SILICON ETCHING DURING THE HFCVD DIAMOND GROWTH

The silicon etching that occurs during the CVD diamond growth has been investigated as a function of the methane content in the gas phase by SEM and AFM in the tapping mode on pristine Si(lll) surfaces. Size, d epth, and angular distributions of the etch pits were recorded. We evi dence the strong effect of the carbon content on the etching process. The silicon etching is slightly increased with addition of 0.1-0.25% o f methane in the feed gas, and depletes with larger addition of carbon . This etching occurs easily along Si(100) directions. This is explain ed by the better stability on (100) planes of the precursor SiH2 to re move silane than on (111) planes. A modelization of the process points out the balance between the drop of the atomic hydrogen concentration in the gas phase and the inhibition of hydrogen bulk diffusion into s ilicon when increasing the methane content and covering the surface wi th carbon. This explains the occurrence of a maximum of silicon etchin g. Possible consequences on the diamond nucleation process are then pu t forward. It is thus expected that the etching of the silicon is gene rally detrimental as generating low-density silicon surface such as Si (100) where diamond nucleation is inhibited.