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 neutral carbon lines at 193.0 nm and 247.9 nm were observed to have a similar 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 the dynamic equilibrium between C(x)H(y) and hydrogen is shifted towards higher hydrogen partial pressures. Thin films of diamond-like carbon deposited at such low flow rates were measured to have a lower density 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 found. 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 ratio between the applied r.f. power and the negative self-bias.