ENERGETIQ) or NXE (manufactured by ASML) can be used for irradiation of extreme ultraviolet rays.
The exposure amount is usually 10 mJ/cm ² or more and 2000 mJ/cm ² or less, and the exposure time is usually 0.1 seconds or more and 180 seconds or less.

<Developing process>
In the developing step, the exposed resist film is developed using a predetermined developing solution described in detail below. Specifically, 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 for bringing the resist film and the developing solution into contact with each other is not particularly limited, and a known method such as dipping the resist film in the developing solution or coating the developing solution on the resist film may be used. it can.

<<Developer>>
The developing solution used in the developing step is represented by the following general formula (I):
^{R 1 -C (= O) -R} 2 ··· (I)
It is necessary to include alkyl ketones represented by

In formula (I), R ¹ and R ² each independently represent an alkyl group which may have a substituent. In the present invention, “which may have a substituent” means “unsubstituted or having a substituent”. When the alkyl group represented by R ¹ and R ² has a substituent, the carbon number of the alkyl group having the substituent does not include the carbon number of the substituent. In the present invention, the term “alkyl group” means a chain (straight or branched) saturated hydrocarbon group, and the term “alkyl group” means a cyclic saturated hydrocarbon group such as “cycloalkyl”. “Group” is not included.

Here, in the formula (I), as the alkyl group of the alkyl group which may have a substituent represented by R ¹ and R ² , a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, A linear alkyl group such as a hexyl group; a branched alkyl group such as an isopropyl group, an isobutyl group, a tert-butyl group, and the like. Among them, the alkyl group preferably has 1 to 10 carbon atoms, more preferably 6 or less carbon atoms, and further preferably 4 or less carbon atoms.

Further, from the viewpoint of improving the solubility of the resist film in a developing solution and enhancing the resolution of the obtained resist pattern, at least one of R ¹ and R ^{2 in} the formula (I) is a branched alkyl group. Are preferred, and it is more preferred that both are branched alkyl groups.

Then, in the formula (I), the substituent of the alkyl group which may have a substituent represented by R ¹ and R ² is a halogen atom such as a fluorine atom, a chlorine atom or a bromine atom; a methoxy group; Examples thereof include an alkoxy group such as an ethoxy group; a nitro group and a cyano group;

Here, specific examples of the alkyl ketones represented by the formula (I) include acetone, diethyl ketone, dipropyl ketone, diisopropyl ketone, dibutyl ketone, diisobutyl ketone, dipentyl ketone, diisopentyl ketone, diheptyl ketone, dioctyl. Examples include ketones and tert-butyl methyl ketone. The alkyl ketones represented by the formula (I) may be used alone or in combination of two or more at an arbitrary ratio.

Among them, from the viewpoint of further improving the solubility of the resist film in a developing solution and further improving the resolution of the obtained resist pattern, the alkyl ketones represented by the formula (I) are diisopropyl ketone, diisobutyl ketone, dialkyl ketone and diisobutyl ketone. It is preferable that at least one of R ^{1 and} R ^{2 in} the formula (I) is a branched alkyl ketone such as isopentyl ketone and tert-butyl methyl ketone, and diisopropyl ketone and diisobutyl are included. It is more preferable that R ¹ and R ^{2 in} the formula (I) include branched alkylketones such that both R ¹ and R ² are branched alkyl groups, and it is more preferable that diisobutyl ketone is included. It is particularly preferred to use diisobutyl ketone alone.

Further, as the developing solution, the alkyl ketones represented by the formula (I) may be used in combination with a known developing solution generally used in resist pattern formation.

When the alkyl ketones represented by the formula (I) and a known developing solution are used in combination, the ratio of the alkyl ketones represented by the formula (I) in the entire developing solution is 90. It is preferably at least mass%, more preferably at least 95 mass%.
From the viewpoint of suppressing variations in the quality of the obtained resist pattern and facilitating the recovery of the developer, it is preferable to use the alkyl ketones represented by formula (I) alone as the developer.

<<Development conditions>>
The development conditions such as the development temperature and the development time are not particularly limited and can be set appropriately. For example, the developing temperature is usually −20° C. or higher and 30° C. or lower, and can be, for example, 5° C. or higher and 25° C. or lower. The developing time is usually 10 seconds or more and 2 minutes or less, preferably 45 seconds or less, and more preferably 30 seconds or less, though it depends on the developing temperature. By setting the development time to 2 minutes or less, the formation time of the resist pattern can be shortened.

Then, according to the resist pattern forming method of the present invention, by exposing the resist film formed using the above-mentioned copolymer with extreme ultraviolet rays and developing with the above-mentioned predetermined developing solution, for example, a half pitch is It is possible to efficiently form a fine resist pattern of 50 nm or less, preferably 30 nm or less, more preferably 20 nm or less with high resolution.

According to the resist pattern forming method of the present invention, a CD value (CD: Critical Dimension) representing the critical dimension of the line width of the resist pattern, an LWR value (LWR: Line Width Roughness) representing the line width roughness, and a line The LER value (LER: Line Edge Roughness) representing the edge roughness can be effectively reduced. Specifically, according to the resist pattern forming method of the present invention, for example, when patterning is performed with a 16 nm half pitch as a target, the CD value variation is suppressed to 5% or less, the LWR value is 6 nm or less, and the LER The value can be reduced to 4 nm or less. The CD value, LWR value, and LER value can be measured, for example, by the method described in the examples of the present specification.

<Rinse process>
The resist pattern forming method of the present invention may optionally further include a rinse step of performing a rinse treatment using a rinse liquid after the developing step. Specifically, in the rinse step, the resist film developed in the developing step is brought into contact with a rinse liquid to rinse the developed resist film. By performing the rinsing step, the resist residue attached to the developed resist film can be effectively removed.

Here, the method of bringing the developed resist film and the rinse liquid into contact with each other is not particularly limited, and a known method such as dipping the resist film in the rinse liquid or applying the rinse liquid to the resist film may be used. Can be used.

The rinse liquid is not particularly limited, and a known rinse liquid depending on the type of developer used can be used. Here, as the rinse liquid, it is preferable to select a rinse liquid which is less likely to dissolve the resist in the unexposed portion than the developing liquid used and is more easily mixed with the developing liquid. For example, isopropyl alcohol or the like can be preferably used as the rinse liquid. At that time, the temperature of the rinse liquid is not particularly limited, but may be, for example, 21° C. or higher and 25° C. or lower. Furthermore, the rinsing time can be, for example, 5 seconds or more and 3 minutes or less.

Hereinafter, the present invention will be specifically described based on Examples, but the present invention is not limited to these Examples. In the 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 copolymer, the number average molecular weight and the molecular weight distribution, the ratio of each molecular weight component in the copolymer, and the CD value representing the critical dimension of the line width of the resist pattern. The LWR value indicating the line width roughness and the LER value indicating the line edge roughness were measured and evaluated by the following methods.

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

<Ratio of each molecular weight component in the copolymer>
A gel permeation chromatograph (manufactured by Tosoh Corporation, HLC-8220) was used, and tetrahydrofuran was used as a developing solvent to obtain a chromatogram of the copolymer. Then, from the obtained chromatogram, the total area of the peaks (A), the total area of the peaks of the components having a molecular weight of more than 70,000 (B) and the total area of the peaks of the components of a molecular weight of more than 80,000 (C) were obtained. It was
Then, the ratio of each molecular weight component was calculated using the following formula.
Ratio (%) of components having a molecular weight of more than 70,000=(B/A)×100
Ratio (%) of components having a molecular weight of more than 80,000=(C/A)×100

<CD value, LWR value, and LER value>
The CD value, LWR value, and LER value of the formed resist pattern are measured by using a high-resolution FEB length measuring device (Hitachi High Technology Co., Ltd., CG5000) and analysis software (Hitachi High Technology Co., Design Based Metrology System). Measured and calculated. In addition, when the resist pattern could not be formed, it was set to "-" (measurement impossible).
In the CD value range of 16 nm±0.5 nm, the lower the LWR value and the LER value, the higher the resolution of the resist pattern.

(Example 1)
<Preparation of Copolymer A>
A separable flask containing 2750 parts of pure water, 3 parts of sodium carbonate, and 225 parts of a solution obtained by dissolving KS soap (Kao Corporation, semi-hardened beef tallow fatty acid potassium soap) in ion-exchanged water at a solid concentration of 17.5 mass%. And melted. 450 parts of α-chloro acrylate as a monomer and 1084 parts of α-methyl styrene were added and emulsified by vigorous stirring. After replacing the inside of the flask with nitrogen, 0.4 part of sodium dithionite, 0.15 part of sodium ethylenediaminetetraacetate trihydrate, 0.375 part of ethylenediaminetetraacetic acid tetrasodium tetrahydrate, sodium formaldehyde sulfoxylate 0.225 parts and cumene hydroperoxide 0.786 parts were sequentially added, and then the mixture was stirred at 5° C. for 48 hours. After adding 7.5 parts of 2,6-di-tert-butyl-4-methylphenol to stop the reaction, 14000 parts of methanol was added dropwise to the reaction solution, and the precipitated solid content was separated by filtration. The obtained solid content was dissolved in 8000 parts of tetrahydrofuran (THF), the obtained solution was added dropwise to 14000 parts of methanol, and the precipitated solid content was separated by filtration. Further, the obtained solid content was dissolved in 8000 parts of THF, and the obtained solution was added dropwise to 14000 parts of methanol. The precipitated solid content was separated by filtration to obtain a solid content A. Then, the obtained solid content A was dried to obtain a polymer containing 750 parts of α-methylstyrene unit and α-methyl chloroacrylate unit. The polymer contained 47 mol% of α-methylstyrene units and 53 mol% of α-methyl methyl acrylate units.
Then, 750 parts of the obtained polymer was dissolved in 9000 parts of dichloromethane to obtain a solution. To the obtained solution, 9000 parts of 0.005N hydrochloric acid aqueous solution (pH: 2.3) was added and stirred to obtain a mixed solution. After allowing the mixed solution to stand, the aqueous layer was removed by decantation.
The remaining dichloromethane layer was added dropwise to 14,000 parts of methanol, and the precipitated solid content was filtered off and dried to obtain 740 parts of Copolymer A containing α-methylstyrene unit and α-methyl chloroacrylate unit. Obtained.
Then, when the copolymer A was measured according to the above, the ratio of the component having a predetermined molecular weight in the copolymer A was 94.13 (%) for the component having a molecular weight of more than 70,000 and more than 80,000 for the molecular weight. The ratio of the components was 92.53 (%), the weight average molecular weight was 342123, the number average molecular weight was 169117, and the molecular weight distribution was 2.023.

<Preparation of positive resist composition>
The obtained copolymer was dissolved in anisole as a solvent to prepare a resist solution (positive resist composition) having a copolymer concentration of 1.5% by mass.

<Formation of resist film>
Using a coating device (CLEAN TRACK (registered trademark) ACT (registered trademark) 12 manufactured by Tokyo Electron Ltd.), a positive resist composition having a concentration of 1.5 mass% was formed on a silicon wafer having a diameter of 12 inches. It was applied so as to have a thickness of 30 nm. Then, the applied positive resist composition was heated on a hot plate at 180° C. for 3 minutes to form a resist film on the silicon wafer.

<Determination of optimum exposure dose for extreme ultraviolet rays>
Using an EUV drawing device (TWINSCAN NXE: 3300B, manufactured by ASML), multiple patterns (dimensions 10 mm x 10 mm) having different irradiation doses of extreme ultraviolet rays are drawn on the resist film, and diisobutyl ketone (Nippon Zeon Corporation) is used as a developing solution. Manufactured by K-90), the development temperature was 23° C., and the development time was 30 seconds. Then, rinsing was performed for 15 seconds using isopropyl alcohol. The irradiation dose of extreme ultraviolet rays was varied by 10 mJ/cm ² within a range of 10 mJ/cm ² to 200 mJ/cm ² . Next, the CD value of the resist pattern in the drawn portion was measured. Then, based on the dose of CD values 80 mJ / cm ² which is closest to the pattern formed 16 nm, within a range of ± 10 mJ / cm ^2, the irradiation amount of extreme ultraviolet 0.1 mJ / cm ² the pitch Patterns were drawn differently in the same manner as above, and the CD value, LWR value, and LER value of the obtained resist pattern were measured and calculated.
Using the obtained data of the relationship between the irradiation amount and the CD value, the LWR value, and the LER value, the optimum exposure amount of extreme ultraviolet rays (when the CD value is in the range of 16 nm±0.5 nm, the LWR value and the LER value are determined to be good) Irradiation dose) was determined. The results are shown in Table 1.

<Formation of resist pattern>
[Exposure, development and rinse]
The resist film was exposed with an optimal exposure dose (extreme ultraviolet rays: 81 mJ/cm ² ) using an EUV drawing device (TWIN SCAN NXE: 3300B, manufactured by ASML) to draw a pattern (exposure step). The resist film formed as described above was used as the resist film. In the pattern drawing (patterning), the line (unexposed region) and the space (exposed region) of the resist pattern were both set to 16 nm (that is, hp was 16 nm).
Then, in forming the resist pattern, diisobutyl ketone (K-90 manufactured by Nippon Zeon Co., Ltd.) was used as a developing solution, and the developing treatment was performed at a developing temperature of 23° C. and a developing time of 30 seconds (developing step).
After that, rinsing was performed for 15 seconds using isopropyl alcohol (rinsing step) to form a resist pattern. Then, for the obtained resist pattern, the CD value, the LWR value and the LER value were measured and calculated. The results are shown in Table 1.

(Example 2)
In the determination of the optimum exposure dose of extreme ultraviolet rays, the copolymer A and the positive resist composition were prepared, the resist film was formed, and the irradiation was performed in the same manner as in Example 1 except that the development time was changed to 10 seconds. Data on the relationship between the amount and the CD value, the LWR value, and the LER value was created. The obtained data was then used to determine the optimal exposure dose. The results are shown in Table 1.
Then, in forming the resist pattern, the resist film was formed in the same manner as in Example 1 except that the resist film was exposed with an optimum exposure amount (extreme ultraviolet rays: 82 mJ/cm ² ) and the developing time was changed to 10 seconds. did. For the obtained resist pattern, the CD value, LWR value and LER value were measured and calculated. The results are shown in Table 1.

(Example 3)
In the determination of the optimum exposure amount of extreme ultraviolet rays, the copolymer A and the positive resist composition were prepared, the resist film was formed, and the irradiation was performed in the same manner as in Example 2 except that the developing temperature was changed to 7°C. Data on the relationship between the amount and the CD value, the LWR value, and the LER value was created. The obtained data was then used to determine the optimal exposure dose. The results are shown in Table 1.
Then, in forming the resist pattern, the resist film was formed in the same manner as in Example 2 except that the resist film was exposed with the optimum exposure amount (extreme ultraviolet rays: 89 mJ/cm ² ) and the developing temperature was changed to 7°C. did. For the obtained resist pattern, the CD value, LWR value and LER value were measured and calculated. The results are shown in Table 1.

(Example 4)
In the determination of the optimum exposure dose of extreme ultraviolet rays, the copolymer A and the positive resist composition were prepared and the resist was prepared in the same manner as in Example 3 except that the development time was changed to 25 seconds and the rinse time was changed to 30 seconds. A film was formed and data on the relationship between the dose and the CD value, the LWR value, and the LER value was created. The obtained data was then used to determine the optimal exposure dose. The results are shown in Table 1.
Then, in forming the resist pattern, the resist film was exposed to the optimum exposure amount (extreme ultraviolet rays: 116 mJ/cm ² ), and the developing time was changed to 25 seconds and the rinse time was changed to 30 seconds. A resist pattern was formed in the same manner. For the obtained resist pattern, the CD value, LWR value and LER value were measured and calculated. The results are shown in Table 1.

(Examples 5 and 6)
In determining the optimum exposure amount of extreme ultraviolet rays, the copolymer A and the positive electrode were prepared in the same manner as in Example 3 except that the thickness of the resist film was changed to 35 nm (Example 5) and 40 nm (Example 6), respectively. A resist composition was prepared, a resist film was formed, and data on the relationship between the dose and the CD value, LWR value, and LER value was prepared. The obtained data was then used to determine the optimal exposure dose. The results are shown in Table 1.
Then, in forming the resist pattern, the resist film is exposed with an optimum exposure amount (extreme ultraviolet rays: 89 mJ/cm ² (Example 5), 95 mJ/cm ² (Example 6)), and the film thickness of the resist film is adjusted. A resist pattern was formed in the same manner as in Example 3 except that the thickness was changed to 35 nm (Example 5) and 40 nm (Example 6). For the obtained resist pattern, the CD value, LWR value and LER value were measured and calculated. The results are shown in Table 1.

(Example 7)
In determining the optimum exposure dose of extreme ultraviolet rays, the procedure of Example 5 was repeated except that the copolymer A was replaced by the copolymer B prepared as follows, and the development time was changed to 25 seconds. A positive resist composition was prepared, a resist film was formed, and data on the relationship between the dose and the CD value, LWR value, and LER value was created. The obtained data was then used to determine the optimal exposure dose. The results are shown in Table 1.
Then, in forming the resist pattern, the resist film was formed in the same manner as in Example 5 except that the resist film was exposed at the optimum exposure amount (extreme ultraviolet rays: 96 mJ/cm ² ) and the developing time was changed to 25 seconds. did. For the obtained resist pattern, the CD value, LWR value and LER value were measured and calculated. The results are shown in Table 1.
<Preparation of Copolymer B>
10 g of the powder of the copolymer A obtained in the same manner as in Example 1 was dissolved in 90 g of THF. The obtained solution was reprecipitated in a mixed solvent of THF and methanol (MeOH) (THF/MeOH=300 g/700 g), and the coagulated component side was recovered to obtain a copolymer B.
Then, when the copolymer B was measured according to the above, the ratio of the component having a predetermined molecular weight in the copolymer B was 100 (%) for the component having a molecular weight of more than 70,000 and for the component having a molecular weight of more than 80,000. Was 100 (%), the weight average molecular weight was 630000, the number average molecular weight was 484615, and the molecular weight distribution was 1.3.

(Example 8)
A positive resist composition was prepared in the same manner as in Example 4 except that the copolymer A was replaced by the copolymer B prepared in the same manner as in Example 7 in the determination of the optimum exposure dose of extreme ultraviolet rays. Preparation, formation of a resist film, and creation of data on the relationship between irradiation dose and CD value, LWR value, and LER value were performed. The obtained data was then used to determine the optimal exposure dose. The results are shown in Table 1.
Then, in forming the resist pattern, a resist pattern was formed in the same manner as in Example 4 except that the resist film was exposed with the optimum exposure amount (extreme ultraviolet rays: 112 mJ/cm ² ). For the obtained resist pattern, the CD value, LWR value and LER value were measured and calculated. The results are shown in Table 1.

(Comparative Example 1)
In the determination of the optimum exposure dose of extreme ultraviolet rays, the copolymer A and the positive electrode were prepared in the same manner as in Example 1 except that amyl acetate (ZED-N50 manufactured by Nippon Zeon Co., Ltd.) was used instead of diisobutyl ketone as the developing solution. A resist composition was prepared, a resist film was formed, and data on the relationship between the dose and the CD value, LWR value, and LER value was prepared. The obtained data was then used to determine the optimal exposure dose. The results are shown in Table 2.
Then, in forming the resist pattern, the same as Example 1 except that the resist film was exposed with an optimum exposure amount (extreme ultraviolet ray: 33 mJ/cm ² ) and the above-mentioned amyl acetate was used instead of diisobutyl ketone as a developing solution. However, the resist film was completely dissolved and the image could not be resolved. The results are shown in Table 2.

(Comparative example 2)
In the determination of the optimum exposure dose of extreme ultraviolet rays, hexyl acetate (ZED-N60 manufactured by Nippon Zeon Co., Ltd.) was used instead of diisobutyl ketone as the developing solution, and the developing temperature was changed to 7° C., and the same as in Example 1. Then, the copolymer A and the positive resist composition were prepared, a resist film was formed, and data on the relationship between the irradiation dose and the CD value, the LWR value, and the LER value was prepared. The obtained data was then used to determine the optimal exposure dose. The results are shown in Table 2.
Then, in forming the resist pattern, the same as Example 1 except that the resist film was exposed with an optimum exposure amount (extreme ultraviolet ray: 47 mJ/cm ² ) and the above-mentioned hexyl acetate was used instead of diisobutyl ketone as a developing solution. To form a resist pattern. For the obtained resist pattern, the CD value, LWR value and LER value were measured and calculated. The results are shown in Table 2.

(Comparative example 3)
In the determination of the optimum exposure dose of extreme ultraviolet rays, copolymer A and a positive electrode were prepared in the same manner as in Example 1 except that hexyl acetate (ZED-N60 manufactured by Nippon Zeon Co., Ltd.) was used as the developing solution instead of diisobutyl ketone. A resist composition was prepared, a resist film was formed, and data on the relationship between the dose and the CD value, LWR value, and LER value was prepared. The obtained data was then used to determine the optimal exposure dose. The results are shown in Table 2.
Then, in forming the resist pattern, the same procedure as in Example 1 was performed except that the resist film was exposed with an optimum exposure amount (extreme ultraviolet rays: 44 mJ/cm ² ) and the above-mentioned hexyl acetate was used instead of diisobutyl ketone as a developing solution. To form a resist pattern. For the obtained resist pattern, the CD value, LWR value and LER value were measured and calculated. The results are shown in Table 2.

(Comparative example 4)
A positive resist composition was prepared in the same manner as in Comparative Example 3 except that the copolymer A was replaced by the copolymer B prepared in the same manner as in Example 7 in the determination of the optimum exposure dose of extreme ultraviolet rays. Preparation, formation of a resist film, and creation of data on the relationship between irradiation dose and CD value, LWR value, and LER value were performed. The obtained data was then used to determine the optimal exposure dose. The results are shown in Table 2.
Then, in forming the resist pattern, a resist pattern was formed in the same manner as in Comparative Example 3 except that the resist film was exposed with the optimum exposure amount (extreme ultraviolet rays: 46 mJ/cm ² ). For the obtained resist pattern, the CD value, LWR value and LER value were measured and calculated. The results are shown in Table 2.

(Comparative example 5)
In the determination of the optimum exposure dose of extreme ultraviolet rays, the copolymer A and the positive electrode were prepared in the same manner as in Example 1 except that heptyl acetate (ZED-N70 manufactured by Nippon Zeon Co., Ltd.) was used instead of diisobutyl ketone as the developing solution. A resist composition was prepared, a resist film was formed, and data on the relationship between the dose and the CD value, LWR value, and LER value was prepared. The obtained data was then used to determine the optimal exposure dose. The results are shown in Table 2.
Then, in forming the resist pattern, Example 1 was repeated except that the resist film was exposed with an optimum exposure amount (extreme ultraviolet ray: 54.5 mJ/cm ² ) and the above-mentioned heptyl acetate was used instead of diisobutyl ketone as a developing solution. A resist pattern was formed in the same manner as in. For the obtained resist pattern, the CD value, LWR value and LER value were measured and calculated. The results are shown in Table 2.

(Comparative example 6)
In the determination of the optimum exposure dose of extreme ultraviolet rays, the copolymer B and the positive electrode were prepared in the same manner as in Comparative Example 4 except that heptyl acetate (ZED-N70 manufactured by Nippon Zeon Co., Ltd.) was used as the developing solution instead of hexyl acetate. A resist composition was prepared, a resist film was formed, and data on the relationship between the dose and the CD value, LWR value, and LER value was prepared. The obtained data was then used to determine the optimal exposure dose. The results are shown in Table 2.
Then, in forming the resist pattern, the same as in Comparative Example 4 except that the resist film was exposed with an optimum exposure amount (extreme ultraviolet ray: 58 mJ/cm ² ) and the above-mentioned heptyl acetate was used instead of hexyl acetate as a developing solution. To form a resist pattern. For the obtained resist pattern, the CD value, LWR value and LER value were measured and calculated. The results are shown in Table 2.

(Comparative Example 7)
<Preparation of positive resist composition>
The copolymer A obtained in the same manner as in Example 1 was dissolved in anisole as a solvent to prepare a solution having a concentration of the copolymer A of 11% by mass (positive resist composition).

<Formation of resist film>
Using a spin coater (MS-A150, manufactured by Mikasa), a positive resist composition having a concentration of 11 mass% was applied on a silicon wafer having a diameter of 4 inches so as to have a film 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.

<Determination of optimum exposure dose of electron beam>
Using an electron beam drawing device (ELS-S50 manufactured by Elionix Co., Ltd.), a plurality of patterns (dimensions 500 μm×500 μm) having different irradiation doses of electron beams were drawn on the resist film, and diisobutyl ketone (Japan) was used as a resist developer. Using Z-K, K-90), the development temperature was 23° C. and the development time was 60 seconds to carry out the development treatment. Then, rinsing was performed for 10 seconds using isopropyl alcohol. The irradiation amount of the electron beam was varied in the range of 100 .mu.C / cm ² of 500μC / 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 VM-1200, manufactured by SCREEN Semiconductor Solutions Co., Ltd.), and the common logarithm of the total electron beam irradiation amount and the resist film after development were measured. And a residual film ratio (=film thickness of resist film after development/film thickness of resist film formed on silicon wafer) were prepared.
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≦remaining film ratio≦1.00)), residual film ratio was 0.20 to 0. The sensitivity curve was fitted to a quadratic function in the range of 0.80, and the obtained quadratic function (a function of the residual film rate and the common logarithm of the total irradiation) at which the residual film ratio was 0 and the residual film ratio was 0.8. A straight line (an approximate line of the slope of the sensitivity curve) connecting the 50 points was created. After that, the total irradiation dose (μC/cm ² ) of the electron beam when the residual film ratio became 0 on the created straight line (an approximate line of the slope of the sensitivity curve) was calculated. The approximate exposure dose in patterning was calculated from the total exposure dose of the electron beams, and the exposure dose with the best pattern shape was determined as the optimum exposure dose. The results are shown in Table 2.

<Formation of resist pattern>
[Exposure, development and rinse]
The resist film is exposed with an optimum exposure amount (electron beam: 400 μC/cm ² ) using an electron beam drawing device (ELS-S50 manufactured by Elionix Co., Ltd.), and the development time is changed to 60 seconds and the rinse time is changed to 10 seconds. Other than the above, the same operation as in Example 1 was performed, but the resist pattern could not be formed. The results are shown in Table 2.

In Tables 1 and 2,
"EUV" indicates extreme ultraviolet rays,
“EB” indicates an electron beam,
“DIK” indicates diisobutyl ketone,
“IPA” refers to isopropyl alcohol.
It should be noted that the smaller the value of the optimum exposure amount, the higher the sensitivity of the resist film.

The following can be seen from Tables 1 and 2.
From Examples 1 to 8, it can be seen that when forming a resist pattern using a predetermined copolymer as a positive resist, if extreme ultraviolet rays and diisobutyl ketone as a developing solution are used, a resist pattern with high resolution can be obtained.
Further, from Comparative Example 1, when a predetermined copolymer is used as a positive resist to form a resist pattern, if extreme ultraviolet rays and amyl acetate as a developing solution are used, even a portion not irradiated with extreme ultraviolet rays will be dissolved. It can be seen that a fine resist pattern cannot be resolved.
Further, from Comparative Examples 2 to 6, in forming a resist pattern using a predetermined copolymer as a positive resist, use of extreme ultraviolet rays and hexyl acetate and heptyl acetate as a developing solution produces a resist pattern with high resolution. You can see that it cannot be formed.
From Comparative Example 7, when a predetermined copolymer was used as a positive resist to form a resist pattern, even when diisobutyl ketone was used as a developing solution, a resist pattern was formed when an electron beam was used. I see that I can't.

Here, the reason why the fine resist pattern can be formed with high resolution in Examples 1 to 8 is not clear, but it is presumed that it is due to the following reason.
That is, even when the extreme ultraviolet rays that can suppress the exposure of the non-irradiated portion as compared with the electron beam are used, the resist film is slightly exposed to the extreme ultraviolet rays in the non-irradiated portion near the irradiated portion of the extreme ultraviolet rays Conceivable. It is considered that the smaller the line width of the resist pattern to be formed, the larger the exposure amount of the resist film in the unirradiated portion. Therefore, when forming a fine resist pattern having a half pitch of 16 nm, the copolymer in the resist film is exposed to an amount of light such that the main chain is broken in the unirradiated part near the extreme ultraviolet irradiation part. It is presumed to receive. In this case, when amyl acetate, hexyl acetate or heptyl acetate is used as the developing solution as in Comparative Examples 1 to 6, the resist film in the unirradiated portion is dissolved in the developing solution, and the pattern cannot be resolved well. However, by using diisobutyl ketone (alkyl ketones represented by the formula (I)), only the resist film in the portion irradiated with extreme ultraviolet rays can be dissolved well, so that a fine resist pattern can be formed with high resolution. It is thought to be possible.

According to the present invention, a fine resist pattern can be efficiently formed with high resolution.

Claims (4)

A resist film forming step of forming a resist film using a positive resist composition containing a copolymer and a solvent;
An exposure step of exposing the resist film to extreme ultraviolet rays,
And a developing step of developing the exposed resist film with a developing solution,
The copolymer contains an α-alkylstyrene unit and an α-chloroacrylic acid ester unit, and the proportion of components having a molecular weight of more than 70,000 is 90% or more,
The developer has the following general formula (I):
^{R 1 -C (= O) -R} 2 ··· (I)
(In the formula (I), R ¹ and R ² each independently represent an alkyl group which may have a substituent.)
A method for forming a resist pattern, which comprises an alkylketone represented by: The resist pattern forming method according to claim 1, wherein at least one of R ¹ and R ² is a branched alkyl group. The resist pattern forming method according to claim 1, wherein the alkyl ketones include diisobutyl ketone. The resist pattern forming method according to claim 1, wherein a proportion of a component having a molecular weight of more than 80,000 in the copolymer is 80% or more.