Increased Thermal Stability of W/Ta2O5 Gate Structure Using Effective Diffusion Barrier of Denuded Tungsten Nitride

We investigated the effect of TiN and WN x diffusion barrier on the thermal stability and electrical properties of W/Ta2O5 gate structure. For TiN/Ta2O5 system annealed at 950°C, both tantalum and oxygen in Ta2O5 films significantly migrated to TiN layer, resulting in the partial oxidation of TiN and the formation of voids in the Ta2O5 layers and increasing the roughness at the TiN/Ta2O5 interface. However, for the WN x /Ta2O5 system annealed even at 950°C, no outdiffusion of tantalum and oxygen from Ta2O5 into annealed-WN x layer was observed. A nitrogen-rich barrier with Ta–O–N bonding formed on Ta2O5 surface during denudation of WN x caused the high thermal stability of WN x /Ta2O5. The electrical characteristics of W/WN x /Ta2O5 system was found to be more superior than that of W/TiN/Ta2O5 in the respect of leakage current and breakdown voltage, thus it can be one of promising metal gate structures with high-dielectric in sub-100 nm metal-oxide semiconductor (MOS) devices.