EUV photon induced surface chemistry can damage multilayer mirrors causing reflectivity loss and faster degradation. EUV photo chemistry involves complex processes including direct photon induced surface chemistry and secondary electron radiation chemistry. Current cleaning techniques include dry and wet cleaning of the contaminated mirror surface, which must be performed outside the vacuum chamber. Thus, current cleaning techniques are not desirable for the sake of the productivity. Controlling these processes at multilayer mirror surfaces under EUV conditions can be very beneficial for ASML and its partners. Our goal is to understand these processes and apply newly obtained knowledge in maintaining mirror performance and extending its lifetime. Irradiations of EUV optics with 13.5 nm EUV photons, as well as the generated secondary electrons, drive chemical reactions in the presence of molecular and atomic species, in which the properties of the surface also play an important role. Our investigation employs temperature programmed desorption, and reflection-absorption infrared spectroscopy techniques in a UHV chamber to characterize the binding and chemical composition of molecular adlayers on a Ru(0001) surface. The photochemical reactions of water and deuterium water (D2O) were studied. We found that the dissociation of water on Ru is enhanced by EUV radiation, which leads to oxidation of the Ru surface. The oxidation of the Ru single crystal surface can be considered as the first step of oxidizing a Ru metal thin film, of which the next step is accumulation of oxygen and diffusion into the sub surface layers. The kinetics of oxidation is influenced by a number of factors. By comparing the reactions using water and D2O any isotope effects can be revealed. To understand the dependency on the morphology of the metal substrate, we carefully modify the surface structure by roughening the surface with the aid of ion bombardment. To mimic the polycrystalline nature of the Ru capped multilayer surface, we optimize the ion sputtering and annealing parameters to reproduce the spatial features we observe on Ru capped multilayers using AFM and STM. Furthermore, the dependence of the EUV induced reactions of water on the presence of co-adsorbed species as oxygen, hydrogen or carbon is investigated. This approach will lead to a set of reaction cross sections for EUV induced oxidation as a function of surface morphology, oxygen coverage, hydrogen coverage and carbon coverage.
|Publication status||Published - 20 Jun 2013|
|Event||14th ASML Technology Conference 2013 - Hotel NH Eindhoven Conference Centre Koningshof, Eindhoven, Netherlands|
Duration: 20 Jun 2013 → 20 Jun 2013
Conference number: 14
|Conference||14th ASML Technology Conference 2013|
|Period||20/06/13 → 20/06/13|