(685f) Material and Electrical Properties of Hf-Ru-N Gate Electrodes on Hafnium Oxide

Many alternative gate dielectric candidates for future generation MOSFET devices, including Hf based dielectrics, will require the use of a metal gate, because of the instability issues, sheet resistance, gate depletion, and dopant penetration experienced with polysilicon gates. Hf based gate electrode materials are promising candidates because they are likely to reduce charge transfer and subsequent dipole formation at the interface as a result of the homo-nuclear bonds that form between the Hf in the metal gate and the Hf in the gate dielectric. This paper discusses the material and electrical properties of Hf-Ru and Hf-Ru-N gate electrodes deposited atop HfO₂. Four compositions of HfRu were synthesized with varying amounts of N (0 - 15 at.%), and their material characteristics before and after annealing, such as composition, interface bonding, and crystalline phases were determined by X-ray photoemission spectroscopy (XPS), Rutherford backscattering (RBS), and X-ray diffraction (XRD). Capacitance-voltage (C-V) and current density-voltage (J-V) characteristics of fabricated metal-oxide-semiconductor (MOS) capacitors are used to determine the effective work functions (EWFs), the barrier heights, and the leakage current density across the metal gate/HfO₂ interface. Pure Hf and pure Ru gate electrodes deposited on HfO₂ exhibited EWFs of 4.1 eV and 5.5 eV, respectively, which correspond well with what has been reported in literature.[1,2] HfRu alloys with EWFs of 4.8eV and 5.2 eV have been achieved, and N incorporation was found to have a modest effect on the attained EWFs. Detailed analyses of EWFs as a function of alloy composition, microstructure, and interfacial bonding will be presented to determine the optimal composition for n-MOSFET devices and p-MOSFET devices.

[1] P. Majhi, et. al., 2005 IEEE VLSI-TSA (2005). [2] M. Tapajna, et. al., Materials Science in Semiconductor Processing 7, (2004).