Swift Heavy Ion Irradiation Induced Effects in Si/SiO x Multi-Layered Films and Nanostructures
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Swift Heavy Ion Irradiation Induced Effects in Si/SiOx Multi-Layered Films and Nanostructures J. W. Gerlach1, C. Patzig1, W. Assmann2, A. Bergmaier3, Th. Höche1, J. Zajadacz1, R. Fechner1, and B. Rauschenbach1 1 Leibniz-Institut für Oberflächenmodifizierung, Permoserstrasse 15, D-04318 Leipzig, Germany 2 Ludwig-Maximilians-Universität München, Maier-Leibnitz Laboratory, Am Coulombwall 6, D-85748 Garching, Germany 3 Universität der Bundeswehr München, Werner-Heisenberg-Weg 39, D-85577 Neubiberg, Germany
ABSTRACT Amorphous Si/SiOx multilayered films and nanostructures were deposited on Si substrates by the glancing angle deposition technique using Ar ion beam sputtering of a Si sputter target in an intermittent oxygen atmosphere at room temperature. The chemical composition of the samples was characterized by time-of-flight secondary ion mass spectrometry, as well as - for quantifying these first results - by elastic recoil detection analysis using a 200 MeV Au ion beam. The latter method was found to lead to a significant alteration of the sample morphology, resulting in the formation of complex nanometric structures within the layer stacks. In order to investigate these swift heavy ion irradiation induced effects in more detail, a series of experiments was performed to determine the dominating influences. For this purpose, specific glancing angle deposited multi-layered films and nanostructures were irradiated to constant ion fluence with the same 200 MeV Au ion beam at different incidence angles. Scanning electron microscopy of the stacks before and after swift Au ion irradiation revealed considerable changes in film morphology and density as a function of the ion incidence angle, such as an increased porosity of the silicon layers, accompanied by layer swelling. In contrast, the SiOx layers did not show such effects, but exhibited clearly visible swift heavy ion tracks. The observed effects became stronger with decreasing ion incidence angle.
INTRODUCTION When during thin film growth by physical vapor deposition the deposition particle flux impinges the substrate surface under grazing incidence, a new class of non-compact thin films with nano-sized structures emerges. This so-called glancing angle deposition (GLAD) technique, put forward in the last decade by Robbie et al. [1, 2], is based on atomic self-shadowing on the substrate surface. In the beginning of the deposition process, the first nuclei that form on the surface act as seeds for the incoming particle flux. Under low adatom mobility conditions, the substrate region opposite the direction of the incoming atoms is thus shadowed. With ongoing deposition time, this experimental setup enables the fabrication of highly underdense, columnar thin films, with the columns slanted towards the flux direction of the atoms to be deposited. In combination with a controlled substrate rotation during deposition, nanostructures of complex shapes can be “sculpted”, resulting in so-called sculptured thin films (STFs). Depending on the
ratio of substrate r
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