Influence of the diffusion barriers on the dielectric reliability of ULK/Cu advanced interconnects

With the scaling down of copper interconnects, the importance of interface engineering becomes more and more crucial. In this paper, we have studied the influence of the diffusion barriers on the electrical performance and dielectric reliability of porous ULK/Cu interconnects, in comparison with a reference dense SiCOH dielectric. The best reliability for the porous ULK is obtained with the thicker barrier, consisting of CVD TiN. With this barrier; the porous ULK can even outperform the dense dielectric in terms of time to failures and dielectric breakdown in certain cases. For the TaN barrier, an H₂ plasma after etch improves the breakdown voltage up to 34%. A voiding at the top Cu comers after storage in the 110°C-150°C range under N₂ has been identified as a possible contribution to the fracture of the SiCN top capping layer. Therefore the Cu itself is critical for the dielectric reliability.