Electromigration in two-level interconnects of Cu and Al alloys

Electromigration in two-level interconnect structures fabricated using both Cu deposited by plating and sputtered Al(Cu), as well as in conventional single-level structures using evaporated Cu, Cu(0.3 at.% Zr) and Cu(0.3 at.% Ta) stripes has been investigated. Both resistance and drift velocity measurement techniques have been used at temperatures from 200 to 395 °C. Open circuit failures in such structures are found to be caused by void growth from the cathode ends of the lines. The mean time to failure in the plated Cu/polyimide structure is found to be about two orders of magnitude longer than that in the Ti/Al(Cu)/Ti/SiO2 structure at 250 °C. The activation energy for electromigration of the plated Cu and the Al(Cu) is found to be 1.1 ± 0.07 eV and 0.81 ± 0.03 eV, respectively. The additions of 0.3% Zr and 0.3% Ta to pure Cu in the single-level test structures of Ta/Cu/Ta have little effect on the mean time to failure. © 1995.