Formation mechanism of interfacial Si–oxide layers during postannealing of Ta2O5/Si

The Si–O–Si bonds formed at the Ta2O5/Si interface by annealing were investigated by using Fourier transform infrared absorption spectroscopy. The Ta2O5 thin films deposited on Si substrates were annealed in different ambient (H2O, O2, and N2) at temperatures between 500 and 800 °C. When annealing is done in H2O, the interfacial silicon–oxide grows very rapidly, because the oxidation species can easily diffuse through Ta2O5 films, and because the Si–O formation is controlled by the diffusion of H2O in the interfacial layer. When annealing is done in O2, the oxidation species can also easily diffuse through Ta2O5, but not through the interfacial layer. The interfacial layer is formed by a reaction between Ta2O5 and Si even if the annealing ambient does not contain oxidation species, as is the case when annealing is done in N2. We conclude that the Si–O formation during postannealing in O2 and N2 is controlled by the diffusion of the Si from the substrate through the interfacial layer with an activation energy of 0.7 to 0.8 eV, and that new Si–O bonds are formed at the interface between the Ta2O5 and interfacial layer. Oxidation species from the annealing ambient enhance the frequency factor of the reaction, but do not control Si–O formation.