The influence of temperature and polarization of the substrate during the in situ treatment under argon plasma of silicon is studied. This treatment is performed before microwave plasma enhanced chemical vapour deposition of alumina. The transitory period preceding the introduction of the aluminium precursor is simulated by a 1.5 min oxygen plasma exposure of the substrate. The surface of the samples is analysed by electron-induced X-ray emission spectroscopy (EXES) to probe the physico-chemical environment around the silicon atoms, and by atomic force microscopy (AFM) to study the surface morphology. A thin superficial silica layer is evidenced, whose thickness is ranging from 0.8 to 1.8 nm, depending mostly on the temperature and subsequently on the polarization. Upon treatment the morphology of the surface is changed and the roughness is increased. Furthermore, AFM observations of substrates exposed to the aluminum precursor during 2 s are showing a columnar growth of the alumina film. (C) 2003 Elsevier Science B.V. All rights reserved.