Nodule contact path of polyvinyl acetal roller brushes on a rotating plate and its relation to cross contamination

Polyvinyl acetal (PVA) brushes are widely used in semiconductor manufacturing for post-CMP cleaning. How-ever, cross-contamination occasionally occurs due to the re-deposition of contaminants during cleaning. To investigate why contamination patterns in the form of nodules occur even when brushes and surfaces are in relative motion, we study the contact path of roller brush nodules on a rotating plate. We reproduced the relative motion of the roller brush and wafer during cleaning of the 300 mm wafer and visualized the contact between the brush nodule and the surface using a total-reflection optical system. We also observed the nodule deformation with high-speed photography from the side. The experimental results showed that the stamped contacts of the nodule shape coincide with the recontamination points. The contacts occur in a certain area on the wafer where the negative relative velocities reach 200 mm/s, i.e., the wafer is faster than the circumferential velocity of the brush in the same speed direction, and it is not zero relative velocity. We expect that cleaning with avoided stamp contact conditions will prevent recontamination.

Automated summary

Research finds that cross-contamination occasionally occurs during the cleaning process in semiconductor manufacturing using polyvinyl acetal (PVA) brushes due to the re-deposition of contaminants. To understand why contamination patterns in the form of nodules still occur even when brushes and surfaces are in relative motion, the contact path of roller brush nodules on a rotating plate was studied. The experimental results showed that the stamped contacts of the nodule shape coincide with the recontamination points, occurring in a certain area on the wafer.