Electrical and Physical Characterization of Zirconium-Doped Tantalum Oxide Thin Films

Abstract

Thin films of zirconium-doped tantalum oxide (Zr-doped TaO x ) deposited by reactive sputtering were studied in an effort to replace silicon dioxide (SiO 2 ) 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 × 10 -9 A/cm 2 at -1 MV/cm in the accumulation regime. The current conduction mechanism of the Zr-doped TaO x films was analyzed and compared with mechanisms of Poole-Frenkel and Schottky emissions. In comparison with pure tantalum oxide (TaO x ) and zirconium oxide (ZrO y ) films, the Zr-doped TaO x 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 SiO x to zirconium silicate (Zr x Si y O) 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 TaO x films showed many advantages over pure TaO x and ZrO y films for the gate dielectric application. © 2004 The Electrochemical Society. All rights reserved.