The Shallow Trench Isolation (STI) Photo step defines the spatial boundaries of the active areas (AA) and the isolation trenches across the semiconductor substrate P1.This step directly patterns a photoresist layer applied over the previously deposited SiO and SiN hard masks T2.Unlike Deep Trench Isolation (DTI) photo, which defines high-aspect-ratio trenches to block deep lateral minority-carrier diffusion and optical crosstalk between image sensor pixels P3, STI photo targets shallow isolation