Pressure dependence of electron temperature using rf-floated electrostatic probes in rf plasmas

Abstract

A new technique, which eliminates ac between probe and plasma by means of a ’’follower’’, permits electrostatic probes to be used in rf plasmas with a degree of confidence and accuracy which is equal, if not better, to that for a dc discharge. Measurements in argon, using this technique, have shown that electron temperature (T_e) in an rf discharge is not higher than in dc discharge. Moreover the values of T_e do not agree with von Engel’s law, but are in close agreement with a theory based on free diffusion and extrapolated up to values of pR=20 Torr cm (pressure times tube radius). These results are in contradiction with published electrostatic probe results for a positive column, but agree with published results as determined by microwave radiometry and optical spectroscopy. The hypothesis is made that the supporting evidence in favor of von Engel’s law, afforded by published electrostatic probe results, could be due to an artifact.