EFFECT OF AL3TI INTERMETALLIC COMPOUND ON ELECTROMIGRATION LIFETIME OF AL-ALLOY INTERCONNECTIONS

The dependence of the electromigration (EM) lifetime and the cross-sec tional structure of interconnections after EM tests on linewidths was investigated in multi-level and single-level Al alloy interconnections consisting of a top-TiN/Ti/Al-0.5%Cu/TiN/Ti-bottom stack. Ln this stu dy, an almost uniform Al3Ti intermetallic compound layer was formed by a well-known reaction between the Ti and Al. We found the following a nomalous behavior: the mean time to failure (MTF) of EM in the multi-l evel interconnections with tungsten diffusion barriers decreased by in creasing the linewidth. We also found that in the multi-level intercon nections after EM tests, independent of linewidths, a local Al thicken ing formed near the anode end of the line and voids formed near the ca thode end. On the other hand, in the single-level interconnections wit h bonding pads, the MTF of EM increased by increasing the linewidth an d, after EM tests, a local Al thickening formed near the anode end eve n though no voids were observed near the cathode end. This directly op posed EM lifetime dependency on linewidth found in the multi-level and single-level interconnections and the observed Al thickening correlat e closely with the fast diffusitivity of Al atoms at the interface bet ween the Al3Ti and Al and/or between the Al3Ti and TiN. (C) 1998 Ameri can Institute of Physics. [S0021-8979(98)03614-7]