Anode layer ion source links for use in a powerful glow discharge plasma cleaner.
" Ion beams have several advantages over glow discharges for in-situ cleaning. An ion beam is much more selective in that the energetic ions can be directed at a substrate, resulting in the removal of contaminants only from the substrate and immediately adjacent surfaces. The ability to vary the ion energy independently of other parameters is also important. For removal of physisorbed contaminants such as water vapor and hydrocarbons from the laboratory environment, low ion energy are effective and energies of less than 100 eV avoid damage to, or significant sputtering of, the substrate surface. An effective cleaning dose for removal of physisorbed contaminants is quite small - less than one mA-sec/cm2 On the other hand, higher ion energies can be used for the removal of chemisorbed layers, such as native oxides. The stronger chemisorbed bonds generally require ion energies of at least 100 eV, with the required dose calculated from the sputter yield of the contaminant and its thickness. The lower background pressure is a major advantage for ionbeam cleaning. The background pressure depends on the vacuum pumping used, but is usually in the 10-4 Torr range, resulting in mean free paths that are thousands of times longer than in glow-discharge cleaning. These longer paths greatly increase the likelihood that contaminants, once they are removed from the substrate surface, will be pumped from the vacuum chamber before they can return to that surface. The low background pressure also permits the deposition of a thin film to start rapidly after cleaning, thereby minimizing the new contamination that can accumulate between the cleaning and deposition steps. The rule-of-thumb is that a monolayer of contamination can accumulate in one second from a contaminant background pressure of 10-6 Torr. But it is important to remember that the background pressure of the contaminant is what counts, not the total background pressure which is typically almost all argon. " - Source