Measurement of the refractive index of thin SiO2 films using tunneling current oscillations and ellipsometry

We use Fowler–Nordheim tunneling current oscillations to accurately determine the thicknesses of ultrathin SiO2 films, and with the thicknesses as input, we employ precision single wavelength ellipsometry to determine the real part of the refractive index for thin SiO2 films in the range of 4–6 nm. An average value for this refractive index was found to be 1.894±0.110. This value is shown to yield SiO2 thicknesses to an accuracy of ±0.1 nm. A SiO2 thickness-refractive index interpolation formula for the thin film regime is given.