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There has been considerable attention given to the printability of reticle defects and their impact on wafer yields. Over the last year the printability risk from small defects increased due to the wider application of optical proximity correction structures and the inclusion of more phase shifting retictles. There have been several simulation studies on the printability of sub-halfmicron defects using lens and illumination parameters of 5X reduction steppers. Since submicron 1X projection systems are being incorporated into numerous fabricant lines, there is a clear need to determine if these system show similar sensitivity to sub- halfmicron defects as reduction steppers. Earlier experimental work examined the printability of several classes of sub-halfmicron 25 micrometers defects on a submicron 1X stepper. To extend this work, a 3D optical lithography simulation tool has been employed to predict the printablity of various reticle defect scenarios. Experimental data was used to validate the 3D simulator by comparing modeling data to SEM measurements of wafers exposed with a reticle containing programmed clear pinhole and opaque pindot defects. A statistically designed simulation study was performed to quantify the critical dimension variation resulting from defects of varying size, proximity to a feature edge and variation in the pitch of the impacted line/space features. An additional statistically designed simulation was then use to predict the printability behavior of defects relative to different features sizes over a range of numerical aperture and partial coherence settings applicable to a 1X lens design. Finally, the impact of defect length and width on printability were characterized for rectangular defects over a range of sizes. Overall, this analysis enhances the understanding of the relationship between reticle defects and 1X projection optics and allows for determination of optical reticle defect specifications for cost effective lithography applications.
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