In a 40nm BSI CMOS Image Sensor, pixel optical isolation is achieved via a backside light shield grid (LS_GRID) (Engineering Practice).The Optical Pad 2 Etch step is a critical patterning process that selectively removes specific intermediate dielectric layers over the peripheral electrical contact pads after the lower optical coating layers (OCL) have been cleared P2.Unlike Optical Pad 1 or 3 etches which target initial hardmask openings or final deep substrate penetrations respectively, Pad 2