Infinite selectivity of wet SiO2 etching in respect to Al
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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·min1. 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.
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Zdrojový dokumentMicromachines. 2020, vol. 11, issue 4, p. 365-371.