Gas-assisted etching and deposition with focused ion beams are unique and flexible methods for the fabrication of nanostructures. To understand and improve these processes the ability to accurately simulate and predict the resulting structures is very important. In this paper we present a nonlocal recoil-based algorithm for topography simulation of ion-beam induced gas-assisted deposition. We have fabricated flying roof like overhanging structures and found very good agreement between simulation and experiment. These structures cannot be explained with a local model. Furthermore, we demonstrate a considerable influence of the beam diameter on the resulting structure by comparing otherwise identical simulations with different beam diameter.

Focused ion beams are an established but inherently slow technique for many nanopatterning applications. One way to increase its processing speed is by gas-assisted ion-beam induced etching. However, to understand and improve this process, the ability to accurately simulate the precursor coverage is very important, because it strongly affects the efficiency of the process. In this paper, the authors present a recoils-based simulation model that considers precursor adsorption, decomposition, and diffusion. The authors provide a non-steady-state solution for translational symmetry, which they use to investigate the influence of the precursor diffusion coefficient on the etching process. They find that the diffusion coefficient influences the shape of the bottom of the irradiated structure. Furthermore, they compare the simulation results to experiments of SiO2 etched by XeF2 using a focused Ga ion beam, and extract model parameters such that the etching rate of numerous experiments with different current densities can be predicted accurately.

The authors have successfully employed the charged particle nanopatterning (CHARPAN) technology for nanostructuring of a metal mold insert for a conventional injection molding machine. High-precision diamond-milled Ni–Cu mold inserts have been nanopatterned with 10 keV argon ion multibeam milling with feature sizes as small as 50 nm. A variety of structures such as circles, hexagons, and lines in different dimensions, with positive and negative shapes, have been fabricated in the metal mold. These structures have been successfully replicated in polymethylpentene samples by injection molding. To the authors’ best knowledge, the CHARPAN technology is one of the very few technologies that allow for resistless nanostructuring a field size of 25×25 μm2 into a metal mold in a single shot. This is of high importance for the practical injection molding fabrication of nanostructured polymer devices such as optical biosensors.

Ion-beam induced etching and deposition rates are proportional to the flux of recoils reaching the surface. Based on this finding we propose an improved algorithm for etching and deposition simulations. In this algorithm the recoil flux at each point on the surface is calculated by summing up the recoil fluxes originating from ions impinging on any other surface point. The latter are determined by interpolation in tables calculated by binary collision simulations. For concave surfaces a correction to this algorithm is proposed. Fluxes calculated by this model are in good agreement with binary collision simulations of collision cascades in the same 2-d structure. Consistent with experimental findings, the model predicts that deposited pillars are broader than the ion beam, while etched trenches do not show such broadening. The pillar broadening is related to the lateral straggling of the recoils.

The main assumption of existing efficient topography simulations is that sputtering is a local process that depends only on the angle of incidence and not on the detailed shape of the surface. If redeposition is considered, sputtered atoms are redeposited and cause no further sputtering when they hit another part of the surface. Furthermore the angular distribution of sputtered atoms follows a cosine law. If ion reflection is considered, ions do not lose energy during backscattering. Using binary collision simulations (IMSIL) and comparing them with results obtained by a topography simulator (IonShaper®) we show that all these assumptions need refinement for the simulation of nanostructures except the neglect of sputtering by sputtered atoms. In addition we show that a nonlocal model is essential for ion beam induced deposition of narrow structures.

The paper demonstrates that the ion beam milling process can be modelled as a local isotropic etching without taking into account the material re-deposition during the sputtering. It also presents a software, IonRevSim, specifically developed to simulate the 3D ion structuring and thus to validate the milling process and if necessary to optimise off-line its processing parameters. In particular, employing the IonRevSim software it is possible to prepare the necessary data for performing 3D ion milling and then to simulate the 3D structuring process with the aim to minimise the deviation of resulting machined surface from the targeted one. These two main functions of the software and their respective operating modes are discussed in the paper. An experimental verification based on an optimised data generated by IonRevSim was performed using both FIB and multi-beam CHARPAN PMLP tools. For both ion-patterning techniques a good agreement between experimental and simulation results was demonstrated when applied for producing relatively low aspect ratio structures.

The capabilities of charged particle nanopatterning (CHARPAN) for photonic device fabrication are investigated. The CHARPAN tool is a proof-of-concept tool for a multi-ion beam system that the authors used to directly pattern photonic structures into both Si and Ni as well as for maskless exposure of hydrogen silsesquioxane resist. The realized structures have a regular array and show adequate roundness of the holes as well as little sidewall roughness. For the development and a better understanding of the processes they extended and used the IonShaper® simulation software. They could achieve excellent agreement between sputtering simulation and experiments. Furthermore, they developed a nonlocal recoil-based algorithm for the simulation of ion beam induced etching and deposition. Simulation results for three dimensional nanopatterning with this algorithm are presented.

Today's focused ion beam (FIB) systems enable the fast and flexible fabrication of 3D structures with dimensions well below 100 nm. Due to secondary effects like redeposition of sputtered material, however, the fabrication of a targeted shape of the structure is not simple at all. In this work, the influence of the patterning strategy during the sputtering on the shape of a 3D structure with rotational symmetry is studied. Highly different shapes of 3D structures are achieved only due to different rastering strategies or duration times of the ion beam at each raster pixel. The final structure shape can be properly modeled with lonShaper(R) simulations. These results clearly prove that the selection of the patterning strategy is the key for appropriate FIB processing of 3D structures. Besides, it is shown that unconventional patterning strategies might enable new types of 3D shapes. (C) 2009 Elsevier B.V. All rights reserved.

A projection mask-less patterning (PMLP) proof-of-concept tool, realised as part of the European FP6-NMP integrated project CHARPAN (Charged Particle Nanotech), has been applied for three-dimensional patterning of a GaAs surface, using a stencil mask with a pre-defined opening distribution. A 10 × 10 matrix of micro-lenses was used as test structure for argon ion multi-beam structuring, while studying the time evolution of the sputtered structures. The kinetic sputtering and re-deposition have been modelled in simulation software, in order to be able to correct for such effects beforehand in the design of datasets to be fed to the future programmable aperture plate.