Barrier layer effects on reliabilities of copper metallization

Copper metallization with three kinds of barrier layers (Ta, TaN and multistacked Ta/TaN) and undoped silicate glass as insulation dielectric layer were investigated and the effects of barrier layer on the reliability of the copper lines were examined. It was found that the Cu lines embedded in Ta had the best anti-electromigration (EM) property among the three kinds of barriers. Continuous current stress using via chain structure revealed that the redundant barrier layers between via plugging-in and the underlayer metal line greatly affected the electromigration properties due to Cu flux divergence caused by the barrier blocking at the via connection point. The voids caused by electromigration were observed by focused ion beam technique and their formation mechanism is discussed.