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The performance of an extreme ultraviolet (EUV) photoelectron spectroscopy (EUPS) as a detector of tin (Sn) contamination on ultralow-level surface is studied using a 4.86-nm photon which is generated from boron-nitride plasma. The signal at 130 ns is normalized by the valence band signal at 105 ns to compensate for possible fluctuation of EUV intensity, which shows that Sn debris by laser ablation of ten shots cover the whole surface of a Si wafer. The intensity of the 130-ns peak decreased as the Sn coverage is decreasing. The Sn 4d electron peak having a binding energy of 25 eV was a good indicator of Sn contamination. The EUPS is proved to be sensitive to one atomic-layer contamination and have detect ability of several-percent coverage Sn contamination or 0.3% reflectivity drop.