Electron Trajectory Analysis in Electron Microscopes

In this article, we will analyze electron trajectories inside an SEM (Scanning Electron Microscope) using PIC-PLASMA 3D (plasma analysis software) or PIC-ELECTRON 3D (electron trajectory analysis software). SEM (Scanning Electron Microscope) is a device that scans the sample surface with a finely focused electron beam to observe microscopic shapes and structures. Even regions that are difficult to observe with an optical microscope can be examined at high resolution by using an electron beam.

Electron Trajectories Inside an SEM

Figure 1: Conceptual illustration of electron trajectories in an SEM

What is an SEM? In an SEM, electrons emitted from the electron source are accelerated and shaped into a narrow beam by electromagnetic lenses and apertures before being directed onto the sample. By detecting secondary electrons and backscattered electrons generated at the sample surface, differences in surface morphology and composition can be observed. Electron Energy The kinetic energy obtained by an electron can be approximately expressed as follows for an accelerating voltage V [V]. In an SEM, the accelerating voltage and lens conditions significantly affect the electron beam diameter, transportability, and incidence conditions on the sample. In this article, we will visualize the process of electron extraction, acceleration, and focusing inside an SEM using PIC-ELECTRON 3D.

SEM Analysis

Let us analyze electron trajectories inside an SEM using PIC-ELECTRON 3D. The analysis model is shown below. Analysis Model

Figure 2: SEM analysis model

We create a simplified analysis model of the SEM interior as shown above and simulate the process from electron beam generation to arrival at the sample. The role of each component in the SEM is as follows. Analysis Conditions The analysis conditions are as follows.

Analysis Software	PIC-ELECTRON 3D
Analysis Type	Electron Trajectory Analysis
Analysis Object	sem.obj
Voltage	Cathode: -3000 [V]　Anode: 0 [V]　Sample: 0 [V]
Relative Permittivity (Dielectric)	Insulator: 9.5
Magnetic Field Condition	Electromagnetic Lens: Set according to the analysis conditions
Number of Generated Electrons per 1 ns	10,000
Initial Velocity of Generated Electrons	1.0×103 [m/s]
Time Step	1.0×10-11 [s]
Total Simulation Time	2.0×10-8 [s]

The figure below shows the input screen for the analysis conditions used in this SEM simulation in PIC-ELECTRON 3D.

Figure 3: SEM analysis condition settings in PIC-ELECTRON 3D

Analysis Results

Figure 4: Electron trajectory analysis inside an SEM

The material above is an example of electron trajectory analysis results inside an SEM actually calculated using PIC-ELECTRON 3D. In Figure 4, you can see electrons emitted from the electron source being transported toward the sample while being focused more narrowly by the accelerating voltage and lens action. In an SEM, the divergence and convergence state of the electron beam affects observation resolution, so this kind of electron trajectory analysis is useful for equipment design and condition optimization. Please note that the CAD model used here was created as a simplified model, so the lens conditions and component shapes are simplified for explanatory purposes. In addition to the calculation results shown above, PIC-ELECTRON 3D can also output various kinds of data. *The above is just one example. Please make full use of PIC-ELECTRON 3D for SEM and electron beam product development and equipment design.*