Single-crystal – oriented-crystal – and epitaxy growth processes; – Apparatus
Patent
1995-09-29
1998-01-13
Garrett, Felisa
Single-crystal, oriented-crystal, and epitaxy growth processes;
Apparatus
C30B 3500
Patent
active
057074461
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a device and a process for producing single crystals from silicon carbide (SiC).
A known process for producing SiC single crystals is the sublimation of technical grade SiC in powder form and growing of this SiC out of the gas phase on a monocrystalline SiC seed crystal. In the case of a first known device for implementing such a process, a cylindrical reaction vessel is provided in a vacuum installation, and the outer wall of this vessel surrounds a hollow cylindrical heating wall and an upper and lower heating plate. The heating wall and the heating plates consist of electrographite and are inductively coupled to a high-frequency (HF) heating coil arranged outside of the vacuum installation. A hollow cylindrical cylinder wall made of porous graphite is arranged inside the heating wall, concentrically to the heating wall. This intermediate wall separates a likewise hollow cylindrical supply chamber between the intermediate wall and the heating wall from a cylindrical reaction chamber inside the intermediate wall. A flat SiC seed crystal is arranged in the lower part of the reaction chamber symmetrically to the cylinder axis. A SiC supply that fills the supply chamber is heated by means of the heating wall and the heating plates to a temperature of about 2000.degree. C. to about 2500.degree. C., and the solid SiC is sublimated. The gas mixture that is formed thereby from the main components Si, Si.sub.2 C and SiC.sub.2, also referred to in the following as "SiC in the gas phase" diffuses through the pores of the graphite into the upper part of the reaction chamber and, from there, to the seed crystal that is retained at a crystallization temperature of about 1900.degree. C. to 2200.degree. C. The SiC crystallizes out on the seed crystal. The temperature gradient between the upper part and the lower part of the reaction chamber is adjusted, at the most, to 20.degree. C. /cm, in that an additional thermal insulation and/or an additional heating is provided for the upper heating plate and an additional cooling is provided for the seed crystal. Moreover, a protective gas, preferably argon (Ar) is fed into the reaction chamber to adjust a pressure of about 1 to 5 mbar, which counteracts the vapor pressure of the SiC in the gas phase. With such a device, it is possible to produce SiC single crystals having a length of at least 30 mm and a diameter of up to 40 mm (German C-32 30 727).
In the case of another known device, in place of a common HF-coil outside of the vacuum vessel, two resistance heaters are disposed inside of the vacuum vessel. One of these two resistance heaters is provided for heating a powdery SiC supply in a supply chamber to a sublimation temperature of typically about 2300.degree. C., and the other resistance heater is provided for heating the crystallization surface on a seed crystal disposed in a reaction chamber to a crystallization temperature of typically 2200.degree. C. The reaction chamber is disposed in this case above the supply chamber and separated from it by a separating wall of porous graphite. The temperature of the SiC powder and the temperature at the crystallization surface can be controlled independently of one another during the manufacturing process by means of the two resistance heaters, which are independent of one another. Therefore, the temperature gradient between the SiC powder in the supply chamber and the crystallization surface in the reaction chamber evolves by itself when these two temperatures are specified in dependence upon the thermal properties of the system, in particular upon the thermal transition coefficients of the materials and its geometry. The growth process of the single crystal growing on the seed crystal can be positively influenced by this independent adjustment of the sublimation temperature and of the crystallization temperature. To adjust a nearly constant temperature gradient during the crystal growth between the crystallization surface on the growing single crystal and the SiC powder, wh
REFERENCES:
patent: 4778559 (1988-10-01), McNeilly
patent: 4866005 (1989-09-01), Davis et al.
patent: 4956046 (1990-09-01), McNeilly
Patent Abstracts of Japan, vol. 14, No. 211, 2 May 1990 & JP-A-02 048 495 (Sanyo Electric) 19 Feb. 1990.
Patent Abstracts of Japan, vol. 13, No. 328, 24 Jul. 1989 & JP-A-01 108 200 (Sanyo Electric) 25 Apr. 1989.
Journal of Crystal Growth 109 (1991) pp. 17-23, 1991, Elsevier Science Publishers B.V. (North-Holland), D.L. Barrett et al.: SiC boule growth by sublimation vapor transport.
Berichte der Deutschen Keramischen Gesellschaft e.V., A. Dietzel, Wurzburg, DE, vol. 32, No. 8, pp. 229-250, Aug. 1955.
Lanig Peter
Volkl Johannes
Garrett Felisa
Siemens Aktiengesellschaft
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