Detection and characterization of carbon contamination on EUV multilayer mirrors

Juequan Chen, Eric Louis, Chris J. Lee, Herbert Wormeester, Reinhard Kunze, Hagen Schmidt, Dieter Schneider, Roel Moors, Willem van Schaik, Monika Lubomska, Fred Bijkerk

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In this paper, we detect and characterize the carbon contamination layers that are formed during the illumination of extreme ultraviolet (EUV) multilayer mirrors. The EUV induced carbon layers were characterized ex situ using spectroscopic ellipsometry (SE) and laser generated surface acoustic waves (LG-SAW). We show that both LG-SAW and SE are very sensitive for measuring carbon layers, even in the presence of the highly heterogeneous structure of the multilayer. SE has better overall sensitivity, with a detection limit of 0.2 nm, while LG-SAW has an estimated detection limit of 2 nm. In addition, SE reveals that the optical properties of the EUV induced carbon contamination layer are consistent with the presence of a hydrogenated, polymeric like carbon. On the other hand, LG-SAW reveals that the EUV induced carbon contamination layer has a low Young’s modulus (<100 GPa), which means that the layer is mechanically soft. We compare the limits of detection and quantification of the two techniques and discuss their prospective for monitoring carbon contamination build up on EUV optics.
Original languageEnglish
Pages (from-to)16969-16979
Number of pages11
JournalOptics express
Issue number19
Publication statusPublished - 2009


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