Identification and roles of nonstoichiometric oxygen in amorphous Ta ₂ O ₅ thin films deposited by electron beam and sputtering processes

The morphology and composition of tantalum oxide (Ta ₂ O ₅ ) thin films prepared by electron-beam (EB) evaporation and radio-frequency sputtering (SP) were investigated by grazing incidence X-ray diffraction (GIXRD), X-ray reflectometry (XRR), atomic force microscopy, Fourier transformed infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). GIXRD revealed an amorphous nature for both films, and XRR showed that the density of the Ta ₂ O ₅ -EB films was lower than that of the Ta ₂ O ₅ -SP films; both films have lower density than the bulk value. A larger amount of molecular water and peroxo species were detected for the Ta ₂ O ₅ -EB films by FTIR performed in ambient atmosphere. XPS analyses performed in vacuum confirmed the presence of hydroxyl groups, but no trace of chemisorbed molecular water was detected. In addition, a higher oxygen nonstoichiometry (higher O/Ta ratio) was found for the EB films. From these results, we conclude that the oxygen nonstoichiometry of the EB film accounted for its lower density and higher amount of absorbed molecular water. The results also suggest the importance of understanding the dependence of the structural and chemical properties of thin amorphous oxide films on the deposition process.