The Metal 4 Cu deposition step is a critical back-end-of-line (BEOL) process responsible for forming the intermediate or semi-global routing interconnects in the 40nm BSI CMOS Image Sensor architecture P4.Unlike the Metal 0 Tungsten (W) step used for local contacts due to its high conformal fill in ultra-small vias P1, and the Metal 1 to Metal 3 layers which feature minimum-pitch tight routing to minimize local cell area T2, Metal 4 is typically designed with comparatively relaxed pitches to han