Effect of CeO2 addition on the performance of a Ta barrier for high-density memory device applications

초록

The effects of the amount of CeO<inf>2</inf> added in the Ta film on the barrier performance of a Ta barrier layer were investigated. For the film, Ta<inf>2</inf>O<inf>5</inf>, Pt-silicides, and Pt-Ta compounds formed after annealing at 650 °C by a reaction involving O, Pt, Ta, and Si, followed by the complete destruction of bottom electrode structure, due to the polycrystalline structure of the Ta film possessing grain boundaries which act as fast diffusion paths as well as reaction sites for O, Pt, Ta, and Si. Meanwhile, in the case of the Ta film being deposited with CeO<inf>2</inf> addition, no reaction products were observed even after annealing at 800 °C, leading to a retention of the bottom electrode structure up to 800 °C without an increase in resistance. The amorphous microstructure formed by strong chemical bonds of Ta-Ce-O or Ta-O resulted in the reduction of diffusivity of O, Pt, Ta, and Si through the diffusion barrier due to its lack of grain boundaries, followed by an enhancement of the Ta+CeO<inf>2</inf> diffusion barrier performance. The oxidation resistance of the Ta+CeO<inf>2</inf> diffusion barrier itself is completely degraded after annealing at 550 °C, owing to a larger amount of Ta-Ta bonds as compared to that of Ta-O bonds due to the small amount of CeO<inf>2</inf> added in the Ta film. Consequently, we suggest that, in order to improve both barrier properties and the oxidation resistance simultaneously, the oxide added in the matrix metal should be a large amount of the conductive oxide (more than 50 atom %).