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Combination of X-ray reflectometry and optical spectroscopy as a new tool for thin films parameter determination

: Pflug, A.; Ruske, F.; Sittinger, V.; Werner, W.; Szyszka, B.

Puetz, J. ; Leibniz-Institut für Neue Materialien gGmbH -INM-, Saarbrücken:
Advanced coatings on glass & plastics for large-area or high-volume products : Proceedings of the 5th International Conference on Coatings on Glass, ICCG 5, July 4 - 8, 2004, Congress Hall, Saarbruecken, Germany
Saarbrücken: INM, 2004
International Conference on Coatings on Glass (ICCG) <5, 2004, Saarbrücken>
Fraunhofer WKI ()
film characterization; X-ray reflectometry; optical spectroscopy; thickness determination

The optical determination of thin film parameters like thickness and complex refractive index is a standard tool to assist the developpement of funcional multilayer stacks. For dielectric films with a thickness of least 1000 nm, ellipsometry in combination with reflectrance and transmittance is known to be adequate to determinate the relevant parameters with good accuracy. However, for thin films with d << 100 nm or films that exhibit a more complicated dielectric function, e.g. transparent conductive oxides, information obtained only by optical spectroscopy can be insufficient. With X-ray reflectometry, an alternate tool for analyzing very thin films is available. As the refractive index in the X-ray regime is very close to unity, a very precise film thickness determination is possible even at a film thickness well below 100 nm, while this method is utilizable for thickness up to 300 nm. The simulation system RIG-VM developed at Fraunhofer IST is capable to combine both methods within a thin film parameter determination by simultaneously fitting off all available spectra. In this work the determination of optical constance of very thin Al2O3 films on glass by combination of those methods is demonstrated. Furthermore, the improved accuracy in the evaluation of optical filters comprising sequences of high- and low-index materials will be shown.