Experimental and modeling study on increasing accuracy of strain measurement by ion beam analysis in SiGe strained layer thin films

We have used Rutherford backscattering spectrometry to characterize Si/ε-Si_0.8Ge_0.2/Si strained-layer heterogeneous epitaxial structures. Two-dimensional yield mapping of backscattered 2 MeV He atoms as a function of tilting angles around off-normal 〈1 1 0〉 axis are obtained. For Si/Si_0.8Ge_0.2/Si with buried strained layer, we observe distortion of (1 1 0) planar minimum in yield mapping from Ge. The distortion features slightly decreasing angular offsets with decreasing tilting away from 〈1 1 0〉 axis. Our finding suggests that strain measurements using one dimensional angular scan within or close to (1 0 0) plane will lead to strain underestimation. A two dimensional yield mapping is preferred over one dimensional angular scan for high accuracy in strain measurements, so the angular off-set can be measured in a region free of distortion. The experimental observations are in good agreement with our modeling prediction