Reduction of interfacial SiO₂ at HfO₂/Si interface with Ta₂O₅ cap

We investigated SiO₂ interfacial layer (IL-SiO₂) reduction with a Ta₂O₅ cap to realize the direct contact formation of HfO₂ on a Si substrate for the equivalent oxide thickness scaling of Hf-based high-k gate dielectrics. X-ray reflectivity and x-ray photoelectron spectroscopy measurements revealed that the Ta ₂O₅ cap was effective in taking oxygen from the IL-SiO₂ and caused SiO₂ reduction, which resulted from Ta diffusion into the HfO₂ layer from the Ta₂O₅. With this technique, the Ta₂O₅ cap deposited on the HfO₂/SiO₂/Si reduced the IL-SiO₂ by 0.2 nm without any thermal treatment. Rapid thermal annealing at 300 °C enhanced the IL-SiO₂ reduction. This result reveals that our method is a promising approach to achieve direct contact between the high-k layer and the Si substrate. Therefore, Ta₂O₅ has good potential as a cap for SiO₂ interfacial layer reduction.