Addition of a small amount of oxygen to the CH4 and H2 feed gas permits hot filament assisted chemical vapor deposition (HFCVD) of diamond at significantly lower filament and substrate temperatures. The former can be reduced to as low as 1400 °C and the latter to 450 °C. The amount of oxygen required is much lower than what has been used in most studies of the oxygen effect. For each CH4%, there is a narrow window in the O/C ratio, where diamond can be deposited at low temperature. This window shifts to higher O/C ratios as the CH4% increases and expands with increases in filament temperature. The effect of changing substrate and filament temperatures on growth rate and film quality are often not consistent with previous experiences with HFCVD of diamond. Increasing the filament temperature does not always improve the growth rate and film quality, and the non-diamond carbon content in the film is dramatically reduced at lower substrate temperatures. Optimum conditions were found that gave reasonable growth rates (~0.5 µm/h) with high film quality at filament temperatures below 1750 °C and substrate temperatures below 600 °C. With these reductions in operating temperatures, power consumption can be significantly reduced and the filament lifetime extended indefinitely.
