Optical simulation, optimized design and fabrication of (ZrO 2) x–(Al 2O 3) 1− x composite films with thin inserted TiO 2 layers for ArF-line high transmission attenuated phase shift mask blank applications

Abstract

The tunable optical constants of the stoichiometric (ZrO 2) x –(Al 2O 3) 1− x composite films with thin inserted TiO 2 layers are simulated as π-phase shifters. The optimized composition range of the superlattices to be used as a high transmission attenuated phase shift mask (HT-APSM) blank is found. The absorption edge shifts to the longer wavelengths when the thickness fraction of the TiO 2 layer increases. The optimized film for ArF-line HT-APSM blank applications must have the lower inspection transmittance for the better inspection and the lower reflectance at the exposure wavelength for a better aerial image as π-phase shifters, and they will be easier to fabricate than a superlattice. In order to find such a film, (ZrO 2) x –(Al 2O 3) 1− x composite films with various inserted TiO 2 layers are simulated. The optimal deposition processes of such a film are also determined. For example, a (ZrO 2) 0.187–(Al 2O 3) 0.813 composite film with two inserted TiO 2 thin layers is fabricated. The optical properties are as follows: a transmittance of 19.8%, a reflectance of 9.1%, a calculated phase shift of ∼181.5° at the exposure wavelength of 193 nm, and a transmittance of 18.9% at the inspection wavelength of 257 nm. Such a film should be used as an optimized HT-APSM blank.