Wave Optical Modeling of the SEM Column From Source to Specimen

Area of Science:

• Physics
• Materials Science
• Electron Microscopy

Background:

• Traditional scanning electron microscope (SEM) probe formation models often simplify the optical system.
• Existing models rely on point-spread functions or Fourier transforms, limiting accuracy.
• A complete wave optical model for the entire SEM column is lacking.

Purpose of the Study:

• To develop the first complete wave optical model for an entire SEM column.
• To address challenges in plane-by-plane electron beam propagation and aliasing.
• To accurately simulate electron beam distribution from source to specimen.

Main Methods:

• Developed a general wave optical propagation method using plane-by-plane electron beam wavefunction propagation.
• Employed a two-step propagator to model beam distribution throughout the SEM column.
• Overcame aliasing problems caused by sampling limitations through careful propagator selection and combination.

Main Results:

• Achieved appropriate probe widths by successfully overcoming aliasing.
• Demonstrated accurate modeling of electron beam distribution from virtual source to specimen plane.
• Validated simulation results against geometrical theory of probe formation.

Conclusions:

• The developed wave optical model provides a more accurate representation of SEM probe formation.
• Combined lens aberrations (condenser and objective) require a full column model for accurate representation.
• Novel applications include designing beam shaping experiments and studying partial coherence effects.