COMPARISON OF FINITE-ELEMENT STRESS-ANALYSIS RESULTS WITH PEEL STRENGTH AT THE COPPER-POLYIMIDE INTERFACE

An exploratory stress analysis has been performed on dense wiring stru ctures, such as those used for multichip modules, with the objective o f 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 top of a nd 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 energ y release rate) which could act on any preexisting microcrack or delam ination. It was found that delaminations propagating from the base of the copper line up the sidewall were a strong possibility. The predict ions of the stress analysis were substantiated by transmission electro n microscopy photographs of real structures which showed the same type of delamination as that anticipated by stress analysis. For these par ts, the adhesion between the copper line and the polyimide insulator w as mediated by a liner of tantalum, which gives weak adhesion to coppe r under certain circumstances. X-ray photoelectron spectroscopy and pe er test analyses were used to verify the suspected failure modes.