Characterization of tantalum oxy-nitrides deposited by ECR sputtering

We have investigated the electrical characteristics of tantalum oxy-nitride (TaON) films deposited using electron cyclotron resonance (ECR) plasma sputtering. A pure tantalum metal target was used as raw material combined with gases of oxygen and nitrogen. The electrical properties have been measured using metal–insulator–metal (MIM) structures of Al/TaON/Ru/Si or metal–insulator–semiconductor (MIS) structure of Al/TaON/Si. By controlling the oxygen gas flow in a moderate low gas flow rate at fixed nitrogen gas flow, TaON films have been stably obtained with the refractive indices of over 2.5 at 632.8 nm wavelength, and the dielectric constants of over 30. However, the leakage currents have increased with an increase in the dielectric constants. To improve the leakage current, we have investigated the periodical deposition process, in which the ECR plasma irradiation was additionally introduced after thin TaON film was deposited. The breakdown strength of about 1 MV/cm was obtained by the measurement using MIM structure. By the estimation of the C–V characteristics of the silicon–MIS structure using TaON, the dielectric constant of 34 was obtained for a TaON thickness of 12 nm.