Metal 3 (M3) Cu deposition fills the dual-damascene trenches and vias patterned in the inter-metal dielectric, establishing the intermediate routing layer in the 40nm BEOL flow A1.Following the Ta-based liner and Cu seed deposition, electrochemical deposition (ECD) is utilized to achieve a void-free bulk copper fill P3.Unlike Metal 0 W, which serves as a local interconnect with higher resistivity, Cu provides the low-resistivity pathway required to minimize resistive-capacitive (RC) delays in in