In the fabrication of nanoscale Backside Illuminated (BSI) CMOS Image Sensors, the bondpad module requires sequential penetration through a thick multi-tier dielectric stack (Engineering Practice). The ILD 5-1 SiCN Etch specifically targets the silicon carbon nitride (SiCN) barrier layer located between the fifth and fourth interlayer dielectrics P1. This sequential flow (from ILD 6 down to ILD 3) is designed to carefully manage the aspect ratio and etch-stop requirements for deep bondpad or TSV