Measurement of residual stress and elastic modulus of polycrystalline 3C-SiC films deposited by low-pressure chemical vapor deposition

Abstract

Residual stress and in-plane biaxial modulus of polycrystalline 3C-silicon carbide (poly-SiC) films are studied using bulk and surface micromachined microstructures. The poly-SiC films are deposited on 100-mm-diameter (100) silicon wafers in a high-throughput, low-pressure chemical vapor deposition furnace at 1173 K using dichlorosilane (SiH 2Cl 2) and acetylene (C 2H 2) precursors at deposition pressures from 61 to 666 Pa. The resulting 0.5 to 2.7 μm films are highly textured, (111) oriented, polycrystalline 3C-SiC. Suspended diaphragms of these films are fabricated by standard wet chemical bulk micromachining of the silicon substrate from the back side. The load-deflection technique is used to extract the residual stress and in-plane biaxial modulus. For the center slot position in the boat, the films' residual stress changes from high (e.g., 726 MPa) to a relatively lower (e.g., 265 MPa) tensile stress as the deposition pressure increases from 61 to 333 Pa at fixed precursor flow rates. The average biaxial modulus of the films is 482 GPa; accordingly, the average Young's modulus is 401 GPa, assuming a Poisson's ratio of 0.168. However, the poly-SiC diaphragms fabricated from films deposited in the 380 to 666 Pa pressure range buckle due to compressive residual stress. Therefore, micro strain gauges are also fabricated and used to measure compressive residual strains in these films, which are − 0.032% at 500 Pa and − 0.024% at 666 Pa. Using 401 GPa as Young's modulus, these correspond to residual stresses of − 129 MPa and − 98 MPa, respectively.