In the 40nm BSI CMOS Image Sensor flow, the Oxide Grid Seal Layer Etch is a critical pattern transfer step within the Light Shield Grid (LS_GRID) module P4.Positioned after the Optical Pad 1 Etch and before the Lower Vertical Grid Barrier Deposition, this step clears the protective oxide seal layer at the bottom of the grid trenches P4.The primary purpose of this etch is to expose the underlying substrate or primary isolation structure, preparing a pristine, fully opened interface for the subseq