Statistical Characterization of Fracture Strength and Fatigue Lifetime of Polysilicon Thin Films with Different Stress Concentration Fields

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This paper presents an evaluation of strength distribution and fatigue behavior of polycrystalline silicon thin film specimens patterned by etching into arbitrary shapes. The static strength distribution of specimens is described by a two-parameter Weibull distribution applied to local points along the etched surface. The fatigue lifetime is formulated also locally as a crack extension process, starting from initial cracks which represent the etching damage and thus determine the strength distribution, by applying the well-known Paris law. The parameters in the Weibull distribution and in Paris' law were fit to the results of tensile static strength and fatigue tests performed on the specimens with three different shapes fabricated under the same conditions. Parameter distribution ranges were analyzed using inferential statistics. It was found that the fracture and fatigue behaviors of the specimens can be described by using a unique set of parameters despite the different stress distribution. This means that the local characteristics of etching damage and subsequent damage accumulation under fatigue loading was independent of the shapes and thus of the stress distributions of specimens.