Self-ion sputtering yield determinations of (100) nickel thin films

Several methods for determining the sputtering yield of a nickel thin film have been examined. One of the more promising techniques is based on measuring the change in electrical resistance of the single-crystal film on its NaCl substrate. This is done as the thin film thickness is decreased by sputtering with 180 keV nickel ions. Since the resistivity of the material is altered only slightly by the ion beam, the measured resistance is expected to increase as the film thickness decreases during sputtering. Plotting the reciprocal resistance vs. time initially results in the anticipated straight line and this is followed by a non-linear portion of the plot. The non-linearity accompanied the complete erosion of the thin film and the ion-beam interaction with the NaCl substrate. The starting thickness of the film was measured using three independent techniques to complete the determination of the sputtering rate. These techniques included optical interference microscopy over a step, transmission electron microscopy of a cross-section of the film prepared using an ultra-microtome, and measuring the characteristic X-ray yield from the film when it was excited by 100 keV electrons and comparing this yield with that from a nickel sample of known thickness. The sputtering yield measured in this manner for the film oriented perpendicular to the ion beam and with the ion beam along a <100> direction was 3.2±0.5 nickel atoms per incident ion. (orig.)