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 O 2 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.
- Auger electron spectroscopy
- Real-time monitoring
- Reflection high-energy electron diffraction (RHEED)
- Surface chemical reaction