Dielectric Function of Tantalum Nitride Formed by Atomic Layer Deposition on 300 mm Wafers for Josephson junction applications

In this research, we describe the dielectric function of atomic layer deposition (ALD) tantalum nitride (TaN) from 0.03 eV to 6.5 eV determined from spectroscopic ellipsometry.

Tantalum nitride layers with 12 nm and 25 nm thickness were formed on top of SiO₂ by atomic layer deposition. The TaN layer thicknesses and surface roughness were confirmed by x-ray reflectance (XRR). On a vertical J.A. Woollam ellipsometer (V-VASE), the ellipsometric angles ψ and Δ were acquired at room temperature at incidence angles from 50° to 80° and photon energies from 0.5 to 6.5 eV. We also acquired the infrared ellipsometric spectra at the same angles of incidence from 0.03 to 0.70 eV on a J.A. Woollam infrared ellipsometer. We developed an ellipsometry model for the optical constants of the oxide using three Gaussian oscillators at 56, 132, and 146 meV in the infrared spectral region and a pole at 11 eV (fixed) with variable amplitude. The TaN layers were described with a Tauc-Lorentz oscillator centered at 3.2 eV with a band gap at 1.7 eV, one UV pole, and one Gaussian in the UV. We also performed measurements at low temperatures of 80 K and 190 K at an angle of incidence of 70° to investigate the temperature dependence of the optical constants and oscillators for the TaN layer.