The original chemical state of Ta2O5 thin films grown by reactive ion-beam-sputter deposition (RSD) and ion-beam-assisted sputter deposition (IBAD) was XPS-sputter-depth profiled using a 3 keV oxygen ion beam of 30 degrees incidence angle. The metallic Ta component found at the Ta2O5/Si interface of the film grown using the RSD method was not found at the interface of the film grown using the IBAD method. The same results were observed using the in situ XPS analysis for the initial stage of the thin film growth. The difference in the chemical state and the thickness of the interfacial SiO2 layer of the thin films grown by the 2 processes could be related to the reactivity of the silicon surface. In the case of the IBAD process, the silicon surface was depassivated in the initial film growth stage by oxygen-ion-beam sputtering of hydrogen atoms.