Normal force and behavior of containing water during the compression of PVA brush

Polyvinyl acetal (PVA) brushes have been widely used in the Post CMP cleaning applications. To better understanding the mechanical characteristics of the PVA brushes, we measured the normal force during the compression and its relation to the water behavior contained inside the brushes. The normal force is directly related to the shear force which is important to the cleaning performance. In this study, especially we focus on the brush compression speed. As a result, the increase with compression speeds the maximum value of normal force also increased in the all brushes of several shapes. The normal force reached the order of several N, even in the single nodules of small size. In addition, water is spattered to the surrounding air just after the brush compression, and the region where water seeping out is depends on the brush shape and surface structure. From these results, we conclude that the PVA brushes have viscoelastic properties, and behavior of water inside the brushes and the shape are greatly affect the normal force.