The deposition of a thin magnesium metallic interlayer on an Si substrate prior to the deposition of an oxide thin film using rf-sputtering was investigated. The deposition of high-kappa HfO2 thin film was more particularly studied and it was demonstrated that the metallic interlayer acts as an oxygen barrier, preventing the formation of a low-kappa layer at the high-kappa/Si interface during the deposition. A post-deposition annealing treatment performed on the films induced the diffusion of the metal barrier into the HfO2 film and allowed obtaining a sharp interface. However, the degree of diffusion depends not only on the interlayer thickness, but also on the thickness of the high-kappa film. X-ray photoelectron spectroscopy was used to study the degree of oxidation of the Mg interlayer. High resolution transmission electron microscopy and energy filtered transmission electron microscopy were used to characterize the films and the diffusion of the Mg interlayer into the high-kappa film after annealing. In this work we will stress on the engineering of the interface via the diffusion of the Mg interlayer during the growth process and on annealing. (C) 2012 Elsevier B.V. All rights reserved.