Evolution of surface morphology of Si(100)-(2×1) during oxygen adsorption at elevated temperatures

We used scanning tunneling microscopy and low-energy electron microscopy to study the etching of the Si(100)-(2×1) surface by oxygen at low pressures and elevated temperatures. At 5×${10}^{\mathrm{-}8}$ torr partial pressure of oxygen, the transition from random etching of terraces to step etching occurs at ∼580 °C, while at the higher partial pressure of 5×${10}^{\mathrm{-}7}$ torr, the transition temperature is ∼625 °C. The diffusing species is a dimer vacancy, formed by the desorption of two SiO molecules. Anisotropic diffusion of the vacancies is observed, with a preferred direction along the dimer rows. The reaction probability, defined as the number of desorbed SiO molecules to the number of incident ${\mathrm{O}}_2$ molecules, is estimated to be 0.010±0.005.