Multilayer micromechanics process with thick functional layers (EPyC40)

The EPyC process (Epi-Poly-Cycle) (by Robert Bosch GmbH) opens up unique opportunities for manufacturing complex 3D MEMS structures having high effectiveness in small space. EPyC40 is an EPyC process with up to 40 mm thick polysilicon layers and sacrificial silicon technique. For successful manufacturing a 40 mm EPyC the epitaxial polysilicon layer must be electrically and mechanically optimized. A vertical deep trench patterns the functional and sacrificial areas. A passivation must be deposited homogeneously and has to be tight and robust towards silicon-etching gases. For more than one cycle it is necessary to tailor the layer stress of the epitaxial polysilicon and the wafer-bow. The full process for stacking up 5 EPyC cycles with two 40 mm epitaxial polysilicon layers was investigated in detail. A true 3D MEMS device providing high z deflection by use of a vertical comb drive with 40 mm electrodes was built up successfully to prove the feasibility of the EPyC process.