HfO2 thin films have been deposited onto p-Si(100) substrates by atomic layer deposition (ALD) using Cp2Hf(CH3)(2) (Cp = cyclopentadienyl) or Cp2HfCl2 and water or ozone as precursors. The purity of HfO2 films was better when ozone instead of water was used as oxygen precursor. The use of Cp2Hf(CH3)(2) together with ozone in the ALD window range, viz. 350-400 degrees C, yielded HfO2 films with less than 0.1 atom % C and H impurities. Cp2HfCl2/H2O-processed film contained C and Cl, but again the use of ozone considerably reduced the impurity levels. When using Cp2Hf(CH3)(2) as the metal source, the higher reactivity of ozone as compared to H2O yielded slightly higher growth rate, smoother morphology, higher degree of crystallinity for thicker films, and a close to ideal density. Furthermore, with ozone no inhibition of the growth during initial ALD cycles could be detected. The growth of HfO2 film on H-terminated Si with the Cp2Hf(CH3)(2)/H2O process was retarded and the initial island-like growth took place resulting in rougher surface. With the Cp2Hf(CH3)(2)/O-3 process, the films showed the best leakage current density characteristics. Slightly higher capacitance equivalent oxide thickness values were calculated for the ozone-processed films. (c) 2006 The Electrochemical Society.