ELECTROMIGRATION INDUCED TRANSGRANULAR SLIT FAILURES IN NEAR BAMBOO AL AND AL-2-PERCENT CU THIN-FILM INTERCONNECTS

We report the morphology of electromigration induced transgranular slit-like voids in Al and Al-2% Cu thin-film interconnects with near bamboo microstructures. The grain structure surrounding fatal voids was determined from images produced by scanning electron and focused ion beam microscopy. Fatal voids were seen to traverse grains near to, but apart from, bamboo boundaries or grain triple points, and often appear to emanate from small wedge-shaped voids at the interconnect edge. The small volume slit voids are consistent with an observed decrease in fatal void volume with reduced linewidth/grain size ratio. However, the transgranular void pathway represents a new failure mechanism responsible for reduced reliability in the narrow interconnects which are more relevant for advanced integrated circuit technologies. The conditions for stress-induced transgranular slit voiding are briefly discussed.