Poly-Si surface micromachining

Case Study II Poly-Si Surface Micromachining and Angular Rate Sensor... 

While the roughness of the polished surface is of very high importance for More Moore because of the further decreasing layer and stracture dimensions, optically flat, that is, mirror-like, surfaces are especially required for MOEMS devices. For mirror stmctures using poly-Si surface micromachining, processes based on those developed for atomically flat surfaces for Si wafer fabrication can be employed successfully. 

The morphological, electrical, and mechanical effects of etched poly-Si structures have been extensively investigated by Stoldt and coworkers (Miller et al. 2005, 2007, 2008 Becker et al. 2010a, b, 2011). Micromachined //-type polysilicon in contact with a Au layer demonstrated heterogeneous cracking or porosity across the poly-Si surface as a result of etching. This resulted in greatly increased electrical resistance and decreased the characteristic frequency of mechanical resonators. 

Strasser, M., Aigner, R., Franosch, M., Wachutka, G., 2002. Miniaturized thermoelectric generators based on poly-Si and poly-SiGe surface micromachining. Sensors and Actuators A 97-8, 535-542. 

Figures 14.2 and 14.3 show closeups of poly-Si micromachines from Sandia Labs, manufactured by using several poly-Si CMP processes. Figure 14.2 depicts the gear wheels of a 10 1 transmission. Due to CMP, the gears are completely planar. Figure 14.3 shows the alignment clips for positioning the gears. The two layers of gears are clearly visible. More examples that show where the five-layer surface micromachining process has been employed are...

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