POTENTIAL OSCILLATIONS IN AN ELECTRONEGATIVE PLASMA DRIVEN BY AN ASYMMETRY RF DISCHARGE

Potential oscillations of electronegative plasmas have been experiment ally studied in a strongly asymmetric rf (13.56 MHz) discharge. Oscill ation amplitudes in the plasma were found to increase suddenly from 10 to 60V with increasing concentration of SF6 gas in He gas, while grad ually from 10 to 40V in CF4 mixed plasma. The electron energy distribu tion functions (EEDFs) measurement predicted an electron beam travelli ng from the plasma towards the rf electrode because of the potential d ouble layer in the sheath picked up by an emissive probe. A clear diff erence in potential formation and EEDFs profiles in comparison to thos e in electropositive plasmas has been detected. A more marked gas conc entration dependence was obtained in a SF6 gas than in a CF4 one due t o the more active production of negative ions in a SF6 plasma.