A novel setup for spectroscopic ellipsometry using an acousto-optic tuneable filter

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Abstract
A rotating‐analyzer ellipsometer for fast measurements at multiple wavelengths as well as for spectroscopic measurements has been developed. The most important novelty of the setup is the use of an acousto‐optic tuneable filter (AOTF) as dispersing element. This offers advantages with respect to the speed of measurement, the adjustment of the intensity of the light, the use of lock‐in techniques, and the stability and size of the setup. Advantages and limitations of the use of AOTF’s in ellipsometry as well as possible changes in the ellipsometric setup are discussed. The ellipsometer has been mounted on an electron cyclotron resonance plasma deposition chamber. As an example, the deposition of amorphous hydrogenated carbon layers has been studied in situ and are compared to ex situ measurements by variable angle of incidence spectroscopic ellipsometry of the same samples.