Electrical characteristics of capacitive RF discharges over a wide frequency range

Electrical characteristics have been measured for a parallel plate RF discharges in argon that were symmetrically driven at frequencies of 6.78, 13.56, 27.12, 54.24 and 81.36 MHz. Over a wide range of gas pressure (3mTorr--3 Torr) and discharge power (10-2--102 W), the discharge current, voltage and phase shift between them were mapped to display scaling laws for the frequency dependent parameters. It was observed that in an RF sheath controlled discharge at a fixed current, the discharge voltage is inversely proportional to the square of frequency while the discharge power is independent of frequency at small currents and is proportional to the inverse of frequency at large currents. At low discharge power and high frequency the authors were able to maintain the RF discharge in the resonance mode where the discharge voltage reaches a minimum (just a few volts) and the phase shift crosses zero. Scaling laws found in these experiments for the discharge electrical characteristics in the RF sheath controlled mode and the resonance mode are in good agreement with predictions of the plasma-sheath sandwich model developed by Godyak