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 quanti tative measurements of the composition of the gas-phase species preval ent during diamond hot filament CVD using a variety of nitrogen-contai ning source gas mixtures. The ratio of C:N in the feedstock was mainta ined at 1:1, and the gas mixtures used were 0.5% each of CH3NH2 and HC N 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 optimu m growth temperatures depend critically on the origin of carbon-contai ning species. At the relevant process temperatures, most of the gas-ph ase carbon exists in the form of unreactive HCN (similar to 70-90%) fo r all precursor gas mixtures (except CH4/N-2, with very little C,H, de tected. As a result, poor quality diamond films were deposited at rate s of less than 0.1 mu m h(-1). For CH4/N-2 mixtures, however, equal am ounts of HCN and C,H, were detected, and well-faceted diamond films we re produced at higher deposition rates (similar to 0.45 mu m h(-1)). T hese 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 particul ar, 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 che mistry. (C) 1997 Elsevier Science S.A.