Pushing the Limits of Diffraction Imaging in the Scanning Electron Microscope for the Structural Characterisation of Semiconductor Thin Films and Microstructures

To achieve the best performance from the next generation of wide bandgap semiconductor-based devices, it is crucial that we understand and optimise the structural properties (i.e., crystal structure, extended defects, misorientation and strain) of the new materials used in their manufacture. Many new materials are produced using non-planar growth techniques such as selected area growth or epitaxial overgrowth, resulting in material where defect densities, misorientation and strain vary on the micron and/or nanoscale. To fully understand and optimise subsequent devices requires a characterisation tool capable of rapidly and non-destructively mapping structural properties on the micron and nanoscale.<br/>Using advanced electron diffraction techniques in the scanning electron microscope (SEM), namely electron channelling contrast imaging (ECCI) and electron backscatter diffraction (EBSD) imaging, together with bespoke analysis software utilising pattern matching to accurate simulations of EBSD patterns and novel strain and defect analysis software, we are now able to map microstructure, defects, misorientation and strain in semiconductor thin films and 3-D microstructures with a spatial resolution of order 100 nm, a misorientation resolution of order 0.5 mrad (0.03°) and a strain resolution of order 5 × 10^-4. To date, we have characterised GaN thin films containing both wurtzite and zincblende material; mapped polarity in GaN microstructures; determined dislocation density and types in planar and non-planar GaN, AlGaN and AlN thin films; imaged misfit dislocations in AlGaN HEMT structures; imaged stacking faults in non-polar and semi-polar wurtzite GaN; and mapped strain in GaN thin films [1-5]. The benefits of imaging in the SEM include minimal sample preparation and the ability to produce images from areas ranging in size from square microns to square centimetres. Diffraction analysis can also be combined with energy dispersive X-ray spectroscopy; hyperspectral cathodoluminescence imaging; and electron beam induced current to provide complementary, non-destructive high resolution information on the structural, compositional, luminescence and electrical properties of materials [1-3]. In our presentation we will illustrate our present capabilities with recent results and explore the potential of diffraction imaging in the SEM to underpin fast optimisation of new materials and device structures.<br/>[1] C. Trager-Cowan et al., Semicond. Sci. Technol. <b>35</b> 054001 (2020).<br/>[2] F. C.-P. Massabuau et al., in "Characterisation and control of defects in semiconductors". Ed. F. Tuomisto (Institution of Engineering and Technology) (2019).<br/>[3] J. Bruckbauer et al., J. Appl. Phys., <b>127</b> 035705 (2020).<br/>[4] A. Vilalta-Clemente et al., Acta Mater. <b>125</b> 125 (2017).<br/>[5] G. Naresh-Kumar et al., Mater. Sci. Semicond. Process <b>47</b> 44 (2016).