Composition profile of ion-plated Au film on Cu analyzed by AES and SIMS during Xe ion bombardment

Abstract

An ion-plated 7-μ thick Au film on a Cu sheet was prepared by using a conventional ion-pumped system with 10−2 Torr of back-filled argon. The film was sputter etched at a rate of 0.5 Å/sec by 1-keV, 12-μA/ cm2 Xe ions. Sputtered species were anlyzed by a quadrupole mass spectrometer (QMS), while a cylindrical mirror Auger electron analyzer was producing spectra of the surface. The simultaneous observation was carried out throughout the sputter etching from the 7-μ-thick Au film to the bare Cu surface. Na and K ions were the predominant peaks in the observed secondary ion mass spectra (SIMS), whereas these species were less evident in the Auger spectra. Calibration for Na peaks for both spectrometers were made. Two plausible sources of these alkali species are (i) contributions from the peripheral area of ion bombardment and (ii) impurities produced in the proximity of the ion gun. Experiments reveal that the extent of Na impurities from (i) and (ii) are separated in the interpretation of the SIMS profile; for example, they are 3.7×10−9 and 1.8×10−9 A, respectively, at the average depth of 1 μ, while the current expected from the calibration is 2.5×10−9 A as AES gives 0.5% of monolayer of Na in the same depth. A full in-depth composition profile shows that impurities segregate in the top 3-μ layer and in the interface.