Ellipsometric examination of optical property of the Si–SiO2 interface using the s-wave antireflection

Using variable-angle spectroscopic ellipsometry and introducing two models (a three-phase and a two-film model), we examined the optical properties of thermally grown ${\mathrm{SiO}}_2$ layers on Si, with special focus on phase difference $\Delta$ and amplitude ratio $\tan \mathrm{ \psi }$ for the s and p waves. We found an abrupt flip of the $\cos \mathrm{ \Delta }$ curve from which the s and p-wave antireflection conditions were determined and evaluated the interface sensitivities for $\cos \mathrm{ \Delta }$ and $\tan \mathrm{ \psi }$ based on the three-phase (ambient-oxide substrate) and the two-film (ambient-oxide-interlayer substrate) model. The sensitivities for $\cos \mathrm{ \Delta }$ and $\tan \mathrm{ \psi }$ were shown to have maximum values at the same angle of incidence and photon energy in the s-wave antireflection condition. By fitting the variable-angle spectroscopic ellipsometry data measured in the s-wave antireflection condition, the thickness of the ${\mathrm{Si–SiO}}_2$ interface was determined as $\text{0.784±0.003}$ nm for a 52-nm thick oxide sample and $\text{0.764±0.002}$ nm for a 150-nm-thick oxide one. We also found that the effective refractive index of the interface was 2.060 at 546 nm for the 52 nm sample and 1.981 for the 150 nm sample, respectively.