Changes in effective work function of HfxRu1−x alloy gate electrode

Effective work function (ϕm,eff) values of Hfx Ru1−x alloy gate electrodes on SiO2 metal-oxide-semiconductor (MOS) capacitors were carefully examined to assess whether the ϕm,eff was determined by the crystalline structure or the composition of the HfxRu1−x alloy. X-ray diffraction results indicated that the crystalline structures of HfxRu1−x alloy were divided into hexagonal-Ru, cubic-HfRu or hexagonal-Hf with the increase of Hf content. The ϕm,eff values could be controlled continuously from 4.6 to 4.0 eV by changing the Hf content. The experimental ϕm,eff value showed a good agreement with theoretical results considering the compositional ratio of pure Hf and Ru. These results suggest that the ϕm,eff of HfxRu1−x alloy gates on SiO2 MOS capacitors is dominantly determined by the HfxRu1−x composition rather than the crystalline structure.