In advanced Back-Side Illuminated (BSI) CMOS Image Sensors, inter-pixel optical crosstalk is mitigated by constructing deep metallic light shield grids between adjacent photodiodes (Engineering Practice).Following the deposition of the mid vertical grid, where conformal tungsten completely fills the high-aspect-ratio trench structures, the resulting thick metallic overburden must be entirely removed (Engineering Practice).The Tungsten Chemical Mechanical Polishing (W CMP) step serves to globally