Optical properties of amorphous and polycrystalline tantalum oxide thin films measured by spectroscopic ellipsometry from 0.03 to 8.5 eV

Amorphous tantalum oxide thin films were deposited by reactive r.f. magnetr on sputtering onto silicon[001] substrates. Growth temperature, oxygen part ial pressure and total gas pressure have been varied for optimizing thin fi lm density. The as-deposited films were annealed in atmosphere at 700 degre esC and transformed into a polycrystalline state. The thin films were analy zed by glancing-angle-of-incidence X-ray diffraction, and variable angle-of -incidence spectroscopic ellipsometry in the near infrared (NIR) to vacuum- ultra-violet (VUV) spectral region for photon energies from 1 to 8.5 eV, an d in the infrared (IR) region from 0.03 to 1 eV. We present the IR dielectr ic functions of amorphous and polycrystalline tantalum oxide, which were ob tained by analyzing the experimental ellipsometric data with Lorentzian lin eshapes for each phonon resonance absorption. We observe a shift of the cha racteristic phonon absorption in tantalum oxide to lower frequencies upon s ample annealing. The optical properties in the NTR to VUV were analyzed by using a parametric model approach. The dielectric functions obtained thereb y were further locally fitted by Lorentzian lineshapes in order to analyze critical point structures due to electronic band-to-band transitions. (C) 2 001 Elsevier Science B.V. All rights reserved.