Poole-Frenkel conduction in Al/ZrO2/SiO2/Si structures

Leakage currents through Al/ZrO2/SiO2/n-Si metal-insulator-semiconductor (MIS) capacitors were studied. Thin SiO2 films were chemically grown on monocrystalline phosphorous doped silicon wafers. Zirconia films with thicknesses of 15 and 50 nm were deposited by radio frequency (rf) magnetron sputtering and, then, annealed in oxygen ambient at 850 degrees C, for 1 h. The dielectric constant of the sputtered and annealed ZrO2 layer was of about 17.8. The equivalent oxide thickness (EOT) of the stack 15 nm and 50 nm-ZrO2/SiO2 structure was estimated to be 3.2 nm and 10.7 nm, respectively. The temperature dependence of the leakage currents was explained by Poole-Frenkel (PF) conduction mechanism. Shallow trap levels in the studied structure of about 0.2 eV and 0.46 eV were calculated. The existence of A and D-defects, due to the sputtering and high temperature annealing in oxygen, was suggested.