Surface damage formation during atomic layer etching of silicon with chlorine adsorption

As semiconductor device structures continue to approach the nanometer size range, new challenges in the fabrication of such devices have arisen. For example, the need for high-aspect-ratio, highly selective, controllable, and isotropic or anisotropic etching at the nanometer scale are some of them. Recently, atomic layer etching (ALE) has attracted much attention as an alternative to the conventional reactive ion etching (RIE) to address these issues. In comparison with RIE, ALE offers highly uniform etching over a large area with a precise etched depth and little damage to the underlying material surface. However, the extent of the surface damage formation in ALE processes has not been extensively reported yet. In this study, molecular dynamics simulation is used to examine the surface damages and reaction mechanisms during plasma-assisted (PA-) ALE of silicon (Si) with chlorine (Cl) radical adsorption and low-energy Ar$+$ ion irradiation for desorption. Several ALE cycles have been simulated and reproducible etched depths per cycle have been obtained. Based on the depth profiles, a damaged surface layer with a thickness of about 1.5 nm is found to be caused by the ALE process even at a very low ion incident energy of 20 eV in the simulation. The thickness of a damaged-layer on the etched surface slightly increases with the ion incident energy for the energy range examined in this study (20–60 eV), and Cl atoms deposited on the surface in the ALE adsorption step are transported deeper in the damaged-layer by the ion bombardment. Our simulation results indicate that a certain damage formation cannot be avoided on the “as-etched” surface of a PA-ALE process and, if the damaged-layer inadvertently affects the device performance, further action to mitigate the damage needs to be taken.