Imaging characteristics of 0.12 μm dynamic random access memory pattern by KrF excimer laser lithography

Imaging characteristics of a 0.12 mum dynamic random access memory (DRAM) cell pattern by KrF excimer laser lithography are investigated by optical image calculations. Using modified illuminations optimized for specific patterns and an attenuating phase shift mask (atten-PSM), depth of focus (DOF) can be achieved up to similar to0.8 mum with high numerical aperture (NA) of 0.70-0.75. However, the image quality is significantly degraded by lens aberration of -0.06 lambda in root-mean-square optical pass difference (RMS-OPD), which is observed in a stepper for 0.25 mum generation devices, Accordingly, the development of a low aberration lens is necessary to realize 0.121 mum DRAM cell pattern formation by KrF excimer laser lithography.