Stress transfer across polyimide passivation layers

An X-ray tensile testing technique for studying the stress transfer across polyimide passivation layers is reviewed. The advantage of this direct technique over indirect techniques is discussed, and results are presented for a model system consisting of a nickel substrate, a polyimide passivation layer, and a copper conducting layer. The stress transfer behavior is compared to the behavior predicted by theory, and the ability of the X-ray tensile technique to measure appropriate parameters for modeling the stresses in multilayer thin-film structures is discussed. In addition, the effect of polyimide thickness on stress transfer is reviewed, and the effect of copper line width on stress transfer is reported. The assumption of an ideal interface behavior is not valid for calculating the stress transfer across passivation layers in the loading geometry used for this study. The stress values in the Cu thin films were about 70% less than the predicted values. As predicted by the closed form solution, there is no effect of PI properties and thickness on the stress transfer behavior at room temperature