![Page 1: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/1.jpg)
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
![Page 2: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/2.jpg)
Helicons are RF plasmas in a magnetic field
UCLA
Prf % 200 16% 400 21% 600 35% 800 38%
1000 42%
Density increase over ICP
![Page 3: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/3.jpg)
Helicon sources usually use heavy magnets
UCLA
The MØRI source of Plasma Materials Technologies, Inc.
![Page 4: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/4.jpg)
UCLA
Size of the MØRI source
![Page 5: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/5.jpg)
UCLA
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
![Page 6: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/6.jpg)
UCLA
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
![Page 7: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/7.jpg)
Examples of HELIC results: Pr , Pz
UCLA
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
![Page 8: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/8.jpg)
Most important, RnB: power deposition
UCLA
![Page 9: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/9.jpg)
RnB results organized in matrices
UCLA
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.
![Page 10: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/10.jpg)
Optimized discharge tube: 5 x 5 cm
UCLA
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
![Page 11: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/11.jpg)
Design of matching circuit (1)
UCLA
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
![Page 12: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/12.jpg)
Design of 50W matching circuit (2)
UCLA
Let the load be RL + jXL :
R and X have first to be transformed by cable length
k = R0C, R0 = 50W
![Page 13: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/13.jpg)
Forbidden regions of L, R, and Z (N = 8)
UCLA
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
![Page 14: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/14.jpg)
Instead, we can use annular PMs
UCLA
-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
![Page 15: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/15.jpg)
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
![Page 16: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/16.jpg)
UCLA
Optimization of the B-field
Peak density in Port 2 vs. B and Prf @ 27 MHz
30-60 G is best
![Page 17: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/17.jpg)
UCLA
Typical scan of “Low-field peak”
![Page 18: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/18.jpg)
UCLA
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
![Page 19: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/19.jpg)
Vertical probe for inside plasma
UCLA
![Page 20: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/20.jpg)
UCLA
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.
![Page 21: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/21.jpg)
UCLA
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
![Page 22: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/22.jpg)
UCLA
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.
![Page 23: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/23.jpg)
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%
![Page 24: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/24.jpg)
UCLA
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"
![Page 25: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/25.jpg)
Ion energy distribution by Impedans SEMion
UCLA
![Page 26: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/26.jpg)
IEDFs vs. Prf in Port 1
UCLA
0E+00
5E-07
1E-06
2E-06
2E-06
0 5 10 15 20 25 30V
IED
F
600W500W400W400W repeat300W200W100W
Vs
![Page 27: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/27.jpg)
Conditions at Port 1 (r = 0) at 400W
UCLA
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
![Page 28: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/28.jpg)
Mach probe (in Port 2)
UCLA
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
![Page 29: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/29.jpg)
UCLA
helicon ARRAY sources
SUBSTRATE
TO PUMP
DISTRIBUTOR
MEDUSA MEDUSA 1
![Page 30: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/30.jpg)
The Medusa 2 large-area array
UCLA
![Page 31: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/31.jpg)
An array source for roll-to-roll processing
UCLA
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
![Page 32: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/32.jpg)
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
![Page 33: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/33.jpg)
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.
![Page 34: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/34.jpg)
Operation with cables and wooden magnet tray
It’s best to have at least 3200W (400W per tube) to get all tubes lit equally.
![Page 35: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/35.jpg)
Details of distributor and discharge tube
UCLA
The top gas feed did not improve operation.
![Page 36: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/36.jpg)
A rectangular 50W transmission line
50-W line with ¼” diam Cu pipe for cooled center conductor
![Page 37: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/37.jpg)
Operation with rectangular transmission line
![Page 38: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/38.jpg)
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
![Page 39: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/39.jpg)
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
![Page 40: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/40.jpg)
UCLA
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.
![Page 41: Permanent-magnet helicon sources for etching, coating, and thrust](https://reader035.vdocuments.mx/reader035/viewer/2022070500/5681684d550346895dde4c28/html5/thumbnails/41.jpg)
Plans for an 8-tube array for round substrates
UCLANo center tube is necessary!