CMOS Integrated Poly-SiGe Piezoresistive Pressure Sensor

Abstract

This chapter describes the fabrication and testing of an integrated poly-SiGe-based piezoresistive pressure sensor directly fabricated above 0.13 \(\upmu \)m Cu-backend CMOS technology. This represents not only the first integrated poly-SiGe pressure sensor directly fabricated above its readout circuit, but also the first time that a poly-SiGe MEMS device is processed on top of Cu-backend CMOS. In the past, imec already proved the potential of poly-SiGe for MEMS-above-CMOS integration by presenting, for example, an integrated poly-SiGe micromirror array and an integrated gyroscope , both of them fabricated on top of Al-based CMOS. However, the aggressive interconnect scaling, essential to the continuation of Moore’s law, has led to the replacement of the traditional aluminum metallization by copper metallization, due to its lower resistivity and improved reliability. The described integrated sensor includes a surface-micromachined poly-SiGe based piezoresistive pressure sensor (fabricated following the process flow described in Chap. 4) and an instrumentation amplifier that acts as the sensor readout circuit. The amplifier has been fabricated using imec’s 0.13 \(\upmu \)m CMOS technology, with Cu- interconnects (two metal layers), oxide dielectric and Cu-filled metal-to-metal vias. The chapter begins with a description of the design, fabrication and testing of the instrumentation amplifier used as the sensor readout circuit. The processing of the integrated sensor is explained next, with special attention to the development of the CMOS (Cu) to MEMS (Al) interface. The effect of the MEMS processing on the underlying CMOS performance is also characterized. Finally, the performance of the fabricated integrate sensor is evaluated.KeywordsCMOS-integrated circuitsCu-backend CMOS technology CMOS post-processingSurface micromachiningMEMSPiezoresistive devicesSilicon Germanium