In a 40nm Back-Side Illuminated (BSI) CMOS Image Sensor, minimizing optical crosstalk between adjacent pixels is critical for overall image quality (Engineering Practice).To achieve this, a metallic light shield or aperture grid consisting of Tungsten (W) and Titanium Nitride (TiN) is employed to physically block stray light (Engineering Practice).The Oxide Grid Seal Layer Etch step directly follows the photoresist patterning and transfers the lithographic aperture pattern into the oxide layer P