THERMAL CLUSTERING OF VERY THIN OXIDE FORMED ON SI SURFACES BY N2O/O-2 ADSORPTION

Thermal clustering of ultrathin oxide layers with 1 monolayer thickness on Si(111) and Si(001) surfaces was studied using Auger electron spectroscopy (AES) and ultraviolet photoelectron spectroscopy (UPS). Uniform oxide layer formed by self-limited adsorption of N2O or O-2 at room temperature is deformed inhomogeneously to form oxide clusters by annealing at about 400 degrees C, which is a much lower temperature than oxide decomposition temperature (about 650 degrees C). AES analysis showed that the area of the bare Si surface exposed as a result of this clustering is 10%-15% of the original surface. Exposure of the clean surface was confirmed by the reappearance of surface state in UPS after annealing. Consideration of surface energy reported in the literature suggests that the driving force of the clustering phenomenon is mainly due to an increase of the Si-O-Si bond angle on annealing.