Dot Pattern Formation on Silicon Surfaces by Low-Energy Ion Beam Erosion
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Dot Pattern Formation on Silicon Surfaces by Low-Energy Ion Beam Erosion B. Ziberi, F. Frost, T. Höche# and B. Rauschenbach Leibniz-Institut für Oberflächenmodifizierung e.V., Permoserstrasse 15, 04318 Leipzig, Germany. # also affiliated with: 3D-Micromac AG, Max-Planck-Straße 22b, D-09114 Chemnitz, Germany.
ABSTRACT Experimental studies of low-energy (≤ 2000 eV) Ar+ ion beam erosion of Si surfaces under normal and oblique ion incidence with simultaneous sample rotation at room temperature show a variety of topographies. At oblique ion incidence, between 70° and 80° with respect to surface normal, dot patterns evolve (dot size ~ 30 nm) with a remarkably high degree of ordering comparable to dot nanostructures reported for different III/V compound semiconductors. The mean size and ordering of these nanostructures can be adjusted by various process parameters like ion beam energy and erosion time, respectively. Scanning force microscopy (AFM) has been used to characterize the evolution of the surface topography.
INTRODUCTION Various approaches for the fabrication of nanostructures with dimension below 100 nm on macroscopic areas are known. In contrast to cost-intensive top-down lithographic techniques, various bottom-up methods based on self-organization to form large arrays of nanostructured surfaces have been developed [1-3]. Low-energy ion sputtering or erosion of solid surfaces is a promising alternative approach for the generation of self-organized nanostructures. It is well known that under certain conditions sputtering can roughen the surface resulting in a pronounced topography evolution in some cases producing well-ordered patterns, like ripples or dots [4-7]. For the technological most important semiconductor, silicon, the results reported so far are partly controversial. Dot patterns were observed on Si surfaces after 1200 eV Ar+ ion beam bombardment at normal ion incidence, but the degree of ordering of nanostructures is much less compared to III/V semiconductors [8]. By using a slightly lower ion energy (1000 eV) no dot patterns were found on Si surfaces [9]. Additionally, different kind of nanostructures with two distinct individual length scales were reported for normal ion incidence and ion energies ≤ 500 eV [10]. In this work recent results for pattern formation on Si surfaces caused by low-energy Ar+ ion beam erosion (Eion ≤ 2000 eV) at normal or oblique ion incidence with simultaneous sample rotation (i.e., no anisotropy on surface topography evolution is expected), at room temperature are summarized. In particular, it is demonstrated that complex pattern formation processes do arise during erosion of Si surfaces. Depending on ion beam parameters remarkably high ordered dot patterns with structure sizes below 50 nm can be obtained. Also the influence of ion energy and erosion time on the evolution of the nanostructures and their ordering are studied.
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EXPERIMENT The samples used in this work were standard epi-polished (100) Si substrates with a root-meansquare (rms) roughness
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