In order to modify atomic layer deposition (ALD) characteristics of Al2O3, three-dimensional gas transports and film depositions are investigated through reactor scale simulations inside two different viscous flow reactors. In the top-inlet reactor (TIR), the gaseous species are directly injected into the substrates from the upper surface of the reactor while in the bottom-inlet reactor (BIR), the inlet is at the bottom of the reactor and next to the substrate. The numerical procedure to simulate the ALD process is thoroughly explained by using the multi-species and multi-reaction chemistry phenomena. The reactants are trimethylaluminum (TMA) and ozone, and the simulations are performed in an operating pressure of 10 Tort (1330 Pa) and two substrate temperatures of 250 degrees C and 300 degrees C. Due to the chemistry mechanism used in this study, a long ozone exposure is a crucial parameter to deliver a sufficiently oxidized substrate. For a specific reactor type, deposition rates are higher on the hotter substrate due to both a larger surface reaction rate constant and greater concentrations of the oxygen atoms on the substrate. At a fixed substrate temperature, higher deposition rates are obtained by using the TIR. The same deposition rate distributions are obtained among all cycles for each ALD process that result in the dependency of the film thickness only on the numbers of ALD cycles. For the substrate at 250 degrees C, the growth rates are equal to 3.78 angstrom/cycle and 4.43 angstrom/cycle in the BIR and the TIR, respectively, and for the substrate at 300 degrees C, the growth rates are equal to 4.52 angstrom/cycle and 6.49 angstrom/cycle in the BIR and the TIR, respectively. (C) 2014 Elsevier Ltd. All rights reserved.