The ion-beam-assisted etching of silicon in O-2 environment is considered. The theoretically calculated dependences of silicon etching rate on the flux of Cl-2 molecules at different ion current densities are compared with experimentally measured. The composition of the adsorbed layer is determined. It is found that SiCl2 molecules prevail in the adsorbed layer. The reciprocal of relative concentration of SiCl2 molecules in the adsorbed layer linearly depends on the ion-to-neutral flux ratio. (c) 2006 Elsevier B.V. All rights reserved.