Growth Behavior, Lattice Expansion, Strain, and Surface Morphology of Nanocrystalline, Monoclinic HfO2 Thin Films

Abstract

Nanocrystalline HfO2 films have been produced by sputter deposition under varying growth temperatures (Ts). The effect of Ts, which is varied from room temperature (RT) to 500 °C, on the structural characteristics of HfO2 films has been investigated employing X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The results indicate that the monoclinic HfO2 nanocrystals are highly oriented along the (1̅11) direction with increasing Ts. The lattice expansion increases with a reduction in grain size (L), while minimum strain energy occurs at a maximum lattice expansion. The strain factor increases linearly from 2.4 to 4% with increasing Ts from RT to 500 °C. The corresponding surface roughness also increases linearly with Ts. L values increase from ∼10 to 50 nm with increasing Ts. The L–Ts data derived from XRD and SEM are in good agreement and exhibit a relationship, which follows an Arrhenius' relation. A thermally activated growth process with an activation energy of ∼0.12 eV is evident from the structural analysis of nanocrystalline HfO2 films.