A Helicon Plasma Source for Large-area Materials Processing
DMI-0115570: Francis F. Chen, UCLA
Part 1
Proof of Concept
DISTRIBUTOR
Medusa
Part 3
Planned Innovations
Part 2
Why Helicons?
Typical density limits in plasma sources
Part 4
Applications
A. Dry processing of flat panel displays: e.g. etching of ITO
and aluminum. Also, deposition of SiO2 on plastic for flexible
displays.
QUARTZ TUBE
7 cm
HELICON
BNC connector
ANTENNA
5 mm
1 cm
ICP
MAGNET WINDING
2.5 c m
17 mm
54 m m
2.4 m m
1 cm
6.4 m m
B
ECR
(a)
10 c m
+
13 cm
--
ST UBBY MU L TI-TUBE SOU RC E
PVC PIPE
--
SUBSTRATE
(b)
1E+08
+
RIE
1E+09
10 cm
Maximum useful
density at wafer
level, normally
1E+10
1E+11
1E+12
1E+13
1E+14
PERMAN ENT MAGNETS
Electron density (per cc)
Helicon sources produce much higher density at the same
power as other commercial sources.
(c)
--
+
+
--
RO TATING P ROBE A RRAY
An arbitrarily large array of individual sources can be made to cover large
substrates uniformly. This is easier if permanent magnets can be used. Though
ideal for semiconductor processing, that industry currently has large enough
sources.
A. Optimization of source type and
size; antenna type; magnetic field
coils, and source spacing.
TO PUMP
In Greek mythology, Medusa was a monster who was so ugly that a single glance at her
would turn you into stone. She had a tangle of snakes for hair.
5 cm
They do this with antennas that generate a helicon
wave IN A DC MAGNETIC FIELD. This wave then
couples to a cyclotron wave on the outside, and it is
THIS wave that is absorbed very efficiently.
Our first experiment with multiple helicon sources looked like a Medusa, with its cables
distributing the RF power to each tube. This was a previous project.
B. Web coating of plastic or glass sheet, for instance for paint
adhesion or water repellency. Permanent magnets.
RF
GAS
Power scan at z = 7 cm, 5 mT A, 20 G, 13.56 MHz,
300
3.0
2.5
2.0
1.5
1.0
-3
cm )
12
400
P(r)
P(kW)
1.5
B. Replace coils with permanent magnets
Helicon mode
500
ARGON
N (10
R = 1.7 W
600
2.0
PROBE
Trivelpiece-Gould mode
700
1.0
200
100
0
0
2
4
r (cm)
6
8
10
0.5
7-tube m=0 array
0.0
0
5
10
R (cm)
15
20
25
30
There are TWO kinds of helicon discharges: the BIG BLUE
MODE (left), and the LOW-FIELD PEAK (right). At high fields,
the BLUE mode gives very high density, fully ionized, in a
narrow core. At low fields, a more uniform, lower density, more
useful plasma is created.
At 7 cm below the sources, a uniform plasma is achieved over a ~400 mm diameter without
optimization of the array. With 3kW of RF power, the plasma density approaches 2  1012 cm-3.
4"
Single Tube Test Stand
This has been constructed and is operating
20
R (c m)
2
5
8
15.93
11
14
-2 0
20
14.34
17
L O W -F IE L D D E N S IT Y P E AK
4 -cm tub e , unifo rm fie ld
13.54
2 .0
17.47
-2 0
1 .0
n (10
12
-3
cm )
1 .5
0 .5
5.18
Azimuthal scans show no evidence of m = 6 asymmetry due to the individual sources. The
uniformity over a 400-mm diam circle is +/- 3%. This shows that an array of helicon sources can
produce dense plasma efficiently over arbitrarily large areas.
0 .0
0
20
40
60
B (G )
80
100
120
C. The BIG BLUE MODE can be used to produce intense, focused
ion beams for machining of nanostructures.
Gate Valve
The L.F. density peak occurs at economical fields. It is caused
by constructive interference of the wave.reflected from the
endplate.
To Turbo Pump
First light!