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2009 CST Korean user meeting1
Development of VHF Inductively Coupled Plasma (ICP) Source using a CST Microwave Studio
KAIST, Low-temperature plasma lab. Samsung electronics, Etch process team
Hyun-su Jun
Electronic mail: [email protected]
Development of VHF Inductively Coupled Plasma (ICP) Source using a CST Microwave Studio
KAIST, Low-temperature plasma lab. Samsung electronics, Etch process team
Hyun-su Jun
Electronic mail: [email protected]
2009 CST Korean user meeting2
CONTENTSCONTENTS
1. Introduction
1.1. Inductively coupled plasma 1.2. Necessity for low-electron-temperature plasma1.3. Problems in VHF-ICP operation1.4. Antenna voltage and plasma uniformity
2. VHF-ICP source development
2.1. Antenna theory of VHF-ICP source2.2. Capacitor Distributed Resonance Antenna (C.D.R.A.)2.3. Plasma model setup in CST-MWS2.4. Impedance matching in CST-MWS2.5. Analysis of field simulation results
3. Experimental results
3.1. Structure of Capacitor Distributed Resonance Antenna3.2. Plasma parameter measurements
4. Summary
2009 CST Korean user meeting3
1. Introduction1. Introduction
Inductively coupled plasma (ICP)Inductively coupled plasma (ICP)
Gas inlet
Gate Valve
Ground Turbo Pump
RotaryPump
Single Langmuir Probe
Plasma, ne~1011/cm3
I.M.B.
13.56 MHz RF
Antenna GND
Plasma medium
Powered end
Groundedend
tHE∂∂
−=×∇ 0µ
Faraday’s law
θE
LVrf ω~
Sheath layercmnTlengthDebyes eem )/740(5)(5~ =
Dielectric window
Antenna
)(
2
c
pr iνωω
ωεε
−−= ∞
Applications: spacer etch, trench etch, contact etch… Debye length
2009 CST Korean user meeting4
1. Introduction1. Introduction
Necessity for lowNecessity for low--electronelectron--temperature plasmatemperature plasma
High electron temperature
Low etch selectivityProfile angle problem
Radical density ratio [CFx/F] as a function of electron temperature
H. Kokura, 2000 Jpn. J. Appl. Phys.
311103 −×= cmne
MaxwellianeVTb 75.2=
MaxwellianbieVTtempTail t
−= 5.3.
MaxwellianbieVTtempTail t
−= 0.5.
Trench etch (0.2 mm wide by 4 mm deep)in single-crystal silicon
Ion trajectory bending
Electron
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1. Introduction1. Introduction
Necessity of lowNecessity of low--electronelectron--temperature plasmatemperature plasma
Measured EEPFsD. S. Lee, H. S. Jun Thin Solid Films, 2006
Measured EEPFsH. S. Jun Applied Physics Letters, 2007
→ The Electron temperature (Teff) decreased with an increase in the driving frequency.
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1. Introduction1. Introduction
Problems in VHFProblems in VHF--ICP operationICP operation
E-field distribution at 13.56MHz
Antenna current -vector at 13.56 MHz
E-field distribution at 60 MHz
Antenna current -vector at 60 MHz
→ Because of the node-effect in the VHF-ICP source, an inductive discharge(H-mode) is practically impossible over the frequency of 60 MHz.
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1. Introduction1. Introduction
Antenna voltage and plasma uniformityAntenna voltage and plasma uniformity
Antenna’s powered end
Sputtering map on dielectric window Azimuthal electric field distribution
Antenna’s powered end
→ Antenna voltage distribution is the key factor in uniform plasma generation.
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2. VHF-ICP source development2. VHF-ICP source development
Antenna theory of VHFAntenna theory of VHF--ICP sourceICP source
TL LIV ω=
2T
RLIV ω=
4T
RLIV ω=
TL
TC2 TC2
TC4 TC4 TC4 TC4
2/TL 2/TL
4/TL 4/TL 4/TL 4/TL
V
LI
RI
RI
GND
GND
GND
0
0=N
2=N
4=N
22 1
⎟⎟⎠
⎞⎜⎜⎝
⎛Ω+−+==
TTLT C
LRIIZVω
ω
TL LX ω= TC CX ω/1=
RCL atXX ωω == 22 Ω+== RIZIV RLRT
Ti NCC = Tic NCX ω1= TRicRic NCIXIV ω==
NLL Ti /= NLX TiL /ω= NLIXIV TRiLRiL /ω==
Total antenna impedance
L-C series resonance condition
Local antenna voltage drop
→ The local voltage drop of each antenna segment is inversely proportional to the number of segments N.
2009 CST Korean user meeting9
Capacitor Distributed Resonance Antenna (C.D.R.A.) Capacitor Distributed Resonance Antenna (C.D.R.A.)
Main purpose of CST-MWS simulation Verification of the azimuthal E&H field distribution at the antenna resonance freq. Analysis of the impedance match condition
Low antenna voltage & high antenna current
Antenna L-C series resonance
High density & low electron temperature plasma
capacitors
Power input Antenna ground
2. VHF-ICP source development2. VHF-ICP source development
2009 CST Korean user meeting10
Plasma model setup in CSTPlasma model setup in CST--MWSMWS
)(
2
c
pr iνωω
ωεε
−−= ∞
e
ep m
ne
0
2
εω =
1=∞ε
)( egc TKn=ν
2. VHF-ICP source development2. VHF-ICP source development
Ref. Michael A. Lieberman “Principles of plasma discharges and materials processing”.
Plasma dielectric constant
Electron plasma frequency
2009 CST Korean user meeting11
Impedance matching in CSTImpedance matching in CST--MWSMWS
2. VHF-ICP source development2. VHF-ICP source development
Direct calculation: MWS stand-alone type
Indirect calculation: MWS-DS co-simulation type
0 20 40 60 80
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
S11
para
met
er
Driving frequency (MHz)
13.56 MHzImpedance matching point
Load impedance calculation from MWS simulation
Matching condition analysis
Load impedance
Lumped elements
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Analysis of field simulation results Analysis of field simulation results
0 60 120 180 240 300 360
0
1000
2000
3000
4000
5000
Azimuthal angle [degree]
Azi
mut
hal E
elec
tric
fiel
d [V
/m]
Single turn 13.56 MHz Single turn 27.12 MHz Single turn 40.68 MHz C.D.R.A. 61.40 MHz
0 60 120 180 240 300 3601.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Single turn 13.56 MHz Single turn 27.12 MHz Single turn 40.68 MHz C.D.R.A. 61.40 MHz
Azimuthal angle [degree]
Azi
mut
hal M
agne
tic fi
eld
[A/m
]M
agne
tic fi
eld
ampl
itude
Ele
ctri
c fie
ld a
mpl
itude
2. VHF-ICP source development2. VHF-ICP source development
According to the field simulation results, the C.D.R.A. gives a uniform distribution in the electric and magnetic fields.
Evaluate field onpredefined curve
2009 CST Korean user meeting13
Structure of Capacitor Distributed Resonance AntennaStructure of Capacitor Distributed Resonance AntennaC
.D.R
.A.
base
-PC
B
Plas
ma
disc
harg
e a
t 40
MH
z
Con
vect
ion
cool
ing
syst
em
Cooling fan
Diameter = 450 mm
Capacitor
Cap
acito
r co
nnec
tion
Power portAntenna ground
Capacitance uncertainty is
100 pF ± 1 pF for 12 capacitors
Top plateBase plate
Ref. H. S. Jun, H. Y. Chang, Appl. Phys. Lett. 92, 041501 (2008).
3. Experimental results 3. Experimental results
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Plasma parameter measurements Plasma parameter measurements
3. Experimental results 3. Experimental results
0 5 10 15 20 25 300.0
2.0x1011
4.0x1011
6.0x1011
8.0x1011
1.0x1012
1.2x1012
1.4x1012
1.6x1012
δ=-9.21E8
δ=-4.35E9
δ=-7.12E9
Ele
ctro
n de
nsity
(cm
-3)
Position (cm)
rf power 1.6 KW 5 mTorr 10 mTorr 30 mTorr
0 5 10 15 20 25 300.0
2.0x1011
4.0x1011
6.0x1011
8.0x1011
1.0x1012
1.2x1012
1.4x1012
1.6x1012
δ=1.19E8
δ=6.02E8
δ=2.32E9
Ele
ctro
n de
nsity
(cm
-3)
Position (cm)
rf power 1.6 KW 5 mTorr 10 mTorr 30 mTorr
0 5 10 15 20 25 300
1x1011
2x1011
3x1011
4x1011
5x1011
6x1011
7x1011
8x101110 mTorr Ar plasma
Position (cm)
Ele
ctro
n de
nsity
(cm
-3)
0.8 KW δ=-2.12E9 1.0 KW δ=-2.93E9 1.2 KW δ=-3.66E9 1.4 KW δ=-4.13E9 1.6 KW δ=-5.14E9
0 5 10 15 20 25 300
1x1011
2x1011
3x1011
4x1011
5x1011
6x1011
7x1011
8x1011
Ele
ctro
n de
nsity
(cm
-3)
Position (cm)
10 mTorr Ar plasma 0.8 KW δ=4.29E8 1.0 KW δ=4.75E8 1.2 KW δ=3.88E8 1.4 KW δ=5.91E8 1.6 KW δ=6.02E8
The worst radial plasma uniformity exists at the powered
end of the antenna.
Power input
Probe scanning direction
Single turn antenna
Single turn antenna
C.D.R.A.
C.D.R.A.
Symmetric plasma density
2009 CST Korean user meeting15
““CSTCST--MWSMWS”” based plasma source developmentbased plasma source development
Plasma uniformity prediction through the E/H-field and power loss distribution.
Plasma source S-parameter analysis.
Impedance-matching-network design for different antenna types.
High-frequency & large-area plasma source analysis.
SummarySummary
See also…Wave-cutoff probe
H. S. Jun, B. K. Na, H. Y. Chang, and J. H. Kim, Phys. Plasmas 14, 093506 (2007).
Wave-cutoff probe simulation