In the F2 laser lithography, it is essential to reduce the loss of the optical coatings deposited on calcium fluoride lenses. In order to make low loss optical coatings, we have developed measurement apparatus, evaluated the coatings with various analyses, and found a correlation with the optical constants. In this paper we describe the optical loss measurement apparatus and the evaluation results analyzed for either single layer coatings or multi-layer anti-reflection coatings.
A new Coblentz type scatterometer is developed for evaluation of 157-nm optical coatings. The Coblentz hemisphere has ellipsoidal design for higher sensitivity and stability. The scatterometer works under nitrogen atmosphere keeping away from the organic contamination. Some kind of antireflective coatings are obtained from several Japanese suppliers and evaluated by the scatterometer. Results of the scatter measurement are almost equal except one sample that includes Na3AlF6 layer as low refractive index material. Its extremely high scatter loss could be ascribed degradation by reaction to the water in the air.
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