Universal Model for Local Anodic Oxidation Based on Surface Chemistry of Oxide Islands

Abstract

We propose a new model for local anodic oxidation using atomic force microscopy (AFM), where surface chemistry is controlled through the voltage applied during the oxidation. The AFM oxidation was performed on Si surfaces with oxide layers as base surfaces, the hydrophilicity of which was controlled by thermal annealing before AFM oxidation. We found that the chemistry on the anodic oxide islands is only determined by the applied voltage and not by the chemical property of the base surface. When the base oxide is too thick to be further oxidized, the surface chemistry remains unchanged with respect to the applied voltage. When the oxide thickness is so thin that anodic re-oxidation occurs, the surface chemistry of the oxide islands is changed by the second anodic oxidation. These experimental results can be interpreted using a universal model for local anodic oxidation that involves the diffusion of OH- molecules in the oxide, the oxidation of Si at the interface accompanying the emission of Si atoms, and the oxidation of the emitted silicons at the oxide surface.