Time dependent changes in 13.5 nm extreme ultraviolet (EUV) reflectivity of Ru mirrors due to variations in surface composition were investigated. The surface properties of Ru films were analyzed in situ by means of X-ray photoelectron spectroscopy (XPS), and further verified by Auger electron spectroscopy (AES). Moreover, the impact on EUV reflectivity (EUVR) with time was examined in situ via continuous and/or discrete EUV exposures. The rapid decrease in EUVR was observed in the presence of photoelectrons (PEs) from Ru mirror of the EUV setup, whereas no significant variation was recorded by screening out additional PEs. Detailed XPS and AES analyses suggest that carbon deposition via dissociation of residual hydrocarbons plays a dominant role in the presence of additional PEs, and thus reduces the reflectivity rapidly. Using EUV photoelectron spectroscopy, systematic reduction of the secondary electron yield from the Ru mirror surface was observed in consecutive scans, and therefore supports the formation of carbonaceous Ru surface in the presence of additional PEs. V

Extreme ultraviolet (EUV) radiation mediated carbon contamination and oxidation of the Ru mirror surface, and the corresponding impact on reflectivity were studied. In particular, time-dependent systematic decrease in EUV reflectivity with a 13.5 nm wavelength of light in high vacuum atmosphere was recorded and correlated with the change in chemical composition on the Ru surface as derived from in situ x-ray photoelectron spectroscopy (XPS). The contamination on Ru surface is caused by residual impurities of the test chamber. The recorded XPS spectra show a sudden increase in carbon concentration in the first 1 h followed by a slow but linear growth in the presence of EUV radiation. Further analyses show a slight increase in Ru oxide, whereas the concentration of water molecules decreases continuously. Moreover, the carbon monoxide level at the surface was stabilized after initial increase in concentration for an hour. The impact of water molecules and the accumulation of carbon atoms on the Ru surface are discussed in details.

A real time contamination of the Ru surface and corresponding effect on its work function were studied using extreme ultraviolet photoelectron spectroscopy with a 13.5-nm wavelength of light. The change in work function indicates formation of molecular dipoles, oriented outward from the Ru surface. X-ray photoelectron spectroscopy investigations suggest variation in electromagnetic interaction with the components of the adsorbed foreign species when the emission angle from the target surface was changed from 0 to 50 ; H 2 O and C-O n show a strong coupling at lower angles and OH dominates at higher angles, whereas carbon is found in the mid-range peaking at 30 .In order to continue the steady growth of the semiconductor industry, next generation computer chips are required to have features as small as 20 nm. To meet this goal, next generation photolithography systems are looking to employ extreme ultraviolet (EUV) radiation at a wavelength of 13.5 nm. The mirrors to be used in these systems consist of alternating layers of Mo and Si. 1 Because there are concerns about potential oxidation of the surface Si layer, a thin Ru protective layer has often been used on the top Si layer. 1 A Mo/Si multilayer mirror with a Ru capping layer can reflect up to 70% of the EUV light 2 near normal incidence. 3 Ruthenium films can also reflect 92 eV photons at a grazing angle. 4 Since short wavelengths can be attenuated by most materials 5 and even by background gases, 1 an EUV lithography system requires a vacuum chamber. Now, the issue is how to keep the optics clean, as carbonaceous and/or oxidized Ru surfaces are often formed during EUV exposure and, as a consequence, degrade the overall reflectivity of Mo/Si mirrors. Several cleaning processes 1 have been proposed to circumvent and mitigate this problem. In fact, a large number of groups have been working on understanding the processes involved to mitigate the oxidation and/or carbonization of the top Ru layer (Ref. 6 and references therein). 6 It has so far been established that the secondary electrons from the Ru surface mainly take part in dissociating hydrocarbons and/or water molecules under EUV radiation, 6 creating chemically active fragments on the Ru surface. 7 Although several reports are available in the literature that deal with EUV radiation-induced growth of contaminants on Ru surfaces, 8 knowledge of the adsorption dynamics and of the emission angle (h from the target surface) dependency are still scarce. In fact, detailed analyses of the latter will help to figure out which of the components of the adsorbed species are mainly responsible for degrading the mirror performance.In this communication, we show real time contamination of the Ru surface in the presence of a 13.5-nm wavelength of light using EUV photoelectron spectroscopy (EUPS). This approach is extremely surface sensitive due to low photoelectron escape depth. 9 Using the measured cutoff energy shift, we show the formation of dipoles on the Ru surface. The in situ angular-resolved x-ray photoelectro...

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Extreme ultraviolet (EUV) radiation induced growth of carbon and oxygen desorption were investigated on a Ru surface by Auger electron spectroscopy (AES) in the presence and absence of additional photoelectrons (PEs) from a focusing Ru mirror. A decrease in EUV reflectivity with carbon growth in the presence of additional PEs has been observed. Conversely, a carbonaceous Ru surface was cleaned in sequential AES, and discussed in terms of secondary electron assisted dissociation of residual hydrocarbons and water molecules, followed by a chemical reaction between adsorbed carbon and oxygen atoms. V

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Primary electron energy (E p) dependent change in target current was studied on a grounded Au film in the range of 40 to 3500 eV. The current jumped suddenly from a negative to a positive value at $650 eV with increasing E p , while it disappeared in reverse sweep and with increasing substrate temperature. Detailed analysis suggests that E p dependent surface charging plays a pivotal role in flashover. Prior to critical E p in the forward sweep, a gradual shift of a double peaklike structure towards high kinetic energy region in the secondary electron spectra also confirms surface charging effect. V

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