Oxidation processes on the H₂O-chemisorbed Si(100) surface studied by in-situ infrared spectroscopy

The oxidation processes on the Si(100)-(2 x 1) surface during exposure to H₂O and subsequent thermal annealing were investigated using in-situ infrared absorption spectroscopy in the multiple internal reflection geometry. Exposure to H₂O results in the oxidation of Si-Si bonds (dimer bond and backbonds) even at room temperature. Upon annealing up to 500°C the dimer bond is cleaved to produce dihydride Si (Si-H₂), and the backbonds are attacked by atomic oxygen released from the surface Si-OH species to produce intermediate oxidation species such as SiH₂(SiO). We demonstrate that most of the hydride species are driven out from the surface by annealing up to 500°C, but an intermediate oxidation species (SiH(O₃)) persists up to 600°C. A model of wet oxidation is presented in which dissociation of water molecules, attack of the Si-Si bonds by atomic oxygen and hydrogen and hydrogen desorption are involved in the oxidation.