The Spectroscopic Ellipsometry measurement method has many advantages. First of all, it is an optical technique, so it is non-contact and non-destructive. It measures the layer thickness and optical functions of each layers in a multilayer structure. It has high sensitivity, because it is based on measuring the phase shift of a light beam travelling through a layer structure, and phase angle measurement does not depend on the absolute intensity of light. Using white light sources and monochromators, spectral information can be obtained about the sample.

Ellipsometry measures the ratio of the complex Fresnel reflection coefficients. As this is a complex number, it can be divided to an amplitude term, and a phase shift term, which correspond to the ellipsometric angles, Ψ and Δ. These parameters contain the physical properties of the layer structure, such as the layer thickness and refractive index. As this is a transcendental and highly nonlinear equation, it needs to be solved by numerical methods, on a model-based approach. During this procedure, the layer structure is considered with thickness and optical functions in the model. The relative phase shift is calculated and compared to measured quantities during a numerical regression procedure.