Electron kinetics in the afterglow of cc-rf oxygen plasma- two discharge modes

The contribution discuss the electron kinetics in the afterglow phase of a 10 Hz pulsed (duty cycle of 50 %) capacitively coupled (cc-rf) oxygen plasma at 13.56 MHz. The line integrated electron density is measured by means of 160.28 GHz microwave interferometry. It is found two modes of the rf plasma, characterized by different behavior of the electron kinetics during the initial afterglow phase. On the one hand the rf plasma at higher rf power (P> 50 W) reveals a typical electropositive behavior like in argon. On the other hand the rf plasma is strongly electronegative at lower rf power (P < 50 W). In the afterglow an initial increase of the electron density is observed, which is six times larger than in the plasma-on phase. Solving a set of relevant rate equations in a 0d model, the electron kinetics agrees well with the experimental data. 1