Influence of doping on the etching of Si(111)

Abstract

Exposure of solid surfaces to reactive gases (or radicals) often leads to chemical reactions which produce volatile products. These are frequently called etching reactions. The example discussed in this paper involves the reaction of ${\mathrm{XeF}}_2$ with Si(111) to produce ${\mathrm{SiF}}_4$(gas). It will be shown that the etch rate depends strongly upon the concentration and type of dopant. It also depends upon the thickness of the fluorosilyl (${\mathrm{SiF}}_{\mathrm{x}}$) layer on the surface. The trends previously observed in plasma-assisted etching environments are shown to also occur in the ${\mathrm{XeF}}_2$-Si reaction. A simple model will be developed which indicates a strong correlation between the number of negative ions on the surface and the etch rate. The model is based upon some of the ideas originally proposed by Mott and Cabrera to describe oxide growth and on the Poisson-Boltzmann equation which describes the space charge at a semiconductor interface.