material dependence of nbti stress & recovery in sion p-mosfets
DESCRIPTION
Material Dependence of NBTI Stress & Recovery in SiON p-MOSFETs. S. Mahapatra, V. D. Maheta, S. Deora, E. N. Kumar, S. Purawat, C. Olsen 1 , K. Ahmed 1 , A. E. Islam 2 , M. A. Alam 2 Department of Electrical Engineering, IIT Bombay, Mumbai, India - PowerPoint PPT PresentationTRANSCRIPT
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
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
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
D# NDOSE(x1015cm-2) N% EOT(Å)
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
D# NDOSE(x1015cm-2) N% EOT(Å)
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
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
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%
PNO (proper PNA) trend line
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
D# NDOSE(x1015cm-2) N% EOT(Å)
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
PNO (proper PNA) trend line
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
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
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
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
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
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
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