ELECTROMIGRATION IN 2-LEVEL INTERCONNECTS OF CU-ALLOY AND AL-ALLOY

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 degrees 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 degrees 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.