The ultrasonic clean step is strategically positioned immediately following the CIS Backside Wafer Edge-Grind and prior to the Backside Si CMP steps A1.The edge-grinding process relies on mechanical abrasion to contour the wafer perimeter, which inherently generates significant quantities of silicon dust and abrasive particulate residue A2.If these submicron particles are not rigorously removed, they will act as parasitic abrasives during the subsequent CMP operations, leading to catastrophic mi