WO1999062964A1

WO1999062964A1 - PURIFIED METHYL α-CHLOROACRYLATE/α-METHYLSTYRENE COPOLYMER AND ELECTRON BEAM RESIST COMPOSITION CONTAINING THE SAME

Info

Publication number: WO1999062964A1
Application number: PCT/JP1999/002999
Authority: WO
Inventors: Kakuei Ozawa; Nobunori Abe
Original assignee: Nippon Zeon Co., Ltd.
Priority date: 1998-06-04
Filing date: 1999-06-04
Publication date: 1999-12-09
Also published as: KR20010052543A

Abstract

A purified methyl α-chloroacrylate/α-methylstyrene copolymer obtained by copolymerizing methyl α-chloroacrylate with α-methylstyrene to produce a methyl α-chloroacrylate/α-methylstyrene copolymer which has a weight-average molecular weight of 10,000 to 3,000,000 and in which the ratio of the methyl α-chloroacrylate units to the α-methylstyrene units, m:n, is 10:90 to 90:10 and by washing the copolymer with an acidic water having a pH lower than 6; a process for producing the purified copolymer; an electron beam resist composition containing the purified copolymer; and a method of forming a pattern using the electron beam resist composition.

Description

Description: Purified α-methyl methyl acrylate / hi-methylstyrene copolymer and electron beam resist composition containing the same

The present invention relates to a purified methyl-methacrylate acrylate 'α-methylstyrene copolymer and an electron beam resist composition containing the same, and more particularly to a resist for microfabrication of semiconductor devices and photomasks. Electron beam resist composition having high sensitivity and excellent dry etching resistance suitable as a composition, a polymer suitable as a photosensitive resin component thereof, a method for producing the polymer, and the electron beam resist composition. The method of forming the butterflies. Background art

When manufacturing semiconductor devices, a resist is applied to the surface of a silicon wafer to form a photosensitive film, and the photosensitive film is irradiated with light (ultraviolet rays, electron beams, X-rays, etc.) through a photomask to form a latent image. Then, it is developed to obtain an image by a lithographic technique that forms a negative or positive image.

A photomask is a component in which a pattern of an electronic circuit is formed of a material that does not transmit light on a transparent substrate, and serves as an original when an electronic circuit is printed. The substrate to which an electronic circuit is to be printed is a silicon wafer when the semiconductor element such as a semiconductor integrated circuit (LSI) is a semiconductor element, but is a glass substrate or a print substrate (PWB) when a liquid crystal display panel (LCD) is used. In this case, it becomes a resin substrate. Formed on a plane like this The technology for transferring the resulting pattern onto a flat substrate is called lithography.

In recent years, as the integration, density, miniaturization, and speeding up of semiconductors have progressed toward ICs, LSIs, and even VLSIs, the demand for fine processing of semiconductor devices has increased. Techniques for forming the following fine patterns are required. To form such a fine pattern, a photomask having a corresponding fine pattern is indispensable.

To manufacture a photomask, first, a light-shielding film or a light-shielding film and an interference film are formed on a transparent substrate to form a mask substrate. Normally, a transparent glass plate is used as the transparent substrate.Chromium is used as the material for forming the light-shielding film, but silicon, iron oxide, molybdenum silicide, etc. are also used. . The interference film plays a role in lowering the reflectance of the light-shielding film, and usually uses chromium oxide, and is formed as a chromium oxide film on the surface of the chromium metal film (two-layer film). A three-layer type in which a thin film is also provided on the back of the chromium metal film is also used.

Next, the resist composition is formed by applying a resist composition on the light-shielding film or the interference film of the mask substrate. The application, drying, and pre-pressing of the resist composition are performed by photolithography technology. This can be done according to the usual method. Such a resist composition usually contains a resin component that changes the solubility in a developing solution used in a subsequent developing step by exposure. When the resin component is not photosensitive, an appropriate photosensitive component is added to impart photosensitivity to the resist composition. After that, the resist film is irradiated with a radiation beam to draw a pattern. Usually, electron beam lithography equipment —The drawing apparatus is used, and an electron beam or a laser is scanned based on the mask pattern data, and a pattern is drawn on the resist film. After the drawing step, development is performed by an ordinary method such as immersion development using an organic solvent-based developer or an alkaline developer. A negative or positive resist pattern is formed by the resist film portion that is not dissolved in the developing solution. After development, post baking and descum (surface treatment with oxygen plasma or the like) can be performed as necessary.

After the development step, the light shielding film is etched. The etching is a step of transferring the resist pattern formed by the resist pattern forming method to the underlying light-shielding film or the light-shielding film and the interference film. There are two etching methods, wet etching using a liquid and dry etching using a gas.ゥ In the case of jet etching, a cerium nitrate ammonium-based etchant (Kodak specification) is generally used. Etching is performed by a dipping method or a spray method. In dry etching, a halogenated carbon such as carbon tetrachloride or a chlorine-based etching gas is used.

After the etching step, the remaining resist film is removed. The resist film can be stripped by a chemical method using an organic solvent, concentrated sulfuric acid plus hydrogen peroxide or ozone, or a physical method using oxygen plasma or UV-ozone ashesing. It is also possible to apply a combination of technical methods. As a result, a photomask in which the mask pattern of the light-shielding film is formed can be obtained.

Among the above processes, one of the important steps in manufacturing a photomask having a fine pattern is an etching step. The conventional etching process is a method in which the chromium layer is corroded and dissolved with an etching chemical (エッチング Etch etching) was the mainstream. However, in this method, since side etching occurs, it is difficult to control the dimensions when forming a fine pattern. On the other hand, according to the dry etching method that has recently been widely used, Since side etching does not occur, pattern dimensional control is easy, and it is particularly suitable for forming fine patterns.

However, the dry etching process has not been used entirely because there are few electron beam resists for photomasks having excellent dry etching resistance.

Conventionally, Japanese Patent Publication No. 8-36636 discloses a copolymer of α-methyl acrylate and α-methylstyrene (α-methyl acrylate / α-methylstyrene copolymer). It has been reported that electron beam registries containing (polymer) as a resin component have high sensitivity and excellent dry etching resistance. That is, in the copolymer, since the α-methyl acrylate unit has a highly sensitive α-chloro group at the α-position, the main chain scission efficiency by irradiation with radiation is excellent. On the other hand, α-methylstyrene unit contributes to dry etching resistance due to the protective stability of the benzene ring.

This publication does not disclose a specific method for producing an α-methyl methyl acrylate · α-methylstyrene copolymer. Conventionally, in the production process of such a copolymer, after the polymerization process, a method in which the copolymer separated from the reaction mixture is dissolved in an organic solvent, and the resulting solution is dropped into a non-solvent and precipitated. Thus, a method of recovering a purified copolymer has been adopted. In general, a sufficiently highly purified copolymer can be obtained by such a reprecipitation method.

However, monochloroacetic acid purified by such reprecipitation method The electron beam resist composition containing the methyl acrylate / α-methylstyrene copolymer had a serious problem that foreign matter was generated in the dry etching process and defects were likely to occur in the photomask. Specifically, an electron beam resist composition containing a monomethyl acrylate / α-methylstyrene copolymer is applied on a mask substrate to form a resist film, and then an electron beam Draw a pattern by scanning. Next, development is performed to form a resist pattern. It was found that when dry etching was performed after the development process, a large number of foreign substances were generated in the resist film forming the pattern. When a large number of foreign substances are generated, defects such as black spots, white spots, dents, and protrusions are generated in a pattern (a pattern-like chromium film) transferred by the etching process. Such defects can have serious adverse effects, especially when forming fine patterns. If there is a shape defect in the light-shielding pattern of the photomask, it becomes difficult to finely process a semiconductor element or the like. Disclosure of the invention

An object of the present invention is to provide an electron beam resist composition containing a methyl methyl acrylate α-methylstyrene copolymer as a resin component, wherein the electron beam resist composition does not generate foreign matter during dry etching. It is to provide things.

It is another object of the present invention to provide a highly purified α-methyl methyl acrylate / hyr-methylstyrene copolymer which does not generate foreign substances during dry etching, and a method for producing the same. .

Another object of the present invention is to provide a method for forming a pattern using an electron beam resist composition containing a methyl methyl acrylate α-methylstyrene copolymer as a resin component, the method comprising the steps of: Foreign matter is generated on The object of the present invention is to provide a pattern forming method that does not require the use of a pattern.

The inventors of the present invention have conducted intensive studies to solve the problems of the prior art, and as a result, obtained as a result of copolymerization of α-methyl methyl acrylate and α-methylstyrene. α-Methylstyrene copolymer was washed with acidic water with ρ Η6 or less to suppress the generation of foreign substances during dry etching. Purified ο; —Methyl chloroacrylate-methyl methylstyrene copolymer I found that merging could be obtained.

a-methyl methacrylate and α-methylstyrene copolymer obtained by copolymerizing a-methyl methacrylate and α-methylstyrene, and purifying and recovering by a conventional method, is probably treated by dry etching. It is presumed to contain small amounts of impurities (residues such as catalysts and emulsifiers, oligomers, etc.) that sometimes become foreign substances. It is presumed that these impurities are efficiently removed by washing with acidic water having ρρ6 or less. Alternatively, it can be considered that the copolymer itself has undergone some modification by washing with an acidic water having ρΗ6 or less, and has been modified so that foreign matter is not generated even by dry etching. However, the present invention is not limited in any way by these putative mechanisms. It was impossible to predict from the prior art that foreign matter during dry etching treatment was extremely significantly suppressed by washing the copolymer with an acidic water having ρΗ6 or less. It is. The present invention has been completed based on these findings.

Thus, according to the present invention, the formula (I) obtained by copolymerizing α-methyl methyl acrylate and α-methylstyrene is obtained. CI CH ₃

II CH ₂ — C ½ _r CH ₂ — C-(I) COOCH ₃

Wherein the weight average molecular weight is 100,000 to 3,000,000, the ratio of α-methyl acrylate units to α-methylstyrene units, m: n is 10: 90 to 90: Purified α-methyl methyl acrylate by washing the α-methyl methyl acrylate copolymer 'with α-methylstyrene copolymer of ρ スチレン 6 or less —A methylstyrene copolymer is provided.

Further, according to the present invention, the α-methyl methyl acrylate-α-methylstyrene copolymer obtained by copolymerizing α-methyl methyl acrylate and α-methylstyrene is less than ρρ6. The present invention provides a method for producing a purified methyl α-methyl acrylate / α-methylstyrene copolymer which is washed with acidic water.

Further, according to the present invention, an α-methyl methyl acrylate-α-methylstyrene copolymer obtained by copolymerization of α-methyl methyl acrylate and α-methylstyrene is obtained by ρ Η Provided is an electron beam resist composition containing a purified methyl α-chloroacrylate / methylstyrene copolymer washed with less than 6 acidic water.

Furthermore, according to the present invention, there is provided a method for forming a pattern on a substrate by lithography using an electron beam resist composition containing a methyl monoacrylate methyl a-methylstyrene copolymer. -As a copolymer of methyl acrylate and a-methylstyrene. A- Copolymer of methyl acrylate and -methylstyrene The purified α-methyl methyl acrylate / α-methylstyrene copolymer is washed with acidic water with ρΗ6 or less, and the purified α-chloromethyl acrylate · α-methylstyrene copolymer is used. A method for forming a pattern is provided. BEST MODE FOR CARRYING OUT THE INVENTION

1. α-Methyl acrylate / α-methylstyrene copolymer α-Methyl chloroacrylate / α-methylstyrene copolymer can be obtained by the usual method using α-methyl chloroacrylate and α-methylstyrene. Can be obtained by copolymerizing

Examples of the polymerization method include a radical polymerization method using α, a'-azobisisobutyronitrile as a catalyst, an anion polymerization method using sodium naphthene or butyllithium as a catalyst, Examples thereof include a cationic polymerization method using a metal halide as a catalyst, and a polymer modification method in which α-chloroacrylic acid · α-methylstyrene copolymer is synthesized by reacting diazomethane.

The radical polymerization method includes a solution polymerization method in which a monomer and a catalyst are reacted in an organic solvent, a bulk polymerization method in which only a monomer is polymerized by heating without a catalyst, and a method in which a monomer is emulsified in an aqueous medium containing an emulsifier. After that, there is an emulsion polymerization method in which a catalyst acts to carry out polymerization.

In the present invention, a copolymer obtained by any of the polymerization methods can be used, but in order to obtain a copolymer having a high molecular weight, a radical polymerization method is preferable, and among them, an emulsion polymerization method is more preferable. .

When α-methyl methyl acrylate and α-methylstyrene are copolymerized, the formula (I) CI CH ₃

I I

~ i CH ₂ -C ½ CH ₂ — C-(I) COOCH3

An a-methyl methyl acrylate-a-methylstyrene copolymer represented by the following formula is obtained.

The molecular weight of a-methyl methyl acrylate / a-methylstyrene copolymer is measured by gel permeation chromatography (GPC) when used as a resin component of an electron beam resist composition. The weight-average molecular weight in terms of monodisperse polystyrene is usually 10 000 to 3 000, preferably 0 0 000 to 2 000, and more preferably Preferably, they are 30, 00 00 to 1, 00 00, and 00 0. If the weight average molecular weight of the copolymer is too small, the reduction of the resist film during development tends to increase. Conversely, if the weight average molecular weight is too large, the coatability is poor and the uniformity of the coating film is affected. coming out. As long as the weight average molecular weight is within the above-mentioned range, there is no particular problem in the reduction of the resist film during development and the uniformity of the coating film. The degree of dispersion (MwD) of the copolymer by GPC analysis is usually 1 to 4, preferably 1 to 2.5 when expressed as a ratio of weight average molecular weight (Mw) to Z number average molecular weight (Mn). Degree.

The ratio (m: n) of the a-methyl acrylate unit to the a-methylstyrene unit is usually 10:90 to 90:10, preferably 30:70 to 70: 30. When one unit of each of these monomers is within the above range, a copolymer having high sensitivity and excellent dry etching resistance can be obtained. The weight average molecular weight, the degree of dispersion, the ratio of each monomer unit and the like of the copolymer do not substantially change even after the washing treatment with acidic water.

2. Cleaning with acidic water

In the present invention, the α-methyl methyl acrylate / α-methylstyrene copolymer obtained by copolymerization of α-methyl methyl acrylate and para-methylstyrene is purified by a reprecipitation method, if necessary. After the treatment, wash with acidic water with ρΗ6 or less.

Washing with acidic water is carried out by dissolving the α-methylmethyl acrylate · α-methylstyrene copolymer obtained by copolymerization of α-methyl methyl acrylate and para-methylstyrene in a suitable organic solvent. It is preferable to carry out the treatment by bringing the solution into contact with acidic water. As the organic solvent, those which can dissolve the copolymer such as dichloromethane and chloroform are preferable and have low compatibility with water.

The contact between the copolymer solution and the acidic water can be suitably performed by mixing and stirring the two. If phase separation between the organic solvent and water occurs after washing, separate the aqueous phase. The aqueous phase can be separated, for example, by leaving the mixed solution to separate into an organic solvent layer and an aqueous layer, and then removing the aqueous layer by decantation or the like. The copolymer can be recovered from the organic solvent layer by, for example, pouring the organic solvent layer into a non-solvent such as alcohol and precipitating the copolymer. In the case where the phase separation between the organic solvent and water does not occur. In the case where the phase separation is insufficient, the mixture may be poured into a non-solvent to precipitate the copolymer. A copolymer can also be precipitated by pouring a non-solvent into the organic solvent layer. The precipitated copolymer is filtered and dried according to a conventional method, and recovered as a purified copolymer.

To adjust ρ Η of acidic water, for example, A method of contacting fat with water, and a method of adding acid to pure water.

Specific examples of the acid used to prepare the acidic water include inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid; and carboxylic acids such as formic acid, acetic acid, trichloroacetic acid, trifluoroacetic acid, oxalic acid, and malonic acid. Acids; sulfonic acids such as methanesulfonic acid, trifluorenesulfonic acid, and Ρ-toluenesulfonic acid; and the like, and these can be used alone or in combination of two or more.

Among these acids, volatile acids (for example, hydrochloric acid, etc.) and low-boiling acids (for example, nitric acid, formic acid, acetic acid, trifluoroacetic acid, etc. having a boiling point of 0 to 120 ° C.) are preferable. When the acid used for the acidic water is an acid having a high boiling point or a non-volatile acid, the acid may remain in the copolymer after the washing treatment and deteriorate the storage stability of the electron beam resist composition. On the other hand, volatile acids and acids having a low boiling point are preferred because they hardly remain in the copolymer and do not cause a problem in storage stability.

The upper limit of the pH of the acidic water used for washing is less than 6, preferably less than 5, and more preferably less than 4.If the pH of the acidic water is 6 or more, the influence of the emulsifier used in the emulsion polymerization This makes it difficult to separate the organic solvent layer from the aqueous layer. The lower limit of the pH of the acidic water is preferably 1 or more. If the pH of the acidic water is less than 1, hydrolysis of the ester portion of the α-methyl methyl acrylate unit of the copolymer is likely to occur, which is not preferable. Washing with acidic water may be performed once or may be repeated two or more times, but is usually about 1 to 4 times.

In the present invention, after washing with acidic water, washing with water having ρΗ6 to 8, preferably ρΗ6.5 to 7.5 can be performed. After washing with acidic water, the remaining water in the copolymer is obtained by washing with water. Can prevent cleavage of the ester bond in the copolymer, and can enhance long-term storage.

3. Electron beam resist composition

An electron beam resist composition containing a purified methyl acrylate / α-methylstyrene copolymer obtained by washing with acidic water is prepared by dissolving the purified copolymer in a solvent. I do. As the solvent, those generally used as a solvent for the resist composition can be used.

Specific examples thereof include ketones such as acetone, methylethylketone, getylketone, cyclohexanone, and cyclopentyne; ethers such as ethylene glycol dimethyl ether, ethylene glycol dimethyl ether, and dioxane; Alcohol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether; propyl formate, butyl formate, propyl acetate, propyl acetate, butyl acetate, methyl propionate, Esters such as ethyl propionate, methyl butyrate, ethyl butyrate, ethyl lactate, and getyl malonate; methyl 2-oxypropionate, 2-ethyl ethyl oxypropionate, and 2-methoxypropyl Oxycarboxylates such as methyl acrylate, 2-ethyl ethoxypropionate; cell-solvents such as cellosolve acetate, methylcellulose solvent acetate, ethylserum-solvent acetate, propyl cellosolve acetate, and propylserum-solvent acetate; Propylene glycols such as propylene glycol, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, and propylene glycol monobutyl ether; diethylene glycol; I 3 Diethylene glycols such as monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol dimethyl ether, diethylene glycol dimethyl ether; halogenated hydrocarbons such as trichloroethylene; toluene; xylene Aromatic compounds such as benzoyl, anisol, o-dichlorobenzene, and ethyl benzoate; N, N-dimethylformamide, N, N-dimethylacetamide, N_methylacetamide, N— Examples thereof include polar solvents such as methylpyrrolidone.

Of these, diethylene glycols and aromatic compounds are preferred because of their excellent solubility of α-chloroacrylic acid / α-methylstyrene copolymer, and particularly, diethylene glycol dimethyl ether, anisol, And ο-dichloromouth benzene is preferred. These solvents can be used alone or in combination of two or more.

As a developer for the resist composition of the present invention, generally, a solvent for the resist as described above can be used. Among these, xylene, butyl acetate, amyl acetate, getyl ketone, methyl ethyl ketone, getyl malonate, diethylene glycol dimethyl ether, anisol and the like are preferable. These solvents can be used alone or in combination of two or more as a developer.

In the pattern forming method using the resist composition of the present invention, it is possible to perform a treatment with a rinse solution after development. Usually, xylene, butyl acetate, isopropyl alcohol, methyl isobutyl ketone, and the like are preferably used as the rinse solution. These solvents may be used alone or in combination as a rinse liquid. Can be used.

The electron beam resist composition of the present invention can be used as a resist for forming a photomask or the like of a semiconductor element by the above-mentioned lithography technique. The electron beam resist composition of the present invention is suitable as a resist for manufacturing a photomask having no shape defect, since generation of foreign matter during dry etching is suppressed.

Example

EXAMPLES Hereinafter, the present invention will be more specifically described with reference to Examples and Comparative Examples. The present invention is not limited to only these Examples. Parts and percentages are by weight unless otherwise specified. Evaluation methods for physical properties are as follows.

(1) pH measurement

The pH of the acidic water was measured by the following method.

Device H M—12 P (Toa Denpa Kogyo Co., Ltd.)

Measurement temperature 25 ° C

Test solution volume 100 ml

Turn on the power of the PH meter and stabilize it for about 30 minutes. Rinse the detector with pure water at least three times and wipe it with clean absorbent cotton. Calibration with standard solution is performed by one-point calibration. Immerse the electrode in pH 6.86 neutral phosphate standard solution and shake it a few times to remove air bubbles. After standing for 10 minutes, read the measured value and calibrate. When calibration is completed, wash the electrode with pure water at least three times and wipe it with clean cotton wool. Then, immerse the electrode in the test solution and shake it a few times to remove air bubbles.

After standing for 10 minutes, read the pH display value.

(2) GPC analysis PT / JP99

The GPC analysis of the 15 copolymer was performed under the following conditions.

Apparatus: HLC — 8120GPC (Tosoh Corporation)

Column: TSKGelG500HXL, internal diameter 7.8 mm x length

2 stations of 30 cm (made by Tohso)

Temperature: 40 ° C

Solvent: Tetrahydrofuran (THF)

Flow velocity: 1.0 m 1 / min.

Sample: 0.1 ml injection of a sample having a concentration of 0.05 to 0.6% by weight. In calculating the molecular weight of the sample, a molecular weight calibration curve prepared from a monodisperse polystyrene standard sample was used.

Under the above conditions, the weight average molecular weight is measured as follows.

Stabilize the column in a heating chamber at 40 ° C, flow THF at a temperature of 1 m / min as a solvent through the column at this temperature, and use a sample concentration of 0.05 to 0.1 wt. The THF sample solution of the copolymer adjusted to 50% is injected in a range of 50 to 200 a1 for measurement. In measuring the molecular weight of a sample, the molecular weight distribution of the sample is calculated from the relationship between the logarithmic value of a calibration curve prepared from several types of monodispersed polystyrene standard samples and the number of counts. As standard polystyrene samples for preparing a calibration curve, for example, the molecular weights of Tosoh I. Co., Ltd. are 5.0 X 102, 2.5 X 103, 9.83 X 103, 3.72 X ^{1 0 4, 1. 8 9} X 1 0 5, γ. ο 7 X 1 05, l. using 1 1 X 1 06 ones, at least using the standard polystyrene samples 7 points. An RI detector is used as the detector. In order to accurately measure the molecular weight region of 1 × 10 3 to 2 × 10 6, a plurality of commercially available polystyrene gel columns are preferably used, and the combination used under the above conditions is preferably used ₍ [ Synthesis Example 1] Synthesis of copolymer (A-1) 2750 parts of pure water, 3 parts of sodium carbonate, KO RR- 18 (trade name; manufactured by Kao Corporation, aqueous solution of semi-hardened tallow fatty acid limestone) with a solid content of 17.5 to 18.5% 2) 25 parts were placed in a separable flask and dissolved. To the mixture were added 450 parts of α-methyl methyl acrylate and 104 parts of α-methylstyrene, followed by vigorous stirring to emulsify. After the atmosphere in the flask was replaced with nitrogen, 0.4 parts of sodium dithionite, 0.15 parts of sodium iron ethylenediaminetetraacetate trihydrate, and 0.15 parts of sodium ethylenediaminetetraacetate tetrahydrate 0.3 75 parts, sodium formaldehyde sulfoxylate 0.225 parts, and cumene hydroxide oxide 0.786 parts were added in that order, followed by stirring at 5 ° C. for 48 hours. After adding 7.5 parts of 2,6-di-tert-butyl-1-methylphenol to stop the reaction, 1400 parts of methanol was added dropwise to the reaction solution, and the precipitated solid was separated by filtration. . The obtained solid was dissolved in 800 parts of tetrahydrofuran, and the obtained solution was dropped into 1400 parts of methanol, and the precipitated solid was separated by filtration. Further, the obtained solid content was dissolved in 800 parts of tetrahydrofuran, and the obtained solution was added dropwise to 1400 parts of methanol. The precipitated solid content was separated by filtration and dried to obtain 750 parts of methyl ethyl acrylate / α-methylstyrene copolymer (A-1).

The weight average molecular weight in terms of polystyrene of the copolymer (A-1) determined by GPC analysis was 338,000, and the polydispersity was 2.1.

As a result of one NMR analysis, the monomer composition ratio in the copolymer (A-1) was α-methyl methyl acrylate: h-methylstyrene = 53Ζ47 (molar ratio).

[Synthesis Example 2] Synthesis of copolymer (Α-2)

750 parts of the copolymer (A-1) obtained in Synthesis Example 1 was added to 900 parts of The solution was dissolved in dichloromethane, and 900 parts of a 0.05 N aqueous hydrochloric acid solution was added to the obtained solution, followed by stirring. After allowing the mixture to stand, the aqueous layer was removed by decantation. The pH of the 0.05 N hydrochloric acid aqueous solution used here was 2.3.

The remaining dichloromethane layer was dropped into 1,400 parts of methanol, and the precipitated solid was separated by filtration and dried, and 740 parts of α-methyl methyl acrylate / α-methylstyrene copolymer was obtained. (Α-2) was obtained.

[Synthesis Example 3] Synthesis of copolymer (Α-3)

750 parts of the copolymer (A-1) obtained in Synthesis Example 1 was dissolved in 900 parts of dichloromethane, and the same solution as used in Synthesis Example 2 was added to the solution obtained. 900 parts of an aqueous hydrochloric acid solution of 0.5% was added and stirred. After allowing the mixture to stand, the aqueous layer was removed by decantation. 900 parts of pure water was added to the remaining dichloromethane layer, followed by stirring. After allowing the mixture to stand, the aqueous layer was removed by decantation. This washing operation with pure water was repeated twice more.

The remaining dichloromethane layer was added dropwise to 1400 parts of methanol, and the precipitated solid was separated by filtration and dried to obtain 738 parts of a copolymer (Α-3).

[Examples 1 to 6, and Comparative Examples 1 to 3]

The copolymers (A-1) to (Α-3) obtained in the above Synthesis Examples 1 to 3 were respectively dissolved in the solvents shown in Table 1, and the resulting solutions were each dissolved in a solvent having a pore size of 0.

The mixture was filtered through a filter (1) to prepare a resist solution.

This resist solution is applied to the surface of a glass substrate with a 5-inch chrome film, and prebaked with a hot plate at 18 O: for 3 minutes to form a resist film having a thickness of 0.5 m. did.

The substrate on which the resist film was formed was replaced with an MR IE type dry etchant. Processed on an 8 g device.

The processing conditions for dry etching are as follows:

Gas: C12 / O2 = 4/1 (molar ratio),

Pressure: 15 Pa,

RF power: 350 W,

Gas flow: 50 S C C M,

Processing time: 5 minutes

Met.

The surface of the resist film on the substrate after the treatment was observed under a visual field of an optical microscope. The number of foreign substances (observed as bright spots) observed in a visual field of 200 times was counted. The results were as shown in Table 1. table 1

From the results shown in Table 1, it was found that, in an electron beam resist composition containing α-methyl methyl acrylate / α-methylstyrene copolymer as a resin component, an acid value of ρΗ6 or less was obtained in the purification step of the copolymer. Clean with water Thus, it can be seen that foreign matter can be extremely effectively prevented from occurring during the dry etching process in the resist pattern forming step. In particular, by performing washing with water having a pH of 6 to 8 after washing with acidic water having a pH of less than 6, it is possible to prevent the generation of foreign substances during dry etching treatment. The storage stability can be improved. Industrial applicability

ADVANTAGE OF THE INVENTION According to this invention, the electron beam resist composition which does not generate | occur | produce a foreign material during a dry etching process is provided. Further, according to the present invention, there is provided a highly purified methyl methyl acrylate / α-methylstyrene copolymer which does not generate foreign matter during dry etching, and a method for producing the same. Further, according to the present invention, there is provided a pattern forming method in which a foreign substance is not generated during a dry etching process.

Therefore, the resist composition for an electron beam of the present invention can be suitably used for fine processing of a semiconductor device, a photomask, and the like.

Claims

The scope of the claims

1. Formula (I) obtained by copolymerization of α-methyl acrylate and α-methylstyrene

CI CH ₃

I I

-^ CH _2-

Where the weight average molecular weight is 10,000, 3,000 to 4,000, and the ratio of α-methyl methacrylate unit to α-methylstyrene unit m: n force 10:90 -90: purified α-methyl methyl acrylate α-methyl styrene copolymer by washing the α-methyl styrene copolymer of α-methylstyrene with ρΗ6 or less in acidic water Styrene copolymer.

2. The purified α-methyl methyl acrylate ′ α-methylstyrene copolymer according to claim 1, wherein the acidic water having ρΗ6 or less is an acidic water having ρΗ1 or more and less than 6.

3. The purified α-chloroacrylic acid according to claim 1, wherein the acidic water having ρ 未満 6 or less is an acidic water containing at least one acid selected from the group consisting of inorganic acids, carboxylic acids, and sulfonic acids. Methyl · α-methylstyrene copolymer.

4. The acid is a volatile or boiling acid having a temperature of 120 ° C or lower. 3. The purified α-methyl methyl acrylate · α-methylstyrene copolymer described in 3.

5. Washing with acidic water with ρ 未満 6 or less, the α-chloromethyl acrylate / α-methylstyrene copolymer obtained by copolymerization of α-methyl methyl acrylate and monomethyl styrene 2. The purified monomethyl acrylate / α-methylstyrene copolymer according to claim 1, which is carried out by bringing a solution dissolved in a solvent into contact with acidic water.

6. The purified α-methyl methyl acrylate / high-methylstyrene copolymer according to claim 1, wherein the copolymer is washed with an acidic water having a ρΗ6 or less and then washed with water having a ρΗ6 to 8.

7. α-methyl methyl acrylate and a-methylstyrene copolymer obtained by copolymerization of a-methyl acrylate and a-methylstyrene are obtained by emulsion polymerization using a radical initiator. 2. The purified a-methyl acrylate / QL-methylstyrene copolymer according to claim 1, which is obtained by the following method.

8. Purification by washing the a-methyl acrylate / a-methylstyrene copolymer obtained by copolymerization of a-methyl acrylate and a-methylstyrene with acidic water having a pH of less than 6. Mouth Methyl acrylate · a-Methylstyrene copolymer production method.

9. Wash with acidic water below pH 6, a- 9. The method is carried out by contacting a solution prepared by dissolving an α-methyl methyl acrylate / α-methylstyrene copolymer obtained by copolymerization of methyl and α-methylstyrene in an organic solvent with acidic water. Manufacturing method as described.

10. The production method according to claim 8, wherein after washing with an acidic water having a ρΗ6 or less, washing with water having a ρΗ6 to 8 is performed.

1 1. Wash the copolymer of methyl methyl acrylate and methyl styrene obtained by copolymerization of methyl methyl acrylate and methyl methyl styrene with acidic water of less than Η6. An electron beam resist composition comprising a purified methyl methyl acrylate / α-methylstyrene copolymer.

12. The electron beam resist composition according to claim 11, which is a resist composition for fine processing of a semiconductor device or a photomask.

1 3. A method for forming a pattern on a substrate by lithography using an electron beam resist composition containing a methyl acrylate / α-methylstyrene copolymer. As the methyl acrylate / α-methylstyrene copolymer, α-methyl methacrylate / α-methylstyrene copolymer obtained by copolymerization of α-methyl chloroacrylate and α-methylstyrene was used as a copolymer of ρΗ6 A method for forming a pattern, comprising using a purified methyl α-chloroacrylate / α-methylstyrene copolymer obtained by washing with less than acidic water.

14. The pattern forming method according to claim 13, wherein dry etching is performed in an etching step of lithography.