Optical property simulation of single-layer halftone phaseshifting masks for DUV microlithography

Abstract

An optical simulation for a single-layer halftone phaseshifting mask (SLHTPSM) has been established and verified by the experimental data from several different sources. This simulation is suitable for a wide lithography exposure wavelength; for example, i-line, Krf and ArF etc. Theoretical analyses give some important tendencies of the optical parameters such as refractive index, extinction coefficient and film thickness. The optimum SLHTPSM structures for KrF (248 nm) have been derived by the simulation processes, which include the optimized combinations of extinction coefficient/refractive index and film thickness/refractive index achieved to deliver the 5%, 10% and 20% transmittance and 180 degrees phaseshifting. The simulation shows the film refractive index to be in the region of 1.7-3. The simulation program also provides guidance for the SLHTPSM fabrications.