Comprehensive Analysis of
Ion Variation in Metal Gate
FinFETs for 20nm and Beyond
T. Matsukawa, Y.X.Liu, S. O’uchi, K. Endo,
J. Tsukada, H. Yamauchi, Y. Ishikawa,
H. Ota, S. Migita, Y. Morita, W. Mizubayashi,
K. Sakamoto and M. Masahara
National Institute of AIST, Japan
1
Outline
• Introduction
• Sample FinFET fabrication
• Analysis of Ion variation components
- ΔVt contribution
- ΔRpara evaluation and its contribution
- ΔGm evaluation and its contribution
• Scalability of ΔVt and ΔGm
• Variability prediction for Lg=20 and 14nm
• Summary
2
Introduction
Variability of FinFETs : Previous studies
G
S
D
Work function
variation
(WFV) of MG
Oxide charge
variation
in gate
dielectrics.
Undoped
channel
No RDF
9 Excellent SCE immunity :
Low ΔVt
against ΔLg and ΔTfin
9 Undoped channel :
No ΔVt due to RDF
Dominant ΔVt origins:
- WFV due to MG grains
- Oxide charge variation
Matsukawa et al.(AIST), VLSI2009
Liu et al.(AIST), VLSI2010
3
Id
log Id
Importance of Ion variability
ΔIon
ΔVt
Ioff
degradation
Ion
degradation
Vg
9ΔVt
Stand-by
power
Vg
9ΔIon
Circuit
performance
4
Objective
Comprehensive study of Ion variation of FinFET.
Ion variability sources
ΔIon
ΔVtt
D
S
G
channel
gate
dielectrics
NiSi
ΔRpara
para
ΔGmm
9 Three sources of ΔIon
Analysis Strategy
¾ ΔVt, ΔGm, and ΔRpara are
analyzed as Ion variation
components.
¾ Scalability analysis of
the 3 components.
Goal of this work :
¾ Prediction Ion variation for Lg=20 nm and beyond.
5
Outline
• Introduction
• Sample FinFET fabrication
• Analysis of Ion variation components
- ΔVt contribution
- ΔRpara evaluation and its contribution
- ΔGm evaluation and its contribution
• Scalability of ΔVt and ΔGm
• Variability prediction for Lg=20 and 14nm
• Summary
6
FinFET Process flow
(100) SOI wafer
(110) fin channel patterning
Gate oxidation (Tox~2nm, 3nm)
TiN (10nm) deposition (PVD)
n+ poly-Si HM depo.
Gate patterning
Extension I/I (As, 5 keV, 4x1014 cm-2)
Side wall (TSWS=40nm) formation
S/D I/I (P, 10 keV, 1015 cm-2)
Dopant activation RTA (~870oC, 2s)
Ni (7nm) sputtering, salicide process
Metallization
Etching
condition
vs
variability
Tox vs
variability
7
Overview of fabricated FinFET
Paired transistor
G1
G2
D1
D2
S
Top view SEM
SWS
G
S
D
100nm
TiN
NiSi
fin
channel
50nm
TEM of channel
and gate stack
S
n+Si
G
SWS
D
extension 100nm
TEM of channel and S/D
8
Outline
• Introduction
• Sample FinFET fabrication
• Analysis of Ion variation components
- ΔVt contribution
- ΔRpara evaluation and its contribution
- ΔGm evaluation and its contribution
• Scalability of ΔVt and ΔGm
• Variability prediction for Lg=20 and 14nm
• Summary
9
Analysis Strategy of ΔIon Sources
Error propagation law:
σ
2
Id
⎛ ∂I d
⎞
⋅σVt ⎟⎟
≈ ⎜⎜
⎝ ∂ Vt
⎠
ΔVt
2
2
2
⎛ ∂I d
⎞ ⎛ ∂I d
⎞
⎜
⎟
+
⋅σR para + ⎜⎜
⋅σG m ⎟⎟
⎜ ∂R para
⎟ ⎝ ∂G m
⎠
⎝
⎠
ΔRpara
ΔGm
9 Each source is assumed to be independent.
9 Each contribution is given experimentally:
“sensitivity” x “variation”
10
Variability in Vg-Id : ΔVt contribution
10-7
10-9
ΔIon
Δ Vt
Tox=2nm
200
10-11
10-13
-0.5
300
100
0
0.5
Vg [V]
0
1
ρ=0.799
400
400
Id [μA/μm]
Lg=80nm Vd=1V
Tfin=25nm
Id [A/μm]
10-5
500
500
Id@Vd=1V [μA/μm]
0.001
300
200
100
0
0.3
Slope:
∂Id/∂Vt_lin
0.35
0.4
Vt_lin[V]
0.45
0.5
9 Significant ΔVt recognized
9 ΔVt strongly correlates with ΔIon
11
2
σ
2
Id
⎛ ∂I d
⎞
≈ ⎜⎜
⋅σVt ⎟⎟
⎝ ∂ Vt
⎠
2
⎞
⎛ ∂I d
+⎜
⋅σR para ⎟
⎟
⎜ ∂R para
⎠
⎝
2
⎛ ∂I d
⎞
+ ⎜⎜
⋅σG m ⎟⎟
⎝ ∂G m
⎠
9 ΔVt contribution
experimentally obtained.
3
2
Vt distribution
1
0
-1
σ Vt
-2
-3
500
Id@Vd=1V [μA/μm]
Error propagation law
Normal quantile σ
ΔVt Contribution on ΔIon
400
ΔIon - ΔVt correlation
ρ=0.799
300
200
∂Id/∂Vt_lin
100
0
0.3
0.35
0.4
Vt_lin[V]
0.45
0.5
12
Id variation vs gate overdrive
Id [μA/μm]
500
Lg=80nm Vd=1V
400 Tfin=25nm
300
200
Vt
100
0
-0.5
0
Vov
=0.7V
0.5
Vov (=Vg-Vt_lin) [V]
1
Id @Vov=0.7V [μA/μm]
For ΔRpara and ΔGm estimation
Id@Vov=0.7V vs ΔVt
500
400
300
200
ρ=0.0233
100
0
0.2
0.3
0.4
0.5
Vt_sat [V]
9 Influence of ΔVt is excluded
from Id at identical gate overdrive.
Utilized for analysis of ΔRpara and ΔGm.
13
ΔRpara evaluation strategy
Ron fluctuation of
identical Lg/Tfin design.
Ron (=Vd/Id@Vov=0.7V)
for various Lg/Tfin design.
Thin
1000
Thick
500
0
0
Tfin=20,30,
40,60 nm
100
Identical
slope
800
Ron [Ω-μm]
Ron [Ω-μm]
1500
1000
200
Lg [nm]
300
400
Intercept (Lg=0):
Parasitic Resistance Rpara
600
400
<Lg>=80 nm
<Tfin>=25 nm
200
0
0
20
40
60
80
Measured L g[nm]
100
Projection to y-axis:
Rpara variation
14
Id @Vov=0.7V [μA/μm]
ΔRpara contribution on ΔIon (1)
500
ρ=0.639
400
300
Slope: ∂ ( I d @Vov = 0.7V )
200
∂R para
100
0
0
100 200 300 400 500 600
Rpara [Ω-μm]
9ΔRpara has significant correlation with ΔIon.
9ΔRpara causes Ion fluctuation as well as ΔVt.
15
ΔRpara contribution on ΔIon (2)
2
σ
2
Id
⎛ ∂I d
⎞
≈ ⎜⎜
⋅σVt ⎟⎟
⎝ ∂ Vt
⎠
2
⎞
⎛ ∂I d
+⎜
⋅σR para ⎟
⎟
⎜ ∂R para
⎠
⎝
2
⎛ ∂I d
⎞
+ ⎜⎜
⋅σG m ⎟⎟
⎝ ∂G m
⎠
9 ΔRpara contribution
experimentally obtained.
Id @Vov=0.7V [μA/μm]
Error propagation law
Normal quantile σ
3
Rpara distribution
2
σRpara
1
0
-1
-2
-3
500
ρ=0.639
400
300
∂ ( I d @Vov = 0.7V )
∂R para
200
100
0
ΔIon – ΔRpara correlation
0
100 200 300 400 500 600
Rpara [Ω-μm]
16
ΔGm evaluation strategy
Gm_max
Gm_lin [μS/μm]
160
120
Vd=
50mV
80
40
0
-0.5
Gm@
Vov=0.7V
Gm@
Vov=
50mV
0
0.5
Vov (=Vg-Vt_lin) [V]
1
9ΔGm is evaluated by 3 different criteria.
Correlation with ΔRpara is examined.
17
ΔGm – ΔRpara correlation
3 different criteria of ΔGm compared
Gm_max
Gm@Vov=0.7V
Gm@Vov=50mV
Rpara [Ω-μm]
600
500
400
300
200
ρ=0.725
100
0
80
100
120
140
Gm_max [μS/μm]
ρ=0.088
ρ=0.713
40
60
80
100
40
60
80
100
Gm_lin @Vov=0.7V [μS/μm] Gm_lin@Vov=50mV [μS/μm]
9 ΔGm at Vov=50mV is almost independent from ΔRpara.
Gm variation is correctly evaluated
as independent variation sources.
18
Id @Vov=0.7V [μA/μm]
ΔGm contribution on ΔIon (1)
500
ρ=0.562
400
300
200
∂ ( I d @Vov = 0.7V )
Slope:
∂Gm _ lin
100
0
40
50
60
70
80
90
Gm_lin @Vov=50mV [μS/μm]
9ΔGm has significant correlation with ΔIon.
9ΔGm causes Ion fluctuation as well as ΔVt.
19
ΔGm contribution on ΔIon (2)
2
σ 2 Id
⎛ ∂I d
⎞
≈ ⎜⎜
⋅σVt ⎟⎟
⎝ ∂ Vt
⎠
2
⎞
⎛ ∂I d
+⎜
⋅σR para ⎟
⎟
⎜ ∂R para
⎠
⎝
2
⎛ ∂I d
⎞
+ ⎜⎜
⋅σG m ⎟⎟
⎝ ∂G m
⎠
9 ΔGm contribution
experimentally obtained.
Id @Vov=0.7V [μA/μm]
Error propagation law
Normal quantile σ
3
2
1
0
Gm distribution
σGm
-1
-2
-3
500
ρ=0.562
400
300
∂ ( I d @Vov = 0.7V )
∂Gm _ lin
200
100
0
ΔIon – ΔGm correlation
40
50
60
70
80
90
Gm_lin @Vov=50mV [μS/μm]
20
Origins of ΔGm
Gm ∝
ΔGm vs ΔTox
ΔTox in wafer
12
Variation [%]
10
8
6
4
2
0
σ Gm
σ Tox
Gm
Tox
μ Wg
Tox Lg
No correlation to ΔLg
Gm@Vov=50mV [μS/μm]
Negligible ΔTox
SOI thick. uniformity.
Negligible
90
80
ρ=0.0658
70
60
O.Weber et al.,
IEDM2008
50
40
30
40
50
60
70
80
90
Measured ΔLg [nm]
100
9 Remaining component : Mobility μ
9 Mobility is possible origin of ΔGm
21
Summary of measured ΔIon sources
Total ΔIon
(Vg=Vd=1V)
ΔVt
ΔIon
ΔGm
sources
ΔRpara
Lg=80nm
0
2
4
6
8
10
Variation σId/<Id> [%]
12
9 ΔIon sources are evaluated successfully.
9 ΔVt is a dominant ΔIon source for Lg=80nm FinFETs.
9 ΔGm and ΔRpara have significant influence on ΔIon. 22
Outline
• Introduction
• Sample FinFET fabrication
• Analysis of Ion variation components
- ΔVt contribution
- ΔRpara evaluation and its contribution
- ΔGm evaluation and its contribution
• Scalability of ΔVt and ΔGm
• Variability prediction for Lg=20 and 14nm
• Summary
23
Vt variation under scaling
Tox=2nm
Tox=3nm
m
V-
μm
30
Vt =
10
2.
85
20
A
σVt_lin [mV]
Pelgrom plot 40
for ΔVt
0
0
AV
=t 2
6
.0
m
Tox
scaling
m
μ
V-
Gate size scaling
5
10
15
1/(LW)1/2 [μm-1]
9ΔVt increases with gate size scaling : Scaling factor = AVt
9ΔVt origin : WFV + oxide charge fluctuation
9AVt can be reduced by Tox reduction.
24
Gm variation under scaling
Pelgrom plot for ΔGm
σGm/<Gm> [%]
20
Tox=2nm, by RIE
Tox=3nm, by RIE
15
2
2
.
1
=
10
AG
5
0
-μ
%
m
AG
0
5
m
.
1
=
m
11
%
m
μ
-
Gate size scaling
10
15
1/(LW) 1/2 [μm-1]
9ΔGm increases with gate size scaling : Scaling factor = AGm
9 AGm can not be reduced by Tox reduction
25
ΔGm reduction possibility
Pelgrom plot for ΔGm
σGm/<Gm> [%]
20
Tox=2nm, by RIE
Tox=2nm, by wet etching
15
11
.
=1
10
5
0
0
AG
%
-μ
m
m
6
.
0
=
1
m
μ
3%
A Gm
5
Fin channel
formed by
RIE
10
1/(LW)1/2 [μm-1]
15
Smooth/
damage-less
wet etching
9 Less scattering
9 μ-related variability
suppression
Liu et al.(AIST), VLSI2010
9Process innovation necessary to reduce AGm.
26
ΔGm improvement mechanism
Smooth/
damageless etching:
Fin channel by RIE:
Roughness &
plasma damage
Si(111) anisotropic etching
Gate
Fin
channel
Gate
Scattering by roughness
and defect charges
Phonon scattering
Liu et al.(AIST), VLSI2010
9 Roughness / Defects
9 Tr.-to-tr. variation
Mobility variation
9 Suppressed scattering
9 μ variation improvement
Suppressed ΔGm
27
Outline
• Introduction
• Sample FinFET fabrication
• Analysis of Ion variation components
- ΔVt contribution
- ΔRpara evaluation and its contribution
- ΔGm evaluation and its contribution
• Scalability of ΔVt and ΔGm
• Variability prediction for Lg=20 and 14nm
• Summary
28
Prediction of ΔIon for Lg=20/14nm
TCAD calculation
based on ITRS
Total ΔId
Δ Vt
ΔGm
AVt=1.35 mVμm :
Smallest AVt for FinFETs
ΔRpara
Liu et al.(AIST), VLSI2010
Total ΔId
AGm=1.11 %μm :
RIE etched Fin case
σRpara/<Rpara>=13%
Lg=20nm
Δ Vt
ΔGm
Lg=14nm
ΔRpara
0
5
10
15
σId/<Id> [%]
9 ΔGm becomes dominant ΔIon origin
with Lg scaling to 14 nm.
20
25
29
ΔIon improvement for Lg=14nm
w/ conv. process
Process innovations
taken into account.
Total ΔId
AVt=0.89 mVμm :
Smallest AVt for FD-SOI
ΔRpara
K.Chang et al., IEDM2009
AGm=0.61 %μm :
Smooth/
damageless
etching
Δ Vt
ΔGm
Process
innovation
Total ΔId
Δ Vt
ΔGm
ΔRpara
0
5
10
15
σId/<Id> [%]
20
25
9 Process innovations reduce both the contribution
and keep ΔIon comparable to Lg=20nm.
30
Summary
• Sources of Ion variability were analyzed for FinFETs.
• ΔVt, ΔGm and ΔRpara were successfully evaluated as
independent variation sources of ΔIon.
• ΔGm can not be scaled by Tox reduction,
and thus will be more significant with scaling.
• ΔGm will be a dominant origin of ΔIon for 14nm FinFETs
unless process innovations are introduced.
Acknowledgement:
This work was supported in part by NEDO
under the Development of Nanoelectronics Devices Technology.
31