Effects of metal thickness variations on IC metal lifetime due to electromigration

In this paper the effect of Al-metal-thickness variations on the IC metal lifetime is investigated. Because the flow of currents in IC metals is mainly dictated by the front-end circuitry, metal thickness variations result in current-density changes in the IC metals. The change of current density, in turn, results in metal lifetime variations caused by Electromigration (EM). This effect is investigated and modeled in this work. Experimental data from eight month´s of EM tests performed as part of the wafer-level reliability (WLR) tests on the BCD technology in STMicroelectronics were used as the basis for the approach. Accurate metal thickness at each measured site was extracted and used in lifetime extractions. Summarized results show that a 22% metal thickness reduction is sufficient to reduce the metal lifetime below 10 years.