Leakage currents in amorphous Ta2O5 thin films

Abstract

Tantalum oxide (Ta2O5) is an important material for future dynamic random access memory application owing to its high dielectric constant. This work examines the structural and electrical properties of Ta2O5 thin films deposited by plasma-enhanced chemical vapor deposition using a penta ethoxy tantalum Ta(OC2H5)5 liquid source. The x-ray diffraction patterns indicate that the as-deposited thin films are amorphous and become polycrystalline after rapid thermal annealing above 650 °C. The level of carbon contamination is below that which can be detected by Auger electron spectroscopy measurement. Electrical measurements performed on amorphous Ta2O5 using a Au/Ta2O5/Pt/Ti/Si metal-tantalum oxide-metal structure exhibit a low leakage current, reasonable breakdown field (5.4 MV/cm), and high dielectric constant (23–25). The leakage current is 2×10−8 A/cm2 at 1 MV/cm. In addition, the leakage current mechanism of amorphous Ta2O5 capacitors is investigated by plotting the ln(J) vs E1/2 curves at a low electric field (<2 MV/cm) and plotting ln(J/E) vs E1/2 curves at a high electric field (>2 MV/cm). The dominant conduction mechanism is due to Schottky emission at low electrical field and Poole–Frenkel emission at high electrical field. According to our results, the Ta2O5 thin films annealed in N2 or O2 at 800 °C exhibit a much higher leakage current than amorphous Ta2O5 , possibly due to the out-diffusion of Ti during high temperature annealing.