Dark-Field Electron Holographic Moire Method

Abstract

A strain measurement method based on the quantum interference of coherent electron waves scattered from adjacent strained and unstrained regions of a device is discussed. The method is related to the off axis electron holography technique and is carried out in analytical TEMs equipped with an ultra-stable electron source, Lorentz lens, electron biprism and quantitative HREM software. The hologram obtained by interference of two diffracted beams from a set of lattice planes is analyzed by Fourier transformation to obtain the phase image. The geometric phase analysis used previously for strain mapping in HREM images is performed on the phase image to give the strain with high spatial resolution. This resolution is determined by the hologram fringe spacing. Moreover, all components of the strain tensor can be obtained if more than one diffracted beam is used. The method has been demonstrated for strained silicon device structures and silicon-silicon germanium epitaxial layers.

Keywords: Electron holography, Moire, Fourier transform, Geometric phase analysis, Transmission electron microscope.

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