Ellipsometer

Overview

An elipsometer is used measure the dielectric properties (including refractive index and dielectric function) of thin films. It is useful for determining these properties

film thickness
refractive indices
surface roughness
interfacial mixing
composition
crystallinity
anisotropy
uniformity

Significance

The ellipsometer directly measures Psi the amplitude ratio and Delta the phase difference of the polarization of light as it reflects off a sample surface. The data is collected at several incident angles and across a broad spectrum of wavelenghts. Given these parameters the data is then fit to a set of mathematical models that is appropriate for the materials or multiple layers of materials. Once the other parameters are adjusted and the curves fit the desired property can be inferred.

<math>\rho</math> (a complex quantity), which is the ratio of <math>r_p</math> over <math>r_s</math>:

<math>\rho = \frac{r_p}{r_s} = \tan ( \Psi ) e^{i \Delta}</math>

<math>\Delta = \delta_p - \delta_s\,\!</math> is the phase difference

<math>\Psi\,\!</math> is the amplitude ratio

Other common variables associated with this are;

<math>C= sin(2\Psi) cos (\Delta)\,\!</math>

<math>S= sin(2\Psi) sin (\Delta)\,\!</math>