The films are used in making integrated circuits. Failure of the packaged circuit often results from poor adhesion between the copper and polymer films. Copper is replacing aluminum as the metal of choice for making connections between components in large, multi-chip modules, Menezes said. Not only does copper conduct better than aluminum, it also offers superior resistance to the effects of electromigration - thus permitting a greater level of miniaturization in the circuitry.
Copper has at least one serious drawback, however.
Thermal stresses created during fabrication and operation can cause the films to delaminate, ruining the device. To increase the adhesion at the film interface, Menezes and advisers Howard Birnbaum, professor of physical metallurgy and director of the Materials Research Laboratory on campus, and Ian Robertson, professor of materials science and engineering, developed a novel method for physically interlocking the two surfaces. The technique involves embedding copper clusters in the polymer and then coating the clusters and substrate with a continuous layer of metal. Then, by controlling the time and temperature of the annealing process, we partially embed the clusters into the polymer before depositing the metal layer. The clusters act as nano-nails, anchoring the metal layer above in much the same way that anchor bolts secure a wall to a foundation.