Petr Mikulík

High-resolution three-dimensional imaging of flat objects by synchrotron-radiation computed laminography

Computed laminography with synchrotron radiation is developed and carried out for three-dimensional imaging of flat, laterally extended objects with high spatial resolution. Particular experimental conditions of a stationary synchrotron source have been taken into account by a scanning geometry different from that employed with movable conventional laboratory x-ray sources. Depending on the mechanical precision of the sample manipulation system, high spatial resolution down to the scale of 1μm can be attained nondestructively, even for objects of large lateral size. Furthermore, high beam intensity and the parallel-beam geometry enables easy use of monochromatic radiation for optimizing contrast and reducing imaging artifacts. Simulations and experiments on a test object demonstrate the feasibility of the method. Application to the inspection of solder joints in a flip-chip bonded device shows the potential for quality assurance of microsystem devices.

On the implementation of computed laminography using synchrotron radiation

Hard x rays from a synchrotron source are used in this implementation of computed laminography for three-dimensional (3D) imaging of flat, laterally extended objects. Due to outstanding properties of synchrotron light, high spatial resolution down to the micrometer scale can be attained, even for specimens having lateral dimensions of several decimeters. Operating either with a monochromatic or with a white synchrotron beam, the method can be optimized to attain high sensitivity or considerable inspection throughput in synchrotron user and small-batch industrial experiments. The article describes the details of experimental setups, alignment procedures, and the underlying reconstruction principles. Imaging of interconnections in flip-chip and wire-bonded devices illustrates the peculiarities of the method compared to its alternatives and demonstrates the wide application potential for the 3D inspection and quality assessment in microsystem technology.

Self-assembled carbon-induced germanium quantum dots studied by grazing-incidence small-angle x-ray scattering

We present a structural investigation of buried C-induced Ge quantum dot multilayers grown on (001) Si by molecular-beam epitaxy. Using grazing-incidence small angle x-ray scattering, we determine the shape, the mean radius, height, and dot distance. The dot distribution is isotropic within the (001) interfaces, and no correlation of the dot positions along growth direction was found.

Coplanar and non-coplanar x-ray reflectivity characterization of lateral W/Si multilayer gratings

Structural characterization of a fully etched amorphous W/Si multilayer grating with a lateral periodicity of 800 nm is performed by x-ray reflectivity in the coplanar and non-coplanar modes using a scintillation detector and a two-dimensional gas-filled detector, respectively. Three-dimensional reciprocal space constructions were used to explain the scattering features recorded in both geometries. Coplanar coherent grating truncation rods were fitted by a dynamical theory for rough gratings. Comparison of the reflectivity from the reference planar multilayer completes the study.

High-resolution three-dimensional imaging by synchrotron-radiation computed laminography

The methodical development and first instrumental implementation of computed laminography / tomosynthesis using synchrotron radiation are presented. The technique was developed for three-dimensional imaging of flat and laterally extended objects with high spatial resolution. This paper introduces the fundamental principle of the imaging process and discusses the methods particularities in comparison to computed tomography and computed laminography / digital tomosynthesis. Introducing a simple scanning geometry adapted to the particular experimental conditions of synchrotron imaging set-ups (such as the stationary source and a parallel beam) allows us to combine the advantages of laminography and those provided by synchrotron radiation, for instance monochromatic radiation in order to avoid beam hardening artefacts, high beam intensity for achieving high spatial resolution and fast scanning times or spatial coherence for exploiting phase contrast. The potential of the method for three-dimensional imaging of microelectronic devices is demonstrated by examples of flip-chip bonded and wire-bonded devices.

In-line Bragg magnifier based on V-shaped germanium crystals

In this work an X-ray imaging system based on a recently developed in-line two-dimensional Bragg magnifier composed of two monolithic V-shaped crystals made of dislocation-free germanium is presented. The channel-cut crystals were used in one-dimensional and in two-dimensional (crossed) configurations in imaging applications and allowed measurement of phase-contrast radiograms both in the edge-enhanced and in the holographic regimes. The measurement of the phase gradient in two orthogonal directions is demonstrated. The effective pixel size attained was 0.17 µm in the one-dimensional configuration and 0.5 µm in the two-dimensional setting, offering a twofold improvement in spatial resolution over devices based on silicon. These results show the potential for applying Bragg magnifiers to imaging soft matter at high resolution with reduced dose owing to the higher efficiency of Ge compared with Si.

Local wing tilt analysis of laterally overgrown GaN by x-ray rocking curve imaging

We report on recent advances in spatially resolved x-ray diffraction, extending the technique known as rocking curve imaging down to 1–2 µm spatial resolution. Application to a set of gallium nitride samples grown by epitaxial lateral overgrowth (ELO) shows the potential of the technique. Quantitative information on crystallographic misorientations and lattice quality can be obtained by direct imaging with high lateral resolution. Results from two samples of ELO-GaN grown on different substrates are compared. Tilt in individual lateral periods of the ELO structure can be quantified. Local tilt fluctuations are distinguished from macroscopic variations (curvature). The local lattice quality can be investigated via the peak width of diffraction profiles recorded in individual camera pixels. The peak broadening previously observed in laboratory x-ray diffraction measurements is found to have (at least) two different reasons. In both cases, peak broadening does not indicate a degradation in local crystalline quality.

Synchrotron area diffractometry as a tool for spatial high-resolution three-dimensional lattice misorientation mapping

We have developed a high-resolution diffraction imaging method for determination of the complete three-dimensional rotational local lattice misorientation of crystalline samples. The method, called synchrotron area diffractometry, is based on recording double-crystal diffraction rocking scans in three mutually non-coplanar scattering planes with a two-dimensional area detector. The subsequent multiple-peak analysis of the rocking curve image series for all pixels and their backprojection to the wafer surface provides local misorientation angles (Euler angles) with spatial resolution up to micrometre range over the wafer surface. We applied this technique to determine the distribution of tilt and twist angles of the lattice misorientation of a macroscopic defect localized in a 6 inch semi-insulating GaAs(001) wafer.

Strain relaxation in periodic arrays of Si/SiGe quantum wires determined by coplanar high-resolution x-ray diffraction and grazing incidence diffraction

Elastic relaxation in dry-etched periodic wires fabricated from molecular beam epitaxy grown Si/SiGe multilayers was studied by coplanar and grazing incidence (GID) high-resolution x-ray diffraction. The inhomogeneous strain distribution in the wires was calculated by the finite element method, which provided the input data for simulations of the scattered intensities using kinematical diffraction theory used for comparison with measured reciprocal space maps. A fabrication-induced layer covering the wire surfaces, modifies the strain distribution. Using GID, the geometrical shape of the wires and their in-plane strain can be determined independently of each other.

Diffractive-refractive optics: (+,-,-,+) X-ray crystal monochromator with harmonics separation.

A new kind of two channel-cut crystals X-ray monochromator in dispersive (+,-,-,+) position which spatially separates harmonics is proposed. The diffracting surfaces are oriented so that the diffraction is inclined. Owing to refraction the diffracted beam is sagittally deviated. The deviation depends on wavelength and is much higher for the first harmonics than for higher harmonics. This leads to spatial harmonics separation. The idea is supported by ray-tracing simulation.