Nanoscale Three-Dimensional Imaging of Integrated Circuits Using a Scanning Electron Microscope and Transition-Edge Sensor Spectrometer
<p>(<b>A</b>) MINT overview, consisting of an electron column, energy-dispersive spectroscopy (EDS) source-term monitor, SEM chamber, and TES spectrometer. (<b>B</b>) View inside the SEM chamber, showing the electron beam incident on a sample in the sample holder and the generated X-rays going to the TES and EDS. (<b>C</b>) Schematic demonstrating the MINT sample configuration and X-ray generation in sample layers: an electron beam incident on a target layer generates X-rays in a nanoscale spot size, which are attenuated by the IC and detected by the TES. Electrons not stopped in the target layer spread into a larger spot size and generate X-rays in other layers of the sample. Sample thicknesses are not drawn to scale. Part B is reprinted from Ref. [<a href="#B18-sensors-24-02890" class="html-bibr">18</a>] with permission (<a href="http://creativecommons.org/licenses/by/4.0/" target="_blank">http://creativecommons.org/licenses/by/4.0/</a>, accessed on 10 October 2023).</p> "> Figure 2
<p>PENELOPE simulation results for the candidate target materials, showing the predicted imaging speed for the coadded TES array. A 100 nm thick Pt layer at an electron accelerating voltage of 25 keV yields the best imaging speed on the selected IC and was thus chosen for the MINT imaging demonstration.</p> "> Figure 3
<p>(<b>A</b>) The Au-on-C sample. Line scans over the edge of Au grains were collected, and the Au M<sub><span class="html-italic">α</span></sub> counts detected by the EDS were extracted. (<b>B</b>) Au M<sub><span class="html-italic">α</span></sub> counts versus distance along a line scan (blue points) using the 60 μm aperture, fitted to a Gaussian integral (black line) to estimate the electron beam full-width half-maximum (FWHM). (<b>C</b>) Estimated Gaussian FWHM versus the SEM aperture size. An aperture size of 150 μm was chosen for tomography in this measurement. At smaller aperture sizes (60 μm and below), the measured spot size becomes limited by the sharpness of the Au edge rather than the size of the electron beam.</p> "> Figure 4
<p>Geometric magnification in MINT. Nanometer-scale features in the IC are magnified onto TES pixels. The design magnification is proportional to the TES pixel pitch (<math display="inline"><semantics> <msub> <mi>D</mi> <mi>p</mi> </msub> </semantics></math>) and the desired resolvable feature size (<math display="inline"><semantics> <msub> <mi>F</mi> <mi>S</mi> </msub> </semantics></math>), while the system magnification is proportional to the ratio of the source-to-detector (<math display="inline"><semantics> <msub> <mi>S</mi> <mi>D</mi> </msub> </semantics></math>) and source-to-feature (<math display="inline"><semantics> <msub> <mi>S</mi> <mi>F</mi> </msub> </semantics></math>) spacing. The system magnification should be higher than the design magnification to resolve the desired feature size. This figure is reprinted from Ref. [<a href="#B21-sensors-24-02890" class="html-bibr">21</a>].</p> "> Figure 5
<p>(<b>A</b>) Schematic of a TES. The TES and absorber are weakly thermally coupled to a silicon substrate serving as a thermal bath via a silicon nitride membrane. The TES is cooled into its superconducting state and voltage-biased onto the superconducting-to-normal transition. When a photon is absorbed, the small increase in absorber and TES temperature results in a relatively large change in the TES resistance. Higher energy photons cause a larger change in temperature and thus a larger change in the TES resistance. (<b>B</b>) The change in TES resistance caused by photon absorption is read out as a negative-going pulse in the TES current (shown inverted here), with the pulse height proportional to the energy of the incident photon.</p> "> Figure 6
<p>(<b>A</b>) Energy-calibrated TES spectrum combined over all TES pixels in the array and over all dwell positions. Purple arrows indicate the Pt L<sub><span class="html-italic">α</span></sub> characteristic X-rays used for tomographic reconstruction. All other characteristic X-ray peaks are background peaks from sources such as the SEM chamber, sample holder, or cryostat. A selection of higher-intensity background peaks is indicated by orange arrows. (<b>B</b>) Fit to the Pt L<sub><span class="html-italic">α</span></sub> line for the full TES array over all dwell positions. This fit separates the Pt X-rays generated in the target layer from the bremsstrahlung background photons. (<b>C</b>) Fit to the Cu K<sub><span class="html-italic">α</span></sub> line for the full TES array over all dwell positions. The Cu K<sub><span class="html-italic">α</span></sub> intrinsic line shape is well characterized, [<a href="#B36-sensors-24-02890" class="html-bibr">36</a>,<a href="#B37-sensors-24-02890" class="html-bibr">37</a>], and this spectrum was used to establish the energy resolution of the TES spectrometer at 8 keV.</p> "> Figure 7
<p>(<b>A</b>) Three-dimensional reconstruction of an IC fabricated at the 130 nm node, using X-rays in the 9.1–10.1 keV energy band. This band includes all Pt L<sub><span class="html-italic">α</span></sub> photons. (<b>B</b>) Spectrum from the TES detector, with the 9.1–10.1 keV energy band used for reconstruction highlighted in orange (top). Reconstruction results, separated by the IC layer, are shown under the spectrum. These slices were taken from the reconstruction shown in A. (<b>C</b>) Multi-energy reconstruction results, using the 9.1–10.1 keV and the 5.4–6.4 keV band, shown under the TES spectrum, with the X-ray energies used highlighted in orange. Here, only the first via layer is resolved more clearly than when only using 9.1–10.1 keV photons, indicating a material other than Cu may be present. (<b>D</b>) GDS ground truth for each of the metal via and wiring layers, for comparison with the reconstruction results. A portion of this figure appeared in Ref. [<a href="#B21-sensors-24-02890" class="html-bibr">21</a>]. All scale bars in (<b>A</b>–<b>C</b>) are 2 μm wide.</p> ">
Abstract
:1. Introduction
2. MINT System Description
2.1. X-ray Source
2.1.1. Target Selection
2.1.2. Electron Aperture Selection
2.2. System Geometry and Magnification
2.3. TES Spectrometer
2.4. Source-Term Monitor
3. Data Processing
3.1. TES Data Processing and Analysis
3.2. Image Generation
4. Reconstruction Results
5. Future Outlook
6. Conclusions
Supplementary Materials
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Nakamura, N.; Szypryt, P.; Dagel, A.L.; Alpert, B.K.; Bennett, D.A.; Doriese, W.B.; Durkin, M.; Fowler, J.W.; Fox, D.T.; Gard, J.D.; et al. Nanoscale Three-Dimensional Imaging of Integrated Circuits Using a Scanning Electron Microscope and Transition-Edge Sensor Spectrometer. Sensors 2024, 24, 2890. https://doi.org/10.3390/s24092890
Nakamura N, Szypryt P, Dagel AL, Alpert BK, Bennett DA, Doriese WB, Durkin M, Fowler JW, Fox DT, Gard JD, et al. Nanoscale Three-Dimensional Imaging of Integrated Circuits Using a Scanning Electron Microscope and Transition-Edge Sensor Spectrometer. Sensors. 2024; 24(9):2890. https://doi.org/10.3390/s24092890
Chicago/Turabian StyleNakamura, Nathan, Paul Szypryt, Amber L. Dagel, Bradley K. Alpert, Douglas A. Bennett, William Bertrand Doriese, Malcolm Durkin, Joseph W. Fowler, Dylan T. Fox, Johnathon D. Gard, and et al. 2024. "Nanoscale Three-Dimensional Imaging of Integrated Circuits Using a Scanning Electron Microscope and Transition-Edge Sensor Spectrometer" Sensors 24, no. 9: 2890. https://doi.org/10.3390/s24092890