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6 May 1985 Design And Fabrication Of Carbon-Tungsten Multilayers Using Ellipsometry
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Recently, there has been increased interest in near normal incidence optical sytems for use in the soft x-ray domain (10Å < A < 100A). This region of the x-ray spectrum is important because many organic constituents have their K-absorption edges in this range. One important application of near normal incidence soft X-rays optical systems is lithography, for which 44.7Å radiation is particularly well suited. Hence we have concentrated our studies at this wavelength. Stacks of alternating layers with low and high electron densities can be used to obtain mirrors with substantial reflection coefficients. We have developed a model to obtain the optical properties of such a stack in a fashion similar to that used for visible light. This model can be shown to be quite accurate for near normal incidence and for wavelengths long compared to the interatomic spacing. We have also shown from this model that a smooth, 200 layer, carbon-tungsten stack would provide a reflectivity of approximately 25% at 44.7Å when used in normal incidence. Sputtering techniques (diode, triode) were used to produce carbon-tungsten multilayers with each tungsten film approximately 10A thick. Grazing X-ray reflection and X-ray photoelectron spectroscopy have shown that layers with minimal roughness and adequate densities have been achieved. The dielectric functions for the materials have been determined by ellipsometry. We have been able to calculate and to show experimentally that an ellipsometry monitoring system allows very precise in-situ control of layer growth. Calculations and preliminary measurements show the use of ellipsometry to achieve an ideal multilayer growth.
© (1985) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Eric Ziegler, Philippe Houdy, and Louis Nevot "Design And Fabrication Of Carbon-Tungsten Multilayers Using Ellipsometry", Proc. SPIE 0563, Applications of Thin Film Multilayered Structures to Figured X-Ray Optics, (6 May 1985);

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