The refractive index determines how much the light is refracted when passing the interface between two materials. The refractive index varies with wavelength (dispersion), but in the vast majority of materials the refractive index is reported at 633nm wavelength (He-Ne laser) due to the large number of tools operating at this wavelength.
In refractive index formula, n=n+i*k, the real part (n) determines the refraction of light and the imaginary part (k) is related to the absorbance. Several models have been developed to describe the refractive index of a material with the most characteristic be: Cauchy, Sellmeier, Forouhi-Blummer, and Lorenz.
in optical measurements, the film thickness and the refractive index of the material are coupled parameters and it is difficult to measure both values (thickness and refractive index) simultaneously, especially when film is thin.
FR-Monitor, the S/W that accompanies all FR-tools is loaded with a materials database with 650+ materials to facilitate the measurement of film thickness from 1nm to more than 1mm. It is equipped with all major refractive index models and powerful algorithms that along with the state-of-the-art H/W, allow for the simultaneous measurement of film thickness and refractive index when thickness is >100nm (for tools operating at wavelengths >400nm) and >50nm (for tools operating at wavelengths >200nm).
In addition to those generic specifications, the simultaneous measurement of thickness and refractive index has been demonstrated at even thinner transparent films (e.g. 20nm polymer/Si).
Typical Application Notes: