Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With decomposition of a precursor
Reexamination Certificate
1999-05-26
2001-04-10
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
With decomposition of a precursor
C117S088000, C427S255120
Reexamination Certificate
active
06214108
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing silicon carbide (SiC) single crystals in which micropipe defects are closed and silicon carbide single crystals with closed micropipe defects manufactured by the method.
2. Description of the Related Art
When an SiC single crystal is produced by the modified Lely method (sublimation method) using an SiC single crystal as a seed crystal, hollow tubes called micropipe defects with a diameter ranging from sub-microns (&mgr;m) to several microns (&mgr;m) are extended approximately along the growth direction, and contained in a grown crystal. An SiC single crystal having micropipe defects is not suitable as a substrate for electronic device formation since the micropipe defect significantly degrades the electric property of the device. Therefore, reduction of the micropipe defects is an important task for producing the SiC single crystal.
The methods for reducing the micropipe defects have been proposed in U.S. Pat. No. 5,679,153 and laid-open Japanese Patent Publication No. 5-262599(Japanese Patent No. 2804860).
In the method disclosed in U.S. Pat. No. 5,679,153, an epitaxial layer having reduced micropipe defects (defect density: 0 to 50 cm
−2
) is allowed to grow on a SiC substrate having micropipe defects (defect density: 50 to 400 cm
−2
) utilizing a phenomenon that micropipe defects are closed in the epitaxial layer on the SiC substrate by a liquid phase epitaxy from a melt of SiC in silicon.
In the method described in laid-open Japanese Patent Publication No. 5-262599(Japanese Patent No. 2804860), a single crystal revealing no hexagonal etch pit at all in alkali etching, that is, a single crystal having no micropipe defect is grown on the seed crystal by using a plane vertical to (0001) plane as a growing plane of the seed crystal.
In any of the above-described two methods, the single crystal is newly grown on the seed crystal and micropipe defects in the growing layer are reduced.
In the former method, an epitaxial layer having a thickness of 20 to 75 &mgr;m has to be grown by the liquid phase epitaxy technique for obtaining portions containing no micropipe defects, and micropipe defects are still existing below in this thickness range. Further, if the single crystal is grown again by a sublimation method using the above-formed epitaxial layer as a seed crystal, there is a possibility that sublimation from the closed portions of micropipe defects generates micropipe defect openings again since the closed portions of micropipe defects are thin. Therefore it is difficult to prepare a seed crystal and to suitably regulate sublimation growing condition to present in the closed portions from sublimating.
Meanwhile, although the latter method is effective for inhibiting the micropipe defect generation, stacking faults are newly generated in the grown single crystal. The substrates with stacking faults are known to exhibit an anisotropy of electron transport. Therefore, the crystal is not suitable for the substrate for the electronic device.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing problems, and an object thereof is not to suppress generation and succession of micropipe defects in a newly grown layer but to make it possible to close the micropipe defects existing in a silicon carbide single crystal within the crystal.
In order to accomplish the above-described object, in the present invention, at least a portion of a surface of a silicon carbide single crystal is coated with a coating material to seal up the micropipe defects openings, then, the single crystal is subjected to heat treatment to close micropipe defects existing in the silicon carbide single crystal.
Thus, micropipe defects existing in a silicon carbide single crystal can be closed by coating at least a portion of the surface of the silicon carbide single crystal with a coating material, then, performing heat treatment thereon. By this process, micropipe defects existing in silicon carbide single crystal can be closed within the silicon carbide single crystal, not in a newly grown layer on the silicon carbide single crystal. The silicon carbide single crystal includes a single crystal substrate, a single crystal ingot or the like.
Besides, when the heat treatment is performed such that the inside of the micropipe defects is saturated with silicon carbide vapors, the micropipe defects can be closed. In particular, micropipe defects existing in a silicon carbide single crystal can be closed by forming on at least a portion of a surface thereof, a silicon carbide, preferably, a silicon carbide single crystal or a silicon carbide oriented in the same direction as that of the crystal axis of the silicon carbide single crystal, a 3C-SiC (hereinafter, the Arabic numerals mean repetition period of a pair of Si-C in <0001> axis direction, C means a cubic system, H means a hexagonal system, R means a rhombohedral system.) epitaxial film, or the same/different polytype silicon carbide epitaxial film, then, performing heat treatment thereon.
Thus, crystal of the formed layer acts as a template during depositing in tubular voids so that micropipe defects can be closed more efficiently by forming the silicon carbide single crystal, the oriented silicon carbide and 3C-SiC epitaxial film.
As another feature of the present invention, a surface protecting material which protects a surface of a coating material is succeedingly provided on the coating material, then the heat treatment is performed. During the heat treatment, the coating material is protected from thermal etching by the surface protecting material, so that the coating material is prevented from being removed by sublimation and closed voids can be formed with certainly. As a result, the thickness of the coating material does not change compared to that before the heat treatment so that removing amount can be easily recognized when removing the coating material after forming closed voids.
Moreover, the heat treatment can be performed after providing the surface protecting material on the coating material, and then, fixing the silicon carbide single crystal on a seat to be installed in a crucible in which a silicon carbide source material is accommodated. As a result, the supply of the silicon carbide vapors to the coating material is performed in a preferable ambience so that thermal etching of the coating material is restricted more effectively. There is a possibility that the coating material sublimates if a several &mgr;m opening exists between the surface protecting material and the coating material. On the other hand, sublimating of the coating material is restricted even if the opening exists, when the heat treatment is performed under a saturated vapor pressure of silicon carbide vapors.
Furthermore, the surface protecting material can be made of a substance exhibiting a high melting point, a carbon material, i.e. a silicon carbide substrate or a silicon carbide powder. The substance exhibiting a high melting point, such as tungsten or tantalum, the carbon material and the silicon carbide are desirable because they are stable in the heat treatment.
On the other hand, micropipe defects can be closed more efficiently by previously filling the micropipe defects with a silicon carbide material, utilizing supercritical fluid and the like before the heat treatment. The micropipe defects can be closed further efficiently by coating the surface of a silicon carbide single crystal subsequent to filling the micropipe defects with the silicon carbide material.
The coating material can be formed of, for example, silicon carbide substrates or silicon carbide powders, 3C-SiC, silicon carbide single/poly-crystals having the same/different polytype as that of the silicon carbide single crystal, amorphous silicon carbides, materials exhibiting a high melting point (for example, tungsten), carbon materials (for example, graphite), or composite materials of a material containing silicon and the carbon material
Fukushima Yoshiaki
Hara Kazukuni
Hara Kunihiko
Hasegawa Takeshi
Hirose Fusao
Hiteshew Felisa
Kabushiki Kaisha Toyota Chuo Kenkyusho
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Method of manufacturing silicon carbide single crystal and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of manufacturing silicon carbide single crystal and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of manufacturing silicon carbide single crystal and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2472099