A Zr–Al composite-cathode sputter-ion pump

Abstract

The performance of a diode sputter-ion pump which has a pair of cathode plates made of Zr and Al has been studied. The main purpose of the study was to reduce the memory effect of prepumped gases, especially hydrogen. Sputtered Zr and Al atoms from each cathode plate form deposits of Zr–Al alloy which have gettering properties superior to those of pure Zr or Al. Results showed that trapping on the sputtered deposits reduced the re-emission of trapped gases from the sputtered region by ion bombardment. The composition of the deposited layers was determined by Auger electron spectroscopy. The pumping characteristics of the Zr–Al cathode were compared to a Ti cathode of the same configuration. Ratios of the pumping speeds (SZr–Al/STi), at 10−5 Pa are 1.8 and 3.3 for N2 and Ar, respectively. Re-emission of D2 by subsequent pumping of Ar was measured after 1.3×10−2 Pa m3 of D2 were pumped by each cathode. At an Ar pressure of 1×10−5 Pa, re-emission of D2 for the Zr–Al cathode is less than 40% of that for the Ti cathode.