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Reduction of absorption losses in ion beam sputter deposition of optical coatings for the visible and near infrared

Absorption losses in ion beam sputtered films of SiO2 and TiO2 were examined. Two different processes contribute to the absorption of the films. The first process is the incorporation of impurities from the target itself, the ion source and the target surroundings into the films. The second is the damage of the films if a too large amount of energy is transferred to them by the sputtered and reflected particles. Impurity incorporation was minimized by a special coating chamber configuration and the use of electron cyclotron resonance ion and electron sources. The contaminations are examined by Secondary Ion Mass Spectrometry, using ion implantations for quantification. The influence of the main impurity parts on absorption is determined by controlled addition of impurities to the films. Experimental results show a large influence of the sputter gas, the reactive gas flow and the kind of target on absorption. Numerical sputter simulations revealed the correlation of these results with energy transport to the films. Reducing energy deposition in the films reduces their absorption. Low absorption in ion beam sputtering can only be achieved using metal targets.