JPS5929853B2 - Heat development method for electron beam resist - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for thermally developing a high-resolution electron beam resist, and more specifically to the creation of minute patterns such as selective diffusion and selective etching in the semiconductor industry, and the method disclosed in Japanese Patent Laid-Open No. 47-37415. In a submicron image recording device that retains recorded information by converting the recorded information into irregularities on the surface, such as that seen in the production of video discs, which is known in Japanese Patent Publication No. Regarding a developing method.

Since positive electron beam resists are indispensable for submicron microfabrication techniques, various resists have been devised.

Among them, polymethyl methacrylate (PMMA) is known to have the best resolution, but its drawback is low sensitivity. Therefore, many studies have been reported in recent years to improve the sensitivity of positive electron beam resists, such as polybutyl methacrylate, copolymers of methyl methacrylate and methacrylic acid, and copolymers of methyl methacrylate and isobutylene. Positive-working electron beam resists have been announced, such as polymer, polybutene-1-sulfone, polyisopropenylketone, polymethacrylamide, polycyanoacrylate, fluorine-containing, and polymethacrylate, but none of them have sufficient sensitivity and resolution. It is difficult to say that this is a resist that satisfies customers. In order to solve the above-mentioned drawbacks, the present inventors conducted various studies on electron beam resists, and as a result found that good results could be obtained by improving the developing method, and completed the present invention.

5 The electron beam resist used in the present invention has the following general formula: [However, in the formula, X is the same or different and is a cyano group (-C
R represents a lower alkyl group such as methyl, ethyl, propyl, butyl, etc., and n represents a positive integer.

] The main component is poly-α-cyanoacrylate, poly-α-carbamyl acrylate, or a copolymer of both.

Electron beam resists containing polymers represented by this general formula as main components are well known, and have been reported to have higher sensitivity than PMMA, but to be inferior in resolution (Japanese Patent Laid-Open No. 1983-1972-1). No. 153671).

To briefly explain the development method when using an electron beam resist mainly composed of poly-α-cyanoacrylate, poly-α-cyanoethyl acrylate (molecular weight: 400,000) is dissolved in cyclohexanone to a concentration of 5%, and this solution is applied to a glass plate. On a substrate on which chromium was vapor-deposited, spin coating was performed at about 300 rpm to form a film with a thickness of 4000λ, and then 1
After heat treatment at 30℃ for 15 minutes, the irradiation dose was approximately 4×
The film was irradiated with an electron beam at 10-6 coulombs/Cd and an accelerating voltage of 15 KV, and then developed at room temperature using a mixed solvent of ethyl acetate and methyl isobutyl ketone. Next, it is washed with isopropyl alcohol and dried, and the following results are obtained. That is, when two patterns after development with a development time of 20 seconds and 60 seconds are observed using an electron microscope at a magnification of 10,000 times, the skin of the resist film does not come off in the case of the pattern with a development time of 20 seconds, and the bottom surface of the irradiated area is A very uneven and rough surface was observed, and although the development time was 60 seconds, the development was done to the bottom, but there were roughness on the developed side and whiskers were observed on the bottom surface. Note that when PMMA is used, such a surface roughening phenomenon is hardly observed regardless of the level of the 11ζ irradiation amount. This is thought to be because the electron beam resist using poly-α-cyanoethyl acrylate has better solubility in a developer than PMMA, and therefore the sensitivity is increased by sensitization development. The present inventors thought that the resolution of electron beam resists using polycyanoacrylate etc. is poor and that this occurs during the development and rinsing process, and as a result of intensive research to solve this phenomenon, the above-mentioned general In the development process after applying electron beam irradiation to a resist made of a polymer represented by the formula, instead of developing with a mixed solvent containing ethyl acetate, methyl isobutyl ketone, cyclohexanone, etc., the substrate coated with the resist is heated. Then, the irradiated part evaporates and the unirradiated part remains, and the present invention was completed based on the discovery that a pattern could be formed by this.

That is, in the heat development method of the present invention, after electron beam irradiation is applied to a resist whose main component is polyα-cyanoacrylate or the like represented by the above general formula, the substrate is placed in a constant temperature bath, and the irradiated area is exposed to the irradiated area after development. It is characterized by forming a pattern by heating according to the depth. The present invention provides that when the electron beam resist represented by the above general formula is heated in a constant temperature bath, the higher the heating temperature, the greater the film thickness reduction rate as shown in FIG.
This is also based on the knowledge that when the heating temperature is constant, the smaller the molecular weight of the polymer that is the main component of the resist, the greater the film thickness reduction rate as shown in FIG.

Therefore, the molecular weight of the polymer forming the electron beam resist film made of poly α-cyanoacrylate, poly α-carbamyl acrylate, or a copolymer of both used in the present invention is better as it is larger; for example, from 1 million to 30
A value of about 0,000 is preferable. It is desirable that the molecular weight distribution be narrow from the viewpoint of resolution. The thicker the resist film, the better; for example, 0.5 to 1.5 μm is preferable.

Further, the lower the pre-baking temperature is, the more convenient it is. In the thermal development method according to the present invention, heating of the substrate after electron beam irradiation is preferably carried out in a constant temperature bath at 140 to 180°C, and the heating time is preferably determined according to the depth of the irradiated area after development. is carried out by heating for 5 to 60 minutes.

Note that the decomposition products that volatilize during heating are highly irritating, so sufficient ventilation is required. Further, an electron beam irradiation characteristic curve obtained by the above thermal development method is shown in FIG.

When a pattern is formed by this heat development method, the film thickness in the non-irradiated areas is also slightly reduced, but no surface roughness is observed as in the irradiated areas, and the pattern is in good condition. The polymer represented by the above general formula used in the present invention can be obtained, for example, by the following method (see Japanese Patent Application No. 5171535).

Note that R in the above general formula is preferably a lower alkyl group, because this lowers the glass transition temperature of the resist and makes it difficult to dry.

40 parts of α-cyanoethyl acrylate monomer was dissolved in 320 parts of acetonitrile, and 0.1 part of dimethylformamide was added dropwise as a polymerization initiator.
Time anionic polymerization.

Thereafter, the polymer is precipitated into a large amount of methanol and dried under vacuum. The heat development method according to the present invention, unlike conventional solvent development methods, can eliminate the trouble of selecting a solvent, determining the concentration, and post-processing, and is also good with no surface roughness or scratches on the bottom surface. You can get a pattern.

Furthermore, in terms of use, it is a revolutionary developing method, as it is particularly effective for forming master patterns on video discs, where surface irregularities in patterns become noise as they are. The present invention will be explained in detail below with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Example 1 Poly α-cyanoethyl acrylate (molecular weight 2.6 million)
was dissolved in cyclohexanone to a concentration of 5% and applied to a glass substrate with chromium vapor-deposited using a spin coating method at approximately 3000 rpm.
A resist film with a thickness of 1.0 μm was formed.

After that, the amount of irradiation charge was 4.0×10-6 coulombs/Cr!
1. An electron beam with a beam width of 1.5μ was scanned at an acceleration voltage of 15K. After irradiation, take out the substrate from the irradiation device and
Heat development was carried out for 15 minutes in a constant temperature bath at 60°C. The portion irradiated with the electron beam became a concave portion with a depth of 4000λ. When this was observed using an electron microscope at a magnification of 10,000 times, no cracks were found in the irradiated and non-irradiated areas, as shown in the micrograph of FIG. Comparative Example Poly α-cyanoethyl acrylate (molecular weight: 2.6 million) was dissolved in cyclohexanone at a concentration of 4%, and a resist film having a thickness of 5000λ was formed on a similar chromium substrate by spin coating at about 1200 rpm.

Thereafter, heat treatment was performed at 130° C. for 15 minutes, and then an electron beam with a beam width of 1.5 μm was scanned with an irradiation charge amount of 4×10 −6 coulombs/Cd and an acceleration voltage of 15 K. After irradiation, the substrate was taken out of the irradiation device, immersed in a developer consisting of 1:1 ethyl acetate, ethyllimethylisobutylketone for 45 seconds, and then rinsed in isopropyl alcohol for 15 minutes and dried. When observed using an electron microscope at a magnification of 10,000 times, as shown in the photograph in FIG. 5, 4000λ elution was observed in the irradiated area, and a severely uneven surface was observed at the bottom. Example 2 As in Example 1, a substrate coated with a copolymer of poly α-cyanobutyl acrylate and poly α-carbamyl butyl acrylate to a thickness of 1.0 μm was irradiated with a charge amount of 5×10 −5 coulombs/c Bu. An electron beam with a beam width of 1.5μ was scanned at an acceleration voltage of 15K.

After irradiation, the substrate was taken out from the irradiation device and developed by heating in a constant temperature bath at 160° C. for 30 minutes. The part irradiated with the electron beam became a recess, and the substrate surface was completely exposed. At this time, the film thickness of the unirradiated area decreased to 8200λ, but when observed using an electron microscope at a magnification of 10,000 times, there was almost no breakage in the resist film or edges. When this developed substrate was immersed in a chromium etching solution of ceric ammonium nitrate and perchloric acid for 2 minutes, the 800λ chromium layer was corroded, and after washing and drying, the resist film was peeled off with acetone to obtain a chrome mask.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between heating time and film thickness ratio when resist is heated at various temperatures, and Figure 2 is a graph showing the relationship between heating time and film thickness ratio when resist of each molecular weight is heated at a constant temperature. FIG. 3 is a graph showing an electron beam irradiation characteristic curve according to the developing method according to the present invention.
FIG. 4 is an electron micrograph (×10,000) showing the developed surface obtained in Example 1, and FIG. 5 is an electron micrograph (×10,000) showing the developed surface obtained in Comparative Example.

Claims (1)

[Claims] 1 General formula: ▲ Numerical formula, chemical formula, table, etc.▼ (However, in the formula, X is the same or different and represents a cyano group or a carbamyl group, and R is the same or different and represents a lower alkyl group. (where n represents a positive integer) An electron beam resist mainly composed of poly α-cyanoacrylate, poly α-carbamyl acrylate, or a copolymer of both is irradiated with an electron beam and then heated. A method for thermally developing an electron beam resist, characterized in that a pattern is formed by vaporizing an irradiated area.