Aberration effects in the region of 0.18-μm lithography with KrF excimer stepper

Abstract

The most critical issues for lithographers, resolution, depth of focus, exposure latitude and proximity effect, have been frequently discussed. In addition to those issues, lens aberration effects such as astigmatism, coma, field curvature and distortion have been emphasized in view of process stabilization. Deep UV lenses have undergone improvements in the field curvature, distortion, and other aberrations to the point that they can be implemented for near quarter micron patterning. KrF excimer laser stepper and scanner have made Deep UV technology as a practical choice for lithographers to develop their own DRAM processes. In order to adopt process development beyond the region of ultimate resolution limit, precise lens aberration analyses are necessary. KrF excimer laser stepper (NA equals 0.55), used for 0.18 micrometers design rule patterning, is examined. Several types of real device pattern, such as word and bit line, active, storage node, contact hole patterns, are tested under various illumination conditions (conventional, various partial coherence, off-axis illumination). These results are compared with simulation results.