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The performance of semiconductor devices depends critically on structural integrity at both surface/interface and bulk, making nanoscale defect characterisation essential. Techniques such as TEM, DLTS, EBIC, and ECCI involve trade-offs between non-destructive analysis, spatial resolution, and surface sensitivity. Although SEM avoids the destructive sample preparation required for TEM, SEM-based methods such as EBIC and ECCI still lack the combination of true nanometric resolution and high surface sensitivity needed for comprehensive defect characterisation.[1][2]
To overcome these limitations, this work introduces Secondary Electron Emission Spectroscopy (SEES) and Reflection Electron Energy Loss Spectroscopy (REELS) for defect analysis. SEES detects defect-induced local electronic perturbations through characteristic secondary-electron spectral fingerprints,[3] while REELS probes defect-related disruptions to material periodicity via changes in electron energy loss, such as surface-sensitive collective excitations. Together, they form a non-destructive framework for nanoscale surface defect characterization.
SEES and REELS are implemented through a cross-platform strategy for semiconductor defect analysis. Both techniques are optimised on an Ultrafast SEM equipped with a Cylindrical Mirror Analyser (CMA) under Ultra-High Vacuum (UHV), while SEES is additionally performed on a commercial high-vacuum (HV) SEM by implementing a custom energy analyser.
Epitaxial Ge/Si heterostructures serve as the test system, where lattice mismatch generates threading dislocations that degrade the device performance. A correlative microscopy workflow (EBIC, ECCI) first maps dislocations, followed by cross-platform SEES and REELS analysis. Both techniques reveal a clear contrast between defective and defect-free regions, showing that dislocations measurably modify secondary electron emission and energy loss behaviour.
SEES–REELS correlation in Ge/Si heterostructures reveals spectral contrast from defects, confirming their suitability for nanoscale characterisation. Future work targets 2D spectral mapping and extension to an Ultrafast SEM (USEM) to probe photoexcitation effects on secondary electron emission and collective excitations such as plasmons in the loss spectrum, and their impact on excitation and loss cross-sections. This includes defect-induced changes in work function, carrier diffusion, and inelastic scattering. Overall, SEES and REELS are poised to be a non-destructive, high-resolution and surface-sensitive metrology platform.
This work is funded by the European Union – NextGenerationEU – Project Number 2022LA3TJ8 –CUP D53D23002280006, Project P2022YM8J3 – CUP D53D23018720001, Project PE0000021 -CUP D43C22003090001
[1] H. J. Leamy, "Charge collection scanning electron microscopy," J. Appl. Phys. 53, R51 (1982).
[2] S. Zaefferer and N.-N. Elhami, "Theory and application of electron channelling contrast imaging under controlled diffraction conditions," Acta Mater. 75, 20-50 (2014).
[3] W. Han, M. Zheng, A. Banerjee, Y. Z. Luo, L. Shen, and A. Khursheed, "Quantitative material analysis using secondary electron energy spectromicroscopy," Sci. Rep. 10, 22144 (2020).