Si100 SiO2 Interface properties following rapid thermal processing

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Si(100) SiO2 Interface properties following
rapid thermal processing
Based on OSullivan et al. J. Appl. Phys., Vol.
89, No. 7, 1 April 2001
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• Intention of the work
• Study the Si(100)-SiO2 interface properties
  after RTP
• Effect of RTP (RTA and RTO) upon
• - CV-curve
• - Dangling bonds

• Why
• It is central to the performance and long
  thermal stability of MOS based devices.

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• Why use RTP
• Reduce the overall thermal budget
• Maintain the desired device electrical
  properties
• Used for - Dopant activation
• - Defect annealing
• - (Avoid) dopant
  redistribution
• - Formation of contacts and metal silicides
• Does not reach thermal equilibrium

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• Measurements techniques
• Capacitance-Voltage (CV) measurements
• Four Dimensions CV map
• Electron Paramagnetic Resonance (EPR)

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Capacitance-Voltage (CV) measurements

• Capacitance-voltage curves are measured on MIS
  capacitors.
• Determination of - insulator charges
  - interface traps - volume traps
  - mobile ionic charges 

• Information on the electrical properties of
  insulating materials.

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Low frequency signal (ex. 50Hz) - Quasistatic
CV - Minority carriers in the inversion layer
completely follow the AC gate voltage.
High frequency signal (ex. 1MHz) - Moves the
majority carriers
CV curve is a combination of both
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1
3
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Accumulation Depletion Inversion

• Inversion (p-type)
• - Negatively charged layer at the
  oxide-semiconductor interface (in addition to the
  depletion-layer).
• - Due to minority carriers, which are attracted
  to the interface by the positive gate voltage.

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1
3
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Accumulation Depletion Inversion

• 2. Flat-band
• The voltage separating the accumulation and
  depletion regime is referred to as the flatband
  voltage, VFB.
• When the applied gate voltage equals the
  workfunction difference between the gate metal
  and the semiconductor

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1
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Accumulation Depletion Inversion

• 3. Accumulation (p-type)
• Occurs when one applies a voltage, which is less
  than the flatband voltage.
• - The negative charge on the gate attracts holes
  from the substrate to the oxide-semiconductor
  interface.

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Four Dimensions CV map Use liquid metal Mercury
to form temporary non damaging electrical
contacts on numerous materials.

• The contact formed on semiconducting materials
  can be of MOS or Schottky barrier type.
• Various electrical characterizations of ex.
  silicon and compound semiconductors without the
  need of metal deposition processes.

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Electron Paramagnetic Resonance (EPR)

• Spectroscopic technique that detects chemical
  species that have unpaired electrons.
• Technique is like NMR, but uses electron spins
  instead of spin of nucleus.

• Detects
• Dangling bonds
• Impurities in Semiconductors
• Electrons in unfilled conduction bands
• Transition ions etc.

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• Dangling bonds
• Occurs when an atom is missing a neighbor to
  which it would be able to bind.

• Defects that disrupt the flow of electrons
• Are able to collect the electrons.

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• Samples
• Polysilicon-oxide-silicon (MOS) structures
• Si(100) SiO2 exposed to RTA
  (600-1050oC, 10 sek. in N2)
• 2) Si(100) SiO2 undergone RTO
  (1000-1100oC, 8-33 sek.
  in O2 or N2)

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• Results CV Both RTO and RTA
• Distortion in accumulation
• Distortion between accumulation and inversion /
  Induced a flat band voltage shift.
• Extra peak at strong inversion.

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1
2
Conclusion CV 1 and 2 Indicate interface states
at the Si-SiO2 surface 3 Extra peak, indicate
that there is interface state distribution at a
certain energy.
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• Results EPR
• Interface states are due to Si-atoms with
  dangling bond (Pb) orbitals.

• Conclusion EPR
• Temperatures below 500oC the Hydrogen is damping
  off the dangling bonds.
• Si3 SiH Si3 Si? H (Pb center)
• Dangling bonds occur only if we rapidly cool or
  cool in H2 free atmosphere. Or else
• Si3Si? H2 Si3Si-H H (no Pb center)

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• Conclusion
• Dangling bonds occur during RTP if rapid cooling
  under T 500oC or in H2 free ambient
• Dangling bonds result in an increased voltage
  over the gate and will lead to a decrease in
  stability of the MOS.

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