CVD diamond: controlling structure and morphology

For many industrial applications such as cutting tools, optical components and microelectronic devices the control of film structure and morphology is of critical importance. The crystallite size, orientation, surface roughness and the degree of sp(3) character have a profound effect on the mechanical, electrical and optical properties of the films deposited. In this paper we present new results on the effects of substrate pre-treatment, biasing and nitrogen doping on the growth rate, orientation, crystallite size, surface roughness and film resistivity. Preliminary results on the effects of pulsed biasing of the substrate on the film morphology are reported. It has been shown that as the particle size of the polishing material, for both diamond powder and alumina powder, is reduced the nucleation density is enhanced due to the creation of a greater number of nucleation sites. Diamond is harder than alumina and therefore creates more nucleation sites giving a higher deposition rate than alumina. Increasing the bias voltage can significantly alter the crystallite size, surface roughness and texture of the films deposited. For nitrogen doping it has been shown that the growth rate, resistance and the degree of sp3 character optimises at 200 ppm of nitrogen and all these properties degrade considerably with increasing nitrogen concentration. This has been related to carbon supersaturation of the surface. (C) 2000 Elsevier Science Ltd. All rights reserved.