Process Integration for active polysilicon resonant microstructures

Abstract

Microsensors based on active polysilicon resonant microstructures are attractive because of their wide dynamic range, high sensitivity and frequency shift output. In this paper, we discuss processing issues for integrating electrostatically-driven and -sensed polysilicon microstructures with on-chip nMOS device. Surface-micro-machining using sacrificial spacer layers is used to obtain relased microstructures. A novel feature is the use of rapid thermal annealing (RTA) for strain relief of the ion-implanted, phosphorous-doped polysilicon. Resonance frequencies of cantilever beams indicate a lower-bound Young's modulus of about 90 GPa and an upper-bound compressive residual strain of only 0.002%, indicating that RTA is potentially useful for strain relief.