Examination of the effects of nitrogen on the CVD diamond growth mechanism using in situ molecular beam mass spectrometry

Molecular beam mass spectrometry (MBMS) has been used to obtain quantitative measurements of the composition of the gas-phase species prevalent during diamond hot filament CVD using a variety of nitrogen-containing source gas mixtures. The ratio of C:N in the feedstock was maintained at 1:1, and the gas mixtures used were 0.5% each of CH3NH2 and HCN in H-2, and 0.5% CH4 in H-2 with added NH3 and N-2 at 0.5 and 0.25% respectively. The deposition rate and resulting film quality at optimum growth temperatures depend critically on the origin of carbon-containing species. At the relevant process temperatures, most of the gas-phase carbon exists in the form of unreactive HCN (similar to 70-90%) for all precursor gas mixtures (except CH4/N-2, with very little C,H, detected. As a result, poor quality diamond films were deposited at rates of less than 0.1 mu m h(-1). For CH4/N-2 mixtures, however, equal amounts of HCN and C,H, were detected, and well-faceted diamond films were produced at higher deposition rates (similar to 0.45 mu m h(-1)). These observations are explained in terms of the effects that nitrogen, and its resulting reaction products (NH3, HCN, CH3NH2, etc.), have on the gas-phase chemistry occurring during the CVD process. In particular, we suggest that N, can act as a catalyst for the destruction of H atoms, which in turn leads to significant changes in the gas-phase chemistry. (C) 1997 Elsevier Science S.A.