Multilayer coating requirements for extreme ultraviolet lithography masks

摘要

To meet critical dimension control error budgets for extreme ultraviolet lithography (EUVL) tools, the reflectivity bandpass of multilayers on the mask must be well matched to the bandpass of the optical system in the exposure tool. The reflectivity bandpass and peak reflectivity of the mask multilayers must also be highly uniform to minimize illumination uniformity errors in the exposure tool. Calculations were performed to determine the required mask multilayer matching to exposure tool optics. Calculated ideal reflectivity curves and measured reflectivity versus wavelength values for typical masks made with ion beam sputtering and for the coatings on the optics for the Engineering Test Stand (ETS) were used. The impact on the mask coating requirements when using more than 6 multilayer-coated optics in production exposure tools was also quantified. To meet error budgets established for the ETS, the mask multilayer coating centroid wavelength at all points in the image field should be 13.334+-0.040 nm, and peak reflectivity must be uniform to within +-0.5% absolute. A roadmap is proposed for mask multilayer reflectivity requirements for future industry roadmap nodes.