The reaction between predeposited ultrathin Hf and native SiO2 on Si substrate was investigated using in situ X-ray photoelectron spectroscopy (XPS). During Hf metal sputtering, the initially arriving highly reactive atoms consume the oxygen of the native SiO2 to form HfO2. This preformed interlayer is helpful in suppressing interfacial diffusion and reaction during the subsequent thermal oxidation process, by which stoichiometric HfO2 films can be successfully obtained. Compared with HfO2/SiO2/Si samples deposited directly by reactive sputtering, the interface thickness is greatly reduced from 3.3 to 1.4 nm. (C) 2003 Elsevier B.V. All rights reserved.