Nonequilibrium water permeation in SiO2 thin films

Abstract

Nuclear resonance profiling was used to measure the distributions of hydrogen incorporated into dry SiO₂ films by thermal treatments in steam. Thermal oxides were grown on silicon to a thickness of 260 nm in dry O₂ and were subsequently treated in steam at temperatures of 320 and 500 C for periods lasting between 390 and 6×10⁵ s. The concentrations of hydrogen carried in by permeating water were then profiled with 6.4 MeV ¹⁵N ions using the resonant nuclear reaction ¹H(¹⁵N, αγ)¹²C. Water was seen to penetrate the films rapidly and to slowly react with the SiO₂ uniformly throughout the films. Two distinct stages were observed in the buildup of H, indicating that the water/SiO₂ reaction involves at least two concurrent processes rather than a single‐stage process.