The RIE etch ILD 2-1 process is a critical intermediate step in the bond pad module of a 40nm BSI CMOS Image Sensor A1.It follows the ILD 1 etches and precedes the ILD 3 etches to progressively clear the thick dielectric stack overlying the metal contact pads A2.Unlike shallow standard oxide or nitride etches (steps #9, #10) or the highly anisotropic silicon full trench etch (step #16) which targets the substrate, this step must navigate complex multi-layer interconnect-level dielectric stacks A