Small free energy barrier and postdesorption collisions: The keys towards the understanding of reactive ion etching of silicon.

Abstract

Reactive ion etching of Si with C${\mathrm{l}}_{2}$ as the reactive gas has been examined with molecular dynamics simulations. The volatility of ${\mathrm{SiCl}}_{x}$ molecules is determined by Gibbs free energy calculations as a function of temperature. The high entropy of activation of the desorbing molecules results in an unexpected low desorption barrier under etching conditions. Etching simulations show that many sputtered molecules undergo one or more collisions with protrusions on the corrugated surface. This results in a redistribution of the kinetic energy and a consistent interpretation of experimental results.