LaAlO3 and HfAlxOy thin films have been deposited by magnetron sputtering for replacement of SiO2 in new Complementary Metal Oxide Semiconductor applications. A three-layer model was found both in X-ray reflectivity (XRR) and spectroscopic ellipsometry (SE) analysis to be the best optical model for these two high-kappa materials. It was composed of an interfacial layer, covered by a layer of pure LaAlO3 or HfAlxOy, and a surface-roughness layer. In the case of LaAlO3 and HfAlxOy directly deposited on Si, the interfacial layer is a mixture of high-k material and amorphous-Si inclusions, which thickness is growing after post-deposition annealinu (PDA) in O-2 at 600 degrees C. On the contrary, for films deposited on thermally nitrided Si, the SiON-like interface did not change significantly after a PDA in 0, XRR analysis showed that the dielectric/Si interface of HfAlxOy/SiON/Si structure had a significantly smaller roughness than those of HfAlxOy/Si. When being deposited on SiON/Si substrates, HfAlxOy, and to a lesser extent LaAlO3, demonstrate superior diffusion barrier properties pointed out by X-ray photoelectron spectroscopy. (C) 2008 Elsevier B.V. All rights reserved.