Electromigration Study of Cu Dual-damascene Interconnects with a CVD MSQ Low k Dielectric

Electromigration reliability in Cu dual-damascene interconnects with a CVD MSQ low k dielectric was investigated. Statistical studies were carried out using the critical length (LC) test structures containing multi-link line/via elements with varying line lengths. EM lifetime characteristics, critical current density-length product (jL)c, and failure mechanisms were discussed and compared with Cu/oxide structures. Our results suggested that the diffusion at the cap layer interface was the dominant mechanism for EM mass transport. The confinement effect, in terms of an effective modulus B, can be used to account for the shorter EM lifetime and smaller critical current density-length product (jL)c observed for Cu/CVD MSQ low k interconnects. Failure analysis by FIB confirmed the presence of multiple failure modes including voiding at the via bottom, Cu extrusion and delamination at Cu/cap layer interface.