Following the deposition of the Optical Pad 1 layer in the LS_GRID module, the wafer must undergo a Pre Litho Cleaning step before the Lower Vertical Grid Trench photoresist application P4.This step is distinct from other pre-litho cleans because it specifically prepares an optical pad dielectric surface for a high-aspect-ratio trench patterning process, which is critical for optical isolation in 40nm BSI CMOS image sensors P3.The primary objective is to remove any adventitious airborne contamin