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A 300 keV scanning transmission electron microscope was used to obtain tilt-series images of two two-level copper integrated circuit samples. The center-to-center layer spacing obtained from the tilt series showed internal consistency at the level of 15%, and external validity at the level of 20%.

As part of an effort to develop high resolution microtomography for engineered structures, a two-level copper integrated circuit interconnect was imaged using 1.83 keV x rays at 14 angles employing a full-field Fresnel zone plate microscope. A major requirement for high resolution microtomography is the accurate registration of the reference axes in each of the many views needed for a reconstruction. A reconstruction with 100 nm resolution would require registration accuracy of 30 nm or better. This work demonstrates that even images that have strong interference fringes can be used to obtain accurate fiducials through the use of Radon transforms. We show that we are able to locate the coordinates of the rectilinear circuit patterns to 28 nm. The procedure is validated by agreement between an x-ray parallax measurement of 1.41±0.17 μm and a measurement of 1.58±0.08 μm from a scanning electron microscope image of a cross section.

Most integrated circuit interconnects are principally composed of a few metals, including aluminum alloyed with copper, tungsten, titanium, Al3Ti, and Al2Cu, in a silica matrix. Integrated circuit interconnects have recently been proposed as a candidate system for visualization by computerized microtomography using absorption in the soft x-ray region. In this work, we demonstrate the feasibility of materials identification using volume-resolved x-ray absorption near edge spectra (XANES) obtained by tomographic reconstruction. A similar experiment could be performed with an energy-resolved high-voltage transmission electron microscope. We calculate the XANES for interconnect materials near the Al K edge, the Cu LI, LII, and LIII edges, and the Ti LII and LIII, and compare them to experiment when possible. The signal-to-noise ratio required to distinguish among the aluminum compounds from their Al K edge spectra is shown to be about one order of magnitude higher than that needed to detect elemental aluminum.

A design for a transmission x-ray microscope with 20 nm transverse spatial resolution is presented. The microscope, which is based on the electron-optical imaging of the photoemitted electrons from an x-ray shadowgraph, consists of a transmission x-ray photocathode coupled to a photoelectron emission microscope (PEEM—also called a PEM for photoelectron microscope). Unlike the conventional PEEM, which produces a surface map of photoelectron yield, this microscope can provide information on the subsurface properties of thin samples. The analysis of the microscope’s electron-optical performance is based on the evaluation of Gaussian focusing properties and third-order aberration coefficients computed using several complementary methods. The electron optical properties of the microscope are examined with an emphasis on issues affecting overall performance and achieving the best possible resolution. Preliminary experimental results using a cesium iodide photocathode are shown.

Two regions of interest on a copper/tungsten integrated circuit interconnect were imaged using two techniques: (a) the absorption spectrum was measured at 15 x-ray energies between 1687 and 1897 eV, and (b) the x-ray fluorescence spectrum was recorded with incident photon energies of 1822, 1797, and 1722 eV. The energies were chosen to optionally excite tungsten and tantalum above their M5 edges yet stay below the silicon K edge. Four materials in the circuits, tantalum, tungsten, silica, and copper were mapped using both techniques. The two sets of images agree in their main features, but differ for finer features.

To date, nearly all tomography based on electron microscopy has been performed on samples 1 μm or less thick. It has also relied on Beer’s Law. In this work, tomographic reconstructions of simulated scans of a photonic band-gap crystal based on bright-field imaging with a scanning transmission electron microscope are made assuming (1) multiple scattering or (2) the standard Beer’s Law model. The results suggest that it should be possible to treat systems several times larger than those which appear in literature, albeit at a worse resolution. The multiple scattering theory leads to high-quality reconstructions. Beer’s Law does only a little worse despite being applied outside its range of validity.

Two-dimensional images of model integrated circuit components were collected using the technique of scanning confocal electron microscopy. For structures embedded about 5 μm below the surface of a silicon oxide dielectric, a lateral resolution of 76±9 nm was measured. Elemental mapping via x-ray emission spectrometry is demonstrated. A parallax analysis of images taken for various tilt angles to the electron beam allowed determination of the spacing between two wiring planes. The results show that scanning confocal electron microscopy is capable of probing buried structures at resolutions that will be necessary for the inspection of next-generation integrated circuit technology.

An Al–W-silica integrated circuit interconnect sample was thinned to several μm and scanned across a 200 nm focal spot of a Fresnel zone plate operating at photon energy of 1573 eV. The experiment was performed on beamline 2-ID-B of the Advanced Photon Source, a third-generation synchrotron facility. Thirteen scanned projections of the sample were acquired over the angular range ±69.2°. At least 301×301 pixels were acquired at each angle with a step size of 77×57 nm. A three-dimensional image with an approximate uncertainty of 400 nm was reconstructed from projection data using a standard algorithm. The two layers of the integrated circuit and the presence of the focused ion beam markers on the surface of the sample are clearly shown in the reconstruction.

We report calculations for the dielectric constant e∞ and the second‐harmonic susceptibility d for BN, AlN, and GaN in both zincblende and wurtzite structures within the Kohn–Sham local‐density approximation. For wurtzite AlN and GaN, the computed dxxz(w) and dzzz(w) closely agree with experiment. For zincblende AlN and GaN as well as zincblende and wurtzite BN, we predict d. Our results show that the simple relation between the independent components of d predicted by bond additivity works for BN, breaks down for GaN, and completely fails for AlN.

Radiation transport theory is applied to electron microscopy of samples composed of one or more materials. The theory, originally due to Goudsmit and Saunderson, assumes only elastic scattering and an amorphous medium dominated by atomic interactions. For samples composed of a single material, the theory yields reasonable parameter-free agreement with experimental data taken from the literature for the multiple scattering of 300-keV electrons through aluminum foils up to 25μm thick. For thin films, the theory gives a validity condition for Beer’s law. For thick films, a variant of Moliere’s theory [V. G. Moliere, Z. Naturforschg. 3a, 78 (1948)] of multiple scattering leads to a form for the bright-field signal for foils in the multiple-scattering regime. The signal varies as [tln(e1−2γt∕τ)]−1 where t is the path length of the beam, τ is the mean free path for elastic scattering, and γ is Euler’s constant. The Goudsmit–Saunderson solution interpolates numerically between these two limits. For samples with ...

Potential theory and graph theory are used to create a specialized automatic router. Members of one set of points are completely connected to members of another set of points by nonintersecting curves all contained in the plane. Choices are offered for the linking paths from local information. The problem domain may be the plane or a bounded subset of the plane containing excluded areas