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Development and investigation of high-quality CaF2 used for 157-nm microlithography

The 157 nm lithography technology is supposed to become the system setup for the 100 nm respectively the 70 nm node. The first 157 nm Full-Field Scanner system is expected in 2002. Every currently evaluated optical design of such lithography systems makes a very intensive use of Calcium Fluoride as one of the few optical materials having the required transmittance at the F2 laser wavelength solely. Additionally the required further industrial production processes e.g. polishing and development of coatings are known from the 193 nm lithography where CaF2 is already in use. In this paper we report about R&D activities of the material development used for the high quality CaF2. Thus the main aspects on quality are discussed in detail.