XPS investigation of UV-annealed ultrathin Ta₂O₅ films on silicon

We report the use of UV lamp sources, providing high photon fluxes over large-areas, to initiate the photo-deposition of ultrathin tantalum pentoxide (Ta₂O₅) films with physical thickness between 4-10 nm at low temperatures (below 350°C). The photo-deposited film properties, determined using various standard methods and electrical measurements, have shown that good quality films can be produced. We have found that although a thin sub-stoichiometric silicon oxide layer (SiO_X) was present at the Ta₂O₅/Si interface. The electrical properties of these tantalum oxide films are significantly improved following an UV annealing step in 1000 mbar of pure oxygen. XPS profiles revealed that the SiO_X layer could be transformed to SiO₂ after the UV annealing process. These XPS results are critically important for the understanding of the interface properties of the tantalum oxide films on Si in the quest to further improve the photo-CVD process.