Investigation on reliability improvement for next generation Cu/ULK interconnects

The long-term reliability of ultralow-k (ULK) and copper/barrier metal, especially for time-dependent dielectric breakdown (TDDB) and electro-migration (EM), in Cu/ULK interconnects is rapidly becoming one of the most critical challenges for technology qualification as continuous advanced VLSI technology scaling. To explore the root cause to improve reliability, ULK deposition process and barrier metal process were studied. Increasing flow rate of the Si-based precursor or spacing between shower head to wafer stage was found to help dielectric breakdown voltage improvement for ULK material. Enhancing the ratio of Si-CH3/Si-O, which enables to improve the damage resistance, is considered as the main reason. As a result, TDDB enables to be improved significantly by >1000 times with comparable RC delay at a high flow rate of Si-based precursor. Meanwhile, improvement of the quality of the initial barrier film between barrier metal and ULK is found to improve EM lifetime at advanced generation when the thickness of barrier metal need to be reduced gradually as technology node continuous scaling.