Monocrystalline silicon carbide is an extremely stable, high performance material which is used in the manufacture of electronic devices. It is particularly useful for applications requiring high resistivity. These applications can include power electronics, high frequency devices, and other electronics. The physicochemical properties of monocrystalline SiC can vary with different manufacturing techniques. For example, the crystal polytype of the monocrystalline silicon carbide can be changed based on the method used. Therefore, it is important to determine the proper dopant concentration for obtaining the desired electrical and mechanical properties.
Monocrystalline silicon carbide can be manufactured in two ways: sublimation and heteroepitaxial. The sublimation method is used to produce smaller, single crystals. However, it is difficult to control the crystal polytype. In addition, it is also very expensive. Furthermore, the quality of the produced silicon carbide may not be sufficient for semiconductor devices.
The heteroepitaxial method is used to produce large monocrystals. This can be achieved by designing a crucible with two separate spaces. One space is devoted to the SiC material and another space is devoted to the solid material containing the dopant element. Both of these spaces are then heated to a predetermined temperature. During the heating process, a high frequency current is used to heat the graphite crucible to the specified temperature.
Compared with the sublimation method, the heteroepitaxial method provides a much more uniform dopant concentration. Moreover, the dopant element can be pre-heated before being applied to the solid material. Thus, the rate of the etching of the solid material can be reduced. As a result, the specific surface of the solid material can be reduced to 0.5 m2/g or less.
Although the heteroepitaxial method offers a higher monocrystalline silicon carbide quality, it can be more costly. Consequently, monocrystalline SiC ingots are only produced in a limited number. Also, the amount of impurities can increase. Since these impurities can affect the quality of the monocrystalline silicon carbide, they are not desirable.
A modified Lely method is also used to produce monocrystalline SiC wafers. During the growth process, SiC vapours are generated and removed from the growth zone. Because SiC vapours contain more silicon atoms than carbon atoms, the vapours can drift away from the growth zone. But the drift can be balanced by a continuous enrichment of the vapour phase with carbon atoms. Over time, this can contribute to a more perfect structure.
Another method of manufacturing monocrystalline silicon carbide is by ion implantation. This technique can be used to obtain high-resistivity silicon carbide. Moreover, it is possible to apply an appropriate ratio of the dopant to other dopants. For example, the dopant can be aluminum or boron. Generally, coarse-sized impurities are entrapped by the SiC powder grains. If the dopant concentration is not controlled, it will result in defects on the growing surface of the SiC crystal. Moreover, a longer growth process can cause the embedding of dust.
Nevertheless, the monocrystal silicon carbide produced by the ion implantation technique is not as uniform as the monocrystal silicon carbide produced using the sublimation and heteroepitaxial methods. Moreover, it is more difficult to control the size of the monocrystal.
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