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A hydrogen plasma cleaning technique to clean Sn (tin) off EUV collector optics is studied in detail. The cleaning process uses hydrogen radicals and ions (formed in the hydrogen plasma) to interact with Sn-coated surfaces, forming SnH 4 and being pumped away. This technique has been used to clean a 300mm-diameter stainless steel dummy collector optic, and EUV reflectivity of multilayer mirror samples was restored after etching Sn from them. Previous experiments have shown etch rates of greater than 10 nm/min over a 2 inch diameter circular plasma area with an SWP launcher. An etch experiment was conducted with a sweep over sample bias to investigate the influence of hydrogen ions. Radial etch rates for each hydrogen ion energy were measured using profilometry. Langmuir probe and radical measurements were also taken. Langmuir probe measurements of the surface wave plasma show a two temperature distribution for electrons: a bulk temperature of 2.3 eV and some population at 8.6 eV. The bulk electron density was measured to be 2.7e11 cm -3 . Radical probe measurements give the hydrogen radical density at 1.96e15 cm -3 . A COMSOL model of this experiment was also built and simulation results will be presented. In this work, experiments elucidating the fundamental processes of tin removal are conducted by varying pressure, power, surface temperature and gas flow rate. The ion bombardment reduces the number of radicals needed to etch a single tin atom to the range of -. The linear SWP antenna yields plasma densities on the order of and radical densities on the order of , allowing for greater utilization of ion etch enhancement. Etch rates of up to 200 nm/min have been achieved. The surface temperature of the samples is an important factor in the etching process such that decrease of the surface temperature increases the etch rates and decreases the hydrogen desorption rates. In addition, a kinetic etch model is developed to explain the behavior of the etch rates as function of the surface temperature. Furthermore, results from experiments performed in Illinois NXE:3100 chamber will be discussed.
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