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

Electrical properties of metal-oxide-semiconductor structures composed of MOCVD grown Ru or RuO
2
metal gates, rf sputtered Ta
2
O
5
oxide layers, and nitrided Si was investigated. The dielectric constant of Ta
2
O
5
as extracted from capacitance-voltage characteristics was found to be 24 and 28 for Ru and RuO
2
gated structures, respectively. Interfacial SiO
2
-like layer with a thickness of ~2 nm was observed from X-ray reflectivity analysis. The effective work functions of Ru and RuO
2
in contact with Ta
2
O
5
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 SiO
2
-like interfacial layer under gate as well as substrate injection.