Molecular dynamics simulations of plasma-enhanced atomic layer etching of silicon nitride using hydrofluorocarbon and oxygen plasmas

Abstract

Molecular dynamics simulations were performed to study the influence of oxygen (O2) in the hydrofluorocarbon (HFC) plasma-enhanced atomic layer etching (ALE) of silicon nitride (Si3N4).
ALE is known to etch a surface with atomic-scale control and precision. Its in-depth understanding is essential for the advancement of fabrication technologies for semiconductor devices. It was presented earlier that such a Si3N4 ALE process can lead to an etch stop due to the accumulation of C atoms on the surface [1]. It was then shown that, by introducing an O2 plasma irradiation step, a stable etch was observed and the etch stop was prevented [2]. In this study, molecular dynamics (MD) simulations were used to clarify the interaction mechanisms of an O2 plasma with the modified Si3N4 surface during the HFC-based ALE process. To do this, CH2F radicals were used in the adsorption step. It was then followed by Ar+ bombardment in the desorption step.
Subsequently, O2 plasma was introduced as an additional step to help the removal of the remaining HFC species. This series of steps corresponds to one ALE cycle. Our simulations have shown that, during the desorption step of the first ALE cycle, HFC species assist the removal of the Si and N atoms of the Si3N4 by the formation of volatile by-products such as SiFx, CNx, and NHx species.
On the other hand, due to the momentum transfer from incident Ar+ ions, some HFC species were pushed into the bulk layer, forming chemical bonds with Si and N atoms therein. By the addition of the O2 plasma irradiation step, it was observed that HFC species interact with O atoms adsorbed on the surface. The removal of C atoms was also enhanced by the formation of COx. In this way, our MD simulations have shown that the additional O2 plasma irradiation step prevents the etch stop and allows stable Si3N4 ALE cycles.