Abstract: Causes of intra field critical dimension variation using KrF scanner for 0.18 micrometer lithography have been investigated. Scanner is different from traditional stepper system. Scanner might have synchronization error, which results in degrading contrast over full intra field. Aberration of illumination optics brings about coherence difference between field center and edge. In a scanner system, vertical patterns (cross scan direction) are geometrically tangential, and horizontal patterns are sagittal. Such a H/V different ray tracing results in horizontal pattern having better contrast than vertical one under diffraction limited design rule patterning. Mask error can be a very critical issue in 4X system. Focus drift and exposure dose change during scan exposing result in intra field CD variation, and some stray light is a cause of intra field CD variation also. !9
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