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.

Measurement of Young’s modulus and residual stress of thin SiC layers for MEMS high temperature applications

“…Table 1 gives an overview of some published results. Bulge testing is widely employed for determining Young's modulus and residual stress of polycrystalline 3C-SiC (Fu 2005); (Roy et al 2006);(von Berg et al 1996) as well as single crystal 3C-SiC (Mehregany et al 1997);(von Berg et al 1996); (Zhou et al 2008); (Mitchell et al 2003). In this method, pressure-dependent membrane deflection is measured.…”

Ab initio calculations of some electronic and elastic properties for SiC polytypes

“…All this enables one to consider SiC as a very interesting material for industrial applications and represents a strong motivation for its theoretical studies. In particular, the exploration of electronic [3][4][5][6][7][8][9][10] and mechanical properties [11], specifically the elastic ones [12][13][14][15][16][17][18][19][20][21][22][23][24][25], look rather important for future engineering applications.…”

Micro‐ and nanomechanical structures for silicon carbide MEMS and NEMS

“…More recently, the Young's modulus of undoped poly-SiC films deposited by LPCVD using the DCS/acetylene precursor system was reported to be 401 GPa [86], which decreased to 330 GPa when the films were heavily doped with nitrogen [77]. It has been shown that films deposited by APCVD on polysilicon using the 3C-SiC epitaxial growth process have a Young's modulus that depends upon the microstructure of the films [32]. Poly-SiC films with an equiaxed microstructure had a Young's modulus of 452 GPa to 492 GPa while those with a columnar texture had values ranging from 340 GPa to 357 GPa.…”

“…[77] and [86], while being deposited by LPCVD, also had a columnar microstructure. The burst strength for the APCVD poly-SiC films, as determined using micromachined membranes, was highest for the columnar films at 1718 MPa and lowest for the equiaxed films at 1321 MPa [32].…”

“…Simple experiments that combine measurements of the pressure at which a membrane bursts with a finite element model (FEM) derived from the loaddeflection behaviour of the membrane prior to failure can be used to determine the burst stress of the films. It has been reported that the burst strength for 2 µm thick 3C-SiC films is 2159 MPa [32].…”