Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from solid or gel state
Reexamination Certificate
2001-03-20
2002-08-20
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from solid or gel state
C117S007000, C117S008000, C117S009000, C117S084000, C117S088000, C117S951000
Reexamination Certificate
active
06436186
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a material for growing single crystal SiC and a method of producing single crystal SiC, and more particularly to a material for growing single crystal SiC which is used as a substrate wafer for a high temperature/high frequency semiconductor electronic element such as a light-emitting diode, an X-ray optical element, a switching element, an amplifying element, and an optical sensor, and also to a method of producing such single crystal SiC.
BACKGROUND ART
SiC (silicon carbide) is superior in heat resistance and mechanical strength than existing semiconductor materials such as Si (silicon) and GaAs (gallium arsenide), and 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 property, a dielectric property, and a resistance to environments which cannot be realized by the above-mentioned existing semiconductor materials. SiC receives attention and is expected as a semiconductor material for a next-generation power device.
As a method of producing (growing) single crystal SiC of this type, conventionally known are: the modified sublimation and recrystallization method (modified Lely method) in which a seed crystal is placed in a graphite crucible and the gas sublimating from SiC serving as a raw material is diffusively transported in a closed space to be recrystallized on the seed crystal that is set to a low temperature; the high-temperature epitaxial method in which epitaxial growth is conducted on a silicon substrate by using the chemical vapor deposition method (CVD method), thereby growing single crystal cubic SiC (&bgr;-SiC); the magnetron sputtering method; and the plasma CVD method.
Among the above-mentioned conventional production methods, in the modified sublimation and recrystallization method, however, impurities enter during a step of growing a crystal to lower the impurity, two or more polytypes mixedly exist in the same crystal, and crystal defects are easily introduced into the interface. In addition, pin holes which are called micropipe defects, which cause a leakage current when a semiconductor device is produced, which pass through the crystal in the growing direction, and which have a diameter of several microns easily remain at about 300 to 1,000/cm
2
in a grown crystal. Therefore, the method is problematic in quality.
In the high-temperature epitaxial method, the substrate temperature is so high that the amount of reevaporation is large, and it is therefore required to produce a high-purity reducing atmosphere. Consequently, the method has problems in that it is difficult to practically conduct the method from the viewpoint of installation, and that, because of epitaxial growth, the crystal growth rate is naturally limited, and hence the productivity of single crystal SiC is very poor.
In the magnetron sputtering method and the plasma CVD method, the installation is massive, and defects such as micropipe defects are inevitably produced.
As described above, in the conventional methods of producing single crystal SiC, satisfactory single crystal SiC cannot be obtained from the viewpoints of installation, and the quality due to production of micropipe defects or the like. These problems are the main cause of blocking a practical use of single crystal SiC which has superior characteristics as compared with existing semiconductor materials such as Si and GaAs as described above.
Under these circumstances, the inventors have developed and proposed a method in which a complex configured by stacking in a closely contacted state a single crystal SiC base material and a polycrystalline plate consisting of Si atoms and C atoms is heat-treated under a condition where the base material side is placed in a lower low-temperature side of a heat treatment oven, whereby polycrystal members of the polycrystalline plate are transformed in imitation of single crystal of the single crystal base material so that single crystal SiC oriented in the same direction as single crystal of the single crystal base material is integrally grown.
According to the above-mentioned method of producing single crystal SiC which has been developed and proposed by the inventors (hereinafter, referred to as the proposed production method), Si atoms and C atoms do not constitute large crystal grains between the single crystal SiC base material and the polycrystalline plate, and a heat treatment is conducted under a state where an SiC layer in which a part of or the substantial whole of the Si and C atoms exist as a single member is interposed. Therefore, Si atoms and C atoms diffusively move in an interface between the single crystal SiC base material and the polycrystalline plate, and a single crystal can be integrally grown by solid-phase growth in which the diffusively moving Si and C atoms are simultaneously rearranged over a substantially whole area of the surface of the single crystal SiC base material which is on the low-temperature side, in imitation of single crystal of the single crystal SiC base material. Furthermore, impurities are prevented from entering from the atmosphere to the interface, whereby occurrence of crystal defects and distortion can be suppressed, and also occurrence of micropipe defects can be reduced. Therefore, the proposed production method has an advantage that single crystal SiC of a high quality can be grown with high productivity as compared with the above-mentioned conventional production methods.
The above-mentioned proposed production method has been further investigated. Finally, it has been found that, in order to grow single crystal SiC of a higher quality with higher productivity, the followings are important: to uniformly maintain the closely contacted state between the single crystal SiC base material and the polycrystalline plate, over the whole face; not to apply distortion on single crystal of the base material; and to uniformly maintain the temperature difference between opposing faces of the single crystal SiC base material and the polycrystalline plate over the whole region during heat treatment, to expedite lattice rearrangement of Si and C atoms which sublimate from the polycrystalline plate, in the surface of the base material in imitation of the underground single crystal SiC. The proposed production method has room for improvement in these points.
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 material for growing single crystal SiC that enables single crystal SiC of a very high quality in which micropipe defects and the like hardly occur, and a method of producing single crystal SiC which can produce single crystal SiC of a high quality easily and with high productivity from the viewpoints of installation and workability, thereby expediting practical use of single crystal SiC as a semiconductor material.
The material for growing single crystal SiC according to the first invention is characterized in that the base material is configured by a complex formed by stacking in a closely contacted state a single crystal SiC base material and a polycrystalline plate consisting of Si atoms and C atoms with interposing an organic or inorganic substance between opposing faces of the two members in a laminated manner, fundamental components of the substance being Si and O, and the complex is heat-treated to cause polycrystal members of the polycrystalline plate to be transformed in a same direction as single crystal of the single crystal SiC base material, thereby enabling single crystal to be grown. The method of producing single crystal SiC according to the second invention is characterized in that a single crystal SiC base material and a polycrystalline plate consisting of Si atoms and
Hiramoto Masanobu
Tanino Kichiya
Hiteshew Felisa
Jones Tullar & Cooper P.C.
Nissin Electric Co. Ltd.
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