A New Phase in Imaging

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A New Phase in Imaging
Finding the odd atom by Jason Han and
Michael Kemeny
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Hitchhikers Guide to Our Presentation

• Aims and Introduction to Phase Imaging
• Semiconductors
• Quantum theory
• Transmission Electron Microscope
• Phase Extraction using TEM
• Data Preparation and Errors
• The Results

Jason Michael Jason
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Semiconductors and Phase Imaging

• Project partially funded by
• Semiconductor industry is highly interested in
  viewing dopant profiles at extremely high
  resolutions for
• device evaluation
• control of production process
• Current techniques that allow this heavily
  involve Phase Imaging

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Phase Retrieval and Holography
Standard Sine Waveform
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Phase Retrieval and Holography

• Phase can be found by electron holography /
  interferometry
• - Special technical requirements
• - Limited field of view
• - Phase retrieval using Transmission Electron
  Microscopy is much more flexible
• -Easily extends to many other areas including
  biological TEM

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Transmission Electron Microscope
Biofilter TEM
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Semiconductors

• Silicon is typically used for chips and
  semiconductor devices

• Impurities are deposited in extremely small
  concentrations

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Semiconductors
- Semiconductors have a band structure
-The introduction of dopants adds extra energy
levels into gap
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CMOS and Field-Effect Transistors
Complementary Metal-Oxide Semiconductor
Metal-Oxide-Semiconductor Field-Effect
Transistor
Drain
Source
Distribution of dopants in a transistor gate

• Terminals in Field-Effect Transistor are called
  gate, source and drain
• Typically made from SiO2

• Used in Microprocessors, SRAM and other digital
  logic circuits.
• CMOS devices use much less power than other
  devices

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Wave Particle Duality of Electrons
- Bohrs Principle of Complementarity an
electron may behave as a particle or a wave in
different circumstances, but never as both
simultaneously

• The de Broglie equation (1923) assigns a
  wavelength to an electron

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Rayleigh Criterion
- The Rayleigh criterion shows that resolution is
proportional to wavelength
- Visible light has a wavelength of 400 700 nm.
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An Overview of the TEM
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Using the TEM
Top right Sample holder Above Michael
studying sample Left Viewing Hole
- Vacuum leaks may occur during insertion of
specimen holder.
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Aberrations and alignments
- Diffraction patterns (Kikuchi lines) can be
used to ensure sample is correctly aligned
- The GIF filters out non-elastic electrons
Above Diffraction Pattern Top Right Tim
fiddling with knobs Right Fluorescent Screen
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What does phase represent?

• Normal TEM Imaging (Amplitude based) shows
• - Mass-Thickness contrast
• - Diffraction contrast
• Phase contrast highlights
• - Magnetic fields
• - Electrostatic fields
• - Topography
• Doping changes internal electric fields
• Electrostatic potentials can be viewed by Phase
  Imaging

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Extracting the Phase
Under focus
Sample Objective Lens Focal Plane
In Focus
Over focus
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Extracting the Phase
Transport of Intensity Equation
Probability current is conserved between planes
Phase map (thickness profile)
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Cleaning up the mess
MgO Crystal
Underfocus In Focus
Overfocus
Phase Map
FFT Masking
High Band Pass Filtered Image
- Alignment - Beam instability during data
acquisition
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The Results
Silicon based transistor source and drain region
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The Results
Section of Junction in Silicon Transistor
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The Results
Phosphorus Dopants
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Comparing and Evaluating
Phase image showing contrast in doped regions
(A.C. Twitchett and P.A. Midgley)
Phase image of transistors revealing souce and
drain areas. (W.D. Rau et al.)
Holographically reconstructed phase image of
cross section of a field effect transistor. (H.
Lichte)
Our results of cross-section transistor phase
image.
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Conclusions and Consequences

• Semiconductors are doped with extremely small
  impurities and are used to make many modern
  electronic components
• Production needs control of accurate doping to
  nanometre scales
• Phase retrieval methods in Transmission Electron
  Microscopy is a promising technique to analyse
  semiconductor devices and help with accurate
  production
• The area still needs much more development,
  including resolving errors to do with contrast
  and Fourier transforms
• Combine or confirm results with other techniques
  such as off-axis electron holography
• Current research for Intel may result in such
  possibilities as correcting chip malfunctions,
  more efficient doping and consequently the next
  generation of semiconductor devices

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Acknowledgements
Lichte H. The Royal Society (March 2002),
Electron Interference Mystery and Reality, 360,
897 920. McMahon P.J., Barone-Nugent E.D.,
Allman B.E., Journal of Microscopy (June 2002)
Quantitative phase-amplitude microscopy II
Differential interference contrast imaging for
biological TEM. pp. 204 - 208 Nagayama K. and
Danev R., Asia/Pacific Microscopy and Analysis
(July 2003) Image Enhancement with Phase Plates
in Electron-Phase Microscopy. MacCartney M.R. et
al. Applied Physics Letters (April 2002),
Quantitative analysis of one-deminesional dopant
profile by electron holography 8017 3213
3215 Rau W.D., Schwander P., Ourmazd A.,Phys.
Stat. Sol. (March 2000) Two-Dimensional mapping
of pn Junctions by Electron Holography 213 -
222 http//universe-review.ca We would like to
thank Tim Petersen and Vicki Keast for all their
input!