Mechanical Characterization of Polycrystalline and Amorphous Silicon Carbide Thin Films Using Bulge Test

Abstract

This paper aims at determining the mechanical parameters such as Young's modulus, Poisson's ratio, and intrinsic stress of polycrystalline and amorphous silicon carbide thin films using the bulge test. A suitable method for the bulge test of highly compressive amorphous SiC films was devised by developing tensile composite layers involving a highly tensile substrate layer. A setup suitable for use in high temperatures was developed to hold membrane chips mechanically for applying pressure. The center deflection was measured with optical interferometry. The bulge test was done on square and rectangular membranes in order to ascertain the Poisson's ratio and the exact Young's modulus of the material. The tests in this paper were conducted at room temperature. The tensile polycrystalline SiC films were obtained by low-pressure chemical vapor deposition (LPCVD) at 825°C, using monomethylsilane as the precursor. The amorphous SiC (a-SiC) films were deposited by plasma enhanced chemical vapor deposition (PECVD) process at a temperature of 870°C with silane and acetylene as precursors. Test chips were pressurized from outside the membrane cavity, and membrane deflection was measured for each pressure step. The poly-SiC layers indicated a Young's modulus of 280 GPa with a Poisson's ratio of 0.237. The Young's modulus of a-SiC films was found to be 232 GPa, but the Poisson's ratio could not be determined as we used a composite layer. A comparison with the existing literature values of Young's modulus was also done.