Enhancement of silicon etching rate in XeF2 ambient is considered by a proposed model, which includes processes of adsorption, activation. chemical reactions, relaxation, desorption, and sputtering. The enhancement of silicon etching rate is explained by considering hydrocarbon species present in the vacuum chamber and assuming that activated sites (radicals) in the polymer film enhance the etching rate. The composition of the adsorbed layer during silicon etching in XeF2 ambient is calculated. It is found that activated polymer intensifies reaction of XeF2 molecules with Si atoms on the surface and causes the variation of the etching rate. Using the obtained theoretical results the difference in kinetics of the etching rates of first and subsequent runs is explained. (C) 2004 Elsevier B.V. All rights reserved.