In the fabrication of Backside Illuminated (BSI) CMOS image sensors, the bulk silicon handle must be drastically thinned to allow direct backside illumination, which maximizes the fill factor and light absorption efficiency A1.Following mechanical grinding and the primary CMP1 step, which removes severe mechanically induced subsurface damage, the CIS Backside Si CMP2 step acts as the final, highly precise target thickness adjustment P3.This secondary polishing step is critical for achieving a st