LEAKAGE CURRENTS IN AMORPHOUS TA2O5 THIN-FILMS

Tantalum oxide (Ta2O5) is an important material for future dynamic ran dom access memory application owing to its high dielectric constant. T his work examines the structural and electrical properties of Ta2O5 th in films deposited by plasma-enhanced chemical vapor deposition using a penta ethoxy tantalum Ta(OC2H5)5 liquid source. The x-ray diffractio n patterns indicate that the as-deposited thin films are amorphous and become polycrystalline after rapid thermal annealing above 650 degree s C. The level of carbon contamination is below that which can be dete cted by Auger electron spectroscopy measurement. Electrical measuremen ts performed on amorphous Ta2O5 using a Au/Ta2O5/Pt/Ti/Si metal-tantal um oxide-metal structure exhibit a low leakage current, reasonable bre akdown field (5.4 MV/cm), and high dielectric constant (23-25). The le akage current is 2 x 10(-8) A/cm(2) at 1 MV/cm. In addition, the leaka ge current mechanism of amorphous Ta2O5 capacitors is investigated by plotting the In(J) vs E-1/2 curves at a low electric field (<2 MV/cm) and plotting In(J/E) vs E-1/2 curves at a high electric held (>2 MV/cm ). The dominant conduction mechanism is due to Schottky emission at lo w electrical field and Poole-Frenkel emission at high electrical field . According to our results, the Ta2O5 thin films annealed in N-2 or O- 2 at 800 degrees C exhibit a much higher leakage current than amorphou s Ta2O5, possibly due to the out-diffusion of Ti during high temperatu re annealing. (C) 1997 American Institute of Physics.