RELATIONSHIP BETWEEN EMISSION-SPECTROSCOPY AND STRUCTURAL-PROPERTIES OF DIAMOND FILMS SYNTHESIZED BY PLASMA-ASSISTED CHEMICAL VAPOR-DEPOSITION

Diamond films were prepared on silicon substrates by microwave plasma chemical vapor deposition in a gaseous mixture of methane and hydrogen. A systematic study of emission from the plasma was performed as a function of methane concentration for various pressures. The variations in signals from H, H2, CH, C2 and C3 were recorded. No evolution of the emission spectra with time was observed during deposition. The emission intensity of these different species was found to vary abruptly with methane concentration up to 2% then to change smoothly, as do the morphology and structural quality of the deposits. The ratio of the emission intensities of the CH and H radicals with methane concentration, observed for any pressure above 5 Torr, evolved in the same way. Differences sometimes observed in the structural quality of the deposits prepared under identical conditions of pressure and gas composition could not be related to appreciable changes in the emission spectra. They are thought instead to be controlled by substrate parameters such as temperature and surface state.