Process Development for Very Deep Etching of Silicon Using Two Layer Masks for Fabrication of Mechanically Decoupled MEMS Gyroscope

This work discusses the key issues associated with the process development for 200 μm thick structure for mechanically decoupled Silicon on Glass (SOG) MEMS gyroscope. The gyroscope discussed here is a single axis, in-plane moving device with capacitive driving, differential capacitive sensing and has an area of 2.6 × 2.4 cm2. Challenges involved in defining masks for High Aspect Ratio (HAR) etching of silicon using Bosch process to a depth of 200 μm through an opening of 8 μm are discussed. The HAR etching of silicon is achieved by using a novel approach of having dual layer masks of Aluminum and photoresist.