Torque measurements generated by a rotating PVA brush without a skin layer

Inhalt:
Polyvinyl acetal (PVA) brushes are widely used in the post CMP cleaning. The earlier studies about PVA brushes were basically conducted using sponge with a skin layer which have a lower porosity as compare with the inner structure. In this study, we measured a torque generated by a rotating PVA brush without a skin layer. The torques were measured with different wettability plates under several chemicals. The torque shows two different tendency with the brush rotating speeds. In the cases with typical silicon based films, glass, and PMMA, the measured torques were decreased with increase the brush rotating speeds. The magnitudes of the torques has no correlation with the plate wettability. On the other hand, in the case with PTFE and Tungsten, the torques were not influenced the brush rotating speeds. In addition, the combination between Cu film and NH4OH solutions showed different tendency. We concluded that the brush without skin layer is different contact condition from the brush with a skin layer. Keywords: Post CMP Cleaning, PVA brushes, Skin layer, Friction, Wettability