The ILD 4-2 Oxide Etch step is a critical phase within the BONDPAD module of the 40nm BSI CMOS Image Sensor packaging flow A1. It follows the sequential removal of overlying ILD 6 and ILD 5 layers and immediately precedes the ILD 4-1 SiCN etch P1. The primary objective is to selectively remove the bulk silicon dioxide of the fourth interlayer dielectric tier to progress toward the underlying metal bond pad P1. What distinguishes this step from front-end oxide etches (such as shallow trench isola