Influence of the methane concentration on HF-CVD diamond under atmosphericpressure

The most common approach for chemical vapor deposition (CVD) of diamond is the utilization of hydrocarbon gases highly diluted in hydrogen at low pres sure (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 ca rried out CVD diamond growth under atmospheric pressure. A dramatic increas e of the growth rate could be achieved when using the hot-filament (HF)-CVD technique at atmospheric pressure. Such an increase could already be obser ved in a previous experiment, however, under varying pressure and at a cons tant methane concentration of 0.5%. Furthermore, the crystalline quality of the diamond grains could be improved by hydrogen etching at atmospheric pr essure. 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 relationsh ip between the quality of the deposited diamond and the methane concentrati on has been investigated by Raman spectroscopy. The amount of activated hyd rogen was estimated from the etching rate of non-diamond components. At hig h 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 de pend on the residence time of the precursor in the reactor. Finally, Ran-ta n analysis revealed an increasing quality of diamond with decreasing methan e concentration. (C) 2001 Elsevier Science Ltd. All rights reserved.