Intitial Oxidation of Si(100) Surface at Cryogenic Temperature

The interaction of oxygen with the Si(100) surface has been investigated based on time-of-flight secondary ion mass spectrometry and ultraviolet photoelectron spectroscopy as a function of temperature. The probability for dissociative adsorption of oxygen increases with decreasing surface temperature. The O-2 molecules deposited at 20 K tend to charge negatively during desorption, suggesting that a chemisorption state is entered transiently. No metastable molecular precursors are identified on the surface after desorption of physisorbed O-2. The nascent oxide layer is metastable as confirmed not only from a drastic change in photoemission spectra but also from a surface compositional change at 140-150 K The result is explainable as oxygen atoms chemisorbed initially at the dimer bridge site move to the most stable backbond site at this temperature. Hydrogen atoms segregate to the surface during the structural transformation of oxides.