Thermal atomic layer etching (ALE) can be achieved with sequential, self-limiting surface reactions. One mechanism for thermal ALE is based on fluorination and ligand-exchange reactions. For metal oxide ALE, fluorination converts the metal oxide to a metal fluoride. The ligand-exchange reaction then removes the metal fluoride by forming volatile products. Previous studies have demonstrated the thermal ALE of amorphous Al₂O₃ films. However, no previous investigations have explored the differences between the thermal ALE of amorphous and crystalline Al₂O₃ films. This study explored the thermal ALE of amorphous and crystalline Al₂O₃ films. HF, SF₄, or XeF₂ were used as the fluorination reactants. Trimethylaluminum (TMA) or dimethylaluminum chloride (DMAC) were used as the metal precursors for ligand-exchange. Spectroscopic ellipsometry measurements revealed that the amorphous Al₂O₃ films had much higher etch rates than the crystalline Al₂O₃ films. When using HF and TMA at 300 °C, the amorphous Al₂O₃ film was removed at an etch rate of 0.78 Å/cycle. For the crystalline Al₂O₃ film, an etch rate of 0.06 Å/cycle was initially observed prior to the stoppage of etching after removing about 10 Å of the film. Thermal ALE with HF and DMAC resulted in similar results. Etch rates of 0.60 and 0.03 Å/cycle were measured for amorphous and crystalline Al₂O₃ films at 300 °C, respectively. Other fluorination agents, such as SF₄ or XeF₂, were also used together with TMA or DMAC for Al₂O₃ ALE. These reactants for fluorination and ligand-exchange were able to etch amorphous Al₂O₃ films at 300 °C. However, they were unable to etch crystalline Al₂O₃ film at 300 °C beyond the initial 10–20 Å surface layer. The investigations also examined the effect of annealing temperature on the etch rate per cycle using HF and TMA as the reactants at 300 °C. Amorphous Al₂O₃ films were etched at approximately the same etch rate of 0.78 Å/cycle until the crystallization of amorphous Al₂O₃ films at ≥ 880 °C. The differences between amorphous and crystalline Al₂O₃ thermal ALE could be used to obtain selective thermal ALE of amorphous Al₂O₃ in the presence of crystalline Al₂O₃.

中文翻译：

---

非晶和结晶 Al2O3 薄膜的热原子层蚀刻

热原子层蚀刻 (ALE) 可以通过顺序的、自限性的表面反应来实现。热 ALE 的一种机制是基于氟化和配体交换反应。对于金属氧化物 ALE，氟化将金属氧化物转化为金属氟化物。然后配体交换反应通过形成挥发性产物去除金属氟化物。先前的研究已经证明了非晶Al ₂ O ₃薄膜的热ALE 。然而，之前没有研究探讨过非晶和结晶 Al ₂ O ₃薄膜的热 ALE 之间的差异。本研究探讨了非晶和结晶 Al ₂ O ₃薄膜的热 ALE 。HF、SF ₄或 XeF₂用作氟化反应物。三甲基铝 (TMA) 或二甲基氯化铝 (DMAC) 用作配体交换的金属前体。光谱椭偏测量显示非晶Al ₂ O ₃膜具有比结晶Al ₂ O ₃膜高得多的蚀刻速率。当在 300 °C 下使用 HF 和 TMA 时，以0.78 Å/周期的蚀刻速率去除非晶 Al ₂ O ₃膜。对于结晶Al ₂ O ₃在去除约 10 埃的薄膜后停止蚀刻之前，最初观察到的蚀刻速率为 0.06 埃/周期。使用 HF 和 DMAC 的热 ALE 产生类似的结果。分别在 300°C 下对非晶态和结晶态 Al ₂ O ₃膜测量了 0.60 和 0.03 埃/周期的蚀刻速率。其他氟化剂，例如SF ₄或XeF ₂，也与TMA 或DMAC 一起用于Al ₂ O ₃ ALE。这些用于氟化和配体交换的反应物能够在 300 °C 下蚀刻无定形 Al ₂ O ₃薄膜。然而，他们无法蚀刻结晶的 Al ₂ O ₃薄膜在 300°C 超出初始 10-20 Å 表面层。研究还使用 HF 和 TMA 作为反应物在 300 °C 下检查了退火温度对每个循环的蚀刻速率的影响。无定形 Al ₂ O ₃薄膜以大约相同的 0.78 埃/周期的蚀刻速率进行蚀刻，直到在 ≥ 880 °C 下结晶出无定形 Al ₂ O ₃薄膜。无定形和结晶Al ₂ O ₃热ALE之间的差异可用于在结晶Al ₂ O ₃存在下获得非晶Al ₂ O _{3 的}选择性热ALE 。