The impact of secondary electrons induced contamination of the Ru surface was investigated. Mirror-like Ru sample
was bombarded with low energy (100 eV) electrons and the change in surface chemistry was investigated using X-ray
photoelectron spectroscopy (XPS).Along with XPS studies the corresponding effect on in-situ EUV reflectivity
was examined by exposing the Ru surface to photons at a wavelength of 13.5 nm in an ultrahigh vacuum chamber.
Detailed XPS analyses showed a sudden increase in carbon concentrations on the Ru surface in the first 60 min,
followed by a slow but linear growth in carbon concentration. In parallel, a noticeable decrease in water content was
observed during the time of electrons irradiation along with slight oxidation of pure Ru surface. All chemical
changes were discussed in terms of the electrons bombardment mediated dissociation of water and hydrocarbon
molecules. A time dependent EUV reflectivity measurements show insignificant change in reflectivity up to 510 min
of electrons bombardment. The impact of water molecules on the Ru surface and the accumulation of carbon
through dissociation of residual hydrocarbons is discussed in details.
We investigated Ru mirror contamination and subsequent EUV reflectivity loss using the IMPACT facility at Purdue
University. Because Ru can either be used as a grazing mirror or as a capping layer for multilayer normal mirror, we
examined the angular dependency of XPS peak area intensity at the O 1s and Ru 3d regions as well as the effects of
sputtering. Although no change in intensity has been observed at lower take-off angles from the target surface, the peak
area intensity starts changing with increasing θ (i.e., emission observation angle, representing the angle between the
target surface plane and detector entrance). Among different components, the effect of water and oxidized carbon are
found to be most notable when viewed at lower θ, and primarily responsible for degrading the reflectivity of the Ru
layer. On the other hand, the effect of OH becomes dominant with increasing observation angle θ, and thus plays a key
role to suppress optical transmission. Moreover, atomic carbon effect is found to peak when observed at 30°, and most
likely plays an important role in degrading both reflectivity and transmission. This is also because of the total photon
path length in the Ru film at different angles. During the contamination process, the EUV reflectivity of the Ru film is
found to significantly degrade in the presence of additional secondary electrons from the focusing Ru mirror of the EUV
setup. This effect could be explained in the light of a competition between oxidation and carbonization processes on Ru
surface.
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