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)

Advanced high-κ dielectric stacks with polySi and metal gates: Recent progress and current challenges

“…Low-damage deposition processes such as ALD or CVD are preferred, since physical vapor deposition (PVD) processes result in sputter damage to the thin oxynitride dielectric layer. Such stringent requirements on deposition processes are not required for the integration of metal/HfO 2 gate stacks, since these stacks have a physically thicker high-j dielectric (compared with SiON) that results in lower gate leakage; more significantly, these stacks are more thermodynamically stable at elevated temperatures than metal/SiO 2 stacks [90]. This allows for the possibility of a ''gate-first'' conventional process integration scheme.…”

Lanthanum silicate gate dielectric stacks with subnanometer equivalent oxide thickness utilizing an interfacial silica consumption reaction

“…Ta is predicted to be stable in contact with La 2 O 3 . However, Ta is not stable in contact with SiO 2 , 29 thus it may not be stable in contact with the silicate. The stability of Ta in contact with a La-silicate will thus require further study.…”

Thermal response of Ru electrodes in contact with SiO2 and Hf-based high-k gate dielectrics

“…These experimental data suggest a dual reaction mechanism for the Ru/ SiO 2 / Si film system, proposed by Peterson et al, for ruthenium silicidation from Ru on bulk Si. 15 16,17 However, in thin SiO 2 films, especially near the Si/ SiO 2 interface, Si and O atoms may not be forming complete tetrahedral structures as in the bulk SiO 2 film and thus could be more reactive with the Ru atoms, easily traveling into three monolayers of SiO 2 . Another possible reaction mechanism is dielectric degradation due to oxygen diffusing upward into the Ru, which could not be detected because of instrumentation limits.…”