Electrical characterization of a single grain MOS capacitors

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Electrical characterization of a single grain MOS
capacitors
EDFAS Lone Star Chapter Jan 24, 2007

• T. Zheng and B.E. Gnade
• Materials Science Engineering
• University of Texas at Dallas
• Richardson, Texas 75083

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Acknowledgements

• University of Texas at Dallas
• Profs. Moon J. Kim, Eric M. Vogel
• Dr. H. Jia
• D. K. Cha, J. Huang, G. Pant
• Texas Instruments
• Drs. L. Colombo, H. Edwards, R. Irwin
• Sematech
• Dr. G. Brown
• Financial support
• Texas Instruments/SRC

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Outline

• Motivation
• Introduction of Nanoprobe inside SEM
• E-beam damage to MOS capacitor
• C-V Measurement on single grain MOS capacitor
• Shunt capacitance reduction
• Noise analysis
• Formation of single grain Al gate MOS
  capacitor
• Grain Orientation Determination
• Summary

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Outline

• Motivation
• Introduction of Nanoprobe inside SEM
• E-beam damage to MOS capacitor
• C-V Measurement on single grain MOS capacitor
• Shunt capacitance reduction
• Noise analysis
• Formation of single grain Al gate MOS
  capacitor
• Grain Orientation Determination
• Summary

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Potential Issues with Scaling Polycrystalline
Metal Gates
Will the orientation dependence of the metal work
function affect the flat-band voltage of a MOS
capacitor?
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Effective Work Function
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Target and Task

• Target
• Will the orientation dependence of metal work
  function affect the flat-band voltage of a MOS
  capacitor?
• What is the effective work function of a metal
  gate with different orientations?

• Task
• Deposition of gate metal with different
  orientations
• Isolation/patterning of single grains
• Electrical characterization of a single grain
  capacitor
• Determination of the orientation of electrically
  characterized single grain

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Outline

• Motivation
• Introduction of Nanoprobe inside SEM
• E-beam damage to MOS capacitor
• C-V Measurement on single grain MOS capacitor
• Shunt capacitance reduction
• Noise analysis
• Formation of single grain Al gate MOS
  capacitor
• Grain Orientation Determination
• Summary

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Spatial Limitation of Conventional C-V
Measurements
Same pattern under SEM
Image of 1?m x1?m pads taken by optical
microscope at 100X
Cascade Probe station
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SEM based Probing PlatformZyvex Nano Probe with
low-noise update
Zyvex F-100 Nano Manipulator/ Probe system
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Probing Nanostructures
Probing 90 nm Transistor with 10 nm spatial
movement resolution

• DC measurements on nanostructures demonstrated !
• AC measurements of small capacitance on
  nanostructures ?

• courtesy of Zyvex Corp.

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Sample holder noise
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Sample Mounting for Measurements Using Nano
Manipulator/Probe
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C-V Measurements by Nano Manipulator/Probe
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Small Capacitance Measurements by Nano
Manipulator/Probe

• Measuring 3?m diameter MOS capacitor with 75 Å
  SiO2 at 1MHz by Nano Manipulator bias reversed

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Whats the problem?
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Modification of Nano Manipulator for small value
CV Measurements

• Control signal and measurement signal need to be
  separated.
• Measurement signal needs to be guarded to the
  very end of the probe
• Cable length needs to be reduced.

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Outline

• Motivation
• Introduction of Nanoprobe inside SEM
• E-beam damage to MOS capacitor
• C-V Measurement on single grain MOS capacitor
• Shunt capacitance reduction
• Noise analysis
• Formation of single grain Al gate MOS
  capacitor
• Grain Orientation Determination
• Summary

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E-beam Damage to MOS Structure
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Electron-MOS structure interaction Monte Carlo
simulation
28nm
320nm
5kV
1kV
Simulation is done by using software CASINO
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Electron-MOS structure interaction Monte Carlo
simulation
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E-beam damage to MOS structureusing 1KeV E-beam
imaging
100KHz
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E-beam damage to the uncapped oxide
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Comparison of CV measurements by Cascade and
Nanoprobe

• Flat-band region is consistent between the two
  measurement platforms

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3-Element model correction
K. J. Yang et al., IEEE Trans. Electron. Dev.,
vol. 46, 1500(1999).
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CV measurements of 5um vs. 50um
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Outline

• Motivation
• Introduction of Nanoprobe inside SEM
• E-beam damage to MOS capacitor
• C-V Measurement on single grain MOS capacitor
• Shunt capacitance reduction
• Noise analysis
• Formation of single grain Al gate MOS
  capacitor
• Grain Orientation Determination
• Summary

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Shunt Capacitance Phenomenon on Cascade Probe
station
Accurately measuring shunt capacitance is
critical to small capacitance measurement
Assumed shunt capacitance
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Shunt capacitance reduction
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Outline

• Motivation
• Introduction of Nanoprobe inside SEM
• E-beam damage to MOS capacitor
• C-V Measurement on single grain MOS capacitor
• Shunt capacitance reduction
• Noise analysis
• Formation of single grain Al gate MOS
  capacitor
• Grain Orientation Determination
• Summary

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Small signal method
If the noise is constant, increasing V or ? will
increase the signal-to- noise ratio
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Noise analysis
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AC signal effect on Nanoprobe
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Noise analysis
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Mechanical Vibration related noise
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Expected Grain Size Calculation
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Outline

• Motivation
• Introduction of Nanoprobe inside SEM
• E-beam damage to MOS capacitor
• C-V Measurement on single grain MOS capacitor
• Shunt capacitance reduction
• Noise analysis
• Formation of single grain Al gate MOS
  capacitor
• Grain Orientation Determination
• Summary

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Selection of gate metal
Al has a low melting temperature of 660C,
resulting in a possible higher Tsub/Tm Al is
stable on SiO2 up to 400C.
H. B. Michaelson, J.A.P. 48 (1977) 4729
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Room temperature deposited Al gate
Out of plane mode XRD
300C
150C
RT
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Effect of deposition time
1hours
2hours
4hours
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Formation of single Al grain gate
Before etching
Al

• Al grains are
• deposited by Ar sputtering at 300 C substrate
  temperature
• annealed at 360 C in Vacuum
• etched for 40 seconds by using Al etchant type-A
  to remove the nano grains

SiO2
After etching
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Outline

• Motivation
• Introduction of Nanoprobe inside SEM
• E-beam damage to MOS capacitor
• C-V Measurement on single grain MOS capacitor
• single grain MOS capacitor measurement
• Grain Orientation Determination
• Summary

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Single grain CV measurements (continued)
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Single grain CV measurements
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Mechanical stress effect on Nanoprobe
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Single grain CV measurements
1MHz

• So far, all the grains show similar Flat-band
  voltage

Capacitor area analysis is done by using
software Image Tool
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Grain Orientation Determination

• Orientation Imaging Microscopy (OIM)
• Transmission Electron Diffraction

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Cross section Transmission Electron Diffraction
Pt
Al
Si
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Orientation characterization of grain which has
been probed
tilted 40 degree
no tilt
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Orientation Imaging Microscopy (OIM)
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Example OIM Data
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Summary

• CV measurements inside SEM using Nanoprobe is
  demonstrated
• E-beam damage to MOS device can be minimized by
  using low energy electrons
• CV measurements of single grain Al metal gate
  MOS capacitors can be achieved by carefully
  controlling the contact resistance

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Future Work

• Probe more Al grains
• Study of FIB patterning of MOS CAP
• Explore single Al grain on high-K (HfO2) system