Effects of microstructure on interconnect and via reliability: Multimodal failure statistics

Abstract

The reliability of interconnects and contacts depends on their microstructure. However, a large change in the average grain size does not necessarily positively affect reliability. When grain sizes and feature sizes are comparable, interconnect and via reliability depends much more strongly on the nature of the grain size distribution and the probability of occurrence of specific microstructural features, than on the average grain size. Also, when grain sizes and feature sizes are comparable, different microstructure-specific failure mechanisms can occur, and multimodal failure statistics are often observed. In this case, if failure data are incorrectly fit to a single failure-time distribution, the resulting reliability assessment may be pessimistic or optimistic, but is in any case, incorrect. In this regime, accurate reliability assessment requires a detailed knowledge of the microstructure of the interconnects, and a characterization of the failure of the weakest microstructural features present in the population to be assessed.