Tomographic Mapping Analysis in the Depth Direction of High-Ge-Content SiGe Layers with Compositionally Graded Buffers Using Nanobeam X-ray Diffraction.

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.