Ti layer thickness dependence on electromigration performance of Ti-AlCu metallization

Electromigration lifetime tests on TiN-Ti-AlCu-TiN-Ti stacked structures with various upper Ti film thicknesses have been carried out on two-level interconnect structures connected with W-plugs. We found that a high electromigration resistance was obtained with thin Ti, resulting in an island shaped Al/sub 3/Ti intermetallic. This result is inconsistent with a well-known bypass model. We propose a new model in which the Al/sub 3/Ti-Al interface mass transport is faster than that of others.