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]