The packaging module for a 40nm Backside Illuminated (BSI) CMOS Image Sensor requires creating deep bondpad openings through multiple dielectric tiers to connect external terminals to internal routing A2.The alternating etch sequence—proceeding through ILD 5-1 SiCN, ILD 4-2 Oxide, ILD 4-1 SiCN, and finally ILD 3-2 Oxide—indicates a step-by-step unlanding of a deeply buried pad structure P2.Unlike early front-end oxide etches or shallow pad oxide clearing steps, this step must selectively remove