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

초록

The effects of the amount of RuO<inf>2</inf> added in the Ta film on the electrical properties of a Ta-RuO<inf>2</inf> diffusion barrier were investigated using n++-poly-Si substrate at a temperature range of 650-800°C. For the Ta layer prepared without RuO<inf>2</inf> addition, Ta<inf>2</inf>O<inf>5</inf> phase formed after annealing at 650°C 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 RuO<inf>2</inf> incorporation, not only a lower total resistance and ohmic characteristics exhibited, but also the bottom electrode structure was retained up to 800°C, attributing to the formation of a conductive RuO<inf>2</inf> 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 RuO<inf>2</inf> added. Since a kinetic barrier for nucleation in formation of the crystalline Ta<inf>2</inf>O<inf>5</inf> phase from an amorphous Ta(O) phase is much higher than that of crystalline RuO<inf>2</inf> phase from nanocrystalline RuO<inf>x</inf> phase, the formation of the RuO<inf>2</inf> phase by reaction between the indiffused oxygen and the RuO<inf>x</inf> nanocrystallites is kinetically more favorable than that of Ta<inf>2</inf>O<inf>5</inf> phase.

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