Amorphous Ta-nanocrystalline RuOx diffusion barrier for lower electrode of high density memory devices

The effects of the amount of RuO2 added in the Ta film on the electrical properties of a Ta-RuO2 diffusion barrier were investigated using n(++)-poly-Si substrate at a temperature range of 650-800 degreesC. For the Ta layer prepared without RuO2 addition, Ta2O5 phase formed after annealing at 650 degreesC by reaction between Ta and external oxygen, leading to a higher total resistance and a non-linear I-V curve. Meanwhile, in the case of the Ta film being deposited with RuO2 incorporation, not only a lower total resistance and ohmic characteristics exhibited, but also the bottom electrode structure was retained up to 800 degreesC, attributing to the formation of a conductive RuO2 crystalline phase in the barrier film by reaction with the indiffused oxygen because of a Ta amorphous structure formed by chemically strong Ta-O or Ta-Ru-O bonds and a large amount of conductive RuO2 added. Since a kinetic barrier for nucleation in formation of the crystalline Ta2O5 phase from an amorphous Ta(O) phase is much higher than that of crystalline RuO2 phase from nanocrystalline RuOx phase, the formation of the RuO2 phase by reaction between the indiffused oxygen and the RuOx nanocrystallites is kinetically more favorable than that of Ta2O5 phase.