Nucleation and early growth of CVD diamond on silicon nitride

The initial growth process of CVD diamond on polycrystalline silicon nitride substrate, a typical cutting tool material, was elucidated in some detail. For the generation of diamond crystallites a gas mixture of hydrogen and methane in a microwave plasma-assisted chemical vapour deposition (MW PACVD) system was used. In order to gain insight into the formation and development of nuclei and the early stages of film growth different series of samples were investigated with deposition times between 5 min and 2 h. Owing to the supposed dependence of the process parameters on diamond nucleation and growth, substrate temperature, reactor pressure and CH4 concentration were varied. An incubation stage, shortened by high CH4 percentages, prior to the formation of diamond nuclei was proved. The nucleation density is favoured by high CH4 concentrations and low process pressures. Our results reveal that, independent of the deposition process parameters investigated, the nucleation step is terminated after similar to 25 min. Grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy were employed to detect intermediate layers, which could be formed during the chemical interaction of reactive plasma species and the substrate surface. A tentative model of the early stages of CVD diamond growth is presented. (C) 1998 Elsevier Science S.A.