New Insight On Electromigration Failure Mechanism And Its Impact On Design Guidelines

INTRODUCTION A fundamental understanding of electromigration (EM) failures at W plug contact / via areas is essential in formulating design guidelines for VLSI interconnects. EM at the W plug areas has been found to occur through two stages, namely an incubation stage (consisting of A1,Cu precipitate dissolution followed by Cu diffusion beyond a critical length) and an A1 drift stage, which leads to increase in resistance. In this paper, it is first shown that the use of incubation time as the electromigration failure criterion enables realistic lifetime prediction of VLSI interconnects. Furthermore, we have studied electromigration in a temperature regime where precipitate dissolution and subsequent diffusion of Cu is dominant. The results yield markedly different activation energies which have an enormous impact on electromigration design guidelines for these interconnects. It is also shown how some accelerated EM tests can lead to erroneous conclusions and thereby mask the physical processes operative at use conditions.