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18 October 2004 Smoothing of substrate roughness by carbon-based layers prepared by pulsed laser deposition (PLD)
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In order to obtain high reflectance of EUV and X-ray multilayer mirrors, highly polished substrate surfaces with rms roughness σrms = 0,1-0.2 nm are necessary. However, the simultaneous achievement of low micro-roughness and precise surface figure is very challenging and often not accomplished. Therefore deposition techniques capable to deposit layers with smoothing properties are very desirable. One potential method that enables the formation of such layers is the pulsed laser deposition (PLD). This technique generates particles with high kinetic energies of up to several 100 eV. We investigated the deposition of carbon based smoothing layers by PLD on numerous substrates with roughness between σrms = 0.15 and 0.75 nm using different laser power densities and film thicknesses. Besides pure carbon layers we also used metal/carbon (metal = Ni, W, Pt) multilayers with respect to their capabilities to smooth surface roughness. As a general trend it turns out that a better smoothing can be obtained with higher laser power densities, whereby diamond-like carbon films are created. Furthermore, the intrinsic stress of the smoothing layers has been investigated. Due to the high kinetic energy of the impinging particles during the film growth, the layers show compressive stress. The degree of the stress depends on the concrete metal that is combined with carbon in the multilayer stack. Up to now the lowest compressive stress is obtained with Ni/C multilayers.
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Stefan Braun, Beatrice Bendjus, Thomas Foltyn, Maik Menzel, Jurgen Schreiber, and Andreas Leson "Smoothing of substrate roughness by carbon-based layers prepared by pulsed laser deposition (PLD)", Proc. SPIE 5533, Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications II, (18 October 2004);

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