Copper Bridge Defects with Wafer Center Signature Induced by Litho Rework Process

Abstract

This work explored the formation of Copper Bridge (Cu BG) defects with wafer center signature which is one of the key defect types in VLSI IC device fabrication and can result in high yield loss. Defect transition analysis and transmission electron microscopy analysis revealed that the damage on the oxide layer induced by the litho rework led to the formation of Cu BG defects. Further partition and cliff tests suggested that the severity of the ashing and cleaning conditions in the litho rework process resulted in the damage of the oxide layer. DOE studies demonstrated that lowering the power in the ashing step along with reducing the cleaning duration can largely eliminate this defect source of yield loss.