POST-CMOS MODULAR INTEGRATION OF POLY-SIGE MICROSTRUCTURES USINGPOLY-GE SACRIFICIAL LAYERS

摘要

Polycrystalline silicon-germanium (poly-SiGe) microstructuresrnhave been fabricated on standard CMOS wafers withrnaluminum metallization. Hydrogen peroxide (H_2O_2) etches thernsacrificial polycrystalline germanium (poly-Ge) layer withoutrnsignificantly etching the p-type poly-SiGe structural layer. Inrncontrast to HF sacrificial release etches, no special protectionrnof the underlying CMOS layers is needed. For the first time, thernfabrication of LPCVD surface microstructures directly on top ofrnstandard electronics is demonstrated, which leads to dramaticrnreductions in both MEMS-CMOS interconnect parasitics andrndevice area.rnInitial measurements indicate that poly-SiGe hasrnpromising material properties. Its fracture strength is 1.2 ±rnO.l%, which is comparable to that of poly-Si. A folded flexurernlateral resonator has a quality factor in vacuum as high asrn～15,000. No stress or dopant-activation anneal of the structuralrnlayer is needed, since the in-situ boron-doped poly-SiGe isrnfound to have an as-deposited stress of only -10 MParn(compressive) and a resistivity of only 1.8 mΩ-cm. From arncantilever-beam array, the strain gradient is found to be ratherrnhigh (+1.4 × 1O~(-4) (μm)~(-1)), so that a 120 μm cantilever bendsrnaway from the substrate by 1 μm at its tip. Deposition andrnannealing conditions have yet to be optimized to minimizernstrain gradient.