New insight into desorption step by Ar⁺ ion-bombardment during the atomic layer etching of silicon

An ideal atomic layer etching (ALE) process must fulfill these requirements: (1) synergistic interaction between the steps of surface modification and removal of the modified material, (2) self-limiting etching, and (3) linear correlation between etched depth and number of cycles. This paper, however, focuses on the nonidealities that may impede the realization of ALE. To this end, the authors report an observation from their studies on silicon ALE - a recurrence of monotonic increase in etched depth after the silicon etching had already self-limited - that deviates from an ideal ALE characteristic. From this data, the authors infer that Ar⁺ ions may play more than one role during the silicon ALE. In addition to the desorption of halogenated silicon, Ar⁺ ion-bombardment may also generate additional active sites for the adsorption of chlorine. Therefore, the conventional assumption that the steps of adsorption and desorption are inherently decoupled must be reevaluated.