The mechanical properties of polycrystalline 3C-SiC films grown on polysilicon substrates by atmospheric pressure chemical-vapor deposition

Abstract

This paper presents the results of a study to determine Young’s modulus, residual stress, and burst strength of polycrystalline 3C silicon carbide (poly-SiC) films grown on as-deposited and annealed polysilicon substrate layers. The biaxial modulus and residual stress were determined for bulk micromachined poly-SiC diaphragms using an interferometric load-deflection measurement apparatus. The load-deflection data were analyzed using a least-squares fitting technique to extract the biaxial modulus and residual stress values, and Young’s modulus was calculated assuming a Poisson ratio of 0.15. Poly-SiC films comprised of equiaxed grains exhibited Young’s modulus values ranging from 452 to 494GPa, while columnar films with a high degree of (110) texture exhibited Young’s modulus values between 340 and 357GPa. The residual stress for these films did not exhibit a discernable relationship with microstructure; however, the values exhibited a general dependence on growth temperature. Poly-SiC films grown at 1280 °C had residual stress values ranging from 401 to 486MPa, while a film grown at 1160 °C had a residual stress value of 113MPa. Burst strength was determined using a combination of finite element analysis and burst pressure measurements of the suspended diaphragms. Poly-SiC films grown at 1280 °C exhibited an average burst strength value of 1718MPa, while the poly-SiC film grown at 1160 °C had an average burst strength value of 1321MPa.