Optimizing electron emitter module geometry for improved lifetime through test-particle Monte Carlo (TPMC) simulation

Thermal field emitters (TFEs), particularly Schottky emitters, are widely used in scanning electron microscopes (SEMs) due to their extended lifespan over other types. These emitters need UHV (Ultra-High Vacuum) – below 5x10^-9 Torr range for optimal operation. A TFE typically consists of a cylindrical suppressor cap which is mounted above the SEM column. There has been growing interest in reducing the gap between the TFE module and first lens of the column to a few hundred microns. Reducing this gap helps lower the extraction voltage of the column; however, it also results in low vacuum conductance which contributes to increased local pressure in this region. To address this, a vacuum simulation study has been conducted to understand the local pressure change as a function of geometry changes of the TFE suppressor cap module. The results from this study were used to determine an optimized suppressor cap geometry for TFE modules, allowing for high conductance, and with the goal of improving TFE stability and lifetime.