Interface reaction analysis of La O /SiC upon annealing by ... presen.pdf · • Effective...
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Interface reaction analysis of La 2 O 3 / SiC upon annealing by ATR - FTIR Tokyo Tech. FRC 1 , Tokyo Tech. IGSSE 2 , Mitsubishi Electric Corp. 3 , ○ Y. M. Lei 1 , S. Munekiyo 1 , K. Kakushima 2 ,T. Kawanago 2 , Y. Kataoka 2 , A. Nishiyama 2 , N. Sugii 2 , H. Wakabayashi 2 , K. Tsutsui 2 , K. Natori 1 , H. Iwai 1 , M.Furuhashi 3 , N.Miura 3 and S. Yamakawa 3 Tokyo Insititute of Technology
Transcript of Interface reaction analysis of La O /SiC upon annealing by ... presen.pdf · • Effective...
Interface reaction analysis of La2O3/SiC
upon annealing by ATR-FTIR
Tokyo Tech. FRC 1, Tokyo Tech. IGSSE 2, Mitsubishi Electric Corp.3, ○Y. M. Lei 1, S. Munekiyo 1, K. Kakushima 2,T. Kawanago 2, Y. Kataoka 2, A. Nishiyama 2, N.
Sugii 2, H. Wakabayashi 2, K. Tsutsui 2, K. Natori 1, H. Iwai 1, M.Furuhashi 3, N.Miura 3 and S. Yamakawa 3
Tokyo Insititute of Technology
An issue for SiC MOSFETs
Most report
http://jstshingi.jp/abst/p/10/1
018/naist1.pdf
Improvement of
channel mobility
is necessary
Mobility limits the on-resistanceRelationship of mobility and Dit
http://www.iisb.fraunhofer.de/de/mobisic.html
Inverse proportional relationship of
mobility with interface state density
Reduction of Dit is critical to make low loss SiC power devices
Approaches for interface improvement
NO,N2O gas annealing
• Effective passivation of interface trap by annealing the gate
oxide in NO,N2O gas.
SiO2/LaSiOx gate oxides on SiC
• Recently a passivation of interface trap on SiC has been found
by forming LaSiOx interface layer on SiC substrate.
Drain
LaSiOx
SiO2
TaN/W
sicSource
Interface improvement can
be achieved by reaction of
La2O3 and SiC！
[1] X. Yang, et al., ICSCRM Th-2B-5 (2013).
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Purpose and outline of this presentation
Investigate the interface reaction of La2O3 with 4H-nSiC to find the best process for gate dielectric application
1.Introduction2.Interface reaction model for La2O3 on Si substrates3.Interface reaction of La2O3 on 4H-nSiC substrates4.SiN barrier layer for La-silicate dielectrics5.Conclusions
1.Introduction2.Interface reaction model for La2O3 on Si substrates3.Interface reaction of La2O3 on 4H-nSiC substrates4.SiN barrier layer for La-silicate dielectrics5.Conclusions
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Binding energy (eV)
Inte
nsit
y (
a.u
)
300 oC
annealing
Si sub.
La-silicateas depo.
500 oC
annealing
Si substrate
La2O3
La-silicate
W
500 oC, 30 min
1 nm
k=8~14
k=23
La2O3+Si+nO2 → La2SiO5, La10(SiO4)6O3
La9.33Si6O26, La2Si2O7, etc.
XPS (Si 1s)TEM
Supply of oxygen atoms triggers silicate reactionThicker silicate layer with higher temperature
(XRD database)
(アモルファス)
High T
Interface reaction of La2O3 on Si
kT
Ert a
silicate
2exp)(0
0 200 600 800 1000
Annealing temprature (oC)
0.0400
0.4
1.2
1.6
2.0
0.8
0.0
2.0
1.0
3.0
EO
T (
nm
)
tsilic
ate
(nm
)
La2O3
La-silicate
Si
La-silicate
La-silicate
SiLa2O3500oC
300oC
T
zCzC
exp)( 0
C(z)(a.u.)
Distance from Si interface (a.u.)
500oC 300oC350oC400oC450oC
(773K)
(573K)
La2O3
La-silicate
Si
La-silicate
La-silicate
SiLa2O3500oC
300oC
T
zCzC
exp)( 0
C(z)(a.u.)
Distance from Si interface (a.u.)
500oC 300oC350oC400oC450oC
(773K)
(573K)
0(r) : oxygen ionic conduction in La-silicate (r: La conc.)Ea : activation energy for r)
Ea=0.3 eV
Thickness of silicate can be modeled by simple equation
(tsilicate: silicate層の膜厚)
Composition of silicate is assumed to be constant
Interface reaction model
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200 300 400 500 600 700 800 900 1000
アニール温度(oC)
30min 2s
0
0.2
0.4
0.6
0.8
1
1.2
1.4
EO
T(n
m)
W/La2O3(3.5nm)/n-Si
Annealing temperature (oC)
Equ
ival
ent
oxi
de
th
ickn
ess
(n
m)
La2O3+Si+nO2
→ La2SiO5, La10(SiO4)6O3
La9.33Si6O26, La2Si2O7
-controlling the oxygen atoms supply
-controlling the annealing time
(it may reach to thermal equilibrium)
1. SiO2, La2O3: solid solution
(glass structure)
2. k-value depends on Si conc.
silicate growth(from XRD database)
Silicate reaction can be controlled by
Amount of interface reaction
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10 15 25 30
-2 (deg)20
Inte
nsity (
a.u
.)
Si sub.h=15keV, GIXD
900oC
500oC
544 540 532 528
Binding energy (eV)536
La-O-LaLa-O-SiSi-O-Si
700oC
as-depo.
300oC
500oC
5.54eV
5.58eV
5.52eV
6.17eV
hex-La2O3
Eg (eV) structure
La2O3 5.5~5.6 hexagonal
La-silicate 6.2 amorphous
La-silicate is amorphous
C(20nm)/La2O3(4nm)/n-Si
(at least with semeconductor processes)
Properties of La-silicate
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Structrue of La-silicate (amorphous)
La atoms act as network modifier to relax the SiO4 network
Si
O O
O
O
Si
O O
O
OO
OO
O
SiBO
BO
Si Si
Si
BO: bridging oxygen atom
NBO:non-bridging oxygen atom
Si
O O
O
O
Si
O O
O
OO
O
O
O
La NBO
BO
Si Si
La
BO
BO
NBO
BO
La atomBO
NBOSiO4-tetrahedron
SiO4-tetrahedoron network with La atoms
Si-O-Si bonding
La-O-Si bonding
Atomic configuration of La-silicate
1.Introduction2.Interface reaction model for La2O3 on Si substrates3.Interface reaction of La2O3 on 4H-nSiC substrates4.SiN barrier layer for La-silicate dielectrics5.Conclusions
n-SiC(0001)substrate
La2O3 Deposition（EB）
FTIR measurement
Oxidation（5%O2/95%N2）
TEM analysis
Substrate cleaning(SPM, HF)
Sample preparation La2O3/SiC
FTIR measurement n-SiC substrate
La2O3 (2nm)
n-SiC substrate
Sample 1
(control)
Sample 2
500oC
1000oC
SiC(without La2O3))
5%O2 anneal:500oC—1000oC
12501300 1200 11001150 1050 1000
wavenumbers(cm-1)
Ab
sorb
an
ce (
a.u
.)
(a)
1000oC
600oC
La2O32nm/SiC)
Ab
sorb
an
ce (
a.u
.)12501300 1200 11001150 1050 1000
wavenumbers(cm-1)
(b)5%O2 anneal:500oC—1000oC
1000oC
950oC
900oC
Oxidation on SiC substrate was enhanced by La2O3 film
Accompanied by La-silicate formation
Si-O-SiLa-O-Si
Si-O-Si
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FITR spectra of oxidized SiC surface
(SiO2)
(SiO2)
(La-silicate)
SiO2
SiC
La-silicate
SiC
SiO2
Might be due to radical oxygen generation by La atoms
sample：La2O3 (2nm)/SiC
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SiC(0001) SiC(0001)50nm 10nm
La-silicateSiO2
TEM image of La2O3/SiC oxidized at 1000oC
• Agglomeration of La-silicates above SiO2/SiC interface• La-silicate grains positioned at bunches of SiC substrate (4o)• Thick SiO2 of 11nm is formed (enhanced oxidation rate)
Enhanced growth rate over thermal oxidation
SiC(0001) 10nm
11.8nm
sample：La2O3 (2nm)/SiC
after oxidation in 1000℃ 5%O2 30min
K. Kita, et al., ECS Trans, vol. 61(2), p. 135-142 (2014).
Higher oxidation rate of 1.5 order of magnitude can been
achieved by La2O3 capped oxidation
However, rough interface/surface may degrade reliability
This study
100
10-1
10-2
10-3
1300oC 1200oC 1100oC 1000oC
Gro
wth
rat
e co
nst
ate(
nm
/min
)
Temperature(oC)
SiO2 Growth rate of thermal oxidation
Oxidation rate comparison
1.Introduction2.Interface reaction model for La2O3 on Si substrates3.Interface reaction of La2O3 on 4H-nSiC substrates4.SiN barrier layer for La-silicate dielectrics5.Conclusions
n-SiC substrate
La-silicate
n-SiC substrate
SiO2
SiO2
n-SiC substrate
La2O3
SiN
La2O3 /SiC reaction
La2O3 /SiN reaction
n-SiC substrate
La2O3
SiN barrier layer against agglomeration
La-silicate formation by reaction of La2O3 and SiN layer(SiN: oxygen barrier to suppress oxidation of SiC)
n-SiC(0001)substrate
EB-La2O3 deposition
FTIR measurement
FTIR measurement
SPM,HF cleaning
PECVD-SiN deposition
XPS, TEM analysis
PECVD-SiO2 deposition
annealing
（5%O2/95%N2）
FTIR
TEM
La2O3（4nm）
SiN(2nm, 1.5nm, 0nm)
n-SiC
substrate
La2O3（4nm）
SiN(2nm)
TEOS
n-SiC
substrate7
Sample preparation with SiN barrier
annealing
（5%O2/95%N2）
La2O3 4nm/SiC)
Ab
sorb
an
ce (
a.u
.)
12501300 1200 11001150 1050 1000
wavenumbers(cm-1)
(C)O2 anneal:500oC—1000oC
1000゜C
950゜C
900゜C
La2O3 4nm/SiN2nm/SiC)
Ab
sorb
an
ce (
a.u
.)
12501300 1200 11001150 1050 1000
wavenumbers(cm-1)
(A)O2 anneal:500oC—1000oC
1000゜C
950゜C
900゜C
La2O3 4nm/SiN1.5nm/SiC)
Ab
sorb
an
ce (
a.u
.)
12501300 1200 11001150 1050 1000
wavenumbers(cm-1)
(B)O2 anneal:500oC—1000oC
1000゜C
950゜C
900゜C
Formation of La-silicate confirmed above 900oC
Slight suppression of SiO2 with thicker SiN
La-O-Si-O
Si-O-Si
SiN 2nmSiN 1.5nmWithout SiN
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Si-O-Si
La-O-Si-OLa-O-Si-O
FTIR spectra of La2O3/SiN/SiC
10 20 30
10
20
30
40
50
80
60
70
Sputter time (min)
Ato
mic
co
nce
ntr
atio
n (
%)
0 10 20 30
10
20
30
40
50
80
60
70
Sputter time (min)
Ato
mic
co
nce
ntr
atio
n (
%)
0
O
O
SiSi
Si
C
La
NC
O
O
SiSi
Si
C
La
NC
SiO2(40nm)/La2O3 (4nm)/SiN (2nm)/SiC sub.
Annealing temperature：500oC
LaSiON layer broadens with higher temperature
Concentration of nitrogen decrease with annealing9
XPS depth profile on annealing temperature
Annealing temperature：800oC
• Suppression of agglomeration by SiN barrier layer
• Some protrusion of La-silicates presented at the interface
SiC(0001) SiC(0001)
Sample： SiO2/La2O3 4nm/SiN 2nm/SiC
50nm 10nm
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Annealing temperature：1000oC
SiO2La-silicate
La2O3/SiN/SiC interface section TEM image
protrusion
0 5 10 15 20 25 30 35
Intensity[a.u.]
Distance[nm]
N-K
O-K
La-M
EELS analysis location(ADF-STEM image)
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EELS spectra of the protrusion
N La
O
• No nitrogen at the protrusion• Failure of barrier to oxidize SiC substrate
Annealing time, temperature to preserve N atoms at the interface
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Conclusion
• Oxidation with La2O3 capped SiC substrate• Enhanced oxidation rate with radical oxygen atoms
generated by La atoms• Grain growth, agglomeration of La-silicates• Surface roughness due to step enhanced oxidation
• SiN barrier layer for La2O3/SiC substrates• Formation of LaSiON interface layer• Some protrusion from substrates presumably due to
lack of nitrogen atoms at the interface
Issue of thermal oxidation of SiC
Oxidation rate
dispairity
Radical oxygen generation from
La2O3 to enhance oxidation on Si
Enhanced oxidation on SiC is achievable by La2O3 capped annealing
