Permanent-magnet helicon sources for etching, coating, and thrust
description
Transcript of Permanent-magnet helicon sources for etching, coating, and thrust
Permanent-magnethelicon sources for
etching, coating, and thrust
Francis F. Chen, UCLA
Low Temperature Plasma Teleseminar, June 14, 2013; originally prepared for (but not given at):2013 Workshop on Radiofrequency Discharges, La Badine, La Presqu’ile de Giens, France, 29-31 May 2013
Helicons are RF plasmas in a magnetic field
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Prf % 200 16% 400 21% 600 35% 800 38%
1000 42%
Density increase over ICP
Helicon sources usually use heavy magnets
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The MØRI source of Plasma Materials Technologies, Inc.
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Size of the MØRI source
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The source has been simplified to this
This uses a commercially available 2 x 4 x 0.5 inch
NeFeB magnet
The discharge is 5 cmhigh and 5 cm in diameter
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How did we get here?
Lc
a b
h
Loop antennaHelical antenna
B0
D. Arnush, Phys. Plasmas 7, 3042 (2000).
First, the HELIC code of Arnush
Examples of HELIC results: Pr , Pz
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0
1000
2000
3000
4000
5000
0.000 0.005 0.010 0.015 0.020 0.025r (m)
P(r
) (a
rb.)
2.5E+114.0E+116.3E+111.0E+12
n (cm-3)
0
1
2
3
4
5
6
0 5 10 15 20 25 30z (cm)
P(z
)
1.6E+122.5E+124.0E+126.3E+121.0E+13
13 MHz, 80G
Most important, RnB: power deposition
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RnB results organized in matrices
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100W
300W
500W
D = 7.4" D = 11" D = 13"
Folder Folder Folder
1 mTorr, ei = -1D = 0
Folder
Folder Folder Folder
FolderD13W100 D0W100
Folder
D7W100Folder
D11W100Folder
D0W500
D7W300 D11W300 D13W300 D0W300
D7W500 D11W500 D13W500Folder
conductor
insulator
1 mTorr 10 mTorr
Folder FolderP1cond P10cond
D = 0, 300W
Folder FolderP1ins P10ins
Matrix A: B-field Matrix C: pressure
Similar matrices for tube size determined the tube design.
After that, there are matices for the experimental results.
Optimized discharge tube: 5 x 5 cm
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1. Diameter: 2 inches
2. Height: 2 inches
3. Aluminum top
4. Material: quartz
5. “Skirt” to prevent eddy currents canceling the antenna current
5.1 cm
10 cm
5 cmANTENNA
GAS INLET (optional)
The antenna is a simple loop, 3 turns for 13 MHz, 1 turn for 27 MHz. The antenna must be as close to the exit aperture as possible.
Antenna: 1/8” diam tube, water-cooled
Design of matching circuit (1)
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R, L
R, L
R, L
R, L
PS
N loads
Z2 - short cables
Distributor
Z1Z2
Z1 - long cable
Matching ckt.(standard) 50W
C1C2
Matching ckt.(alternate)
C1C2
Design of 50W matching circuit (2)
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Let the load be RL + jXL :
R and X have first to be transformed by cable length
k = R0C, R0 = 50W
Forbidden regions of L, R, and Z (N = 8)
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0
500
1000
1500
2000
0.5 1.5 2.5 3.5 4.5R (ohms)
C (p
F)
C1(S)C2(S)
0
200
400
600
800
1000
1200
1400
1600
0 50 100 150 200Z2 (cm)
C (p
F)
C1(S)C2(S)
0
200
400
600
800
0 0.5 1L (mH)
C2
(pF)
86421
N
0
500
1000
1500
2000
0 0.5 1 1.5 2 2.5L (mH)
C1
(pF)
86421
N
Instead, we can use annular PMs
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-16
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
8
-10 -8 -6 -4 -2 0 2 4 6 8 10
NdFeB ring magnet3” ID, 5” OD, 1” high
Stagnation point
Put plasma here
or here, to adjust B-field
The far-field is fairly uniform
PM Permanent magnet
Experimental chamber
UCLAGate Valve
To Turbo Pump
PUMP BAFFLE AND GROUND PLANE
WALL MAGNETS
Port 1
Port 3
Port 2
38
46
6.8
16.9
27.2
19 cm
Langmuir probes at three ports
The magnet height is set for optimum B-field
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Optimization of the B-field
Peak density in Port 2 vs. B and Prf @ 27 MHz
30-60 G is best
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Typical scan of “Low-field peak”
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Density of ejected plasma
0
1
2
3
4
5
-25 -20 -15 -10 -5 0 5 10 15 20 25r (cm)
n (1
011
/cm
3 )
n11, 65Gn11, 280G
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
-20 -10 0 10 20r (cm)
n (1
011
cm
-3)
6.816.927.2
62 G, 400Wcm below source
Gate Valve
To Turbo Pump
PUMP BAFFLE AND GROUND PLANE
WALL MAGNETS
Port 1
Port 3
Port 2
38
46
6.8
16.9
27.2
19 cm
Vertical probe for inside plasma
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0
2
4
6
8
10
12
14
16
0 2 4 6 8 10 12z (cm)
n 11
Jan. 4 w. Mk2Jan. 5 w. ESPion
Bottom of tube
400W, 62G
Horiz. Probe point
0
4
8
12
16
0 2 4 6 8 10 12z (cm)
n 11
400W, 13.56 MHz, 15 mTorr
Axial density profile inside the tube
Density inside the tube is low (<1013 cm-3) because plasma is efficiently ejected.
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Downstream density: 6 x 1011 cm-3
0
1
2
3
4
5
6
7
0 200 400 600 800 1000 1200Prf (W)
n (1
011 c
m-3
)
HeliconICP
15 mTorrPort 2
Prf % 200 16% 400 21% 600 35% 800 38% 1000 42%
Density increaseover ICP
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Port 2 density is higher at 13 MHz
0
1
2
3
4
5
6
7
8
9
0 200 400 600 800 1000 1200Prf (W)
n (1
011 c
m-3
) 13 MHz
27 MHz
Port 2
This was a surprise and is contrary to theory.
Cause and location of the “double layer”
1/20½, /s sn n e
1/2 2( / ) ½ ½is s e is is ev c KT M W Mv KT
20 0 0/ / ( / )B B n n r r
F.F. Chen, Phys. Plasmas 13, 034502 (2006)
n
xs x
ne = ni = n
PLASMA
SHEATH
ni
ne
+
ns
PRESHEATH
v = cs
0 , where e /e en n e V KT Maxwellian electrons
Bohm sheath criterion
1/40/ 1.28r r e
A sheath must form here
Single layer forms where r has increased 28%
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Where a diffuse “double layer” would occur
0
50
100
150
200
250
5 10 15 20 25 30z (cm)
B (G
)
Approx. location of "double layer"
Ion energy distribution by Impedans SEMion
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IEDFs vs. Prf in Port 1
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0E+00
5E-07
1E-06
2E-06
2E-06
0 5 10 15 20 25 30V
IED
F
600W500W400W400W repeat300W200W100W
Vs
Conditions at Port 1 (r = 0) at 400W
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0
1
2
3
4
5
6
-20 -10 0 10 20r (cm)
n (1
011 c
m-3
)
Port 1400W
Te (eV)
n11
0
1
2
3
4
5
6
7
-100 -80 -60 -40 -20 0 20V
I2 (mA
)2
Ii squaredIi squared (OML)
0.01
0.1
1
10
100
-5 0 5 10 15 20V
I e (m
A)
IeIe(fit)Ie (0)
Te eVs iVs n11
2.14 15.9 27 4.21
Plasma potential
Mach probe (in Port 2)
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0.50
1 ln 0.75ln
( 1.34)
flow up up
s down down
v I Ic K I I
K
Hutchinson:
Result:
0.14f
s
vc
0.14f
s
vc
This seems very low. It should be much higher in Port 1
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helicon ARRAY sources
SUBSTRATE
TO PUMP
DISTRIBUTOR
MEDUSA MEDUSA 1
The Medusa 2 large-area array
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An array source for roll-to-roll processing
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165 cm
30 cm
15 cm
Probe ports
Aluminum sheetHeight can be adjusted electrically if desired
The source requires only 6” of vertical space above the process chamber. Two of 8 tubes are shown.
Z1Z2
65"
21"
7"
7"
7"
7"29"
3.5"
12"
7"3/4” aluminum
Endplates: gas feed and probe port at each end.
Tubes set in deeply (½ inch)
1/2" aluminum
Top view of Medusa 2
Possible positions shown for 8 tubes.
Substrate motion
Two arrangements of the array
Staggered array
Covers large area uniformly for substrates moving in the y-direction
165 cm
53.3 cm
17.8
17.8
17.8
35.6 cm
x
y
165 cm
53.3 cm
17.8
17.8
17.8
x
yTop view 17.8 Compact array
Gives higher density, but uniformity suffers from
end effects.
Operation with cables and wooden magnet tray
It’s best to have at least 3200W (400W per tube) to get all tubes lit equally.
Details of distributor and discharge tube
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The top gas feed did not improve operation.
A rectangular 50W transmission line
50-W line with ¼” diam Cu pipe for cooled center conductor
Operation with rectangular transmission line
Radial profile at Z2 across rows
0
0.5
1
1.5
2
2.5
3
3.5
-25 -20 -15 -10 -5 0 5 10 15 20 25r (cm)
n (1
011 c
m-3
) nKTe
Density profiles with staggered array
Staggered configuration, 2kW
Bottom probe array
0
1
2
3
4
5
-8 -6 -4 -2 0 2 4 6 8 10 12 14 16x (in.)
n (1
011 c
m-3
)
-3.503.5
Staggered, 2kW, D=7", 20mTorr
y (in.)
Argon
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Density profiles with compact array
Compact configuration, 3kW
Bottom probe array
0
2
4
6
8
10
-8 -6 -4 -2 0 2 4 6 8 10 12 14 16x (in.)
n (1
011 c
m-3
)
3.5-03.5
Compact, 3kW, D=7", 20mTorr
y (in)
Data by Humberto Torreblanca, Ph.D. thesis, UCLA, 2008.
Plans for an 8-tube array for round substrates
UCLANo center tube is necessary!