Characterization of an ultrahigh vacuum sputtering system

Abstract

The design and characterization of a custom-designed ultrahigh vacuum sputter deposition system capable of background pressures in the 10−9 Pa range is described. Four pressure gauges, a Bayard–Alpert nude ion gauge, a cold cathode gauge, a capacitance manometer, and a spinning rotor gauge were available to characterize the system performance. The useful lower limit of the 133 Pa capacitance manometer was 3×10−2 Pa. Above that value, it was in good agreement with the spinning rotor gauge. The hot filament ion gauge was compared to the spinning rotor gauge over the range 510−5–5×10−2 Pa. The ion gauge was then used to determine the sensitivities of the partial pressure analyzers. Two residual gas analyzers, an open source and a closed-source instrument were used to measure partial pressures in the system. Both open- and closed-source instruments showed significant scatter in sensitivity at pressures below 10−5 Pa. The useful range of the closed source analyzer was limited to pressures above 10−6 Pa. Below this pressure, background currents prevailed. It was found that these background currents limited the sensitivity of the closed source analyzer when used at sputtering pressures. Finally, the total gas contamination in the system at sputtering pressures was shown to be system, rather than source gas, limited. This contamination was shown to be less, when this system was configured with a helium gas cryogenic pump than with a turbomolecular pump. However, the speed of the cryogenic pump system was somewhat greater than that of the turbomolecular pump system. Some of that reduction in contamination could be attributed to increased pumping speed.