SYSTEMATIC INVESTIGATION OF PLASMA EMISSION-SPECTRA DURING MICROWAVE DIAMOND DEPOSITION FROM CH4-CO2 AND C2H2-CO2 GAS-MIXTURES

As a test of the unifying scheme recently proposed by Bachmann et al., we studied the growth of diamond films from microwave plasma using non-conventional gas mixtures, i.e. CH4-CO2 and C2H2-CO2. For CH4-CO2, we observed a sharp compositional threshold between the diamond-yielding range and the no-growth range. By investigating systematically the plasma emission spectra, we found that this compositional threshold correlates with the onset of a broad emission line ascribed to CH. Moreover, moving into the diamond range, the onset and the increase in amplitude of an emission band attributed to C2 correlate with the increase in non-diamond carbonaceous species in the films. The same spectral features were observed for the C2H2-CO2 gas mixture, for which the diamond-yielding range appears to be very narrow.