Surface roughness effect on the tensile strength of micromachined polysilicon films

In this paper, a new accurate microtensile test device using a magnetic-solenoid force actuator was developed to investigate the influence of surface roughness on polysilicon thin film mechanical properties. The microfabricated polysilicon thin films are 660 mum long, 40 mum wide and 2.4 mum thick with two kind of surface feartures which surface roughness is 19.46 nm and 26.09 nm, respectively. It was found that the measured average fracture strength is 1.35 GPa +/- 0.147 GPa and 1.22 GPa +/- 0.131 GPa, respectively. Statistical analysis of the surface roughness effects on the tensile strength predicated the surface roughness characterization of polysilicon films being tested and the direct relation of the mechanical properties with the surface roughness features. The fracture strength decreases with the increase of the surface roughness. The test data accounts for the uncertainties in mechanical properties and the influence of surface roughness on polysilicon thin film mechanical properties, which may be used to enhance the reliability design of polysilicon MEMS designs.