Dispersion-controlled low-coherent interferometry for thin-film characterization

In this work, a novel experimental procedure for thin-film characterization and its data analysis is described. The presented technique is based on low-coherence interferometry and resolves thicknesses with nm-precision. An element with known dispersion is placed in the interferometer's sample arm and delivers a controlled phase variation in relation to the wavelength. This phase variation is dependent on the thickness of the material and its wavelength-dependent refractive index. Furthermore, the phase variation is characterized by a stationary point, the so called equalization wavelength. Changes in the thickness of the material under test will shift the equalization wavelength and transform its interference amplitude. In combination with an imaging spectrometer thin films are spatially resolved with a spatial resolution of 4 μm within a single acquisition. This makes data acquisition fast. The advantage over other conventionally used methods, like reflectometry and ellipsometry, is that signal processing is greatly simplified and therefore much faster