An evaluation of errors in determining the refractive index and thickness of thin SiO2 films using a rotating analyzer ellipsometer

Errors are examined in determining the refractive index and thickness of very thin SiO2 films on c-Si substrates as measured with the commonly used rotating analyzer ellipsometer. Systematic errors in the ellipsometric parameters Δ, ψ, δΔ, and δψ are calculated from the experimental hardware errors. Random errors are measured. The propagation of errors from δΔ and δψ to errors in refractive index (n) and film thickness (d), δn and δd, are calculated for oxide thicknesses from 30 to 200 Å. It is verified that the thinner the oxide is and the lower the photon energy where c-Si becomes less absorbing, the larger the errors become. A minimum error of δn and δd is observed at the spectral region of 3.6–4.0 eV and around 5.2 eV. From the reported results for a high precision ellipsometer, judgments are made about the value of the extracted parameters for thin films, and recommendations are offered to minimize the errors.