Effect of pressure on nanocrystalline diamond films deposition by hot filament CVD technique from CH_4/H_2/Ar gas mixture

The effect of pressure on the deposition of nanocrystalline diamond(NCD) films in a hot filament chemical vapor deposition(HFCVD) system was investigated using CH4/H2/Ar gas mixture.The reactor pressure was found to have the strongest influence on nucleation of nanocrystalline diamond films.The range of Ar concentration in the CH4/H2/Ar mixture that permits the deposition of nanocrystalline diamond(NCD) film at 40 torr is 90%,while the Ar concentration needed for the transition into nanocrystalline diamond phase is 50% at 5 torr.Such pressure dependence of the nanocrystalline diamond film growth was suggested to result from two competing effects of pressure on the concentration of reactive species near the film growth surface,and the C2 density at lower pressure(5 torr) is higher than that at high pressure(40 torr) at the same Ar concentration.