Ultra-thin Cr2O3 well-crystallized films for high transmittance APSM in ArF line

Ultra-thin Cr2O3 well-crystallized thin films are deposited on UV grade fused silica substrates and Si wafers by using r.f. reactive unbalanced magnetron sputtering from a Cr metal target in an atmosphere of Ar and (X at 350DGC. The optical constants of such thin films were found to be a sensitive function of oxygen-to-argon flow rate ratio. At the ratio of 0.2, a Cr2O, well-crystallized thin film with appropriate refractive index and extinction coefficient at a wavelength of 365 nm can be used as attenuated phase-shifting mask (APSM) blank as well as being good for inspection. The simulated thickness range of a Cr2O3 well-crystallized thin film was found to be between 28.2 and 30.3 nm. This meets the optical requirements for high transmittance APSM (HT-APSM) with a transmittance of 18-20% at 193 nm for the pattern fabrication and with transmittance less than 50% at 365 nm for the mask inspection. One such Cr2O3 well-crystallized thin film that satisfies the optical requirements was fabricated.