Interfacial sliding in Cu/Ta/polyimide high density interconnects as a result of thermal cycling

A scanning probe microscope was used to observe thermally induced deformation of 1 μm thick Cu/Ta/polyimide test structures on Si. Relative height changes in arrays of parallel Cu and polyimide lines of various aspect ratios were examined in air at room temperature before and after a 25-350-25°C thermal cycle conducted in gettered nitrogen. Grain elevation and hillock formation at grain boundaries were observed on the Cu surface as a result of the thermal cycling. It was also observed that significant sliding occurs at the Cu/Ta interface with 1 μm wide Cu lines. Less or no sliding was observed at the interface with 10 μm wide Cu lines.