Mechanism of silicon etching in the presence of CF2, F, and Ar+

Abstract

Molecular dynamics simulations of CF2, F, and Ar+ impacting silicon surfaces reveal the spontaneous formation of segregated layers of Si-C and SiFx, formed due to Ar+ ion impact and ion-induced mixing. The mechanisms of steady-state etching under these conditions involve a leading front of SiFx that fluorinates the Si substrate, followed by a region or zone of Si-C. The SiFx and Si-C layers move through the substrate Si during steady-state etching. Si is generally etched from the surface of the Si-C layer by an ion impact. Carbon reaction with Si in the Si-C zone raises the total atomic density in the Si-C layer to nearly three times the value observed in undisturbed Si and reduces the Si etch rate by limiting ion mixing. Etching stops completely if the Si-C layer becomes so impervious that ions cannot reach the SiFx front. The importance of the depth profile of ion energy deposition in sustaining etching is very clearly observed in the simulations.