Low-cast PDMS seal ring for single-side wet etching of MEMS structures

We describe a new O-ring setup for wet-etching processes of microelectromechanical systems (MEMS). Our new low-cost approach using siloxane-based seal rings entails the single-side etching of silicon and silicon dioxide using potassium hydroxide and buffered hydrofluoric acid, respectively. With this approach, the wafer is not immersed into the etching solution, but only the side to be etched is in contact with the solution, hence the previously fabricated device elements on the other side of the wafer an not damaged. In one process for etching silicon the etch solution is heated by an infrared lamp. We describe the fabrication of various cantilever-based sensors, such as arrays of 0.8-mu m-thick levers for a chemical/electronic nose, and 5-mu m-thick silicon cantilevers having piezoresistive sensors. Our technique has good uniformity and process control and, in addition, eliminates mechanical stress on the fragile wafers incurred by wafer chucks, which are required for the conventional immersion approach. It has improved process yield and reduces the waste of chemicals. (C) 1998 Elsevier Science S.A. All rights reserved.