In the 40nm BSI CMOS Image Sensor flow, this specific Pre Litho Cleaning step acts as the critical bridge between the dual-layer ILD 1 deposition (ILD 1-1 and ILD 1-2) and the Via 1 photolithography module A2.Unlike previous pre-litho cleans that prepare bulk silicon or gate materials, this iteration must condition a newly deposited, potentially textured dielectric surface P3.The goal is to achieve a pristine surface with uniform density and chemical composition to bring the entire wafer within