Comparison of finite element stress analysis results with peel strength at the copper-polyimide interface

Abstract

An exploratory stress analysis has been performed on dense wiring structures, such as those used for multichip modules, with the objective of anticipating possible delamination failure mechanisms. The structure consists of an array of parallel copper lines imbedded in a polyimide insulator, all of which is supported by an underlying silicon wafer. Different versions include thin layers of silicon nitrides on lop of and at the base of the copper lines. Using the finite element technique, several models were constructed to explore where delamination could occur in this structure by calculating the driving force (strain energy release rate) which could act on any preexisting microcrack or dclamination. It was found that delaminations propagating from the base of the copper line up the sidewall were a strong possibility. The predictions of the stress analysis were substantiated by transmission electron microscopy photographs of real structures which showed the same type of delamination as that anticipated by stress analysis. For these parts, the adhesion between the copper line and the polyimide insulator was mediated by a liner of tantalum, which gives weak adhesion to copper under certain circumstances. X-ray photoelectron spectroscopy and peel test analyses were used to verify the suspected failure modes. © VSP 1993.