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 $O2.$ For an $O2/Ar$ 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.