Neil Loxley

A Novel Beam-Conditioning Monochromator for High-Resolution X-ray Diffraction

This paper describes a novel duMond-configuration monochromator for high-resolution X-ray diffraction. The device consists of two single-crystal blocks of silicon each containing two beam channels cut respectively parallel to and 17.65° from the (011) planes. In the high-intensity mode, with Cu Kα 1 radiation, the beam divergence is 11.5″ and the dispersion is 1.3×10 -4 with intensity comparable with that from a symmetric Ge 022 device. The high-resolution setting has a divergence of 4.4″ and dispersion of 4.9×10 -5 , the intensity being a factor of ten lower than in the high-intensity setting. Parallel lateral translation of the two elements permits a rapid switch between the high-resolution and high-intensity settings

X-Ray Reflectometry from Semiconductor Surfaces and Interfaces

X-ray reflectance measurements at grazing incidence provide non-destructively a measure of the thickness of thin layers, the electron density as a function of depth, and interface and surface roughness. We show that the effect of roughness at a buried interface is only to reduce the visibility of the interference fringes, whereas roughness at the top surface leads also to an overall increase in the rate of fall of intensity with angle (or energy). These two contributions can then be readily distinguished. Most work has been performed in monochromatic angular dispersive mode. We present here a preliminary study of the application of the high-energy, fixed-angle, energy dispersive mode for the study of thin epitaxial layers, Langmuir-Blodgett films, surface damage on silicon chemi-sol polished wafers and ion implanted silicon and aluminium. Data has been analysed using the theory of Parratt, which we have adapted for use in the energy dispersive method.

A Grazing Incidence X-Ray Reflectometer for Rapid Nondestructive Characterization of Thin Films and Interfaces

We describe a novel instrument dedicated to making rapid angular-dispersive grazing incidence X-ray reflectivity measurements. A novel, automatic, optical technique for rapid specimen alignment, is incorporated into the control software. We discuss the information content of diffuse scattering data collected in non-standard modes. Examples of data are presented showing the application to the characterization of semiconductors and metal multilayers. The technique is shown to be particularly powerful for measurement of the thickness of epitaxial films of AlGaAs on GaAs less than 50 nm thick and where high resolution X-ray diffraction becomes impracticable. We demonstrate that, as the method is insensitive to dislocation density, high quality data can be taken rapidly from heavily relaxed multilayers. Minimum criteria for adequate information content in the data are explored and the effect of specimen curvature is examined.

High resolution X-ray diffraction using a high brilliance source, with rapid data analysis by auto-fitting

Abstract In a production environment in particular, fast data collection and analysis, which are also highly reliable, are desirable. Measurement can be speeded up by increasing the diffracted intensity, thus reducing the time required to measure it reliably. Increased intensity with a smaller beam footprint at the sample have been achieved in a double-crystal diffractometer by the use of a novel ellipsoidal mirror working by total external reflection, positioned before the reference crystal. To optimise the performance of the mirror and provide high brightnesses, an X-ray source with a very small focal spot is required. Such a high brightness source has been made that uses electromagnetic focusing of the electron beam onto the target. Rapid data analysis is achieved by the use of an auto-fitting program that employs a genetic algorithm and the full dynamical theory of X-ray diffraction. Choice of an appropriate error function produces a deep global minimum while the genetic algorithm avoids convergence on local minima. From the model that produces the best fit, samples parameters such as layer thickness and alloy composition are extracted with quantified goodness of fit.

Dislocation images in X‐ray section topographs of curved crystals

The contrast of dislocation images in X-ray section topographs of curved crystals has been investigated both experimentally and by computer simulation. Good agreement is found between experiment and simulation in both symmetric and asymmetric Laue geometries. Very little change is observed in the symmetric Laue images for radii of curvature as small as 18m. In the asymmetric geometry, the background intensity rises and the Kato fringe visibility decreases as the curvature increases. The dynamical image becomes more localized and dominates the image as the direct image visibility falls. Our results explain the reversal of dislocation contrast in Lang projection topographs of curved crystals taken in asymmetric geometry. 1987). The differences reported in the literature can all be ascribed to artefacts of the bending process. In the asymmetric Laue geometry, however, very substantial differences occur, the most striking being a reversal of the dislocation contrast from thin crystals as the curvature is increased. This contrast reversal is also found in Lang topographs of curved crystals and was reported many years ago by Meieran & Blech (1972). Until now, this phenomenon has never been satisfactorily explained. We have undertaken an experimental and computer simulation study of the changes occurring in X-ray section topographs of a deliberately curved silicon wafer. From the results it is possible to understand the changes in the images of the (integrated wave) Lang and Hirst topographs.

Novel diffractometer optimized for the study of weak superlattice reflections using crossed parabolic mirrors

We present the development of a novel laboratory-based diffractometer optimized for high intensity and resolution matched to that of flux grown single crystal transition metal–oxide samples studied in solid state physics. This has been implemented using crossed graded d-spacing parabolic multilayer mirrors, a severely off-cut asymmetric analyzer crystal, and a microminiature cryostat. We demonstrate that the wider bandpass of the multilayer mirrors provides a significant increase in intensity compared to the use of silicon and germanium optics, but still provides the necessary resolution to obtain accurate measurements for inverse correlation lengths. The increase in flux allows the observation of features that were previously only visible with third generation synchrotron x-ray sources, shown by the observation of the very weak charge order peak without the use of a synchrotron source. Results on samples previously studied show an increase of a factor of 10 in intensity, coupled together with a factor of...

Innovative x-ray optics for laboratory

We report on recent developments of innovative grazing incidence X-ray optics for laboratory applications. These efforts focus on the developments of grazing incidence micromirrors with ellipsoidal and paraboloidal profiles and apertures well below 1 mm, as well as on the developments of innovative arrangements and approaches such as X-ray collimators based on the Lobster Eye X-ray lenses. The applications of these elements will be indicated and discussed. Moreover, we will discuss the innovative alternative technologies for X-ray optics elements in study and-or under considerations

Rapid high-resolution X-ray diffraction measurement and analysis of MOVPE pHEMT structures using a high-brilliance X-ray source and automatic pattern fitting

A novel micro-focus X-ray tube in combination with a focusing optic that uses total external reflection has been used to enhance the diffracted intensity in a double-crystal experiment, whilst simultaneously reducing the beam footprint on the sample. The increased intensity allows data to be collected more quickly. Advances in auto-fitting using the full dynamical theory of X-ray diffraction mean that sample material parameters can be extracted quickly and objectively, opening the way to automatic data analysis. Both features are attractive for non-destructive quality control of semiconductor device structures, as well as for process development and research purposes.

Microfocusing with grazing incidence x-ray micromirrors

Grazing incidence micromirrors of ellipsoidal or parabolic shape with apertures below 1 mm have numerous potential applications in many areas of applied physics, molecular biology and material research. One of the most important applications of such optics is in its combination with microfocus x-ray generator. Extremely intense collimated or focused high-quality x-ray beams from tabletop equipment can be obtained in this way. It is shown that though developed primarily for macromolecular crystallography, this combination gave excellent results also in other fields of science and technology. Computer ray-tracing and experimental data characterizing mirror and x-ray beam parameters in typical applications are presented.

Application of a Desk-Side Double-Axis X-Ray Diffractometer for Very Large Area Epilayer Characterization

A new desk-side double-axis X-ray diffractometer capable of rapid, automatic measurement of lattice mismatch between epitaxial thin films and substrate in a two dimensional grid 150 mm square has been built. The design principles behind the five independent axis systems, specimen loading, and the fail-to-safety X-ray shutter are elucidated, and examples of typical data from substrate material and thin epitaxial films of III-V compounds are presented.