The Band Model and the Etching Mechanism of Silicon in Aqueous  KOH

Abstract

The energy band d iagram of n-St in aqueous 2M KOH is constructed by the measured open-circuit potential and the f latband voltage. A photocurrent suseeptivity method was proposed to determine the flatband voltage. A flatband voltage of- 1.04 V /SCE (saturated calomel electrode) for the n-St in 2M KOH was determined by this new method. The energy band d iagram of the p-St in the same electrolyte is also constructed. Accumulat ion of carriers at the n-S i /KOH interface is predicted by the band d iagram and conf i rmed by the ohmic-contact-l ike I-V curve. Depletion of carriers at p-S i /KOH interface is predicted by the band d iagram and conf i rmed by the rectifying I-V characteristics. The passivation of Si under anodic bias is attributed to the formation of an oxide film. The competit ion between the oxidation rate and the diffusion rate of oxidation product determines whether the anodic oxidation is an etching or passivation process. The etching oxidation is assumed to be dominated by the electrochemical reaction. The transport of these carriers wh ich participate in the electrochemical reaction can be explained by the energy band diagram. All etching or passivation phenomena are consistent wi th the prediction f rom the band d iagram viewpoint. The etch stop for heavily doped Si is attributed to the enhanced growth rate of oxide film under high carrier concentration. The energy band d iagram of the semiconductor electrode is a useful tool for understanding transport phenomena of