A Ring Type Residue Formation in Post Cu CMP Cleaning

A chemical mechanical planarization (CMP) of copper (Cu) damascene structure is prone to defect formation due to variety of chemical agents in slurry and chemical complex formation. In post CMP cleaning process, which should remove such defects, a mechanical scrubbing of wafer by porous and elastic brushes are eligibly used. Although, chemical effects are the main mechanism of defect detachment and dissolution during cleaning process, mechanical effects also play key role by transportation of chemical agent and discharge of reacted species. The most relevant defect caused by mechanical effect is ring shaped scratch due to exceeding contact pressure. In this study, however, we focused on ring shaped residue after post Cu CMP cleaning which is not caused by direct solid contact. To investigate root cause, analysis are carried out such as chemical composition of residue, surface charge map on a wafer, kinematic analysis on brush and wafer motion, and fluid dynamic simulation on chemical motion. In conclusion, it is revealed that both chemical and mechanical effects are interacted to form ring shaped residue. Elimination of defects by chemical effect is suppressed by mechanical motion of brush and chemical fluid. Figure 1