Aaron, as you certainly know, it is not only the mask but, I believe, the all optics elements, suffering from similar problems. Defectivity problem solution was, and I think still is art rather than science, or maybe better to say, science-loaded art... I was involved in CMP since its early introductory stages into the IC fabrication, and the same outcry (Defects!!! Particles!!! Scratches!!!) was loudly voiced from every corner. Not anymore. The EUV optics defectivity problem, I believe, will be resolved, just a good team of right people with deep understanding of Physics and Chemistry of material transformations induced by 90 eV photons, or maybe better to say by quite energetic secondary electrons. 10-100 eV electrons are extremely chemically active and are inducing quite a complex set of surface and near surface chemical material transformations (physi-to-chemisorption, adsorbate fragmentation, surface charge driven material migration, accumulation and consequent polymerizaton at the charged spots. And a couple of other specific features, which alltogether can yield formation of bumps or pits. People in e-beam surface inspection know well about these e-beam induced material transformations for years. A couple of concepts helping to reduce these effects down to the current specifications is known, and similar approaches could be helpful mand should be considered for the EUV optics and masks. Also the quality of substrate slabs, as far as I know, is also super critical, and here the CMP and especially the post-CMP clean experience could be very helpful.
Sorry for writing these notes during the Yom Kippur day.
Aaron, here is one more point to add. For CMP it was resolved by a strongly focused teams of technologists at IBM and Intel. Technologists, with deep understandings of Processes, Physics, and especially Chemistry, not equipment engineers, were driving this effort. This is what, I think, is needed in the EUV situation, a focused team and a right leadership.
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