Dynamic global model of Cl₂/Ar plasmas: Applicability to atomic layer etching processes

A global zero-dimensional (0D) model has been developed to describe the Cl₂/Ar plasma discharge in dynamic mode. Our model computes the time evolution of the plasma composition under conditions similar to fast-paced plasma processes, such as atomic layer etching (ALE), characterized by alternations in the feed gas. The study focuses on calculating the densities of charged and neutral species for various gas switch durations, (⁠ $t s$⁠). Simulations demonstrate the impact of gas switching time (⁠ $t s$⁠) on the temporal evolution of Cl₂, Cl, and ion densities, as well as the electron temperature (⁠ $T e$⁠) during the gas switch. A parametric study reveals that the temporal evolution of $T e$ can be represented by a semiempirical exponential law during the transition from a pure Cl₂ plasma to Ar as a function of (⁠ $t s$⁠). During the gas switch, the extinction of chlorinated species, which plays a crucial role in the adsorption step in ALE, persist during the argon plasma phase. The duration of this extinction decreases with longer $t s$⁠. Finally, our model shows a good reproducibility of ALE cycles modeled for the chosen input parameters, including the densities of neutral and charged species and $T e$⁠, relative to the ALE period. This work aims to provide insights into the kinetics of transient plasmas occurring in the ALE cycle, the importance of purging, and lifetime residual species, such as residual chlorine in a plasma with pure argon.