Phase transition from Langmuir-type adsorption to two-dimensional oxide island growth during oxidation on Si(0 0 1) surface

The phase transition from Langmuir-type adsorption to two-dimensional (2D) oxide island growth during initial oxidation on the Si(0 0 1) surface was investigated by real-time Auger electron spectroscopy (AES) combined with reflection high-energy electron diffraction (RHEED). Curve-fitting analysis of the oxygen uptake curve obtained by O-KLL Auger electron intensity revealed that the phase transition occurs steeply at ∼630 °C and no oxidation occurs after completion of 2D growth of oxide islands, whereas oxides grows gradually at the interface following Langmuir-type adsorption. It was observed that the very thin oxide layer grown at 616 °C is more easily decomposed than that grown at 653 °C in spite of almost the same thickness. Furthermore, the RHEED intensity ratio between half-order spots indicated that etching of the surface starts suddenly just at the phase transition temperature of ∼630 °C. The steepness of the phase transition, the sudden start of SiO desorption and the difference in the interfacial oxidation and decomposition between two oxidation schemes are comprehensively interpreted using a surface reaction model in which O2 adsorption on the Si(0 0 1) 2×1 surface changes drastically from barrier-less adsorption into dimer backbonds for Langmuir-type adsorption to formation of desorption precursor SiO∗ in pairs with dimer vacancies for 2D oxide island growth, and coalescence of SiO∗ leads to nucleation and 2D growth of oxide islands.