Density functional theory is employed to investigate atomic layer deposition mechanism of HfO2 on hydroxylated silicon surfaces with different oxygen levels. Calculations show that the surface bridged oxygen can enhance the adsorption of HfCl4 and weaken the adsorption of H2O. In addition, temperature effects on the chlorine loss has been discussed. In particular, two possible pathways for the second chlorine loss at low temperature are explored. However, both of them are limited at higher temperature for two main reasons: (a) the decrease in the number of surface hydroxyl sites and (b) the dehydroxylation of as-grown WO, surface. (c) 2006 Elsevier B.V. All rights reserved.