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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]
2
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)
3
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)
4
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)
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)
6
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)
7
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)
8
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)
9
→
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)
10
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)
11
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)
12
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)
13
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)
14
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)
15
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)
16
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)
17
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)
18
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)
19
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)
20
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
1
21
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)
22
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)
23
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)
24
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)
25
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)
26
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)
27
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)
28
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)
29
Three peak structure?Three peak structure?
© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘ August 5. 2008 Hoboken, NJ (USA)
30
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)
31
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)
32
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)
33
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)
34
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)
35
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)
36
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)
37
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)