Laser durability improvement of deep UV fluoride coatings

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.