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Crossing the Resolution Limit in Near-Infrared Imaging of Silicon Chips: Targeting 10-nm Node Technology

Krishna Agarwal, Rui Chen, Lian Ser Koh, Colin J. R. Sheppard, and Xudong Chen
Phys. Rev. X 5, 021014 – Published 6 May 2015
Physics logo See Synopsis: Zooming in on Failures

Abstract

The best reported resolution in optical failure analysis of silicon chips is 120-nm half pitch demonstrated by Semicaps Private Limited, whereas the current and future industry requirement for 10-nm node technology is 100-nm half pitch. We show the first experimental evidence for resolution of features with 100-nm half pitch buried in silicon (λ/10.6), thus fulfilling the industry requirement. These results are obtained using near-infrared reflection-mode imaging using a solid immersion lens. The key novel feature of our approach is the choice of an appropriately sized collection pinhole. Although it is usually understood that, in general, resolution is improved by using the smallest pinhole consistent with an adequate signal level, it is found that in practice for silicon chips there is an optimum pinhole size, determined by the generation of induced currents in the sample. In failure analysis of silicon chips, nondestructive imaging is important to avoid disturbing the functionality of integrated circuits. High-resolution imaging techniques like SEM or TEM require the transistors to be exposed destructively. Optical microscopy techniques may be used, but silicon is opaque in the visible spectrum, mandating the use of near-infrared light and thus poor resolution in conventional optical microscopy. We expect our result to change the way semiconductor failure analysis is performed.

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  • Received 9 June 2014

DOI:https://doi.org/10.1103/PhysRevX.5.021014

This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Synopsis

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Zooming in on Failures

Published 6 May 2015

A near-infrared microscopy technique can detect defects in electronic devices with a resolution better than the diffraction limit of light.

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Authors & Affiliations

Krishna Agarwal1,*, Rui Chen2, Lian Ser Koh3, Colin J. R. Sheppard4, and Xudong Chen2

  • 1Singapore-MIT Alliance for Research and Technology (SMART) Centre, CREATE Tower, Singapore 138602
  • 2Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583
  • 3Semicaps Private Limited, Singapore 139959
  • 4Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genoa, Italy

  • *Corresponding author. uthkrishth@gmail.com This author was affiliated with the Department of Electrical and Computer Engineering, National University of Singapore when conducting the work.

Popular Summary

Nondestructive imaging of silicon chips is important for failure localization and analysis without disturbing the functionality of integrated circuits. High-resolution imaging techniques such as scanning electron microscopy and tunneling electron microscopy require transistors to be exposed destructively. Optical microscopy techniques may also be used, but silicon is opaque to visible and ultraviolet rays, mandating the use of near-infrared waves. Although long near-infrared wavelengths and Rayleigh’s resolution limit of a half wavelength make the minimum resolved distance prohibitively large, significant improvements can be obtained by using a solid immersion lens. Even then, the best reported resolution is 120-nm half pitch; the current and future industry requirement for semiconductor failure analysis of 10-nm node technology is 100-nm half pitch. We demonstrate the first experimental evidence of resolving features of 100-nm half pitch buried in silicon, thus fulfilling the industry requirement.

We employ 1064-nm near-infrared waves to localize physical defects on silicon chips. We show that pinhole size is critical for obtaining the resolution since it controls the impact of longitudinal currents in the focal region upon the image. Interestingly, of the pinholes that we investigate—with radii of 5, 12.5, 17.5, and 25  μm—we demonstrate that smaller pinhole sizes do not always yield higher resolutions. In fact, we show that the pinhole with a radius of 17.5  μm yields the highest spatial resolution.

We expect that our results will change the way in which failure analysis is conducted in the semiconductor industry. Our findings have applications in bioimaging and biotechnology.

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Vol. 5, Iss. 2 — April - June 2015

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