Printability of nonsmoothed buried defects in extreme ultraviolet lithography mask blanks
Résumé
One of the most important challenges in extreme ultraviolet lithography is the need to provide mask blanks free of defects. In order to provide experimental results on the printability of buried defects, a dedicated extreme ultraviolet (EUV) mask blank was manufactured using ion beam sputtering (IBS) with a nonsmoothing process. Using this kind of process, the effect of the buried defect is apparent throughout the entire multilayer stack. The disturbance generated in the multilayer, measured using an atomic force microscope (AFM), shows lateral growth and a slight vertical smoothing effect. Here we report the printability results obtained with this kind of defect. One result concerns the influence of the defect density on the printability. We show that the major effect can be attributed to local flare, which depends on the pattern density. In order to better understand the printability mechanism of this kind of buried defect, we also compared the experimental results with electromagnetic simulation.