1. Circuit Modeling of Dynamic Secondary Electron Contrasts in an SEM
By: Elroy Tatem
Advisors:
Dr. Cherrice Traver
Dr. Bradley Thiel (U Albany)

2. Background How the SEM works
Electrons are used instead of visible light
The electron optics use magnetic fields which are analogous to optical lenses in an optical microscope
The electrons excite the surface of the material
Secondary electrons that exit the sample are detected

3. Background How the SEM works
SEM raster circuit is the same raster circuit that goes to the CRT.
CRT also gets contrast/ intensity information from the electron detector.
Image created by changes in the amount of secondary electrons that are seen by the electron detector.

4. Charging Effects “Artifacts”
Show up as unwanted contrasts in the image produced by the SEM
Can be random or have a pattern
Sometimes repeatable
Caused by excessive negative charge build up on a sample.

5. Charging Effects Sample/ Surface interaction
Secondary emission energy vs Initial beam energy

6. close-up showing SiO2 surface structure
Charging Effects
dielectric (SiO2)
Cu pad
Cu pads
close-up showing SiO2 surface structure

7. Charge Density Charge density as a function of time
Considering δ is small compared to the specimen dimensions, input beam density σ for each frame is:
Taking into account the electrons that escape in the form of secondary electron emission:
Adding the discharging time constant

8. Charge Density Charge density as a function of time
A composite plot of the two graphs of σ depends on
is comparable to F

9. Short Term Research Goals
New model for charging specimens under an SEM using a circuit model
Make an interactive program in Microsoft™ EXCEL® where users can input microscope and specimen parameters and get information about charge density.

10. Long Term Goals
Expand model for the environmental scanning electron microscope (ESEM)
Expand program for low vacuum microscopes