Nitrogen Doped Polcrystalline 3C-Sic Films Deposited by LPCVD for MEMS Applications

This paper reports our latest results in developing and characterizing low-stress, heavily- nitrogen-doped polycrystalline 3C-silicon carbide (poly-SiC) films by low pressure chemical vapor deposition. Deposition pressure and NH₃ gas concentration are used to control residual stress, stress gradient and conductivity at a deposition temperature of 900degC using SiH₂O₂ (100%) and C₂H₂ (5% in H₂) as the Si and C precursors. The residual stress is tensile and increases from near zero to near a maximum of 250 MPa with increasing doping concentration; the resistivity decreases from 0.14 Omega-cm to 0.006 Omega-cm in the same doping concentration range. The average TCR decreases from -2050.3 ppm/degC to -1957.0 ppm/degC over approximately the same doping concentration range. The Young´s modulus of the films is estimated at 330 GPa, assuming a Poisson´s ration of 0.163 for poly-SiC.