Ta2O5−x films prepared on Si(100) by chemical vapor deposition and annealed in oxygen gas, both natural abundance and isotope labeled [16O2(77%)+18O2(23%)], were analyzed by in situ x-ray photoelectron spectroscopy and ex situ time-of-flight secondary ion mass spectroscopy (TOFSIMS). Before annealing at 800 °C, the film was oxygen deficient, i.e., Ta2O5−x, and there was a very small amount of interfacial SiOy. During annealing in O2, additional Si was oxidized and the Ta2O5−x approached stoichiometric composition. Based on TOFSIMS depth profiles of O18-labeled ions, Si at the interface is oxidized during O2 annealing mainly by transfer of O from Ta to Si, not by migration of gas phase O2 through Ta2O5−x to the unoxidized Si. The atomic oxygen from the dissociative reaction of gas phase O2 is transported through Ta2O5−x by a vacancy mechanism and replenishes the loss of O from Ta2O5−x to Si.

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