Roles of Tihyphen;intermetallic compound layers on the electromigration resistance of Alhyphen;Cu interconnecting stripes

摘要

Various suggestions for the origin of the beneficial effect of TiAl3layers on the electromigration resistance of Alhyphen;Cu interconnect stripes have been evaluated experimentally. The leading candidate for this effect, the shunting of current through the intermetallic compound layer that spans opens (voids) in the Alhyphen;Cu layer, cannot account for the correlation found in the present investigation between the median time to failure and the median rate of increase of electrical resistance in the Alhyphen;Cu layer of different multilayer interconnect configurations. When the TiAl3layer lies above the Alhyphen;Cu conducting layer, the major enhancement of median lifetime to failure is an effect the TiAl3layer has on the lsquo;lsquo;electromigration resistancersquo;rsquo; of the Alhyphen;Cu layer. This effect arises from the overlayer acting to decrease the rate of mass transport in the Alhyphen;Cu layer rather than from any effect on the grain size or texture of the Alhyphen;Cu layer. It is believed that the TiAl3overlayer acts to produce triaxiality in the local stress fields developed at mass sinks and sources. This triaxiality of the stress field should act to increase the local yield strengths. A model analysis shows that the yield strengths required to reduce the mass flux by the observed amount are reasonable for a near triaxial state of stress. Only when the TiAl3layer is below the Alhyphen;Cu layer is it possible that shunting is the cause of the enhancement in the median time to failure relative to that for a single Alhyphen;Cu interconnect layer. thinsp;