In the 40nm BSI CIS flow, after the ILD layers are etched to form the pad openings, the underlying Metal 7 interconnect barrier must be etched to establish electrical contact A2.The integration of high-density copper interconnects dictates the use of reliable barrier layers, such as Ta or TaN, to inhibit copper diffusion into adjacent dielectrics P2.This step specifically removes the exposed barrier material at the bottom of the bond pad via, preparing the surface for final packaging connections