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

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.

Comparison of nanometer-thick films by x-ray reflectivity and spectroscopic ellipsometry

“…These results are consistent with the results reported in literature. 16,17 In the past, the refractive index of tantalum oxide films had been shown to be dependent on the O/Ta ratio. 16,18 Tantalum sub- 20 Since the films were deposited under the same conditions, it is likely that the lower refractive index of the 10 nm Ta 2 O 5 was due to an increased number of voids or pores in the film.…”

Energy Loss Function of Solids Assessed by Ion Beam Energy-Loss Measurements: Practical Application to Ta2O5

“…In Figure 2, we also show, by a magenta dash-dotted line, the optical ELF of Ta 2 O 5 built from eq 4, where the outer (leastbound) electron excitation contribution is obtained from eq 2, with the parameters resulting from the REELS measurements, which are given in Table 1, and where the inner-shell contribution is also included. The measurements by Franke et al 23 at very low transferred energies are depicted by orange dots.…”

“…20−22 From experimental ellipsometry data, Franke et al 23 got the dielectric function of Ta 2 O 5 thin films in the spectral region 0.03−8.5 eV. Reflection electron energy loss measurements are an established way of determining the energy loss function of a material, 1,24 and the spectrum of amorphous Ta 2 O 5 for 200 eV electrons has been measured up to 60 eV energy losses, but being expressed in arbitrary units it is not an immediate task to obtain the energy loss function.…”

Charge Transport Through Thin Amorphous Titanium and Tantalum Oxide Layers

“…47,48 The Fresnel equations are evaluated for normal incidence, taking into account the bulk dielectric properties of the oxide layers [49][50][51][52] and of the metals. 53 Deviations from the bulk dielectric properties of the oxide and metal layers are not taken into account in the present work.…”