Sean P. Frigo

Noninterferometric quantitative phase imaging with soft x rays.

We demonstrate quantitative noninterferometric x-ray phase-amplitude measurement. We present results from two experimental geometries. The first geometry uses x rays diverging from a point source to produce high-resolution holograms of submicrometer-sized objects. The measured phase of the projected image agrees with the geometrically determined phase to within +/-7%. The second geometry uses a direct imaging microscope setup that allows the formation of a magnified image with a zone-plate lens. Here a direct measure of the object phase is made and agrees with that of the magnified object to better than +/-10%. In both cases the accuracy of the phase is limited by the pixel resolution.

Tomographic reconstruction of an integrated circuit interconnect

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.

Tomography of integrated circuit interconnect with an electromigration void

An integrated circuit interconnect was subject to accelerated-life test conditions to induce an electromigration void. The silicon substrate was removed, leaving only the interconnect test structure encased in silica. We imaged the sample with 1750 eV photons using the 2-ID-B scanning transmission x-ray microscope at the Advanced Photon Source, a third-generation synchrotron facility. Fourteen views through the sample were obtained over a 170° range of angles (with a 40° gap) about a single rotation axis. Two sampled regions were selected for three-dimensional reconstruction: one of the ragged end of a wire depleted by the void, the other of the adjacent interlevel connection (or “via”). We applied two reconstruction techniques: the simultaneous iterative reconstruction technique and a Bayesian reconstruction technique, the generalized Gaussian Markov random field method. The stated uncertainties are total, with one standard deviation, which resolved the sample to 200±70 and 140±30 nm, respectively. The t...

Quantitative nanoscale metrology study of Cu/SiO2 interconnect technology using transmission x-ray microscopy

This letter describes quantitative nondestructive measurements of multilayer submicron Cu/SiO2 interconnect structures such as Cu lines, vias, and W lines with lateral dimensions down to 300 nm and electromigration defect structures using scanning transmission x-ray microscopy employing a 0.2 μm x-ray beam. Typical measurement accuracies are ⩽60 nm for widths and lengths and ⩽10% in height. The high-resolution and nondestructive nature of this technique provide a very powerful probe of physical properties of nanoscale and submicron materials and structures.

Multilayer spherical grating monochromator for 1- to 4-KeV x rays

In this paper we discuss the design and anticipated optical performance of a multilayer spherical grating monochromator for x- rays with energies of 1-4 keV. The monochromator is to be used for x-ray microscopy and coherence experiments on the 2-IDB soft x-ray beamline at the Advanced Photon Source. The layout, design considerations, and resolving power with various single and multilayer grating coatings are discussed.

Accurate pattern registration for integrated circuit tomography

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.

Methods to remove distortion artifacts in scanned projections

Artifacts induced by distortions which sometimes occur in two- dimensional projection images can appear in the resulting tomographic reconstructions. We describe a procedure for analyzing, correcting and removing experimental artifacts, and hence reducing reconstruction artifacts. Two-dimensional and three-dimensional images acquired with scanning transmission x-ray microscopy of a sample containing an integrated circuit interconnect show how these procedures can be successfully applied.

Effect of focusing optics on x-ray speckle contrast

We investigated the behavior of speckle contrast and size under various experimental conditions using 1.82 keV x-rays. In this paper, we report the comparison of two different setups for x-ray speckle experiments: one employing a focusing zone plate and one in which a pinhole selects the size of the coherent x-ray beam. We found a strong dependence of the speckle contrast and size on the type of setup. In general, the pinhole setup results in higher contrast but smaller speckle size. On the other hand, the zone plate setup allows one to target much smaller areas of interest in the sample, down to submicron dimensions, and also to adjust the speckle size. We anticipate that these results will be useful in future time-correlation spectroscopy experiments.

Effects of feature orientation in tomographic reconstructions

We performed an x-ray nanotomography experiment at the Advanced Photon Source for the purpose of making a 3D image of a sample contain an integrated circuit interconnect. Nine projections of the sample were made over an angular range of 140 degrees using 1573 eV photons and scanning transmission x-ray microscope having a focal spot size of about 150 nm. Reconstructions of experimental and simulated data, using a simultaneous iterative reconstruction technique, show that a sample that is highly opaque along certain lines of sight must be strategically oriented with respect to the rotation axis to minimize the attenuation of photons through the sample and maximize the contrast in each image.