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UCLA
Optimization of Source Modulesin ICP-Helicon Multi-Element Arrays for
Large Area Plasma Processing
John D. Evans & Francis F. Chen
UCLA Dept of Electrical Engineering
LTPTL - Low Temperature Plasma Technology Laboratory
AVS 2002, Denver, Co, November 4, 2002
ELECTROSTATIC CHUCK
WAFER
PE
RM
AN
EN
T M
AG
NE
T A
RR
AY
UCLA
ELECTROSTATIC CHUCK
WAFER
PE
RM
AN
EN
T M
AG
NE
T A
RR
AY
Conceptual multitube m=0 helicon source for large area processing
UCLAUCLAOne-tube configuration using large-area Bo-field
coils and radially scannableLangmuir probes
QUARTZ TUBE
PVC PIPE
ANTENNA
MAGNET WINDING
7 cm
5 cm
13 cm
BNC connector
5 mm
17 mm
1 cm
1 cm
10 cm
COIL COIL
Single source tube with individual solenoidal Bo
UCLAUCLASchematic proof of low-field Helicon mode; RH-t-III antenna
Helicity pitch sense B up (down) launches m=+1 up (down) Np and VL enhanced in region that m=+1 mode propagates towards
B m = -1
m = +1
B m = +1
m = -1
UCLA
RH 1/2-helical antenna
0
2
4
6
8
10
0 50 100 150 200 250
B (Gauss)N
(10
11cm
-3)
down
up
B direction
Dependence of N(B) on the direction of B reverses when the sense of the helicity of the antenna is reversed; thus it is
m = +1 helicon mode
Sense of helicity
“LH” “RH”
0
2
4
6
8
10
0 50 100 150 200 250
B (Gauss)
N (1
011
cm-3
)
up
down
B direction
LH 1/2-helical antenna
Experimental evidence: Half-helical antennas launch m = +1Helicon mode from source tube when “low field peak” is present.
UCLA
Verification of Low-field Helicon Excitation
Low-field “peak” in N vs B plot
Dependence of occurrence of peak on B-field direction
Dependence of N vs B on B-direction reverses with antenna helicity
UCLA
Low-field peak increases, broadens and shifts to higher B at higher Po.
Po = 25 mTorr
0
2
4
6
8
10
0 50 100 150 200 250
B (Gauss)
N (1
011
cm-3
)
down
up
B direction
Po = 10 mTorr
0
2
4
6
8
10
0 50 100 150 200 250
B (Gauss)
N (1
011
cm-3
)downup
B direction
Po = 5 mTorr
0
2
4
6
8
10
0 50 100 150 200 250
B (Gauss)
N (1
011
cm-3
)
down
up
B direction
Po = 1 mTorr
0
2
4
6
8
10
0 50 100 150 200 250
B (Gauss)
N (1
011
cm-3
)
down
up
B direction
UCLAUCLALeft Hand (LH) Helical Antenna Nomenclature Defined
Lant = Physical length of active antenna element
ant = Antenna Wavelength - pitch of helical straps
Half Helix
Lant = 10 cm
ant = 20 cm
Full Helix
Lant = 10 cm ant = 10 cm
2Double Helix
ant = 5 cmLant = 10 cm
UCLA
Radial Np profiles for 3 RH-helical antennas
1kW, 13.56MHz, 15mT Ar, 150G, z=3cm, next slide
Same antenna length, but different “antenna wavelengths”
Top: double-helix; Middle: full-helix; Bottom: half-helix
Wider profiles observed in “B-down” configuration in all cases
Most total downstream Np produced in full-helix case
More total downstream Np produced in “B-down” case
m=1 helicon mode enhances profile width as well as Np
UCLA
0
2
4
6
8
10
0 4 8 12 16 20
R (cm)
N (
10
11 c
m-3) down
up
B direction
Lant =10cm
ant =20cm
EdgeRtube
0
2
4
6
8
10
N (
10
11 c
m-3)
down
up
B direction
Lant =10cm
ant =10cm
0
2
4
6
8
10N
(1011 c
m-3)
down
up
B direction
Lant =10cm
ant = 5cm
Radial Np profiles for 3 “antenna wavelengths”
UCLA
Radial Np profiles for 3 RH-helical antennas
1kW, 13.56MHz, 15mT Ar, 150G, z=3cm, next slide
Same antenna length, but different “antenna wavelengths”
Top: double-helix; Middle: full-helix; Bottom: half-helix
Wider profiles observed in “B-down” configuration in all cases
Most total downstream Np produced in full-helix case
More total downstream Np produced in “B-down” case
m=1 helicon mode enhances profile width as well as Np
UCLAUCLA
Half-helical m = +1 antenna
Lant = 10cm, ant = 20cmLangmuir Probe @ z = 3 cm
below mouth of source tube
0
2
4
6
8
10
-10 -5 0 5 10 15 20R (cm)
Np
m=+1
m= -1
B orientation
EdgeCenter
Lant = 10 cm
1kW, 15mT, 150G
UCLAUCLA
0
2
4
6
8
10
-10 -5 0 5 10 15 20R (cm)
Np
m=+1
m= -1
B orientation
EdgeCenter
Full-helical m = +1 antenna
Lant = 10cm, ant = 10cm
Langmuir Probe @ z = 3 cmbelow mouth of source tube
QUARTZ TUBE
ant = 10 cm
BNCconnector
Lant = 10 cm
UCLAUCLA
0
2
4
6
-10 -5 0 5 10 15 20R (cm)
Np
m=+1
m= -1
B orientation
EdgeCenter
Double-helical m = +1 antenna
Lant = 10cm, ant = 5 cm
Langmuir Probe @ z = 3 cmbelow mouth of source tube
ANTENNA
ant = 5 cmLant = 10 cm
UCLAUCLA
1kW, 10mT Ar, 13.56MHz, Lant =10cm = lant, z=3cm, 150G
0
2
4
6
8
10
-12 -8 -4 0 4 8 12 16 20
R (cm)
N (
1011
cm-3
)
down
up
B direction
EdgeCenter
UCLA
M = 0 radial profiles
4 equispaced source tubes,Enough for uniform plasma?
YES, for axial distance z > 10cm from source tubes
UCLA
Schematic of multi-turn loop “m=0” source element
54 mm
2.4 mm
6.4 mm10 cm
2.5
cm
antenna
Pyrex
UCLANumerical label convention: 7 tube source, aerial view
“w,x,y,z” = Antennas # W, X, Y, Z “ON”, others “OFF”
PROBE
12
3 4
5
67
“1,2,4,6”
PROBE
12
3 4
5
67
“1,2,4,5”
UCLA
0
2
4
6
8
10
12
-22.5 -15 -7.5 0 7.5 15 22.5R (cm)
N (
1011
cm-3
)
1,2,4,5
1,2,4,6
Tubes
PROBE
123 4
567
“1,2,4,6”PROBE
123 4
567
“1,2,4,5”
UCLA
Np radial nonuniformity vs axialdistance z from source tubes
Broad/flat cannot be explained by streaming of plasma along B-lines and normal diffusion
PROBE
12
3 4
5
67
“1,2,4,5”
UCLA
0
2
4
6
8
10
-22.5 -15 -7.5 0 7.5 15 22.5R (cm)
N (
1011
cm-3
) 3
10
Z (cm)
N(R) vs Z for 3-turn loops, 4 symmetric (1,2,4,6)
UCLA
CONCLUSIONS
4 equispaced source tubes good enough,due to Helicon-enhanced uniformity
Multitube concept appears to be applicable to arbitrarily large area.