Diamond synthesis on silicon nitride by the hot filament chemical vapor deposition technique

Diamond filins have been deposited by hot filament chemical vapor deposition on hot-pressed silicon nitride substrates using a mixture of hydrogen and methane with a CH₄/H₂ volume ratio fixed to 0.5%. Scratching with diamond paste of the as-received substrates was necessary to obtain high nucleation densities (10⁸-10⁹ cm^-2) in the 750-1000°C deposition temperature range, while, on scratched substrates, the nucleation density decreased at 1050°C. The diamond deposition rate has its maximum at around 850-900°C. The film texture was {111}〈100〉 at the low deposition temperatures, while became {111} {100}〈110〉 at temperatures higher than 750°C. A careful analysis of the Raman spectra allowed us to identify the best deposition conditions for the growth of high quality diamond. Silicon nitride as a substrate for diamond CVD is better than cemented tungsten carbide due to the lower level of residual stress and to the higher phase purity of the coating.