Quantifying the stability of the probe current of scanning electron microscopes

Abstract Probe current stability in a scanning electron microscopy (SEM) is a critical factor related to the realization of high-resolution imaging and accurate nanoscale metrology, including critical dimension measurements and depth estimations. While prior research has predominantly focused on noise sources and long-term drift, systematic quantifications of sensitivity coefficients and measurement uncertainties across various electron gun configurations remain insufficient. Without a clear understanding of how structural parameters such as the tip radius and extractor gap affect probe current stability, optimizing electron sources for advanced metrology continues to be a challenge. Moreover, the lack of experimental validation hinders reliable uncertainty analyses. In this study, we evaluate both short-term and long-term probe current stability levels for thermal field emission and cold field emission sources using Allan deviation and autocorrelation function analyses. Sensitivity coefficients with respect to the extraction voltage are systematically simulated over a range of tip radius and extractor gap distances, revealing direct correlations between geometric design parameters and current stability levels. Experimental measurements are combined with simulation results to quantify the combined standard uncertainty and expanded uncertainty of the probe current for various electron gun configurations. These results establish a clear correlation between emission structure parameters and probe current variations, providing a practical basis for the optimization of electron-optical systems in SEM applications for improved stability and metrology performance outcomes.