Improved reliability of copper interconnects using alloying

As device dimensions and wire dimensions are reduced, it is desirable to increase the electromigration lifetime of Cu. A simple method to improve the electromigration lifetime is to dope the Cu with impurities, such as Al, Ag, Ti, or Mn, using an alloy seed layer. During subsequent anneals, the impurities segregate at grain boundaries and interfaces, including the critical interface between the Cu and the capping layer. The presence of the impurities at the interfaces reduces Cu diffusion, resulting in an enhancement of electromigration lifetimes of up to 10x. The main challenge with the use of alloy seed layers is the increase in resistivity caused by doping. With alloy seed layers, there is always a trade-off between increased reliability and increased resistivity.