Plasma-assistedALDofSiliconassisted ALD of...
Transcript of Plasma-assistedALDofSiliconassisted ALD of...
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Plasma assisted ALD of SiliconPlasma-assisted ALD of Silicon Nitride and Gallium Nitride
Harm KnoopsHarm KnoopsOxford Instruments Plasma Technology
Page 1© Oxford Instruments 2014 CONFIDENTIAL
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SiNx and GaN ALD applicationsThe Business of Science®
ALD spacers for transistors ALD for GaN HEMTs
Oxide
AlGaN
Gatesource drain
Poly-Si
SiNSiN SiO
xHKMG
GaN
buffer
substrate
Koehler et al., IOP Conf. S.: Mater. Sci. Eng. 41, 012006 (2012) • Achieving low defect density at
low deposition temperature.
substrate
• Oxygen and processing barrier• Spacing source and drain
p p• Potential ALD layers
• Al2O3
• HfAlO• HfAlOx
• AlN• SiNx ALD of nitrides
Conformal high-quality ALD of SiNx
Page 2© Oxford Instruments 2014 CONFIDENTIAL
• GaN
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This presentationThe Business of Science®
Challenges:• ALD f it id ft diffi lt• ALD of nitrides often difficult
(e.g., low reactivity for thermal processes).• Desire for robust process and high material quality.p g q y
This presentation:• Recent SiNx and GaN processes:
• SiNx using BTBAS and N2 plasmaKnoops et al presented at ALD 2013 conference San Diego
• GaN using TEGa and H2/N2 plasma
Knoops et al., presented at ALD 2013 conference San Diego and ALD 2014 conference in Kyoto
Sharp et al., poster at ALD 2013 conference San Diego
• Indentify important plasma parameters:• Pressure gas mixture gas residence time
p , p g
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Pressure, gas mixture, gas residence time.
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OutlineThe Business of Science®
• IntroductionIntroduction
• ALD of SiNx:
• Process characteristics
• Effect of residence time• Effect of residence time
• ALD of GaN:
• Process characteristics
• Eff t f H /N ti d l• Effect of H2/N2 ratio and plasma pressure.
• Conclusions
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Experimental detailsThe Business of Science®
FlexAL at NanoLab@TU/eALD cycle
N2 plasma10 s
SiH2(NHtBu)2
(BTBAS)
ALD cycle
10 s600 W
40 mTorr
(BTBAS)150 ms50 oC
N N + NN2, N2 , N, etc.
Turbo pump and load-lock for low moisture background.
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Saturation curvesThe Business of Science®
0 5 BTBAS dose time N2 plasma exposure
0.4
0.5
e (Å
)
0 6
0.8
e (Å
) 100°C
0.2
0.3
h pe
r cyc
le
0.4
0.6
200°C
th p
er c
ycl
0 0
0.1
Gro
wth
0 0
0.2500°CG
row
t
200 °C0 5 10 15
0.0
N2 plasma exposure time (s)0 100 200 300
0.0
BTBAS dose time (ms)
• ALD behavior (soft saturation)• Growth-per-cycle (GPC) decreases
with increasing temperatures
• GPC shows first fast increase and then a slow decrease to final value
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with increasing temperatures. final value
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Growth versus temperatureThe Business of Science®
Linear growth Growth versus temperature
40
200 °C
nm)
100 °C1.0
1.2
Å)
g p
20
30
500 °C
ickn
ess
(n
0.6
0.8
per c
ycle
(Å
10
Film
Th
0.2
0.4
Gro
wth
p
0 500 1000 1500 2000 25000
Number of Cycles100 200 300 400 500
0.0
Temperature (°C)
• Linear growth with no growth delay for all temperatures.• Growth-per-cycle (GPC) decreases with increasing temperatures.
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Effect of temperature and plasma exposureThe Business of Science®
Substrate temperature Plasma exposure time
20
25
at%
) C 20
25
(at%
)
200 °C10 s plasma
10
15
entra
tion
(a
H 10
15
cent
ratio
n
C
H
0
5
Con
ce
O
0
5 Con
c
O
100 200 300 400 5000
Temperature (°C)0 2 4 6 8 10 12 14 16
0
Plasma exposure time (s)
• Decrease of C and H with temperature and plasma exposure• Decrease of C and H with temperature and plasma exposure• Films are N-rich but become nearly stoichiometric at 500 °C• Decreasing plasma pressure to 10 mTorr less impurities: 6% C, 5% O
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Decreasing plasma pressure to 10 mTorr less impurities: 6% C, 5% O
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Oxford Instruments FlexAL systemThe Business of Science®
rapidRemote plasma• High radical density at
Plasma gas flow
pplasmastriking
low ion bombardment enabling high material quality Fast saturation
fast ALDvalves
even at low temperatures
APCFast pressure control and turbo pump• Efficient use of precursor
fully open in 150 ms
turbopump
pand fast saturation• Quick removal of reaction products even at
150 ms
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pump room temperature
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Effect of pressure and residence timeThe Business of Science®
Versus pressure Versus gas residence time
1.9
100 sccm N2 + 200 sccm Ar100 sccm N2
40 sccm N2
(@2e
V)
1.9
100 sccm N2 + 200 sccm Ar100 sccm N2
40 sccm N2
(@2e
V)
1.8
ctiv
e in
dex
1.8
tive
Inde
x
1.7
200 °C10 s plasma R
efra
c
1.7
Ref
rac
200 °C10 s plasma
0 20 40 60 80 100
Plasma pressure (mTorr)0 1 2 3 4
Residence Time (s)
M i l i ff d b h f fl d l• Material properties affected by change of flow and pressure control.• Data from films with different flow, follow residence time trend.
• Best material properties for short residence time.
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Best material properties for short residence time.
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Redeposition and saturation of plasma stepThe Business of Science®
0 5 200 °C High redeposition
High C content
0.4
0.5
= 1.7s
High redeposition
Plasma
A B
0 2
0.3
PC (Å
) = 0.58 s
= 0.35 s
0.1
0.2
GP 0.35 s
Plasma
Low redeposition
0 2 4 6 8 10 12 14 160.0
Plasma exposure time (s)
A B
Gas residence time: p ( )Gas residence time:• Long: high GPC due to C from redeposition at short plasma
exposures; long plasma exposure to “clean” surface
Page 11© Oxford Instruments 2014 CONFIDENTIAL
• Short: only small effect from redeposition
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OutlineThe Business of Science®
• IntroductionIntroduction
• ALD of SiNx:
• Process characteristics
• Effect of residence time• Effect of residence time
• ALD of GaN:
• Process characteristics
• Eff t f H /N ti d l• Effect of H2/N2 ratio and plasma pressure.
• Conclusions
Page 12© Oxford Instruments 2014 CONFIDENTIAL
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Experimental detailsThe Business of Science®
FlexAL system
GaN ALD cycle at 300 °C
H2/N2 plasma30:10 sccm5 s, 300 W
GaEt3 (TEGa)250 ms30 oC ,
5 mTorr30 C
H2, N2, H2+,
N2+, H, N,
NH3, etc.
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GaN – achieving saturationThe Business of Science®
• 20:20 H2/N2 plasma (G.R.). 0,6 G.R. G.R.*
• Slow soft saturation.
• 30:10 H2/N2 plasma and APC l d (G R *)
0,4
0,5
ate
(Å/c
ycle
)
closed (G.R.*).
• Faster/normal saturation.
Å0,2
0,3
Gro
wth
Ra
• Lower GPC of ~0.4 Å/cyc
• Comparison dosing methods:
0 500 1.000 1.500 2.000
Dose Time (ms)
• Restricting the flow leads to a shorter half-cycle than in full flow.
Dose
Fl R t i ti
• Increase in precursor consumption efficiency.
Flow Restriction
Purge
Page 14© Oxford Instruments 2014 CONFIDENTIAL
0 1 2 3 4 5Time (s)
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GaN – plasma gas mix and pressureThe Business of Science®
• Moving to H2-rich plasmas f
2,200,6) G R R Iincreases the refractive index• Also drops growth rate –
implication of increase in film2,00
2,10
0,4
0,5
tive
Inde
x
ate
(Å/c
ycle
) G.R. R.I.
implication of increase in film quality or precursor absorption effect. 1,80
1,90
0,2
0,3
0,0 0,5 1,0
Ref
ract
Gro
wth
Ra
• Decreasing the plasma pressure again shows the same t d
H2:N2 Ratio
2,200,6
e) G R R Itrend• Previous learning is that lower
pressure = higher ion energy =2,00
2,10
0,4
0,5
ctiv
e In
dex
Rat
e (Å
/cyc
le G.R. R.I.
pressure = higher ion energy = higher film quality
• Or redeposition effect.1,80
1,90
0,2
0,3
0 5 10 15 20
Ref
ra
Gro
wth
R
Plasma Pressure (mTorr)
Page 15© Oxford Instruments 2014 CONFIDENTIAL
O edepos t o e ect Plasma Pressure (mTorr) H2:N2 20:20
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GaN – improving the qualityThe Business of Science®
90
100 C N O Si 90
100 C N OSi 90
100 C N O Si
40
50
60
70
80
Con
cent
ratio
n(%
)
Ga
40
50
60
70
80 Ga
once
ntra
tion(
%)
40
50
60
70
80 Ga
Con
cent
ratio
n(%
)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00
10
20
30
Atom
ic C
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00
10
20
30
40
Atom
ic C
o
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00
10
20
30
Atom
ic C
• 15 mTorr for 5
Sputter time(min) Sputter time(min) Sputter time(min)
• 7 mTorr for 5 • 7 mTorr for 30 dseconds
• 15 at% C
seconds• 2 at% C
seconds• 2 at% C
• 10 at% O • 4 at% O • 2 at% O
Page 16© Oxford Instruments 2014 CONFIDENTIAL
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Effect of temperatureThe Business of Science®
2,200,6
2,10
2,20
0,5
0,6
Inde
x
Å/c
ycle
) G.R. R.I.
1,90
2,00
0,3
0,4
frac
tive
I
h R
ate
(Å
1,800,20 100 200 300 400
Ref
Gro
wth
Temperature (ºC) 10 l
• ALD window found between 150 and 350 ºC
Temperature ( C) 10 s plasma
ALD window found between 150 and 350 C• Increase in temperature yields an increase in R.I. up to
2 11 at 300 ºC
Page 17© Oxford Instruments 2014 CONFIDENTIAL
2.11 at 300 C.
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High quality materialThe Business of Science®
AES of 65nm ALD GaN layer
Best material obtained so far at:
90
100 C N O Sifar at:
• 350 °C temperature• 10 s plasma at 5 mTorr 60
70
80 Ga
tratio
n(%
)
p• H2/N2 plasma (30:10)• 400W power 30
40
50
Atom
ic C
once
nt
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.00
10
20A
Sputter time(min)Close to GaN stoichiometry
Page 18© Oxford Instruments 2014 CONFIDENTIAL
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ConclusionsThe Business of Science®
• ALD of SiNx using BTBAS and N2 plasma• Reduced carbon and hydrogen content with longer
plasma exposure or lower pressure.Wid t t i d Cl t Si N f hi h• Wide temperature window. Close to Si3N4 for high temperature deposition.
• Residence time an important “hidden” parameter, p p ,due to redeposition effect.
ALD f G N i TEG d H /N l• ALD of GaN using TEGa and H2/N2 plasma• Higher quality with higher H2:N2 ratio and low
lplasma pressure.• ALD window between 150 °C and 350 °C• Close to GaN composition.
Page 19© Oxford Instruments 2014 CONFIDENTIAL
Close to GaN composition.