Mechanism maps for electromigration-induced failure of metal and alloy interconnects

Abstract

Numerical simulation of electromigration-induced stress evolution provides a versatile technique for analyzing the reliability of interconnects under a wide range of conditions. We study the evolution of stress in confined, layered, stud-terminated, pure metal, and alloy interconnects. Failure times are estimated using different failure criteria associated with different failure modes for broad ranges of line lengths and current densities. The simulation results can be conveniently catalogued through construction of failure mechanism maps that display domains of dominance of different failure modes. Failure mechanism maps are constructed for several different failure criteria, illustrating regimes of line immortality, void-nucleation-limited failure, void-growth-limited failure, and compressive failure as a function of line length and current density. The effects of changes in failure criteria, geometry, and composition are studied for representative interconnect stacks at accelerated and service temperatures. Failure maps may be used to: (i) provide an overview of predicted reliability behavior, (ii) assess how data from accelerated tests can be accurately scaled to service conditions, and (iii) predict the effects of changes in interconnect and shunt-layer materials and dimensions on interconnect reliability. (C) 1999 American Institute of Physics. [S0021-8979(99)07024-3].