Thermal decomposition of ultrathin oxide layers on Si(100) surface was investigated with temperature programmed desorption. The SiO desorption spectra for the initial coverages between 1.7 and 2.6 ML exhibit a dominant peak with a subpeak at lower temperature. The desorption rate corresponding to the dominant peak follows Avrami kinetics, suggesting that the decomposition process is spatially inhomogeneous with void formation and growth and is rate-limited by the desorption of SiO molecules at the void perimeter. The desorption energy was determined to be 3.39±0.07 eV from the reactive scattering measurement of the active oxidation process. The fact that Avrami kinetics reproduces the whole decomposition process until the oxide layer has completely decomposed shows that the reaction mechanism is still valid even if the overlap between voids becomes quite large. The Avrami exponent deduced from our measurement indicates that the increase in the initial coverage makes the oxide layer more stable and reduces the void nucleation rate.
