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

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

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.

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.

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

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

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

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

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.

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