Bulk-micromachined structures inside anisotropically etched cavities

In the present work, we have demonstrated a novel process for fabricating suspended micromechanical structures of P + silicon and SiO 2 inside anisotropically etched rectangular cavities in (100) Si wafer. Using this new process, the moving parts are 'recessed' in the substrate and can be easily secured with a flat surface of any type of substrate as compared to non-recessed structures. We have used a standard spin coating process for photoresist application instead of the electrodeposition process reported elsewhere which requires an electroplating base. There is a common problem of thinning of photoresist on convex edges of the cavity during photolithography steps. As a result, silicon dioxide is etched away from these edges in buffered hydrofluoric acid. During subsequent anisotropic etching of silicon to release the microstructures, the unprotected convex edges are also etched, resulting in failure of the process. To overcome this problem, two different methods are used. Recessed microstructures have been successfully fabricated using this process. A prototype micro-relay is demonstrated using a P + silicon recessed cantilever beam.