atomic-scale theory of radiation-induced phenomena sokrates t. pantelides department of physics and...
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ATOMIC-SCALE THEORY OF RADIATION-INDUCED PHENOMENA
Sokrates T. Pantelides
Department of Physics and Astronomy, Vanderbilt University, Nashville, TN
The theory team:
Leonidas Tsetseris, Matt Beck, Ryan Hatcher, George Chatzisavvas,
Sasha Batyrev, Yevgenyi Puzyrev, Nikolai Sergueev, Blair Tuttle
AFOSR/MURI FINAL REVIEW 2010
OVERVIEW OF THE LAST FIVE YEARS
AND NEW RESULTS
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THEORY OBJECTIVES
• DISPLACEMENT DAMAGE
Defects, charging
electrons
• ALTERNATE DIELECTRICS
Interface structure, interface defects, NBTI,…
• CARRIER MOBILITIES
• LEAKAGE CURRENTS
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dE
/dx
(eV
A-1)
Experimental data, Eisen, 1968
Channeled beam
Energy loss by channeled ions in Si
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Motion of an ion thru Si<110>
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n(t) – n(0)
0.08-0.080
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dE
/dx
(eV
A-1)
Data: Eisen (1968)Ryan Hatcher
Theory
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Single-Event Gate Rupture
Metallization burnout after SEGR
Lum et al., IEEE TNS (2004)
Massengill et al., IEEE TNS (2001)
I-V following biased irradiation of 3.3 nm SiO2 capacitors
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Leakage-induced rupture
Breakdown results from local heating due to ion-excited carriers…
Is it defect mediated?
Cha
nnel
Gat
e
Oxi
de
Ene
rgy
VG
EF…AND carriers injected by applied fields
Sexton, et al., IEEE TNS (1998)
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Low-energy recoil dynamics in SiO2
Dangling Bond
Extra Bond
Defect
Atom
Sili
con
Oxy
gen
“Self Bond” Big Ball
Damage in amorphous material: Network defects
6 fs 32 fs 58 fs
100 eV Si recoil
14 Å
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Defect states in SiO2
Increasing numbers of defects…
…increasing number of defect states within the bandgap!
14 Å
Defect states separated by ~2-5 Å!
Conducting path!
0 30 60 femtoseconds after recoil
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Defect-mediated leakage
Ch
ann
el
Ga
te
Oxi
de
En
erg
yVG
EF
Displacement-damage-induced defect states facilitate field-injected leakage
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MULTISCALE TRANSPORT THEORY
Data by Massengill et al. 2001
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H+
H+
Si SiSi
Hf
H+
suboxide
Si-sub
SiO2
HfO2
bond
H
NEGATIVE BIAS
H+
H+
Si SiSi
Hf
H+
suboxide
Si-sub
SiO2
HfO2
bond
H
Si-SON-HfO2
Vanderbilt team
POST-IRRADIATION SWITCH-BIAS ANNEALING
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8 Å
Van Benthem & Pennycook, ORNL
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substitutional Hf: local lattice expansion
interstitial Hf: rebonding
perfect structure
E(int) = E(sub)+5 eV
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Possible new defect complex
PASSIVATED DB (Si-H) ACROSS FROM A SUBOXIDE BOND (Si-Si)
OR Hf-Si BOND
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Proton hopping from dangling bond to suboxide bond
BARRIER > 2.2 eV
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Alternative: DB ACROSS FROM Hf-Si BOND
BARRIER ~ 1.1 eV
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NEW RESULTS
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DEFECT DYNAMICS IN SiGe/strained-Si
• FREE HYDROGEN
• PASSIVATION OF DOPANTS BY HYDROGEN
• VACANCIES AND INTERSTITIALS
L. Tsetseris, D. M. Fleetwood, R. D. Schrimpf, and S. T. Pantelides, submitted to Appl. Phys. Lett.
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(a) (b)
xGe Charge E (eV)
11.1% 0 0.01
22.2% 0 0.07
33.3% 0 0.05
11.1% + -0.23
22.2% + -0.53
33.3% + -0.65
11.1% - 0.46
22.2% - 0.60
33.3% - 0.81
Hydrogen in SiGe and strained Si
H0,H+H-
H0 prefers SiGe
H+ prefers s-Si
H- prefers SiGe
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Hydrogen-boron complexes in SiGe and s-Si
H prefers to stick to B in s-Si.
xGe Charge Eb (eV) E (eV)
11.1% 0 0.61 0.00
22.2% 0 0.63 -0.22
33.3% 0 0.57 -0.54
11.1% - 0.48 0.00
22.2% - 0.54 -0.08
33.3% - 0.44 -0.13
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Hydrogen-boron complexes in SiGe and s-Si
H prefers to stick to B in s-Si.
xGe Charge Eb (eV) E (eV)
11.1% 0 0.61 0.00
22.2% 0 0.63 -0.22
33.3% 0 0.57 -0.54
11.1% - 0.48 0.00
22.2% - 0.54 -0.08
33.3% - 0.44 -0.13
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xGe Charge Eb (eV) E (eV)
11.1% 0 0.70 0.00
22.2% 0 0.45 0.18
33.3% 0 0.52 0.42
11.1% + 0.31 0.00
22.2% + 0.27 0.01
33.3% + 0.30 0.01
P-H complexes in SiGe and s-Si
H prefers to stick to P sites in SiGe.
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xGe Charge Eb (eV) E (eV)
11.1% 0 0.70 0.00
22.2% 0 0.45 0.18
33.3% 0 0.52 0.42
11.1% + 0.31 0.00
22.2% + 0.27 0.01
33.3% + 0.30 0.01
P-H complexes in SiGe and s-Si
H prefers to stick to P sites in SiGe.
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IMPACT ON DEVICE OPERATION
NBTI, PBTI
INCREASE IN INTERFACE TRAP DENSITYBIAS, MODERATE TEMPERATURES (~150° C)
H prefers to stick to P sites in SiGeBTI IMPROVEMENT
H prefers to stick to B in s-SiBTI GETS WORSE
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Vacancies in SiGe/strained Si
Vacancies have lower energy in SiGe
Vacancy
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Agglomeration of Ge atoms around vacancies in SiGe
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Ge atoms in vacancy
Eb (e
V)
No. of Ge atoms surrounding vacancy
1.4 eV
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Self-interstitials in SiGe/strained Si
• Ge atoms agglomerate around Ge self-interstitial (trend weaker than that for vacancies)
• Si self-interstitial moves from s-Si to SiGe energy gain 0.23 eV for xGe = 11%
• Si interstitial goes substitutional, creating a Ge interstitial
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IMPACT ON DEVICE OPERATION
PRESENCE OF SiGe SUBSTRATE REDUCES
RADIATION-INDUCED DISPLACEMENT DAMAGE
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Ge/high-k systemsGe volatilization products in high-k dielectrics
Annealing of Ge substrates initiates volatilization and desorption of GeO molecules
In Ge-based gate stacks, GeO must out-diffuse through the gate dielectric
Some of the GeO molecules may be trapped in the gate oxides
Experimental evidence: out-diffusion of Ge-related species causes degradation of the dielectric (e.g. charge trapping, enhanced leakage current)
V. Golias, L. Tsetseris, A. Dimoulas, and S. T. Pantelides, Microelectr. Eng., submitted
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(a) (b)
GeO impurities in La2O3
• Hex-La2O3: layered structure with La-rich slices and O atoms in-between.
• Stable configurations of GeO impurities within and inside the layers.
• GeO transfer from La2O3 bulk to vacuum: energy gain of 2.7 eV
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E (eV)
VB
CB
DO
S (
stat
es/e
V)
GeO in La2O3: Electronic properties
• Energy levels in the gap cause charge trapping and enhance leakage currents
• Hydrogen binds to GeO impurities, but some levels in the gap remain
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(a) (b)
GeO impurities in HfO2
GeO transfer from HfO2 bulk to vacuum: energy gain of 1.5 eV
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E (eV)
DO
S (
stat
es/e
V)
VB C
B
GeO in HfO2: Electronic properties
• Energy levels in the gap cause charge trapping and enhance leakage currents
• Hydrogen binds to GeO impurities, but some levels in the gap remain
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CRACKING OF H2 IN SiO2
• Conley and Lenahan (1993):
Experimental evidence in support of H2 cracking at O vacancies
• Contrary to theoretical results (Edwards and coworkers 1992,1993)
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Oxygen Vacancies
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
2 2.2 2.4 2.6 2.8 3
d (Si - Si ) [ Ang. ]
Rel
ativ
e En
ergy
[ eV
]Low energy
Vacancy Energies
T ~ 1200 K NL / NH ~ e1eV/kT ~ 104
High energy
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H2 reacting at V
H2 Dissociation
0
0.5
1
1.5
2
2.5
3
0
Reaction Coordinate
Rea
ctio
n E
ner
gy
[ eV
]
2.6 eV
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H2 reacting at V+
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 2 4 6 8 10 12 14 16 18 20
Reaction Coordinate
En
erg
y [
eV ]
H2 does not crack at room temperature at low-energy vacancies!
1.2 eV
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Si-H + hole Si- + H+
0
0.1
0.2
0.3
0.4
0.5
0 20
Reaction Coordinate
En
erg
y (
eV )
ALTERNATIVE MECHANISM: Si DANGLING BONDS
H2 cracks at a bare dangling bond without an energy barrier
0.42 eV