Electromigration lifetime enhancement of CoWP capped Cu interconnects by thermal treatment

In order to develop highly reliable Cu interconnects, temperature dependence of the electromigration (EM) lifetime of metal (CoWP) capped Cu interconnects is investigated. It is found that the EM lifetime is enhanced as the test temperature rise from 275 to 380°C. NH₃ plasma treatment before the dielectric cap layer deposition on the CoWP capped Cu interconnects influenced the temperature dependence of EM lifetime, that is, the interconnects without the NH₃ plasma treatment have longer EM lifetime than those with the NH₃ plasma treatment at the higher test temperatures. In order to investigate the mechanism for this lifetime enhancement, micro-analysis and failure mode analysis were carried out. It is concluded that the Co alloying with Cu and the CoWP coverage repair due to Co diffusion at the high temperature lead to the EM lifetime enhancement.