SINGLE CRYSTAL SILICON CARBIDE AND PROCESS FOR PREPARING THE SAME

Abstract: According to the invention, a complex (M) which is formed by growing a polycrystalline β-SiC plate (2) on the surface of a single crystal α-SiC base material (1) by the thermal CVD method is heat-treated at a high temperature of 1,900 to 2,400°C, whereby polycrystals of the polycrystalline cubic β-SiC plate (2) are transformed into a single crystal, so that the single crystal is oriented in the same direction as the crystal axis of the single crystal α-SiC base material (1) and integrated with the single crystal of the single crystal α-SiC base material (1) to be largely grown. As a result, single crystal SiC of high quality which has a very reduced number of lattice defects and micropipe defects can be efficiently produced while ensuring a sufficient size in the term of area.

Description: Technical Field The present invention relates to a method of producing a single crystal SiC which is used as a substrate wafer for a light-emitting diode and an electronic device, or the like. Background 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, 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 resistance to environments 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 as a semiconductor material for a next-generation power device. As a method of growing (producing) single crystal SiC of this type, known are a method in which single crystal SiC is grown by the sublimation and recrystallization method using a seed crystal, and that in which, in the case of a high temperature, epitaxial growth is conducted on a silicon substrate by using the chemical vapor deposition method (CVD method), thereby growing single crystal cubic SiC (β-SiC). In the above-described conventional production methods, however, the crystal growth rate is as low as 1 µm/hr. Furthermore, the sublimation and recrystallization method has a problem in that pin holes which have a diameter of several microns and which pass through the crystal in the growing direction 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. These problems block a practical use of single crystal SiC which has superior characteristics as compared with other existing semiconductor materials such as Si and GaAs as described above. In the case of the high-temperature CVD method, the substrate temperature is as high as 1,700 to 1,900°C, and it is required to produce a high-purity 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 growth rate is naturally limited. Disclosure of Invention The invention has been conducted in view of the above mentioned circumstances of the prior art. It is an object of the invention to provide a production method in which the growth rate of the single crystal SiC is enhanced so that the area of the single crystal is sufficiently ensured, and which can expedite the practical use of the single crystal as a semiconductor material, and further to produce a single crystal SiC of a high quality in which lattice defects and micropipe defects are largely reduced. The method of producing single crystal SiC of the invention is characterized by depositing on a single crystal SiC substrate a polycrystalline plate consisting of Si and C atoms by a thermochemical vapor deposition in a temperature range of 1300 to 1900°C to provide a complex (M), applying heat treatment to the single crystal SiC substrate and the stocked polycrystalline SiC plate under a saturated SiC vapor atmosphere at an temperature range of 1900 to 2400°C, whereby the polycrystalline plate is solid-phase-transformed into the single crystal integrated with the single crystal SiC substrate. Such a single crystal is oriented in the same direction as the crystal axis of the single crystal SiC base material on which it is integrally grown. According to the thus configured invention, the complex consisting of the single crystal SiC base material and the polycrystalline plate stacked on the surface of the base material is subjected to a heat treatment at a high temperature, whereby polycrystals of the polycrystalline plate are phasetransformed while impurities from the external are prevented from entering between the single crystal SiC base material and the polycrystalline plate, and the crystal is oriented in the same direction as the crystal axis of the single crystal SiC base material and is integrated with the single crystal of the base material, thereby enabling a single crystal of high quality which has a very reduced number of lattice defects and micropipe defects, to be grown largely in the term of area. As a result, 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. The invention attains an effect that single crystal SiC of high purity and high quality can be obtained while entering of impurities between the single crystal SiC base material ad the polycrystalline plate on the surface thereof, and diffusion of the impurities are suppressed. Brief Description of Drawings Fig. 1 is a diagram showing a complex before the single crystal SiC of the invention is heat-treated, Fig. 2 is an enlarged view of a main portion before the single crystal SiC of the invention is heat-treated, and Fig. 3 is an enlarged view of a main portion after the single crystal SiC of the invention is heat-treated. Best Mode for Carrying Out the Invention Hereinafter, an embodiment of the invention will be described. Fig. 1 diagrammatically shows a complex M before single crystal SiC is heat-treated. The complex M is formed by growing a polycrystalline cubic β-SiC plate 2 on the surface of a single crystal hexagonal α-SiC base material 1 (6H type or 4H type) by the thermochemical vapor deposition method (hereinafter, referred to as the thermal CVD method) in the temperature range of 1,300 to 1,900°C. As clearly shown in a microphotograph of an etched section of Fig. 2, in the stage of growing the polycrystalline β-SiC plate 2, polycrystals 4 of the polycrystalline β-SiC plate 2 are grown on the surface of the single crystal α-SiC base material 1 containing lattice defects, and the single crystal α-SiC base material 1 and the polycrystalline β-SiC plate 2 are contacted with each other at crystal faces of different crystal forms so as to show a clear linear interface 3. Thereafter, the whole of the complex M is heat-treated in a saturated SiC vapor pressure and in a temperature range of 1,900 to 2,400°C, preferably 2,000 to 2,200°C. As a result, polycrystals 4 of the polycrystalline β-SiC plate 2 are phase-converted into α-SiC, oriented in the same direction as the crystal axis of the single crystal α-SiC base material 1, and integrated with the single crystal of the single crystal α-SiC base material 1, so that a large single crystal 5 is grown. When the complex M in which polycrystals 4 of the polycrystalline β-SiC plate 2 are formed on the surface of the single crystal α-SiC base material 1 by the thermal CVD method is subjected to a heat treatment as described above, crystal growth mainly consisting of solid-phase growth, such as that lattice vibration occurs in the interface 3 to change the atom arrangement. As a result, as clearly shown in a microphotograph of an etched section of Fig. 3, single crystal SiC of high quality which is substantially free from lattice defects and micropipe defects (10 or less per 1 cm 2 ) can be produced in a state where a sufficiently large size is ensured also in the term of area. In the embodiment, the single crystal α-SiC base material 1 is used as the single crystal SiC base material. Alternatively, for example, an α-SiC sintered member or a single crystal β-SiC member may be used. In the embodiment, the polycrystalline cubic β-SiC plate 2 which is grown on the surface of the single crystal α-SiC base material 1 by the thermal CVD is used as the polycrystalline plate. Alternatively, for example, a polycrystalline cubic α-SiC plate, an SiC sintered member of high purity, or an amorphous plate of high purity (10 14atm /cm 3 or less) may be used, and it is possible to obtain single crystal SiC of high quality in the same manner as the embodiment. As the single crystal α-SiC base material 1 in the embodiment, either of the 6H type or the 4H type may be used. When the 6H type is used, a single crystal which is converted from polycrystals of the polycrystalline β-SiC plate 2 into α-SiC as the progress of the heat treatment is easily grown in the same form as that of a single crystal of the 6H type. When the single crystal base material 1 of the 4H type is used, a single crystal in the same form as that of a single crystal of the 4H type is easily converted and grown. Preferably, the temperature conditions of the heat treatment of the complex M are set to be 1,900 to 2,400°C, and the process time period is 1 to 3 hours. When the temperature of the heat treatment is lower than 1,900°C, the kinetic energy of atoms cannot be given to many SiC constituting the interface. When the temperature is higher than 2,400°C, thermal energy which is very higher than the decomposition energy of SiC is supplied and crystals of SiC themselves are decomposed. Industrial Applicability As described above, the invention is a technique that a complex in which a polycrystalline plate consisting of Si and C atoms is stacked on the surface of a single crystal SiC base material is subjected to a heat treatment, so that a single crystal oriented in the same direction as the crystal axis of the single crystal SiC base material is integrally grown to a large size, whereby a single crystal of high quality which is superior in heat resistance and mechanical strength and which can realize a large capacity, a high frequency, a high dielectric strength, and a high resistance to environments that cannot be realized by existing semiconductor materials can be supplied efficiently and stably in the term of area and quantity.

Claims: Method of producing a single crystal SiC comprising the steps of: depositing on a single crystal SiC substrate a polycrystalline plate consisting of Si and C atoms by a thermochemical vapor deposition in a temperature range of 1300 to 1900°C to provide a complex (M), applying heat treatment to the single crystal SiC substrate and the stocked polycrystalline SiC plate under a saturated SiC vapor atmosphere at an temperature range of 1900 to 2400°C, whereby the polycrystalline plate is solid-phase-transformed into the single crystal integrated with the single crystal SiC substrate. Method according to claim 1, wherein said plate-shaped SiC plate is deposited on the surface of said single crystal consisting of a α-SiC material. Method according to claim 1 or 2, wherein said heat treatment temperature is set in a range of 2000 to 2200°C.

Inventors: TANINO KICHIYA, TANINO, KICHIYA, TANINO, Kichiya, Nippon Pillar Packing Co., Ltd
Applicants: NISSIN ELECTRIC CO LTD, NISSIN ELECTRIC CO., LTD.
Application year: 1998
Main classification: C30B29
IPC codes: C30B33, H01L21, C30B29, C30B25, C01B31, C30B1