Abstract
Stoichiometric amorphous Ta 2O 5 and Al 2O 3 thin films and (Ta 2O 5) x /(Al 2O 3) 1 − x multilayer coatings have been successfully deposited on UV grade fused silica by r.f. reactive unbalanced magnetron sputtering in an atmosphere of argon and oxygen. When the O 2/Ar flow-rate ratio is larger than 1, the Al and Ta are completely oxidized. Due to lower reflectance at the exposure wavelength, three-stack (Ta 2O 5) x /(Al 2O 3) 1 − x coatings better aerial images can be produced. The thickness fraction range of Ta 2O 5 in the three-stack (Ta 2O 5) x /(Al 2O 3) 1 − x coatings is found to be between about 27% and about 47% for 193 nm attenuated phase-shifting mask blanks and between about 24% and about 38% for 248 nm high-transmittance attenuating phase-shift masks (HT-AttPSM) blanks. One three-stack (Ta 2O 5) x /(Al 2O 3) 1 − x coating is fabricated for HT-AttPSM with an optimized transmittance of 19% at a wavelength of 248 nm and the other one with maximum transmittance at a wavelength of 193 nm. The three-stack (Ta 2O 5) x /(Al 2O 3) 1 − x coating can be used to design a desirable 193 or 248 nm wavelength (HT-)AttPSM under these conditions.
Published Version
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