Following the bulk Cu CMP step, the Ta-based liner CMP is required to completely remove the residual field barrier metal and electrically isolate the MET1 copper interconnects P3.This step effectively defines the final Cu Damascene structure and prepares the planarized surface necessary for the subsequent Post CMP Cleaning and ILD 1-1 deposition P3.Compared to subsequent upper-level interconnect CMP steps, this MET1 liner CMP is distinct because it encounters the highest local pattern density an