Ultrathin TiO2 amorphous films for high transmittance APSM blanks at 157 and 193 nm wavelength simultaneously

Ultrathin TiO2 amorphous films are deposited on ultraviolet grade fused silica substrates and CaF2 by using rf reactive unbalanced magnetron sputtering from a Ti metal target in atmosphere of Ar and O-2. For an O-2/Ar flow rate ratio of more than 1.5, the deposited TiO2 thin films are stoichiometric. TiO2 thin films that meet the optical requirements of a high transmittance attenuated phase-shifting mask (HTAPSM) at 157 and 193 nm wavelengths can also be properly inspected since the transmittance at 257 nm wavelength is less than 28%. The simulated thickness range of such a TiO2 thin film is found to be between 16 and 20 nm. A TiO2 amorphous thin film with thickness of 23.5 nm, transmittance of 24.9% and reflectance of 15.0% at wavelength of 193 nm, transmittance of 16.3% at 157 nm wavelength and transmittance of 23.0% at 257 nm wavelength is shown to be able to serve as an absorber layer for HTAPSM blanks at 157 and 193 nm wavelength. (C) 2003 American Vacuum Society.