ARTIFICAIL CRYSTAL MEMBER, EXPOSURE SYSTEM, AND PRODUCTON METHOD FOR EXPOSURE SYSTEM

摘要

An artificial crystal member capable of being used as an optical element such as a prism and various optical elements constituting an optical integrator in a device using as a light source an ultrasonic laser such as an excimer laser having a wavelength shorter than 250 nm. An exposure system comprising a lighting optical system for lighting a mask using as a light source a laser beam having a wavelength shorter than 250 nm, and a projection optical system for projecting and exposing the pattern image of the above mask onto a substrate to be exposed, wherein disposed in the lighting optical system and/or the projection optical system is an optical element consisting of an artificial crystal member that has an initial transmittance with respect to a light with a wavelength of 150 nm of at least 60% per cm, striae of a first class or second class as defined by Japanese Optical Glass Industry Standard (JOGIS), an absorption coefficient alpha in an infrared absorption band of hydroxyl positioned at 3585 cm<-1> of up to 0.035/cm, an aluminum content of up to 1 ppm and a lithium content of up to 0.5 ppm.