Direct Experimental Evidence Linking Silicon Dangling Bond Defects to Oxide Leakage Currents
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1 Direct Experimental Evidence Linking Silicon Dangling Bond Defects to Oxide Leakage Currents P.M. Lenahan, J.J. Mele, A.Y. Kang, J. P. Campbell Penn State University, University Park, PA 16802 S.T. Liu Honeywell Corp. Plymouth, MN 55441 R.K. Lowry and D. Woodbury Intersil Corp. Melbourne, FL 32902 R. Weimer, Micron Technologies Boise, Idaho 83707-0006
description
Direct Experimental Evidence Linking Silicon Dangling Bond Defects to Oxide Leakage Currents. P.M. Lenahan, J.J. Mele, A.Y. Kang, J. P. Campbell Penn State University, University Park, PA 16802 S.T. Liu Honeywell Corp. Plymouth, MN 55441 R.K. Lowry and D. Woodbury Intersil Corp. - PowerPoint PPT Presentation
Transcript of Direct Experimental Evidence Linking Silicon Dangling Bond Defects to Oxide Leakage Currents
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Direct Experimental Evidence Linking Silicon Dangling Bond Defects to Oxide
Leakage Currents
P.M. Lenahan, J.J. Mele, A.Y. Kang, J. P. CampbellPenn State University,
University Park, PA 16802
S.T. LiuHoneywell Corp.
Plymouth, MN 55441
R.K. Lowry and D. WoodburyIntersil Corp.
Melbourne, FL 32902
R. Weimer, Micron TechnologiesBoise, Idaho 83707-0006
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Ec
Ev
VB Edge
CB Edge
Si SiO2
CB Edge
VB Edge
EF Inelastic tunneling of silicon
conduction band electrons through oxide defects near
the Si/SiO2 boundary.
Trap
Stress Induced Leakage (SILC)
S.Takagi, et al. Trans.Electron.Dev 46, 348 (1999)E.Rosenbaum and L.F.Register, IEEE Trans.Electron.Dev. 44, 317(1997)
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Literature suggests oxygen vacancy centers (E’ centers):
•J.H.Suehle, et al. IRPS (1994)
•J.H.McPherson and H.Mogul, J.Appl.Phys, 84, 1513 (1998)
•B.Schlund, et al. IRPS (1996)
•D.J.Dumin and J.Maddux, IEEE Trans.Electron.Dev., 40, 886 (1993)
•S.Takagi, et al. IEEE Trans.Electron.Dev., 46, 348 (1999)
•A.Yokozawa, et al. IEDM (1997)
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At least two independent studies indicate that E’ centers are generated when oxides are subjected to high electric fields. ** So, if we could link E’ center density to leakage current, we could establish an important role for the centers in oxide leakage phenomena.
* W. L. Warren and P.M. Lenahan, JAP 62, 4305 (1987), IEEE Trans Nucl. Sci 34, 1355 (1987)* H. Hazama, et al. Proceedings of the Workshop on Ultra Thin Oxides Jap.Soc. Appl. Phys. Tokyo 1998. Cat. No. Ap 982204 pp201-212.
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Ec
Ev
Si SiO2
+ + + + + + + ++ + + + + + + ++ + + + + + + ++ + + + + + + ++ + + + + + + ++ + + + + + + +
Ev
Ec
Si SiO2
Ev
Ev
Ec
Ec
(Any net space charge near the Si/SiO2 boundary will decrease the tunneling barrier and increase oxide current for any gate potential.)
Test E’ hypothesis with neutral E’ centers
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Approach: (a) Generate neutral E’ centers in a wide variety of oxides, annihilate the E’ centers by various means.
(b) Compare generation and annihilation of the E’ centers with generation and annihilation of oxide leakage current. (Are they strongly correlated?)
(c) Compare experimental results and “theoretical work on inelastic tunneling and SILC. (Are the defect densities “reasonable” in terms of the (very crude) theory available.)
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Oxides Utilized in the Study:
3.3nm (forming gas) 3.3nm (no forming gas) 45 nm (forming gas)
(all thermally grown)
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10
3.3nm Oxide (forming gas)
3440 3445 3450 3455 3460 3465 3470 3475 3480 3485
Magnetic Field (Gauss)
Arb
itra
ry U
nit
s
As Processed
Post VUV
Post Anneal
Pb0 E’
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I-V Characteristics of 3.3nm Oxide (forming gas)
0.00
2.00
4.00
6.00
8.00
10.00
12.00
0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3
Voltage
Cu
rre
nt
De
ns
ity
(n
A/c
m2 )
As Processed
90mVUV
90mAnneal
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0.00
2.00
4.00
6.00
0 20 40 60 80 100VUV Illumination Time (min)
E' C
en
ter
De
ns
ity
(101
1 /cm
2)
0
5
10
15
0 20 40 60 80 100
VUV Illumination (minutes)
Cu
rre
nt
De
ns
ity
(nA
/cm
2)
E’ and Leakage Current Generation 3.3nm oxide (forming gas)
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0
5
10
15
0 20 40 60 80 100
Anneal Time (minutes)
Cu
rre
nt
De
ns
ity
(nA
/cm
2)
0.00
2.00
4.00
6.00
0 20 40 60 80 100
Annealing Time (minutes)
E' C
en
ter
De
nsi
tie
s
(101
1 /cm
2 )
E’ and Leakage Current Anneal 3.3nm oxide (forming gas)
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3.3nm Oxide (no forming gas)
3440 3450 3460 3470 3480Magnetic Field (G)
ES
R A
mp
litu
de
(A
rb. U
nit
s)
90 MIN ANNEAL
90 MIN VUV
Virgin
Pb0 E’
14
15
I-V Characteristics of 3.3nm Oxide (no forming gas)
0.00
2.00
4.00
6.00
8.00
10.00
12.00
0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3
Voltage (V)
As P rocessed
90mVUV
90mAnneal
I-V Characteristics of 3.3nm Oxide (no forming gas)
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0
2
4
6
0 20 40 60 80 100VUV Illumination Time (minutes)
E' D
en
sit
ies
(1
011
/cm
2 )
0
2
4
6
8
10
0 20 40 60 80 100
VUV Illumination (minutes)
Cu
rre
nt
De
ns
ity
(nA
)
E’ and Leakage Current Generation 3.3nm oxide (no forming gas)
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0
2
4
6
0 20 40 60 80 100
Annealing Time (minutes)
E' D
ensi
ty (
1011
/cm
2 )
E’ and Leakage Current Anneal 3.3nm oxide (no forming gas)
0
2
4
6
8
10
0 20 40 60 80 100
Anneal Time (minutes)
Cu
rren
t D
en
sity
(nA
)
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3440.5 3445.5 3450.5 3455.5 3460.5 3465.5 3470.5 3475.5 3480.5
Magnetic Field (G)
Arb
itra
ry U
nit
s
Pbo (g=2.0058) E` [g(z.c.)=2.0005]
As Processed
Post VUV
Post VUV and Anneal
45nm Oxides
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45nm Oxide
1.0E-11
1.0E-10
1.0E-09
1.0E-08
1.0E-07
0 10 20 30Voltage (V)
Cu
rren
t D
ensi
ty (
Am
ps
/ cm
2)
10-8
10-9
10-10
10-11
Post VUV
Post VUV and
Anneal
AsProcessed
20
00.5
11.5
2
0 50 100 150VUV Illumination Time (min)C
urr
en
t D
en
sit
y(1
0-8A
/cm
2)
0
0.5
1
1.5
0 50 100 150VUV Illumination Time (min)
E
De
ns
ity
101
2 /cm
2
E’ and Leakage Current Generation 3.3nm oxide (forming gas)
20
21
0
100
200
300
0 20 40 60 80Anneal Time (min)
Cu
rren
t D
ensi
ty
(10
-8 A
/ cm
2)
0
0.5
1
1.5
0 20 40 60 80Anneal Time (min)
E' D
ensi
ty
101
2/c
m2
E’ and Leakage Current Anneal 45nm oxide (forming gas)
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Conclusions
In several quite different oxides we find that:
(1) Generation of E’ centers is accompanied by generation of oxide leakage currents.
(2) A brief 200oC anneal in air annihilates most of the E’ centers and most of the leakage current.
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Since (A) earlier work by two independent groups show that E’ centers are generated by high field stressing oxides,
And (B) recent theoretical and experimental studies indicate that E’ centers are good candidates for leakage current defects, we conclude that E’ centers are important, probablydominating defects in SILC (and RILC) in a widerange of oxides on silicon.
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Many studies report generation of interface states in conjunction with the creation of stress induced leakage currents.
Several studies also report a strong correlation between SILC and interface state generation.
Why is this so?
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Before Stressing
Si
H
After Stressing
Si Si Si Si Si Si Si
Si
H
Si
H
Si
H
Si
H
Si
H
Si
H
Si
H
Si
Si Si Si Si
Oxide
Oxide
Si/SiO2
Si/SiO2
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Consider Statistical MechanicsThe system will approach the lowest Gibbs Free Energy:
G = H-TS
Si
O
O
O
E’
Oxide
Si
O
O
O
E’HH
H
Si
SiSi
Si
Si
SiSi
Si
Si/SiO2
PbH Pb
h 0 (The oxide and interface Si-H bond enthalpies will be about equal)
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Entropy: S = k ln (Ω)Suppose all E’ dbs are unpassivated
OO
O
OO
O
OO
O
Contribution to configurational entropy of N E’ sites: S = k ln(1)
Suppose all Pb dbs are passivated
H
Si
H
Si
H
Si
H
Si
Contribution to configurational entropy of M PbH sites: S = k ln(1)
(Total of N sites)
(Total of M sites)
Si Si Si …
…
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Suppose we remove one H from the M PbH sites; the configurational entropy changes: ∆S = k ln (M)
H
Si
H
Si Si
H
Si
Suppose we add one H to the N E’ sites; the configurational entropy changes: ∆S = k ln (N)
OO
O
OO
O
OO
O
H
The Gibbs free energy of the system will be lowered by the transfer of some hydrogen from Pb sites to E’ sites.
(If kinetics allows it)
…
…Si Si Si
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The process will occur to some extent.
To how great an extent?
PbH + E’ + H2 Pb + E’H + H2
[Pb] [E’H]
[PbH] [E’]= exp ( - ∆G / kT) = K ~ 1
