JP2024055412A - Negative resist material composed of silsesquioxane with cage structure, and negative resist composition comprising silsesquioxane with cage structure - Google Patents

Abstract

To provide a negative resist material composed of silsesquioxane with a cage structure, which demonstrates enhanced resistance to dry etching when exposed to short-wavelength light sources such as electron beams and extreme ultraviolet light (EUV), thereby facilitating the generation of fine patterns.SOLUTION: A negative resist material is composed of silsesquioxane with a cage structure, represented by formula 1: (RmSiO1.5)n. (In formula 1, n is an integer of 3-30, and Rm includes a structure represented by formula 2, where R1 denotes an alkyl group, a cycloalkyl group, an aryl group, or an aralkyl group.)SELECTED DRAWING: None

Description

The present invention relates to a negative resist material comprising a silsesquioxane having a cage structure and a negative resist composition containing a silsesquioxane having a cage structure.

Silsesquioxanes with a cage structure have a rigid polysiloxane skeleton and a molecular size at the sub-nano level, which gives them high transparency, heat resistance, surface hardness, scratch resistance, mechanical strength, etc., and they are being investigated for use as hard coat materials, heat-resistant materials, resist materials, etc.
For example, Patent Document 1 listed below describes a resist composition for lithography that contains silsesquioxane having a cage structure.

JP 2013-28743 A

However, the resist composition described in Patent Document 1 is insufficient for dealing with lithography using a short wavelength light source such as an electron beam or extreme ultraviolet light (EUV) in line with the recent trend toward thinner circuit patterns.
Therefore, an object of the present invention is to solve these problems and to provide a negative resist material comprising a silsesquioxane having a new cage structure, and a negative resist composition containing a silsesquioxane having a cage structure.

The present invention has the following aspects:

[1] A negative resist material comprising a silsesquioxane having a cage structure represented by the following formula 1:
( _RmSiO1.5 ) _n (Formula 1)
(In formula 1, n is an integer of 3 to 30, and Rm includes a structure represented by formula 2 below.

Ｒ^１はアルキル基、シクロアルキル基、アリール基、アラルキル基のいずれかを示す。）

^R1 represents an alkyl group, a cycloalkyl group, an aryl group, or an aralkyl group.

[2] The negative resist material according to [1], in which Rm contains a group Rb that absorbs at least one of extreme ultraviolet light and an electron beam to generate secondary electrons.

[3] The negative resist material according to [1] or [2], in which Rm contains a group Rc having a lactone skeleton.

[4] A negative resist material according to any one of [1] to [3], in which Rm includes a group Rd having a hydrophilic group.

[5] A negative resist composition comprising a silsesquioxane having a cage structure represented by the following formula 1:
( _RmSiO1.5 ) _n (Formula 1)
(In formula 1, n is an integer of 3 to 30, and Rm includes a structure represented by formula 2 below.

Ｒ^１はアルキル基、シクロアルキル基、アリール基、アラルキル基のいずれかを示す。）

^R1 represents an alkyl group, a cycloalkyl group, an aryl group, or an aralkyl group.

[6] A method for forming a resist pattern using the negative resist composition described in [5].

The negative resist material made of the cage-structured silsesquioxane of the present invention can be used in a variety of applications, for example, by having two or more types of functional groups with different physical properties. In particular, the negative resist composition containing the cage-structured silsesquioxane of the present invention has excellent dry etching resistance and can form fine patterns when using a short-wavelength light source such as an electron beam or extreme ultraviolet light (EUV).

1 is a graph showing the relationship between exposure dose and film remaining rate in a resist pattern formed using a negative resist composition according to one embodiment of the present invention.

The present invention will be described based on one embodiment. However, the present invention is not limited to this embodiment.

[Negative resist material]
A negative resist material (hereinafter, also referred to as the present resist material) made of a silsesquioxane having a cage structure according to one embodiment of the present invention is represented by the following formula 1.
( _RmSiO1.5 ) _n (Formula 1)

In formula 1, n is an integer from 3 to 30, and Rm includes a structure represented by formula 2 below.

In the formula 2, R ¹ represents any one of an alkyl group, a cycloalkyl group, an aryl group, and an aralkyl group.

In order to form a fine pattern, it is preferable that the molecular size is small and the molecular chains are weakly entangled, and n is preferably 30 or less, and more preferably 20 or less. In terms of structural stability, n is preferably 3 or more, and more preferably 6 or more.

The mass average molecular weight (Mw)/number average molecular weight (Mn) (polystyrene equivalent by gel permeation chromatography) of this resist material is preferably 1.0 to 2.0, more preferably 1.0 to 1.8, in order to be able to form fine patterns.

The silsesquioxane having a cage structure of the present resist material is a cage structure with n vertices, expressed as (SiO _1.5 ) _n . Such a cage structure may be a complete cage silsesquioxane structure or an incomplete cage silsesquioxane structure. For example, the following compounds are examples of complete cage silsesquioxane structures:

Here, each vertex is a silicon atom containing one substituent, and each edge represents a Si-O-Si bond.

The resist material contains an organosilicon compound with a rigid chemical structure, which gives it, for example, excellent resistance to dry etching.

In this resist material, the Rm of the silsesquioxane contains a structure represented by the following formula 2:

In the formula 2, R ¹ represents any one of an alkyl group, a cycloalkyl group, an aryl group, and an aralkyl group.

By having the structure represented by formula 2, the resist composition is applied to a substrate or the like to form a resist film, and when the resist film is selectively exposed to light, a difference in solubility in an organic developer occurs between the exposed and unexposed areas, and a negative resist pattern is formed by developing the resist film.

The alkyl group preferably has 1 to 10 carbon atoms, and examples thereof include methyl, ethyl, propyl, isopropyl, n-butyl, s-butyl, t-butyl, hexyl, octyl, and decyl groups. At least one carbon atom in the alkyl group may be substituted with a heteroatom such as an oxygen atom.

The cycloalkyl group may be a monocyclic or polycyclic group. As the monocyclic group, a cycloalkyl group having 3 to 10 carbon atoms is preferable, and examples thereof include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cyclooctyl group, and a cyclodecyl group.
The polycyclic group is preferably a cycloalkyl group having 6 to 20 carbon atoms, such as an adamantyl group, a norbornyl group, an isobornyl group, a camphanyl group, a dicyclopentyl group, an α-pinel group, a tricyclodecanyl group, a tetracyclododecyl group, and an androstanyl group.

At least one carbon atom in the cycloalkyl group may be replaced by a heteroatom such as an oxygen atom.

The aryl group is preferably an aryl group having 6 to 20 carbon atoms, and examples thereof include a phenyl group, a naphthyl group, an anthryl group, and a fluorenyl group.
The aralkyl group is preferably an aralkyl group having 7 to 12 carbon atoms, and examples thereof include a benzyl group, a phenethyl group, and a naphthylmethyl group.

The alkenyl group is preferably an alkenyl group having 2 to 10 carbon atoms, such as a vinyl group, an allyl group, a butenyl group, or a cyclohexenyl group.

Rm may have Rb. Rb preferably has a group that absorbs at least one of extreme ultraviolet radiation and an electron beam to generate secondary electrons.

Furthermore, in the present resist material, Rb has a group that absorbs at least one of extreme ultraviolet radiation and an electron beam to generate secondary electrons, and therefore, when used as a resist that utilizes electron beams or extreme ultraviolet radiation, secondary electrons are generated efficiently, thereby achieving high sensitivity.
Examples of the "group that absorbs at least one of extreme ultraviolet radiation and an electron beam to generate secondary electrons" include groups containing metal elements such as tin, antimony, tellurium, xenon, cesium, and barium, and halogen elements such as fluorine and iodine.

From the viewpoint of ease of synthesis and availability, Rb is preferably a group containing a fluorine atom, such as a 2,2,3,3-tetrafluoropropyl group, a 1H,1H,5H-octafluoropentyl group, a 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl group, a 2,2,2-trifluoroethyl group, a 1H,1H-pentadecafluoro-n-octyl group, a 1H,1H,2H,2H-nonafluorohexyl group, a 1H,1H,2H,2H-tridecafluoro-n-octyl group, a 1H,1H,2H,2H-heptadecafluorodecyl group, a 1,1,1,3,3,3-hexafluoroisopropyl group, or a pentafluorophenyl group.

In the present resist material, it is more preferable that Rb contains a structure represented by the following formula 3 having an amino group, since this makes it easier to obtain a cage silsesquioxane.

In formula 3, ^R2 is a group containing a group that absorbs at least one of extreme ultraviolet radiation and an electron beam to generate secondary electrons.

The silsesquioxane having a cage structure in the present resist material may have, as Rm, a group Rc having a lactone skeleton.
Examples of lactone rings include lactone rings having about 4 to 20 members. The lactone ring may be a monocyclic lactone ring or a condensed ring in which an aliphatic or aromatic carbocyclic or heterocyclic ring is condensed to the lactone ring.

As Rc, from the viewpoint of excellent adhesion to a substrate or the like, at least one selected from the group consisting of a substituted or unsubstituted δ-valerolactone ring, and a substituted or unsubstituted γ-butyrolactone ring is preferable, and a group having an unsubstituted γ-butyrolactone ring is particularly preferable.
Specific examples of lactone rings include β-methyl-δ-valerolactone, 4,4-dimethyl-2-methylene-γ-butyrolactone, γ-butyrolactone, β-methyl-γ-butyrolactone, pantoyl lactone, 2,6-norbornane carbolactone, 4-oxatricyclo[5.2.1.02,6]decan-3-one, and 4-oxatricyclo[5.2.1.02,6]decan-3-one.

The lactone skeleton-containing group Rc may be used alone or in combination of two or more kinds.
When the silsesquioxane contains a group Rc having a lactone skeleton, the content thereof is preferably 5 mol % or more, more preferably 10 mol % or more, based on the total constitutional units. From the viewpoint of sensitivity and resolution, the content is preferably 80 mol % or less, more preferably 70 mol % or less.

The group Rc having a lactone skeleton does not have a group that absorbs at least one of extreme ultraviolet rays and electron beams to generate secondary electrons.

The silsesquioxane having a cage structure in the present resist material may have, as Rm, a group Rd having a hydrophilic group.
The "hydrophilic group" is at least one of a monovalent group represented by --C( _CF.sub.3 ) _.sub.2-- OH, a hydroxy group, a cyano group, a methoxy group, a carboxy group, and an amino group.

Examples of Rd include 2-hydroxyethyl, 3-hydroxypropyl, 2-hydroxy-n-propyl, 4-hydroxybutyl, 3-hydroxyadamantyl, 2- or 3-cyano-5-norbornyl, and 2-cyanomethyl-2-adamantyl groups.
From the viewpoint of adhesion to a substrate, etc., 3-hydroxyadamantyl, 3,5-dihydroxyadamantyl, 2- or 3-cyano-5-norbornyl, and 2-cyanomethyl-2-adamantyl groups are preferred.

The Rd may be used alone or in combination of two or more.
The Rd does not have a group that absorbs at least one of extreme ultraviolet rays and electron beams to generate secondary electrons, and does not have a lactone skeleton.
When the silsesquioxane having a cage structure contains the Rd, the content of the Rd is preferably 5 mol % or more, more preferably 10 mol % or more, based on the total constitutional units in terms of the rectangularity of the resist pattern, and is preferably 30 mol % or less, more preferably 25 mol % or less, in terms of sensitivity and resolution.

Next, an example of a method for producing the resist material will be described.
The silsesquioxane compound having a cage structure of the resist material is obtained by hydrolysis and co-condensation of a silane compound having Rm by a known method. In the present invention, the hydrolysis and co-condensation refers to a series of reactions in which two or more kinds of silane compounds are mixed with a predetermined amount of water and a catalyst, and the desired silsesquioxane compound is produced by hydrolysis of the alkoxysilyl group and the subsequent condensation reaction of the silanol group.

Suitable catalysts for the hydrolysis and co-condensation of silane compounds having Rm include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid, and quaternary ammonium salts such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, benzyltriethylammonium hydroxide, ammonium fluoride, tetrabutylammonium fluoride, benzyltrimethylammonium chloride, and benzyltriethylammonium chloride.

Among these, hydrofluoric acid and ammonium fluoride are particularly preferred since they specifically form a cage structure.
The amount of catalyst is preferably 0.001 to 1 times, more preferably 0.005 to 0.5 times, the theoretical total number of moles of hydrolyzable alkoxy groups of the silane compound having Rm. If it is 0.001 times or more, sufficient catalytic activity can be obtained. If it is 1 time or less, gelation can be suppressed.

The amount of water used for hydrolysis of the silane compound having Rm is preferably 0.1 to 10 times, more preferably 1 to 3 times, the theoretical total amount of the number of moles of hydrolyzable alkoxy groups.
The reaction temperature for hydrolysis and co-condensation is preferably 0 to 100° C., more preferably 20 to 50° C. If the reaction temperature is 0° C. or higher, the reaction proceeds sufficiently. If the reaction temperature is 100° C. or lower, there is little possibility of side reactions being induced or gelation being formed.

During hydrolysis and co-condensation, it is preferable to use an organic solvent. There are no particular limitations on the organic solvent as long as it can dissolve the silane compound having Rm, but examples include methyl alcohol, ethyl alcohol, isopropyl alcohol, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, 1-methoxy-2-propanol, and acetonitrile. These organic solvents may be used alone or in combination of two or more.

As the silane compound, those containing the structure represented by the following formula 2 or 3 having the above-mentioned amino group are more preferable because they can easily produce a cage-type silsesquioxane. For example, they can be produced by a Michael addition reaction between a silane compound containing an amino group and a monofunctional acrylate compound.

Examples of silane compounds containing amino groups include 3-(2-aminoethyl)aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and 3-aminopropyltriethoxysilane, with 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane being particularly preferred.

The monofunctional acrylate compound is an acrylate compound having any one of an alkyl group, a cycloalkyl group, an aryl group, and an aralkyl group in R ¹ in formula 2, and examples thereof include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, s-butyl acrylate, pentyl acrylate, 2-ethylhexyl acrylate, n-hexyl acrylate, t-butyl acrylate, 1-methylcyclopentyl acrylate, 1-methylcyclohexyl acrylate, cyclopentyl acrylate, cyclohexyl acrylate, isobornyl acrylate, dicyclopentanyl acrylate, phenyl acrylate, 4-methylphenyl acrylate, dimethylphenyl acrylate, benzyl acrylate, and phenethyl acrylate. From the viewpoints of developer solubility and availability when used as a silsesquioxane compound having a cage structure, methyl acrylate, ethyl acrylate, butyl acrylate, s-butyl acrylate, and t-butyl acrylate are preferred.

In addition, as the acrylate compound having a group that absorbs at least one of extreme ultraviolet rays and electron beams to generate secondary electrons in R ² in formula 3, 2,2,3,3-tetrafluoropropyl acrylate, 1H,1H,5H-octafluoropentyl acrylate, 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl acrylate, 2,2,2-trifluoroethyl acrylate, 1H,1H-pentadecafluoro-n-octyl acrylate, 1H,1H,2H,2H-nonafluorohexyl acrylate, 1H,1H,2H,2H-tridecafluoro-n-octyl acrylate, 1H,1H,2H,2H-heptadecafluorodecyl acrylate, 1,1,1,3,3,3-hexafluoroisopropyl acrylate, and pentafluorophenyl acrylate are particularly preferred from the viewpoint of availability.

This addition reaction may be carried out without a solvent, or a solvent may be used. Specific examples of the solvent include methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol, 1-butyl alcohol, 2-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, benzyl alcohol, 2-methoxyethyl alcohol, 2-ethoxyethyl alcohol, 2-(methoxymethoxy)ethanol, 2-butoxyethanol, furfuryl alcohol, tetrahydrofurfuryl alcohol, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether, diacetone alcohol, acetone, methyl ethyl ketone, 2-pentanone, 3-pentanone, 2-hexanone, methyl isobutyl ketone, 2-heptanone, 4-heptanone, diisobutyl ketone, cyclohexanone, and methylcyclohexanone. acetophenone, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, anisole, phenetole, tetrahydrofuran, tetrahydropyran, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, glycerin ether, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, acetic acid Examples of the alkyl ether acetate include sec-butyl acetate, pentyl acetate, isopentyl acetate, 3-methoxybutyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, methyl propionate, ethyl propionate, butyl propionate, γ-butyrolactone, 2-methoxyethyl acetate, 2-ethoxyethyl acetate, 2-butoxyethyl acetate, 2-phenoxyethyl acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, benzene, toluene, and xylene.
These solvents can be used alone or in combination of two or more kinds. The amount of each solvent used can be appropriately determined.

The reaction molar ratio of the amino group-containing silane compound to the monofunctional acrylate compound is preferably 2 to 10 moles, more preferably 2 to 5 moles, of the monofunctional acrylate compound per mole of the amino group-containing silane compound, because this makes it possible to reduce unreacted materials.
The temperature of the addition reaction is preferably 20 to 100° C., more preferably 30 to 80° C. If the temperature is 20° C. or higher, the addition reaction can proceed sufficiently. If the temperature is 100° C. or lower, the polymerization of the acrylate compound can be suppressed.

The time for the addition reaction is preferably 1 to 60 hours, and more preferably 2 to 48 hours. If it is 1 hour or more, the addition reaction can proceed sufficiently. If it is 60 hours or less, the polymerization of the acrylate compound can be suppressed.
In this addition reaction, a catalyst can be used, which may be any known catalyst used in the Michael addition reaction, such as amines or alkali metal alkoxides.
In order to suppress the polymerization of the acrylate compound, a polymerization inhibitor may be added to the reaction system. The type of the polymerization inhibitor is not particularly limited. One type of polymerization inhibitor may be used, or two or more types may be used in combination.
Examples of the polymerization inhibitor include phenolic compounds such as hydroquinone, p-methoxyphenol, 2,4-dimethyl-6-tert-butylphenol, 2,6-di-tert-butyl-p-cresol, 4-tert-butylcatechol, 2,6-di-tert-butyl-4-methylphenol, pentaerythritol tetrakis (3,5-di-tert-butyl-4-hydroxyhydrocinnamate), and 2-sec-butyl-4,6-dinitrophenol; N,N-diisopropylparaphenylenediamine, N,N-di-2-naphthylparaphenylenediamine, N-phenylene-N-(1 ,3-dimethylbutyl)paraphenylenediamine, N,N'-bis(1,4-dimethylphenyl)-paraphenylenediamine, N-(1,4-dimethylphenyl)-N'-phenyl-paraphenylenediamine, and other amine compounds; 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)sebacate, and other N-oxyl compounds; copper, copper(II) chloride, iron(III) chloride, and other metal compounds; and the like.
The amount of the polymerization inhibitor used can be appropriately set. For example, it is preferably 20 ppm or more relative to the acrylate compound, and more preferably 50 ppm or more to obtain a sufficient polymerization inhibitory effect. On the other hand, from the viewpoint of cost, the amount of the polymerization inhibitor used is preferably 10,000 ppm or less, more preferably 5,000 ppm or less.

Regarding the purification method after the completion of this addition reaction, known purification methods such as separation, water washing, distillation, crystallization, and filtration can be appropriately combined, taking into consideration the physical properties of the product, the raw materials, the presence or absence of a solvent, etc.

[Negative resist composition]
A negative resist composition (hereinafter also referred to as the present resist composition) according to one embodiment of the present invention preferably contains the present resist material, a solvent, and a compound that generates an acid upon irradiation with actinic rays or radiation.

The silsesquioxane having a cage structure may be used alone or in combination of two or more kinds.
The content of the silsesquioxane having a cage structure in the present resist composition (excluding the solvent) is not particularly limited, but is preferably from 70 to 100% by mass.
Examples of the solvent include methyl ethyl ketone, cyclopentanone, cyclohexanone, propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monomethyl ether (PGME), etc. The solvent may be used alone or in combination of two or more kinds.

The amount of the solvent used will vary depending on the thickness of the resist film to be formed, but is preferably in the range of 100 to 10,000 parts by mass per 100 parts by mass of the silsesquioxane having a cage structure.
Furthermore, the resist composition may contain various additives, such as a photoacid generator, a nitrogen-containing compound, an acid compound (an organic carboxylic acid, a phosphorus oxo acid or a derivative thereof), a surfactant, other quenchers, a sensitizer, an antihalation agent, a storage stabilizer, an antifoaming agent, etc. Any additives known in the art can be used.

[Pattern formation method]
A pattern formation method according to one embodiment of the present invention includes a film-forming step of applying the present resist composition to a substrate to form a film, an exposure step of exposing the present resist composition after the film formation, and a development step of developing the present resist composition after the exposure.

<Film-forming process>
The resist composition can be applied to a substrate by any known method, such as spin coating, casting coating, or roll coating.
Examples of the substrate include a silicon wafer, a SiN wafer, an AlN wafer, a wafer coated with aluminum, etc. In order to improve the adhesion of the resist composition and the resolution after development, an organic or inorganic anti-reflective film may be formed on the substrate.

The average thickness of the film formed in this step is preferably 1 nm to 500 nm, because below the lower limit, the function as a resist film is impaired, and above the upper limit, pattern collapse after pattern formation and development is likely to occur.
If necessary, pre-baking may be performed after coating. The pre-baking temperature is preferably 60° C. or more and 140° C. or less. The pre-baking time is preferably 5 seconds or more and 300 seconds or less.

<Exposure process>
The resist layer on the substrate obtained in the film formation process is exposed through a mask having a predetermined pattern. Examples of light sources used for exposure include ultraviolet rays, far ultraviolet rays, extreme ultraviolet rays (EUV), X-rays, and gamma rays.
Of these, EUV and electron beams are preferred.

<Developing process>
After exposure, the resist film is subjected to an appropriate heat treatment (post-exposure bake, PEB) and a developer is brought into contact with the resist film to dissolve part of the resist film. In a negative development process, the unexposed areas are dissolved and removed using an organic developer.
In the silsesquioxane having a cage structure of the present invention, the dissolution rate of the exposed portion in an organic developer decreases upon exposure to light.

As the organic developer, polar solvents such as ketone-based solvents, ester-based solvents, alcohol-based solvents, amide-based solvents, and ether-based solvents, and hydrocarbon-based solvents can be used.
Examples of ketone solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, 2-heptanone, 4-heptanone, 1-hexanone, 2-hexanone, 1-octanone, 2-octanone, 1-nonanone, 2-nonanone, diisobutyl ketone, cyclohexanone, and methylcyclohexanone.
Examples of ester-based solvents include methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, sec-butyl acetate, pentyl acetate, isopentyl acetate, propylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, ethyl-3-ethoxypropionate, 3-methoxybutyl acetate, 3-methyl-3-methoxybutyl acetate, methyl propionate, ethyl propionate, and butyl propionate.
Examples of alcohol-based solvents include methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol, 1-butyl alcohol, 2-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, benzyl alcohol, 2-methoxyethyl alcohol, 2-ethoxyethyl alcohol, 2-(methoxymethoxy)ethanol, 2-butoxyethanol, furfuryl alcohol, tetrahydrofurfuryl alcohol, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and tripropylene glycol monomethyl ether.
Examples of the ether solvent include dioxane and tetrahydrofuran.
Examples of the amide solvent include N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, hexamethylphosphoric triamide, and 1,3-dimethyl-2-imidazolidinone.
Examples of the hydrocarbon solvent include toluene, xylene, hexane, heptane, octane, and decane.
Among these, a developer containing at least one solvent selected from ketone-based solvents, ester-based solvents, alcohol-based solvents, amide-based solvents, and ether-based solvents is preferred. These solvents may be used alone or in combination of two or more.

Development may be carried out by a known method, such as immersing the substrate in a tank filled with a developer for a fixed period of time, piling up the developer on the substrate surface by surface tension and leaving it there for a fixed period of time, spraying the developer onto the substrate surface, or discharging the developer by scanning a nozzle at a fixed speed over a substrate rotating at a fixed speed.
After development, the substrate is appropriately rinsed with pure water, etc. In this manner, a resist pattern is formed on the substrate to be processed.

The substrate on which the resist pattern has been formed is appropriately heat-treated (post-baked) to strengthen the resist, and the portions without resist are selectively dry-etched.
After the dry etching, the resist is removed with a stripping agent to obtain a substrate on which a fine pattern is formed.

An example of the present invention will be described below. The present invention is not limited to the following example as long as it does not deviate from the gist of the invention. In the example, "parts" and "%" are by weight unless otherwise specified.
The number average molecular weight (Mn) and molecular weight distribution (Mw/Mn) of the silsesquioxane compound were determined by gel permeation chromatography in terms of polystyrene.

<Synthesis of silane compound (A1)>
2.00 g (9.0 mmol) of 3-aminopropyltriethoxysilane and 7 mg of 2,6-di-tert-butyl-p-cresol were added to a flask equipped with a stirrer and a thermometer. After 1.7 mL (18 mmol) of methyl acrylate was added dropwise under ice cooling, the mixture was reacted at 40° C. for 6 hours and then at 50° C. for 7 hours. After 0.9 mL (10 mmol) of methyl acrylate was added, the mixture was reacted at 50° C. for 7.5 hours. After the reaction was completed, the mixture was concentrated and dried under reduced pressure to obtain 3.12 g of silane compound (A1) represented by the following formula 4 as a colorless liquid in a yield of 88%. 1H-NMR (400 MHz, CDCl3): δ 3.80 ppm (q, 6H), 3.65 ppm (s, 3H), 2.76 ppm (t, 4H), 2.43 ppm (m, 6H), 1.51 ppm (m, 2H), 1.21 ppm (t, 9H), 0.55 ppm (t, 2H).

<Synthesis of Silsesquioxane Compound>
In a flask equipped with a stirrer and a thermometer, 1.00 g (2.5 mmol) of the synthesized silane compound (A1) and 3.3 ml of methyl alcohol were added and dissolved, and 0.29 g of 3.2% ammonium fluoride aqueous solution was added dropwise. After stirring at room temperature for 5.5 hours, the mixture was concentrated. 10 mL of ethyl acetate was added, and the mixture was washed with 10 mL of water and then with 5 mL of water. The obtained organic layer was concentrated and dried under reduced pressure to obtain 0.71 g of silsesquioxane (SQ1) represented by the following formula 5 as a colorless viscous liquid with a yield of 99%. Mn 1900, Mw/Mn 1.05, and m in the following chemical formula is estimated to be 6 to 8. ^1H -NMR (400 MHz, CDCl3): δ 3.64 ppm (s, 3H), 2.74 ppm (brt, 4H), 2.41 ppm (brt, 6H), 1.48 ppm (m, 2H), 0.55 ppm (brt, 2H).

Example 1
100 parts by mass of the silsesquioxane (SQ1) was dissolved in 3,900 parts by mass of methyl ethyl ketone to prepare a homogeneous solution, which was then filtered through a membrane filter having a pore size of 0.2 μm to prepare a resist composition.
A silicon wafer treated with hexamethyldisilazane was used as a pattern-formed substrate, and the prepared resist composition was spin-coated onto the pattern-formed substrate and dried at 90°C for 60 seconds using a hot plate to obtain a resist layer-containing pattern-formed substrate having a resist layer thickness of 130 nm. This was exposed using an electron beam exposure device (Elionix's "ELS-S50") and developed with propylene glycol monomethyl ether acetate (PGMEA) for 60 seconds. The results of measuring the remaining film ratio by changing the exposure dose are shown in Figure 1.

(result)
From the results in Fig. 1, it was confirmed that the residual film rate increases with increasing exposure dose, and it was therefore made clear that the coating film of the negative resist composition containing the silsesquioxane obtained in the present invention can selectively change the solubility of the coating film only in the light irradiated area by light irradiation, thereby enabling the formation of a desired precise pattern on a substrate. The residual film rate was measured using an optical interference film thickness measuring device.

Claims (6)

A negative resist material comprising a silsesquioxane having a cage structure represented by the following formula 1:
( _RmSiO1.5 ) _n (Formula 1)
(In formula 1, n is an integer of 3 to 30, and Rm includes a structure represented by formula 2 below.

^R1 represents an alkyl group, a cycloalkyl group, an aryl group, or an aralkyl group. The negative resist material according to claim 1, wherein Rm contains a group Rb that absorbs at least one of extreme ultraviolet light and an electron beam to generate secondary electrons. The negative resist material according to claim 1, wherein Rm includes a group Rc having a lactone skeleton. The negative resist material according to claim 1, wherein Rm includes a group Rd having a hydrophilic group. A negative resist composition comprising a silsesquioxane having a cage structure represented by the following formula 1:
( _RmSiO1.5 ) _n (Formula 1)
(In formula 1, n is an integer of 3 to 30, and Rm includes a structure represented by formula 2 below.

^R1 represents an alkyl group, a cycloalkyl group, an aryl group, or an aralkyl group. A method for forming a resist pattern using the negative resist composition according to claim 5.

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