In the 40nm BSI (Backside Illuminated) CMOS Image Sensor process flow, the bond pad opening must progressively penetrate multiple backside dielectric layers to establish low-loss electrical connections for packaging A1.Following the preliminary optical pad etches, the Oxide Grid Seal Layer Etch is executed to remove the structural oxide layer—often deposited via high-density plasma or using a TEOS precursor—that seals the backside metallic optical isolation grids A2.Unlike front-end Pad Oxide Et