Effect of Viscoelasticity of PVA Brush on Friction during Post-CMP Cleaning: A Guideline for Nodule Configuration

The application of new materials and three-dimensional structures are being used to achieve next-generation semiconductor devices. Hence, the role of the chemical-mechanical planarization (CMP) process has gained importance. Polyvinyl acetal (PVA) brushes are widely used as scrubbers during post-CMP cleaning. However, the mechanisms of brush scrubber cleaning are still a matter of debate because direct observation is difficult. Many researchers have proposed the removal mechanisms that operate during brush cleaning based on investigations of the forces acting on particles, friction, and the lubrication characteristics. Hydrodynamic drag forces and direct contact between the brush and the particles have been proposed as cleaning mechanisms [1–5]. Philipossian et al. [6] and Sun et al. [7] focused on the brush design and suggested that the existence of nodules or eccentricity of the roller brush had a significant effect on the friction. The friction system between the roller brush and the surface is complex because of the collision of nodules with the surface. Hence, the shapes of the nodules have been designed through trial and error. In this study, we focus on the friction of a single nodule to investigate the role of nodules in roller brush cleaning. The normal and friction forces are measured during brush sliding. In particular, we focus on the viscoelastic properties of a PVA brush and discuss its effects on friction.