In 40nm Back-Side Illuminated (BSI) CMOS Image Sensors, optical pads are essential for wire bonding or electrical probing, requiring deep openings through the backside dielectric stack over the metal pads T1.This step follows lithography for the grid trench and precedes Lower OCL (On-Chip Lens) coating steps, indicating it is a critical part of the backside light-receiving surface preparation P2.The distinction between the sequentially numbered Optical Pad 1, 2, and 3 etches typically relates to