title: Detection and characterization of carbon contamination on EUV multilayer mirrors.
abstract: 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.
authors.affiliation: FOM-Institute for Plasma Physics Rijnhuizen, Nieuwegein, The Netherlands. J.Chen@rijnhuizen.nl
authors.forename: Juequan
authors.initials: J
authors.lastname: Chen
authors.forename: Eric
authors.initials: E
authors.lastname: Louis
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Lee
authors.forename: Herbert
authors.initials: H
authors.lastname: Wormeester
authors.forename: Reinhard
authors.initials: R
authors.lastname: Kunze
authors.forename: Hagen
authors.initials: H
authors.lastname: Schmidt
authors.forename: Dieter
authors.initials: D
authors.lastname: Schneider
authors.forename: Roel
authors.initials: R
authors.lastname: Moors
authors.forename: Willem
authors.initials: W
authors.lastname: van Schaik
authors.forename: Monika
authors.initials: M
authors.lastname: Lubomska
authors.forename: Fred
authors.initials: F
authors.lastname: Bijkerk