GRAPHITE AS CARBON SOURCE IN CHEMICAL-VAPOR-DEPOSITION OF ALPHA-SILICON CARBIDE

Graphite is used for susceptors in chemical vapour deposition (CVD) pr ocesses as one of the standard materials due to its thermal stability, high electric conductivity and the possibility to form almost every k ind of shape easily. For the CVD of alpha-SiC, graphite is almost the only material used due to the necessity of high temperatures up to 210 0 K. As Si and C sources, SiH4, Si2H6, and C3H8 or other similar short -chain hydrocarbons are used together with hydrogen as a carrier gas. Graphite reacts with the hydrogen to form a lot of different hydrocarb on species at these high temperatures. The partial pressure and compos ition of these hydrocarbons depend on the temperature of the susceptor surface. We calculated the amount of carbon and the various compounds formed at equilibrium conditions. In some experimental setups it is p ossible that the amount of hydrocarbon formed by the graphite suscepto r exceeds the concentration of the input hydrocarbon. In this case the gas phase in the growth region is independent of the carbon source ga s. By a quadrupole mass spectrometer in the outlet part of the reactor , we measured the different CHx fractions in the output gas and found that they are not influenced by any change of the input hydrocarbons.