The influence of thickness of Hf-metal buffer layer on the interfacial diffusion and reaction was investigated using in situ Xray photoelectron spectroscopy, scanning Auger microscope and grazing incident X-ray reflectivity. Hf-metal firstly reacted with native Si oxide forming Hf silicates, and all Si-O was further reduced to be Si-0 after 1 nm Hf-metal deposition. The Hf-metal and Hf-suboxide in Hf(1 nm)/SiO2/Si structure were further oxidized to be Hf4+ during HfO2 sputtering deposition and post-deposition annealing. Si diffused out and reacted with HfO2 during annealing. The Hf(1 nm) buffer layer exhibited a better performance than the Hf(0.3 nm) buffer layer in suppressing the diffusion of Si and the reaction between diffused Si and HfO2. (c) 2004 Elsevier B.V. All rights reserved.