New oxidation state of tantalum oxide formed by reactive ion-beam cosputtering of Ta and Si

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Abstract
Fabrication of composite films of SiO2 and Ta2O5 with various constituent combinations has been attempted on Si substrates by a reactive ion-beam sputter-deposition technique. The films have been studied by Auger electron spectroscopy, infrared absorption spectroscopy, and x-ray diffraction. Infrared absorption spectra of the composite films have shown that the absorption peak corresponding to the Ta–O stretching mode of Ta2O5 (650 cm−1) is strongly suppressed, and instead a new peak appears at 950 cm−1. New peaks have also been noted in x-ray diffraction from the composite films. According to the quantitative analysis of the Auger spectra, there has been no indication of silicide formation in the films. Crystallographic considerations have shown that a plausible oxidation state of the Ta–Si binary system is an oxy-salt composed of Ta cations and silicate anions rather than a simple mixture of SiO2 and Ta2O5 (a complex oxide). The apparent low dielectric constant of tantalum oxides sputter deposited on Si substrates has also been explained by this new oxidation state of the Ta–Si system formed in the initial stage of the sputtering.

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