Initial stage of thermal oxidation of the Si(111)-(7×7) surface

We report a systematic study of the early oxidation process in a wide temperature range (20–700?deC) for the Si(111)-(7×7) annealed surface. Oxygen uptake data obtained by Auger-electron spectroscopy indicate that the surface oxygen uptake increases and then gradually saturates with ${\mathrm{O}}_2$ exposure at 20?deC. At intermediate temperatures, there is no saturation and the oxygen uptake rate is enhanced. At 700?deC, the uptake rate is enhanced in the high-exposure (or high-${\mathrm{O}}_2$-pressure) region, but is significantly reduced in the low-exposure region, presumably because of oxygen desorption as volatile SiO.