Effects of surface relaxation on convergent-beam electron diffraction analysis of stress in silicon

Convergent-beam electron diffraction on cross-sectional transmission electron microscopy specimens can map strains in the silicon substrate of microelectronics devices with high spatial resolution. However, at shallow depths below the interface, most of the diffraction lines within a convergent-beam electron diffraction pattern are split, rendering pattern interpretation impossible in the classic way. The splitting effect was systematically analysed for a variety of materials, and the same qualitative behaviour that can be explained by stress relaxation at the surfaces of the thin transmission electron microscopy specimen was observed. The effects of surface relaxation are modelled by finite elements simulations. The results predict well the experimental magnitude of the splitting for a variety of diffraction lines at different positions below the interface, but fail to simulate the intensity of the secondary lines. Possible reasons for such discrepancies are discussed and assessed.