Infrared spectroscopic study of initial stages of ultraviolet ozone oxidation of Si(100) and (111) surfaces

We have investigated the initial stages of UV ozone oxidation of hydrogen-terminated Si(100) and (111) surfaces using infrared spectroscopy in the multiple internal reflection geometry. Spectral features due to intermediate oxidation species such as SiH₂(0₂) and SiH(0₃), which are generated by the attack of the back bonds of a surface Si atom by oxygen, are clearly observed. Upon UV ozone oxidation the concentration of the intermediate oxidation species initially increases and then drops, while that of surface hydride species Si-Hi decreases with increasing the UV ozone exposure, which indicates that at initial stages of oxidation oxygen attacks both of the Si-H and back bonds of a Si atom in the outermost layer. We find that the generation of the intermediate oxidation species exhibits a strong crystallographic orientation dependence; both SiH₂(0₂) and SiH(0₃) are generated on the Si(100) surface, while the generation of the SiH₂(0₂) species is suppressed on the Si(III) surface.