Comparison of tensile and bulge tests for thin-film silicon nitride

The mechanical properties of thin-film, low-pressure chemical vapor deposited silicon nitride were measured in uniaxial tension and by a bulge test method suitable for wafer-level testing. This research compares the two approaches and presents additional data on silicon nitride. The common property from the two test methods is the Young's modulus. Tensile tests performed at the Johns Hopkins University provided a value of 257 +/- 5 GPa. Bulge tests conducted by Exponent, Inc., an engineering and scientific consulting firm, yielded a value of 258 +/- 1 GlPa. It is concluded that this bulge test is a valid wafer-level test method. These tensile results, when added to earlier results, yield the following properties for low-stress silicon nitride: Young's modulus = 255 +/- 5 GPa, Poisson ratio = 0.23 +/- 0.02, and fracture strength = 5.87 +/- 0.62 GPa.