The thermal atomic layer etching (ALE) of WO₃ and W was demonstrated with new “conversion-fluorination” and “oxidation-conversion-fluorination” etching mechanisms. Both of these mechanisms are based on sequential, self-limiting reactions. WO₃ ALE was achieved by a “conversion-fluorination” mechanism using an AB exposure sequence with boron trichloride (BCl₃) and hydrogen fluoride (HF). BCl₃ converts the WO₃ surface to a B₂O₃ layer while forming volatile WO_xCl_y products. Subsequently, HF spontaneously etches the B₂O₃ layer producing volatile BF₃ and H₂O products. In situ spectroscopic ellipsometry (SE) studies determined that the BCl₃ and HF reactions were self-limiting versus exposure. The WO₃ ALE etch rates increased with temperature from 0.55 Å/cycle at 128 °C to 4.19 Å/cycle at 207 °C. W served as an etch stop because BCl₃ and HF could not etch the underlying W film. W ALE was performed using a three-step “oxidation-conversion-fluorination” mechanism. In this ABC exposure sequence, the W surface is first oxidized to a WO₃ layer using O₂/O₃. Subsequently, the WO₃ layer is etched with BCl₃ and HF. SE could simultaneously monitor the W and WO₃ thicknesses and conversion of W to WO₃. SE measurements showed that the W film thickness decreased linearly with number of ABC reaction cycles. W ALE was shown to be self-limiting with respect to each reaction in the ABC process. The etch rate for W ALE was ∼2.5 Å/cycle at 207 °C. An oxide thickness of ∼20 Å remained after W ALE, but could be removed by sequential BCl₃ and HF exposures without affecting the W layer. These new etching mechanisms will enable the thermal ALE of a variety of additional metal materials including those that have volatile metal fluorides.

中文翻译：

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使用“转化-氟化”和“氧化-转化-氟化”机理的WO ₃和W热原子层蚀刻

通过新的“转化氟化”和“氧化转化氟化”刻蚀机理证明了WO ₃和W的热原子层刻蚀（ALE）。这两种机制都是基于顺序的自限反应。WO ₃ ALE是通过“转化氟化”机理，使用AB暴露顺序以及三氯化硼（BCl ₃）和氟化氢（HF）来实现的。BCl ₃将WO ₃表面转化为B ₂ O ₃层，同时形成挥发性的WO _x Cl _y产物。随后，HF自发地蚀刻B ₂ O ₃层，产生挥发性BF₃和H ₂ O产品。原位光谱椭偏（SE）研究确定BCl ₃和HF反应是自限的，相对于暴露是自限的。WO ₃ ALE蚀刻速率随温度从128°C的0.55Å/循环增加到207°C的4.19Å/循环而增加。W用作蚀刻停止层，因为BCl ₃和HF无法蚀刻下面的W膜。使用三个步骤的“氧化-转化-氟化”机理进行了W ALE。在该ABC曝光顺序中，首先使用O ₂ / O ₃将W表面氧化为WO ₃层。随后，用BCl ₃蚀刻WO ₃层和HF。SE可以同时监测W和WO _3的厚度以及W向WO _3的转化。SE测量表明，W膜厚度随ABC反应循环次数线性减少。相对于ABC过程中的每个反应，W ALE被证明是自限性的。在207°C下，W ALE的蚀刻速率约为2.5Å/循环。在W ALE之后仍保留约20Å的氧化物厚度，但是可以通过连续的BCl ₃和HF暴露去除，而不会影响W层。这些新的蚀刻机制将使多种其他金属材料（包括具有挥发性金属氟化物的金属材料）实现热ALE。