Today’s EUV masks are optimized for maximum reflectivity at 6o angle of incidence to support imaging on the 0.33NA scanners. The High-NA EUV scanner will have an NA of 0.55 and anamorphic optics, as right balance between productivity and keeping the angles on mask level compatible with the current EUV masks. However, for selected use-cases increased Mask-3D effects are observed. The enlarged angular spread on mask for vertical L/S may cause, amongst others, an increased non-telecentricity variation across slit compared to 0.33NA, potentially leading to on-product overlay errors. In this paper, we will show the root-cause of these enhanced M3D effects for High-NA EUV and the role of the EUV mask multilayer. We will show how an ideal EUV multilayer could look like to mitigate these M3D effects and propose a practical embodiment in the form of a RuSi multilayer stack. We will show some first experimental results of an ion beam deposited RuSi test sample, assess the main challenges from manufacturability point of view and what imaging performance can be expected for such a mask multilayer applied for High-NA EUV.
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