Silicon elastomer as a protective layer in 3D microfabrication of micro-opto-electro-mechanical systems

Abstract

The paper presents silicon anisotropy etching experiments in KOH and TMAH solutions in different conditions, using an organic silicon compound as a protective layer for the front side of the wafer.The starting material was a 460 μm thick, 〈100〉 oriented n-type silicon wafer. On the front side can be realised structures by IC standard technology. The last process in 3D microfabrication of micro-opto-electro-mechanical systems (MOEMS) is anisotropic etching. For the protection of the front side of the wafer, usually Si 3N 4 and SiO 2 are used. Si 3N 4 is difficult to be removed in the lithographic process sequence and thermal SiO 2 present strong compressive stress and can be used only in special conditions (shorter time required and lower etching concentrations). The proposed protective layer is a silicon elastomer that provided good adhesion and masking properties and was tested for the manufacturing of thin silicon membranes using bulk micromachining. The experiments were performed in 10% TMAH and 10% TMAH:H 2O 2 aqua solutions at 85°C and KOH (20% and 30%) at 80°C. So, the thin silicon membranes with <10 μm thickness have been obtained. The organic layer assures the protection during etching process and can be chemically removed after this procedure.