Two-dimensional thickness measurements based on internal reflection ellipsometry

An imaging ellipsometer technique on internal reflection geometry that can measure the thickness distribution of a thin film possessing an assumed refractive index is described. Because a prism is used for the internal reflection geometry, it was theoretically predicted that angular derivation from the normal incidence on the prism surface affects only the ^ value by a factor of 0.97 at maximum. Measurements were carried out for an optical system of silica substrate-TiO₂ layer-silica layer-protein film-air, with a thin-film array of dried protein as the sample film. Thickness of the protein films was two-dimensionally estimated only from the measured map of the A value by use of the simulated relationship between the thickness and the A value. The thickness map obtained was coincident on the whole with the results according to a mechanical scanning. The detection limit was approximately ±0.2 nm. These findings validate the optical effect of a high-index additional layer to improve the sensitivity and precision of thickness measurements of the sample film on transparent substrates.