In the packaging module of a 40nm BSI CMOS image sensor, deep bond pad cavities must be excavated through multiple interlayer dielectric (ILD) tiers to expose the underlying metal pads A2.The etching sequence alternates between bulk oxide removal and selective barrier breaching, driven by the stack's structural composition A1.Following the ILD 6-2 Oxide Etch, which selectively stops on the ILD 6-1 SiCN layer, the current ILD 6-1 SiCN Etch step is deployed to penetrate this specific diffusion bar