EEDF evolution measurement in an inductive RF discharge

Abstract

Summary form only given, as follows. Space resolved EEDF measurements were performed over a wide range of external parameters in a cylindrical inductive rf discharge driven by a flat inductor coil at 6.78 MHz. Measurements were made along axial z direction (away from the inductor coil) for two radial positions, on the discharge axis and in the vicinity of the maximal rf electric field at the distance of 4.0 cm from the axis. The axial distributions of the plasma density and the effective electron temperature were found through integration of the measured EEDFs for argon pressure ranging between 1 mTorr and 100 mTorr and rf power dissipated in the plasma between 12 W and 200 W. In general, the electron density increased linearly with discharge power while the effective electron temperature slightly decreased with discharge power. At low pressure and small rf power we were able to resolve a three temperature EEDF structure with a low energy part similar to that found in a capacitive rf discharge and a high energy part in the inelastic energy range. With increasing discharge power the low energy part of the EEDF disappeared and this resulted in the effective electron temperature slightly increasing with discharge power which is opposite to well known election temperature dependency on discharge power. The measurements made with directional Langmuir probes oriented in the radial, axial and azimuthal directions showed a relatively small EEDF anisotropy at the lowest argon pressure. The plasma parameter space distribution, the anisotropy in the EEDF and the origin of three temperature EEDF are discussed in this presentation in the frame of non-local electron kinetics and collisionless electron heating at the plasma boundary.