Leakage current mechanism of metal-Ta2O5-metal capacitors for memory device applications

Tantalum oxide (Ta2O5) is an important material for future dynamic-random access memory capacitor and metal oxide semiconductor field effect transistor gate oxide applications. In this work, the electrical and material properties of amorphous Ta2O5 metal-insulator-metal capacitors deposited by plasma-enhanced chemical vapor deposition (PECVD) on a tungsten bottom electrode are studied. The minimum thickness of Ta2O5 is 14 Mn which is equivalent to a SiO2 thickness of 2.58 nm. High-quality dielectric characteristics such as a leakage current density of 3 x 10(-8) A/cm(2) at 0.75 V for both voltage polarities, a capacitance of 13.8 fF/mu m(2), and a breakdown strength of 8.23 MV/cm when the bias is negative, are obtained. These high-quality characteristics are most likely due to the complete decomposition of the precursor Ta(OC2H5)(5) by oxygen plasma during plasma deposition. The current conduction mechanism of amorphous Ta2O5 is investigated. A comparison between Ta2O5 deposited by PECVD and by low-pressure chemical vapor deposition is also studied. (C) 1999 The Electrochemical Society. S0013-4651(98)03-060-2. All rights reserved.