Source Shot Noise Mitigation in Focused Ion Beam Microscopy by Time-Resolved Measurement

TL;DR

This paper introduces a time-resolved measurement technique combined with maximum likelihood estimation to significantly reduce source shot noise in focused ion beam microscopy, improving image accuracy or reducing dose.

Contribution

The paper presents a novel time-resolved sensing method with maximum likelihood estimation to mitigate source shot noise in FIB microscopy, supported by Fisher information analysis and experiments.

Findings

Reduces mean-squared error by a factor of approximately the secondary electron yield.

Enables about threefold improvement in accuracy at fixed dose.

Allows for reduced dose while maintaining image quality.

Abstract

Focused ion beam (FIB) microscopy suffers from source shot noise - random variation in the number of incident ions in any fixed dwell time - along with random variation in the number of detected secondary electrons per incident ion. This multiplicity of sources of randomness increases the variance of the measurements and thus worsens the trade-off between incident ion dose and image accuracy. Time-resolved sensing combined with maximum likelihood estimation from the resulting sets of measurements greatly reduces the effect of source shot noise. Through Fisher information analysis and Monte Carlo simulations, the reduction in mean-squared error or reduction in required dose is shown to be by a factor approximately equal to the secondary electron yield. Experiments with a helium ion microscope (HIM) are consistent with the analyses and suggest accuracy improvement for a fixed source dose, or reduced source dose for a desired imaging accuracy, by a factor of about 3.