Self-sustained bridges of a-SiC:H films obtained by PECVD at low temperatures for MEMS applications

In this work PECVD obtained a-SiC:H films are utilized to fabricate self sustained microbridges and microtunnels. The deposition conditions for these films, which present optimized properties for MEMS application, were established elsewhere. The utilized a-SiC:H films are 1 μm thick and are obtained at 320 °C from mixtures of CH4 and SiH4, with and without H2 dilution. The microstructures are fabricated by surface micromachining over silicon substrates utilizing 4 μm thick SiOxNy films as sacrificial layer, also obtained by PECVD. The geometry of the bridges and tunnels is varied from 25 μm up to several hundred microns and was defined by plasma RIE process established after a study also presented here. The final aspect of the microstructures and the evaluation of the fabrication process are investigated by scanning electron microscopy. The results show that bridges fabricated with stoichiometric a-SiC:H grown in `silane starving plasmaʹ condition with H2 dilution of the gaseous mixture can be very flat, smooth and free of residual stress. Since this material was previously optimized to be a real amorphous counterpart of crystalline SiC, can be doped very efficiently n- and p-type and can be crystallized by thermal annealing, the results presented here are the first step toward the development of MEMS all based on PECVD materials.