In the 40nm BSI CMOS Image Sensor flow, the PMD 3 Etch step initiates the formation of high-aspect-ratio contact (HARC) holes connecting the first metal layer to the underlying source/drain and gate structures P3.Following the lithographic patterning of the contact openings, this step precisely transfers the photoresist pattern into the topmost pre-metal dielectric layer P4.Because the total PMD stack is thick to minimize parasitic capacitance between the gate and interconnect routing, the overa