In 40nm Backside Illuminated (BSI) CMOS Image Sensors, accessing the front-side metal routing from the thinned backside is essential for forming external electrical connections (Engineering Practice).Following the sequential etching of the Backside Passivation Metal Dielectric (BPMD) and Anti-Reflective/High-k Dielectric layers (HKD/AR2, HKD/AR1), the bulk silicon substrate is locally exposed A1.This specific "RIE etch, Si Back etch" step within the BONDPAD module is tasked with anisotropically