Conduction mechanisms and an evidence for phonon-assisted conduction process in thin high-k HfxTiySizO films
Abstract Electrical behavior of high-k Hf x Ti y Si z O layers with different Hf:Ti ratios in the film have been investigated. The films are prepared by MOCVD using novel single-source precursors chemistry. Oxide and interface charges, leakage currents and conduction mechanisms are found to be a strong function of the film composition. The films with lower Hf content show lower level of oxide and interface charges and higher dielectric constant whereas those with higher Hf content have better leakage current properties. It is established that in the films with lower Hf content the conduction is governed by a phonon-assisted process. The change of the conduction mechanism from Poole–Frenkel emission to phonon-assisted tunneling is assigned to possible structural changes which take place when changing the composition of the films.
Investigation of Ti doped HfO2 thin films deposited by photo-CVD
Abstract TiO 2 -doped HfO 2 thin films, as potential replacements for SiO 2 as high- k gate dielectric material, have been grown by photo-induced CVD using 222 nm excimer lamps at a temperature of 400 °C. Vaporised titanium isopropoxide and hafnium (IV) tetra- t -butoxide were used as the precursors. Films from approximately 45–70 nm in thickness with refractive indices from 1.850 to 2.424 were grown with various Ti:Hf ratios. The as-deposited films were found to be amorphous by X-ray diffraction when the Ti/(Ti+Hf) value was up to 33%, while the crystalline TiO 2 anatase phase formed when the Ti/(Ti+Hf) was 41%. We also found that the refractive index increased sharply when the Ti/(Ti+Hf) was over 25%. Fourier transform infrared spectroscopy, XPS and TEM were also used to monitor as well as the presence of Ti, interface and microstructure of the films on Si-substrate. The effect of UV-annealing on the electrical properties of these films will also be discussed.
Chemical vapour deposition of the oxides of titanium, zirconium and hafnium for use as high-k materials in microelectronic devices. A carbon-free precursor for the synthesis of hafnium dioxide
A brief survey of the precursors used for the chemical vapour deposition of the dioxides of titanium, zirconium and hafnium is presented. The review covers precursors used for the closely related process known as atomic layer chemical vapour deposition (ALCVD or ALD). Precursors delivered by standard carrier gas transport and by direct liquid injection (DLI) methods are included. The complexes fall into four classes based upon the ligands: halides, alkoxides, acetylacetonates (acac) and nitrates. Compounds bearing a mixture of ligand types have also found application in this area. The impact of the ligand on the microstructure of the metal oxide film is greatest at lower temperatures where the deposition rate is limited by the surface reactivity. The first use of anhydrous hafnium nitrate, Hf(NO3)4, to deposit films of hafnium oxide on silicon is reported. The films are characterized by Rutherford backscattering and X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy. Copyright © 2000 John Wiley & Sons, Ltd.