Growth and Material Characterization of Hafnium Titanates Deposited by Atomic Layer Deposition

Abstract

Hafnium titanate (HTO) films were deposited within a large Hf-Ti compositional range by atomic layer deposition using Hf Cl4 /Ti Cl4 / H2 O precursors. The Hf content of the layers is well controlled by the precursor pulse ratio, as indicated by Rutherford backscattering. The saturation conditions of ternary HTOs are different compared to those of the binary oxides. First-principles simulation confirmed the enhancement of the Hf precursor reactivity in the presence of Ti-OH. Growth curves of HTOs showed a good linearity with the number of reaction cycles. A linear correlation between density, quantified by X-ray reflectometry, and composition was observed. X-ray diffraction indicated that the as-deposited films are amorphous up to 500-700°C, depending on the Hf/Ti ratio. The orthorhombic HfTi O4 diffraction lines in the samples (30-64% Hf) annealed at 850°C were observed. For a Hf content higher than 82%, a monoclinic Hf O2 -like structure was reported. The dielectric constant and leakage current depend on the Ti content, the film crystallinity, and the anneal atmosphere. The postdeposition anneal in O2 is found to have a drastic effect in leakage current density reduction and could be a key for further improvements of HTO electrical properties. © 2009 The Electrochemical Society.