Investigation of electrode-driven hydrogen plasma method for in situ cleaning of tin-based contamination

To prolong the service life of the optics, the feasibility of <i>in situ</i> cleaning of multilayer mirror (MLM) of tin and its oxidized contamination was investigated using hydrogen plasma at different powers. Granular tin-based contamination consisting of micro and macro particles was deposited on the silicon by physical vapor deposition (PVD). The electrode-driven hydrogen plasma at different powers was systematically diagnosed using the Langmuir probe and the retarding field ion energy analyzer (RFEA). Moreover, the magnitude of the self-biasing voltage was measured at different powers, and the peak ion energy was corrected for the difference between the RFEA measurements and the self-biasing voltage (Ε_RFEA-eV_self). XPS analysis of O 1s, Sn 3d peaks demonstrated the chemical reduction process after 1 W cleaning. Analysis of surface and cross-section morphology revealed the holes emerged on the upper part of the macroparticles while its bottom remained smooth. Hills and folds appeared on the upper part of the microparticles, confirming the top-down cleaning mode with hydrogen plasma. This study provides <i>in situ</i> electrode-driven hydrogen plasma etching process of tin-based contamination and is of meaningful guidance for understanding the chemical mechanism of reduction and etching.