Flare effect of different shape of illumination apertures in 193-nm optical lithography system

Flare has been important variable to obtain good CD control in the resolution limited lithography area such as sub-90 nm node. So far, many papers have been reported about how to measure flare and how flare impact on CD control. And some papers have tried to understand theoretical mechanism of flare. However, we expect that the illumination apertures such as the partial coherence factors or the modified illumination aperture shapes would also give impact on the flare. The short-range flare is changing as the open ratio variation on the mask. We assume that the illumination aperture shape change will also give similar effect as the open ratio variation on the mask. In this paper, we will show how the illumination aperture shapes give effect on short- range flare. Experiments were done for 100 nm lines surrounded by clear window having different width from 1 mu m to 20 mu m. We utilized the 193 nm scan-and-step exposure tool with the partially coherent conventional and off-axis illuminations apertures. In conclusion, we will prove the relationship between flare and illumination apertures.