Real-time monitoring of initial thermal oxidation on Si(001) surfaces by synchrotron radiation photoemission spectroscopy

The thermal oxidation of Si(001) surfaces at 860K, 895K, 945K and 1000K under the O-2 pressure of 1 x 10(-4) Pa has been investigated by time-resolved photoemission measurements with synchrotron radiation. Based on time evolution analyses by reaction kinetics models, it was found that the oxidation at 860K, 895K and 945K has progressed with the Langmuir adsorption type, whereas the oxidation at 1000k has showed the character of the two-dimensional island growth involving SiO desorption. The oxidation rates increased with increasing surface temperature in the passive oxidation condition. The time evolution of each Si oxidation state (Sin+: n = 1, 2, 3, 4) derived from the Si-2p core-level shifts has also been analyzed. The results revealed that the thermal energy contributed to the migration process of the adsorbed oxygen and the emission of the bulk silicon atoms. Thus, the fraction of the Si4+ bonding state, i.e. SiO2 structure, was increased.