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 • 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.

Optimal phase shift mask and multilayer stack with the evaluation of imaging performance and process latitude in extreme ultraviolet high numerical aperture

“…( 1) was used to improve the contrast by setting the phase difference between the absorption region and the reflection region at 180°. 18) λ is the wavelength of EUV light, θ is the angle of incidence, and n 1 and n 2 , d 1 and d 2 are the refractive coefficients and thicknesses of thin films 1 and 2, respectively. However, an additional 0.2 π phase shift may be required to compensate for the phase difference caused by the mask 3D effect.…”

“…A recent study reported by van Lare et al showed that for EUV imaging, a 1.2 π phase shift is crucial for good performance. 19,20) The effect of the PSM can be maximized when the thickness of the phase shift layer, refractive index, and extinction coefficient are matched to the wavelength of light 18) p l q…”