Simulation of Ion-beam Induced Etching and Deposition Using a Non-local Recoil-based Algorithm
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1181-DD03-04
Simulation of Ion-beam Induced Etching and Deposition Using a Non-local Recoil-based Algorithm Christoph Ebm1 and Gerhard Hobler2 1 2
IMS Nanofabrication AG, Schreygasse 3, A-1020 Vienna, Austria. Institute of Solid State Electronics, Vienna University of Technology, A-1040 Vienna, Austria.
ABSTRACT 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. INTRODUCTION Sputtering and gas-assisted etching and deposition by focused ion beams are established techniques for direct fabrication of nanostructures [1,2]. They are presently used, e.g., for integrated circuits modification, rapid prototyping of photonic structures and photomask repair. With the development of tools providing massively parallel focused ion beams [3,4] higher throughput will be possible, and new applications will emerge like the fabrication of leadingedge photomasks or direct patterning for nanotechnology applications [5] including the fabrication of master stamps for nanoimprint lithography (NIL) [6]. Topography simulation of the gas-assisted etching/deposition process potentially is a valuable tool for investigating the effects of process variations and, in general, to understand the phenomena involved. In particular, nanometer sized pillars formed by ion beam induced gasassisted deposition have been found to be broader than the ion beam [7], which sets a lower limit to the achievable sizes. There are two competing theories of the mechanism responsible for the dissociation of the precursor molecules, by secondary electrons or by recoils. In [8] good evidence is given that the deposition yield is proportional to the sputtering yield and thus recoils yield, while no correlation with the yield of secondary electrons has been found. We therefore prefer the recoils theory and explain pillar broadening by the range and lateral spread of the recoils inside the pillar. Simulation together with appropriate experiments could confirm this model. Existing codes might be extended from sputtering simulation to deposition/etching simulation by assuming that the rate of deposition/etching is proportional to the flux of sputtered atoms. This is justified since the rate of both phenomena is proportional to the
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