A high-Ge-content SiGe/compositionally graded SiGe-stacked structure grown on Si(001) is now considered to be an important platform for the realization of advanced nanometer-scale complementary metal oxide semiconductor devices with high-mobility channel materials, such as III-V materials and Ge, and monolithically integrated photonic modules. The performance of such advanced devices is critically influenced by crystalline inhomogeneity in the stacked structure; therefore, precise characterization of the crystallinity is important. In particular, the development of a characterization method not only for in-plane crystallinity but also for in-depth crystallinity is strongly required. This is because the crystalline quality of the constant composition SiGe is sensitively dependent on that of the compositionally graded SiGe layers underneath. Here, we have demonstrated in-depth tomographic mapping of a high-Ge-content SiGe/compositionally graded SiGe-stacked structure using position-dependent ω-2θ map measurement using nanobeam X-ray diffraction. This mapping technique is based on the correspondence of each 2θ value in the ω-2θ map to the lattice constant of stacked layers in the depth direction. Application of the proposed analytical procedure provides tomographic maps of the local variation in lattice plane tilting (VLPT) from the obtained ω-2θ maps. It is quantitatively verified that the local crystallinity in the layer at a certain depth is strongly influenced by that underneath the layer. The correlation between the local VLPT and real structural defects in the stacked structure is also discussed in detail.

We quantitatively evaluated lattice plane microstructure, which includes lattice plane tilt, spacing, twist, and their fluctuations, in a modified Na-flux GaN bulk single crystal using the synchrotron-based nanobeam X-ray diffraction method. The GaN crystal was fabricated by two-step growth; the first layer had coalescence boundaries as a consequence of faceted growth from the multipoint-seed GaN template, and the second layer grew on the first without faceted growth. Position-dependent ω-2θ-φ mapping analysis revealed in-plane distribution of local lattice plane microstructure along with dislocation morphology around the coalescence boundary and the growth-stage boundary (GSB). Faceted growth from the multipoint seed template led to concentration of a-type dislocations at the coalescence boundary. These dislocations would glide widely on basal planes above the GSB, and then homogeneously propagate toward the surface. As a result, the modified Na-flux GaN crystal had a homogeneous lattice plane microstructure with little bunching of threading dislocations.

This work quantitatively assessed the three-dimensional distribution of crystal lattice distortions in an epitaxial AlN thick film grown on a trench-patterned template, using nanobeam X-ray diffraction. Position-dependent ω-2θ-φ mapping clearly demonstrated local tilting, spacing and twisting of lattice planes as well as fluctuations in these phenomena on a sub-micrometer scale comparable to the pitch of the trench-and-terrace patterning. Analysis of the crystal lattice distortion in the depth direction was performed using a newly developed method in which the X-ray nanobeam diffracted from the sample surface to specific depths can be selectively detected by employing a Pt wire profiler. This technique generated depth-resolved ω-2θ-φ maps confirming that fluctuations in lattice plane tilting and spacing greatly depend on the dislocation distribution and the history of the AlN epitaxial growth on the trench-patterned structure. It was also found that both fluctuations were reduced on approaching the AlN surface and, in particular, were sharply reduced at specific depths in the terrace regions. These sharp reductions are attributed to the formation of sacrificial zones with degraded crystal quality around the trenches and possibly lead to raising the crystal quality near the surface of the AlN film.

We have investigated the three-dimensional configuration of lattice distortions, including lattice plane tilt and twist, in a high-Ge-content constant-composition Si 0.3 Ge 0.7 (CC-SG)/ compositionally graded SiGe strain-relaxed buffer (graded SRB)/Si(001) stacked structure. Position-dependent ω-2θ-j mapping (or three-dimensional reciprocal space mapping) by synchrotron-based nanobeam x-ray diffraction revealed the in-plane distributions of both local tilt and twist within an area of 10×10 μm on the sample surface. Depth-resolved crystal information was extracted analytically on the basis of structural features in the graded SRB layer. As a result, a series of tomographic maps that show the three-dimensional distributions of tilt and twist around the CC-SG/graded SRB interface were obtained. Tomographic analysis indicates that the orientation of lattice planes in the graded SRB abruptly changes at a specific depth and at a specific interval. The misfit dislocation distribution observed using transmission electron microscopy is not homogeneous but concentrated at a specific depth, which accounts for the abrupt changes of lattice plane tilt and twist. Our tomographic results clearly verify the dislocation morphology in the SiGe stacked structure, which demonstrates that this analysis method can be a powerful tool for quantitative and non-destructive elucidation of a three-dimensional lattice structure with high spatial resolution.

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