Influence of post-deposition annealing on the chemical states of crystalline tantalum pentoxide films

We investigate the effect of post-deposition annealing (for temperatures from 848 K to 1273 K) on the chemical properties of crystalline Ta${}_2$O${}_5$ films grown on Si(100) substrates by radio frequency magnetron sputtering. The atomic arrangement, as determined by X-ray diffraction, is predominately hexagonal ($\delta$-Ta${}_2$O${}_5$) for the films exposed to heat treatments at 948 K and 1048 K; orthorhombic ($\beta$-Ta${}_2$O${}_5$) for samples annealed at 1148 K and 1273 K; and amorphous for samples annealed at temperatures below 948 K. X-ray photoelectron spectroscopy for Ta $4f$ and O $1s$ core-levels were performed to evaluate the chemical properties of all films as a function of annealing temperature. Upon analysis, it is observed the Ta $4f$ spectrum characteristic of Ta in Ta${}^{5+}$ and the formation of Ta-oxide phases with oxidation states Ta${}^{1+}$, Ta${}^{2+}$, Ta${}^{3+}$, and Ta${}^{4+}$. The study reveals that the increase in annealing temperature increases the percentage of the state Ta${}^{5+}$ and the reduction of the others indicating that higher temperatures are more desirable to produce Ta${}_2$O${}_5$, however, there seems to be an optimal annealing temperature that maximizes the O% to Ta% ratio. We found that at 1273 K the ratio slightly reduces suggesting oxygen depletion.