Influence of dc bias voltage on the refractive index and stress of carbon-diamond films deposited from a CH4/Ar rf plasma

Abstract

The dc self bias voltage developed during CH4/Ar radio frequency plasma-enhanced vapor deposition of thin films containing polycrystalline diamond grains within an a:C matrix (carbon-diamond) is found to influence the optical and mechanical properties of the films. In particular it is shown that there is a simultaneous etch deposition process which takes place, and that the dc bias can be used to control this etch rate, and hence the net film growth rate. When a balance between etching and deposition is achieved, the films show increased residual stress and optical density with exposure to Ar+ bombardment in the plasma. In addition to the measured dc bias the local electric field developed around the substrate is also found to significantly influence the energy with which ions impinge upon the growing film.