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

Abstract

We report the effects of annealing on the morphology and crystallization kinetics for the high-k 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 ~8.0 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 ~11.0 nm after annealing at 900 �C 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.