Determination of polysilicon Weibull parameters from indentation fracture

A local approach is taken to characterize statistical distribution in fracture behavior of polysilicon thin film using indentation fracture data. Berkovich indentation tests were performed on a three micron thick polysilicon film and the average fracture toughness was evaluated using conventional approach, that ignores the effect of other layers, to be 0.7 MPam. Weakest link theory when applied to an equivalent model of center loaded penny crack that is wedged open with uniform indent pressure is able to estimate the Weibull strength and modulus for the polysilicon to be well within the range reported in literature. Further, using the Weibull parameters, thus determined, on model of standard fracture test specimen, fracture toughness of polysilicon is estimated to be 1.5 MPam. A discussion is developed emphasizing the importance of local approach that accounts for the differences in elastic behavior of the layers while characterizing fracture toughness.