Atomic layer deposition of hafnium oxide from tert-butoxytris(ethylmethylamido)hafnium and ozone: rapid growth, high density and thermal stability

Abstract

HfO₂ thin films were grown by atomic layer deposition (ALD) using a novel heteroleptic precursor, tert-butoxytris(ethylmethylamido)hafnium [HfO^tBu(NEtMe)₃; BTEMAH] and ozone. The structure of BTEMAH is similar to that of tetrakis(ethylmethylamido)hafnium [Hf(NEtMe)₄; TEMAH] except that one of its four amido ligands is replaced with a tert-butoxy ligand. This heteroleptic structure largely improves the ALD growth rate (0.16 nm cycle⁻¹) and Hf density (Hf mass per unit volume of HfO₂ film, 7.6 g cm⁻³) of the HfO₂ films. The self-regulated ALD growth behavior was confirmed at a growth temperature of 300 °C. Higher Hf density induces anti-crystallization properties in the as-grown film. Consequently, the amorphous phase of a HfO₂ film is retained up to ∼15 nm during deposition at 300 °C. The more amorphous-like nature and the higher Hf density of the HfO₂ film also retard crystallization during post-deposition annealing (PDA), which strongly enhances the thermal stability of the electrical performance. The capacitance equivalent thickness of the films with thicknesses ranging from 4 to 13 nm is relatively constant up to a PDA temperature of 1000 °C.