Morphology and crystallization kinetics in HfO2 thin films grown by atomic layer deposition

We report the effects of annealing on the morphology and crystallization kinetics for the high-kappa gate dielectric replacement candidate hafnium oxide (HfO2). HfO2 films were grown by atomic layer deposition (ALD) on thermal and chemical SiO2 underlayers. High-sensitivity x-ray diffractometry shows that the as-deposited ALD HfO2 films on thermal oxide are polycrystalline, containing both monoclinic and either tetragonal or orthorhombic phases. with an average grain size of similar to8.0 nm. Transmission electron microscopy shows a columnar grain structure. The monoclinic phase predominates as the annealing temperature and time increase, with the grain size reaching similar to11.0 nm after annealing at 900degreesC for 24 h. The crystallized fraction of, the film has a strong dependence on annealing temperature but not annealing time, indicating thermally activated grain growth. As-deposited ALD HfO2 films on chemical oxide underlayers are amorphous, but show strong signatures of ordering at a subnanometer level in Z-contrast scanning transmission electron microscopy and fluctuation electron microscopy. These films show the. same crystallization kinetics as the films on thermal oxide upon annealing. (C) 2003 American Institute of Physics.