Continuum models of focused electron beam induced processing

Abstract

SummaryFocused electron beam induced processing (FEBIP) is a suite of direct-write, high resolution techniques that enable fabrication and editing of nanostructured materials inside scanning electron microscopes and other focused electron beam (FEB) systems. Here we detail continuum techniques that are used to model FEBIP, and release software that can be used to simulate a wide range of processes reported in the FEBIP literature. These include: (i) etching and deposition performed using precursors that interact with a surface through physisorption and activated chemisorption, (ii) gas mixtures used to perform simultaneous focused electron beam induced etching and deposition (FEBIE and FEBID), and (iii) etch processes that proceed through multiple reaction pathways and generate a number of reaction products at the substrate surface. We also review and release software for Monte Carlo modeling of the precursor gas flux which is needed as an input parameter for continuum FEBIP models.

Dynamic Pattern Formation in Electron-Beam-Induced Etching

“…We note that the new EBIE model is consistent with all results in the literature that were explained successfully by the conventional EBIE model [1,2,5,[34][35][36][37][38][39][40][41][42][43][44]47]. The scaling of etch rate with beam energy is the same because the secondary electron yield is proportional to the energy transferred from the beam to the surface atoms of the substrate.…”

“…(1) [2,5,[34][35][36][37][38][39][40][41][42][43][44]. However, the model can not explain the etch rate anisotropy seen in Fig.…”

“…3 (solid curves, calculated using the rate equation model presented in the Supporting Information [9]). However, the measured etch rate is approximately independent of temperature up to at least 600 K where it is over three orders of magnitude higher than that predicted by the conventional EBIE model, irrespective of the electron flux used in the simulations (the simulated flux was varied over five orders of magnitude because it affects adsorbate depletion and hence the predicted temperature-dependence of EBIE [1,34]). The measurement is clearly inconsistent with the conventional model, but it is expected from the new model in which the etch rate is proportional to the concentration of chemisorbed oxygen.…”

“…The beam current density and pressure play the same roles in the two models because both the physisorbed and chemisorbed adsorbates are consumed in EBIE, and replenished through the same mechanisms (namely, adsorption from the gas phase and surface diffusion). Electron induced desorption of adsorbates plays the same role in each model [9,34], and dependencies of etch rate on electron dose and time are are governed by the kinetics of the respective adsorbate concentrations. However, the new model provides a more compelling explanation for EBIE observed at cryogenic temperatures [35] since it does not require thermal desorption of the reaction products.…”

Fabrication of FeSi and Fe3Si compounds by electron beam induced mixing of [Fe/Si]2 and [Fe3/Si]2 multilayers grown by focused electron beam induced deposition

“…Here we notice that understanding the reason for the sharp transition of Fig. 1 involves the solution of a system of Langmuir differential adsorption rate equations and the knowledge of the related adsorption, diffusion, desorption and decomposition parameters [19,23,24], which is beyond the aim of the present work. However, as an hint for future investigations, we observe that the residence time of Si 5 H 12 in the SEM was rather long, since it was possible to grow Si-based deposits for some hours after having close the relative Si 5 H 12 dosimeter.…”