An investigation was made of the O diffusivity in ZrO2 and HfO2 thin films deposited onto Si(100) by atomic layer deposition. In particular, a study was made of the kinetics of SiO2 interfacial layer growth upon rapid thermal annealing in an O atmosphere and of the O diffusivity in ZrO2 and HfO2 at high temperatures, using isotopically enriched 18O2. The interfacial oxide growth was studied using time-of-flight secondary ion mass spectrometry and transmission electron microscopy. This permitted measurement of the thickness of the SiO2 layer at the interface between Si and ZrO2 and HfO2 as well as the isotopic composition of O in those films. The oxidation kinetics of Si in the presence of ZrO2 and HfO2 was found to be totally different than those occurring on bare Si when annealed under the same conditions. During short annealing times, a relatively thick SiO2 interfacial layer was formed, regardless of O2 partial pressure; suggesting that ZrO2 and HfO2 were injecting O into the Si. For relatively long annealing times, Si oxidation was slower than bare-Si oxidation. Annealing in 18O2 permitted the clarification of O-exchange mechanisms in ZrO2 and HfO2. Oxygen Diffusion in Atomic Layer Deposited ZrO2 and HfO2 Thin Films on Si (100). S.Ferrari, G.Scarel: Journal of Applied Physics, 2004, 96[1], 144-9