The electromigration (EM) lifetimes of top-TiN/Ti/Al-0.5%Cu/Ti-bottom and top-TiN/Ti/Al-0.5%Cu/Ti/TiN/Ti-bottom stacked structures were investigated using five-level Al-alloy interconnections with tungsten-filled vias. TiN/Ti/AlCu/Ti stacked structures had an EM lifetime ten times longer than TiN/Ti/AlCu/Ti/TiN/Ti ones. This longer EM lifetime is probably due to the small grain-boundary diffusivities for the bamboo microstructure. In the TiN/Ti/AlCu/Ti structure, a localized Al3Ti intermetallic compound layer was formed by the reaction between Al and Ti at the AlCu/Ti interface. On the other hand, in the TiN/Ti/AlCu/Ti/TiN/Ti structures, an almost uniform Al3Ti intermetallic compound layer was formed at the AlCu/Ti interface. In the initial nucleation process in Al, the Al grain growth increased on Ti/SiO2 compared with Ti/TiN/Ti/SiO2 according to atomic force microscopy observation. Using the optimum Ti thickness (10 nm) made it possible to form Iona-EM-lifetime multilevel interconnections without using many metal stacked structures.