Lab meetingsWeek 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?

TopographyPhase variationsChemical composition

BSEEDS

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 GasesWith sufficient accuracy for approximate calculations we may take:

λ = 7 x 10-3/p mbar-cmλ = 5 x 10-3/p Torr-cmλ = 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?