The MET2 Cu Seed deposition step serves as the critical conductive bridge between the highly resistive Ta-based liner and the subsequent bulk electrochemical plating (ECP) process P4.In the dual-damascene interconnect flow for 40nm BSI CMOS image sensors, this layer provides the necessary continuous cathode for uniform electrochemical Cu deposition P4.Since the preceding Ta-based liner has poor electrical conductivity and lacks the surface properties required for direct Cu electroplating, a high