JP7218548B2 - Resist pattern forming method - Google Patents

Description

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

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

For example, in Patent Document 1, α-methylstyrene/methyl α-chloroacrylate containing an α-methylstyrene unit and a methyl α-chloroacrylate unit is disclosed as a high-sensitivity main chain scission type positive resist. A positive resist comprising a copolymer is disclosed.

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

In recent years, EUV lithography technology using extreme ultraviolet (EUV) has attracted attention as a technology that enables the formation of fine patterns with less proximity effect during exposure compared to electron beams. there is Then, for example, in Non-Patent Document 1, a positive resist containing an α-methylstyrene/α-methyl-α-chloroacrylate copolymer containing α-methylstyrene units and methyl α-chloroacrylate units is used. The resist film is evaluated for patterning performance when exposed to extreme ultraviolet rays.

Japanese Patent Publication No. 8-3636 WO2013/145695

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 attempted to form a fine resist pattern using the EUV lithography technique, they found that the positive resist made of the above-mentioned conventional α-methylstyrene/α-methyl chloroacrylate copolymer and the above-mentioned conventional positive resist. It has become clear that it is difficult to form a resist pattern with high resolution using a developer.

SUMMARY OF THE INVENTION Accordingly, 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 made intensive studies to achieve the above object. Then, the present inventors formed a resist film using a positive resist composition containing a predetermined copolymer, exposed the obtained resist film to extreme ultraviolet rays, and then treated the exposed resist film with a predetermined The inventors have found that a fine resist pattern can be formed with high resolution by developing with a developer, and have completed the present invention.

That is, an object of the present invention is to advantageously solve the above problems, and a method for forming a resist pattern of the present invention comprises 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 developer, wherein the copolymer contains α-alkylstyrene units and , an α-chloroacrylate unit, a weight average molecular weight of 6.7×10 ⁴ or more, a proportion of components having a molecular weight of less than 40,000 is 40% or less, and a proportion of components having a molecular weight of more than 100,000 is 27% or less, and the developer has the following general formula (I):
R ¹ -C(=O)-R ² (I)
(In Formula (I), R ¹ and R ² each independently represent an optionally substituted alkyl group). Thus, the ratio of components containing α-alkylstyrene units and α-chloroacrylate units, having a weight average molecular weight of 6.7×10 ⁴ or more, and having a molecular weight of less than 40,000 is 40% or less. A resist film is formed using a resist composition containing a copolymer having a molecular weight of more than 100,000 and the proportion of components having a molecular weight of more than 100,000 is 27% or less, the resulting resist film is exposed to extreme ultraviolet rays, and then the exposed resist A fine resist pattern can be formed with high resolution by developing the film with a developer containing the alkyl ketones represented by the formula (I).

In addition, in this invention, a "weight average molecular weight" can be measured as a standard polystyrene conversion value using a gel permeation chromatography. In the present invention, the "ratio of components having a molecular weight of less than 40,000" uses a chromatogram obtained by gel permeation chromatography, and the total area of peaks in the chromatogram (A) is 40,000 in the chromatogram. It can be obtained by calculating the ratio of the total (B) of the peak areas of the components below (=(B/A)×100%). Furthermore, in the present invention, the "percentage of components with a molecular weight exceeding 100,000" uses a chromatogram obtained by gel permeation chromatography, and the total area of peaks in the chromatogram (A) is 100,000 in the chromatogram. It can be obtained by calculating the ratio of the total (C) of the peak areas of the components exceeding (=(C/A)×100%).

Here, in the resist pattern forming method of the present invention, at least one of R ¹ and R ² in the alkyl ketones represented by formula (I) is preferably a branched alkyl group. In formula (I), if at least one of R ¹ and R ² is an alkyl ketone that is a branched alkyl group, the solubility of the resist film in a developer is improved, and the resolution of the resulting resist pattern is increased. be able to.

Moreover, in the resist pattern forming method of the present invention, it is preferable that the alkyl ketones include diisobutyl ketone. By using a developer containing diisobutyl ketone, the solubility of the resist film in the developer can be further improved, and the resolution of the obtained resist pattern can be further improved.

In the resist pattern forming method of the present invention, the molecular weight distribution (weight average molecular weight/number average molecular weight) of the copolymer is preferably 1.45 or less. If the molecular weight distribution of the copolymer is 1.45 or less, it is possible to form a resist pattern in which the occurrence of bridging defects (bridging between adjacent patterns) is suppressed.

Furthermore, in the resist pattern forming method of the present invention, it is preferable that the proportion of the component having a molecular weight of less than 40,000 is 15% or more and 30% or less. If the ratio of the component having a molecular weight of less than 40,000 in the copolymer is within the above range, it is possible to form a resist pattern in which the occurrence of open defects (pattern discontinuity) is suppressed.

Moreover, in the method of forming a resist pattern of the present invention, it is preferable that the proportion of the component having a molecular weight of more than 100,000 is 18% or more. If the proportion of the component having a molecular weight of more than 100,000 in the copolymer is equal to or higher than the above lower limit, it is possible to form a resist pattern in which the generation of bridging defects is further suppressed.

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

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail.
Here, the method for forming a resist pattern of the present invention is a method for forming a resist pattern using a main chain scission type positive resist whose main chain is scissed to reduce the molecular weight by irradiation with extreme ultraviolet rays. It can be suitably used when forming a resist pattern in the manufacturing process of printed boards such as up boards, semiconductors, photomasks, molds, and the like.

(Method for forming resist pattern)
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 developer (development step). In addition, the resist pattern forming method of the present invention may optionally further include a rinse step for removing the developer after the developing step.

Further, in the method of forming a resist pattern of the present invention, a combination of a predetermined polymer, extreme ultraviolet rays, and a predetermined developer is used, so that a fine resist pattern can be formed with high resolution.
In addition, 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 a high resolution unless a prescribed polymer and a prescribed developer are used in combination.

<Resist film forming process>
In the resist film forming step, a positive resist composition is applied onto a workpiece such as a substrate to be processed using a resist pattern, and the applied positive resist composition is dried to form a resist film. .
The substrate is not particularly limited, and a substrate having an insulating layer and a copper foil provided on the insulating layer, which is used for manufacturing a printed circuit board, and a light shielding layer formed on the substrate. Mask blanks or the like can be used.
Moreover, the coating method and the drying method of the positive resist composition are not particularly limited, and methods generally used for forming a resist film can be used.
Furthermore, the film thickness of the resist film may be appropriately adjusted according to 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.
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 is 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 formation conditions of the resist film.
In the pattern forming method of the present invention, the following positive resist composition is used.

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

[Copolymer]
The copolymer contained in the positive resist composition is an α-alkylstyrene/α-chloroacrylate copolymer containing α-alkylstyrene units and α-chloroacrylate units. The average molecular weight, the proportion of components with molecular weights less than 40,000, and the proportion of components with molecular weights greater than 100,000 are required to be within specified ranges.
Since the copolymer contains a structural unit (α-chloroacrylate unit) derived from α-chloroacrylate having a chloro group (-Cl) at the α-position, it is exposed to extreme ultraviolet rays. Then, the main chain is easily cleaved to lower the molecular weight. In addition, the copolymer has a weight-average molecular weight, a proportion of a component with a molecular weight of less than 40,000, and a proportion of a component with a molecular weight of more than 100,000 within a predetermined range, so that a fine resist pattern can be formed with high resolution. be able to.

<α-alkylstyrene unit>
Here, the α-alkylstyrene unit is a structural unit derived from α-alkylstyrene. Since the copolymer used in the positive resist composition has α-alkylstyrene units, it exhibits excellent dry etching resistance due to the protection stability of the benzene ring when used as a positive resist. do.

The α-alkylstyrene units that can constitute the copolymer are not particularly limited, and examples thereof include α-methylstyrene units, α-ethylstyrene units, α-propylstyrene units, α-butylstyrene units, and the like. and an α-alkylstyrene unit in which a linear alkyl group having 4 or less carbon atoms is bonded to the α carbon. Among them, the α-alkylstyrene unit is preferably an α-methylstyrene unit from the viewpoint of enhancing dry etching resistance.
Further, the copolymer may have only one type of the unit described above as the α-alkylstyrene unit, or may have two or more types.

The copolymer preferably contains 30 mol % or more and 70 mol % or less of α-alkylstyrene units.

<α-chloroacrylate unit>
The α-chloroacrylate unit is a structural unit derived from α-chloroacrylate. Since the copolymer used in the positive resist composition has α-chloroacrylate units, when exposed to extreme ultraviolet rays, chlorine atoms are eliminated and the main chain is easily separated by a β-cleavage reaction. is disconnected.

The α-chloroacrylic acid ester unit that can constitute the copolymer is not particularly limited, and examples thereof include α-chloroacrylic acid units such as methyl α-chloroacrylate units and ethyl α-chloroacrylate units. Alkyl ester units and the like are included. Among them, from the viewpoint of increasing the sensitivity of a resist film formed using a positive resist composition, the α-chloroacrylate unit is preferably the α-methyl chloroacrylate unit.
Here, the copolymer may have only one type of the unit described above as the α-chloroacrylate unit, or may have two or more types.

The copolymer used in the positive resist composition preferably contains 30 mol % or more and 70 mol % or less of α-chloroacrylate units.

The copolymer used in the positive resist composition may contain monomer units other than α-alkylstyrene units and α-chloroacrylate units, but all The ratio of the α-alkylstyrene units and the α-chloroacrylate units in the monomer units (100 mol%) is preferably 90 mol% or more in total, and is 100 mol% (that is, the co- More preferably, the polymer contains only α-alkylstyrene units and α-chloroacrylate units. Copolymers with a large total content of α-alkylstyrene units and α-chloroacrylate units, especially copolymers whose monomer units consist only of α-alkylstyrene units and α-chloroacrylate units , can be suitably used as a positive resist.

<Proportion of components with a molecular weight of less than 40,000>
The copolymer used in the positive resist composition must contain 40% or less of components having a molecular weight of less than 40,000, preferably 15% or more and 30% or less. If the proportion of components having a molecular weight of less than 40,000 is 40% or less, a fine resist pattern can be formed with high resolution. If the ratio of the component having a molecular weight of less than 40000 is 15% or more and 30% or less, it is possible to form a resist pattern in which the occurrence of open defects is suppressed.

<Proportion of components with a molecular weight exceeding 100,000>
The copolymer used in the positive resist composition should contain 27% or less, preferably 18% or more, of components having a molecular weight of more than 100,000. A fine resist pattern can be formed with high resolution if the ratio of components having a molecular weight of more than 100,000 is 27% or less. If the ratio of components having a molecular weight of more than 100,000 is 18% or more, a resist pattern can be formed in which the generation of bridging defects is suppressed.

<Weight average molecular weight>
The weight average molecular weight (Mw) of the copolymer used in the positive resist composition must be 6.7×10 ⁴ or more, preferably 6.8×10 ⁴ or more, and 8.0 ×10 ⁴ or less is preferable, and 7.7×10 ⁴ or less is more preferable. If the weight average molecular weight (Mw) is 6.7×10 ⁴ or more, fine resist patterns can be formed with higher resolution.

<Number average molecular weight>
The number average molecular weight (Mn) of the copolymer used in the positive resist composition is preferably 4.5×10 ⁴ or more, more preferably 4.8×10 ⁴ or more. It is preferably 0×10 ⁴ or less, more preferably 5.5×10 ⁴ or less. If the number average molecular weight (Mn) is within the above range, a fine resist pattern can be formed with extremely high resolution.

<Molecular weight distribution>
The molecular weight distribution (Mw/Mn) of the copolymer used in the positive resist composition is preferably 1.45 or less, more preferably 1.44 or less, and 1.20 or more. is preferred, and 1.35 or more is more preferred. If the molecular weight distribution (Mw/Mn) of the copolymer used in the positive resist composition is 1.45 or less, the use of the positive resist composition containing the copolymer further suppresses the occurrence of bridging defects. be able to. Further, when the molecular weight distribution (Mw/Mn) of the copolymer used in the positive resist composition is 1.20 or more, the copolymer can be easily prepared.

(Method for preparing copolymer)
Then, the copolymer having the properties described above can be obtained, for example, after polymerizing a monomer composition containing α-alkylstyrene and α-chloroacrylate using a known polymerization method such as solution polymerization. , can be prepared by recovering the resulting copolymer and optionally purifying it.
The composition, molecular weight distribution, weight average molecular weight and number average molecular weight of the copolymer, and the ratio of each molecular weight component in the copolymer can be adjusted by changing the polymerization conditions and purification conditions. Specifically, for example, the weight average molecular weight and number average molecular weight can be decreased by increasing the polymerization temperature. Also, the weight average molecular weight and number average molecular weight can be reduced by shortening the polymerization time.

<Polymerization of Monomer Composition>
Here, the monomer composition used for preparing the copolymer includes a monomer containing α-alkylstyrene and α-chloroacrylate, a polymerization initiator, an optionally added solvent, and an optional It is possible to use mixtures with additives added to the Polymerization of the monomer composition can then be carried out using known methods. Among them, cyclopentanone or the like is preferably used as the solvent, and a radical polymerization initiator such as azobisisobutyronitrile is preferably used as the polymerization initiator.

The composition of the copolymer can be adjusted by changing the content ratio of each monomer in the monomer composition used for polymerization.

And the copolymer contained in the polymerization liquid obtained by polymerizing the monomer composition is not particularly limited, for example, after optionally adding a good solvent such as tetrahydrofuran to the polymerization liquid , the polymerization liquid is dropped into a poor solvent such as methanol to solidify the copolymer, and the solidified copolymer is separated using a solid-liquid separation means such as filtration (the solvent and remaining monomers, etc., are separated from the polymerization liquid). can be recovered by removing the reactants).
The method for recovering the copolymer is not limited to the method described above, and the copolymer may be recovered using a known method such as distilling off the solvent and unreacted substances. Moreover, the recovered copolymer can be purified as follows, if necessary.

<Purification of copolymer>
The purification method used for purifying the obtained copolymer to obtain a copolymer having the above-described properties is not particularly limited, and known purification methods such as reprecipitation and column chromatography can be used. can be used. Among them, it is preferable to use a reprecipitation method as the purification method.
In addition, the purification of the copolymer may be repeated several times.

Purification of the copolymer by the reprecipitation method is performed, for example, by dissolving the obtained copolymer in a good solvent such as tetrahydrofuran, and then mixing the resulting solution with a good solvent such as tetrahydrofuran and a poor solvent such as methanol. is added dropwise to the mixed solvent to precipitate a part of the copolymer. In this way, by purifying a copolymer by dropping a solution of a copolymer into a mixed solvent of a good solvent and a poor solvent, it is possible to obtain The molecular weight distribution, weight average molecular weight and number average molecular weight of the resulting copolymer, as well as the ratio of each molecular weight component in the copolymer can be easily adjusted. Specifically, for example, the higher the ratio of the good solvent in the mixed solvent, the greater the molecular weight of the copolymer that precipitates in the mixed solvent.

In the case of purifying the copolymer by the reprecipitation method, the copolymer used in the positive resist composition is a copolymer precipitated in a mixed solvent of a good solvent and a poor solvent, provided that the desired properties are satisfied. may be used, or a copolymer that did not precipitate in the mixed solvent (that is, a copolymer dissolved in the mixed solvent) may be used. Here, the copolymer that has not precipitated in the mixed solvent can be recovered from the mixed solvent using a known technique such as concentration to dryness.

<Solvent>
As the solvent contained in the positive resist composition used in the method for forming a resist pattern of the present invention, known solvents can be used as long as they are capable of dissolving the above-described copolymer. 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 solvents include cyclopentanone, methyl 3-methoxypropionate, methyl crotonate, and anisole. It preferably contains at least one selected from the group consisting of, and preferably contains anisole. Moreover, as a solvent, these components may be used individually by 1 type, and may be used in combination of 2 or more types by arbitrary ratios. Further, as described above, the solvent may be a mixture, but from the viewpoint of ease of recovery and reuse of the solvent, it is preferably a single solvent made of a single substance.

<Exposure process>
In the exposure step, the resist film formed in the resist film formation 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, preferably 13.5 nm.
Also, a known exposure apparatus such as EQ-10M (manufactured by ENERGETIQ) and NXE (manufactured by ASML) can be used for extreme ultraviolet irradiation.
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 second or more and 180 seconds or less.

<Development process>
In the development step, the exposed resist film is developed using a prescribed developer, which will be described in detail below. Specifically, the resist film exposed in the exposure step is brought into contact with a developer to develop the resist film, thereby forming a resist pattern on the workpiece.
Here, the method for bringing the resist film into contact with the developer is not particularly limited, and known techniques such as immersion of the resist film in the developer and application of the developer to the resist film can be used. can.

[Developer]
The developer used in the development step has the following general formula (I):
R ¹ -C(=O)-R ² (I)
It is necessary to contain alkyl ketones represented by.

In formula (I), R ¹ and R ² each independently represent an optionally substituted alkyl group. In the present invention, "optionally having a substituent" means "unsubstituted or having a substituent". In addition, when the alkyl group represented by R ¹ and R ² has a substituent, the number of carbon atoms in the alkyl group having the substituent does not include the number of carbon atoms in the substituent. In the present invention, the "alkyl group" means a chain (linear or branched) saturated hydrocarbon group, and the "alkyl group" includes a cyclic saturated hydrocarbon group "cycloalkyl "base" shall not be included.

Here, in formula (I), the alkyl group of the optionally substituted alkyl group represented by R ¹ and R ² includes a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, linear alkyl groups such as hexyl; branched alkyl groups such as isopropyl, isobutyl, and tert-butyl; Among them, the alkyl group preferably has 1 or more and 10 or less carbon atoms, more preferably 6 or less, and even more preferably 4 or less.

Further, from the viewpoint of improving the solubility of the resist film in a developer, at least one of R ¹ and R ² in formula (I) is preferably a branched alkyl group, and both are branched alkyl groups. is more preferable.

In formula (I), the substituents of the optionally substituted alkyl group represented by R ¹ and R ² include halogen atoms such as a fluorine atom, a chlorine atom and a bromine atom; a methoxy group; alkoxy group such as ethoxy group; nitro group, cyano group; and the like.

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

Among these, from the viewpoint of further improving the solubility of the resist film in the developer, the alkyl ketones represented by the formula (I) include diisopropyl ketone, diisobutyl ketone, diisopentyl ketone, tert-butyl methyl ketone, and the like. , In formula (I), at least one of R ¹ or R ² is preferably a branched alkyl ketone, such as diisopropyl ketone, diisobutyl ketone, diisopentyl ketone, etc., of formula ( In I), it is more preferable to contain branched alkyl ketones in which both R ¹ and R ² are branched alkyl groups, more preferably to contain diisobutyl ketone, and particularly to use diisobutyl ketone alone. preferable.

Further, as the developer, the alkyl ketone represented by the formula (I) may be used in combination with a known developer commonly used in resist pattern formation.

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

[Development conditions]
Developing conditions such as developing temperature and developing time are not particularly limited and can be set as appropriate. For example, the development temperature is usually −20° C. or higher and 30° C. or lower, and can be, for example, 21° C. or higher and 25° C. or lower. The development time is usually 10 seconds or more and 2 minutes or less, preferably 45 seconds or less, and more preferably 30 seconds or less, although it depends on the development temperature. By setting the development time to 2 minutes or less, the resist pattern formation time can be shortened.

Then, according to the method of forming a resist pattern of the present invention, the resist film formed using the above-described copolymer is exposed to extreme ultraviolet rays, and developed using the above-described predetermined developer. A fine resist pattern of 50 nm or less, preferably 30 nm or less, more preferably 20 nm or less can be efficiently formed with high resolution.

According to the method of forming a resist pattern 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 A LER value (LER: Line Edge Roughness) representing 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 target of 16 nm half pitch, the CD value fluctuation is suppressed to 5% or less, the LWR value is 6 nm or less, and the LER value is 6 nm or less. values can be reduced to 5 nm or less. The CD value, LWR value and LER value can be measured, for example, by the methods described in the examples of this 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 solution after the developing step. Specifically, in the rinsing step, the resist film developed in the developing step is brought into contact with a rinsing liquid to rinse the developed resist film. By performing the rinsing step, the resist residue adhering to the developed resist film can be effectively removed.

Here, the method for bringing the developed resist film into contact with the rinse solution is not particularly limited, and known techniques such as immersion of the resist film in the rinse solution and application of the rinse solution to the resist film can be used. can be used.

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

EXAMPLES The present invention will be specifically described below 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 the examples and comparative examples, the weight average molecular weight, number average molecular weight and molecular weight distribution of the copolymer, the proportion of each molecular weight component in the copolymer, the optimum exposure dose, and the critical dimension of the line width of the resist pattern A CD value representing line width roughness, an LWR value representing line width roughness, and a LER value representing line end 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 number average molecular weight (Mn) of the resulting copolymer were measured using gel permeation chromatography, and the molecular weight distribution (Mw/Mn) was calculated.
Specifically, using a gel permeation chromatograph (manufactured by Tosoh Corporation, HLC-8220), using tetrahydrofuran as a developing solvent, the weight average molecular weight (Mw) and number average molecular weight (Mn) of the copolymer were measured using standard polystyrene. It was obtained as a converted value. Then, the molecular weight distribution (Mw/Mn) was calculated.

<Proportion of each molecular weight component in the copolymer>
A chromatogram of the copolymer was obtained using a gel permeation chromatograph (manufactured by Tosoh, HLC-8220) and using tetrahydrofuran as a developing solvent. Then, from the resulting chromatogram, the total peak area (A), the total peak area (B) of the components with a molecular weight of less than 40,000, and the total peak area (C) of the components with a molecular weight of more than 100,000 are obtained. rice field.
Then, the ratio of each molecular weight component was calculated using the following formula.
Percentage (%) of components with a molecular weight of less than 40000 = (B/A) x 100
Percentage (%) of components with a molecular weight exceeding 100,000 = (C/A) x 100

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

(Example 1)
<Preparation of copolymer>
[Polymerization of monomer composition]
3.0 g of methyl α-chloroacrylate and 6.88 g of α-methylstyrene as monomers, 39.564 g of cyclopentanone as a solvent, and 0.0109 g of azobisisobutyronitrile as a polymerization initiator was placed in a glass container, the glass container was sealed and replaced with nitrogen, and stirred in a constant temperature bath at 75° C. for 48 hours under a nitrogen atmosphere. Thereafter, the temperature was returned to room temperature, and after the inside of the glass container was opened to the atmosphere, 30 g of tetrahydrofuran (THF) was added to the obtained solution. Then, the solution containing THF was dropped into 300 g of methanol to precipitate a polymer (unpurified copolymer). After that, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white coagulate (polymer). The obtained polymer contained 50 mol % each of α-methylstyrene units and α-methyl chloroacrylate units.

[Purification of polymer]
Next, the resulting polymer was dissolved in 100 g of THF, and the resulting solution was added dropwise to a mixed solvent of 600 g of THF and 400 g of methanol (MeOH) to produce a white coagulate (α-methylstyrene units and α-chloroacryl A copolymer containing methyl acid units) was precipitated. Thereafter, the solution containing the precipitated copolymer was filtered through a Kiriyama funnel to obtain a white copolymer. Then, the weight average molecular weight, number average molecular weight, molecular weight distribution, and ratio of each molecular weight component in the copolymer were measured for the obtained copolymer. Table 1 shows the results.

<Preparation of positive resist composition>
The resulting 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% by mass was applied to a silicon wafer with a diameter of 12 inches to form a film. It was coated so as to be 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.

<Determining the optimum exposure amount of extreme ultraviolet rays>
Using an EUV drawing device (manufactured by ASML, TWINSCAN NXE: 3300B), a plurality of patterns (size 10 mm × 10 mm) with different irradiation doses of extreme ultraviolet rays are drawn on the resist film, and diisobutyl ketone (Nippon Zeon Co., Ltd.) is used as a developer. (K-90), developed at a developing temperature of 23° C. for a developing time of 30 seconds. After that, isopropyl alcohol was used as a rinsing liquid to rinse for 15 seconds. The irradiation amount of extreme ultraviolet rays was varied by 10 mJ/cm ² within the 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 irradiation dose of 80 mJ/cm ² at which a pattern with a CD value closest to 16 nm was formed, the irradiation dose of extreme ultraviolet rays was adjusted at a pitch of 0.1 mJ/cm ² within a range of plus or minus 10 mJ/cm ² . The CD value, LWR value, and LER value of the resulting resist pattern were measured and calculated by drawing patterns in the same manner as described above.
Using the data on the relationship between the obtained irradiation dose and the CD value, LWR value, and LER value, the optimum exposure dose of extreme ultraviolet rays (CD value is in the range of 16 nm ± 0.5 nm, LWR value and LER value are good) was determined. Table 1 shows the results.

<Formation of resist pattern>
[Exposure, development and rinse]
Using an EUV lithography system (manufactured by ASML, TWIN SCAN NXE: 3300B), the resist film was exposed with an optimum exposure dose (extreme ultraviolet rays: 80 mJ/cm ² ) to draw a pattern (exposure step). As the resist film, the resist film formed as described above was used. In addition, when drawing (patterning) the pattern, both lines (unexposed regions) and spaces (exposed regions) of the resist pattern were 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 developer, and development was performed at a development temperature of 23° C. and a development time of 30 seconds (development process).
After that, it was rinsed with isopropyl alcohol for 15 seconds (rinsing step) to form a resist pattern. Then, the CD value, LWR value and LER value of the obtained resist pattern were measured and calculated. Table 1 shows the results.

(Example 2)
A copolymer and a positive resist composition were prepared in the same manner as in Example 1, except that the development temperature was changed to 7° C., the development time to 25 seconds, and the rinse time to 30 seconds in determining the optimum exposure dose of extreme ultraviolet rays. 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 data obtained was then used to determine the optimum exposure dose. Table 1 shows the results.
Then, in forming the resist pattern, the resist film was exposed to the optimum exposure dose (extreme ultraviolet rays: 100 mJ/cm ² ), and the development temperature was changed to 7 ° C., the development time was changed to 25 seconds, and the rinse time was changed to 30 seconds. , a resist pattern was formed in the same manner as in Example 1. The CD value, LWR value and LER value of the obtained resist pattern were measured and calculated. Table 1 shows the results.

(Comparative example 1)
In the determination of the optimum exposure dose of extreme ultraviolet rays, a copolymer and a positive type 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 a developer. 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 created. The data obtained was then used to determine the optimum exposure dose. Table 1 shows the results.
Then, in forming the resist pattern, the same procedure as in Example 1 was performed, except that the resist film was exposed to the optimum exposure dose (extreme ultraviolet rays: 30 mJ/cm ² ), and the amyl acetate was used instead of diisobutyl ketone as the developer. However, the resist film was completely dissolved and resolution could not be achieved. Table 1 shows the results.

(Comparative example 2)
In the determination of the optimum exposure dose of extreme ultraviolet rays, the copolymer and the positive type were prepared in the same manner as in Example 1, except that hexyl acetate (ZED-N60, manufactured by Nippon Zeon Co., Ltd.) was used instead of diisobutyl ketone as the developer. 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 created. The data obtained was then used to determine the optimum exposure dose. Table 1 shows the results.
Then, in forming the resist pattern, the same procedure as in Example 1 was performed, except that the resist film was exposed to the optimum exposure dose (extreme ultraviolet rays: 42 mJ/cm ² ) and the hexyl acetate was used as the developer instead of diisobutyl ketone. However, the resist film was completely dissolved and resolution could not be achieved. Table 1 shows the results.

(Comparative Example 3)
<Preparation of positive resist composition>
The copolymer obtained in Example 1 was dissolved in anisole as a solvent to prepare a solution (positive resist composition) having a copolymer concentration of 11 mass %.

<Formation of resist film>
Using a spin coater (manufactured by Mikasa, MS-A150), a positive resist composition having a concentration of 11% by mass was applied onto a silicon wafer having a diameter of 4 inches to a film thickness of 500 nm. Then, the applied positive resist composition was heated on a hot plate at a temperature of 160° C. for 5 minutes to form a resist film on the silicon wafer.

<Determination of optimum exposure dose of electron beam>
Using an electron beam lithography system (Elionix, ELS-S50), a plurality of patterns (dimensions 500 μm × 500 μm) with different electron beam irradiation doses are drawn on the resist film. Development processing was performed using K-90 manufactured by Zeon Co., Ltd. at a development temperature of 23° C. and a development time of 60 seconds. After that, isopropyl alcohol was used as a rinsing liquid to rinse for 10 seconds. The dose of the electron beam was varied by 4 μC/cm ² within the range of 100 μC/cm ² to 500 μC/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.). A sensitivity curve showing the relationship between the residual film ratio (=thickness of the resist film after development/thickness of the resist film formed on the silicon wafer) was prepared.
Regarding the resulting sensitivity curve (horizontal axis: common logarithm of the total electron beam dose, vertical axis: residual film ratio of the resist film (0≦remaining film ratio≦1.00)), the residual film ratio is 0.20 to 0. The sensitivity curve was fitted to a quadratic function in the range of 0.80. A straight line connecting the 50 points (an approximation line of the slope of the sensitivity curve) was created. After that, the total irradiation dose (μC/cm ² ) of the electron beam was calculated when the residual film rate was 0 on the created straight line (the approximation line of the slope of the sensitivity curve). The approximate exposure dose in patterning was calculated from the total irradiation dose of the electron beam, and the exposure dose with the best pattern shape was determined as the optimum exposure dose. Table 1 shows the results.

<Formation of resist pattern>
[Exposure, development and rinse]
Using an electron beam lithography system (Elionix, ELS-S50), the resist film was exposed with the optimum exposure dose (electron beam: 370 μC/cm ² ), and the development time was changed to 60 seconds and the rinse time to 10 seconds. The same operation as in Example 1 was performed except that a resist pattern could not be formed. Table 1 shows the results.

In addition, in Table 1,
"EUV" indicates extreme ultraviolet,
"EB" indicates electron beam,
"IPA" indicates isopropyl alcohol.
It should be noted that the smaller the optimum exposure value, the higher the sensitivity of the resist film.

Table 1 shows the following.
From Examples 1 and 2, it can be seen that a high-resolution resist pattern can be obtained by using extreme ultraviolet rays and diisobutyl ketone as a developer in forming a resist pattern using a predetermined copolymer as a positive resist.
Further, from Comparative Examples 1 and 2, when forming a resist pattern using a predetermined copolymer as a positive resist, extreme ultraviolet rays and amyl acetate or hexyl acetate as a developer were used, the area not irradiated with extreme ultraviolet rays It can be seen that the fine resist pattern cannot be resolved.
Furthermore, from Comparative Example 3, in forming a resist pattern using a predetermined copolymer as a positive resist, even when diisobutyl ketone was used as a developer, when an electron beam was used, a resist pattern was formed. I know you can't.

Here, the reason why a fine resist pattern can be formed with high resolution in Example 1 is not clear, but it is presumed to be due to the following reason.
That is, even in the case of using extreme ultraviolet rays that can suppress the exposure of non-irradiated portions by comparing electron beams, it is possible that the resist film is slightly exposed to extreme ultraviolet rays in the non-irradiated portions in the vicinity of the portions irradiated with extreme ultraviolet rays. Conceivable. It is believed that the narrower the line width of the resist pattern to be formed, the greater the amount of exposure of the resist film in the non-irradiated portion. Therefore, when forming a fine resist pattern with a half pitch of 16 nm, the copolymer in the resist film is exposed to an amount that cuts the main chain in the non-irradiated portion near the irradiated portion of extreme ultraviolet rays. presumed to receive. In this case, if amyl acetate or hexyl acetate, which is the conventional developer used in the comparative example, is used, the resist film in the non-irradiated portion is dissolved in the developer, so that the pattern cannot be resolved. However, by using diisobutyl ketone (alkyl ketones), it is possible to satisfactorily dissolve only the resist film in the portion irradiated with extreme ultraviolet rays, so it is thought that a fine resist pattern can be formed with high resolution.

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;
A developing step of developing the exposed resist film with a developer,
The copolymer contains α-alkylstyrene units and α-chloroacrylate units, has a weight-average molecular weight of 6.7×10 ⁴ or more, and contains 40% of components having a molecular weight of less than 40,000. or less, and the proportion of components having a molecular weight of more than 100,000 is 27% or less,
The developer has the following general formula (I):
R ¹ -C(=O)-R ² (I)
(In formula (I), R ¹ and R ² each independently represent an optionally substituted alkyl group.)
Including alkyl ketones represented by
The α-chloroacrylate ester unit is a methyl α-chloroacrylate unit,
The resist pattern forming method , wherein the developer is diisobutyl ketone . 2. The method of forming a resist pattern according to claim 1 , wherein the copolymer has a molecular weight distribution (weight average molecular weight/number average molecular weight) of 1.45 or less. 3. The method of forming a resist pattern according to claim 1 , wherein the proportion of said component having a molecular weight of less than 40000 is 15% or more and 30% or less. 4. The method of forming a resist pattern according to any one of claims 1 to 3 , wherein the proportion of the component having a molecular weight of over 100,000 is 18% or more.