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Towards ultra-precise optical interference filters on large area: Computational and experimental optimization of the homogeneity of magnetron-sputtered precision optical coatings

: Vergöhl, M.; Pflug, A.; Rademacher, D.


Ramón Navarro (Ed.); Colin R. Cunningham (Ed.); Eric Prieto (Ed.) ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II : 1.-6.7.2012, Amsterdam, Netherlands
Bellingham, WA: SPIE, 2012 (Proceedings of SPIE 8450)
ISBN: 978-0-8194-9151-0
Paper 84502J
Conference "Modern Technologies in Space- and Ground-based Telescopes and Instrumentation" <2, 2012, Amsterdam>
Fraunhofer IST ()

The optimization of the uniformity of high precision optical filters is often a critical and time consuming procedure. The goal of the present paper is to evaluate critical factors that influence the thickness distribution on substrates during a magnetron sputter process. A new developed sputter coater "EOSS" was used to deposit SiO2 and Nb2O5 single films and optical filters. It is based on dynamic deposition using a rotating turntable. Two sets of cylindrical double magnetrons are used for the low and the high index layers, respectively. In contrast to common planar magnetrons, the use of cylindrical magnetrons should yield a more stable distribution during the lifetime of the target. The thickness distribution on the substrates was measured by optical methods. Homogenization is carried out by shaping apertures. The distribution of the particle flow from the cylindrical magnetron was simulated using particle-in-cell Monte Carlo plasma simulation developed at Fraunhofer IST. Thickness profiles of the low index and the high index layers are calculated by numerical simulation and will be compared with the experimental data. Experimental factors such as wobbling of the magnetron during rotation, geometrical changes of critical components of the coater such as uniformity shapers as well as gas flow variations will be evaluated and discussed.