Chromium is a frequently encountered material in modern nanofabrication, directly as a functional material (e.g., photomask generation) or indirectly as a hard mask (e.g., to etch quartz). With the continuous downscaling of devices, the control of the feature size of patterned Cr and CrO_x becomes increasingly important. Cr and CrO_x etching is typically performed using chlorine–oxygen-based plasma chemistries, but the nanoscale imposes limitations. In this work, directional etching is demonstrated for the first time using fluorine–oxygen-based plasma. Two cases are studied to demonstrate the Cr etch performance: (i) a plasma mixture of SF₆ + O₂ and (ii) a switching SF₆/O₂ procedure in which the plasmas are used sequentially. The proposed mixture performs with Cr etch rates (ERs) up to 400 nm/min at 300 W platen power and is highest when the SF₆/O₂ gas ratio is ∼0.75%, i.e., almost pure O₂ plasma. The profile shows reasonable directionality but the etch selectivity is low, less than 5 toward Si, due to the high generated self-bias of 420 V. The selectivity of the plasma mixture can be improved at a lower plasma power, but this is accompanied with considerable undercut. The etching of CrO_x proceeds without the need for O₂ in the feed, and, therefore, the ER can reach much higher values (beyond 2000 nm/min at 300 W). As the plasma mixture seems to be inadequate, a sequential process is studied with improved selectivity while preserving directionality. The high selectivity is achieved by using relatively low plasma power (to ensure a low self-bias) and the directionality is due to the time separation of the SF₆ and O₂ plasmas and a controlled directional removal of CrF_x etch inhibiting species. Using such a switched procedure at 30 W plasma power, a selectivity beyond 20 with good profile directionality is achieved and having an etch rate of ∼1 nm per cycle (or 7 nm/min).

中文翻译：

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使用SF6和O2等离子体腐蚀Cr和CrO

铬是现代纳米加工中经常遇到的材料，直接作为功能材料（例如，光掩模的产生）或间接地作为硬掩模（例如，蚀刻石英）。随着器件的不断缩小，对图案化Cr和CrO _x的特征尺寸的控制变得越来越重要。Cr和CrO _x蚀刻通常使用基于氯-氧的等离子体化学方法进行，但是纳米级具有局限性。在这项工作中，首次使用基于氟氧的等离子体进行了定向蚀刻。研究了两种情况以证明Cr蚀刻性能：（i）SF ₆  + O ₂的等离子体混合物和（ii）切换SF ₆ / O ₂顺序使用等离子体的过程。所提出的混合物在300 W的压板功率下具有高达400 nm / min的Cr腐蚀速率（ERs），并且在SF ₆ / O ₂气体比率约为0.75％（即几乎纯净的O ₂等离子体）时达到最高。该轮廓显示出合理的方向性，但由于产生的420 V高自偏压，对Si的蚀刻选择性低，小于5。在较低的等离子体功率下可以提高等离子体混合物的选择性，但这伴随着相当大的咬边。不需要O ₂即可进行CrO _x的蚀刻因此，ER可以达到更高的值（在300 W时超过2000 nm / min）。由于血浆混合物似乎不足，因此在保留方向性的同时研究了选择性提高的顺序过程。通过使用相对较低的等离子体功率（以确保较低的自偏压）来实现高选择性，而方向性则是由于SF ₆和O ₂等离子体的时间分离以及CrF _x腐蚀抑制物质的受控定向去除所致。使用这种在30 W等离子功率下的切换程序，可以实现超过20的选择性和良好的轮廓定向性，并且每个周期的蚀刻速率约为1 nm（或7 nm / min）。