Characterizing Metallization Introduced Polysilicon Corrosion of Surface Micromachined Structures With Submicron Capacitive Gap

Corrosion of polysilicon occurs during the HF release, which may change the surface morphology, film thickness and even its mechanical strength; furthermore, long time exposure to HF and the presence of Au metallization appear to promote this corrosion. In this paper, clamp-clamp beams with a capacitive gap of 100nm have been manufactured to characterize this unusual phenomenon. Changes of the surface morphology are revealed, and the influence on electrical performance of the structure is evaluated. By changing the concentration of the HF, different releasing time thresholds are obtained. Although the origin of this effect is still under investigation, a simplified explanation based on the galvanic is presented. Finally, a novel method is developed to reduce the polysilicon corrosion. A parylene layer is deposited and patterned on top of the metal electrode, which proved to be very effective for isolating the Al layer.