edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 26 NO. 1 20 NIST has pushed into the extreme-UV at 30 nm.[9,16] A shorter wavelength (higher photon energy) may improve the evaporation yield of certain materials by utilizing increased absorption cross-sections and higher photon energies. However, experiments in this regime are sparse, with the benefits and drawbacks not yet fully determined. Concurrently, cryogenic techniques have been implemented, enabling the probing of organic and biological samples.[3,17,18] Although organic materials are typically difficult to accurately analyze, capabilities resulting from the above improvements can be exemplified in the analysis of an organic marine protozoan material (Fig. 7), showing Na segregation between the carbonate skeleton and primary organic sheet.[19] The Ca interface is highlighted (Fig. 7a) and the segregation of Na is shown in the APT reconstruction (Fig. 7b). The composition around the phase boundary can be determined from APT data in the form of a proximity histogram, giving changes in the concentration profiles of specific elements on either side of the complex structure (Fig. 7c-d). The segregation of Na and Mg provides insight into the carbonate nucleation process, supplying new information of diverse carbon-based samples by APT and demonstrating a higher need for element-specific investigation of biomineralization. Despite the numerous progressions in application, APT experiments still have several challenges to overcome. Due to the high applied field, samples are often under high electrostatic stress, which can result in unexpected sample fracture during data collection. If the sample survives through the entirety of the data collection without fracture, the subsequent analysis and reconstruction of the data may be less than trivial, often requiring correlative microscopy techniques to ensure spatial fidelity with the original specimen. In Si-based FinFETs, for example, the varied materials and accompanying thermal and absorption properties in a single device can lead to errors in the reconstructed shape or appear to show unrealistic mixing of layers,[20] requiring careful consideration to produce accurate 3D representations. Nevertheless, computational and experimental techniques continue to improve, offering valuable insights to the compositional microstructure of materials and increasing the likelihood of successful sample analysis. A brief review of APT and the capabilities of this instrumental technique were discussed here, touching on some of the history and research within the field. For additional review articles and information, readers are directed to previous articles.[4,21,22] Although there is a wide range of material experiments and theoretical exploration that was not discussed, the utility of ATP continues to grow. Electronics, semiconductors, and interface analysis will benefit from more accurate characterization with better spatial resolution as APT-based techniques are improved, leading to devices and materials of unparalleled performance and reliability. REFERENCES 1. D.W. Saxey, et al.: “Atomic Worlds: Current State and Future of Atom Probe Tomography in Geoscience,” Scr Mater, Apr. 2018, 148, p. 115–121, doi.org/10.1016/j.scriptamat.2017.11.014. 2. Y.S. Chen, et al.: “Direct Observation of Individual Hydrogen Atoms at Trapping Sites in a Ferritic Steel,” Science, Mar. 2017, 355(6330), p. 1196–1199, doi.org/10.1126/SCIENCE.AAL2418. 3. I.E. McCarroll, et al.: “New Frontiers in Atom Probe Tomography: A Review of Research Enabled by Cryo and/or Vacuum Transfer Systems,” Mater Today Adv, Sep. 2020, 7(100090), p. 1–11, doi. org/10.1016/j.mtadv.2020.100090. Fig. 7 APT analysis of a marine protozoan showing (a) the organic/calcite interface delineated with a 50 at.% Ca isoconcentration surface, (b) Na (red) distribution, and (c-d) composition proximity histograms across the calcite interface in (a). Adapted from Ref 3 under the terms of the Creative Commons Attribution License. (a) (c) (b) (d)
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