Spectral reflectrometry and white-light interferometry used to measure thin films

Two different spectral-domain techniques based on reflectometry and white-light interferometry are used to measure spectral characteristics of thin-film systems. A technique of spectral reflectometry uses a standard configuration with a halogen lamp, a reflection probe and a thin-film system under test to record the reflection spectrum over a wide range of wavelengths. A new white-light spectral interferometric technique uses a slightly dispersive Michelson interferometer with a cube beamsplitter to measure the phase spectra of reflective or transparent thin-film systems over a wide range of wavelengths. This technique is based on a Fourier transform method in processing the recorded spectral interferograms to obtain the ambiguous spectral fringe phase function. Then, using a simple procedure based on the linear dependence of the optical path difference between beams of the interferometer on the refractive index of the beamsplitter material, the ambiguity of the spectral fringe phase function is removed and the beamsplitter effective thickness and the phase spectrum of the thin-film system are determined.