Optimization of Source Modules

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Optimization of Source Modules in 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
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Conceptual multitube m0 helicon source for large
area processing
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UCLA
One-tube configuration using large-area Bo-field
coils and radially scannable Langmuir probes
Single source tube with individual solenoidal Bo
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UCLA
Schematic proof of low-field Helicon mode
RH-t-III antenna Helicity pitch sense ? B up
(down) launches m1 up (down) Np and VL
enhanced in region that m1 mode propagates
towards
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Experimental evidence Half-helical antennas
launch m 1 Helicon mode from source tube when
low field peak is present.
RH 1/2-helical antenna
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
LH 1/2-helical antenna
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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
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Low-field peak increases, broadens and shifts to
higher B at higher Po.
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UCLA
Left Hand (LH) Helical Antenna Nomenclature
Defined Lant Physical length of active antenna
element lant Antenna Wavelength - pitch of
helical straps
l
Half Helix
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Radial Np profiles for 3 RH-helical
antennas 1kW, 13.56MHz, 15mT Ar, 150G, z3cm,
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 ? m1 helicon mode
enhances profile width as well as Np
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Radial Np profiles for 3 antenna wavelengths
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Radial Np profiles for 3 RH-helical
antennas 1kW, 13.56MHz, 15mT Ar, 150G, z3cm,
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 ? m1 helicon mode
enhances profile width as well as Np
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UCLA
1kW, 15mT, 150G
Half-helical m 1 antenna
Lant 10cm, lant 20cm
Langmuir Probe _at_ z 3 cm below mouth of source
tube
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l
UCLA
Full-helical m 1 antenna
Lant 10cm, lant 10cm
Langmuir Probe _at_ z 3 cm below mouth of source
tube
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UCLA
Double-helical m 1 antenna
Lant 10cm, lant 5 cm
Langmuir Probe _at_ z 3 cm below mouth of source
tube
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l
UCLA
1kW, 10mT Ar, 13.56MHz, Lant 10cm lant, z3cm,
150G
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M 0 radial profiles
4 equispaced source tubes, Enough for uniform
plasma?
YES, for axial distance z gt 10cm from source tubes
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Schematic of multi-turn loop m0 source element
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Numerical label convention 7 tube source, aerial
view w,x,y,z Antennas W, X, Y, Z ON,
others OFF
1,2,4,5
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Np radial nonuniformity vs axial distance z from
source tubes
Broad/flat cannot be explained by streaming of
plasma along B-lines and normal diffusion
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N(R) vs Z for 3-turn loops, 4 symmetric (1,2,4,6)
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CONCLUSIONS
4 equispaced source tubes good enough, due to
Helicon-enhanced uniformity
Multitube concept appears to be applicable to
arbitrarily large area.