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

The Ru–Ta–Si–O, Ta–Si–N–O, and Ru–Ta–Zr–O phase diagrams are important for predicting reactions at interfaces between SiO 2 and ZrO 2 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 ZrO 2 and SiO 2 , whereas Ta is not stable in contact with SiO 2 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 TaN x 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)