Electron heating reduction in inductively coupled plasma at conditions of the anomalous skin effect

Abstract

Summary form only given. A simple analytic model of electron heating in inductively coupled plasma (ICP) at the condition of anomalous skin effect (nonlocal regime) has been developed. The model assumes an exponential RF field decay and takes into account both, collisional and electron thermal effects and thus is applicable for an arbitrary degree of collisionality. Simple expressions are obtained for the spatial profile and integral power absorption of RF power in ICP. Negative power absorption regions have been found for a given exponential profile of the electric field in plasma and are shown to be similar to those found in experiment and calculation with a selfconsistent electric field distribution. Thus, the negative power absorption is associated with thermal dispersion of the RF electron current, rather than with the non-monotonic profile of the RF electric field typical for anomalous skin effect. The results obtained from an approximate model are compared with experimental data and with the results of a self-consistent model, showing in both cases a reasonable agreement. A new effect of electron heating reduction in ICP due to electron thermal motion has been predicted in this model. It has been demonstrated that at low driving frequencies accounting for electron thermal motion results in a reduction of the integral RF power absorption in ICP compared with the purely collisional (ohmic) heating for the same electron-atom collision frequency. The reduction of electron heating, found in our simple analytical approach with the exponential RF electric field, has been confirmed in a model with the self-consistent profile of the RF electric field.