In this paper, we have correlated electrical measurements of thin HfO 2 layers deposited on SiO 2 by atomic layer deposition with angle-resolved X-ray photoelectron spectroscopy experiments. Results show that the HfO 2/Si interface layer (IL) is made of a SiO x layer underneath a Si-rich Hf-silicate layer. The increasing of the IL thickness, during annealing, was essentially due to the silicon oxidation by –OH groups remaining in the HfO 2 layer after deposition. Using shorter water pulse time, we were able to limit the SiO x growth during deposition. We have also observed, after annealing at 800 °C under nitrogen, a decreasing of the interfacial layer electrical thickness as well as an improvement of the equivalent oxide thickness of the stack.