We have investigated the oxidation of hydrogen-terminated Si(111) and (100) surfaces stored in air, using synchrotron radiation photoemission spectroscopy and infrared absorption spectroscopy in the multiple internal reflection geometry. We demonstrate that water present in air is predominantly involved in the oxidation of surface Si–H bonds, and that native oxide starts to grow when the surface hydrogen coverage is decreased. In order to explain the latter phenomenon, we propose a kinetic model of oxidation which considers the manner in which native oxide formation preferentially occurs on those portions of the surface where the Si–H bonds are oxidized. We suggest that the oxidation of surface Si–H bonds, the rate of which is strongly dependent on the humidity of air, is a rate-limiting step in the native oxide formation on hydrogen-terminated Si surfaces.

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