In the 40nm BSI CMOS Image Sensor BEOL flow, this specific Pre Litho Cleaning step acts as the critical bridge between Metal 0 Tungsten (W) deposition and the subsequent Metal 0 photolithography module A2.Because the wafer surface is completely covered by a newly deposited blanket layer of W, this step is fundamentally distinct from other pre-litho cleans that typically prepare oxide or low-k dielectric surfaces A2.The primary objective is to remove airborne molecular contaminants (AMCs), trace