A phase-stepped spectroscopic ellipsometer

We describe a spectroscopic ellipsometer which uses a white light source and a variable wave-plate to generate four phase-stepped intensities I(λ) which are recorded by a small spectrometer. At each wavelength, the wave-plate produces a constant, but unknown phase step α(λ). Carré׳s algorithm is used to determine this unknown phase step at each wavelength which subsequently allows the ellipsometric angles ψ(λ) and Δ(λ) to found from the solution to a set of simple equations. We demonstrate our new instrument experimentally by measuring the retardation of an achromatic wave-plate and determining the thickness of a silicon dioxide film on a silicon substrate.