Resolving the Electron Plume within a Scanning Electron Microscope

TL;DR

This paper introduces a modified SEM technique that captures momentum and energy data of secondary electrons, enabling detailed imaging of electric fields and subsurface features in nanostructures, which was previously challenging.

Contribution

The authors develop a simple modification to standard SEM to perform spectroscopic imaging of secondary electrons, revealing material and electronic properties with sub-surface sensitivity.

Findings

Able to image lateral electric fields across silicon p-n junctions

Distinguishes doped regions even when buried

Reveals strong surface band bending in passivated structures

Abstract

Scanning electron microscopy (SEM), a century-old technique, is today a ubiquitous method of imaging the surface of nanostructures. However, most SEM detectors simply count the number of secondary electrons from a material of interest, and thereby overlook the rich material information contained within them. Here, by simple modifications to a standard SEM tool, we resolve the momentum and energy information of secondary electrons by directly imaging the electron plume generated by the electron beam of the SEM. Leveraging these spectroscopic imaging capabilities, our technique is able to image lateral electric fields across a prototypical silicon p-n junctions and to distinguish differently doped regions, even when buried beyond depths typically accessible by SEM. Intriguingly, the sub-surface sensitivity of this technique reveals unexpectedly strong surface band bending within nominally passivated semiconductor structures, providing useful insights for complex layered component designs, in which interfacial dynamics dictate device operation. These capabilities for non-invasive, multi-modal probing of complicated electronic components are crucial in today's electronic manufacturing but is largely inaccessible even with sophisticated techniques. These results show that seemingly simple SEM can be extended to probe complex and useful material properties.