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Characterisation, Optimization and Tuning of Plasma
Parameters in ICP discharge
Vasile Vartolomei
K. MatyashR. SchneiderC. Wilke
M. HannemannR. Hippler H. KerstenA. Knuth
Institute of PhysicsFelix Hausdorff Str. 6D-17489
[email protected]
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OutlookOutlook
Capacitive effect in ICP: how to reduce it?
Interpretation of Ion Distribution Function
Tuning-optimising the IDF
Energy balance to substrate
Conclusions
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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MotivationMotivation
What we want ...
ne Te eVi n*EE
DF
Electron energy
EEDF Species
N.Braithwaite (DPG-Spring Meeting Aachen 2003)
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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MotivationMotivation
What we have ...
RF Power 2FlowPressureRF Power 1
Timer
O2 N2 CH4 CF4
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Experimental deviceExperimental device
Region I
Region II
Sputtered Target and gas inlet
RFEA andLangmuir probe
Grid(with/without)
RFEA andLangmuir probe
Region II
Region I
Sputter target
Grid(without/with)
Gas: Argon
Power range: 100 - 600 W
RF frequency: 13.56 MHz
Magnetic field: 0 - 2.2 mT
Pressure range: 6×10-4 – 1×10-2 mbar
5
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Capacitive effect in ICPCapacitive effect in ICP
Capacitive effects produces undesiredsputtering effects at the
coil
Reduce RF amplitude:Balance the coil and get a factor 2
reduction!
G. K. Vinogradov, Transmission line balanced inductive plasma
sources, Plasma Sources Sci. Technol. 9 (2000) 400-412
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Reduce capacitive effect: step down transformerReduce capacitive
effect: step down transformer
3 Capacitive effects produce undesiredsputtering effects at the
coil
Balanced coil
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Reduce RF amplitude: add magnetic fieldReduce RF amplitude: add
magnetic field
RF
ampl
itude
at c
oil e
nds
Normalised Magnetic Field
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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→
B
The ECWR effectThe ECWR effect
Bz = B(t), By = B = constant
B
B(t)B
λplasma=λvac/nR
stationary wave
H.Oechsner et al., Thin Solid Films 341 (1999), 101-104)
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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The ECWR effect: Plasma DensityThe ECWR effect: Plasma
Density
0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.80.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
0.6 x 10-3 mbar 2.0 x 10-3 mbar
Magnetic Field [mT]
Nor
mal
ised
Pla
sma
Den
sity
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Reduced capacitive effectReduced capacitive effect
Magnetic Field [mT]
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
100 W 300 W 500 W
RF
bias
(V)
coil current (A)
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Experimental measurement of IDFExperimental measurement of
IDF
Collector characteristic
-50 0 50
-0.6-0.4-0.20.00.20.40.60.81.01.21.41.61.82.02.22.42.62.83.0
I c(a.
u.)
Uc(V)
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Experimental measurement of IDFExperimental measurement of
IDF
Retarding Field Energy Analyser (RFEA)
dIc/dUc α IDF
A
I
-100 -75 -50 -25 0 25 500,00
0,04
0,08
0,12
0,16 Selector = - 75 V Selector = -100 V
IDF
[a.u
.]
Ion Energy [eV]-180 -150 -120 -90 -60 -30 0 30 60
0,0
0,3
0,6
0,9
Selector = - 75 V Selector = - 100 V
Col
lect
or C
urre
nt [1
0-6 A
]
Collector Voltage [V]
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Experimental measurement of IDFExperimental measurement of
IDF
IDF α dIc/dUc
∫+∞
=0
)( ndvvf
dEEgdndvvf )()( ==
∫ ∫== dEvfMedvvvfeI
ii )()(
⎟⎟⎠
⎞⎜⎜⎝
⎛−=⎟
⎠⎞
⎜⎝⎛−=
c
cii
dUUdI
eM
dEEdI
eMvf )()()( 2
Where is the Plasma Potential ?Four points of view…
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
dIc/d
Uc(
a.u.
)
U c(V)
A: Lipschultz, I. Hutchingson, B. LaBombard, A. Wan, Electrical
probes in plasmas, J.Vac.Sci.Technol. A 4(3), p.1810-1816
(1986)
B: S. G. Ingram, N. St. J. Braithwaite, Ion and electron energy
analyser at a surface in an RF discharge,
J.Phys.D.: Appl.Phys. 21, 1496-1503, (1988)
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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IDF model 1 (point A)IDF model 1 (point A)
a) in plasma
b) at the pre-sheath entrance
c) at the wall
Ion Velocity Distribution Functionone-dimensional (gaussion)
Allows to calculate ion temperature!
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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IDF model 4: K.U. RiemannIDF model 4: K.U. Riemann
c
zxλ
=e
zi
KTvmy
2
2
=
eKTeU
−=ϕIon Temperature and Plasma potential information are lost
∫∞
−+ =
0
2/1 ),( dyyxfyn
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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PIC-MCC simulationPIC-MCC simulation
0 10 20 30 40 50 60 70 80 90 100 110 120 1300
5
10
15
20
25
30
35
40
45
50
55
60
65
Vp(V)
Z, λd0 10 20 30 40 50 60 70 80 90 100 110 120 130
0.0
0.5
1.0
1.5
2.0
2.5
electrons ions
ne,ni 109 cm-3
Z, λd
Known input data: Plasma potential, Ion temperature and Electron
temperature
Run the code and see how they come to the wall
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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PIC-MCC simulationPIC-MCC simulation
IDF maxima is the plasma potentialsince we have 10% oscillations
in Vp.
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.20.0
0.2
0.4
0.6
0.8
1.0IED
Ei,kin/eVp
Zwall-cell Zwall-2xλDebye-cell Zwall-3xλDebye-cell
Zwall-4xλDebye-cell
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Influence the transport between the two Regions: add a
gridInfluence the transport between the two Regions: add a
gridID
F [a
.u.]
10 15 20 25 30 35 40 450
50
100
150
200
250
Ion Energy [eV]
Region I
Region II
Grid
Origin of double peak structure ?
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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First Concept: Collisionless rf modulated sheathFirst Concept:
Collisionless rf modulated sheath
C. Charles at al, Physics of Plasmas 7 (12), 2000K.Köhler at al,
J. Appl.Phys. 58 (9), 1985
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Experimental Contradiction of First ConceptExperimental
Contradiction of First Concept
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
RFEA 0 degree to axis, d ist=49 m m RFEA 90 degree to axis, d
ist=54 m m
400W, 0.6×10-3 mbar
IDF
[a.u
.]
Ion Energy [eV]
Region I
Region II
1.
2.
1.
2.
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Second Concept: Space potential differenceSecond Concept: Space
potential difference
Axial dependence
Ion
Ene
rgy
(eV
)
Region I Region II
Vplasma (V)
Z (cm)10 15 20 25 30 35 40 45
0
50
100
150
200
250
IDF
[a.u
.]
Ion Energy [eV]
Double peak structure in IDF Explains the contradiction
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Tuning the Ion Distribution FunctionTuning the Ion Distribution
Function
• Can one move the Low Energy Peak ?
• Can one move the High Energy Peak ?
• Can one move them independently ?
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Apply voltage on gridApply voltage on grid
Build a variable gate
Region II
Sheath
Grid wire
electrons
Region I
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Biased GridBiased Grid
Grid bias [V]
Influence on plasma potential in Region II
-40 -30 -20 -10 0 10 20
8101214161820222426283032343638 400W, resonance
Pressure (10-3mbar): 0.6 2.0 6.0 10.0
Plas
ma
Pote
ntia
l [V] × 10
-3mbar
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Biased GridBiased Grid
Influence on plasma density in Region II
-40 -30 -20 -10 0 10 200,00E+000
1,00E+009
2,00E+009
3,00E+009
4,00E+009
5,00E+009
6,00E+009
7,00E+009
8,00E+009
9,00E+009
1,00E+010
400W, resonancePressure (10-3mbar):
0.6 2.0
Grid bias [V]
Elec
tron
Den
sity
[cm
-3]
× 10-3 mbar
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Biased GridBiased Grid
0 5 10 15 20 25 30 35 40 45 50 550.00
0.01
0.02
0.03
0.04 Ugrid:
0 V -20 V -100 V
IDF
[a.u
.]
Ion Energy [eV]
HEP
LEP Bias Grid:
Influence on Low Energy Peak (LEP) in Region II
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Apply DC Bias on Inductive CoilApply DC Bias on Inductive
Coil
-5 0 5 10 15 20 25 30 35 40 45 50 55 60 65
0,00
0,02
0,04
0,06
Ugrid=0V, Grounded coil ! Ugrid=0V, Floating coil Ugrid=-100V,
Floating coilID
F [a
.u.]
Grid bias [V]Shift and form change of IDF in Region II
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Three peak structure?Three peak structure?
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Energy Flux to SubstrateEnergy Flux to Substrate
shield
copperplate
(substrate)
thermalcouple
substratebiasing
andsaturation
current
insulation(marcor)
rod(movable)
⋅ += outSin QHQPlasma ON (heating)
outS QH +=•
0Plasma OFF (cooling)
dtdTmcH SS =
•
Tcool
S
heat
SSSin dt
dTdt
dTmccoolHheatHQ⎩⎨⎧
⎭⎬⎫
⎟⎠⎞
⎜⎝⎛−⎟
⎠⎞
⎜⎝⎛=−=
••
)()(
( )dAJJJJJJdAJQSuSu A
photoncondneurecieA
inin .∫∫ +++++==
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Energy Flux to SubstrateEnergy Flux to Substrate
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.00.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
0.11
0.12
100 W
200 W
300 W
400 W
500 W
600 W
Mea
sure
d En
ergy
Flu
x [J
s-1 c
m-2
]
pressure [×10-3mbar ]
Higher energy contribution at low pressure
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Energy Flux to SubstrateEnergy Flux to Substrate
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.00.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
0.11
0.12
100 W
200 W
300 W
400 W
500 W
600 W
Mea
sure
d En
ergy
Flu
x [J
s-1 c
m-2
]
pressure [×10-3mbar ]
Higher energy contribution at low pressure
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Energy Flux to Substrate: ModellingEnergy Flux to Substrate:
Modelling
400 W
0 1 2 3 4 5 6 7 8 9 10 110.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08 Measurement Ji+Je+Jrec (model) Ion energy flux Ji Electron
energy flux Je Recombination energy Jrec
Mea
sure
d En
ergy
Flu
x [J
s-1 c
m-2
]
pressure [×10-3mbar ]
Missing contributions
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Energy Flux to Substrate: Bias influence on thermal probeEnergy
Flux to Substrate: Bias influence on thermal probe
-80 -70 -60 -50 -40 -30 -20 -10 0 10 200.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0.045
0.050
0.055
0.060
0.065
measurement modelling
300 W, 4×10-3 mbar
Voltage on Thermal probe [V]
Ener
gy F
lux
[Js-
1 cm
-2]
Possible reasons:
- Plasma Radiation
- Excited atoms
- Fast neutrals
important heating chanell
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Fast neutralsFast neutrals
Generation of fast neutrals by one ion by several
charge-exchange collisions:
cascade
Substrate
n
2
1
z
Z = 0
E
1Z
2Z
nZ
trajectories: ion - continuous linefast neutrals - interrupted
lines
Large difference between cross sections of collision
processes:
- ion-neutral collision (CX)
- fast neutral – neutral elastic collision
Many fast neutrals for one ion !
Including this effect gives good results
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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Energy Flux to Substrate: ModellingEnergy Flux to Substrate:
Modelling
0 1 2 3 4 5 6 7 8 9 10 110.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08 Measurement Ji+Je+Jrec (model) Ion energy flux Ji Neutral
energy flux Jn
400 W
Mea
sure
d En
ergy
Flu
x [J
s-1 c
m-2
]
pressure [×10-3mbar ]Better agreement
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)
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ConclusionsConclusions
Capacitive effects in ICP
How to understand the IDF…
Tuning-optimising the IDF:
Grid effect and how to move LEP and HEP
Energy balance to substrate: fast neutrals
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘
August 5. 2008 Hoboken, NJ (USA)