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.

中文翻译：

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氯吸附硅原子层刻蚀过程中表面损伤的形成

随着半导体器件结构继续接近纳米尺寸范围，制造此类器件的新挑战已经出现。例如，在纳米尺度上对高纵横比、高选择性、可控性和各向同性或各向异性蚀刻的需求就是其中的一部分。最近，原子层蚀刻 (ALE) 作为传统反应离子蚀刻 (RIE) 的替代方案来解决这些问题，引起了很多关注。与 RIE 相比，ALE 在大面积上提供高度均匀的蚀刻，蚀刻深度精确，对底层材料表面的损坏很小。然而，ALE 工艺中表面损伤形成的程度尚未得到广泛报道。在这项研究中，${}^{+}$离子辐射解吸。已经模拟了几个 ALE 循环，并获得了每个循环可重复的蚀刻深度。根据深度分布，即使在模拟中 20 eV 的非常低的离子入射能量下，也发现 ALE 工艺会导致厚度约为 1.5 nm 的受损表面层。在本研究中检查的能量范围（20-60 eV）内，蚀刻表面上的损坏层的厚度随着离子入射能量的增加而略微增加，并且在 ALE 吸附步骤中沉积在表面上的 Cl 原子在离子轰击损伤层。我们的模拟结果表明，在 PA-ALE 工艺的“蚀刻”表面上不可避免地会形成某种损坏，如果损坏层无意中影响了器件性能，