A simple analysis on the abnormal behavior of the argon metastable density in an inductively coupled Ar plasma

Abstract

The abnormal behavior of the argon metastable density during the E-H mode transition in argon ICP discharge was investigated. Lots of investigations including global models expected that during and after the mode transition of ICP discharge the argon metastable density increases with applied rf power (i.e. electron density). However, recent measurement of metastable density [A.M. Daltrini, S.A. Moshkalev, T.J. Morgan, R.B. Piejak, W.G. Graham, Appl. Phys. Lett. 92 (2008) 061504] revealed that the argon metastable density decreases with the applied power during and after the mode transition. This result may not be explained by the previous global model which is based on the assumption of the Maxwellian electron energy distribution function (EEDF). In this paper, to explain this abnormal behavior with simple manners, a simple global model taking account of the effect of the non-Maxwellian EEDFs is proposed. The calculated result from the proposed global model showed that the argon metastable density can exhibit an abnormal behavior with electron density which is in good agreement with the measurement results, indicating the close coupling of electron kinetics and the behavior of metastable density. The proposed simple analysis is expected to provide qualitative kinetic insight to understand the behavior of the metastable density in various plasma discharges which typically exhibit non-Maxwellian distribution. (C) 2010 Elsevier B.V. All rights reserved.