Roughness control of polycrystalline diamond films grown by bias-enhanced microwave plasma-assisted CVD

A simple growth technique to control the surface roughness of polycrystalline diamond films is proposed. The films are grown using a microwave plasma-assisted chemical vapor deposition method, with varying the methane (CH4) concentration at the stage of bias-enhanced nucleation. It is found from the field-emission scanning electron microscope spectra that nanocrystalline diamond nuclei are formed at a relatively high methane concentration, causing a secondary nucleation at the accompanying growth step. The RMS value of surface roughness for grown films, which is estimated from the atomic force microscope images, monotonically decreases from 165 to 53 nm with methane concentration. It is also observed that the surface roughness is closely related to the nucleation density. In addition, employing a two-step growth method, which consists of first-growth at 500 W and subsequent second-growth at 800 W, enables the as-grown polycrystalline diamond film to have a smaller roughness of approximately 46 nm. This is believed to be due to the secondary nucleation effect induced during the growth step. (C) 2003 Elsevier Science B.V. All rights reserved.