Evidence that N₂O is a Stronger Oxidizing Agent than O₂ for the Post-Deposition Annealing of Ta₂O₅ on Si Capacitors

Cross-sectional transmission electron microscopy (XTEM), secondary ion mass spectrometry (SIMS) and capacitance measurements were used to study the effect of post-deposition annealing on Ta₂O₅/Si structures. A significantly thicker SiO_x interfacial layer was formed at the Ta₂O₅/Si interface, if N₂O was used instead of O₂ for post-deposition annealing. This indicates that N₂O is a stronger oxidizing agent than O₂. It is known that the leakage current of Ta₂O₅ capacitors is greatly reduced if N₂O is used instead of O₂ for post-deposition annealing. This may also be partially explained by postulating that N₂O annealing is more effective in the suppression of oxygen vacancies. Furthermore, the suppression of Si diffusion from the Si substrate into Ta₂O₅ due to the thicker SiO_x interfacial layer can be another factor. The basic reason for the superiority of N₂O is that the energy required to produce free O atoms is lower than that for O₂. From this point of view, we can also predict that the use of NO will be worse than that of O₂ because the energy required to produce free O atoms is higher than that of O₂.