The PMD 3 Etch step is a critical intermediate phase in the high-aspect-ratio contact (HARC) formation module for 40nm BSI CMOS Image Sensors P2.Following the initial photoresist patterning and upper dielectric breakthrough in the preceding PMD 4 Etch, this step continues the anisotropic pattern transfer deep into the pre-metal dielectric stack (Engineering Practice).This vertical etching sequence ultimately prepares the physical pathway for metallic vias and local interconnects to physically an