Plasma Processing in the SEM:The Reality (or nuisance) of SEM Hydrocarbon Contamination

Have you ever de-magnified when imaging in your electron microscope and notice dark scanlines on your sample?

Chances are most of us who do not have in-situ plasma processing supporting our analysis will see these artifacts. This is hydrocarbon carbon contamination. In the long run this can impede optimum performance of your SEM.

As important as it is to change the oil in your car for long term optimum engine performance it is just as important to regularly in-situ plasma clean your SEM chamber. Hydrocarbons can be introduced into our chambers by outgassing samples or by poor specimen handling.

Analyzing carbon by EDS in an electron microscope is difficult for a number of reasons. The Carbon X-ray K line is of low energy and is easily absorbed. An effectively plasma cleaned SEM chamber will also improve carbon quantification by SEM-EDS analysis.

As carbon has one of the lowest secondary electron coefficients of any material, it almost always appears dark in secondary electron images. Hydrocarbons on samples inhibits secondary electron emission while reducing image contrast. This double negative causes a lack of surface detail and low contrast. More problematic is when carbon accumulates inside the chamber, in the lower column and on the final aperture this makes it more difficult to correct image astigmatism.

Here are the immediate and long term benefits of consistent in-situ plasma processing of the SEM chamber:

• Improved carbon quantification by SEM-EDS analysis.
• Improve clarity of EBSD patterns
• Greater contrast
• Higher resolution
• Cleans BS Detector surfaces yielding improved signal to noise ratio.
• Lower ultimate chamber vacuum and faster pump down.
• prevents column and possible gun contamination.
• Longer aperture lifetime