The electromigration behavior of AlCu dual Damascene lines was compared with that of AlCu metal reactively ion-etched lines. The test structures consisted of 0.18, 0.35 and 1.33μm-wide lines which were terminated by W diffusion barriers. They were tested at 250C. An important result in the case of the 0.18μm-wide Damascene samples was a threshold-length product of almost 40kA/cm. Various failure mechanisms were detected in the dual Damascene and metal reactively ion-etched structures by observing the resistance shift as a function of time, as well as the lifetime versus current-density behaviours. It was found that the Damascene structures exhibited a long resistance incubation period, followed by a rapid increase in resistance. The reactively ion-etched structures exhibited a short resistance incubation period, followed by a gradual increase in resistance. The current density exponent was found to be close to 2 for the Damascene samples, and close to unity for the reactively ion-etched samples. The Damascene samples exhibited an appreciable lifetime improvement over reactively ion-etched samples for low levels of resistance change. The relative lifetime improvement decreased as the maximum allowed resistance shift increased. The average grain size was found to be considerably larger for Damascene lines, due to the higher AlCu deposition temperature.

Electromigration in AlCu Lines - Comparison of Dual Damascene and Metal Reactive Ion Etching. R.G.Filippi, M.A.Gribelyuk, T.Joseph, T.Kane, T.D.Sullivan, L.A.Clevenger, G.Costrini, J.Gambino, R.C.Iggulden, E.W.Kiewra, X.J.Ning, R.Ravikumar, R.F.Schnabel, G.Stojakovic, S.J.Weber, L.M.Gignac, C.K.Hu, D.L.Rath, K.P.Rodbell: Thin Solid Films, 2001, 388[1-2], 303-14