Evolution of Atomic-Scale Surface Structures During Ion Bombardment: A Fractal Simulation

November 1, 1993

J. Vac. Sci. Technol., A ,11, 3085-3091 (1993).

Shaheen, M. A., Ruzic, D. N.

Surfaces of interest in microelectronics have been shown to exhibit fractal topographies on the atomic scale. A model utilizing self-similar fractals to simulate surface roughness has been added to the ion bombardment code trim. The model has successfully predicted experimental sputtering yields of low energy (less then 1000 eV) Ar on Si and D on C using experimentally determined fractal dimensions. Under ion bombardment the fractal surface structures evolve as the atoms in the collision cascade are displaced or sputtered. These atoms have been tracked and the evolution of the surface in steps of one monolayer of flux has been determined. The Ar–Si system has been studied for incidence energies of 100 and 500 eV, and incidence angles of 0°, 30°, and 60°. As expected, normally incident ion bombardment tends to reduce the roughness of the surface, whereas large angle ion bombardment increases the degree of surface roughness. Of particular interest though, the surfaces are still locally self-similar fractals after ion bombardment and a steady state fractal dimension is reached, except at large angles of incidence.