Chemical Mechanism of AlF3 Etching during AlMe3 Exposure: A Thermodynamic and DFT Study,The Journal of Physical Chemistry C

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Chemical Mechanism of AlF3 Etching during AlMe3 Exposure: A Thermodynamic and DFT Study
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2022-04-25 , DOI: 10.1021/acs.jpcc.2c00158
Xiao Hu _{1,

2,

3} , Jörg Schuster _{1,

2,

3}

Affiliation

Thermal atomic layer etching (ALE) is a novel approach for the isotropic etching of materials with atomic-level precision. Previous studies have demonstrated the thermal ALE of Al₂O₃ using sequential, self-limiting reactions with HF and AlMe₃ (Me = CH₃) as the reactants. It was found that the HF exposure leads to the conversion of Al₂O₃ to AlF₃ and the formation of H₂O molecules. The present work aims to investigate the subsequent AlF₃ etching during the AlMe₃ exposure. On the basis of thermodynamic modeling and density functional theory (DFT) calculations, a two-step mechanism is suggested for the etching of AlF₃ by AlMe₃. In the first step, an AlF_3–xMe_x (0 < x < 1.5) layer is formed on the surface through the ligand-exchange reaction between AlMe₃ and AlF₃, with Al₂F₂Me₄ as the main byproduct. The AlF_3–xMe_x surface layer serves as a key intermediate during the etching process. As compared to the original AlF₃, AlF_3–xMe_x has a lower stability and can be removed more readily. In the second step, the AlF_3–xMe_x surface layer can be removed via two possible pathways. Pathway I relies on the formation of volatile dimers between AlMe₃ and the etched species, while Pathway II is accomplished by the direct decomposition of AlF_3–xMe_x. Due to the higher volatility of the reaction products, Pathway I is found to be more favorable than Pathway II. The feasibility of thermal Al₂O₃ ALE using HF with alternative precursors SiCl₄, TiCl₄, and AlClMe₂ is evaluated with the above two-step etching mechanism. To realize the AlF₃ etching during the precursor exposure, both the formation and removal of the AlF_3–xMe_x surface layer are required to be feasible. Consistent with the experimental results, it is found that only the AlClMe₂ precursor meets this requirement and can be considered as a candidate precursor. The presented methodology can be used to guide the development of new precursors for the thermal ALE of Al₂O₃ and other materials.

中文翻译：

AlMe3 暴露过程中 AlF3 蚀刻的化学机理：热力学和 DFT 研究

热原子层蚀刻 (ALE) 是一种用于以原子级精度对材料进行各向同性蚀刻的新方法。以前的研究已经证明了 Al ₂ O _{3的热 ALE，使用以 HF 和 AlMe}₃ (Me = CH ₃ ) 作为反应物的连续自限反应。发现HF暴露导致Al ₂ O ₃转化为AlF ₃并形成H ₂ O分子。目前的工作旨在研究AlMe _{3过程中随后的 AlF}₃蚀刻接触。在热力学建模和密度泛函理论（DFT）计算的基础上，提出了AlMe _3刻蚀AlF₃的两步机制。第一步，通过AlMe ₃和AlF ₃之间的配体交换反应在表面形成AlF _3–_x Me _x (0 < x < 1.5)层，其中Al ₂ F ₂ Me ₄为主要副产物。AlF _3–_x Me _x表面层在蚀刻过程中充当关键中间体。与原来的 AlF ₃相比，AlF _3–_x Me_x稳定性较低，更容易去除。在第二步中，可以通过两种可能的途径去除_{AlF 3– x} Me_{x表面层。}途径 I 依赖于 AlMe₃和蚀刻物质之间挥发性二聚体的形成，而途径 II 是通过 AlF_{3– x} Me_x的直接分解来完成的。由于反应产物的较高挥发性，发现途径 I 比途径 II 更有利。使用 HF 与替代前体 SiCl₄、TiCl₄和 AlClMe₂进行热 Al₂ O_{3 ALE 的可行性}用上述两步蚀刻机制评估。为了在前驱体曝光期间实现 AlF _{3蚀刻，AlF}_{3– x} Me _x表面层的形成和去除都需要可行。与实验结果一致，发现只有AlClMe ₂前驱体满足这一要求，可以作为候选前驱体。所提出的方法可用于指导 Al ₂ O ₃和其他材料的热 ALE 新前体的开发。

更新日期：2022-04-25

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