Low-stress, heavily-doped polycrystalline silicon carbide for MEMS applications

This paper details a process to deposit low-stress, heavily-doped polycrystalline 3C-SiC (poly-SiC) films suitable for MEMS applications. The films were deposited by low pressure chemical vapor deposition (LPCVD) on Si and SiO₂ coated Si wafers at 900°C using dichlorosilane (SiH₂Cl₂) and acetylene (C₂H₂) as precursors and ammonia (NH₃) as a dopant gas. Poly-SiC films with a resistivity of 0.017 Ω-cm and a tensile residual stress of 59 MPa were produced. The average Young´s modulus for these films was found to be around 330 GPa, as determined using bulk micromachined membranes and surface micromachined resonators. Suspended microbridges fabricated from these films were able to operate in air at elevated temperatures for extended periods, thus illustrating the chemical and thermal durability of the thin SiC films.