Peering inside semiconductor chips using x-ray imaging isn’t new, but the technique hasn’t been especially good or easy to accomplish. New advances reported by Swiss researchers in Nature last week suggest practical use of x-rays for fast, accurate, reverse-engineering of chips may be near.
“You’ll pop in your chip and out comes the schematic. Total transparency in chip manufacturing is on the horizon,” said Anthony Levi of the University of Southern California describing the research in an IEEE Spectrum article (X-rays Map the 3D Interior of Integrated Circuits). “This is going to force a rethink of what computing is” what it means for a company to add value in the computing industry.
The work by Mirko Holler, Manuel Guizar-Sicairos, Esther H. R. Tsai, Roberto Dinapoli, Elisabeth Müller, Oliver Bunk, Jörg Raabe (all of Paul Scherrer Institut) and Gabriel Aeppli (ETH) is described in their Nature Letter, “High-resolution non-destructive three-dimensional imaging of integrated circuits.”
“[We] demonstrate that X-ray ptychography – a high-resolution coherent diffractive imaging technique – can create three-dimensional images of integrated circuits of known and unknown designs with a lateral resolution in all directions down to 14.6 nanometres. We obtained detailed device geometries and corresponding elemental maps, and show how the devices are integrated with each other to form the chip,” write the researchers in the abstract.
“Our experiments represent a major advance in chip inspection and reverse engineering over the traditional destructive electron microscopy and ion milling techniques. Foreseeable developments in X-ray sources optics and detectors, as well as adoption of an instrument geometry optimized for planar rather than cylindrical samples, could lead to a thousand-fold increase in efficiency, with concomitant reductions in scan times and voxel sizes.”
Starting with a known structure – an ASIC developed at the institute – and then moving to an Intel chip (Intel G3260 processor) about which they had limited information, the researchers were able to accurate identify and map components in the chips. A good summary of the experiment is provided in the IEEE Spectrum article:
“The ASIC was produced using 110-nanometer chip manufacturing technology, more than a decade from being cutting edge. But the Intel chip was just a couple of generations behind the state of the art: It was produced using the company’s 22-nm process…To produce a 3D rendering of the Intel chip—an Intel G3260 processor—the team shined an X-ray beam through a portion of the chip. The various circuit components—its copper wires and silicon transistors, for example—scatter the light in different ways and cause constructive and destructive interference. Through a technique called X-ray ptychography, the researchers could point the beam at their sample from a number of different angles and use the resulting diffraction patterns to reconstruct chip’s internal structure.”
The experiment was carried out at the cSAXS beamline of the Swiss Light Source (SLS) at the Paul Scherrer Institut, Villigen, Switzerland. Details of the components are as follows. Coherent X-rays enter the instrument and pass optical elements that in their combination form an X-ray lens used to generate a defined illumination of the sample. These elements are a gold central stop, a Fresnel zone plate and an order sorting aperture. The diffracted X-rays are measured by a 2D detector, a Pilatus 2M in the present case. Accurate sample positioning is essential in a scanning microscopy technique and is achieved by horizontal and vertical interferometers.
As the IEEE Spectrum article notes, “Even if this approach isn’t widely adopted to tear down competitors’ chips, it could find a use in other applications. One of those is verifying that a chip only has the features it is intended to have, and that a “hardware Trojan”—added circuitry that could be used for malicious purposes—hasn’t been introduced.”
Link to IEEE article: http://spectrum.ieee.org/nanoclast/semiconductors/processors/xray-ic-imaging
Link to Nature paper: http://www.nature.com/nature/journal/v543/n7645/full/nature21698.html