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Deposition and characterization of non evaporable getter films

Non-evaporable getter (NEG) film coatings were developed at CERN to provide linear pumping for vacuum chambers [1]. These NEG film coatings offer several advantages compared to the existing solutions. Since the whole inner surface of the vacuum chamber can be coated, a large increase of the pumping speed per unit length of chamber is obtained. Additionally, the very clean surface produced by activation reduces significantly both the beam induced desorption [2] and the secondary electron yields [3]. A new approach to the coating technique, the vacuum arc deposition, is proposed at GSI. Vacuum arc deposition might in fact be an interesting alternative to the magnetron sputtering. Its main advantages, compared to the standard sputtering process, are the highly ionized state of the evaporated material, the absence of gases to sustain the discharge (that not only eliminates the rare gas contamination from the film, but also reduces the possible contamination from the impurities present in the sputtering gas or eventually from leaks in the injection line), and the high energy (about 50 eV) of atoms reaching the substrate surface. Its main disadvantage is the production of microdroplets (or macroparticles) emitted from the region of the arc spot, consisting of molten cathode material with typical dimensions in the range from 0.1 to 5 microns [4].