Enhanced thermal stability of a sputtered titanium-nitride film as a diffusion barrier for capacitor-bottom electrodes

초록

The effect of a thin RuO<inf>x</inf> layer formed on the Ru/TiN/doped poly-Si/Si stack structure was compared with that on the RuO<inf>x</inf>/TiN/doped poly-Si/Si stack structure over the post-deposition annealing temperature ranges of 450-600°C. The Ru/TiN/poly-Si/Si contact system exhibited linear behavior at forward bias with a small increase in the total resistance up to 600°C. The RuO<inf>x</inf>/TiN/poly-Si/Si contact system exhibited nonlinear characteristics under forward bias at 450°C, which is attributed to no formation of a thin RuO<inf>x</inf> layer at the RuO<inf>x</inf> surface and porous-amorphous microstructure. In the former case, the addition of oxygen at the surface layer of the Ru film by pre-annealing leads to the formation of a thin RuO<inf>x</inf> layer and chemically strong Ru-O bonds. This results from the retardation of oxygen diffusion caused by the discontinuity of diffusion paths. In particular, the RuO<inf>x</inf> layer in a nonstoichiometric state is changed to the RuO<inf>2</inf>-crystalline phase in a stoichiometric state after post-deposition annealing; this phase can act as an oxygen-capture layer. Therefore, it appears that the electrical properties of the Ru/TiN/poly-Si/Si contact system are better than those of the RuO<inf>x</inf>/TiN/poly-Si/Si contact system.

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