Irradiation Effects of Gas-Cluster Ar Ion Beams on Solid Surfaces

Gas-cluster ion beams can be applied to new surface modification techniques such as surface cleaning, low damage sputtering and shallow junction formation. The effects of energetic Ar cluster impacts on solid surface were studied for cluster energies of 10–30keV. A nozzle-skimmer system was constructed which allowed for generation and acceleration of gas-cluster ions, in-situ analysis of cluster size by electron diffraction, mass-separation by retarding fields and measurement of total ion dose. Irradiation effects were studied by RBS and ellipsometry. The sputtering yield from Cu films, using Ar 300 clusters with acceleration voltage 30kV, was estimated to be 285/ion (i.e.0.95/atom). This value was higher than the sputtering yield of monomer Ar ions having the same energy per atom. A very flat Cu surface was obtained after irradiation with Ar clusters, which indicates lateral sputtering at the surface. For Si(111) substrates, irradiated with Ar ≥500 clusters to a dose of 1 × 10 15 ions/cm 2 at acceleration voltage 15kV, 2 × 10 14 atoms/cm 2 implanted Ar atoms were detected. In this case, the energy per cluster atom was smaller than 30eV; at this energy, no significant implantation occurs in the case of monomer ions.