Standing wave effect of various illumination methods in 0.25 mu m KrF excimer laser lithography

Illumination dependence of the standing wave effect was investigated by experiment and simulation in variously sized line and space (L&S) patterns. A chemically amplified positive resist and a KrF excimer laser stepper with 0.5 Nrl (numerical aperture) were used under various defocus conditions. The amplitude of the swing curve increased with increasing defocus value and showed complicated illumination dependence. At a focused position, higher a (partial coherence) and oblique illuminations induced a larger amplitude of tile swing curve; however, in the defocused region of +/-0.6 mu m, necessary for actual device fabrication, the amplitudes of these illuminations were smaller than that of low a illumination. Moreover, it was found that tile amplitude variation was closely related tu the log-slope value of exposure light intensity distribution at the nominal pattern edge.