Effects of failure criteria on the lifetime distribution of dual-damascene Cu line/via on W

Electromigration lifetime was studied on 0.23 μm wide Cu dual-damascene lines connected to underlying W lines with a TaN/Ta liner and SiNx/SiO2 insulator. The failure criteria used to study electromigration lifetime were based on the increase in test line resistance. Over 900 samples were tested to observe early electromigration Cu lifetime. Experimental results show that the lifetime distribution of samples tested using a failure criterion of 1% (3 Ω) resistance increase at the test temperature is best described by a trimodal function. However, the lifetime distribution of samples tested using a failure criterion of 50% is best described by a bimodal function. This difference in lifetime distribution is due to three types of observed deviant line resistance behaviors (plateau, fluctuating, and uphill) of certain samples which are caused by different types of void growth and a variation in liner stability.