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Deep ultraviolet out-of-band characterization of EUVL scanners and resists

As Extreme Ultraviolet Lithography (EUVL) gets closer to production, an increasing interest is devoted to Deep Ultraviolet Out-of-Band (DUV OoB). In fact, EUV sources are known to emit a broad spectrum of wavelengths, among which DUV could potentially contribute to the exposure and degrade imaging performance. In this paper, the DUV/EUV ratio in pre-production (ASML NXE:3100) and alpha (ASML ADT) EUVL scanners is investigated. The OoB is quantified using a previously proposed methodology [1] based on the use of an aluminum-coated mask capable to provide quantitative in situ information on DUV/EUV ratio without disrupting the tool. The OoB sensitivity of an extensive set of resists is estimated in order to properly guide material development. The impact of OoB on imaging and on Intra-Field Critical Dimension Uniformity (IF CDU) is quantified using resists with large differences in OoB sensitivity. In addition, the impact of mask design on OoB is also investigated. The results indicated that it is in fact possible to reduce the OoB sensitivity of a resist (from 2.5 down to 0.3%) without compromising imaging performance and that tool OoB qualification and monitoring are critical in a production environment.