Importance of Internal Ion Beam Parameters on the Self-organized Pattern Formation with Low-energy Broad Beam Ion Source
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Importance of internal ion beam parameters on the self-organized pattern formation with low-energy broad beam ion sources Marina I. Cornejo, Bashkim Ziberi, Michael Tartz, Horst Neumann, Frank Frost, Bernd Rauschenbach Leibniz-Institut für Oberflächenmodifizierung e.V. (IOM) Permoserstr. 15, D-04318 Leipzig, Germany E-mail: [email protected] ABSTRACT A first qualitative approach to the importance of the divergence angle and angular distribution of the ions within the broad beam (here called internal beam parameters) on the pattern formation by low-energy ion beam erosion is presented. Si (100) surfaces were irradiated with Kr+, with an ion energy of 2 keV, using a Kaufman type broad beam ion source. It is found that the operating parameters of the broad beam ion source which are responsible for the angular distribution of the ions also affect the pattern formation. Especially, the effect of the acceleration voltage, discharge voltage, grid distance and operation time on the transition from ripple to dot pattern with increasing ion beam incidence angle were analyzed. The results represent additional evidence about the significance of the internal beam parameters and the need of the further investigation of their role on the pattern formation by low-energy erosion. INTRODUCTION The low-energy noble gas ion beam erosion of solid surfaces is a simple bottom-up approach for the generation of nanostructures. For certain sputtering conditions well ordered selforganized nanostructures (e.g., ripples, dots) can be formed. Due to the use of broad beam ion sources, low-energy ion beam erosion is particularly suitable as a cost-efficient method to produce large-area nanostructured surfaces in a one-step process. The surface topography evolution is, in general, attributed to the competition of curvature dependant sputtering that roughens the surface and smoothing by different surface relaxation mechanisms [1-5]. It is also well known that the incidence angle of the ions is a critical parameter that determines the surface topography. On Si surfaces, different topographies emerge on the surface due to the bombardment (without rotation of the sample) at different ion beam incidence angles [6]. Ion beam incidence angle refers here to the angle between the substrate normal and the ion source axis (geometrically defined incidence angle). Inherent to all broad beam ion sources, which are essential for large area processing and often used for low-energy ion beam erosion, the ion beam exhibits a certain divergence, i.e. the ion trajectories are not strictly parallel to each other. This generates a spread of the local incidence angles with respect to the geometrically defined ion beam incidence angle. There are only few works about the patterning by low-energy ion beam erosion where the angular distribution was contemplated and considered important for the surface topography evolution [7, 8]. There could be a connection between the variety of results obtained by the different research groups [9-12] and the diverg
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