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

TL;DR

This study examines how post-deposition annealing temperatures affect the chemical states and crystalline structure of tantalum pentoxide films, revealing optimal conditions for maximizing oxygen content and phase purity.

Contribution

It provides detailed analysis of the relationship between annealing temperature, crystal phase, and chemical states in Ta$_2$O$_5$ films, highlighting optimal annealing conditions.

Findings

Higher annealing temperatures increase Ta$^{5+}$ content.

Optimal annealing temperature maximizes O/Ta ratio.

Oxygen depletion occurs at 1273 K.

Abstract

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.