1. Field of the Invention
The present invention relates to a process and apparatus for growing a single crystal of, e.g. silicon carbide by the subliming recrystallization method, particularly a process and apparatus for growing an excellent single crystal with fewer defects.
2. Description of the Related Art
Conventionally, silicon carbide single crystal substrates are prepared as semiconductor substrates for high voltage high power semiconductor devices such as high voltage power transistors and high voltage diodes. The known methods for the manufacture of the silicon carbide single crystal substrates include the Acheson method, the Ley method and the subliming recrystallization method (Modified Lely method). The subliming recrystallization method is often adopted, for preparing semiconductor substrates, since it is advantageous for growing large area and high quality silicon carbide single crystals.
The subliming recrystallization method is disclosed in Japanese Examined Patent Publication (Kokoku) No. 63-57400.
Referring to FIG. 1, a silicon carbide powder 2 is charged in a closed carbide crucible 1 and heated and sublimed by an induction coil 8. A silicon carbide seed crystal 3, made of silicon carbide single crystal, is located in the crucible to face the silicon carbide powder 2. From the sublimed silicon carbide, silicon carbide 4 grows on the surface of a silicon carbide seed crystal 3 made of silicon carbide single crystal. The thus prepared silicon carbide single crystal 4 is supplied as a semiconductor substrate having a large area, controlled in its crystallinity and suitable for use in manufacturing a semiconductor device.
Optionally, liquid phase epitaxy (LPE) or vapor phase epitaxy (CVD) is further applied to the above silicon carbide single crystal substrate to form on the substrate a silicon carbide single crystal layer different in conductivity-type or carrier concentration from that of the substrate, which is also supplied as a substrate for manufacture of a semiconductor device.
However, a single crystal silicon carbide prepared by the above preparing method may have a number of linear defects, called micropipe defects, penetrating through the substrate. The micropipe defects involve electrical conductivity and therefore semiconductor devices manufactured using this semiconductor substrate with the micropipe defects may have defects such as leakage between source and drain or between gate and drain, which was confirmed by experiment
To prevent the problems due to micropipe defects, Japanese Unexamined Patent Publication (Kokai) No. 5-262599 proposed use of a crystal plane perpendicular to (0001) plane as the surface of a silicon carbide single crystal substrate in the subliming recrystallization method.
However, since this method uses crystal growth in the direction perpendicular to (0001) plane, this method cannot be used for semiconductor substrates having (0001) plane as the surface thereof. For example, when the semiconductor device to be manufactured is a vertical-type MOSFET, a semiconductor substrate having a surface of (0001) plane is usually used and the above method cannot be used.
The object of the present invention is to provide a process and apparatus for growing a single crystal substrate of, e.g., silicon carbide, in a large scale while micropipe defects are prevented.