Electromigration early failure distribution in submicron interconnects

The early failure issue in electromigration has been an unresolved subject of study over the last several decades. A satisfying experimental approach for the detection and analysis of early fails has not been established yet. In this study, a new technique utilizing large interconnect arrays in conjunction with the well known Wheatstone Bridge is presented. Three types of structures with varying number of interconnects were used, starring from a small unit of five lines in parallel. A serial arrangement of this unit enabled testing of interconnect arrays encompassing 480 possible failure links. In addition, a Wheatstone Bridge-type wiring using four large arrays in each device enabled simultaneous testing of 1,920 interconnects. In conjunction with a statistical deconvolution to the single interconnect level, the results indicate that the electromigration failure mechanism studied here follows perfect lognormal behavior down to the four sigma level.