The Cu CMP step in the MET6 module serves to remove the electroplated bulk copper overburden and achieve global planarization, strictly stopping on the underlying Ta-based liner P1. As the upper metallization layer in a 40nm BSI CMOS Image Sensor flow, MET6 typically features wider global routing lines and optical shielding structures compared to the finer M1-M3 interconnects T2. Consequently, this specific CMP step must handle larger localized volumes of copper removal while heavily mitigating