Plasma oxidation process of silicon surfaces investigated by infrared spectroscopy

Plasma oxidation processes of hydrogen-terminated Si(100), (110), and (111) surfaces are investigated by infrared absorption spectroscopy (IRAS) in multiple internal reflection (MIR) geometry. We measured IRAS spectra of hydrogen-terminated Si surfaces exposed to oxygen-plasma in the Si-H stretching vibration region. IRAS data demonstrated that oxygen-plasma affects two influences on the Si surfaces; one is that oxygen-plasma removes surface hydrogen to oxidize the Si surfaces. The other is that it forces the hydrogen into the subsurface regions where oxygen species cannot reach. The former effect does not depend on the crystal graphic orientations, but the latter depends on it. Therefore, in order to oxidize perfectly the H-terminated Si surfaces using oxygen-plasma, the sample surfaces need to be heated so that oxygen atoms can diffuse into the subsurface regions.