It is of great importance to predict the level of particulate contamination of wafers or photomasks in semiconductor manufacturing. Thicknesses of 300-mm-wafers of current mass production, 450-mm-wafers of near-future mass production, and EUVL photomask of next-generation lithography are 0.0775, 0.0925, and 0.635 cm, respectively. In this study, the effect of plate thickness on particle deposition velocity onto face-up wafers or EUVL photomasks situated parallel to an airflow was investigated by comparing experimentally measured and theoretically predicted particle deposition velocities, when the theoretical prediction of Yook (Particle deposition velocity onto a wafer or a photomask in a laminar parallel flow. J. Electrochem. Soc. 157, H692-H698, 2010) was based on the neglect of plate thickness. It was found that the correlation of Yook (2010) could accurately predict particle deposition velocities onto the wafers, owing to negligible thicknesses of wafers. On the other hand, in the case of the EUVL photomask, it was found that the effect of photomask thickness on particle deposition velocity was remarkable, but discrepancy between experimental measurement and prediction using the theory of Yook (2010) became smaller with increasing either particle diffusivity or gravitational settling velocity. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3616009] All rights reserved.