Consistent refractive index parameters for ultrathin SiO2 films

Refined values are obtained in the present study for the refractive index parameter $\mathrm{(n)}$ for ultrathin ${\mathrm{SiO}}_2$ films (less than 8 nm in film thickness, $L_{\mathrm{ox}})$ and summarized as ${\text{n=2.139−8.991×10}}^{\text{−2}}{\mathrm{\times L}}_{\mathrm{ox}}{\text{+1.872×10}}^{\text{−3}}{\mathrm{\times L}}_{\mathrm{ox}}^2.$ This formula was obtained starting from variable angle of incidence ellipsometry data on ultrathin ${\mathrm{SiO}}_2$ films, and a previously derived refractive index parameter formula that was based on independently measured thickness’ using Fowler–Nordheim electron tunneling measurements. The new $n$ values are useful for extracting more accurate ultrathin ${\mathrm{SiO}}_2$ film thicknesses from ellipsometry measurements.