AVS 51st International Symposium
    MEMS and NEMS Monday Sessions
       Session MN-MoM

Paper MN-MoM5
Deposition and Characterization of Nitrogen-Doped Polycrystalline SiC Films for MEMS Applications

Monday, November 15, 2004, 9:40 am, Room 213C

Session: Processing and Characterization for MEMS and NEMS
Presenter: C.A. Zorman, Case Western Reserve University
Authors: J. Trevino, Case Western Reserve University
X.-A. Fu, Case Western Reserve University
S. Rajgopal, Case Western Reserve University
M. Mehregany, Case Western Reserve University
C.A. Zorman, Case Western Reserve University
Correspondent: Click to Email
This presentation reports on the development of processes to deposit undoped and nitrogen-doped, polycrystalline silicon carbide (poly-SiC) films on large-area substrates in a high-throughput, low pressure chemical vapor deposition (LPCVD) reactor using SiH2Cl2, C2H2 and NH3 precursor gases. The films were deposited in a customized deposition system constructed around a resistively-heated, horizontal furnace similar in design to a conventional polysilicon furnace and capable of holding up to 100, 150 mm-diameter substrates. To the best of our knowledge, this is the largest furnace designed specifically for the production of poly-SiC films for MEMS. Depositions were performed on 100 mm-diameter Si and SiO2-coated Si wafers using a SiH2Cl2 flow rate of 35 sccm, a C2H2 (5% in H2) flow rate of 180 sccm and NH3 (5% in H2) flow rates ranging from 10 to 90 sccm. The furnace temperature was held at 900C while the deposition pressures ranged from 2.5 to 4 Torr. Stoichiometric poly-SiC films were deposited over this entire range. The films exhibit a strong (111) 3C-SiC texture regardless of pressure. Films having a thickness of up to 2 microns are uniform, with less than a 5% variation across both the wafers and the boat. Four-point probe measurements indicate that the highest conductivities are achieved at a NH3 flow rate of 90 sccm. Wafer-scale residual stresses were measured using an optical curvature measurement technique. The residual stresses in the heavily-doped films are tensile with values decreasing to around 100 MPa in films deposited at 4 Torr. Single-layer, surface mechanical properties test structures, such as cantilever beams, stress pointers and lateral resonators were fabricated, successfully released and used to characterize the films. Likewise, bulk micromachined membranes were fabricated and tested using a load-deflection technique. Stress measurements from these micromachined structures confirm the wafer-scale residual stress measurements.