Fig. 1. Structure and vacuum diagram of ESEM

Fig. 2. Schematic diagram of vacuum resistance structure of double throttle tube

Fig. 3. Relationship between diameter of diffuse circular spot of each aberration and half angle of beam

Fig. 4. Optimized objective structure and simulation results of magnetic field on axis. (a) Diagram of optimized objective structure; (b) field distribution of objective lens axis corresponding to excitation of 936 ampere-turns (1 A)

Fig. 5. Simulation diagram of a single deflection coil in upper deflection. (a) Simulation model; (b) magnetic field distribution on axis

Fig. 6. Beam spot sizes corresponding to different scanning fields when focusing field and deflection field are considered simultaneously (Working distance is 15 mm)

Fig. 7. Simulation results of electron beam spot and aberration spot. (a) Electron beam spots at various locations of deflection field; (b) aberration spots at various locations of deflection field

Fig. 8. Electron beam trajectory

Fig. 9. Three-stage vacuum differential test structure

Fig. 10. Magnetic field test results of objective lens. (a) Corresponding on-axis magnetic field distributions at different currents; (b) on-axis magnetic field distributions at different angles of rotation of rotary table when coil is energized with 1 A current

Fig. 11. Experimental platform and test sample. (a) ESEM experimental platform; (b) physical object of objective lens with a variable vacuum structure; (c) imaging results of target grid samples under high vacuum by ZEISS Gemini SEM

Fig. 12. Imaging results and imageJ analysis results. (a) Scanning field of 20 μm×20 μm; (b) scanning field of 80 μm×80 μm