Bias‐Dependent Etching of Silicon in Aqueous KOH

Abstract

The current‐voltage characteristics and the bias dependence of the etch rates of <100>‐ and <111>‐oriented n‐ and p‐type low doped Si samples in aqueous have been studied. We find that voltages cathodic of the open‐circuit potential have little effect on the p‐type etch rates, while the n‐type etching is stopped. Anodic of the open‐circuit potential, both carrier types stop etching, owing to passivation of the surface. These results are used to characterize the rate‐determining steps of the chemical or electrochemical reactions which take place at the semiconductor surface at various biases. A mechanism is proposed in which the rate‐determining step shifts between among chemical, electrochemical, or diffusion limited. Also, a mechanism involving susceptibility to nucleophilic attack is proposed to explain the vastly different etching rates of <100> and <110> vs. <111> faces.