The effect of ion bombardment with Ar+ at several keV energy ranges resulting in silicide formation at HfO2-Si and ZrO2-Si interfaces has been investigated in situ with x-ray photoelectron spectroscopy. The set of spectra recorded during the growth of thin HfO2 and ZrO2 layers on Si(100) was compared to those obtained during subsequent sputtering with an Ar+ beam. It is shown that the Ar+ ion beam affects the MeO2-Si (Me = Hf,Zr) interface at thickness less than or equal to 3 nm, inducing the formation of a silicide layer similar to2 nm in thickness. The proposed mechanism of silicide formation including the depletion of the interface in oxygen due to its preferential sputtering and subsequent Hf-Si intermixing is corroborated by computer simulations. (C) 2004 American Vacuum Society.