Importance of Internal Ion Beam Parameters on the Self-organized Pattern Formation with Low-energy Broad Beam Ion Sources

Abstract

AbstractThe low energy ion beam erosion of solid surfaces is a simple bottom-up approach for the generation of nanostructures. For certain sputtering conditions caused by self-organization processes well ordered nanostructures on the surface like one-dimensional ripples or regular arrays of dots can be formed [1]. Using broad beam sources, the low energy ion beam erosion can be a cost-efficient method to produce large-area nanostructured surfaces in a one-step process.The processes involved have been studied in the last decades and the pattern formation is attributed to the competition of curvature dependant sputtering and various relaxation mechanisms. It is also well known that the ion beam incidence angle (the angle between the sample surface normal and the axis of the beam source) is one critical parameter that determines the surface topography. However, inherent to all broad beam sources, the ion beam exhibits a certain divergence, i.e. the ion trajectories are not parallel to each other. This generates a spread of the local incidence angle with respect to the geometrically defined beam incidence angle.Recent studies showed that the divergence angle and angular distribution of the ions, here called internal beam parameters, also affect the surface topography [2].The angular distribution can be controlled by the total voltage applied on the geometrical defined ion optical system of the broad beam ion source. For the given multi-aperture two-grid ion optical system the total voltage is the sum of the voltages applied to the first (screen) and second (accelerator) grid. This total voltage, together with the geometrical characteristics of the used grid systems, including the shape of the plasma sheath boundary at the screen grid, define the overall ion-optical parameters of the source, i. e. the divergence angle and angular distribution of the ions within the beam.In this contribution a first approach of the effect of the internal beam parameters on the surface topography is presented. It was analyzed the effect on the topography on Si surfaces of some experimental parameters that affect the internal beam parameters by changing the ion-optical parameters and the shape of the plasma sheath boundary. Explicitly, the influence of the discharge voltage, the operation time and the distance between the screen and accelerator grid is shown.[1] B. Ziberi, M. Cornejo, F. Frost, B. Rauschenbach, J. Phys.: Condens. Matter (submitted).[2] B. Ziberi, F. Frost, M. Tartz, H. Neumann, B. Rauschenbach, Appl. Phys. Lett. 92, 063102 (2008)