The "N FD IIP - Photo" step is a critical lithographic masking process designed to selectively expose the Floating Diffusion (FD) regions in a CMOS image sensor prior to N-type ion implantation P3.Positioned immediately after the general NMOS source/drain and primary FD implants, this specific photo step defines a localized implant window—often between shared transfer gates (T1 and T2)—to tailor the final FD doping profile P1.The primary objective is to create a patterned photoresist barrier tha