Two-dimensional implications of a purely reactive model for plasma etching

A model for plasma etching of silicon by SF₆ at low ion energy is presented. It is shown how this model, which excludes sputtering effects, allows the simulation of most observed two-dimensional effects (dovetail, field effect, barreling, trench bowing). Ion scattering is ignored and only the equilibrium between adsorption, desorption, and surface diffusion is computed, leading to a differential equation with only three independent parameters. The influence of these parameters on trench shapes is discussed. The role of adspecies diffusion on surfaces is emphasized and the possible extension to materials other than silicon and other other process conditions is considered