Determination of optical constants in the VUV range for fluoride thin films

Laser applications in semiconductor industry, metrology and medical applications call for improvement and reliable optical coatings in the short wavelength range. Especially, optical coatings for ArF and F2 laser systems are important for micromachining and lithography applications. For designing and manufacturing multilayer, a good knowledge of refractive indices and absorption coefficients of the coating materials is essential. The intrinsic absorption of fluoride coating materials tends to higher values in the DUV/VUV spectral range, the reliable determination of absorption losses by photometric techniques has to overcome various obstacles caused by light absorption in air, scattering effects of the coating, and absorption related to contamination of the employed fluoride material. In this paper, high-refractive-index materials such as LaF3, NdF3, and GdF3 and low-refractive-index materials such as MgF2, AlF3, and Na3AlF6 single thin films are deposited by a resistive-heating boat at different deposited rates and specific substrate temperatures on single crystal MgF2 substrates. Transmittances of all fluoride thin films are measured through business spectrometer in the ambient atmosphere and measured under vacuum through Synchrotron radiation in the wavelength region from 120nm to 500nm. The optical constants of these materials are determined from Envelope method and iterative algorithm with transmittance measurements. All this work play an important role in the design and manufacturing of cost-effective, mechanically and optically stable optical coatings for VUV region.