The optical constants of composite films are linearly dependent on their mole fraction. The (Al2O3)(x)-(TiO2)(1-x) composite films prepared by using rf unbalanced magnetron sputtering are completely oxidized using an O-2/Ar flow rate ratio of 2.0. By tuning the Al2O3 mole fraction of (Al2O3)(x)-(TiO2)(1-x) composite films, the optical constants can be made to meet the optical requirements for a high transmittance attenuated phase shifting mask (HT-AttPSM) blank. It can be seen that the Al2O3 mole fraction in (Al2O3)(x)-(TiO2)(1-x) composite films which would best meet the optical requirements of a HT-AttPSM blank in ArF (immersion) lithography is calculated to be between 78% and 86%. In order to obtain a HT-AttPSM blank with an optimized transmittance of 20%, one Al2O3-TiO2 composite film is fabricated. All the films meet the requirements of the adhesion test and surface roughness for HT-AttPSM applications. Therefore, a single layer composite film of Al2O3-TiO2 could be applied to HT-AttPSM blanks, which can be utilized to design fine patterns with dimensions as small as 65, 45, and 32 nm. (C) 2007 American Vacuum Society.