Collisionless electron power absorption in capacitive radio-frequency plasma sheaths

Abstract

A capacitively coupled, rf biased electrode mounted in an inductively coupled plasma reactor is used to investigate rf power coupling through the resulting capacitive sheath. Carefully calibrated current and voltage probes provide the electrical measurements necessary for this investigation. An external negative dc bias enables control over the electron component of the total current arriving at the electrode through the capacitive sheath. Sheath models generally assume that electron loss at the end of the rf cycle is negligible but recent theoretical work indicates that there is a significant difference in power coupled through the sheath when electron loss is permitted. The experimental study presented here confirms this result. Retardation of electron loss to the electrode is accompanied with an increase in rf power absorbed by the electrons in the capacitive sheath. Comparing the current signals with and without electron loss establishes that the measured increase in power is associated with the electron loss phase of the rf cycle, which is consistent with predictions of the earlier theoretical work.