X-ray diffraction topography (diffractometry) is a traditional method of visualising crystal structure perfectness on a film with a high spatial resolution. However, angular misorientation inspection requires multiple exposures for several diffraction angles around the Bragg peak by means of a manual film exchange, which is a bit cumbersome. This limitation has been overcome by utilisation of digital 2D detectors which were available at synchrotron imaging beamlines with high flux and parallel beam, thus the rocking curve imaging (RCI) technique has been developed. Recently, RCI was transferred from synchrotron to laboratory set-ups.
Nowadays, RCI is an X-ray diffraction technique which combines full-field X-ray digital topography and Bragg-diffraction rocking curve recording. A large (almost) parallel monochromatic beam irradiates a crystalline sample with a misorientation distribution characterized by local tilt angles. Series of digital topographs are measured by a two-dimensional detector at different sample orientations from which peak characteristics of millions of local Bragg peaks from each series are extracted. The field of view and lateral resolution is given by the camera size, its pixel size and the Bragg angle, while the angular resolution is given by the rocking curve width being typically much smaller than the misorientation angles of the studied crystal. Simultaneous high spatial resolution provided by the two-dimensional detector and high angular resolution (0.001°) allows to quantify crystalline structure perfectness over large sample area which scales with the area of the detector. Therefore the rocking curve imaging is an imaging method with faster recording compared to usual laboratory scanning area diffractometry which requests measurement of the rocking curve at each surface point.
Synchrotron RCI [1,2] profits from large parallel beam, high flux and small detector pixel size down to one micrometre. For small misorientations of the crystal lattice, detector can have any distance from the sample, while larger misorientations due to inherent focusing and defocusing of the diffracted (micro)beams require a dedicated reconstruction procedure.
Laboratory RCI [3] with a slightly diverging beam requires small misorientation angles and very small sample to detector distance, thus a home-made extension for a commercial diffractometer is necessary. Current two-dimensional detectors available at laboratory diffractometers have typical spatial resolution downto 0.1 mm which make it possible to analyze a large sample area at once.
On several examples, we will demonstrate the RCI technique for a characterisation of several large-area semiconductor wafers, such as silicon, silicon carbide, gallium nitride or overgrown silicon-germanium microstructures.