edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 27 NO. 3 26 FIB-induced thermal damage is not widely considered to be a major artifact when milling ceramics, semiconductors, or metals because these materials are not as temperature sensitive as polymers or biomaterials. However molecular dynamic and finite element analysis simulations of 30 kV Ga+ ion impacts into crystalline Si show temperature increases of 1000-3000 K within 10 nm of the impact site over a time range of nanoseconds for both low and high flux scenarios.[10] Experimentalists generally dismiss such extreme temperatures as unphysical, however, Das et al.[11] proposes thermal vaporization of material as the most likely explanation for experimental FIB studies of metals and semiconductors that show otherwise unexplained orders-of-magnitude increases in FIB-milling rates. Figure 6 shows an indium bump bond that was FIBmilled at room temperature on the Helios 5 with a Ga+ ion beam (30 kV, 65 nA) using a modified cleaning crosssection recipe (dwell of 500 ns, beam blur of 1.5 µm, total beam diameter of 2.1 µm, x-overlap of 0%, y-overlap of 90%). This is the same type of indium bump bond sample that volatilizes when FIB-milled at room temperature using a traditional milling recipe but can be successfully milled with the same recipe after it is cooled to -150°C using a cryo stage as is shown in Michael et al.[12] In other words, the defocused ion beam keeps the FIB-milled indium in Fig. 6 below its volatilization temperature which is approximately 540°C under a vacuum of 1E-5 mbar.[13] CONCLUSION This article describes the benefits of defocusing the ion beam for standard FIB processing to mitigate common FIB artifacts. As shown, this simple adjustment leads to several positive outcomes, including increasing the efficiency of material deposition (or even gas-assisted milling) by moving the deposition (milling) regime from precursor-limited to beam-limited, reducing the formation of curtaining by allowing each ion to have a line-of-sight impact on the milling surface and decreasing FIB-induced thermal damage that is largely unaccounted for when milling metals, ceramics, and semiconductors. ACKNOWLEDGMENTS Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC (NTESS), a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration (DOE/NNSA) under contract DE-NA0003525. This written work is authored by an employee of NTESS. The employee, not NTESS, owns the right, title, and interest in and to the written work and is responsible for its contents. Any subjective views or opinions that might be expressed in the written work do not necessarily represent the views of the U.S. Government. The publisher acknowledges that the U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this written work or allow others to do so, for U.S. Government purposes. The DOE will provide public access to results of federally sponsored research in accordance with the DOE Public Access Plan. REFERENCES 1. J.D. Fowlkes, et al.: “High-Fidelity 3D-Nanoprinting via Focused Electron Beams: Computer-Aided Design (3BID),” ACS Applied Nano Materials, 2018, 1(3), p. 1028-1041. 2. I. Utke: Nanofabrication using Focused Ion and Electron Beams: Principles and Applications, Edited by I. Utke, S. Moshkalev, and P. Russell, Oxford, UK, 2012. 3. T. Tao, et al.: “Focused Ion Beam Induced Deposition of Platinum,” Journal of Vacuum Science & Technology B, 1990, 8(6), p. 1826-1829. 4. R. Behrisch: “Sputtering by Particle Bombardment: Experiments and Computer Calculations from Threshold to MeV Energies,” (Topics in Applied Physics, Volume 110), Edited by R. Behrisch, and W. Eckstein, Springer-Verlag, Berlin, DE, 2007. 5. P. Sigmund and M. Szymonski: “Temperature-Dependent Sputtering of Metals and Insulators,” Appl. Phys., 1984, A(33), p. 141-152. 6. S. Kim, et al.: “Minimization of Focused Ion Beam Damage in Nanostructured Polymer Thin Films,” Ultramicroscopy, 2011, 111(3), p. 191-199. 7. K. Narayan and S. Subramaniam: “Focused Ion Beams in Biology,” Nature Methods, 2015, 12, p. 1021-1031. 8. K. Rykaczewski, et al.: “Far-reaching Geometrical Artefacts Due to Thermal Decomposition of Polymeric Coatings Around Focused Ion Beam Milled Pigment Particles,” Journal of Microscopy, 2016, 262, p. 316-325. 9. M. Häublein, et al.: “Investigation on the Flame Retardant Properties and Fracture Toughness of DOPO and Nano-SiO2 Modified Epoxy Fig. 6 Indium bump bond FIB-milled at room temperature on the Helios 5 with a Ga+ ion beam (30 kV, 65 nA) using a modified cleaning cross-section recipe (dwell of 500 ns, beam blur of 1.5 µm, total beam diameter of 2.1 µm, x-overlap of 0%, y-overlap of 90%). THE ADVANTAGES OF SYSTEMATICALLY DEFOCUSING THE ION BEAM(continued from page 23)
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