Influence of the methane concentration on HF–CVD diamond under atmospheric pressure

Abstract

The most common approach for chemical vapor deposition (CVD) of diamond is the utilization of hydrocarbon gases highly diluted in hydrogen at low pressure (e.g. several thousands of Pascals (Pa)). The quality and growth rate of diamond strongly depends on the methane gas concentration, especially at high pressure, because the generation of atomic hydrogen sharply decreases with increasing pressure. In order to increase the growth rate, we have carried out CVD diamond growth under atmospheric pressure. A dramatic increase of the growth rate could be achieved when using the hot-filament (HF)–CVD technique at atmospheric pressure. Such an increase could already be observed in a previous experiment, however, under varying pressure and at a constant methane concentration of 0.5%. Furthermore, the crystalline quality of the diamond grains could be improved by hydrogen etching at atmospheric pressure. In the current study, the methane volume concentration was varied from 0.03% to 2.0% in order to estimate its effect on diamond growth. The relationship between the quality of the deposited diamond and the methane concentration has been investigated by Raman spectroscopy. The amount of activated hydrogen was estimated from the etching rate of non-diamond components. At high atmospheric pressure, high growth rates could be achieved up to a methane concentration of 0.3%. Moreover, the growth rate has also been shown to depend on the residence time of the precursor in the reactor. Finally, Raman analysis revealed an increasing quality of diamond with decreasing methane concentration.