A method of ion beam sputtering fluoride films for a production environment.
By Aiko Ode, Veeco Instruments
Thin film coatings for deep UV wavelengths are predominately produced by evaporation methods (thermal and Ebeam). Factors limiting the performance of evaporated films include surface roughness, porosity, absorption, and defect density. To enhance the films, they are typically deposited at high substrate temperatures (above 300°C.) The thermal stress created upon cooling down from the deposition temperature often restricts these films to be deposited on fluoride substrates. Efforts to improve the quality and performance of deposited fluorides films includes the use of ion beam sputtering. While the energy of ion beam sputtering removes some of the fluorine atoms during the sputtering process, this deficiency was compensated for by introducing a fluorine base gas in the deposition environment. A method of ion beam sputtering fluoride films suitable for a production environment using a commercially available dual ion beam sputtering system is presented in this work. The resulting optical and material properties as well as suitable substrates are discussed for AlF3, LaF3, and GdF3 films. Results for both single layer and multilayer coating designs are presented. Results are focused on the 193 nm wavelength of the ArF excimer laser.
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