After depositing the Ta-based diffusion barrier and a physical vapor deposited (PVD) Cu seed layer, the Metal 4 (M4) Cu deposition step is required to completely fill the dual-damascene trench and via structures P1.This step relies on electrochemical plating (ECP) to form the primary conductive bulk of the interconnect, providing low-resistance pathways crucial for reducing the RC time constant in deep-submicron devices A1.Unlike lower metal layers (M1 to M3) which primarily handle fine-pitch, h