We propose and demonstrate an unconventional method suitable for releasing microelectromechanical systems devices containing an Al layer by wet etching using SiO₂ as a sacrificial layer. We used 48% HF solution in combination with 20% oleum to keep the HF solution water-free and thus to prevent attack of the Al layer, achieving an outstanding etch rate of thermally grown SiO₂ of ≈1 µm·min⁻¹. We also verified that this etching solution only minimally affected the Al layer, as the chip immersion for ≈9 min increased the Al layer sheet resistance by only ≈7.6%. The proposed etching method was performed in an ordinary fume hood in a polytetrafluorethylene beaker at elevated temperature of ≈70 °C using water bath on a hotplate. It allowed removal of the SiO₂ sacrificial layer in the presence of Al without the necessity of handling highly toxic HF gas.

中文翻译：

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湿法 SiO2 蚀刻对 Al 的无限选择性。


我们提出并演示了一种非常规方法，适用于通过使用 SiO ₂作为牺牲层进行湿法蚀刻来释放包含 Al 层的微机电系统器件。我们使用 48% HF 溶液与 20% 发烟硫酸相结合，以保持 HF 溶液无水，从而防止 Al 层受到侵蚀，实现了热生长 SiO ₂的出色蚀刻速率，约为 1 µm·min ^-1 。我们还验证了这种蚀刻溶液对 Al 层的影响很小，因为芯片浸泡约 9 分钟，Al 层薄层电阻仅增加约 7.6%。所提出的蚀刻方法是在聚四氟乙烯烧杯中的普通通风橱中在约70°C的高温下使用热板上的水浴进行的。它允许在Al存在的情况下去除SiO ₂牺牲层，而无需处理剧毒的HF气体。