Chemistry of inorganic compounds – Silicon or compound thereof – Binary compound
Reexamination Certificate
1999-03-31
2001-02-13
Utech, Benjamin L. (Department: 1765)
Chemistry of inorganic compounds
Silicon or compound thereof
Binary compound
C117S001000, C117S007000, C117S009000, C117S951000
Reexamination Certificate
active
06187279
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 element such as a monochromatic sorter, a high-temperature semiconductor electronic element, and a power device, and also to a method of producing the same.
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 perform the valence control of electrons and holes by doping an impurity. Moreover, the SiC has a wide band gap (for example, a single crystal 6H-SiC has a band gap of about 3.0 eV, and a single crystal 4H-SiC has a band gap of 3.26 eV) . Therefore, it is possible to realize large capacity, high frequency, high dielectric strength, and high resistance to environments which cannot be realized by existing semiconductor materials such as Si (silicon) and GaAs (gallium arsenide). For these reasons, the single crystal SiC receives attention and is expected as a semiconductor material for a next-generation power device.
As a method of growing (producing) a single crystal SiC of this type, known are a method in which the single crystal SiC is grown by the sublimation and recrystallization method using a seed crystal, and a high temperature epitaxial method in which, in the case of a high temperature, epitaxial growth is conducted on a silicon substrate by using chemical vapor deposition (namely, CVD), thereby growing a single crystal cubic SiC (&bgr;-SiC).
In the above-described conventional production methods, however, the sublimation and recrystallization method in which it is difficult to control growth of the single crystal owing to gas phase crystal growth under a high temperature, has problems such as lattice defects and micropipe defects, wherein pin holes having a diameter of several microns and passing through the crystal in the growing direction remain at about 100 to 1,000/cm
2
in a growing crystal. Such pinholes are called micropipe defects and cause a leakage current when a semiconductor device is fabricated, thus making it difficult to obtain the single crystal SiC having excellent quality. Moreover, in the high-temperature epitaxial method, the temperature of the substrate is high and it is also required to produce a high-pure reducing atmosphere. Therefore, the method has a problem in that it is difficult to conduct the method from the view point of installation. Furthermore, the method has another problem in that, because of epitaxial growth, the crystal growth rate is slow in the degree of several um per hour, thus resulting in a problem of extremely poor productivity of the single crystal SiC.
These problems block a practical use of the 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
The present invention has been conducted in view of the above mentioned circumstances and problems. The objects of the present invention are to provide an extremely high quality single crystal SiC in which lattice defects and micropipe defects do not exists, and a method of producing a single crystal SiC for making it possible to produce such a high quality single crystal SiC with high productivity, which can expedite the practical use of the single crystal as a semiconductor material.
In order to achieve the above objects, the single crystal SiC has features according to the present invention in which, in a state wherein a single crystal SiC substrate and a polycrystalline SiC plate are laminated to each other so as to be fixed, the single crystal SiC substrate and the polycrystalline SiC plate are subjected to heat treatment under an inert gas atmosphere equal to or lower than an atmospheric pressure and under a saturated SiC vapor atmosphere, whereby the polycrystalline SiC plate is solid-phase-transformed into the single crystal, thereby growing a single crystal integrated with the single crystal SiC substrate.
Moreover, in order to attain the above objects, the method of producing the single crystal SiC according to the present invention comprises the steps of:
laminating a single crystal SiC substrate and a polycrystalline SiC plate to each other so as to be fixed, and applying heat treatment to the single crystal SiC substrate and the polycrystalline SiC plate under an inert gas atmosphere and under the saturated SiC vapor atmosphere, whereby the polycrystalline SiC plate is solid-phase-transformed into the single crystal, thereby growing a single crystal integrated with the single crystal SiC substrate.
The present invention having the above features does not require a troublesome and expensive preliminary process wherein the single crystal SiC substrate and the polycrystalline SiC plate are ground resulting in high accurate smooth surfaces so that their opposed surfaces may be strictly closely fitted, or they are finished to be smooth so that the whole surfaces may be completely fitted to each other. The single crystal SiC substrate and the polycrystalline SiC plate which have low accurate smooth surface are used, and both substrate and plate are simply laminated to each other for fixation so as to apply heat treatment thereto, whereby the single crystallization owing to solidphase transformation of a whole layer surface of the polycrystalline SiC plate and the single crystallization in surface direction wherein the contact point functions as a starting point, thus making a whole layer surface of the polycrystalline SiC plate grow efficiently into a single crystal integrated with the single crystal SiC substrate so that it may be possible to obtain the single crystal SiC having high quality, which is substantially free from lattice defects and micropipe defects, with high productivity. Therefore, the single crystal SiC is expected as a semiconductor material for a power device, which is more superior in view of 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). This can expedite the practical use of the single crystal.
The other features and advantages of the present invention will become more apparent from the following description of preferred embodiments.
REFERENCES:
patent: 4419336 (1983-12-01), Kuriakose
patent: 4686032 (1987-08-01), Seider et al.
patent: 6020600 (2000-02-01), Miyajima et al.
patent: 6053973 (2000-04-01), Tanino et al.
Hiramoto Masanobu
Tanino Kichiya
Champagne Donald L.
Jones Tullar & Cooper P.C.
Nippon Pillar Packing Co. Ltd.
Utech Benjamin L.
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