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.sup.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.