Electrical characterization of Ru-and RuO2/Ta2O5 gate stacks for nanoscale DRAM technology

Abstract

Electrical properties of metal-oxide-semiconductor structures composed of MOCVD grown Ru or RuO₂ metal gates, rf sputtered Ta₂O₅ oxide layers, and nitrided Si was investigated. The dielectric constant of Ta₂O₅ as extracted from capacitance-voltage characteristics was found to be 24 and 28 for Ru and RuO₂ gated structures, respectively. Interfacial SiO₂-like layer with a thickness of ~2 nm was observed from X-ray reflectivity analysis. The effective work functions of Ru and RuO₂ in contact with Ta₂O₅ were found to be 4.65 and 4.8 eV, respectively. Temperature dependent current-voltage measurements indicate the transition from the Pool-Frenkel emission (or thermionic field emission) to the field emission conduction mechanism in combination with the direct tunneling across the SiO₂-like interfacial layer under gate as well as substrate injection.