In the 40nm BSI CMOS Image Sensor flow, the Light Shield/Aperture Grid (LS_GRID) physically isolates adjacent pixels to suppress optical crosstalk and define the precise optical aperture P1.Following the primary Tungsten (W) etch, the underlying Titanium Nitride (TiN) layer must be removed to complete the vertical profile of the grid patterning sequence A1.The TiN layer typically functions as both an adhesion promoter for the bulk tungsten and an anti-reflective coating (ARC) during the precedin