A STUDY OF CR-AL OXIDES FOR SINGLE-LAYER HALF-TONE PHASE-SHIFTING MASKS FOR DEEP-ULTRAVIOLET REGION PHOTOLITHOGRAPHY

A large optical band gap chromium aluminum oxide (Cr1-xAlx)(2)O-3 for deep-ultraviolet photomask applications has been studied using DV-X al pha cluster method and RF sputtering. Theoretical analyses indicate th at the electronic structure and energy gap depend not only on the subs tituted elements but also un the structural relaxation after substitut ion. The energy gap (E-gu) between the highest occupied molecular orbi tal (HOMO) of O2p and the lowest unoccupied molecular orbital (LUMO) o f Cr3d increases almost linearly from 4.28: to 5.21 eV with the increa se of Al concentration is) in the range of 0-0.75. It is expected that a significant increase of such E-gu could happen when x is in the reg ion between 0.8 and 1.0. The evaluation of RF sputtered AI-Cr oxide th in films shows that the material exhibiting variable optical band gap up to 5.6 eV has been obtained which is larger than that of Cr2O3 (E-g approximate to 4.25 eV). The deep-UV region transmittance of 5-20% at reasonable film thickness of about 122 nm reveals the feasibility of such films to be used in single-layer halftone phase-shifting mask (SL HTPSM) photolithographic applications in the exposure wavelength regio n between 170-200 nm.