Optical properties of CrO/ZrO optical superlattice for attenuated phase shifting mask at 193 nm wavelength

CrO/ZrO optical superlattices composed of ten film stacks with ∼9 nm thickness in each stack are obtained in a duel-gun rf magnetic sputtering system. By controlling the thickness percentage of ZrO in a CrO/ZrO stack and the flow-rate ratio of O 2/Ar, the optical requirements for optical superlattices being used as APSM blanks can be met. The dielectric constants of CrO/ZrO optical superlattices are shown to fit the effective medium approximation, and the calculated transmittance, reflectance and total film thickness of CrO/ZrO optical superlattices may thus serve as π-phase shifters.