Nanoscale Surface Patterning of Silicon Using Local Swelling Induced by He Implantation through NSL-Masks
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Nanoscale Surface Patterning of Silicon Using Local Swelling Induced by He Implantation through NSL-Masks Frederic J.C. Fischer1, Michael Weinl1, Jörg K.N. Lindner1,2, and Bernd Stritzker1 Universität Augsburg, Institut für Physik, D-86135 Augsburg, Germany. 2 present address: Universität Paderborn, Department Physik, D-33098 Paderborn, Germany. 1
ABSTRACT A novel technique to form periodically nanostructured Si surface morphologies based on nanosphere lithography (NSL) and He ion implantation induced swelling is studied in detail. It is shown that by implantation of keV He ions through the nanometric openings of NSL masks regular arrays of hillocks and rings can be created on silicon surfaces. The shape and size of these surface features can be easily controlled by adjusting the ion dose and energy as well as the mask size. Feature heights of more than 100 nm can be obtained, while feature distances are typically 1.15 or 2 (hillock or ring) nanosphere radii, which are chosen to be between 100 and 500 nm in this study. Atomic force and scanning electron microscopy measurements of the surface morphology are supplemented by cross-sectional transmission electron microscopy, revealing the inner structure of hillocks to consist of a central cavity surrounded by a hierarchical arrangement of smaller voids. The surface morphologies developed here have the potential to be useful for fixing and separating nano-objects on a silicon surface. INTRODUCTION Nanosphere Lithography (NSL) is a cheap and versatile bottom-up method to create regular arrays of nanoscale surface features [1]. Usually, for this purpose equally-sized nanospheres from a colloidal suspension are self-assembled in a hexagonally close-packed mono- or double layer on a substrate and the free space between each triple of neighbouring spheres is used as a mask opening in a subsequent materials deposition process. In the present paper, NSL masks are used as ion implantation masks. While NSL combined with physical vapour deposition is being used by many groups, the implantation of keV ions through NSL masks has only recently attracted some attention [2,3]. It has been shown that NSL masks made of either SiO2 or polystyrene (PS) beads with diameters of few hundrets of nanometers are comparatively stable during ion bombardment up to medium doses while at high doses deformations occur due to ion beam induced sintering at the sphere contacts and other effects. Here we report on the patterned high-dose implantation of keV He ions through NSL masks into silicon. He implantation into bare Si has been extensively studied in the past due to the possibility of layer splitting and impurity gettering in voids [4,5]. As we have shown in a recent study [6] such implantations through NSL masks lead to a localized swelling of the silicon underneath the mask openings, resulting in a regular surface pattern of hillocks. The aim of the present paper is to study the dependence of the hillock height on the ion energy, the width of the mask openings and the dose, in orde
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