OPTICAL-EMISSION SPECTROSCOPY DURING GROWTH OF DIAMOND-LIKE CARBON FROM A METHANE PLASMA

The influence of the CH4 flow rate on the emission intensity of the CH radical has been investigated by optical emission spectroscopy in the 190-315 nm and 378-503 mm wave bands. Emission intensities of two neu tral carbon lines at 193.0 nm and 247.9 nm were observed to have a sim ilar dependence on process parameters as the intensity of the CH 430.9 nm emission line. For a given r.f. power a critical value of the CH4 flow rate is observed. For flow rates lower than this critical value t he dynamic equilibrium between C(x)H(y) and hydrogen is shifted toward s higher hydrogen partial pressures. Thin films of diamond-like carbon deposited at such low flow rates were measured to have a lower densit y than those grown at higher flow rates. The intensities of the CH 430 .8 nm and the Hgamma lines were studied at pressures from 1 to 30 Pa, and only at the lowest values was a significant pressure dependence fo und. The deposition rate and the intensity of the CH 430.9 nm emission line is found to scale with the effective current defined as the rati o between the applied r.f. power and the negative self-bias.