Silicon carbide crystal growth

Figure 3.23. A growth spiral on a silicon carbide crystal, originating from the point of emergence of a screw dislocation (courtesy Prof, S, Amelinckx).

One method of this type is direct synthesis. In this case silicon is loaded in the low-temperature part (2000-2200°C) of the crucible. Silicon vapors react with the crucible walls and form Si2C, SiC2, and SiC molecules. These molecules form nuclei of silicon carbide crystals and then crystal growth takes place. This method also has disadvantages mentioned above. 

FA Halden. Growth of silicon carbide crystals from solution in molten metal alloys. In Ref.l, p 115. 

Considerable interest in the solid-state physics of silicon carbide, that is, the relation between its semiconductor characteristics and crystal growth, has resulted from the expectation that SiC would be useful as a high temperature-resistant semiconductor in devices such as point-contact diodes (148), rectifiers (149), and transistors (150,151) for use at temperatures above those where silicon or germanium metals fail (see Semiconductors). 

Fig. 2. Researcher Dan Barrett (Westinghouse Science Technology Center) checks the hot (2400°C) crystal growfli furnace that he designed for physical vapor transport growth of single crystals of silicon carbide...

It is not always possible to obtain a low-porosity body by pressureless sintering , i.e. by sintering at atmospheric pressure. For example, difficulties are experienced with silicon nitride and silicon carbide. More commonly it may prove difficult to combine the complete elimination of porosity with the maintenance of small crystal size. These problems can usually by overcome by hot-pressing, i.e. sintering under pressure between punches in a die, as shown in Fig. 8.9. The pressure now provides the major part of the driving force eliminating porosity and the temperature can be kept at a level at which crystal growth is minimized. 

The discussed models of the carbon nanofilaments and nanotubes forma tion allow many other thermodynamic factors to be taken into consider ation, all of which affect the shape, texture, and growth rate of the nano objects under discussion (see, e.g.. Refs. [6, 7]). It is assumed that the forma tion of the fluidized active component of the catalyst nanoparticles due to its stationary oversaturation with the crystallizing component gives rise to the possibility to synthesize nanofilaments and nanotubes from not only carbon but also from different substances, such as silicon carbide (over catalysts capable of dissolving carbon and silicon simultaneously), germanium metal (over gold metal catalysts [8]), and so on. 

A completely amorphous structure was found by X-ray diffraction on fibers which were pyrolysed at temperatures up to 1300 °C. A crystallization starts around 1400 °C and nanocrystalline silicon carbide is formed with a crystallite size of about 2 nm. Compared to an uncured sample the crystallization is retarded. A significant crystallite growth occurs around 1500 °C connected with a decreasing of the fiber properties. The oxygen content of these SiC fibers is less than 1 wt. % found by neutron activation... 

Figure 4.18 is reprinted from Journal of Crystal Growth, Vol. 219, H Sone, T Kaneko and N Miyakawa, In situ measurements and growth kinetics of silicon carbide chemical vapor deposition from methyltrichlorosilane, pp. 245-252, 2000, with permission from Elsevier. 

Thermal oxidation of the two most common forms of single-crystal silicon carbide with potential for semiconductor electronics applications is discussed 3C-SiC formed by heteroepitaxial growth by chemical vapour deposition on silicon, and 6H-SiC wafers grown in bulk by vacuum sublimation or the Lely method. SiC is also an important ceramic ana abrasive that exists in many different forms. Its oxidation has been studied under a wide variety of conditions. Thermal oxidation of SiC for semiconductor electronic applications is discussed in the following section. Insulating layers on SiC, other than thermal oxide, are discussed in Section C, and the electrical properties of the thermal oxide and metal-oxide-semiconductor capacitors formed on SiC are discussed in Section D. 

Sublimation is one of the main methods of growing silicon carbide. This method is employed for growth of the material for abrasive applications as well as for the growth of single crystals and epitaxial layers for use in semiconductor electronics. The idea of the method is fairly simple, and is based on material transport from a hot source of material to a substrate which rests at a somewhat lower temperature. The transport is performed by the intrinsic vapour of the material at a high temperature, usually in the range 1600-2700 °C. 

The studies of growth by the sandwich method have provided a better understanding of the sublimation growth peculiarities and they have formed the basis of the new approach to the bulk crystal growth of silicon carbide. The first successful results in this direction were reported by Tairov and Tsvetkov [7,8]. Currently, similar studies are being performed by a number of research groups and rather impressive progress has been achieved thus far see Datareview 8.1. 

Aluminium contamination is seldom observed for low temperature vacuum sublimation. Aluminium has a low capture coefficient at low temperatures and it does not form refractory carbides with a low vapour pressure. Therefore, traces of aluminium can be easily removed by annealing the furnace in vacuum even if contamination occurs. However, if the material source is insufficiently pure, it can result in noticeable aluminium contamination, especially at elevated growth temperatures. For the bulk crystal growth, aluminium contamination is always observed when abrasive silicon carbide is used as source material [20,22]. The abrasive material usually is highly contaminated [1,22]. 

This includes single crystal silicon [15], germanium [22] and alumina [10] fibers. Polycrystalline fibers can grow either by a VLS or a VS phase transformation when the incident laser power (focal temperature) is intermediate, and supports the growth of a fiber with a semisolid tip. This includes polycrystalline silicon [15], boron [5] and silicon carbide fibers [23]. Amorphous fibers are obtained by a VS phase transformation when the incident laser (focal temperature) is low, and supports the growth of a fiber with a hot but solid tip. This includes amorphous silicon [15], boron [12], carbon [13] [16], silicon carbide [23], and silicon nitride [17] fibers. 

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