HOT-FILAMENT CHEMICAL-VAPOR-DEPOSITION OF DIAMOND ON SIALON AT PRESSURES UP TO 500-TORR

Diamond layers were grown by hot-filament-activated chemical vapour deposition at total gas pressures ranging from 5 to 500 Torr, using hydrogen-methane gas mixtures, filament temperatures of 2200-2500-degrees-C and SiAlON substrates. In the lower pressure range from 5 to 10 Torr, 0.5 vol.% CH4 was the optimum concentration for producing well-faceted diamonds, while concentrations above 1.0 vol.% CH, led to ballas-type diamonds. Between 20 and 300 Torr, faceted diamond layers grew also at CH4 concentrations of 1.0 vol.%, whereby the highest growth rate (1.44 mum h-1) was obtained at 20 Torr, with a filament temperature of 2500-degrees-C. From 50 to 500 Torr the deposition rate decreased with increasing gas pressure, even failing below 0.05 mum h-1 at the highest pressure. This strong decrease in the growth rate with pressure was linked to a strong decrease in the diamond nucleation rate. Increasing filament temperature led to a higher nucleation density and a higher deposition rate over the whole pressure range investigated. The observed effects of gas pressure on diamond nucleation and growth can be explained with changes in the formation and recombination rates and the resulting concentrations of the atomic hydrogen.