Microelectronic devices have continued to reduce in size over the years following the well known Moore's Law as demand for denser chips with greater speed increases. As this trend of down-scaling continues, the thickness of SiO2 dielectric thin films, used in applications such as dynamic random access memories (DRAMs), has to be correspondingly reduced. This causes several problems, most notably the excessive direct tunneling of electrons through the SiO2 layer. The use of alternative materials with a high dielectric constant (k) has been identified as a possible solution because a high k allows for the continued down scaling of devices, while obtaining thicker dielectric thin films, as well as a higher level of capacitance.

The high k material studied in this piece of work was Ta2O5 doped with TiO2 in varying proportions. In previous work, researchers have found that the k of bulk polycrystalline Ta2O5 can be increased from 35 to 126 by a doping of 8% TiO2. This has not yet been achieved in thin films. In this project, I attempt to do it in thin films.

The thin films were deposited on to n-type Si (1 0 0) substrates by a photo-induced Chemical Vapour Deposition (CVD) system, consisting of a 222 nm excimer lamp, at a temperature of 300 oC. Argon was used as the carrier gas for transporting the precursors into the reaction chamber, while nitrous oxide was the oxidising agent. The characterization of the resultant thin films by ellipsometry found that the films were of 6 - 95 nm in thickness and had refractive indices in the range of 1.6 - 2.1. Fourier Transform Infrared (FTIR) Spectroscopy was then carried out, and the outcome showed the presence of Ta2O5 and TiO2 absorption peaks. Electrical measurements were carried out to investigate the capacitance, frequency, current and voltage characteristics of the thin films. The outcome was encouraging and will be discussed in detail during my presentation.