Electrical and physical characterization of zirconium-doped tantalum oxide thin films

Thin films of zirconium-doped tantalum oxide (Zr-doped TaOx) deposited by reactive sputtering were studied in an effort to replace silicon dioxide (SiO2) as the gate dielectric material for future metal-oxide-semiconductor devices. Influences of process parameters, such as Zr concentration, postdeposition annealing temperature, and film thickness, on the film's electrical and physical characteristics were investigated. The lightly Zr-doped film (15 nm thick) showed a low current density, e.g., 1.27 x 10(-9) A/cm(2) at -1 MV/cm in the accumulation regime. The current conduction mechanism of the Zr-doped TaOx films was analyzed and compared with mechanisms of Poole-Frenkel and Schottky emissions. In comparison with pure tantalum oxide (TaOx) and zirconium oxide (ZrOy) films, the Zr-doped TaOx films had higher dielectric constants. A high-temperature annealing step reduced the film's hysteresis and fixed charge density. The interface layer composition changed from SiOx to zirconium silicate (ZrxSiyO) when the Zr concentration in the film was increased. The binding energies of Ta 4f, Zr 3d, and O 1s of the bulk shifted to lower values as the Zr concentration increased due to the charge transfer among elements. In summary, the Zr-doped TaOx films showed many advantages over pure TaOx and ZrOy films for the gate dielectric application. (C) 2004 The Electrochemical Society.