Spectroscopic ellipsometry characterization of nitrogen-incorporated HfO2 gate dielectrics grown by radio-frequency reactive sputtering

Spectroscopic ellipsometry with photon energy 0.75–6.5 eV at room temperature has been used to derive the optical properties of nitrogen-incorporated HfO2 films on Si(100) substrates grown by radio-frequency reactive sputtering using different N2∕(N2+O2+Ar) gas ratios from 20% to 50%. Excellent agreement has been found between the experimental and the simulated spectra, in which an empirical dielectric dispersion relation based on Tauc-Lorentz model has been successfully adopted. Increases in the refractive index n and the extinction coefficient. k, with increases in nitrogen-incorporation content are observed due to the nitrogen-incorporation-induced higher packing density. The change of the complex dielectric functions and reduction in the optical band gap with an increase in nitrogen concentration resulting from the effect of the nitrogen-incorporation on the structure are discussed in detail.