Parameters of Cl-2/Ar plasma were investigated aimed to understand the mechanism of Ar addition influence on etching rate acceleration. Analysis was carried out on the base of combination of experimental methods and plasma modelling. It was found that the addition of Ar to chlorine under a constant total pressure condition cause changes in plasma electro-physical properties (EEDF, mean electron energy) due to the 'transparency' effect. Direct electron impact dissociation of Cl-2 molecules was found as the main source of chlorine atoms while the contributions of dissociative attachment and stepwise dissociation involving Ar metastable atoms are negligible. It was supposed that the main reason of etching rate increasing in Cl-2/Ar mixture plasma is connected with simultaneous action of Ar on volume chemistry and the heterogeneous stage of etching process. (C) 2003 Elsevier Science B.V. All rights reserved.