ANALYSIS OF ELECTROMIGRATION-INDUCED FAILURES IN HIGH-TEMPERATURE SPUTTERED AL-ALLOY METALLIZATION

Electromigration-induced failures in high-temperature sputtered Al-alloy metallization have been studied in terms of Al-alloy microstructure, Si nodules, and reaction products between the Al alloy and the underlayer material. Highly reliable interconnects can be realized by high-temperature sputtered Al-Si-Cu-alloy metallization utilizing a Ti underlayer. The interfacial reaction between the growing Al-Si-Cu him and the Ti underlayer during high-temperature sputtering produces an Al3Ti-alloy layer having a resistivity of about 40 mu Omega cm, and Si in Al alloy is absorbed in the Al3Ti layer without forming Si nodules. As the result, a bilayer structure of Al alloy/Al-Ti-Si alloy is formed. The electromigration resistance of the resultant TiN/Al alloy/Al-Ti-Si/TiN structure is drastically improved. It is speculated from the experimental results that this is because of the high quality of the Al-alloy film microstructure, i.e., an increase in (111) orientation, a decrease in the standard deviation of the grain distribution, and the superior current bypass effect through the Al-Ti-Si alloy and underlying TiN layer. In particular, an electrical current easily flows through the Al-Ti-Si alloy and TiN layer before a void completely crosses the upper Al alloy part of the metal line because the formation of the AlN high-resistance layer is suppressed by laying the Ti film between the Al-Si-Cu him and the underlying TiN film. Accordingly, the local temperature increase in the vicinity of the void is not essential to the subsequent void growth due to the lower resistivity of the Al-Ti-Si-alloy layer, resulting in the low void growth rate. (C) 1995 American Vacuum Society.