Time-resolved plasma diagnostics for a better understanding of the improvement of pulsed MWPACVD of diamond

The deposition of diamond layers from CH4-H-2 microwave discharge operating in pulsed mode has been achieved. It has been shown that the variation of the time parameters of the process (frequency and duty cycle) leads to noticeable modifications of the deposited layers. From plasma diagnostic measurements, the change in plasma composition has been determined and correlated with the quality and growth rate of the diamond thin films. Particular attention has been paid to the concentration of H-atoms, CH and C-2 radicals and their evolution during the discharge regime and the afterglow. Indeed, these species are well known either as agents for graphite etching (H), or diamond precursors (CHx imaged by CH) or graphite precursors (C2Hx imaged by C-2) Optimum values of the power pulse repetition rate (500 Hz) and duty cycle (50%) have been found which are correlated with the variation of the relative concentrations of H, CH and C-2 with time, especially during the afterglow. It has been shown that these optimum conditions correspond to a minimization of C-2 in the afterglow while H and CH concentrations remain high enough to continue the diamond deposition process after the power is switched off.