US3463666A - Monocrystalline beta silicon carbide on sapphire - Google Patents

Description

United States Patent 3,463,666 MONOCRYSTALLINE BETA SILICON CARBIDE 0N SAPPHIRE Edward L. Kern and Dennis W. Hamill, Midland, Mich.,

assignors to Dow Corning Corporation, Midland, Mich., a corporation of Michigan No Drawing. Filed Aug. 27, 1965, Ser. No. 483,340 Int. Cl. H01b 1/04; B44d 1/00 US. Cl. 117--201 1 Claim ABSTRACT OF THE DISCLOSURE A method of producing monocrystalline beta silicon carbide wherein gaseous substances such as alkyl chlorosilanes are decomposed on a monocrystalline sapphire substrate heated to temperatures between 1650 C. and 2000 C. Since the surface crystal lattice of the monocrystalline sapphire closely approximates that of monocrystalline beta silicon carbide, the silicon carbide is deposited in monocrystalline rather than polycrystalline form.

The present invention relates to semiconductor crystals, and more particularly to methods of providing silicon carbide single crystals suitable for semiconductor use in microelectronic circuits for high temperature environments.

Semiconductor electronic devices have opened many new fields of application for electronic circuits. One area of potential use is in high temperature environments where conventional vacuum tubes would fail to function, or even melt. Semiconductor devices made of commonly used materials such as silicon and germanium may be operated at higher temperatures than can conventional vacuum tubes and exhibit power requirements of much diminished magnitude as well. However, there are many potential applications in missiles and equipment controls where circuits having still higher temperature capabilities are desirable or required.

The use of silicon carbide has heretofore been suggested for use in high temperature circuit applications. Due to the large binding energy required to break covalent bonds in silicon carbide, this material has been used at temperatures above 600 C., and the upper limit is not yet known with certainty. The large binding energy also provides excellent radiation resistance. Since single crystal structure is, in general, required for active semiconductor devices, there has recently been expended a large amount of effort in finding an economical method of producing monocrystalline silicon carbide. It is toward this problem that the present invention is directed.

An object of the present invention, therefore, is to provide an economical method of producing monocrys talline silicon carbide suitable for semiconductor device use.

Other objects and many attendant advantages of this invention will become apparent to those skilled in the art from a consideration of the following description and examples.

Basically, the present invention consists in the thermal reduction of a carbon and silicon-containing gas on a monocrystalline sapphire substrate. The gas used may be either an organosilane or a mixture of gaseous silicon compounds and carbon compounds. The thermal reduction is carried on in a stream of carrier gas such as hydrogen or argon. The monocrystalline sapphire substrate has a crystal lattice which very closely approximates the crystal lattice structure of silicon carbide. By thermally decomposing the silicon-and-carbon-containing gas at temperatures above 1650 C. the silicon and car bon form silicon carbide in a monocrystalline configuration presumably caused by the crystal lattice of the substrate.

Any of the gases known heretofore for production of silicon carbide by thermal decomposition of gases are suitable in the present process. Those recited in Canadian Patent No. 657,304, and US Patent 3,011,912, are exemplary. The preferred gases, however, are halogenated, including dimethyldichlorosilane, methyltrichlorosilane, trimethylmonochlorosilane and a mixture of methane and silicon tetrachloride. Hydrogen is preferred as a carrier gas, and the temperature range for deposition may vary between about 1650 C. and 2000 C.

In a specific example of the deposition process, a single crystal sapphire substrate was placed in a reaction chamber and was heated to a temperature of 1700 C. A gas mixture consisting of 7 liters per minute of H and 50 cc. per min. of (CH SiCl was passed over the heated substrate for 30 minutes, the pressure in the reaction chamber being atmospheric. Transparent yellow beta-silicon carbide in oriented single crystal form was formed on the substrate.

Varying the temperature between 1650 C. and 2000 C. had no apparent effect on the process. Below 0 C. polycrystalline SiC was formed. The upper limit of 2000 C. approaches the melting point of the sapphire substrate and apparently has a detrimental effect on the lattice structure of the substrate.

Similar results were obtained when monomethyltrichlorosilane, trimethylmonochlorosilane and a 1:1 mixture of methane and silicon tetrachloride were each substituted for the dimethyldichlorosilane under the same conditions.

If desired, the silicon carbide crystals can be doped to n-type, p-type, or to form p-n junctions by the addition of known gaseous dopants to the gas stream being fed into the reaction chamber. After forming the desired p-n junctions in the crystals, leads may be attached to the various portions of the crystal form active semiconductor devices. The sapphire substrate acts as an electrical insulator so that monolithic circuits can be constructed on the substrate by conventional masking and deposition techniques. Since the sapphire also has a much higher temperature capability than conventional monolithic circuit substrates the resultant circuit may be used in high temperature environments. Alternatively, the silicon carbide crystals may be removed from the substrate by etching the substrate away with suitable etchant materials and the crystals used to form devices or circuits as independent entities apart from the substrate.

We claim:

1. A method of producing monocrystalline beta silicon carbide comprising:

heating to between 1650 C. and 2000 C. a substrate material of monocrystalline sapphire; and providing a gaseous atmosphere of silicon-containing and carbon-containing gases chosen from the group consisting of dimethyldichlorosilane, methyltrichlorosilane, trimethylmonochlorosilane, and a mixture of silicon tetrachloride and methane in contact with said heated substrate whereby said gases are decom- 3 4 posed on said heated substrate to form monocrys- 3,099,534 7/1963 Schweickert et a1. talline silicon carbide thereon. 3,157,541 11/1964 Heywang et a1.

References Cited ALFRED L. LEAVITT, Primary Examiner UNITED STATES PATENTS 5 A. GOLIAN, Assistant Examiner 2,962,388 11/1960 Ruppert et a1. 3,011,912 12/1961 Gareis et al. S. Cl. X-R.

3,065,050 11/1962 Baumert. 117106