Chemical-Mechanical Planarization (CMP) of SiO2 is performed using alkaline silica slurries while CMP of tungsten (W) utilizes acidic slurries with alumina as the abrasive. Proposed mechanisms for the two CMP processes, with more emphasis on SiO2-CMP, have been discussed in literature. However, much less is known about the removal mechanism of residual slurry particles from the planarized surfaces - a crucial step for subsequent device processing. We discuss the chemical and physical basis of post-CMP cleaning by double-side scrubbing using polyvinyl alcohol (PVA) brushes and show how the interactions between the wafer surface, slurry, and the brush material affect the overall cleaning efficiency. Using the zeta potential concept the common features for cleaning surfaces after SiO2-CMP and W-CMP are established and the differences between these two systems are highlighted. We present surface particle levels for two model systems as a function of cleaning chemistries and discuss their influence on post-CMP surface metal levels.