Hf impurities in SiSiO2HfO2 stacks

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Hf impurities in Si/SiO2/HfO2 stacks
Apostolos Marinopoulos1
Xing Zhou3Sasha Batyrev1Ronald Schrimpf3Daniel
Fleetwood3Sokrates Pantelides1,2
Klaus van Benthem2Sergey Rashkeev1,2,4Stephen
Pennycook2,1
(1) Vanderbilt University, Department of Physics
Astronomy(2) Oak Ridge National Laboratory(3)
Vanderbilt University, Department of Electrical
Engineering Computer Science (4) Present
address Idaho National Laboratory
SUPPORT AFOSR and DOE
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• Stray Hf atoms in SiO2 interlayer (Oak Ridge
  National Lab)

SiO2
HfO2
Silicon
SiO2 interlayer formation during post-deposition
annealing
Hf atoms inside SiO2
(van Benthem and Pennycook)

• Electrical measurements under switched-bias
  annealing
• after irradiation and constant-voltage stress
  (Vanderbilt)

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Constant-voltage stress (CVS) and irradiation (10
keV X-rays)
applied to Si/SiOxNy/HfO2 stacks
_at_ 25o 150o C
Pb centers
H reactions at near-interface region
Oscillations of interface-trap density by
switching bias
(Zhou, Schrimpf, Fleetwood)
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Number of Hf atoms versus distance from interface
Single Hf atoms inside SiO2 interlayer
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SUBSTITUTIONAL IMPURITIES
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SUBSTITUTIONAL IMPURITIES
1.4 eV penaltyfor segregation
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No particular crystalline polymorph
quartz
Hf atoms markers
Ordering of Si planes
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Constant-voltage stress (CVS) and irradiation (10
keV X-rays)
applied to Si/SiOxNy/HfO2 stacks
_at_ 25o 150o C
Pb centers
H reactions at near-interface region
Oscillations of interface-trap density by
switching bias
(Zhou, Schrimpf, Fleetwood)
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Proton motion in the presence of interface
defects at Si/SiO2
Passivated Pb-center

Suboxide bond

Hole capture
BARRIER gt 2.2 eV
Depassivation
Proton trapping at bond center
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Hafnium substitutional defect near Si/SiO2
Passivated Pb-center

Hf-suboxide bond

Hole capture
BARRIER 1.1 eV
Depassivation
H near bond center
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CONCLUSIONS
Presence of Hf in SiO2 interlayer important in
near-interface reactions of Hydrogen
Can explain observed oscillations of interface
trap density
Hf lowers the barrier for H shuttling
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H MOTION AND INTERACTION WITH INTERFACE DEFECTS
NEGATIVE BIAS
HfO2
suboxide
Hf
bond
SiO2
H
H
H
Si
Si
Pb centers
Si
Si-sub
H
N B T S
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MECHANISMS FOR ELECTRON EXCHANGE AND H MOTION
NEGATIVE BIAS
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• HfO2 deposition on Si

Silicon
HfO2
SiO2

• annealing at 950o C

formation of SiO2 interlayer
No Hafnium atom observed to segregate
Z-contrast image
(van Benthem and Pennycook)
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MOS capacitors with high-? gate dielectric
Al / HfO2SiOxNy / Si
Switched-bias annealing after constant-voltage
stress
Enhanced magnitude/reversibility of
interface-trap charge