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 noti ceable modifications of the deposited layers. From plasma diagnostic measur ements, the change in plasma composition has been determined and correlated with the quality and growth rate of the diamond thin films. Particular att ention has been paid to the concentration of H-atoms, CH and C-2 radicals a nd their evolution during the discharge regime and the afterglow. Indeed, t hese species are well known either as agents for graphite etching (H), or d iamond 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 c ycle (50%) have been found which are correlated with the variation of the r elative concentrations of H, CH and C-2 with time, especially during the af terglow. It has been shown that these optimum conditions correspond to a mi nimization of C-2 in the afterglow while H and CH concentrations remain hig h enough to continue the diamond deposition process after the power is swit ched off.