Characterization of critical conditions for fracture during wafer testing by FEM and experiments

In this work, we investigate finite element models of an imprinting scenario of a needle into a thin metallic film together with corresponding experiments in order to analyze the critical conditions that lead to brittle fracture in Back End Of Line (BEOL) bond pad stacks during wafer testing. We investigate the elastic-plastic material properties of the individual BEOL material layers and propose a plasticity law in terms of a stress-strain curve for the aluminum layer. Instrumented indentation testing is undertaken in order to reproduce the conditions that BEOL pad stacks are exposed to during wafer testing. Along with this, physical failure analysis reveals the dominant failure modes in the BEOL stack after indentation. We investigate the influence of silicon oxide and copper layers embedded below the first silicon oxide layer on failure. Finally, we provide an approach value for the fracture strength of the silicon oxide film that shows good agreement with previous literature data.