Variation-aware electromigration analysis of power/ground networks

Abstract

Due to shrinking wire dimensions, higher current density, and process variations, electromigration (EM) has become a major reliability problem. The existing backend design flows use the maximum allowed current density as the only practical guidance to prevent EM. There is a need for tools capable of performing comprehensive EM analyses. In this paper, we first explain why current density alone does not determine wire's susceptibility to EM. We introduce our variation-aware EM analysis tool, VEMA, for power/ground networks, which are typically the EM-critical parts of a chip. Our tool considers two types of variations: circuit-level and wire geometry-level. VEMA reports distributions of wire lifetimes for circuit-level variations. Compared to existing EM analyzer SysRel, VEMA filters out EM-immortal wires more efficiently and provides detailed feedback for EM violation corrections. VEMA also provides information of geometry-level tolerance for EM-mortal wires.