Optical materials for microlithography applications

SCHOTT ML (MicroLithography) is presented as the world's first supplier of optical materials for all current generations of wafer steppers: i-line-glasses for 365 nm, fused silica for 248 nm/193 nm and CaF2 for 193-nm microlithography. I-line-glasses are presented optimized in transmission, solarization and refractive index homogeneity for application in high performance i-line-scanner systems for sub 0.25 mu m mix and match technology. The focus for fused silica is laid on laser damage performance, essential for application in 193 nm lithography. An experimental setup is shown, allowing a fast evaluation of materials respecting laser induced fluorescence and absorption. First data of a 193 MI marathon test on SCHOTT ML fused silica are presented. Use of CaF2 in ArF projection optics requires improvement of crystal growth processes and equipment. The progress achieved in refractive index homogeneity, stress birefringence and transmission is presented. High laser damage resistance for ArF illumination optics was also accomplished. Common requirement for mass production of all high grade optical materials is the ability for accurate material characterization. Status of measurement and characterization equipment is presented for selected optical properties.