Electrical properties of the Ta-RuO₂ diffusion barrier for high-density memory devices

The electrical properties of a Ta layer prepared with and without RuO₂ addition were investigated. The Ta+RuO₂/TiSi₂/poly-Si/SiO₂/Si contact system exhibited lower total resistance and ohmic characteristics up to 800 °C. Meanwhile, the Ta/TiSi₂/poly-Si/SiO₂/Si contact system showed higher total resistance and nonohmic behavior after annealing at 650 °C, attributed to the oxidation of both Ta and TiSi₂ layers. In the former case, a Ta+RuO₂ diffusion barrier showed an amorphous Ta microstructure and embedded RuO_x nanocrystals in the as-deposited state. The conductive RuO₂ crystalline phase in the Ta+RuO₂ film was formed by reaction between the nanocrystalline RuO_x and oxygen indiffused from air during annealing. When the Ta layer was deposited with RuO₂ addition, therefore, both the electrical properties and the oxidation resistance of the Ta+RuO₂ diffusion barrier were better than those of TiN, TaN, and Ta-Si-N barriers.