Lab meetings
Week of 6 October
• We will use the FEI Quanta FEG-SEM
• MEB 1555b
• Objectives
– Learn “knobology” of FEI tools
– Learn new detectors
• SSBSE
Feedback from lab 3
• 4 threads = 1.27 mm What is wrong?
• “The diameter of the balls is 1.78 μm.”
– Cite two problems with this statement.
• Future grading:
– -5% for each use of insignificant digits off by more
than one order of magnitude
– -25% for missing copy of lab notes
• “Affect” is always a verb (to influence); if you use
“effect” as a verb, if is probably incorrect.
• Depth of field: compare measurements to theory
in text.
• “Don’t make small changes.” F. Rosenberger
Lab 3
• This class is not an academic exercise:
you get to put on your resume that you
know how to use an SEM. How will you
remember?
• Current path: what is function of gold
coating?
• Report on a systematic variation of
parameters. Trend? Optimum?
Charging
•
•
•
•
What does it mean?
How do you recognize it?
What causes it?
What machine parameters affect it?
– How?
– Why?
– What is the definition of “probe current”?
Electron yield
• How do you
use this figure
to reduce
charging?
• Where did it
appear in your
lab writeup?
E1
E2
Paper-writing Process
•
•
•
•
List conclusions
List data to support conclusions
Collect figures to justify conclusions
“Narrative” must lead reader from what is
known (intro) to techniques used to
generate data to actual data to
conclusions
• Executive summary must contain
conclusions!
Electron Microscopy: Midterm Review
• What information can you gain from an
electron microscope?
Topography
Phase variations
Chemical composition
BSE
EDS
What are the advantages of electron
microscopy over other characterization
techniques?
•High magnification
•Huge dynamic range
•Low magnification
•Huge depth of field
•Ability to image sub-surface features
•How can you image sub-surface features?
•Chemical analysis
SEM components
• What are the major components of an
SEM?
• What is the function of each?
• Why does it need a vacuum pump?
Mean Free Path in Gases
With sufficient accuracy for
approximate calculations we may take:
λ = 7 x 10-3/p mbar-cm
λ = 5 x 10-3/p Torr-cm
λ = 5/p μmHg-cm
How is this useful in understanding
the operation of an SEM?
SEM Midterm Review
• What is the definition of magnification?
• What are the pitfalls of “magnification”?
• What factors limit the sharpness of an
image (resolution) in an SEM?
– How or why do these factors influence
resolution?
SEM Midterm Review
• There are four operating modes for an
SEM. How would you achieve each and
under what circumstances would you use
it?
•
•
•
•
Resolution mode
High current mode
Depth of focus mode
Low voltage mode
SEM Midterm Review
• How many types of electron sources are there?
• What are the advantages and disadvantages of
each?
• What factors determine the brightness of an
electron source?
• What are the functions of the electromagnetic
coils in an SEM?
• What are the different currents flowing in an
SEM?
SEM Midterm Review
• What is meant by “astigmatism”?
• How does an SEM correct for
astigmatism?
• What is the effect of working distance on
– Resolution
– Depth of field
• What factors determine depth of field?
• What factors determine field of view?
SEM Midterm Review
• What parameters determine the Gaussian beam
size?
• What is the expression for the resolution
limitation due to electron diffraction by the final
aperture?
• What is the expression for the wavelength of an
electron as a function of its energy?
• How does chromatic aberration affect probe
diameter?
– What is chromatic aberration?
SEM Midterm Review
• What factors determine the extent of
spherical aberrations?
• How do the various factors combine to
determine the final beam size on the
sample?
Beam Sample interactions
• Define interaction volume
• Define sampling volume
– Same for SE and BSE?
• On what and how does the energy loss of
beam electrons depend?
dE/ds = (2**e4*N0*Z* *ln(1.166Ei/J))/A*Ei
J = (9.76*Z + 58.5*Z-0.19)*10-3
= average energy loss per scattering event
• What is the shape of the interaction
volume?
– Material dependence?
– Beam energy dependence?
• Where is rate of energy deposition the
greatest?
• How does the interaction volume depend
on tilt?
– Define tilt!
What factors determine the range of
electrons in solids?
What is meant by “the range of electrons in
solids”?
•
•
•
•
•
•
RKO = 0.0276 A*E0 5/3/Z0.89 *ρ
A = Atomic weight
E0 = Beam energy
Z = Atomic number
ρ = Mass density (gm/cm3)
RKO (nm) = Range of electron beam in
material
• How does the range depend on tilt angle?
• How does SE coefficient depend on beam
energy?
• How does SE coefficient depend on Z?
• How does SE coefficient depend on tilt
angle? Why?
• How does backscatter coefficient depend
on Z?
• How does backscatter coefficient depend
on beam energy?
• How does backscatter coefficient depend
on tilt? Why?
• How is the beam energy distributed
between SE and BSE?
Pixels
• How do you determine the pixel size on a
sample?
• How does pixel size relate to:
– Probe diameter?
– “Sampling area”
• Under what conditions can the probe
diameter be too small?
• What is the ramification of choosing a
probe diameter that is too small?