This work investigated the electromigration and failure behaviour of layered tungsten vias. It has long been recognized that the flux divergence caused by the tungsten-aluminum interface is an area of high reliability risk. In an attempt to lower this risk, several process experiments were initiated. The thickness (500Å, 800Å, and 1200Å), composition (TiN and Ti), and etch and rinse rates of the underlaying layers of the tungsten plugs were varied. Test structures consisting of a chain of eight M1 to M2 vias were placed on electromigration testing. Their variability in lifetimes, resistance vs. time characteristics and failure behaviour is reported. The fail sites were characterized using TEM analysis and FIB cross-sections. Based on these results process improvements for improved reliability were developed.
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Elliott, L.J., Spooner, T., Rose, J.H. et al. The Electromigration and Failure Behaviour in Layered Tungsten Via Structures. MRS Online Proceedings Library 391, 459 (1995). https://doi.org/10.1557/PROC-391-459