The primary objective of the W CMP (Tungsten Chemical Mechanical Planarization) step is to remove the thick tungsten overburden deposited in the previous step, leaving behind isolated, planarized tungsten plugs in the contact vias A1.In the context of a 40nm BSI CMOS Image Sensor, these precise contacts are critical for routing electrical signals from the active pixel transistors to the Metal 0 routing layers (Engineering Practice).This step is typically designed to halt selectively on the under