We have investigated the behavior of silicon- and carbon-hydride species on the hydrogen-terminated Si(100) surface, during exposure to hydrogen-diluted methane plasma at room temperature, using infrared absorption spectroscopy (IRAS) in the multiple internal reflection (MIR) geometry. We have measured IRAS spectra in the Si-H and C-H stretching vibration regions of the Si surface that was irradiated by hydrogen-diluted methane plasma. IRAS data demonstrated that at the initial stage of methane plasma exposure, atomic hydrogen and CH3 radicals stick on the H-terminated surface to increasingly generate C-substituted hydride species, and eventually one monolayer of C-containing hydride species is formed. At this stage of plasma exposure, atomic hydrogen and CH3 radicals attack the Si surfaces to create the so-called SiHn complex at sub-surface regions. A prolonged exposure to methane plasma induced an additional deposition of CH, species onto the monolayer of C-containing hydride species. (C) 2003 Elsevier Science B.V. All rights reserved.