Following the W and TiN etch of the Light Shield Grid (LS_GRID), the wafer surface is left with a hardened photoresist (PR) crust and halogen-containing organometallic post-etch residues (PER) P1.The metal grid structure physically isolates adjacent pixels to minimize optical and electrical crosstalk in the BSI CMOS Image Sensor (Engineering Practice).Leaving etch residues behind would severely impede the subsequent uniform deposition of the Upper Grid Seal Layer, potentially leading to adhesion