In order to investigate the effects of oxygen addition on diamond synthesis, the behaviors of diamond deposition using Hot-Filament chemical vapor deposition (HFCVD) method, which is simple and easy to control the deposition parameters, are extensively studied by varying the deposition parameters. Diamond films are deposited on silicon wafer at the condition of substrate temperatures ; 530 - 1050℃, total reaction pressures ; 5 - 60 torr and methane concentration ; 0.4% - 2.4% in both $CH_4$-$H_2$ and $CH_4$-$H_2$-$O_2$ systems, and they are characterized by micro-Raman spectroscopy and scanning electron microscopy.
At the deposition condition of low substrate temperature or high $CH_4$ concentration or high total pressure, soot-like carbon and non-diamond components are deposited without oxygen addition. However, if a small amount of oxygen about 0.2% is added, well faceted diamond films can be obtained. Increasing the oxygen concentration, the high quality diamond films are deposited and it is verified through Raman spectrum analysis. Consequently, the deposition ranges for the high quality diamond synthesis (substrate temperature, $CH_4$ concentration and total reaction pressure) are extended due to the oxygen addition. Thus it is evident that oxygen addition promotes the formation of diamond.
As oxygen is added, it is considered that new etchants such as O and OH, which prohibit the deposition of non-diamond components (graphite and amorphous carbon), are formed and the relative concentration of $CH_3$ radical, which is the key species of diamond synthesis, over $C_2H_2$ species increases. Therfore it is suggested that these two effects surely make the diamond synthesis more feasible.
