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Optical Engineering

Reflectivity and surface roughness of multilayer-coated substrate recovery layers for EUV lithographic optics
Author(s): Ileana Nedelcu; Robbert W. E. van de Kruijs; Andrey E. Yakshin; Bernhard von Blanckenhagen; Fred Bijkerk
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Paper Abstract

We investigated the use of separation, or substrate recovery, layers (SRLs), to enable the reuse of optical substrates after the deposition of multilayer reflective coatings, in particular Mo/Si multilayers as used for EUV lithography. An organic material (polyimide), known from other work to reduce the roughness of the substrate, was applied to the optical substrate. It appeared to be possible to remove the multilayer coating, including the SRL, without any damage or roughening of the substrate surface. The SRL was spin-coated at 1500 to 6000 rpm on different substrate types (Si, quartz, Zerodur) with diameters up to 100 mm. For this range of parameters, the multilayer centroid wavelength value remained unchanged, and its reflectivity loss on applying the SRL was limited typically to 0.7%. The latter was shown to be caused by a minor increase of the SRL surface roughness in the high-spatial-frequency domain. The roughness, characterized with an atomic force microscope, remained constant at 0.2 nm during all stages of the substrate recovery process, independent of the initial substrate roughness.

Paper Details

Date Published: 1 June 2008
PDF: 5 pages
Opt. Eng. 47(6) 063801 doi: 10.1117/1.2939403
Published in: Optical Engineering Volume 47, Issue 6
Show Author Affiliations
Ileana Nedelcu, FOM-Instituut voor Plasmafysica Rijnhuizen (Netherlands)
Robbert W. E. van de Kruijs, FOM-Instituut voor Plasmafysica Rijnhuizen (Netherlands)
Andrey E. Yakshin, FOM-Instituut voor Plasmafysica Rijnhuizen (Netherlands)
Bernhard von Blanckenhagen, Carl Zeiss SMT AG (Germany)
Fred Bijkerk, FOM-Instituut voor Plasmafysica Rijnhuizen (Netherlands)

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