The microstructure and the interfaces of HfO2 films deposited by metal-organic chemical vapor deposition directly on silicon (0 0 1) substrates were investigated by means of transmission electron microscopy. For two different precursors, Hf(O-i-but)O-2(mmp)(2) and Hf(diethyl-amide)(4), electron diffraction analysis showed a gradual transformation from the amorphous phase to the monoclinic phase in the deposition temperature range of 350-600degreesC. At an intermediate substrate temperature, 550degreesC, a small amount of tetragonal second phase was additionally observed. For the two types of precursors, the thickness of the interfacial amorphous layer was found to depend on the deposition temperature and showed a major decrease along with the amorphous to crystalline transition of the films. The influence of the substrate surface preparation and of post deposition annealing on the thickness of the interfacial layer is also discussed. (C) 2003 Elsevier B.V. All rights reserved.