Different current conduction mechanisms through thin high-k Hf(x)Ti(y)Si(z)O films due to the varying Hf to Ti ratio

We have investigated the electrical behavior of high permittivity (high-k) hafnium-titanium-silicate (HfxTiySizO) layers with different Hf:Ti ratios in the films. The films are prepared by metalorganic chemical vapor deposition using a mixture of two single source precursors. Oxide and interface charges, leakage currents and conduction mechanisms are found to be a strong function of the film composition. The films with Hf content less than 10 at. % show lower levels of oxide and interface charges and higher dielectric constant whereas those with Hf content higher than 15 at. % have better leakage current properties. A strong evidence is presented that in films with Hf content lower than 10 at. % the conduction process is governed by a phonon-assisted tunneling, i.e., it is defined rather by the intrinsic properties of the material than by its defect structure.