Deposition of High-k Dielectric Oxide Films by Liquid Injection MOCVD

ZrO₂, HfO₂, La₂O₃ and their related silicates are candidates to replace SiO₂ as the gate dielectric material for sub-0.1 μm CMOS technology, and metalorganic chemical vapour deposition (MOCVD) is an attractive technique for the deposition of these materials. However, there are problems associated with many of the existing Zr and Hf oxide precursors. In this paper, we describe the liquid injection MOCVD of ZrO₂ and HfO₂ using the new improved alkoxide precursors [M(OBu^t)₂(OCMe₂CH₂OMe)₂] and [M(OCMe₂CH₂OMe)₄] (M = Zr, Hf). The growth of high quality La₂O₃ or LaSi_xO_y films by MOCVD has also proved difficult due to a lack of suitable precursors, and in this paper we describe the use of [La[N(SiMe₃)₂]₃] for the liquid injection MOCVD of LaSi_xO_y, in the absence of an added Si source. High frequency C-V measurements for MOS-capacitors fabricated from ZrO₂, HfO₂ and LaSi_xO_x demonstrate the feasibility of using liquid injection MOCVD to deposit MOS gate dielectric films at low process temperature.     

The Effect of Stress on the Microwave Dielectric Properties of Ba0.5Sr0.5TiO3 Thin Films

Single phase, (1 0 0) epitaxial Ba_0.5Sr_0.5TiO₃ (BST) films have been deposited onto (1 0 0) LaAlO₃ and MgO substrates by pulsed laser deposition (PLD). The capacitance and dielectric losses of as-deposited and annealed films have been measured from 1–20 GHz as a function of electric field (0–80 kV/cm) at room temperature. The dielectric properties are strongly affected by the substrate type, post-deposition annealing time (6 h) and temperature (1200°C). For epitaxial BST films deposited onto MgO, it is observed that, after a post-deposition anneal the dielectric constant and the dielectric loss decreases. For epitaxial BST films deposited onto LAO, a post-deposition anneal (1000°C) results in an increase in the dielectric constant and an increase in the dielectric loss. The dc electric field induced change in the dielectric constant tends to increase with the dielectric constant and is largest for as-deposited films on MgO and post-deposited annealed films on LAO. In general, for epitaxial BST films, a large electric field effect is observed in films that have a large dielectric loss and a small electric field effect in films that have a low dielectric loss. High resolution X-ray diffraction measurements indicate that deposited film exhibit a significant tetragonal distortion which is strongly affected by a by a post deposition anneal. The observed differences in dielectric properties of the epitaxial BST films on MgO and LAO are attributed to the differences in film stress which arise as a consequence of the lattice mismatch between the film and the substrate and the differences in the thermal coefficient of expansion between the film and the substrate. A thin amorphous buffer layer of BST has been used to relieve stress induced by the lattice mismatch between the film and the substrate. Unlike epitaxial films, stress relieved films do not show an inverse relationship between dielectric tuning and Q (1/tan) and may be superior materials for tunable microwave devices.     

Effect of a Second Annealing Process on the Properties of BaTiO3 Thin Films on Polycrystalline Nickel Substrates Grown by Polymer-Assisted Deposition

Ferroelectric BaTiO₃ thin films were successfully deposited on nickel foils by a chemical solution technique named polymer-assisted deposition. It is found that a second annealing in oxygen using a rapid thermal annealing furnace would strongly affect the electric properties of the as-prepared thin films. Dielectric and ferroelectric properties have been systematically studied. The correlation between the second annealing conditions and dielectric properties was established and discussed. Optimized second annealing condition was found.