Annular Focused Electron/Ion Beams for Combining High Spatial Resolution with High Probe Current

Area of Science:

• Physics
• Materials Science
• Nanotechnology

Background:

• Focused electron and ion beam columns often use large final apertures for high primary beam current.
• Applications like electron beam lithography and spectroscopy require high resolution, which is limited by probe size.
• Conventional hole apertures in these systems contribute to geometric aberrations, limiting spot size.

Purpose of the Study:

• To propose a novel method for reducing the final probe size in focused electron/ion beam columns operating at high primary beam currents.
• To enhance the resolution capabilities of systems used in electron beam lithography, focused ion beams, and electron beam spectroscopy.
• To mitigate the impact of geometric aberrations in objective lenses for improved beam focusing.

Main Methods:

• Introduction of an annular aperture to create a ring-shaped primary beam, replacing the conventional hole aperture.
• Integration of a specialized lens corrector unit designed to eliminate first- and second-order geometric aberrations.
• Utilization of direct ray tracing simulations to verify the aberration correction capabilities of a three-stage core lens corrector for an electric Einzel objective lens.

Main Results:

• The proposed system, using an annular aperture and corrector, is predicted to achieve a final geometric aberration limited spot size approximately 50 times smaller than conventional hole-aperture beams.
• The corrector unit effectively eliminates first- and second-order geometric aberrations of the objective lens.
• Ray tracing simulations confirm the efficacy of a three-stage core lens corrector in correcting aberrations for an electric Einzel objective lens.

Conclusions:

• The proposed annular aperture and lens corrector system offers a significant advancement in reducing probe size for high-current focused electron/ion beam applications.
• This method holds the potential to substantially improve resolution in critical applications such as electron beam lithography and spectroscopy.
• The design provides a viable pathway to overcome the limitations imposed by geometric aberrations in conventional beam column designs.