Tensile Tests of Various Thin Films

Abstract

Test methods for two types of thin-film tensile specimens have been developed in earlier works, and these are reviewed as background for new applications. Two kinds of specimens are tested. The first is 600 μm wide and suspended across a support frame, and the second is 6 to 50 μm wide and fixed to the silicon substrate at one end. Test systems incorporating force, strain, and displacement measurement are used, and Young's modulus can be obtained by three methods, which yield equivalent results. Tensile stress-strain curves of polysilicon have been recorded over the temperature range 30 to 250°C. The modulus decreases at a rate of 0.043 GPa/°C, and the strength increases slightly, although the scatter of the data is large in both cases. Polysilicon specimens produced by three vendors show essentially the same Young's modulus, but the fracture strengths vary by almost a factor of two. The first tensile tests of silicon nitride film are reported. The specimens are 0.5 μm thick, 600 μm wide, and 4 mm long in the gage section. Young's modulus is measured as 255 ± 2.6 GPa, Poisson's ratio is 0.22 ± 0.02, and the fracture strength is 6.42 ±1.11 GPa.