The PMD 3 Etch step is a critical intermediate dielectric removal process within the BONDPAD module for a 40nm Backside Illuminated (BSI) CMOS Image Sensor P4.Because BSI architectures require exposing underlying metal pads through a thick, multi-layer dielectric stack for final packaging connections, the bulk etch is divided into multiple sequential stages (PMD 1 through PMD 5) to carefully manage thermal budgets, profile tapering, and micro-loading effects A1.By stepping the etch process, the