NUCLEATION AND EARLY GROWTH OF CVD DIAMOND ON SILICON-NITRIDE

The initial growth process of CVD diamond on polycrystalline silicon n itride substrate, a typical cutting tool material, was elucidated in s ome detail. For the generation of diamond crystallites a gas mixture o f hydrogen and methane in a microwave plasma-assisted chemical vapour deposition (MW PACVD) system was used. In order to gain insight into t he formation and development of nuclei and the early stages of film gr owth different series of samples were investigated with deposition tim es between 5 min and 2 h. Owing to the supposed dependence of the proc ess parameters on diamond nucleation and growth, substrate temperature , reactor pressure and CH4 concentration were varied. An incubation st age, shortened by high CH4 percentages, prior to the formation of diam ond nuclei was proved. The nucleation density is favoured by high CH4 concentrations and low process pressures. Our results reveal that, ind ependent of the deposition process parameters investigated, the nuclea tion step is terminated after similar to 25 min. Grazing incidence X-r ay diffraction and X-ray photoelectron spectroscopy were employed to d etect intermediate layers, which could be formed during the chemical i nteraction of reactive plasma species and the substrate surface. A ten tative model of the early stages of CVD diamond growth is presented. ( C) 1998 Elsevier Science S.A.