The Photocathode IIPX - Photo step is a critical photolithography operation in the Backside Illuminated (BSI) CMOS Image Sensor flow, defining the spatial boundaries of the N-type charge collection well T1. Unlike the preceding Periphery N-Well lithography, which patterns deep logic and routing wells for peripheral control circuits (Engineering Practice), this step specifically targets the active pixel array to construct the core p-n junction of the pinned photodiode P2. In the process sequence,