Online Beam Current Estimation in Particle Beam Microscopy

TL;DR

This paper introduces a method for online estimation of beam current in particle beam microscopy using secondary electron count data, improving micrograph accuracy and enabling real-time instrument diagnostics.

Contribution

It presents novel estimators for joint beam current and secondary electron yield estimation, leveraging time-resolved measurements and inter-pixel correlation models.

Findings

Estimated beam current improves micrograph accuracy to near-perfect levels.

Joint estimators outperform state-of-the-art methods in synthetic data tests.

The approach enables online diagnostics and better milling outcomes.

Abstract

In conventional particle beam microscopy, knowledge of the beam current is essential for accurate micrograph formation and sample milling. This generally necessitates offline calibration of the instrument. In this work, we establish that beam current can be estimated online, from the same secondary electron count data that is used to form micrographs. Our methods depend on the recently introduced time-resolved measurement concept, which combines multiple short measurements at a single pixel and has previously been shown to partially mitigate the effect of beam current variation on micrograph accuracy. We analyze the problem of jointly estimating beam current and secondary electron yield using the Cramer-Rao bound. Joint estimators operating at a single pixel and estimators that exploit models for inter-pixel correlation and Markov beam current variation are proposed and tested on synthetic microscopy data. Our estimates of secondary electron yield that incorporate explicit beam current estimation beat state-of-the-art methods, resulting in micrograph accuracy nearly indistinguishable from what is obtained with perfect beam current knowledge. Our novel beam current estimation could help improve milling outcomes, prevent sample damage, and enable online instrument diagnostics.