THE BAND MODEL AND THE ETCHING MECHANISM OF SILICON IN AQUEOUS KOH

The energy band diagram of n-Si in aqueous 2M KOH is constructed by th e measured open-circuit potential and the flatband voltage. A photocur rent susceptivity method was proposed to determine the flatband voltag e. A flatband voltage of -1.04 V/SCE (saturated calomel electrode) for the n-Si in 2M KOH was determined by this new method. The energy band diagram of the p-Si in the same electrolyte is also constructed. Accu mulation of carriers at the n-Si/KOH interface is predicted by the ban d diagram and confirmed by the ohmic-contact-like I-V curve. Depletion of carriers at p-Si/KOH interface is predicted by the band diagram an d confirmed by the rectifying I-V characteristics. The passivation of Si under anodic bias is attributed to the formation of an oxide film. The competition between the oxidation rate and the diffusion rate of o xidation product determines whether the anodic oxidation is an etching or passivation process. The etching oxidation is assumed to be domina ted by the electrochemical reaction. The transport of these carriers w hich participate in the electrochemical reaction can be explained by t he energy band diagram. All etching or passivation phenomena are consi stent with the prediction from the band diagram viewpoint. The etch st op for heavily doped Si is attributed to the enhanced growth rate of o xide film under high carrier concentration.