Density functional theory is employed to investigate the reaction mechanism of HfSixOy and HfO2 grown by atomic layer deposition (ALD) on H-terminated silicon surface. The ALD process is designed into two reaction sequences based on either hafnium or oxygen precursors as the starting pulses. We find that Si(OCH3)(4) would be less oxidizing toward silicon surface due to its low adsorption energy and high activation barrier, whereas H2O is much easier to oxidize the silicon surface and form the OH surface sites. We also find that it is more kinetically and thermodynamically favorable for HfCl4 adsorption and decomposition on H2O-pretreated silicon surface than Si(OCH3)(4)-pretreated silicon surface. In conclusion, although silicon alkoxide as oxygen source can limit effectively the formation Of SiO2-rich interfacial layer, it has substantially slow kinetics for HfSi(x)Q(y) ALD as compared to H2O for HfO2 ALD. (C) 2007 Elsevier B.V. All rights reserved.