The Chemical Mechanical Planarization (CMP) of Copper at the Metal 2 (MET2) module serves to remove the electroplated Cu overburden, achieving global planarization for the 40nm Backside Illuminated (BSI) CMOS Image Sensor P3.This step is intentionally positioned after the M2 Cu deposition and prior to the Ta-based liner CMP P3.By utilizing a specialized two-step approach, the bulk Cu is first cleared while stopping precisely on the Ta-based liner, which prevents excessive damage to the delicate