JPS5893048A - Positive radiation resist - Google Patents

Abstract

PURPOSE:To improve sensitivity and dry etching resistance by using a copolymer of methyl methacrylate and oxime methacrylate having acyl oxyimino groups and having 10,000-800,000 number average mol.wt. CONSTITUTION:A copolymer of 70-99mol% methyl methacrylate and 1- 30mol% oxime methacrylate having acyl oxyimino groups is used as resist acting in positive type to radiations such as far ultraviolet rays, electron rays, X- rays gamma-rays and alpha-rays, and the number average mol.wt. of the copolymer is made 10,000-800,000, whereby the resist having high sensitivity, high resolution and heat resistance and excellent dry etching resistance is obtained. Said copolymer is obtained by block polymn. using a, a'-azobisisobutyronitrile as an initiator.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to radiation (deep ultraviolet rays) used when forming fine patterns for semiconductor elements, integrated circuits, etc.

electron beams, X-rays, gamma rays, alpha rays, etc.) that drip onto the resist.

Mask transfer technology using ultraviolet light has traditionally been used to form circuit patterns in the integrated circuit manufacturing process. The practical limit of resolution when using ultraviolet light is 2 μm even if a reduction projection method (10:1) is used due to the phenomenon of light diffraction.

However, as the density of integrated circuits has increased in recent years, even higher resolution has been required, and the transfer technology using ultraviolet light has become unable to meet these demands. To improve this, far-ultraviolet,
Electron beams and X-rays have been studied and are now being used. Polymethyl methacrylate (hereinafter abbreviated as PMMA) has been widely studied and used as one of the radiation resists suitable for this purpose.

As an electron beam resist for PMMA, it has excellent resolution and etching resistance. However, it has the disadvantage of low sensitivity. Here, in the case of a positive resist, sensitivity is the minimum amount of electron beam irradiation required to remove 10% of the resist coated on the substrate by a developing operation. PMMA
is far ultraviolet light.

Although it has been considered as an X-ray resist, it has the disadvantage of low sensitivity as described above, and therefore, various positive resists are being actively developed from the viewpoint of increasing sensitivity.

Methods for increasing the sensitivity of positive radiation resists include (a) increasing the sensitivity by increasing the molecular weight of PMMA, and (o) increasing the sensitivity by using a polymer in which the methyl ester side chain of PMMA is converted to other alkyl or allyl Nisder side chains. (c) Sensitivity enhancement using a copolymer of methyl methacrylate (MMA) and other vinyl compound system having quaternary carbon; (2) Sensitization enhancement using a collapsible three-dimensional polymer (positive cross-linked resist) Improvements in sensitivity are being considered. All of these methods of increasing sensitivity are attempts to widen the difference in dissolution rate between the radiation-exposed area and the non-irradiated area in the developing solution.

The present invention relates to the above item (c).

Conventional examples of radiation resists related to item (c) above include (1) copolymer of MMA and methacrylic acid, (il) M
Copolymer of MA and inbutyl methacrylate, (lii) Copolymer of MMA and benzyl methacrylate, OV) Copolymer of MMA and isopropyl methacrylate, (v) Copolymer of MMA and methacrylic acid chloride Copolymer, (Vi) Copolymer of MMA and n(,-hexyl methacrylate, 6IiD Copolymer of MMA and methacrylimide, Q
iiD A copolymer of diacetyl monooxime methacrylate into which an 8-element group (oxime group) has been introduced and MMA has been proposed. P for these resists in terms of characteristics such as sensitivity, resolution, and dry etching resistance.
When compared with MMA, it exhibits characteristics that are superior to PMMA in some aspects but inferior in other aspects, and from a comprehensive standpoint, it cannot be put to practical use as a resist film.

The present invention aims to eliminate the above-mentioned drawbacks of conventional positive radiation resist films, and aims to provide a resist with excellent sensitivity, resolution, and dry etching resistance.

The positive number ray resist of the present invention is composed of methyl methacrylate and the general formula (wherein R1 is CH3, C2H6, C3H7, C4H
9 or phenyl, R2U phenyl or naphthyl)
It consists of a copolymer with methacrylic acid oxime represented by:

The positive radiation resist of the present invention has improved photosensitivity due to the acyloxyimino group, and improved heat resistance and dry etching resistance due to the aromatic cyclic compound such as phenyl group and naphthyl group bonded to the acyloxyimino group. It was measured.

As a result, it was possible to obtain a positive radiation resist having high resolution characteristics comparable to those of PMMA, and having excellent sensitivity and dry etching resistance.

The positive 1-irradiation film of the present invention can be manufactured, for example, as follows. That is, it is obtained by copolymerizing with MMA by bulk polymerization using al-azobisinbutyronitrile as an initiator. Further, an oxime methacrylate monomer having an acyloxyimino group can be obtained by a dehydrochlorination reaction with an oxime derivative shown in the blank space below with methacryloyl chloride. When these copolymers of oxime methacrylate monomer and MMA are applied to positive radiation resists,
A number average molecular weight of 10,000 to 800,000 is practical.

When the number average molecular weight is 800,000 or more, film forming properties on St substrates are poor and adhesion to the substrates is also poor.

Further, if the number average molecular weight is 10,000 or less, the difference in dissolution rate in a developer between the unirradiated area and the irradiated area during development is small, which is not practical. Furthermore, based on the present invention (in the copolymer of MMA and oxime methacrylate, the molar concentration of the oxime monomer is selected from 1% to 30%. If the molar concentration of the oxime monomer is 30% or more, the molecular weight is large. Like copolymers, film forming properties and adhesion are not good.Also,
When the molar concentration of the 7-oxime is 1% or less, the sensitivity to radiation is not good, as it is on the same level as PMxA.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 9 g of pyridine and 161 ml of benzophenone oxime in 150 ml of methylene chloride. and methacryloyl chloride 7) was added dropwise at room temperature. This mixture was heated at 40°C.
After distilling off the methylene chloride reacted for 2 hours, the mixture was recrystallized from cyclohexane to obtain benzophenone oxime methacrylate.

A copolymer with MMA was obtained by bulk polymerization using benzophenone oxime methacrylate and methyl methacrylate f, &, 2L'-azoisobutyronitrile as an initiator. The obtained copolymer (molar ratio of benzophenone oxime methacrylate = 5%, number average molecular weight = 300,000) was dissolved in ethyl cellosolve acetate to prepare a resist solution. This melt was applied onto a silicon substrate by the spinconi-nido method at a rotational speed of 200 rpm for 25 seconds, and the silicon substrate was heat-treated in air for 170'Cl2O to remove the solvent. The film thickness at this time was 0.9 μm. Thereafter, sensitivity to electron beams and deep ultraviolet rays and dry etching resistance were measured under the following test conditions.

1 The exposure conditions for the electron beam are: electron beam acceleration voltage = 25KV;
Electron beam current: l x 10"m, exposure area = 11ff x 5
It is 0 μm. Under these conditions, the irradiation time was changed to adjust the exposure amount. From the relationship curve between the exposure amount and the remaining film thickness after development, the sensitivity of the resist was set at the exposure amount at which the film thickness became zero. Under these conditions, the electron beam sensitivity is 2, I X 10-5C76m
It was 2.

For exposure to far ultraviolet rays, light with a wavelength of 250 mm was used, and the amount of exposure was measured by the Light Index (LI value), that is, the integral value of the amount of light. Sensitivity was measured using a method similar to that used for electron beams. Further, under these conditions, the far ultraviolet sensitivity was LI-5ρ.

Next, the resistance of the resist film to dry etching was evaluated under the following conditions. That is, the discharge conditions of the plasma etching apparatus are 0C1a:o,
The test was carried out under the following conditions: 1 torr, PA7: 150 W, target: Mu 1205 plate, and distance between electrodes: 6 cIrL. At this time, when the change in film thickness per unit time was measured, it was 2 oOm/min.0 Example 2 The same operation as in Example 1 was repeated using various oximes instead of benzophenone oxime. The results obtained are shown in Table 1.

In this case, in any copolymer, the oxime amount is 5 to 8 mol% and the number average molecular weight is 2. Table 2 shows the publicly known PMMA or diacetyl! The results of actual measurements of the sensitivity to electron beams and deep ultraviolet rays and dry etching resistance of a copolymer of monooxime O methacrylate and MMA are shown. The experiment was conducted as follows.

PMMA [commercial product (TOKYO 0EBR-1ooo) was used, diacetyl! A copolymer of monooxime methacrylate and MMA was polymerized in the same manner as in Example 1.

The number average molecular weight of the obtained copolymer was 300,000 when the amount of diacetyl monooxime methacrylate was 5 mol. The sensitivity to electron beams and deep ultraviolet rays and dry etching resistance of the resist film thus obtained were measured in the same manner as in Example 1.

Below is a margin, ``( Table 2 Comparing the LI value and etching rate of the resist film shown in Example 1 and Table 1 with Table 2, it is found that The copolymer of the compound and MMA has the following sensitivity to electron beams:
PMMA and MMA and diacetyl I belonging to the prior art
It is twice as good as monooxime/methacrylate copolymers and four times as sensitive to ultraviolet light. In particular, it exhibits dry etching resistance useful as a resist material, which is 2 to 4 times more resistant than iPMMA and MMA/diacetyl monoxime/methacrylate copolymers.

As is clear from the above, the positive resist film 1d according to the present invention has a resolution as high as that of PMMA, and has unprecedented characteristics in terms of sensitivity and dry etching resistance. , its industrial value is incredible.

Claims (2)

[Claims] (1) A copolymer of methyl methacrylate and a methacrylic acid oxime compound represented by the general formula % or phenyl, R2 is phenyl or naphthyl, and the molecular weight of this copolymer is 10,0
1. A positive radiation resist, characterized in that the number is in the range of 00 to 800,000. (2) The positive radiation resist 2 according to claim 1, wherein the copolymerization rate of the copolymer of methyl methacrylate and methacrylic acid oxime compound is in the range of 1 to 30 mol. .