Laser-induced damage and defect analysis of calcium fluoride window caused by the high pulse repetition rate of ArF excimer laser radiation

The lifetime of optics, especially windows, has grown to reach 100 Bpls, and its evaluation lasts for several years at least. In elementary testing (short term), focusing on each damage phenomenon must be established. The degradation of calcium fluoride windows used as laser chamber windows in ArF excimer lasers (193-nm wavelength, 30-ns pulse width, 10-mJ output energy, ~80-mJ/cm2, 6-kHz and several dozen billion pulses) is analyzed. The results of analysis such as TEM-EDX, Nomarski-type differential interference contrast (DIC) microscope, AFM, etc. is shown. The damage mechanism can be estimated from these results. Comprehensive durability evaluation becomes more efficient by creating accelerated element tests (short term).