Composition of Ta2O5 stacked films on N2O- and NH3-nitrided Si

The composition and microstructure of rf sputtered 20 nm Ta2O5 on N2O or NH3 Rapid Thermal Nitrided (RTN) Si substrates have been investigated by X-ray photoelectron spectroscopy. RTN at 800 and 850 °C is effective to suppress active oxidation of Si. There is no evidence for the presence of SiO2 at Si interface. A lightly nitrided surface is established in both cases without a formation of detectable oxynitride layer at Si. A layered nature of the films is observed, with stoichiometric tantalum pentoxide at and close to the films' surface. In the depth, the films are mixed ones whose composition depends on the nitridation ambient. N2O treatment stimulates oxidation processes during the film deposition while NH3 nitridation results to a less effective oxidation and produces Ta-silicate like film. The correlation between the composition of the interfacial regions and the nitridation gas is also discussed. The results suggest that hydrogen, as a component of nitridation ambient, plays significant role in the reactions controlling the exact composition of the deposited Ta2O5, activating reactions with nitrogen. Nitrogen related reactions likely occur with NH3 processing but do not with N2O one. The presence of nitrogen feature is not detected in N2O-samples spectra at all. In the integration perspective, preliminary RTN of Si in N2O or NH3 could be a suitable way to produce layered Ta2O5-based films with more or less presence of tantalum silicate with a trace of nitrogen, either only at the interface with Si (N2O-process) or in the whole film (NH3-process).