Chemistry of inorganic compounds – Silicon or compound thereof – Binary compound
Reexamination Certificate
1998-11-06
2001-03-20
Utech, Benjamin L. (Department: 1765)
Chemistry of inorganic compounds
Silicon or compound thereof
Binary compound
C117S004000, C117S007000, C117S009000, C117S951000
Reexamination Certificate
active
06203772
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a single crystal SiC and a method of producing the same, and more particularly to a single crystal SiC which is used as a semiconductor substrate wafer for a light-emitting diode, an X-ray optical device such as a monochromatic sorter, a high-temperature semiconductor electronic element, and a power device, and also to a method of producing the single crystal SiC.
2. Description of the Prior Art
SiC (silicon carbide) is superior in heat resistance and mechanical strength, and also has good resistance to radiation. In addition, it is easy to achieve valence control of electrons and holes by doping an impurity. Moreover, SiC has a wide band gap (for example, single crystal 6H—SiC has a band gap of about 3.0 eV, and single crystal 4H—SiC has a band gap of 3.26 eV). Therefore, it is possible to realize a large capacity, a high frequency, a high dielectric strength, and a high environmental resistance to which cannot be realized by existing semiconductor materials such as Si (silicon) and GaAs (gallium arsenide). For these reasons, single crystal SiC receives attention and is expected to be used as a semiconductor material for a next-generation power device.
As a method of growing (producing) a single crystal SiC of this type, the Achison method and the sublimation and recrystallization method are employed. These methods, are generally known as industrial methods for producing an SiC abrasive material. In the Achison method, a seed crystal substrate is heated from the outer circumference by using a high frequency electrode, so as to generate many nuclei in a center portion of the seed crystal substrate, whereby a plurality of spiral crystal growths are developed, which are centered at the center portion of the seed crystal substrate. In the sublimation and recrystallization method, powder SiC produced by the Achison method is used as a raw material, and a crystal is grown on a single crystal nucleus.
In the Achison method of the above-described conventional production methods, however, a single crystal is grown slowly over a long time period, so that the crystal growth rate is as low as about 1 mm/hr. In addition, a large number of crystal nuclei are generated in an initial growth stage, and they propagate to an upper portion of the crystal as the crystal growth advances. Thus, it is difficult to singly obtain a large-size single crystal.
In the sublimation and recrystallization method, a high-speed growth of about 1 mm/hr is adopted mainly for an economical reason (production cost), so that impurities and pin holes which have a diameter of several microns and which pass through the crystal in the growing direction are likely to remain at about 100 to 1,000/cm
2
in a growing crystal. Such pin holes are called micropipe defects and cause a leakage current when a semiconductor device is fabricated. Accordingly, there exists a problem in that a single crystal SiC having sufficiently good quality cannot be obtained. In the Achison method and the sublimation and recrystallization method, moreover, it is very difficult from a technical point of view to maintain cleanness of the atmosphere in the vicinity of a growing crystal, thereby producing a problem in that the quality is impaired also by contamination from the outside in the vicinity of a single crystal. These problems block a practical use of a single crystal SiC which has superior characteristics as compared with other existing semiconductor materials such as Si and GaAs as described above.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a large-size single crystal SiC in which impurities, micropipe defects, and the like do not remain, in which contamination from the outside is suppressed to a minimum level, and which has high quality, and to a method of producing a single crystal SiC which is large and has high quality, and which can expedite the practical use of SiC as a semiconductor material.
In order to attain the above-mentioned object, the single crystal SiC of the invention is characterized in that two complexes in each of which a polycrystalline film of &bgr;-SiC or &agr;-SiC is grown on a surface of a single crystal &agr;-SiC substrate by thermochemical deposition are subjected to a heat treatment under a state where the complexes are piled via the surfaces of the polycrystalline films of the complexes so that crystal orientations of the single crystal &agr;-SiC substrates of the complexes are directed in the same direction, whereby the polycrystalline films of the complexes are recrystallized to integrally grow a single crystal on the single crystal &agr;-SiC substrates of the complexes.
In order to attain the same object, the method of producing a single crystal SiC according to the present invention is characterized in that two complexes are produced respectively by growing a polycrystalline film of &bgr;-SiC or &agr;-SiC on a surface of a single crystal &agr;-SiC substrate by thermochemical deposition, the two complexes are piled via surfaces of the polycrystalline films of &bgr;-SiC or &agr;-SiC so that crystal orientations of the single crystal &agr;-SiC substrates of the complexes are directed to the same direction, and the two piled complexes are then heat-treated, whereby the polycrystalline films of the complexes are recrystallized to grow a single crystal which is integrated with the single crystal &agr;-SiC substrates of the complexes.
According to the present invention having the above-mentioned characteristics, two complexes in each of which a polycrystalline film of &bgr;-SiC or &agr;-SiC is grown on a surface of a single crystal &agr;-SiC substrate by thermochemical deposition are piled via the surfaces of the polycrystalline films and then collectively heat-treated, whereby each of the polycrystalline films of the complexes is recrystallized so that a single crystal which is integrated with each of the single crystal &agr;-SiC substrates of the complexes, and which is large and particularly thick can be grown.
Furthermore, the heat treatment is performed under a state where the two complexes are piled via the surfaces of the polycrystalline films of the complexes, and particularly a state where the surfaces of the polycrystalline films are smoothly ground and the smooth surfaces are closely fixed to each other. This suppresses contamination which is caused by adhesion of suspended substances and the like in the vicinity of the surfaces of the polycrystalline films, to a minimum level. Moreover, even when the ambient atmosphere is varied during the heat treatment, a phenomenon by which the variation of the ambient atmosphere causes a surface portion of the polycrystalline films to decompose and disappear, or crystals deposited in the vicinity to adhere to the surfaces of the polycrystalline films can be suppressed to a minimum level. Therefore, impurities, micropipe defects, and the like do not substantially remain. Furthermore, contamination from the outside, and an effect of the variation of the ambient atmosphere during the heat treatment can be suppressed to a minimum level so that a large-size single crystal SiC which stably has very high quality is obtained with high productivity. Thus, it is possible to attain the effect of expediting the practical use of single crystal SiC which is superior in a large capacity, a high frequency, a high dielectric strength, and a high resistance to environments to existing semiconductor materials such as Si (silicon) and GaAs (gallium arsenide) and which is expected as a semiconductor material for a power device.
Other objects and effects of the present invention will be clarified in embodiments which will be described below.
REFERENCES:
patent: 5846638 (1998-12-01), Meissner
patent: 6053973 (2000-04-01), Tanino et al.
Copending Application 09/147,620, filed Feb. 3, 1999.
Hiramoto Masanobu
Tanino Kichiya
Champagne Donald L.
Jones Tullar & Cooper P.C.
Nippon Pillar Packing Co. Ltd.
Utech Benjamin L.
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