CMOS compatible polycrystalline silicon-germanium based pressure sensors

This work demonstrates, for the first time, the use of poly-SiGe for the fabrication of both piezoresistive and capacitive pressure sensors at CMOS-compatible temperatures. Despite the low processing temperature (455 degrees C), a sensitivity of 4.6 mV/V/bar for a membrane of 200 x 200 mu m(2) is reached by piezoresistor design optimization. The possibility of further enhancing the sensor sensitivity by tuning the piezoresistor's annealing time is investigated, leading to a 30% improvement. Single capacitive pressure sensors with sensitivities up to 73 fF/bar have been successfully fabricated. Annealing tests, performed at a fixed temperature of 455 degrees C with different annealing times, prove that the presented pressure sensor process flows are compatible with post-processing above 0.13 mu m Cu-backend CMOS devices. The increase in metal-to-metal contacts (more than 8% after 6h annealing), rather than transistor performance or degradation of the metal interconnects, is what limits the post-processing thermal budget. (C) 2011 Elsevier B.V. All rights reserved.