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A hybrid algorithm for reengineering the refractive index profile for inhomogeneous coatings from optical in-situ broadband monitoring data

: Wilbrandt, S.; Stenzel, O.; Gäbler, D.; Kaiser, N.

Guangxue-jingmi-gongcheng = Optics and precision engineering 13 (2005), No.4, pp.487-491
ISSN: 1004-924X
Journal Article
Fraunhofer IOF ()
inhomogeneous coating; hybrid algorithm; broadband monitoring; refractive index profile

Reengineering the refractive index profile of inhomogeneous coatings is a troublesome task. Multiplicity of solutions may significantly reduced by providing additional information. For this reason an in-situ broadband monitoring system was developed to measure the transmittance of the growing film directly at the rotating substrate. For characterization of these coatings a new model was developed, which significantly reduces the number of parameters. The refractive index profile may be described by a proper number of equally spaced volume fraction values using the Bruggeman effective media approach. A good initial approximation of the refractive index profile can be generated based an deposition rates for both materials recorded with quartz crystals monitor during manufacturing. During the optimisation process, a second order minimization algorithm was used to vary the refractive index profile of the whole coating and film thickness of the intermediate stages. Finally, a significantly improved accuracy of the modelled transmittance was achieved