P+ silicon recessed micromechanical structures for MEMS applications

In the present work, we have demonstrated a novel process for fabricating suspended P⁺ silicon micromechanical structures such as cantilever beam, microbridge etc. which are recessed in the substrate. The recessed structures formed inside anisotropically etched rectangular cavity, can be further secured by a low temperature planar wafer-bonding process, which also provides the "pull down electrode" for electrostatic actuation of the beam, if required. It is visualized that the recessed structures can be advantageously adapted for many applications such as accelerometer, IR detector, pressure sensors and micro-relay. Since the delicate moving parts are recessed in the substrate, these can be handled and packaged more easily compared to non-recessed structures. We have used standard spin coating process for photoresist application instead of electrodeposition process reported elsewhere which requires an electroplating base. The issues related to photolithography and subsequent etching process on silicon substrate with sharp topographic features are addressed.