Dielectric function of amorphous tantalum oxide from the far infrared to the deep ultraviolet spectral region measured by spectroscopic ellipsometry

Eva Franke, C. L. Trimble, M. J. DeVries, J. A. Woollam, M. Schubert, F. Frost

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Abstract

Amorphous tantalum oxide thin films were deposited by reactive rf magnetron sputtering onto [001] silicon substrates. Growth temperature, oxygen partial pressure, and total gas pressure have been varied to obtain thin films with different densities. The thin films were analyzed by glancing angle-of-incidence x-ray diffraction, atomic force microscopy, and variable angle-of-incidence spectroscopic ellipsometry in the near infrared to vacuum ultraviolet spectral region for photon energies from E= 1 to 8.5 eV, and in the infrared region from E=0.03 to 1 eV. We present the dielectric function of amorphous tantalum oxide obtained by line shape analysis of the experimental ellipsometric data over the range from E=0.03 to 8.5 eV (40 μm-145 nm). In the infrared spectral region the ellipsometric data were analyzed using Lorentzian line shapes for each absorption mode observed in the spectra. Amorphous tantalum oxide optical properties in the near infrared to vacuum ultraviolet spectral region were extracted by using a Kim and Garland parameter algorithm [C. C. Kim et al., Phys. Rev. B 45, 11 749 (1992)] in order to model the absorption due to the fundamental band gap of the material. We consider thin film porosity, and therefore analyzed the experimental ellipsometric data by an effective medium approach. We obtain information on the tantalum oxide optical properties, a percentage of void fraction, and film thickness. The "optical" percentage of void fractions corresponds to surface roughness measured by atomic force microscopy and depends on deposition parameters.

Original languageEnglish (US)
Pages (from-to)5166-5174
Number of pages9
JournalJournal of Applied Physics
Volume88
Issue number9
DOIs
StatePublished - Nov 1 2000

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tantalum oxides
ellipsometry
thin films
line shape
voids
incidence
atomic force microscopy
optical properties
vacuum
gas pressure
partial pressure
magnetron sputtering
surface roughness
x ray diffraction
film thickness
porosity
photons
silicon
oxygen
temperature

ASJC Scopus subject areas

  • Physics and Astronomy(all)

Cite this

Dielectric function of amorphous tantalum oxide from the far infrared to the deep ultraviolet spectral region measured by spectroscopic ellipsometry. / Franke, Eva; Trimble, C. L.; DeVries, M. J.; Woollam, J. A.; Schubert, M.; Frost, F.

In: Journal of Applied Physics, Vol. 88, No. 9, 01.11.2000, p. 5166-5174.

Research output: Contribution to journalArticle

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