The space-time-averaging procedure and modeling of the RF discharge

Abstract

An approach to modeling RF discharges and the ensuing analysis of fast electron and ion motions for the case of electrode sheaths in the high-pressure RF discharge is discussed. Time-averaging over fast electron motions with the applied voltage frequency gives analytic expressions for the average electric field and average ionization density. The resulting relatively simple equations for the ion density profile describe drift, diffusion, ionization, and recombination processes. The simple scaling rules, the approximate expressions for the density profile in various regions, the sheath length, the ion density at the plasma-sheath boundary, and the dimensionless criteria for various discharge regimes can be deduced. For the non-self-sustained discharge, it is demonstrated that the ion drag towards the electrode and the diffusion results in significant lowering of the ion density in the sheath compared with the positive column at not too high a pressure. The analytic transition criterion from alpha to gamma forms of the self-sustained discharge is obtained. The numerical solution of the averaged ion equations yields the results which nearly coincide with the results of full-scale modeling.