Early failure of short-lead metal line and its EM characterization with Wheatstone bridge test structure in advanced Cu/ULK BEOL process

Early failure of the short-lead metal line EM (Electromigration) is investigated. Applying Wheatstone bridge (WSB) test structure and 3-parameter lognormal distribution enables to reduce sample size and time-to-fail (TTF) variation governed by early fails causing a poor standard deviation, EM lifetime is accurately predicted and improved by ~280×. In particular, EM TTF at lower percentiles can be well represented by 3-parameter lognormal. With respect to physical aspects of void, EM behaviors of the short-lead and long-lead metal line are addressed based on experimental results compared with Monte-Carlo simulations to support the Blech's back-stress effects.