Analysis of Thermally Induced Distortion of Optics for Soft-X-Ray Projection Lithography,
SANDIA NATIONAL LABS ALBUQUERQUE NM
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The development of less systems for soft x-ray projection lithography presents significant challenges associated with the fabrication and testing of ultra-precise optical surfaces. Once assembled, these projection lenses must further be dimensionally stable to tolerances determined by the wavelength of the soft x-rays used for illumination, typically between 100 A and 300 A. Lens systems capable of printing over large areas will contain a number of mirrors with reflectivities in the range of 6010. For these systems, the first element will be subjected to a significant incident x-ray flux, of which about 40 will be absorbed in the multilayer coating. This absorbed power causes differential thermal expansion from temperature gradients and, hence, distortion of the optical surface. These thermal distortions should be less than about 10 angstroms in order to preserve accuracy.