W. Rodrigues

Measurement of strain in Al–Cu interconnect lines with x-ray microdiffraction

We report measurement of strain in patterned Al–Cu interconnect lines with x-ray microdiffraction technique with a ∼1 μm spatial resolution. Monochromatized x rays from an undulator were focused on the sample using a phase fresnel zone plate and diffracted light was collected by an area detector in a symmetric, angle dispersive x-ray diffraction geometry. Measurements were made before and after the line sample was stressed for electromigration. Results show an increase in inter- and intra-grain strain variation after the testing. Differences in strain behavior of grains with (111) and (200) crystallographic planes parallel to the substrate surface were observed. A position dependent variation of strain after the testing was measured whereas no such dependence was found before the testing.

Synchrotron x-ray microdiffraction diagnostics of multilayer optoelectronic devices

Synchrotron-based x-ray microbeam techniques have been used to map crystallographic strain and multilayer thickness in micro-optoelectronic devices produced with the selective area growth technique. Our main results show that growth enhancements in InGaAsP multilayer device material are different for well and barrier material. Comparison with a vapor-phase model for selective area growth suggests that this difference is due to different vapor-phase incorporation rates for the group III metals.

Near-field stacking of zone plates in the x-ray range.

We use Fresnel zone plates as focusing optics in hard x-ray microprobes at energies typically between 6 and 30 keV. While a spatial resolution close to 0.1 μm can currently be achieved, highest spatial resolution is obtained only at reduced diffraction efficiency due to manufacturing limitations with respect to the aspect ratios of zone plates. To increase the effective thickness of zone plates, we are stacking several identical zone plates on-axis in close proximity. If the zone plates are aligned laterally to within better than an outermost zone width and longitudinally within the optical near-field, they form a single optical element of larger effective thickness and improved efficiency and reduced background from undiffracted radiation. This allows us both to use zone plates of moderate outermost zone width at energies of 30 keV and above, as well as to increase the efficiency of zone plates with small outermost zone widths particularly for the energy range of 6 - 15 keV.

X-ray microdiffraction study of Cu interconnects

We have used x-ray microdiffraction to study the local structure and strain variation of copper interconnects. Different types of local microstructures have been found in different samples. Our data show that the Ti adhesion layer has a very dramatic effect on Cu microstructure. Strain measurement was conducted before and after electromigration test, Cu fluorescence was used to find the mass variations around voids and hillocks, and x-ray microdiffraction was used to measure the strain change around that interested region.

X-ray microdiffraction studies to measure strain fields in a metal matrix composite

An x-ray diffraction microscope (XDM) has been used to map the strain field in a fiber-reinforced composite material. The monochromatic x-ray (11 keV) beam was focused by a phase zone plate to produce a focal spot of 1×4 μm2 on the specimen. The microfocusing method using a zone plate enables the XDM to produce a high spatial resolution of ∼1 μm. The change in the peak position of diffraction patterns due to interatomic spacing change, caused by stress in the sample, was measured by using a two-dimensional charge coupled device detector. The radial residual strain field in the fiber-reinforced composite (SCS–6/Ti–14Al–21Nb) was measured from diffraction patterns with a sensitivity of ∼10−4 and an average standard deviation of 9.4×10−5.

Using x-ray microprobes for environmental research

Understanding the fate of environmental contaminants is of fundamental importance in the development and evaluation of effective remediation strategies. Among the factors influencing the transport of these contaminants are the chemical speciation of the sample and the chemical and physical attributes of the surrounding medium. Characterization of the spatial distribution and chemical speciation at micron and submicron resolution is essential for studying the microscopic physical, geological, chemical, and biological interfaces that play a crucial role in determining contaminant fate and mobility. Hard x-ray spectroscopy and imaging are powerful techniques for the element-specific investigation of complex environmental samples at the needed micron and submicron resolution. An important advantage of these techniques result from the large penetration depth of hard x-rays in water. This minimizes the requirements for sample preparation and allows the detailed study of hydrated samples. This paper discuses some current problems in environmental science that can be addressed by using synchrotron- based x-ray imaging and spectroscopy. These concepts are illustrated by the results of recent x-ray microscopy studies at the Advanced Photon Source.

Advanced zone plate microfocusing optics

Fresnel zone plates (ZP) have gained popularity as the optics of choice for advanced microfocusing applications. The main virtues of ZP are high resolution, high efficieny, low background, coherence preservation, and ample working distance. Zone plates are also unique because they are a normal incidence x-ray optics, which are much easier to align and use compared to other grazing incidence optics. We will report here recent progress that has drastically enhanced the performance of ZPs in 1) higher spatial resolution, 2) higher focusing efficiency, and 3) extension to higher energies. With the new developments, zone plates have proven to be one of the best microfocusing optics for monochromatic x-ray beams.

X-ray microdiffraction studies of an integrated laser-modulator system

The authors report the use of a spatially resolved x-ray microdiffraction technique for the structural study of an integrated laser-modulator system. The monochromatic (11 keV) x-ray beam microfocused to less than 1 {micro}m in the vertical direction was obtained using a phase zone plate. The photon flux at the focal spot exceeded 3 {times} 10{sup 10} photons/s/0.01% bw/{micro}m{sup 2}. The intense flux density and high spatial resolution of the focused beam was used to study the structure of a laser-modulator system, which is a 1-{micro}m-wide and 1-mm-long multi-quantum well structure on an InP substrate. The superlattice d-spacing and the strain field in the direction normal to the diffracting planes were mapped as a function of position along the length of the device.

Beam size measurement of the stored electron beam at the APS storage ring using zone plate optics and undulator radiation

Beam sizes of the stored electron beam at the Advanced Photon Source storage ring were measured using zone-plate optics and undulator radiation. A gold Fresnel zone plate (3.5 {micro}m thick) located 33.9 meters from the x-ray source focused radiation of 18 keV, selected by a cryogenically cooled Si(111) crystal in horizontal deflection, and formed a source image in a transverse plane 2.41 m downstream. The sizes of the source image were determined from measured intensity profiles of x-ray fluorescence from a smooth nickel edge (1.5 {micro}m thick), fabricated using a lithographic technique, while the nickel edge was scanned across over the beam in the transverse plane. The measured vertical and horizontal sizes of the electron beam were 60 {+-} 4.3 {micro}m and 300 {+-} 13 {micro}m, respectively, in reasonable agreement with the expected values.

The complementarity of PIXE and synchrotron induced X-ray methods for the characterisation of combustion sources contributing to urban air pollution

Abstract Current knowledge of fine-particle airborne pollution concentrations and constituents with diameters below 2.5 μm (PM2.5) is limited. Sources are both natural and man-made. Here we describe two types of experiments performed using the advanced photon source facility at Chicago, and compare the results with PIXE analysis on the same fine particle filters. These are firstly broad beam (2 mm) studies with tuned synchrotron beam energies to help resolve over-lapping X-rays, and secondly highly focused X-ray beam studies (0.2 μm) of individual fine particles from airborne pollution combustion sources.