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Mechanical stress in fluoride coatings

: Ullmann, J.; Keck, H.G.; Thielsch, R.; Uhlig, H.; Kaiser, N.

Amra, C. ; European Optical Society -EOS-; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Advances in Optical Interference Coatings : 25 - 27 May 1999, Berlin, Germany
Bellingham, Wash.: SPIE, 1999 (Europto series)
ISBN: 0-8194-3212-1
Conference on Advances in Optical Coatings <1999, Berlin>
Conference Paper
Fraunhofer IOF ()
evaporation; fluorides; high reflectors; stress; thin optical films

The mechanical behavior of fluoride single layers and thick model layer systems were carried out ex-situ after deposition at laboratory conditions. The samples on substrates with different thermal expansion coefficients have been prepared by a low loss evaporation process. Investigation were performed for single layers deposited at different film thickness, substrate temperature and storage time. All investigated fluorides posses tensile stress of various amounts. The thermal stress component seems to be the major contribution to the total stress MgF2 films of about 100 nm thickness deposited onto silicon substrate. The stress and force per unit width of model multilayer systems formed from different fluorides were examin ed and correlated to the ability of crack formation on thick rigid fused silica substrates. Optimization of the stress values, the bending force and the crack formation was performed by adjusting the deposition temperature and by introducing a third stress re ducing m aterial in the stack. An example of a stress optimized high reflector will be shown.