Improvement of the Electromigration Resistance of Al Thin-Film Interconnection by Controlling the Crystallinity of Grain Boundaries

Abstract

The degradation process of the crystallinity of grain boundaries in Al thin-film interconnections was visualized by applying EBSD analysis under high current density. The grain boundary diffusion was accelerated by electromigration only along random grain boundaries with low crystallinity. The crystallinity (IQ value obtained from EBSD analysis) of grain boundaries varied drastically as strong functions of manufacturing process such as deposition method, temperature of thin-film deposition, gas pressure during the deposition, substrate material, and so on. The effective activation energy of self-diffusion of component element along random grain boundaries was found to be dominated by the crystallinity of random grain boundaries. The measured activation energy obtained from the low-crystallinity interconnections was much lower than that obtained from the thermodynamically stable bulk material, and therefore, the diffusion constant due to electromigration was drastically increased, resulting in the drastic decrease of the lifetime of the interconnections. The lifetime of the interconnections was, therefore, improved by increasing the crystallinity of grain boundaries.