A systematic study was made of the microstructural and electromigration characteristics of Ti/Al-Cu/Ti laminate structures which were fabricated from 2 metal wiring levels that were 1 in width. The total Cu content in the Al-Cu core layers ranged from 0.5 to 2.0wt%. A high incidence of <111> textures was found for all of the Cu concentrations except the lowest. The grain size was independent of the Cu concentration. The Al grains were supersaturated with Cu, and this led to changes in resistance during low-temperature baking and during electromigration tests. The electromigration lifetimes of stripes which were connected to large reservoirs of Cu and Al were found to be linearly dependent upon the total Cu content, but there was a decrease in the lifetimes of 2-level W stud structures as the Cu content was increased. The activation energy for electromigration-induced failure was found to be between 0.78 and 0.93eV. Resistance changes during electromigration and temperature-only stressing, and the microstructural characteristics of failed structures, were explained in terms of the Cu distribution in the Al matrix and the geometry of the structures.

A.G.Domenicucci, R.G.Filippi, K.W.Choi, C.K.Hu, K.P.Rodbell: Journal of Applied Physics, 1996, 80[9], 4952-9