The absorption of fused silica, CaF2, MgF2, and sapphire at VUV region (193.4 nm) and IR region (1070 nm) were measured. For this measurement, LID (Laser Induced Deflection) method was used because of its high sensitivity. We report the degradation behavior of materials by comparison of absorption before and after ArF laser irradiation, and also the ultra-minute absorption at IR wavelength. At each wavelength, the absorption of low OH fused silica before the laser irradiation showed the smallest. At ArF wavelength, sapphire and CaF2 showed higher laser durability than MgF2 and fused silica. At IR wavelength, VUV-transmissive sapphire showed a lower absorption compared to general sapphire.
Fluoride materials are typically used as optical coatings for Deep UV applications such as semiconductor lithography
steppers/scanners equipped ArF excimer laser (193nm). To extend its lifetime, laser durability of fluoride optical
coatings deposited by conventional thermal evaporation method were investigated. From relation between coating
defects amount and LIDT, it was apparent the laser durability of fluoride multilayer coatings are strongly spoiled by their
coating defects. These defects are observed by naked eyes, Nomarski microscopy, AFM and SEM for more details.
Finally it was found that defects broke the coating structures.
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.
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