To simulate an atomic layer deposition (ALD) process in a reactor scale, three-dimensional deposition of Al2O3 from trimethylaluminum and ozone inside a viscous flow reactor is investigated. The chemistry mechanism used includes both gas-phase and surface reactions. The simulations are performed for a fixed operating pressure of 10 torr (1330 Pa) and two substrate temperatures at 250 degrees C and 300 degrees C. The Navier-Stokes, energy, and species transport equations are discretized through the finite volume method to simulate transient, laminar and multi-component reacting flows. It is found that the larger surface reaction rate constant, and the greater concentrations of gaseous reactants at the substrate result in higher deposition rates on the substrate at 300 degrees C. At a fixed substrate temperature, the deposition rate distributions are the same among all the cycles that indicate a constant growth rate at each cycle. As a result, Al2O3 growth rates of 3.78 angstrom/cycle and 4.52 angstrom/cycle are obtained for the substrate temperatures of 250 degrees C and 300 degrees C, respectively. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.