EVOLUTION OF ATOMIC-SCALE SURFACE-STRUCTURES DURING ION-BOMBARDMENT -A FRACTAL SIMULATION

Surfaces of interest in microelectronics have been shown to exhibit fr actal topographies on the atomic scale. A model utilizing self-similar fractals to simulate surface roughness has been added to the ion bomb ardment code TRIM. The model has successfully pred ed experimental spu ttering yields of low energy (less then 1000 eV) Ar on Si and D on C u sing experimentally determined fractal dimensions. Under ion bombardme nt 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 be en determined. The Ar-Si system has been studied for incidence energie s of 100 and 500 eV, and incidence angles of 0-degrees 30-degrees, and 60-degrees. As expected, normally incident ion bombardment tends to r educe the roughness of the surface, whereas large angle ion bombardmen t increases the degree of surface roughness. Of particular interest th ough, the surfaces are still locally self-similar fractals after ion b ombardment and a steady state fractal dimension is reached, except at large angles of incidence.