It has recently been reported that nitrogen oxide species (e. g., N2O5, NO2, NO3, and/or N2O) can have an impact on ozone based atomic layer deposition (ALD) of metal oxides when ozone is generated by dielectric barrier discharge (DBD) in O-2/N-2 mixtures. In this work, we further investigate the effect of the O-2/N-2 ratio in the DBD for HfO2 ALD using HfCl4 as metal precursor. Using O-3 in the absence of nitrogen oxides, uniform HfO2 layers are obtained between 200 and 250 degrees C in a hot wall cross flow reactor. The self-limiting nature of the O-3 and HfCl4 reaction is demonstrated at 225 degrees C and the growth-per-cycle is 0.12 nm. At higher temperature, O-3 decomposes at the HfO2 coated reactor walls, resulting in a decreasing HfO2 thickness over Si substrates in the direction of the gas flow. Using O-3 in combination with nitrogen oxides by DBD in N-2/O-2 mixtures, we obtained uniform HfO2 layers in the 200-300 degrees C temperature range. At 300 degrees C, the GPC is 0.14 nm and the HfO2 films show a low impurity content. Both processes produce high quality dielectric layers in Pt gated capacitors. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3561423] All rights reserved.