Thin (45 nm) and ultrathin (4.5-1 nm) Al2O3 layers deposited on HF-stripped Si or thin SiO2 surfaces by atomic layer deposition were studied by angle-resolved x-ray photoelectron spectroscopy. before and after rapid thermal annealing (RTA) at 800degreesC for 15 min in N-2 or annealing in a conventional furnace under ultrahigh vacuum (UHV) (p= 10(-6) mbar) and N-2 at the same temperature. Samples were characterized in terms of chemical defects and interfacial regrowth upon annealing. Chemical defects as Al-OH groups are evidenced from the O 1s spectra even after RTA. Interfacial regrowth, estimated from the Si 2p components intensity, was found (1) to occur upon every kind of annealing, (2) to be dependent on the initial Al2O3 thickness (the thicker the layer the greater the regrowth), and (3) to be significantly reduced on SiO2 surfaces as thin as 0.5 nm. In agreement with previous studies, we also consistently found the presence of an oxidized Si component at the Al2O3/substrate interface centered at 102 eV for which an assignment to silicate groups (Si-O-Al) is proposed, on the basis of other x-ray photoelectron spectroscopy parameters. Given the influence of UHV annealing in interfacial regrowth, AI-OH defects may play an important role in interface oxidation. 2002 American Vacuum Society.