Low Stress Polycrystalline SiC Thin Films Suitable for MEMS Applications

Abstract

This paper details the development of low residual stress and low stress gradient unintentionally doped polycrystalline SiC (poly-SiC) thin films. The films were deposited in a large-volume, low-pressure chemical vapor deposition (LPCVD) furnace on 100 mm-diameter silicon (Si) wafers using dichlorosilane (SiH2Cl2) and acetylene (C2H2) as precursors. We found that the flow rate of SiH2Cl2 could be used to control the residual film stress in the as-deposited films. Wafer curvature measurements for ∼2 μm-thick films indicated that tensile stress ranging from 4 to 55 MPa across a 25 wafer boat had been achieved. A variety of micromachined structures including lateral resonant structures, stress pointers and cantilevers were fabricated for characterization of the deposited SiC films. The average Young’s modulus was found to be 403 GPa. Residual stress measurements were consistent with those obtained using a wafer curvature technique. Interferometric measurements of cantilever beams indicated stress gradients with an upper bound of 52 MPa/μm for ∼2 μm-thick films with tensile stress less than 55 MPa.