In the 40nm BSI CMOS Image Sensor flow, the Ashing & Strip/Clean step immediately following MET0 Tungsten (W) Etch is critical for completely removing patterned photoresist, hardmask remnants, and highly reactive etch byproducts A1.Unlike subsequent Ashing & Strip/Clean steps that primarily target copper dual-damascene structures and porous low-k dielectrics P4, this specific MET0 operation must manage dense, fine-pitch tungsten lines and barrier materials such as TiN or WN (Engineering Practice