FEI Quanta FEG 250, User'S Operation Manual

Page: 202 / 228

System Options: Plasma Cleaner
9-54
Plasma Cleaner
The Tools menu / Sample Cleaning… item starts the Sample
Cleaning procedure, which is efficient process for removing very thin
contamination layers, which are typically formed by hydrocarbons
residues remaining on vacuum parts after conventional cleaning or
could be transferred into the microscope chamber with a sample.
The plasma cleaner generates free oxygen radicals, which react with
hydrocarbon molecules on the surfaces to form CO, CO
2
, and H
2
O
molecules that can be pumped away. It is operated at vacuum
conditions similar to the low vacuum operation (~50 Pa).
FIGURE 9-46 PLASMA CLEANER
The Sample Cleaning procedure uses cleaning times up to 5 min,
which is possible to set in the
104 - Plasma Cleaning Alignment (see
below).
For avoiding of typical “weak” contamination artefacts during high
resolution imaging (image darkening), 1-2 minutes plasma cleaning
duration in combination with cryo cleaning (see above) should be
sufficient. When bulky deposition is visible (mostly on image corners),
5 minutes duration is recommended.
Note:
Porous, biological or hydrocarbon based samples cannot typically be
viewed without presence of contamination artefacts even after plasma
cleaning, which is caused by presence of contamination source in the
sample itself.
Sometimes, poor image quality could be caused by e-beam etching
and re-deposition of etched material also.