qingyu wei, mpi für physik, hll
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Qingyu Wei, MPI für Physik, HLL
Radiation Damage on MOS-Structure
Q. Wei, L. Andricek, H-G. Moser, R. H. RichterMax-Planck-Institute for Physics Semiconductor Laboratory
RD50, Vilnius, 2007
Motivation
Radiation damage & effects on MOS-structure
Experimental Conditions and Results
Conclusion
Outline
Motivation Unexpected phenomena Mechanism of electroweak symmetry breaking New physics: SUSY; extra dimension; link to
cosmology
TESLA TDR Design
Depleted P-channel FET
precise vertex detector (DEPFET)
Radiation on MOS-structure(MOS-Capacitance & -DEPFET )
Research of radiation effect(damage mechanism & model)
Radiation hardness structure
International Linear Collider
Physics topics
To do
Radiation Damage I
MOS-Structure
Ionization in SiO2
Carrier injectionfrom contacts
e-h pair creationin SiO2
Bond breaking
e-h transportin SiO2
Hole trapping+
Electron capture
Oxide charge
Defect generation
Release of mobile
Impurities(H, OH, Na, etc.)
Migration ofimpurities
Defect migrationin strained region
Interface trap
Device degradation or failure
Accumulated TID reach its tolerance limits
Interaction with electronic structure of atoms by photoelectric, Compton & pair-production
Radiation Damage II
Radiation damage in MOS-Structure:
Surface damage due to Ionizing Energy Loss (IEL)
accumulation of charge in the oxide (SiO2) and Si/SiO2 interface
Oxide charge shifts of flat band voltage, (depleted enhancement)
annealing at RT Interface traps leakage current, degradation of transconduction,
… no annealing below 400 0C
S/N Ratio deteriorated!
Nox: positive oxide charge and positively charged oxide traps have to be compensated by a more negative gate voltage negative shift of the threshold voltage (~tox
2)
Nit: increased density of interface traps higher 1/f noise and reduced mobility (gm)
Gate
Electron/Hole Pairs Generated by ionizing
radiation
SiO2
Si
1.12ev
Hopping Transport of Holes through localized states in
SiO2 Bulk
Long-term Hole trapping near Si/SiO2 Interface
Radiation induced Interface trap
Ionizing radiation (positive oxide charge)
Shifts of flat band voltage: ~ Nox Stretch-out of CV curve: ~ Nit
OxidethefromremovedElectronsfree
holestrappingselfSTHhHolesfree
Excitons
h
SiExcitonHSi O H
2HHe H
Si Si
Electric activeInterface state
STHH H
Damage mechanisms: interface state
Damage mechanism (MOS) I
Damage mechanism (MOS) II
Saturation mechanism
• Reservoir: hole traps are not exhausted, unless a larger bias voltage is applied on the gate!
• Saturation: equilibrium between trapped filling and recombination
-Generated holes are pushed away!
-Recombination of trapped holes with electrons
- Recombination of tunneled electrons from silicon into interface with trapped holes!
Begin
SiO2
Si
Saturation equilibrium
Recombination
Rejection
Trapp filling
Recombination
Experiment Conditions and Methods
DEPFET MOS-C
Nox
(method)
Δ Vt
(IV-Measurement)
ΔVFB
(CV-Measurement)
Nit
(method)
Subthreshold slope(Subthreshold
technique)
Stretch-out (High-low
frequency based on the CV)
Other parameters
gm
(IV-Measurement)
•Irradiation (X-Ray): •Co60 (1.17 MeV and 1.33 MeV)
•GSF – National Research Center for Environment and Health, Munich•CaliFa (17.44 KeV)
•Max-Planck-Institute Semiconductor Labor, Munich•Roentgen facility (20 KeV)
•Research center, Karlsruhe•Dose: irradiation up to 1 Mrad with different dose rate (1rad=0.01J/kg)•Process: No annealing during irradiation ~ irradiation duration from 1 day to 1 week•Radiation levels at the ILC VTX: Dionization≈ 100 .. 200 Krad
≈ 1010 .. 1011 neq(1MeV )/cm2•Comparison of different semiconductor devices
"OFF"
"ON"
Bias during irradiaton:
1: empty int. gate, in „off“ state, VGS= 5V, VDrain=-5V Eox ≈ 02: empty int. gate, in „on“ state, VGS=-5V, VDrain=-5V Eox ≈ -250kV/cm
Results for MOSDEPFET
Transconductance and Subtreshold slope
s=85mV/dec
s=155mV/dec
Vth=-0.2V
Vth=-4.5V
Literature: After 1Mrad 200 nm (SiO2):
Nit ≈ 1013 cm-2
300 krad Nit≈2·1011 cm-2
912 krad Nit≈7·1011 cm-2
No change in the transconductance gm
)()10ln( 12 DDox
it SSkTCN
Al/Poly1/2-Ox-It
0,000E+00
2,000E+11
4,000E+11
6,000E+11
8,000E+11
1,000E+12
1,200E+12
1,400E+12
1,600E+12
0 200 400 600 800 1000Dose(krad)
Nit
& N
ox (
cm
-2)
Al-ox
Poly1-Ox
Poly2-Ox
Al-it
Poly1-it
Poly2-it
CV-Poly2(HF)
0.00E+00
2.00E-10
4.00E-10
6.00E-10
8.00E-10
1.00E-09
1.20E-09
1.40E-09
1.60E-09
1.80E-09
-12 -7 -2 3 8
Vgate (V)
C (
F)
0krad
4.5krad
13.5krad
22.5krad
36krad
63krad
189krad
225krad
382.5krad
423krad
1003.5krad
CV-Poly2(LF)
0.00E+00
2.00E-10
4.00E-10
6.00E-10
8.00E-10
1.00E-09
1.20E-09
1.40E-09
1.60E-09
1.80E-09
-13 -8 -3 2 7
Vgate (V)
C (
F)
0krad
4.5krad
13.5krad
22.5krad
36krad
63krad
189krad
225krad
382.5krad
423krad
1003.5krad
Flat band voltage Shift Nox
HF/LF CV
Nit
Results for MOS-C
B. B. Abhaengigkeit
0
2
4
6
8
10
12
14
16
18
20
-15 -10 -5 0 5 10 15
Vg (V)
Vfb
(V
)
DIO318A
For MOS-C
+ 0 -
SiO2
Si
VG
Bias Effect
B.B. Abhaengigkeitat different dose, 0V
y = 0.0818x0.9974
R2 = 1
y = 0.0257x0.9712
R2 = 0.9458
y = 0.0351x1.0192
R2 = 0.9569
0.10
1.00
10.00
100.00
10 100 1000dox (nm)
Vfb
(V
)
1000
234
100
Power (1000)
Power (100)
Power (234)
B.B. Abhaengigkeit
y = 0.0053x1.863
R2 = 0.971
y = 0.002x1.7379
R2 = 0.9886
0.1
1
10
100
1000
10 100 1000
Oxide Dicke (nm)
U (
V)
111krad
962krad
Power (962krad)
Power (111krad)
thickness dependence dn1.08.1 n 1nDEPFET
For MOS-C
Radiation hardness by Nitride-layer
(MNOS)Vg=+10V
Vg=+5V
Vg=-10V
Vg=-5V
Damage mechanism (MNOS) IEnergy band diagram of MNOS
structure
Discontinuity of current density Jn-J0 in short time lead to charge carriers accumulation & trapping in N/O strained interface
field dependence of current density & thickness of the dielectrics plays an important role!
charge in Si/SiO interface donot affect the field distribution in dielectrics!
h:
e:
Mobility of electron is faster than hole in SiO2, and reversely in Nitride
Me Nitride Oxide Si
EFM
Vg
EC
EF
J0
Vg > 0
Jn
Qni
Qox
Me Nitride Oxide Si
EFM
Vg
EC
EF
J0
Vg < 0
Jn
Qox
Qni
Recombination
+ 0 -
SiO2
Si
VG
Nitride
Trapp source fore & p
Damage mechanism II
10000 1000001.40E+012
1.50E+012
1.60E+012
1.70E+012
1.80E+012
1.90E+012
2.00E+012
yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 3.05658E12 5.47588E10B -2.84185E11 1.08554E10------------------------------------------------------------
R SD N P-------------------------------------------------------------0.99637 1.75366E10 7 <0.0001
measurement data linear fit of data
No
x (cm
-2)
Time (s)
Annealing-Al
Oxide charge decrease with time:
(Tunnel annealing @ RT)
Annealing for surface damage
Conclusion
Radiation experiment
● Study of saturation effect for surface damage (equilibrium between generation and recombination)
● Study of bias dependence(“+“,“0“,“-“)● Study of different semiconductor devices, which are
with different oxide thickness - to see the kind of relation between Vfb and oxide thickness (dox
n )
Radiation hardness
● Reduced oxide thickness improves radiation hardness
● Additional Nitride layer serve as a good protection against ionizing radiation (electron trapping!)
● Surface damage can be reduced through annealing process with time
MradtN hox 1~%5/
Backup slides
Results for gated diode
Shifts of generated current:
Surface generation velosity
0,0E+00
2,0E+01
4,0E+01
6,0E+01
8,0E+01
1,0E+02
1,2E+02
1,4E+02
1,6E+02
0 100 200 300 400 500 600 700 800 900 1000
dose (krad)
So
(cm
/s)
Al
poly
surface generation lifetime
0.000E+00
5.000E+03
1.000E+04
1.500E+04
2.000E+04
2.500E+04
3.000E+04
3.500E+04
4.000E+04
4.500E+04
5.000E+04
0 100 200 300 400 500 600 700 800 900 1000
dose (krad)
tau
(m
icro
seco
nd
)
al
poly
Increase of maximal current:
Increase of surface generation velocity & decrease of lifetime due to radiation:
Mathematics Expression I
-1,4
-1.4
Pre-Rad
VFB(V)
86/10
100/10
Oxide/Nitride thickness
91
105
EquivalentOxide
thickness
Chip thickness (nm)
85
103
Electrically measured equivalent
oxide thickness(CV)
5.1
2
Post-RadVFB(V)
~1MradVg=-10V
-0,6
-0,7
86
100
76 2
95 2
86
100
Post-RadVFB(V)
~1MradVg=-5V
Post-RadVFB(V)
~1MradVg=0V
Post-RadVFB(V)
~1MradVg=+5V
Post-RadVFB(V)
~1MradVg=+10V
1918,64,16
22,716,42,33,34,4
29,416,667,1
31,521,32,63,45
5,3
5,5
Dnie
Dnih
Doxhoxhnihnie
nini
ni
oxeq
oxFB
nienihoxh eQeQeQQQQCC
Q
C
QV ,,,
,,,,,,,
1
oxni
oxnioxeq ddd
, oxeqoxg dEV , Ad
Coxeq
oxoxeq
,,
oxhoxhoxhoxhoxhoxoxhoxoxoxhThoxhox QQQQEdEfF
dD
dQ
dD
dQ,,,,,,,
,
nienieoxenihnihnihnienihni QQQQ
dD
dQ
dD
dQ
dD
dQ..,,,,
,,
DQQ oxhoxhox ,, exp1
oxoxhoxoxhoxoxh EEE ,,,
DQDQQ oxenienihnihni ,,,, exp1exp1
niox
oxni
d
d
1
Mathematics Expression II
factordependentfield
NOorSiOSierfaceinddistributeogenelyapproximat
nitrideoxideinelectronholeofdensitytrappN
nitrideoxideinelectronholeoftioncrosscapture
nitrideoxideinelectronorholefortcoefficiengenerationechdependentfield
shiftvoltagebandflatV
electronorholegeneratedradiationforechtrappedoffractionf
electronorholegeneratedradiationfordoseunitperfluenceF
nitrideoxideinfieldelectricE
oxidenitrideinechtrappedQ
cecapacioxideequivalentC
areagateA
oxidenitrideoftypermittivi
voltagegateV
thicknessnitrided
thicknessoxided
thicknessoxideequivalentd
doseD
nihoxeoxh
nihoxeoxh
nihnieoxh
nihoxeoxh
FB
T
eh
niox
oxni
oxeq
oxni
g
ni
ox
oxeq
:
//inthom
//:
//sec:
/arg:
:
arg:
:
/:
/arg:
tan:
:
/:
:
:
:
:
:
,/,/,
,/,/,
,/,/,
,/,/,
/
/
/
,
/
,
Mathematics Expression III
Assumption (positive gate bias)
Recombination at interface (Si/SiO or N/O) should be neglected
Electron or hole trapps are distributed approximately homogen at interface
There are no trapped charge at interface (pre-Rad)
MOS-Gated Diode (device profile)
P+
Al/PolyGa
te
AAl
Substrate
V
Edge
N
V
Erde
Poly-gateAl-gate
Al
P+
grounding
Edge
Al
P+
Annealing for MOS-C (PXD4)
0 200000 400000 600000 800000 1000000 1200000
22
24
26
28
30
32
34
36
38
40
Data: Data1_BModel: ExpGro1Equation: y = A1*exp(x/t1) + y0Weighting: y No weighting Chi^2/DoF = 1.04481R^2 = 0.96629 y0 24.65756 ±0.61048A1 13.3868 ±0.89247t1 -126727.17537 ±24099.02704
Vo
t (V
)
Annealing time (s)
measured points fitting curve
Annealing for Al-Structure under 0V
Tau= 35h
0 200000 400000 600000 800000 1000000 1200000
6.0
6.1
6.2
6.3
6.4
6.5
6.6
6.7
Data: Data1_BModel: ExpGro1Equation: y = A1*exp(x/t1) + y0Weighting: y No weighting Chi^2/DoF = 0.00099R^2 = 0.97965 y0 6.05497 ±0.03188A1 0.56032 ±0.03233t1 -281569.98508 ±43754.94842
Vo
t(V)
Annealing time (s)
measured data fitting data
Tau= 3.3day
Annealing for poly-structure under 0V
0 200000 400000 600000 800000 100000018
20
22
24
26
28
30
Data: Data1_BModel: ExpGro1Equation: y = A1*exp(x/t1) + y0Weighting: y No weighting Chi^2/DoF = 0.1429R^2 = 0.99288 y0 19.26974 ±0.21813A1 11.5246 ±0.34892t1 -203869.42496 ±16821.92098
Vo
t (V
)
Annealing time (s)
measured data fitting data
Annealing for Al-structure under -5V
Tau= 2.4day
0 200000 400000 600000 800000 1000000
4.8
5.0
5.2
5.4
5.6
Data: Data1_BModel: ExpGro1Equation: y = A1*exp(x/t1) + y0Weighting: y No weighting Chi^2/DoF = 0.00128R^2 = 0.98809 y0 4.80353 ±0.02847A1 0.84045 ±0.033t1 -276420.46773 ±33847.03536V
ot (
V)
Annealing time (s)
measured data fitting data
Annealing for Poly-structure under -5V
Tau= 3.2day
Dose rate effect
High dose rate
SiO2
Si
Low dose rate
Flat band voltage shift
0
5
10
15
20
25
30
35
40
0 200 400 600 800 1000Dose (krad)
U (
V)
medium
high
10
15
20
25
30
35
40
0 50 100 150 200
Annealing RT
medium
high
Radiation Damage
Two types of radiation damage in MOS-Structure:
Surface damage due to Ionizing Energy Loss (IEL) accumulation of charge in the oxide (SiO2) and Si/SiO2
interface Oxide charge shifts of flat band voltage, (depleted
enhancement) Interface traps leakage current, degradation of
transconduction,…
Bulk damage due to Non Ionizing Energy Loss (NIEL) displacement damage, built up of crystal defects
Increase of leakage current increase of shot noise,… Change of effective doping concentration higher depletion
voltage,… Increase of charge carrier trapping signal loss!
S/N Ratio deteriorated!
10000 1000001.40E+012
1.50E+012
1.60E+012
1.70E+012
1.80E+012
1.90E+012
2.00E+012
yscale(Y) = A + B * xscale(X)where scale() is the current axis scale function.
Parameter Value Error------------------------------------------------------------A 3.05658E12 5.47588E10B -2.84185E11 1.08554E10------------------------------------------------------------
R SD N P-------------------------------------------------------------0.99637 1.75366E10 7 <0.0001
measurement data linear fit of data
Nox
(cm
-2)
Time (s)
Annealing-Al
Annealing
For bulk damage:
For surface damage:
Oxide charge decrease with time:
(Tunnel annealing @ RT)
1 10 100 1000 10000annealing time at 60oC [minutes]
0
1
2
3
4
5
6
(t)
[10
-17 A
/cm
]
1
2
3
4
5
6
oxygen enriched silicon [O] = 2.1017 cm-3
parameterisation for standard silicon [M.Moll PhD Thesis]
80 min 60C
Leakage current decrease with time: “Beneficial annealing” & “Reverse annealing”
NC
NC0
gC eq
NYNA
1 10 100 1000 10000annealing time at 60oC [min]
0
2
4
6
8
10
N
eff [
1011
cm-3
]
[M.Moll, PhD thesis 1999, Uni Hamburg]
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