Electrical properties of amorphous tantalum pentoxide thin films on silicon

The electrical characteristics of Al/Ta2O5/Si metal-insulator-semiconductor (MIS) capacitors were studied. Ta 2O5 thin films on n- and p-type silicon had been prepared by thermal oxidation of sputter or electron-beam deposited Ta films. The direct current leakage was found to be about 3×l0-6 (Al positive) or 6×l0-5 A/cm2 (Al negative) at an applied field of 1 MV/cm. The breakdown strength is between 3 and 4 MV/cm (Al negative on p-type Si). The dielectric constant is 22-30 when measured at 1 MHz. The flat-band voltage is positive (+0.81±0.09 V) and exhibits an instability with respect to voltage-time stresses at room temperature. It can shift to more positive (maximum shift ∼-2 V) or more negative values (maximum shift ∼-2 V), depending on the conditions of the voltage-time stress. A post-metal (after the deposition of the Al electrodes) anneal of the MIS structure at 400 °C for 30 min in 90% Ar-l0% H2 yields a negative flat-band voltage (-0.08±0.11 V) and partly removes the instability.