Ultra-thin Cr 2O 3 well-crystallized films for high transmittance APSM in ArF line

Abstract

Ultra-thin Cr 2O 3 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 O 2 at 350 °C. 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 Cr 2O 3 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 Cr 2O 3 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 Cr 2O 3 well-crystallized thin film that satisfies the optical requirements was fabricated.