Depth profiling of Mo/Si multilayers: the effect of Ar-ion energy on layer structure

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Periodic molybdenum silicon multilayers can be used as reflecting optical elements for many applications including extreme ultra-violet lithography (EUVL) as a most demanding example. Key task is to develop these artificial Bragg reflectors with properties as close as possible to natural, crystal Bragg reflectors. In the EUVL application the stack of 3 to 4 nm thick layers that forms the multilayer shows a close to perfect reflectance of about 70% with a theoretical limit of 75%, indicating relative small interface thickness compared to the layer thickness. Usually Ar-ion erosion of these structures together with either X-ray Photo-electron Spectroscopy or Auger Electron Spectroscopy is used to investigate the in-depth layer composition, but the erosion process can affect the structure. Therefore, we studied the Ar erosion process in detail. Variable ion energy was used in the range of 0.25 to 2 keV to erode a molybdenum silicon multilayer. The underlying in-depth concentration profile was reconstructed by using Hoffman’s MRI approach [1] and Cumpson’s estimate for attenuation lengths [2]. It is shown that the resulting in-depth profile of these multilayers is to a large extent erosion energy dependent. Furthermore, due to this erosion dependency, it is found that the less surface sensitive X-ray Photo-electron Spectroscopy provides a better estimate for the in-depth elemental concentration profile than can be obtained by Auger Electron Spectroscopy.
Original languageEnglish
Place of PublicationParis, Fr
Publication statusPublished - 2011


  • METIS-304974


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