Sputtering Yields for Gold Using Argon Gas Cluster Ion Beams

Measurements are reported of the sputtering yields of gold using Ar n + gas cluster ion beams of energies E of 5, 10, and 20 keV with 100 ≤ n ≤ 5000. In measuring the sputtering yields for 30 nm gold layers on silicon wafers with a thin thermal oxide, the analysis is conducted using SIMS with 25 keV Bi 3 + primary ions. The measured Au t – signals for 1 ≤ t ≤ 6 show an enhancement of intensity beyond the Au/SiO 2 interface arising from the presence of the oxide on the Si wafer, but this intensity enhancement is reduced by a factor t –1.38 between the secondary ions so that it may be removed to establish the sputtering dose at the interface. The sputtering yield, Y, so determined, exhibits a consistent dependence of Y / n on E / n for all beam energies showing that their effects are linearly additive in this regime (i.e., doubling the number of atoms in the cluster at the same energy per atom doubles the total yield). An empirical description of these sputtering yields is provided for 100 ≤ n ≤ 5000. The trend at low n values is consistent with Sigmund and Claussen’s thermal spike model valid here for 1 ≤ n ≤ 10. This confirms that the maximum yields occur for 10 ≤ n ≤ 200. No indication of a threshold below which sputtering ceases was found.