SrTa 2 O 6 thin films for high-K dielectric applications grown by chemical vapor deposition on different substrates

SrTa 2 O 6 thin films with thickness between 6 and 150 nm were deposited by metal-organic chemical vapor deposition in a multiwafer planetary reactor. The monomolecular precursor, strontium-tantalum-(methoxyethoxy)-ethoxide, was dissolved in toluene and injected by a liquid delivery system. A rather narrow process window for the deposition of stoichiometric SrTa2O6 was found for this precursor at low pressures and a susceptor temperature around 500 °C. Films were grown on Pt∕TiO2∕SiO2∕Si, TiNx∕Si, and SiO2∕Si substrates. The as-deposited films were x-ray amorphous and could be crystallized by postannealing at a temperature ⩾700°C. The distorted tetragonal tungsten bronze phase of SrTa2O6 was dominating within a broad range of compositions (Sr∕Ta: 0.4–0.7) and a perovskite-type phase was additionally observed for Sr∕Ta>0.7 and predominated for Sr∕Ta>1. The electrical properties have been investigated with metal-insulator-metal and metal-insulator-semiconductor capacitors after sputter deposition of Pt top electrodes. The amorphous films had a dielectric constant K in the range of 35–45 and low leakage currents. For stoichiometric SrTa2O6 the dielectric permittivity reached values of K=100–110, but the leakage currents were increased. Remarkably, the permittivity is not very sensitive to deviations from the exact stoichiometry of the SrTa2O6 phase (Sr∕Ta: 0.4–0.7), but a decrease to values of K=30–40 is observed along with the transition to the perovskite phase at high Sr contents.