Nonequilibrium Water Permeation in SiO2 Thin Films

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 deg C for periods lasting between 390 and 6 x 10 expn 5 s. The concentrations of hydrogen carried in by permeating water were then profiled with 6.4 MeV 15N ions using the resonant nuclear reaction 1H15N, alpha gamma12C. 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 waterSiO2 reaction involves at least two concurrent processes rather than a single-stage process.