The FS-1 uses the power of ellipsometry to optically characterize samples. In an ellipsometer system, the Polarization State Generator (PSG) emits light with a known polarization, which is obliquely incident on the sample, and the Polarization State Detector (PSD) measures the polarization state of the light reflected from the sample.
The change in polarization state caused by the sample reflection can be defined by the ratio of the sample reflectivity for p-polarized light (Rp), over the sample reflectivity for s-polarized light (Rs). This ratio is a complex number, which is typically denoted by ρ (rho), and is often reported in terms of the ellipsometric parameters Ψ (Psi) and Δ (Delta), as defined by the following equation. According to this equation, tan(Ψ) defines the magnitude of the reflectivity ratio for p- and s- polarized light, and Δ defines the phase difference between the reflected p- and s- polarized light.
An alternate representation of the ellipsometric parameters is shown below. The N, C, and S ellipsometric parameters can be calculated in terms of the Ψ (Psi) and Δ (Delta) parameters, assuming the sample is isotropic and non-depolarizing. One of the advantages of the N,C,S representation of the ellipsometric parameters is that if the sample is depolarizing, the degree of polarization P can also be reported.
The ellipsometric parameters measured on the sample (and reported in either the Ψ/Δ or N,C,S representation) can be further analyzed to determine sample properties of interest, such as film thicknesses and optical constants.