Electrical characteristics and electron heating mechanism of an inductively coupled argon discharge

The external electrical characteristics of inductively coupled argon RF discharges at 13.56 MHz have been measured over a wide range of power at gas pressures ranging from 3 mTorr to 3 Torr. External parameters, such as coil voltage, current and phase shift, were measured. From these measurements the equivalent discharge resistance and reactance, the power transfer efficiency and the coupling coefficient between the primary coil and the plasma were determined as a function of discharge power and gas pressure. The efficient RF power transfer and the large value of the effective electron collision frequency found here at low gas pressure suggest some collisionless electron heating mechanisms. This mechanism is identified as non-local electron heating in the inhomogeneous RF field due to spatial dispersion of the plasma conductivity.