Secondary Electron Count Imaging in SEM

TL;DR

This paper introduces a secondary electron count imaging method in SEM that improves image quality by reducing noise, achieving about 30% better signal-to-noise ratio with minimal hardware changes.

Contribution

The authors develop a simple, hardware-efficient SE count imaging technique that enhances SEM image quality by directly counting secondary electrons instead of averaging signals.

Findings

Achieved approximately 30% increase in signal-to-noise ratio.

Implemented SE counting with minimal external hardware requirements.

Demonstrated compatibility with existing SEM systems.

Abstract

Scanning electron microscopy (SEM) is a versatile technique used to image samples at the nanoscale. Conventional imaging by this technique relies on finding the average intensity of the signal generated on a detector by secondary electrons (SEs) emitted from the sample and is subject to noise due to variations in the voltage signal from the detector. This noise can result in degradation of the SEM image quality for a given imaging dose. SE count imaging, which uses the direct count of SEs detected from the sample instead of the average signal intensity, would overcome this limitation and lead to improvement in SEM image quality. In this paper, we implement an SE count imaging scheme by synchronously outcoupling the detector and beam scan signals from the microscope and using custom code to count detected SEs. We demonstrate a ~30% increase in the image signal-to-noise-ratio due to SE counting compared to conventional imaging. The only external hardware requirement for this imaging scheme is an oscilloscope fast enough to accurately sample the detector signal for SE counting, making the scheme easily implementable on any SEM.