Wafer cleaning following chemical-mechanical planarization, especially brush scrubbing, is a critical step in semiconductor device manufacturing that is not adequately understood. A critical particle Reynolds number approach is used to assess whether hydrodynamic forces can remove adhering particles from wafer surfaces during brush scrubbing, or whether brush-particle contact must occur. Model systems of 0.1 and 1.0 mm diameter alumina particles adhering to polished silicon dioxide and copper surfaces are considered. Results indicate that hydrodynamic forces can remove some of the adhering particles, but brush-particle contact must occur to remove all of the adhering particles. (C) 2003 The Electrochemical Society.