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1 April 2008 Sub 50 nm cleaning-induced damage in EUV mask blanks
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Defects are still one of the main challenges of extreme ultraviolet (EUV) mask blanks. In particular, a majority(~75%) of substrate defects are nanometer size pits. These pits are usually created during final surface polishing of the synthetic, quartz glass substrates. This study presents data that indicates cleaning may also induce pits in the substrate surface. These pits are typically 20 nm and larger, and are contained in a circular area on the surface, which is scanned by a megasonic nozzle during cleaning. Concentrated collapse of cavitation bubbles in the areas scanned by megasonic is expected to be one of the main mechanisms of pit creation. The data indicates the existence of a hard surface layer with an estimated thickness of approximately 30 to 60 nm, which is resistive to pit creation. After this layer is removed, the number of pit defects present on the substrate increases dramatically with megasonic cleaning. It is also demonstrated that, within the detection limits of the atomic force microscope (AFM), the size of a pit does not change due to cleaning.
© (2008) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Abbas Rastegar, Sean Eichenlaub, Vivek Kapila, Arun John Kadaksham, and Pat Marmillion "Sub 50 nm cleaning-induced damage in EUV mask blanks", Proc. SPIE 6921, Emerging Lithographic Technologies XII, 692120 (1 April 2008);


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