Silicon anisotropic etching without attacking aluminum with Si and oxidizing agent dissolved in TMAH solution

We study silicon anisotropic etching using TMAH containing Si and several oxidizing agents. We focus on the Al etch rate and the formation of micropyramids. In addition to the previously reported TMAH with Si and ammonium persulfate, Si anisotropic etching without Al etch can be achieved by dissolving Si and ammonium nitrate in TMAH. By surface analysis of the etched aluminum, we have found that thin oxide layers, which cannot be etched by TMAH, form on the aluminum surface. Formation of micropyramids is dependent on the (111)/(100) etch rate ratio. We demonstrate that micropyramids formation can be prevented by increasing the (111)/(100) etch rate ratio. For TMAH with Si and ammonium persulfate, the Si(100) etch rate and the occurrence of micropyramids changes according to the sequence that the materials are dissolved in. Consequently, dissolving Si before ammonium persulfate is important.