1 Material Dependence of NBTI Stress & Recovery in SiON p-MOSFETs S. Mahapatra, V. D. Maheta, S....

1

Material Dependence of NBTI Stress & Recovery in SiON p-MOSFETs

S. Mahapatra, V. D. Maheta, S. Deora, E. N. Kumar, S. Purawat, C. Olsen1, K. Ahmed1, A. E. Islam2, M. A. Alam2

Department of Electrical Engineering, IIT Bombay, Mumbai, India

1Applied Materials, Santa Clara, CA, USA

2School of Electrical Engineering & Computer Science, Purdue University, W. Lafayette, IN, USA

Email: [email protected]

2

Outline

Introduction, measurement delay (recovery) issues, fast measurements

Material dependence: Time evolution, time exponent

Material dependence: Field & temperature acceleration

Physical mechanism, isolation of different components

Conclusion

Recovery – material dependence

3

What is NBTI?

Issue: p-MOSFET in inversion

VG < (VS, VD, VB)

Parametric shift

Aggravated for SiON films

What is the N dependence?

VDD

VDD

VG=0Aggravated with –EOX and T

EOX1, T1

VT

time

EOX1, T2EOX2, T2

4

Motivation

Proper stress, measurement

VT

time

StressExtrapolation to operating condition

Operation

Extrapolation to end of lifeLifetime

Check if passed

Specification

Need to know physical mechanism for reliable extrapolation to obtain lifetime

5

NBTI measurement challenge

Conventional approach – stress / measure / stress

10-7 10-5 10-3 10-1 101 103 1050.10.20.30.40.50.60.70.80.91.01.1

PNO, low N%

recovery time (s)

fra

ctio

n r

em

ain

ing

tSTR

=1000sV

STR / V

REC (V)

-1.7 / -1.3-2.3 / -1.8-2.3 / -1.3-2.3 / -1.0

Recovery of degradation as soon as stress is stopped

Recovery depends on stress to measure voltage difference, time

Stress

Measurement-VG (M)

-VG (S)

6

Impact of Measurement Delay Time

Stress-Measure-Stress (SMS)

Stress

Measurement-VG (M)

-VG (S)

M-time

100 101 102 10310-2

7x10-2

T=150OC

EOT=2.2nm (nitrided)V

G(stress)=-3.0V

VG(meas)=-1.5V

50ms, 0.185100ms, 0.20350ms, 0.213

VT (

V)

stress time (s)

Lower magnitude, higher slope for higher measurement delay

7

Impact of Measurement Bias

Stress

Measurement-VG (M)

-VG (S)

M-time

100 101 102 1034x10-3

10-2

6x10-2

On-the-fly

delay=100ms

T=50OC, V

G=-3.0V (stress)

EOT=2.2nm (nitrided)3.0V, 0.1521.5V, 0.1741.0V, 0.197

VT (

V)

stress time (s)

Higher recovery & higher slope for lower (absolute) measurement bias

DC On-the-fly: Rangan, IEDM 2003

Stress-Measure-Stress (SMS)

8

On-The-Fly IDLIN (Conventional Scheme)

SMU

PGU Start ID sampling

SMU triggers PGU

PGU provides stress pulse at gate

Continue ID sampling without interrupting stress

Uncertainty in IDMAX measurement: t0 ~ 1ms

I DL

IN

time

Rangan, IEDM 2003

VT = -ID/IDMAX * VGT0

9

On-The-Fly IDLIN (Fast Scheme)

Start ID sampling

SMU triggers PGU

PGU provides stress pulse at gate

Continue ID sampling without interrupting stress

Uncertainty in IDMAX measurement: t0 ~ 1s

I DL

IN

time

SMU

PGU

IVC

DSO

VT = -ID/IDMAX * VGT0

10

Captured IDLIN Transients

Peak IDLIN (IDLIN0) captured within 1s of stress (VG=VGSTRESS)

Gate pulse transition time adjusted to avoid IDLIN overshoot

-4 0 4 8 12 16 20

500

550

600

650

700

750

time (s)

I DLI

N (A

)

-4.0-3.6-3.2-2.8-2.4-2.0-1.6-1.2-0.8-0.4

VGSTRESS

T=125OC

PNO (23.5AO, 17%)

VG (V

)

RTNO shows rapid and larger IDLIN degradation w.r.t PNO

11

Outline





Conclusion


12

Impact of Time-Zero Delay

RTNO shows very large initial and overall degradation and much larger impact of t0 delay compared to PNO

Reduction in measured degradation magnitude for higher t0 delay

13

Time Exponent (Long-time): Impact of t0 Delay

Power law time dependence at long stress time

Lower time exponent (n) for RTNO compared to PNO

10-2 10-1 100 101 102 1035x10-3

10-2

10-1

t0=1s

EOX=8.5MV/cm, T=125OC

n=0.06

n=0.12

RTNO (22.5AO, 6%)

PNO (23.5AO, 17%)

stress time (s)

V(V

)

Reduction in n with reduction in t0 delay, saturation for t0<10s

10-6 10-5 10-4 10-3 10-2

0.06

0.09

0.12

0.15

0.18PNO (14A

O-23.5A

O; 17%-22%)

RTNO

time

expo

nent

(t=

10s-

1000

s)

t0 delay (s)

14

Time Exponent: Impact of Oxide Field and Temperature

EOX independence of n: No bulk trap generation

0 30 60 90 120 150 180

0.04

0.06

0.08

0.10

0.12

0.14

RTNO (22.5AO, 6%)

PNO (14AO-23.5A

O, 17%-22%)

t0=1s

EOX

~ 8.5 MV / cm

T (0C)

tim

e ex

pone

nt (

10s

-100

0s)

6 7 8 9 10

0.04

0.06

0.08

0.10

0.12

0.14

RTNO (22.5AO, 6%)

PNO (14AO-23.5A

O, 17%-22%)

time

exp

on

en

t (1

0s

- 1

000

s)

EOX

(MV / cm)

T = 1250C

t0 = 1s

T independence on n: Arrhenius T activation

PNO shows higher n compared to RTNO

15

NBTI Transient: PNO / RTNO / RTNO + PN

N density at Si/SiON interface controls degradation transients

Higher Si/SiON N density Higher (short time & overall) NBTI

10-6 10-3 100 1033x10-3

10-2

10-1

V (

V)

stress time (s)

RTNO

N%=6

EOT=18.5A0

NDOSE

=0.8+ 0.0(x1015cm-2)

3x10-3

10-2

10-1

V

(V

)

RTNO+PN

N%=39

EOT=13.05A0

NDOSE

=0.8+ 5.1(x1015cm-2)

3x10-3

10-2

10-1 EOX

~ 8.5 MV/cm

T ( 0C)12555

V

(V

)

PNO

t0=1s

N%=35

EOT=15.55A0

NDOSE

=0.0+ 5.3(x1015cm-2)SiON

RTNOPNO

RTNO+PN

Poly-SiSi-substrate

N

Shallenberger JVST 99; Rauf, JAP 05

16

Time Exponent: PNO / RTNO / RTNO + PN

6 7 8 9 100.04

0.06

0.08

0.10

0.12

0.14

0.16ABC

time

expo

nent

(10

s -

1000

s)

EOX (MV / cm)

T = 1250C

t0 = 1s

25 50 75 100 125 1500.04

0.06

0.08

0.10

0.12

0.14

0.16

t0=1s

EOX

~ 8.5 MV / cm

T (0C)

tim

e e

xpo

ne

nt

(10

s -1

00

0s)

A B C

D# NDOSE(x1015cm-2) N% EOT(Å)

A 0.0+5.3 35 15.6

B 0.8+5.1 39 13

C 0.8+0.0 06 18.5

Lower n (independent of EOX, T) for larger Si/SiON N density

17

Impact of Post Nitridation Anneal (PNO)

PNO without proper PNA: Higher degradation & lower n (like RTNO)

10-6

10-3

100

1033x10

-3

10-2

10-1

V (

V)

stress time (s)

EOX

~ 8.5 MV/cm T (

0C)

12555

B

At0=1s


A 0.0+2.9 (Correct PNA) 19 17.7

B 0.0+2.0 (Worst PNA) 12 22.2

C 0.0+2.7(Moderate PNA) 16 20.2

6 7 8 9 100.04

0.06

0.08

0.10

0.12

0.14

0.16

A B C

time

expo

nent

(10

s -

1000

s)EOX (MV / cm)

T = 1250C t0 = 1s

18

Time exponent: Impact of PNO dose

Reduction in n with increase in N%

25 50 75 100 125 150 1750.04

0.06

0.08

0.10

0.12

0.14

0.16

t0=1s

EOX

~ 8.5 MV / cm

T (0C)

tim

e ex

pone

nt (

10s

-100

0s)

A B C

6 7 8 9 100.04

0.06

0.08

0.10

0.12

0.14

0.16

ABC

time

expo

nent

(10

s -

1000

s)

EOX (MV / cm)

T = 1250Ct0 = 1s


A 0.0+2.9 19 17.7

B 0.0+5.3 35 15.55

C 0.0+6.8 42 14.6T independence of n for all N%

EOX independence of n for all N%

19

Time exponent: Process dependence

PNO (proper PNA) trend line

0 10 20 30 40 50

0.04

0.06

0.08

0.10

0.12

0.14

0.16

Control

TBASE(AO) 15 20 25

%N (atomic)

time

exp

on

en

t (1

0s-

10

00

s)

t0 = 1s

RTNO ImproperPNA (PNO)

Long-time power law time exponent depends on SiON process (PNO, PNA, RTNO) & N%

20

Outline





Conclusion


21

Temperature Activation

RTNO shows higher degradation and lower EA compared to PNO

0 10 20 30 40 50

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

ImproperPNA (PNO)

RTNO

t0 = 1s

EA (

eV

)

%N

28 30 32 34 36 38 4010-2

10-1

EA = 0.08 eV

V

(V

) a

t t-

stre

ss=

10

0s

1/KT ( eV -1 )

PNO (23.5AO, 17%)

RTNO (22.5AO, 6%)

EOX

~ 8.5 MV / cm t0=1s

EA = 0.04 eV

T activation governs by SiON process; shows similar (as time exponent, n) dependence on N%


22

Field Dependence: PNO / RTNO / RTNO + PN

PNO: Increased degradation & lower field dependent slope for higher N%

6 7 8 9 1010

-4

10-3

10-2

= 0.32

= 0.53

V /

EO

T (

a.u)

EOX

( MV / cm)

t0 = 1sT=125

0C

A B C

= 0.51


A 0.0+2.9 19 17.7

B 0.0+5.3 35 15.6

C 0.0+6.8 42 14.6

D 0.8+5.1 39 13.1

E 0.8+0.0 6 18.5

D E

RTNO, RTNO+PN: Very high degradation and low slope

Si/SiON interface density governs overall degradation magnitude & oxide field-dependent slope

SiON

RTNOPNO

RTNO+PN

Poly-SiSi-substrate

N

23

Field Acceleration Factor: Process Dependence

0 10 20 30 40 50

0.2

0.3

0.4

0.5

0.6

0.7

RTNO

ImproperPNA (PNO)

Control

(c

m /

MV

)

%N (atomic)

T=1250C

t0=1s


Field acceleration governs by SiON process; more importantly by N density at Si/SiON interface

24

Summary: Material Dependence

Si/SiON interfacial N density plays important role

High Si/SiON N density for RTNO process, PNO without proper PNA, or PNO with very high (>30%) N density

Si/SiON N density:

NBTI magnitude:

Time exponent:

T activation:

EOX acceleration:

Low (PNO, proper PNA, lower N, less than 30% at.)

Lower

High (~0.12 @1s delay)

High (~0.08-0.09 eV)

High (~0.6 cm/MV)

Increase

Increase

Reduce

Reduce

Reduce

25

Outline





Conclusion


26

Very Long Time Degradation

Universally observed very long time power law exponent of n = 1/6

TSMC, IRPS ‘05

Stress Time > 1000 Hr

Tech A, V1

Tech A, V2

Tech B, V1

Vm

in f

or

SR

AM

~t1/6

Haggag, Freescale, IRPS ‘07

1.2 1.8 2.40.05

0.10

0.15

0.20

0.25

0.30

Vstress

[Volts]

-250C 450C

1050C 1450C

Deg

rad

ati

on

Slo

pe, n

1/6 line

Stress time ~ 28HrTI, IEDM ‘06

27

Interface Traps: Reaction Diffusion Model

Poly

Si

H

Si

H

Reaction: Si-H bond breaks into Si+ and H

Si

H

Diffusion: Released H diffuse away and leave Si+

Si

H

Jeppson, JAP 1977; Alam, IEDM 2003

Species Slope

HO 1/4

H2 1/6

H+ 1/2

Power-law dependence, exponent depends on H

Chakravarthi, IRPS 2004; Alam, IRPS (T) 2005

Long time experimental data suggests H2 diffusion

28

NBTI physical mechanism

Tunneling of inversion holes to Si-H Generation of NITSi H

p

n-Si SiON

p+-poly

Tunneling barrier

Tunneling of inversion holes to N related traps Trapping of Nh

Hole trapping when added to interface traps reduces n & EA of overall NBTI

Identical EOX (governs both inversion holes and tunneling) dependence for NIT and Nh

29

NBTI Physical Mechanism (Stress)

Low Si/SiON N density NIT dominated process, low Nh

VT (log-scale)

stress time (log-scale)

Strong T activation

Higher Si/SiON N density Significant additional Nh component (fast, saturates, weak T dependence)

High short-time and overall degradation

Low T activation at longer stress time

-VG -VG

30

Isolation of Interface Trap Generation and Hole Trapping

Total degradation sum of NIT and Nh contribution

10-1 100 101 102 1033x10-3

10-2

6x10-2

VSTR

=-2.1V

T=125OC

VT (=V

IT+V

h)

VIT

Vh

n=0.125measured

extracted

extracted

14AO,23%

n=1/6

degr

adat

ion

(V)

stress time (s)

Assumption 1: Fast (t<1s) saturation of Nh contribution

Assumption 2: Power law n=1/6 dependence for NIT contribution at longer stress time

Slides 54 – 56: Mahapatra, TED 2009 (Feb)

31

Field and Temperature Dependence

Identical EOX dependence – same barrier controls NIT, Nh and hence total degradation

6 7 8 9 1010-3

10-2

10-1

T=125OC

tSTR

=100sV

T

VIT

Vh

14AO,23%

de

gra

da

tion

(V

)

EOX

(MV/cm)24 26 28 30 32 34 36 383x10-3

10-2

6x10-2

EA=0.04eV

EA=0.094eV

EA=0.078eV

VSTR

=-2.1VtSTR

=100sV

T

VIT

Vh

14.0AO,23%

de

gra

da

tion

(V

)1/kT (eV-1)

Low T activation of Nh, when added to higher T activation of NIT lowers T activation of overall degradation

32

Hole trapping – Impact of N% (PNO)

Increase in hole trapping with increase in N% causes reduction in n & EA at higher N%

15 20 25 30 35 40 450.04

0.06

0.08

0.10

0.12

0.14

n;

EA(e

V)

N% (atomic)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

EA

n V

h /V

T (10

00

s)24 26 28 30 32 34 36

0.003

0.01

0.1 14.0AO,22%, 21.4A

0,29%

15.6AO,35%, 19.9A

O,36%

12.3AO,41%, 14.6A

O,42%

lines: EA=0.04eV

ext

ract

ed

V

h (V

)

1/kT (eV-1)

Identical T activation of hole trapping over a wide N% range suggests correctness of isolation method

33

T Activation of NIT: Universal Scaling Scheme

10010

110

210

310

410

510

610

710

810

96x10-3

10-2

10-1

PNO (1.2nm, 14% at.) V

G=-1.9V

50OC

100OC

150OC

VT

(V)

time (s)

R-D model solution:

VT = (kF.N0/kR)2/3 (Dt)1/6

EA(kF) ~ EA(kR), VT(T,t) ~ [D(T)t]n

EA ~ ED * n

X-axis scaling provides ED

Identical n at all T

Y-axis scaling provides EA

34

Universal T Activation of Diffusion

26 28 30 32 34 36 38 4010

-1

100

101

102

103

104

ControlIDlin / C1 / 8.0C-P / C2 / 9.1

DPNOEA ~ 0.58eV Probe/W#/-V

G(V)

IDlin / P1 / 2.1 IDlin / P1 / 1.9 IDlin / P2 / 2.1 IDlin / P2 / 1.9 IDlin / P3 / 2.3 IDlin / P4 / 3.0 C-P / P4 / 3.0

X-a

xis

sca

le f

act

or

(a.u

.)

1/kT (eV-1)

X-axis scaling

P1: 1.2nm (14%), P2: 1.2nm (21%) P3: 1.7nm (28%), P4: 2.2nm (29%)

Identical EA for PNO & Control

Identical EA for Idlin & C-P measurements

ED consistent with power law slope (n) from R-D model

EA suggest neutral molecular H2 diffusion*

*Reed, JAP 1988

35

T Activation of NIT: Impact of N% (PNO)

Validation of EA ~ ED * n for a wide N% range suggests the robustness of isolation method

24 26 28 30 32 34 36 38 40100

101

102

103

104

EA=0.095eV

ED=0.58eV

14.0AO,23%

17.7AO,19%

23.5AO,17%

X-a

xis

& Y

-axi

s sc

ale

fact

or (

a.u.

)

1/kT (eV-1) 15 20 25 30 35 40 454x10-2

10-1

100

n=EA/E

D

ED

EA

N% (atomic)E

D,

EA (

eV

); E

A/E

D

36

Outline





Conclusion


37

Recovery Transients (UF-OTF IDLIN)

Low N% (low hole trapping) – delayed start of recovery

10-6 10-4 10-2 100 102 1040.10.20.30.40.50.60.70.80.91.01.1

N=23%, EOT=14AO

recovery time (s)

fra

ctio

n r

em

ain

ing

tSTR

=1000sV

STR / V

REC (V)

-1.7 / -1.3-2.3 / -1.8-2.3 / -1.3-2.3 / -1.0

10-6 10-4 10-2 100 102 1040.10.20.30.40.50.60.70.80.91.01.1

N=42%, EOT=12.3AO

tSTR

=1000sV

STR / V

REC (V)

-1.7 / -1.3-2.3 / -1.8-2.3 / -1.3-2.3 / -1.0

recovery time (s)fr

actio

n r

em

ain

ing

High N% (high hole trapping) – fast start of recovery

Difference in recovery shape certainly not ~log(t)

Kapila, IEDM 2008

38

Recovery Analysis

Recovery:

Hole detrapping (electron capture in bulk traps)

Interface trap passivation

Stress: Interface trap generation and hole trapping in pre-existing bulk traps

Si Hp

Trap Trap

n-Si SiON p+-poly

Tunneling barrier (T.B.)

Neutralization of interface trap charge by electron capture; valid for recovery at low VG (~ VT) only [Reisinger, IRPS 2006; Grasser, IRPS 2008]

Gate

n-Si

At stress VG

Isolation of components important to model recovery

Gate

n-Si

At recovery VG

39

Recovery Analysis (contd..)

Stress Fast hole trapping and gradual interface trap buildup

VT (log-scale)

stress time (log-scale)

Stress

recovery time (log-scale)

VT (linear-scale)

Recovery

Recovery Fast hole detrapping and gradual (lock-in) interface trap passivation

Nh

NIT

Overall recovery spans several orders of time scale

40

Recap: Hole Trap Fraction from Stress

Based on NIT & Nh isolation scheme

101

102

103

0.1

0.2

0.3

0.4

0.5

0.6

T=125oC tSTR

=1000s

ho

le tra

p fra

ction

ho

le tr

ap

fra

ctio

n

stress time(s)50 70 90 110 130

0.1

0.2

0.3

0.4

0.5

0.6EOT(nm)/N%

2.35/20 1.8/201.4/23 1.55/351.46/42

Temperature(oC)

Hole trap fraction:

Increases with N%

Reduces with stress time (Nh saturation at short stress time)

Reduces with stress T (lower T activation for Nh)

Slides 65 – 67: Deora, unpublished

41

Recovery Contribution by Trapped Holes

Assumption: Early recovery phase due to hole detrapping

Hole detrapping time:

Independent of stress time

Independent of stress T

10-6 10-4 10-2 100 102 1040.10.20.30.40.50.60.70.80.91.01.1

N=23%, EOT=14AO

T=125OC

VSTR

=-2.3VV

REC=-1.3V

tSTR

(s)101001000

recovery time (s)

fra

ctio

n r

ema

inin

g

Find Nh fraction (from stress)

101

102

10310

-5

10-4

10-3

10-2

10-1

100

101

102

stress time=1000s

T=125oC

recovery time corr. to hole trap fraction (s)

reco

very

tim

e co

rr. t

o ho

le tr

ap fr

actio

n (s

)

stress time(s)50 70 90 110 130 10

-5

10-4

10-3

10-2

10-1

100

101

102EOT(nm)/N%

2.35/20 1.8/201.4/23 1.55/351.46/42

Temperature(oC)

Find corresponding recovery (hole detrapping) time

42

Recovery: T Dependence

Early phase due to hole detrapping weak T dependence

Later part due to NIT passivation T activated

MSM Larger delay time, T dependent recovery T dependence of n; Not seen for OTF

10-7 10-5 10-3 10-1 101 103-0.08

-0.06

-0.04

-0.02

0.00

T(oC) 85 125

EOT=1.46nm,N=42%

reco

very

(V

)

Recovery time(s)

EOT=1.8nm,N=20%

50 75 100 125 150

0.12

0.16

0.20

0.24

0.28

0.32

MSM

1ms 1s

delay 35ms 50ms 1s

pow

er la

w ti

me-

expo

nent

(n)

Temperature(oC)

OTF

43

Outline





Conclusion


44

Summary

N density at Si/SiON interface plays important role PNO better than RTNO, proper PNA important for PNO

Higher N at Si/SiON higher degradation magnitude, lower time exponent, T activation, EOX acceleration

Significant contribution from Nh (in addition to NIT) for devices having high Si/SiON N density

NIT and Nh contributions can be separated consistently

Nh detrapping and NIT passivation determines early and long-time recovery respectively

NBTI recovery impacts measurement lower captured magnitude, higher “n” & EA uncertain parameters

1 Material Dependence of NBTI Stress & Recovery in SiON p-MOSFETs S. Mahapatra, V. D. Maheta, S....

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Transcript of 1 Material Dependence of NBTI Stress & Recovery in SiON p-MOSFETs S. Mahapatra, V. D. Maheta, S....