Yoshinori Chikaura

Determination of the three-dimensional structure of dislocations in silicon by synchrotron white X-ray topography combined with a topo-tomographic technique.

The determination of the three-dimensional dislocation structure, i.e. the configuration and nature of the dislocations, in silicon by synchrotron white X-ray topography combined with a topo-tomographic technique is demonstrated. A [001]-oriented CZ-Si crystal of diameter approximately 7 mm was fixed on a subsidiary goniometer with three rotation axes (omega, Rx, Ry) and x-y-z stages, keeping its growth axis parallel to the omega-axis. This goniometer was mounted on the swivel stage of the main diffractometer installed at the experimental hutch of beamline BL28B2 of SPring-8. After adjusting the (110) plane to be perpendicular to the incident white X-ray beam by observing transmission Laue patterns, the crystal was inclined by 4.3 degrees so that the 004 Laue spot could be formed by 60 keV X-rays. Laue topographs observed by rotating the omega-axis of the subsidiary goniometer were recorded using X-ray films and a cooled CCD camera. The direction of the dislocation lines, Burgers vectors and glide planes were determined by following the variation in features of the dislocation images in the 004 Laue spot and by examining the contrast of the dislocation images in the Laue spots concerning the [111] and [022] planes. It is concluded that white X-ray topography combined with the omega-rotation technique is useful for clarifying the three-dimensional dislocation structure.

Sharper image of breast cancer cells and stroma in dense breast using thinner angular filter under X-ray dark-field imaging

The visibility of breast cancer was studied by two types of Laue angular filter (LAF) under x-ray dark field imaging. One was designed so that a field size of 90 ×90 mm2 was available by a 2.124-mm-thick LAF with a 35 keV x-ray energy. The second was a thin LAF of 125.6 µm thickness with a view field of 10 ×10 mm2 using a 13.7 keV x-ray. The estimated spatial resolutions for the cases of the 2.124-mm-thick LAF and the 125.6-µm-thick LAF were 139 and 23 µm, respectively. This is in good agreement with our experiment.

Three-dimensional structure of dislocations in silicon determined by synchrotron white x-ray topography combined with a topo-tomographic technique

We have studied the propagation and elimination of dislocations generated at the early stage of Czochralski silicon crystal growth using synchrotron white x-ray topography combined with a topo-tomographic technique. Two silicon crystals with [001] growth-axes were examined. One was intentionally grown without enlarging its diameter to easily observe the features of the dislocation propagation, and the other was grown with Dash necking, followed by a 2 inch enlargement of its diameter in order to observe the elimination of the dislocations. The three-dimensional structure of the individual dislocation, i.e. the direction of the dislocation line, its Burgers vector and the glide plane, were determined. These investigations revealed that dislocation half loops, which were generated from tangled dislocations, were expanded on their glide planes and were often deformed by their interaction, cross slip and collision with the crystal surface, followed by a gradual decrease in their density. The dislocation-elimination effect of the Dash necking was caused by the expansion of the dislocation half loops being terminated within the crystal and by their pinning on the crystal surface.

X-Ray Orientation Topography

In order to observe orientation distribution in a single crystal, X-ray orientation topography has been devised by applying X-ray scattering radiography. A single crystal of iron-3%(wt)silicon alloy was examined to demonstrate the capability of the system. An accuracy of 20 arc seconds has been attained by the present apparatus with a spatial resolution of less than 48 µm.

New topographic method of detecting microdefects using weak-beam topography with white X-rays

We describe a new topographic method of detecting microdefects in nearly perfect crystals. By this method, faint kinematical images of microdefects are observed with minimized dynamical background intensity using the interference effects of X-rays in a sample crystal. We demonstrate the capability of the method by observing A-swirl defects in floating-zone (FZ) silicon. The dynamical background intensity is markedly reduced, and weak kinematical images could be observed.

X-ray reconstruction topography for observation of the orientation distribution in a single crystal

A microcomputer-assisted reconstruction topography technique has been devised for observation of the distribution of subgrain orientations in a single crystal. The orientation at a specific location is computed, with data from X-ray scattering topographs, by a microcomputer. The reconstruction topograph showing the orientation distribution consists of two topographs, one showing the rotation-angle distribution around an axis and the other the orientation distribution of the rotation axis. The system capability has been demonstrated by observations of an iron-3wt% silicon alloy with an orientational resolution of 2.0′ and a spatial resolution of less than 48u2005μm. Emphasis is placed on the fact that this is the first proposal for X-ray topography involving spectroscopy.

High-Resolution X-Ray Scattering Topography Using Synchrotron Radiation Microbeam.

Although spatial resolution is the most essential factor determining the function of X-ray topography, it has not been improved in 30 years in spite of increasing requirements for highly-resolvable topography in materials science. X-ray scattering topography using a microbeam is a method capable of overcoming this resolution problem. Because the maximum resolution of an apparatus using a sealed-off tube is limited to 20 µ m, we designed and constructed scattering topography equipment using a synchrotron radiation microbeam. In the experiment, the slit system forms the microbeam 7 µ m in diameter. We observed a cellulose distribution in bamboo as a testing material. When the scanning step was 2 µ m, we attained spatial resolution less than 5 µ m.

X-ray scattering topography involving local spectroscopy

X-ray scattering topography using multichannel detectors as a position sensitive detector and an energy dispersive solid state detector is described. The system involves measuring the X-ray spectrum at each local place. The new topography system adds another dimension to X-ray scattering topography proposed by the present authors over the past ten years. It produces topographs, constructed with certain physical quantities, such as crystal orientation, as well as an ordinary integrated intensity map. Included in the paper is the orientation topography for an Fe-3%Si alloy single crystal, structural observation of an Al-4%Cu alloy polycrystal having a welded region, and the nondestructive testing of an amorphous rubber tyre. Emphasis is placed on the first proposal of X-ray spectroscopy topography.

X-ray reciprocal space maps and x-ray scattering topographic observation of GaN layer on GaAs (001) in plasma-assisted molecular beam epitaxy

We have characterized plasma-assisted N+ molecular beam epitaxy-grown polymorphous GaN epitaxial layer on GaAs by x-ray reciprocal mapping using four-circle x-ray diffractometer and a personal computer controlled x-ray scattering topography system by ourselves. x-ray reciprocal mapping indicates that GaN wurtzite epitaxial film was grown along only [1¯1¯1] direction. While GaN wurtzite and zinc-blende crystals were contracted along the surface normal, those of lattice constants were expanded along lateral direction. The values of expansion were larger than our instrumental resolution. The lateral expansion rate of lattice constants in GaN wurtzite was larger than that in GaN zinc blende. It was found that zinc-blende phase was unevenly distributed, but wurtzite one was uniformly distributed by growth condition.

Laue-Case Plane Wave Topography Using Synchrotron Radiation to Reveal Microdefects in a Thinned Silicon Crystal

X-ray plane-wave topography in a Laue-transmission case has been widely used to observe microdefects in otherwise perfect silicon crystals. To show the experimental effect of specimen thickness, plane-wave topographic observations were conducted before and after the stepwise chemical etching of the specimen crystal. The observations showed a heightening of the strain sensitivity when reducing the specimen thickness to less than several times the extinction distance of the relevant diffraction. The thickness effect was interpreted through X-ray dynamical diffraction theory for distorted crystals (Takagi-Taupin theory). The computer simulations of the diffraction theory proved that correlations exist amongst the divergence of the incident X-ray beams, the crystal thickness, and the quantity of the minute strain.