Morphological changes of Si(100) induced by focused ion beam irradiation

High current density (∼1 A cm−2) scanning focused Ga and Au ion beams of a few tens of keV are employed to modify Si(100) surfaces under high and ultra-high vacuum conditions. The morphology of the substrate is measured in air using atomic force microscopy. The ion-irradiated areas are found to protrude to different heights in nanometer scales depending on the dose, energy and current density of the ion beam as well as the vacuum conditions. Small height differences are observed in the areas irradiated by Ga and Au ions of comparable energies. The results indicate that protrusions are caused by a combination of beam-induced amorphization of the crystal and beam-induced deposition of the residual gas. By carefully adjusting the beam current and the scanning scheme, the effect of residual gas deposition can be practically eliminated even under high vacuum conditions.