Depth profiling of strain and defects in Si∕Si1−xGex∕Si heterostructures by micro-Raman imaging

Abstract

We have reported depth and in-plane profiling of strain, Ge composition, and defects in strained-Si∕Si1−xGex∕Si heterostructures using micro-Raman imaging. Raman profiling in the depth direction was carried out with a depth resolution of ∼15nm using a small-angle beveled sample and ultraviolet (UV) excitation. Depth profiles of the Ge composition and Raman bandwidth clearly show that the defect density depends strongly on the Ge-grading rate in a compositionally graded Si1−xGex layer. The in-plane strain variation at a given depth in each layer has been evaluated. The in-plane strain variations in the Si1−xGex are closely related to clustering of misfit dislocations in the graded Si1−xGex layer. For the top strained-Si layer, two-dimensional UV-Raman images of the frequency and bandwidth of the Si band reveal that film crystallinity is correlated with the magnitude of in-plane strain. The close correlation between the frequency and bandwidth is attributed to inhomogeneous strain fields associated with misfit dislocation clusters, which induce complete relaxation of strain in constant composition Si1−xGex layers.