Metallorganic Chemical Vapor Deposition of TaO[sub x]N[sub y] as a High-Dielectric-Constant Material for Next-Generation Devices

Abstract

Tantalum oxynitride films were deposited by metallorganic chemical vapor deposition. Pentaethoxytantalum [Ta(OC2H5)5], the most widely used source gas for depositing Ta2O5, was used as the source gas and NH3 as the reaction gas. The activation energy of the surface reaction was estimated to be 1.1 eV for a single-source deposition (Ta2O5 deposition), and to decrease to ca. 0.37 eV with the addition of over 50 sccm NH3. Deposition rate at the surface-reaction-controlled regime increased to 2.6 nm/min with 100 sccm NH3 but decreased upon adding more than 100 sccm of NH3. The overall deposition rate of the surface-reactioncontrolled regime was as predicted by the Langmuir-Hinshelwood model. With an increase in both deposition temperature and NH3 flow rate, the TaON phase predominated over Ta2O5. The dielectric constants of the as-deposited and N2-annealed TaOxNy films were 51 and 146, respectively. It is believed that TaOxNy films are attractive high-dielectric-constant materials for the next generation of gigabit dynamic random access memory devices. However, TaOxNy films exhibit relatively high current leakage densities of 10-5 to 10-3 A/cm2 at 1.0 MV/cm. A porous TaOxNy film microstructure was observed by transmission electron microscopy, and this seemed to be responsible for these high leakage currents. Further systematic optimization of the deposition and annealing processes is needed to produce a dense microstructure with a low leakage current level. © 2002 The Electrochemical Society. All rights reserved.