Tantalum–ruthenium dioxide as a diffusion barrier between Pt bottom electrode and TiSi2 ohmic contact layer for high density capacitors

Abstract

The effects of RuO2 addition on the barrier properties of the Ta layer were investigated at the temperature range of 650–800 °C in air. For the Pt/Ta/TiSi2/poly-Si/SiO2/Si structure, its layer structure was completely collapsed after annealing at 650 °C, resulting in higher total resistance and Schottky characteristics. For the Pt/Ta+RuO2/TiSi2/poly-Si/SiO2/Si structure, however, it exhibited the lower total resistance and ohmic characteristics, and its layer structure was retained up to 800 °C. A Ta amorphous structure by the chemically strong Ta–O or Ta–Ru–O bonds and nonstoichiometric, nanocrystalline RuOx resulted in the formation of a conductive RuO2 phase in the Ta+RuO2 barrier film after an annealing, leading to the prevention of the interdiffusion of Pt, Si, and external oxygen through the diffusion barrier as well as surface oxidation up to 800 °C. Therefore, the thermal stability for the Pt/Ta+RuO2/TiSi2/poly-Si/SiO2/Si structure was higher than that for Pt/Ta/TiSi2/poly-Si/SiO2/Si structure.