The W Etch step in the MET0 module of a 40nm BSI CMOS Image Sensor directly follows lithographic patterning and is responsible for defining the first level of local interconnects A1. Tungsten is widely used in integrated circuits as metal interconnects and diffusion barriers due to its excellent step coverage and electromigration resistance A1. In this specific process flow, a blanket CVD W layer has been deposited over the wafer, and the Metal 0 photoresist mask defines the desired circuit layo