The downscaling of high-k/metal gate transistor devices requires thin-film deposition processes that deliver not only an outstanding high-k oxide quality, but also a strict interfacial oxide thickness control in the sub-1 nm thickness range. To study the impact of atomic layer deposition (ALD) process conditions and chemistry on the HfO2 quality and interfacial oxide thickness, we have used tetrakis[ethylmethylamino]hafnium (TEMAH) as a metal precursor and H2O and O-3 as oxidants. The deposition temperature ranged from 285 up to 365 degrees C, where TEMAH decomposition plays a role in the growth mechanism. Physical characterization and Pt dot capacitor devices have been used to study the impact of the oxidant and process conditions on the equivalent oxide thickness and gate leakage current of 2-4 nm thin HfO2 films. By combining X-ray reflectometry and ellipsometry, we evaluated the Si/high-k interfacial oxide layer thickness. Time-of-flight secondary-ion mass spectroscopy was used to determine the C impurity levels. Both the interfacial oxide layer thickness and the C impurity level in the Si/SiO2/HfO2 stacks are strongly dependent on the oxidant. The temperature dependence of the C impurity level is opposite for O-3 and H2O. Furthermore, SiO2 regrowth was found for the O-3 process. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3258664] All rights reserved.