Thermal atomic layer etching (ALE) of silicon was performed using O₂, HF, and Al(CH₃)₃ as the reactants at temperatures from 225 to 290 °C. This thermal etching process is based on Si oxidation using O₂ and conversion of SiO₂ to Al₂O₃ using trimethylaluminum (TMA). Al₂O₃ is then fluorinated by HF to produce AlF₃ prior to removal of AlF₃ by a ligand-exchange reaction with TMA. Thermal Si ALE was studied using silicon-on-insulator wafers. In situ spectroscopic ellipsometry was employed to monitor simultaneously both the thickness of the top SiO₂ layer and the underlying silicon film during Si ALE. These studies revealed that the silicon film thickness decreased linearly with the number of reaction cycles while the thickness of the SiO₂ layer remained constant. Using an O₂–HF–TMA exposure sequence, the Si ALE etch rate was 0.4 Å/cycle at 290 °C. This etch rate was obtained using static reactant pressures of 250, 1.0, and 1.0 Torr and exposure times of 10, 5, and 5 s for O₂, HF, and TMA, respectively. The SiO₂ thickness was 10–11 Å under these reaction conditions at 290 °C. The Si ALE etch rate increased with O₂ and TMA pressure before reaching a limiting etch rate at higher O₂ and TMA pressures. The order of the reactants affected the Si etch rate. Changing the exposure sequence from O₂–HF–TMA to O₂–TMA–HF decreased the etch rate from 0.4 to 0.2 Å/cycle at 290 °C. Decreasing the etch temperature below 290 °C also resulted in a decrease in the Si etch rate. Atomic force microscopy measurements determined that the root-mean-square (RMS) roughness of the surface was 2.0 ± 0.2 Å before and after Si ALE using the optimum reaction conditions. Decreasing the static O₂ pressures below 250 Torr decreased the etch rate and also increased the RMS surface roughness. There was no evidence of any change in the Si ALE process for ultrathin Si films with thicknesses of <100 Å in the quantum confinement regime. Thermal Si ALE should be useful for silicon applications in many areas, including electronics, optoelectronics, thermoelectrics, and photonics.

中文翻译：

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以O ₂，HF和Al（CH ₃）₃为反应剂的硅热原子层刻蚀

使用O ₂，HF和Al（CH ₃）₃作为反应物在225至290°C的温度下进行硅的热原子层蚀刻（ALE）。该热蚀刻工艺基于使用O _2的Si氧化和使用三甲基铝（TMA）的SiO ₂到Al ₂ O _3的转化。的Al ₂ ø ₃然后通过HF氟化以产生的AlF ₃去除的AlF之前₃通过与TMA的配体交换反应。使用绝缘体上硅晶片研究了热Si ALE。原位使用光谱椭圆偏振法同时监测Si ALE期间顶部SiO ₂层的厚度和下面的硅膜的厚度。这些研究表明，硅膜的厚度随反应循环数的增加而线性减小，而SiO ₂层的厚度保持恒定。使用O ₂ -HF-TMA曝光顺序，在290°C时Si ALE蚀刻速率为0.4Å/循环。使用250、1.0和1.0 Torr的静态反应物压力以及O ₂，HF和TMA的暴露时间分别为10 s，5 s和5 s来获得该蚀刻速率。在290°C的这些反应条件下，SiO _2的厚度为10-11Å。O ₂使Si ALE蚀刻速率增加在较高的O ₂和TMA压力下达到极限刻蚀速率之前，先选择TMA和TMA压力。反应物的顺序影响Si蚀刻速率。在290°C下，将曝光顺序从O ₂ –HF –TMA更改为O ₂ –TMA–HF，可将蚀刻速率从0.4降至0.2Å/循环。将蚀刻温度降低到290°C以下还会导致Si蚀刻速率的降低。原子力显微镜测量确定，在最佳反应条件下，Si ALE前后的表面均方根（RMS）粗糙度为2.0±0.2Å。减少静态O ₂低于250 Torr的压力会降低蚀刻速率，并且还会增加RMS表面粗糙度。没有证据表明在量子限制范围内，厚度小于100的超薄硅薄膜的硅ALE工艺会发生任何变化。热Si ALE应该在许多领域的硅应用中有​​用，包括电子，光电子，热电和光子学。