Influence of Tungsten/Carbon Interactions On Carbon Erosion Behavior In D 2 Plasma
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Influence of Tungsten/Carbon Interactions On Carbon Erosion Behavior In D2 Plasma
Nick Lyon, Florian Weilnboeck, and Gottlieb S. OehrleinDepartment of Material Science and Engineering and
Institute for Research in Electronics and Applied PhysicsUniversity of Maryland, College Park, Maryland, 20742
Russ P. Doerner Center for Energy Research, University of California – San Diego
July 2009
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Outline
Experimental apparatus and diagnostics Erosion of hard a-C:H in deuterium plasma Influence of W near-monolayer coverage on a-
C:H erosion Conclusions
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University of Maryland Cluster System for Plasma Processing of Materials
Multi-TechniqueSurface Analysis
Chamber(XPS, AES, ...)
Evaporator
Capacitively Coupled Plasma (CCP) Reactor
LoadLock I
ICP Reactor
LoadLock II
Inductively
Coupled PlasmaReactor Evaporator
Numerous Plasma and SurfaceDiagnostic Techniques Shared
Between All Systems
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Experimental Setup Inductive Power 600W to 800W (13.56 MHz)
Operating Pressure 10 mTorr Erosion
RF Bias -100 V, 3.7 MHz
CH4, D2, Ar
Total gas flow = 40 sccm
Planar Coil ICP
Network
RF power
RF bias power
Laser Detector
Confinement Ring
In situ ellipsometry real time monitoring of processesXPS: surface characterization
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ICP Device Measurements used as basis of computer simulations and model validation by several major
plasma modeling groups – Sandia National Labs, M. J. Kushner In turn has helped us refine the measurements
Xi Li, Li Ling, X. Hua and G. S. Oehrlein, Y. Wang, A. V. Vasenkov and M. J. Kushner, J. Vac. Sci. Technol. A 22, 500 (2004). V. Vasenkov, Xi Li, G. S. Oehrlein, and M. J. Kushner, J. Vac. Sci. Technol. A 22, 511 (2004).
Geometry and B-Field Measurements
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Process Sequences to be Discussed
D2 erosion of
• a-C:H films• a-C:H + in-situ deposited W (below and
above 1 monolayer)• a-C:H + in-situ deposited W above 1
monolayer and air-exposed for oxidation
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25 30 35 4020
30
40
50
60
70
80
De
lta [d
eg
.]
Psi [deg.]7
WOx on W2nm Steps
Deuteration/Roughening5 nm steps
W coverage 1 mL (0.3nm) steps
Ellipsometry Interpretation
a-C:H
deposition
erosion
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Erosion of a-C:H Film in D2 Plasma
D2 Plasma
32 33 34 35 3640
45
50
55
De
lta [D
eg
.]
Psi [Deg.]
Deposition Fit Erosion Data Model of soft Layers
11 12 13 14 15268
272
276
280
284
De
lta [d
eg
.]
Psi [deg.]
Deposition Data Erosion Data Model of soft layers
Deposition
Deposition
Erosion
Erosion
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Simulation of a-C:H:W Materials in ReactorExperimental
• W sputter onto a-C:H film• Ar 10 mTorr 30 sccm• 600 W Source Power• -100V bias
a-C:H
Ar
W
C, H
a-C:H-W
D2
W
C, H, W
• D2 erosion of a-C:H/W films• D2 10 mTorr 30 sccm• 600 W Source Power• -100 V bias
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Erosion of W/a-C:H Film in D2 Plasma
0 20 40 600
50
100
150
200 a-CH Deposition Deuterium Erosion
D
elta
[Deg
.]
Psi [Deg.]
Erosion start
Erosion stop
120s
240s
0 10 20 30 40 50
30s W 40mTorr
Inte
nsity
[arb
. uni
ts]
Binding Energy [eV]
valence band
0 10 20 30 40 50
30sW 40mTorr240s D2
Inte
nsity
[arb
. uni
ts]
Binding Energy [eV]
valence band
0 10 20 30 40 50
30s W 40mTorr120s D2
Inte
nsity
[arb
. uni
ts]
Binding Energy [eV]
valence band
0 10 20 30 40 50
30sW 40mTorretch stop
Inte
nsi
ty [a
rb. u
nits
]Binding Energy [eV]
valence band
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Impact of W Monolayer Coverage On a-C:H Erosion
0.0 0.5 1.0 1.50
5
10
15
20
25
30
35
40
45
Ero
sio
n R
ate
[nm
/min
]
Monolayer W Coverage0.0 0.5 1.0 1.50
30
60
90
Monolayer W Coverage
Tim
e T
o r
em
ove
10
nm
a-C
H [s
]
0 50 100 1500
10
20
30
40
0 mL W 0.48 mL W 1.16 mL W
a-C
H R
emov
ed [n
m]
Exposure Time [s]
0 50 100 1500
25
50
75 0 mL W 0.48 mL W 1.16 mL W
a-C
H T
hic
knes
s [n
m]
Exposure Time [s]
~8x lower
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28 30 32 34 36 38 40
W 4f30s 40mTorretch stop D2 erosion
Inte
nsi
ty [a
rb. u
nits
]
Binding Energy [eV]28 30 32 34 36 38 40
W 4f30s 40mTorr4min D2 erosion
Inte
nsi
ty [a
rb. u
nits
]
Binding Energy [eV]28 30 32 34 36 38 40
W 4f30s 40mTorr2 min D2 erosion
Inte
nsi
ty [a
rb. u
nits
]
Binding Energy [eV]28 30 32 34 36 38 40
W 4f30s 40mTorr
Inte
nsi
ty [a
rb. u
nits
]
Binding Energy [eV]
280 282 284 286 288 290
C 1s30s 40mTorr
Inte
nsi
ty [a
rb. u
nits
]
Binding Energy [eV]280 282 284 286 288 290
C 1s30s 40mTorr 2min D2 erosion
Inte
nsi
ty [a
rb. u
nits
]
Binding Energy [eV]280 282 284 286 288 290
C 1s30s 40mTorr 4min D2 erosion
Inte
nsi
ty [a
rb. u
nits
]
Binding Energy [eV]280 282 284 286 288 290
C 1s30s 40mTorr groundedetch stop
Inte
nsi
ty [a
rb. u
nits
]
Binding Energy [eV]
XPS Time Sequence:After W Deposition, 2min D2, 4min D2, Erosion Stop
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W depositionRMS=2.4 nm
2min D2RMS=3.4 nm
Etch stop D2RMS=9.24 nm
4min D2RMS=17.38 nm
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24 28 32 3620
40
60
80
100 Deposition Data Erosion Data aCH + W aCH + Rough Layer + W aCH + Deuteration
D
elta
[de
g.]
Psi [deg.]
PlasmaStart
Roughness Formation Dominates Surface Modification
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Real-Time Roughness Measurements
0.0 0.5 1.0 1.50
15
30
45
60
75
Max
imum
Ro
ugh
ness
[nm
]
Monolayer W Coverage0 100 200 300
0
20
40
60
80 20 mTorr Ar W Sputter 40 mTorr Ar W Sputter 40 mTorr W Grounded Sputter 50 mTorr Ar W Sputter 50 mTorr W Grounded Sputter
Rou
gh L
ayer
Thi
ckne
ss [n
m]
Plasma Time [s]
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27 30 33 36
25
50
75
100a-CH depositionDeuterium erosionW on a-CHMaximum Roughness
De
lta [d
eg
.]
Psi [deg.]
1.2nm WWOx W
Roughness 40 nm
0 10 20 30 40 50
30s 40mTorrgrounded
Inte
nsi
ty [a
rb. u
nits
]
Binding Energy [eV]
valence band
0 10 20 30 40 50
30s 40mTorrgrounded120s D2 erosion
Inte
nsi
ty [a
rb. u
nits
]
Binding Energy [eV]
valence band
Fate of Oxidized W During a-C:H Erosion
0 s
120 s D2
120 s D2
0 s
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28 30 32 34 36 38 400
1000
2000
3000
4000
5000
6000
7000
8000
9000W 4f30s 40mTorr grounded
2min D2 erosion
Inte
nsi
ty [C
PS
]
Binding Energy [eV]
28 30 32 34 36 38 400
1000
2000
3000
4000
5000
6000
7000
8000
9000W 4f30s 40mTorr grounded
Inte
nsi
ty [C
PS
]
Binding Energy [eV]
Oxygen removal after grounded deposition during D2 erosion
280 282 284 286 288 290
0
1000
2000
3000
4000
5000C 1s30s 40mTorr grounded
Inte
nsi
ty [C
PS
]
Binding Energy [eV]
280 282 284 286 288 290
0
1000
2000
3000
4000
5000C 1s30s 40mTorr grounded
2min D2 erosion
Inte
nsi
ty [C
PS
]
Binding Energy [eV]
526 528 530 532 534 536 538
0
2000
4000
6000
8000
10000
12000O 1s30s 40mTorr grounded
Inte
nsi
ty [C
PS
]
Binding Energy [eV]
526 528 530 532 534 536 538
0
2000
4000
6000
8000
10000
12000O 1s30s 40mTorr grounded
2min D2 erosion
Inte
nsi
ty [C
PS
]
Binding Energy [eV]
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Optical Emission Spectroscopy
Although W emission is not detected for D2 plasma, exposure of test coupons show that W transport during D2 plasma exposure of W takes place for conditions employed
0 10 20 30 40 50
Inte
nsi
ty [a
rb. u
nits
]
Binding Energy [eV]
valence band 10min D2 erosionSi sample grounded
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Conclusions
W monolayer coverage of a-C:H has profound influence on erosion behavior, including
• Initial retardation of erosion
• Lower steady-state erosion rate
• Slow removal of W
• Microscopic blocking of sites and surface roughening The complex surface processes taking place can be efficiently
studied by a combination of
• Real-time
• Post-plasma
surface diagnostics
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Acknowledgements
We gratefully acknowledge financial support of this work by the Department of Energy