The composition of polycrystalline hafnium oxide thin films has been measured by heavy-ion elastic recoil detection analysis (HI-ERDA). The films were deposited by high-pressure reactive sputtering (HPRS) on silicon wafers using an oxygen plasma at pressures between 0.8 and 1.6 mbar and during deposition times between 0.5 and 3.0 h. Hydrogen was found to be the main impurity and its concentration increased with deposition pressure. The composition was always slightly oxygen-rich, which is attributed to the oxygen plasma. Additionally, an interfacial silicon oxide thin layer was detected and taken into account. The thickness of the hafnium oxide film was found to increase linearly with deposition time and to decrease exponentially with deposition pressure, whereas the thickness of the silicon oxide interfacial layer has a minimum as a function of pressure at around 1.2 mbar and increases slightly as a function of time. The measurements confirmed that this interfacial layer is formed mainly during the early stages of the deposition process. (c) 2005 Elsevier B.V. All rights reserved.