Lattice strain mapping using circular Hough transform for electron diffraction disk detection

Scanning Electron NanoDiffraction (SEND) is a powerful and versatile technique for lattice strain mapping in nano-devices and nano-materials. The measurement is based on Bragg diffraction from a local crystal volume. However, the resolution and precision of SEND are fundamentally limited by the uncertainty principle and scattering that govern electron diffraction. Here, we propose to measure lattice strain using a focused probe and circular Hough transform to locate the position of non-uniform diffraction disks. Methods for fitting a 2D lattice to the detected disks for strain calculation are described, including error analysis. We demonstrate our technique on a FinFET device for strain mapping at the spatial resolution of 1 nm and strain precision of ∼3×10⁻⁴. Using this and simulations, the experimental parameters involved in data acquisition and analysis are thoroughly investigated to construct an optimum strain mapping strategy using SEND.