Wet Etching Of Sio2 As Sacrificial Layer With Infinite Selectivity To Al

Abstract

This work presents an unusual method for releasing microelectromechanical systems which contain an Al layer. This is done by wet etching of SiO2 as a sacrificial layer. Mixture of 49% HF acid and 20% H2SO4∙SO3 (oleum) is used. Oleum keeps the solution water-free and subsequently prevents the attack of Al layer. Exceptional etch rate (≈ 1 μm·min−1) of thermally grown SiO2 is achieved by this method. The infinite selectivity to Al layer is verified by measuring the thickness of layer before and after etching. The etching itself is done in an ordinary fume hood in polytetrafluorethylene (PTFE) beaker.