Imaging characteristics of 0.12 /spl mu/m DRAM pattern by KrF lithography

Abstract

Feasibility of 0.12 /spl mu/m DRAM pattern formation by KrF lithography is investigated by optical image calculations. Using modified illumination optimized for the specific pattern and attenuating phase shift mask (PSM), depth of focus (DOF) can be achieved up to /spl sim/0.8 /spl mu/m under high numerical aperture (NA) of 0.75. However, the image quality is significantly degraded by lens aberration. Accordingly, the development of low aberration lens is inevitable to realize 0.12 /spl mu/m DRAM by KrF lithography.