Stability of Ru- and Ta-based metal gate electrodes in contact with dielectrics for Si-CMOS

Abstract

The Ru–Ta–Si–O, Ta–Si–N–O, and Ru–Ta–Zr–O phase diagrams are important for predicting reactions at interfaces between SiO2 and ZrO2 gate dielectrics and novel Ru and Ta-based metal gate electrodes. Simplified quaternary phase diagrams of the Ru–Ta–Si–O, Ta–Si–N–O, and Ru–Ta–Zr–O systems at 900 °C were constructed from known and estimated Gibbs free energy data, respectively. Ru is predicted to be stable in contact with ZrO2 and SiO2, whereas Ta is not stable in contact with SiO2 at temperatures around 900 °C. Stoichiometric RuTa and TaN compounds were estimated to be stable in contact with both dielectrics at 900 °C. Experimental observations of gate electrode/dielectric interfaces are discussed. They are consistent with the thermodynamic predictions within the limitations of these phase diagrams. Metastable phases, often found in TaNx films, and diffusion of species from the vapor (e.g., oxygen), in particular along grain boundaries in columnar gate electrodes, may lead to reactions not predicted by the equilibrium phase diagrams. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)