We investigated evolution of hydrocarbon species on a Si surface during methane plasma both with and without substrate bias, using infrared spectroscopy in multiple internal reflection geometry (MIR-IRAS). We found that the relative density of the sp(3)-CH or sp(3)-CH, species to the sp(3)- CH3 species was low in the low exposure regions, but that the relative density of the sp(3)-CH or sp(3)-CH, species increased as the exposure was higher. Substrate temperatures rose as the plasma exposure was higher. The changes of ratios would be ascribed to the substrate heating effect by plasma exposure, which would enhance the etching and/or hydrogen abstraction effects. We also found the change of CH1-2/CH3 ratios was enhanced when the high substrate bias was applied. The enhancement of the ratio was due to ion effects. (C) 2007 Elsevier B.V. All rights reserved.