Following the deposition of the backside passivation (BPMD SiO) and pre-litho cleaning, the Backside Substrate Contact - Photo step defines the localized openings required to electrically ground the silicon substrate of the BSI image sensor A2.This step is distinct from front-side contact patterning (such as Metal 0/1 Source/Drain Contacts) because it operates on the chip's backside, defining pathways that will eventually be filled with metal to create deep vias traversing the thick dielectric s