In order to overcome roughening and charging of the Zerodur® substrate for extreme ultra violet lithography (EUVL) optics during 0.5-10 keV Ar+ion beam machining, we had already proposed a method in which a thin Si layer was deposited on the Zerodur® substrate and figuring the deposited Si layer. In this experiment, in order to get smoother surface than Si layer, carbon which has smaller atomic size than that of Si was deposited on the Zerodur® substrate. Then, we investigated ion energy and machined depth dependence of the surface roughness of the carbon layer machined by Ar+ion beam in the range of 0.3-3 keV and obtained the following results; surface roughness of the carbon layer machined by 1.0 keV Ar+ion beam to the machined depth of 50 nm becomes 0.08 nm rms and this value is smaller than that (0.12 nm rms) of Si. Therefore, the proposed processing method can be applicable for the figuring of substrates for EUVL projection optics. © 2011 Elsevier B.V. All rights reserved.
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