Metrology - University of Kansas
Transcript of Metrology - University of Kansas
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MetrologyScanning profilometry (contact and non-contact)
SEM
AFM
Contact angle
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By Emok - Own work, GFDL, https://commons.wikimedia.org/w/index.php?curid=3783176
Contact Profilometry
A tip, called a stylus, is scanned over the surface of a sample with a given applied force and measures variations in the surface topology
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• Stylus radius ranges from 20 nm
to 50 mm. (Typical 2-15 mm)
• Can measure heights ranging
from 10 nm to 1 mm.
• Extremely quick measurement
• Very common tool – present in
most cleanrooms
• Typically only scans a line
across the sample
• 3D imaging possible, but at
much lower resolution
Contact
Profilometry
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Contact Profilometry Data
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Optical Profilometry
• Non-contact profilometer based on
optical feedback
• Much faster than contact (stylus)
based profilometry
• 3D mapping is more practical than
with a stylus based system
• Lateral resolution ranges from a few
microns to sub micron
Most common types of optical
profilometers
• Optical Interference
• Confocal Aperture
• Focus Detection
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http://www.laserfocusworld.com/articles/print/volume-46/issue-1/features/optical-surface-profiling.html
Interference Profilometry
• Sample moves up and down
• Light from sample and a
reference mirror recombine at
the detector to produce
interference fringes.
• Height at which the
interferogram is in best focus is
recorded for each point
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The optical path difference = height difference
Each transition (dark/light) =1/2 wavelength
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Confocal Aperture
http://www.nanoscience.com/technology/optical-profiler-technology/confocal-wli-pattern-projection-focus-detection/confocal-profilometry/ 7
1. Illumination wavelength is 409
nm.
2. 0.5 nm linear scale module (Z-
resolution).
3. Resolution Repeatability, Z-axis:
≤10 nm.
4. Smallest Feature Detection: ≤10
nm.
5. Spatial Resolution (X/Y): ≤ 180
nm.
6. Motorized Stage: X-Y-Z ; 100 mm
x 100 mm range min.
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Optical Resolution
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Practical limit obtained when imaging very small objects
by magnification
diffraction causes blurring of objects when imaging
smaller than 200-500 nm
(diffraction limit)
“broadening” of a point caused by diffraction is
known as the “point spread function, PSF” ()
x-y = (0.61 )/( sin())
= refractive index medium
= half-cone angle of focused light
=𝜆
2 𝑁𝐴
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Optical Profilometry Examples
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Stylus versus Optical Profilometry
http://www.filmetrics.com/opticalprofilers/profilm3d-vs-stylus10
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Scanning Electron Microscopy
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http://www.ammrf.org.au/myscope/sem/background/
Light Microscope versus SEM
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Scanning Electron Microscopy (SEM)
X-rays
SEM detected electrons
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1. Tungsten filament
2. Solid state crystal (Cerium hexaboride or Lanthanum
hexaboride)
3. Low energy (50 eV)
4. Image formed by inelastic scattering
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Secondary Electron Image
1. Secondary electrons are knocked out of the sample by the primary electron beam.2. Escape Depth = ~2 nm. 3. SE image is an image of surface topography
i.e. reveals topographical contrast.
SE generation indicates the shape, edges produce more electrons – better contrast, looks brighter
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Back Scattered Electrons• BSE are primary electrons that scatter back out of the sample.
• BSE signal arises from a much deeper depth than secondary electrons
• Images show less surface topology, but more atomic number contrast
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SE vs BSESecondary
Electron Image
Backscattered
Electron Image
Solder on a circuit board16
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ChargingA buildup of negative charge on a specimen irradiated with an electron beam.
http://www.ammrf.org.au/myscope/sem/practice/principles/troubleshooting.phphttp://classes.mst.edu/civeng120/extra/galena_rose/index.html
Sample preparation considerations:• In a traditional SEM, non-conductive samples should
be coated with metal, carbon to prevent charging (a thin conductive film)
• An environmental SEM (ESEM) can be used to prevent charging (allows wet samples visualization, water vapor is an imaging gas)
gaseous secondary electron detector
https://itg.beckman.illinois.edu/microscopy_suite/equipment/downloads/how_it_works.pdf17
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Charging
http://www.ammrf.org.au/myscope/sem/practice/principles/troubleshooting.phphttp://classes.mst.edu/civeng120/extra/galena_rose/index.html
Sample preparation considerations:
• In a traditional SEM, non-conductive samples should be coated with metal to prevent charging
• An environmental SEM can also be used to prevent charging
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Atomic Force Microscopy
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https://en.wikipedia.org/wiki/Atomic-force_microscopy#/media/File:Atomic_force_microscope_block_diagram.svg
AFM Schematic
Tapping mode
• Most common imaging mode
• Tip oscillates at its resonant frequency and
taps along the surface
• Helps to prevent damage to the tip/sample
Contact mode
• A constant force is applied between the tip
and the surface.
• The tip will move up and down to track the
surface topology and keep the force
constant
• Can cause damage to the tip/sample
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https://en.wikipedia.org/wiki/Atomic-force_microscopy#/media/File:AFM_(used)_cantilever_in_Scanning_Electron_Microscope,_magnification_1000x.JPG
AFM Tips
• Wide variety of AFM tips:
• Different materials (Si, Si4N3)
• Different spring constants
• Different geometries
• Different surface chemistries
• AFM tips are much sharper
(end radius of <10 nm) than
profilometer tips
Tips with high aspect ratios may be required to
image nanochannels
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AFM of Nanochannels
FIB milled nanochannel
Resin stamp produced from FIB milled nanochannel
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Advantages of AFM• Creates a 3D map of surface
• Can calculate surface roughness
• Many other types of experiments possible (force curves, imaging
in fluid, electrical measurements, etc.)
• Can achieve atomic lateral resolution and sub nm resolution in z
Graphenehttp://blogs.lt.vt.edu/sustainablenano/2015/09/28/atomic-force-microscopy-application-in-nanoscience/
Disadvantages• Scans take much longer than
SEM (5-10 minutes per image)
• AFM artifacts can cause
distortions
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AFM Artifacts• The AFM image is a combination of surface topology and tip geometry.
Tip is not sharp enough for the feature.
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https://upload.wikimedia.org/wikipedia/commons/7/71/Afm_artifact2.pnghttp://www.nanophys.kth.se/nanophys/facilities/nfl/afm/fast-scan/bruker-help/Content/Service%20and%20Apps/Troubleshooting/AFM%20Image%20Quality.htm
AFM Artifacts
Tip is wider than
the feature.
Tip is dirty.
25Dull/dirty tip
Double tip
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http://www.ramehart.com/images/ca2.jpg
Contact Angle
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http://www.ramehart.com/images/ca2.jpg
Contact Angle
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ssg = ssl + slg • cos q
θ = contact angleσsg = surface free energy of the solidσsl = interfacial tension between liquid and solidσlg = surface tension of the liquid
Young’s Equation
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Contact Angle for Treated COC Surfaces
Can we add functionality by UV/Ozone treatment?-C-OH -COOH
Data from Colleen O’Neil, Soper lab
Polyethylene (PE)Cyclic Olefin Copolymer (COC)
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Thank You!
Any Questions?
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