Quantifying the Full Damage Profile of Focused Ion Beams via 4D-STEM Precession Electron Diffraction and PSNR Metrics

TL;DR

This paper introduces a novel 4D-STEM method combined with PSNR metrics to accurately quantify the full damage profile of focused ion beams, including the often-overlooked beam tail, enhancing precision in nanofabrication applications.

Contribution

The work demonstrates a new approach using 4D-STEM and PSNR to resolve and quantify the complete ion beam damage profile, including the beam tail, surpassing traditional core-focused techniques.

Findings

4D-STEM effectively detects ion beam tails at low defect densities.

PSNR metrics provide robust defect quantification against scanning artefacts.

The method offers comprehensive damage profiling beyond conventional resolution metrics.

Abstract

Focused ion beams (FIBs) are widely used in nanofabrication for applications such as circuit repair, ultra-thin lamella preparation, strain engineering, and quantum device prototyping. Although the lateral spread of the ion beam is often overlooked, it becomes critical in precision tasks such as impurity placement in host substrates, where accurate knowledge of the ion-matter interaction profile is essential. Existing techniques typically characterise only the beam core, where most ions land, thus underestimating the full extent of the point spread function (PSF). In this work, we use four-dimensional scanning transmission electron microscopy (4D-STEM) to resolve the ion beam tail at defect densities equivalent to $<$0.1 ions nm$^{-2}$. Convergent beam electron diffraction (CBED) patterns were collected in calibration regions with known ion fluence and compared to patterns acquired around static dwell spots exposed to a 30 keV Ga$^{+}$ beam for 1-10 s. Cross-correlation using peak signal-to-noise ratio (PSNR) revealed that 4D-STEM datasets are ultra-sensitive for defect quantification and more robust against scanning artefacts than conventional dark-field imaging. This approach is complementary to image resolution methods enabling a comprehensive profiling of ion-induced damage even at low-dose regimes, offering a more accurate representation of FIB performance and supporting application tailoring beyond the conventional resolution metrics focused solely on the beam core.