PATTERN-FORMING PROCESS UTILIZING RADIATION-INDUCED GRAFT POLYMERIZATION REACTION

Abstract: A pattern-forming process utilizing radiation-induced graft po­ lymerization reaction, which comprises conducting pattern formation us­ ing a resist capable of undergoing radiation-induced graft polymeriza­ tion reaction and having excellent dry etching resistance, i.e., a phenyl group-containing polymethacrylate, or polystyrene or its derivative. This process enables a fine resist pattern to be formed even in an extremely low dose, and permits good etching work utilizing existing dry etching technique.

Description: Technical Field The present invention relates to pattern fabrication by radiation-induced graft copolymerization employed in the processing of semiconductor devices and particularly to a resist having excellent dry etching durability. Background Art In the processing of ultra large scale integraters (ULSI), studies on the pattern fabrication by radiation-induced graft copolymerization using a radiation, such as X-ray, are in progress. This pattern fabrication typically comprises an exposure step of irradiating a predetermined region of a resist layer formed on a wafer through coating with a radiation, a graft copolymerization step of introducing a monomer to graft-copolymerize the resist layer with the monomer, a development step of developing the resist layer to fabricate a predetermined resist pattern, and an etching step of etching the surface of the wafer by making use of the resist pattern as a mask. The feature of the above-described pattern fabrication resides in that the resist can sufficiently be exposed even when the exposure dosage to the resist is small, i.e., an enhancement in the sensitivity of the resist can substantially be attained. This feature enables the pattern fabrication process to be expedited, which makes it possible to attain a high throughput. Conventional pattern fabrication by radiation-induced graft copolymerization is described in, for example, Japanese Patent Laid-Open No. 137671/ 1978 (corresponding to U.S. Patent No. 4195108). In this literature, an example wherein poly(methyl methacrylate) (PMMA) is used as a resist is described. This resist is widely employed as a model resist in the field of lithography. However, the above-described PMMA resist has the drawback that when the surface of the substrate is dry-etched by making use of the fabricated resist pattern as the mask, the mask per se is etched, i.e., the dry etching resistance is low. Therefore, an improvement in the dry etching resistance of the resist has been desired in order to put the pattern fabrication by radiation-induced graft copolymerization to practical use. WO 85/02030 describes the use of a polymeric resist material in a dry development process, in which by irradiation and exposure to an oxygen-containing atmosphere peroxides or hydroperoxides are created, which are thermally decomposed and reacted with a silicon-containing compound. Among useful resist polymers there are mentioned polystyrene, poly(methylmethacrylate) and poly(benzylacrylate). Disclosure of Invention An object of the present invention is to provide pattern fabrication by radiation-induced graft copolymerization which enables an improvement in the dry etching resistance. In order to attain the above-described object, the resist according to the present invention is made of a resist material capable of undergoing radiation-induced graft copolymerization and having excellent dry etching resistance. The present invention provides a method of pattern fabrication by radiation-induced graft copolymerization comprising a coating step of forming, on the surface of a substrate (1,1',2) to be provided with a pattern, a resist layer (3,3') composed of a poly(methacrylate) which can undergo graft copolymerization having a phenyl group in each methacrylate moiety an exposure step of irradiating a predetermined region of said resist layer with a radiation (10), a graft copolymerization step of introducing a monomer (6) to graft-copolymerize said resist layer with said monomer, a development step of developing said resist layer to fabricate a predetermined resist pattern (5'), and an etching step of conducting dry etching of the surface of said substrate by making use of said resist pattern as a mask. The poly(methacrylates) having a phenyl group in each methacrylate moiety according to the present invention, such as poly(phenyl methacrylate) or poly(benzyl methacrylate), have excellent dry etching resistance, so that the current dry etching process can be employed as it is. Further, since these polymers generate radicals having a long life by irradiation, it is possible to conduct copolymerization with a monomer through graft copolymerization. Therefore, the present invention enables not only the formation of a fine pattern of a resist in a very small exposure dosage but also excellent etching performance through the use of the current dry etching process, which greatly contributes to an improvement in the reliability. Brief Description of Drawings Figs. 1A to 1E are each a schematic flow diagram illustrating Example 1 according to the present invention; Figs. 2A to 2E are each a schematic flow diagram illustrating comparative Example 2 ; and Fig. 3 is a graph showing the dry etching resistance of a typical resist. Best Mode for Carrying Out the Invention Example 1 Figs. 1A to 1E are each a schematic flow diagram illustrating Example 1. A Si wafer 2 having a silicon oxide film 1 containing phosphor deposited on the whole surface thereof is coated with poly(phenyl methacrylate) (PPhMA) to form a resist 3 having a thickness of 1 µm. The resist was exposed to an X-ray 10 in a nitrogen atmosphere containing air in an amount reduced to 1 % or less through an X-ray mask 4 having a predetermined circuit pattern 7 (see Fig. 1A). The X-ray 10 was emitted from an electron-bombardment type source with a molybdenum target (not shown) and had a dominant wavelength of 0.54 nm, and the exposure dosage was about 10 mJ/cm². After the completion of the exposure, the sample 2 was transferred to a reactor (not shown) evacuated to 1 Pa or less, followed by a reaction with vapor of an acrylic acid monomer 6 introduced into the reactor for 5 min, thereby forming a graft copolymer 5 (see Fig. 1B). The reaction temperature was 25 ± 0.5°C. The sample 2 was then immersed in a developer (2-methoxyethyl acetate) for 30 sec (at 25 ± 0.5°C) and then dried to prepare a negative resist pattern 5' (see Fig. 1C). The silicon oxide film 1 of the substrate was subjected to dry etching by making use of the above-fabricated resist pattern 5' as a mask (see Fig. 1D). The dry etching was conducted by making use of parallel type dry-etching equipment and a reactant gas comprising CF₄ (67Pa) at a rf power of 100 W. Excellent dry etching of the silicon oxide film 1 could be attained. Then, the resist pattern 5' was removed (see Fig. 1E). Comparative example. Figs. 2A to 2E are each a schematic flow diagram illustrating comparative Example. A Si wafer 2 having an aluminum film 1' deposited on the whole surface thereof is coated with chlorinated polymethylstyrene (CPMS) to form a resist 3' having a thickness of 1.5 µm. The resist 3' was exposed to an X-ray 10 in the same manner as that of Example 1 (see Fig. 2A). However, in this case, the exposure dosage of the X-ray 10 was 5 mJ/cm². Then, graft copolymerization with an acrylic acid monomer 6 (see Fig. 2B) and development (see Fig. 2C) were conducted in the same manner as that of Example 1, thereby fabricating a resist pattern 5'. Thereafter, the aluminum film 1' of the substrate was subjected to dry etching by making use of the above-fabricated resist pattern 5' as a mask (see Fig. 2D). The dry etching was conducted by making use of reactive ion etching equipment and a reactant gas comprising BCl₃ (50Pa) at a rf power of 200 W. Excellent dry etching of the aluminum film 1' could be attained. Then, the resist pattern 5' was removed (see Fig. 2E). Fig. 3 is a thickness loss curve with respect to the etching (silicon oxide film) of the resists used in the two above-described Examples. It is apparent from the results that the dry etching resistance of these resists is on the level of photoresist AZ1350J (Trade Mark), a conventional novolak based resist. For comparison, a thickness loss curve with respect to a PMMA resist for graft copolymerization employed in the conventional process is also shown in Fig. 3. In the above-described Example of this invention, PPhMA was used as the resist. Besides this compound, the resist may be made of poly(benzyl methacrylate), poly(2-phenylethyl methacrylate), poly(benzhydroxy methacrylate), or poly(bromophenyl methacrylate). With respect to the monomer, besides the above-described acrylic acid, an aqueous solution of acrylic acid, methacrylic acid and an aqueous solution thereof, methyl methacrylate, methyl acrylate, may also be used. The temperature of the graft copolymerization of the resist material with the monomer may be 15 to 100°C. Further, besides the above-described X-ray for example an electron beam, an ultraviolet ray, may be used as the radiation. When an electron beam is used, it is possible to conduct the exposure of a predetermined region without use of any mask.

Claims: A method of pattern fabrication by radiation-induced graft copolymerization comprising a coating step of forming, on the surface of a substrate (1,1',2) to be provided with a pattern, a resist layer (3,3') composed of a poly(methacrylate) which can undergo graft copolymerization, having a phenyl group in each methacrylate moiety an exposure step of irradiating a predetermined region of said resist layer with a radiation (10), a graft copolymerization step of introducing a monomer (6) to graft-copolymerize said resist layer with said monomer, a development step of developing said resist layer to fabricate a predetermined resist pattern (5'), and an etching step of conducting dry etching of the surface of said substrate by making use of said resist pattern as a mask. A method of pattern fabrication by radiation-induced graft copolymerization according to claim 1, wherein said poly(methacrylate) is poly(phenyl methacrylate) or poly(benzyl methacrylate). A method or pattern fabrication by radiation-induced graft copolymerization according to claim 1, wherein said monomer (6) is selected from the group consisting of acrylic acid, an aqueous solution of acrylic acid, methacrylic acid, an aqueous solution of methacrylic acid, methyl methacrylate, and methyl acrylate. A method of pattern fabrication by radiation-induced graft copolymerization according to claim 1, wherein said graft copolymerization step is conducted at a temperature of 15 to 100°C. A method of pattern fabrication by radiation-induced graft copolymerization according to claim 1, wherein said resist material is a poly(methacrylate) having a phenyl group and said development step is conducted by making use of a developer composed of 2-methoxyethyl acetate. A method of pattern fabrication by radiation-induced graft copolymerization according to claim 1, wherein said exposure step is conducted by irradiating said resist layer (3,3') with said radiation (10) through a mask (4,7) having a predetermined pattern. A method of pattern fabrication by radiation-induced graft copolymerization according to claim 1, wherein said radiation (10) is an X-ray.

Inventors: KIMURA TAKESHI, MOCHIJI KOZO, OGAWA TARO, OIZUMI HIROAKI, SODA YASUNARI, KIMURA, TAKESHI, MOCHIJI, KOZO, OGAWA, TARO, OIZUMI, HIROAKI, SODA, YASUNARI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1988
Main classification: G03C5
IPC codes: H01L21, G03F7, G03C5