Mapping strains at the nanoscale using electron back scatter diffraction

In this paper, we describe the use of electron back scatter diffraction (EBSD) to study strain variations in crystalline samples at the nanoscale. The analysis relies on cross correlation measurements of small shifts in the EBSD pattern measured at many points dispersed across the pattern. The method allows the full strain tensor, and lattice rotations to be obtained at a sensitivity of ∼10−4. The method is applied to study variations of strains and rotations near the surface of 200 nm thick epitaxial layers of Si0.85Ge0.15 grown on a Si substrate patterned with rectangular and square mesa. Linescans across rectangular mesas show that strain relaxation and accompanying lattice rotations are restricted to the edges of wide mesas but that the relaxation extends across the entirety of mesas narrower than ∼6 μm. Two dimensional maps of the strain variation in a ∼3 μm wide square mesa are also presented.