Simulations of mask error enhancement factor in 193nm immersion lithography

Abstract

In general, better resolution and lower mask error enhancement factor (MEEF) are obtained when a higher numerical aperture (NA) is used. However, simulations in this study show that, if Y-polarized light and off-axis illuminations were used, higher NA leads to higher MEEF for smaller and dense feature line sizes in 193nm immersion lithography. The reversal of the MEEF was clearly observed, especially in the presence of a dipole. When the feature size decreased to the resolution limit, the MEEF rose enormously. Simulations also show that the MEEF is inversely proportional to the cubic root of image contrast in most cases in this study.