Investigations of Capacitively-Coupled Plasmas by Electrostatic Probe Technique
Abstract
This work reports on the electric characterization of capacitively-coupled RF plasmas by employing electrostatic (Langmuir) probes. Experiments with argon, oxygen and sulfur hexafluoride (SF6) plasmas were carried out. The floating potential and cathode self-bias, as well as the shape of the Langmuir probe current-voltage characteristics were measured and interpreted. The current-voltage characteristic for SF6 plasmas showed a strong variation in the floating potential, and a distortion in the region of electron retarding. An unexpected behavior of the curves was observed for the higher pressure discharge regime, at 100 mTorr. The cathode self-bias also was very different for SF6 plasmas when compared to more electropositive oxygen and argon discharges. The results obtained pointed to the massive presence of negative ions in SF6 plasmas.