The residue of the two-dimensional (21)) oxide-island growth was directly investigated by observing the morphology change of the SiO2/Si (111) interface with atomic force microscopy, after removing SiO2. It was found that oxidation progressed by the bilayers in the (111) orientation instead of by the monolayers. Oxidation created the oxide-islands in an atomic layer, while the Si-islands were found to exist in the previous atomic layer. This result indicates that thermal oxidation progresses not by a strict layer-by-layer process. Furthermore, the deviation from the layer-by-layer process was increased as the oxidation temperature was decreased. This morphology degradation at low-oxidation temperatures (< 1050 degrees C) is due to the constraint of the 21) expansion rate of the oxide-island. (C) 2007 Elsevier B.V. All rights reserved.