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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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Optimization of Source Modules


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slide1

Optimization of Source Modules

in ICP-Helicon Multi-Element Arrays for Large Area Plasma Processing

John D. Evans & Francis F. Chen

UCLADept of Electrical Engineering

LTPTL- Low Temperature Plasma Technology Laboratory

AVS 2002, Denver, Co, November 4, 2002

slide3

COIL

COIL

UCLA

One-tube configuration

using large-area Bo-field

coils and radially scannable

Langmuir probes

Single source tube with

individual solenoidal Bo

slide4

B

m=-1

m=+1

B

m=+1

m=-1

UCLA

Schematic 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

slide5

Sense of helicity

“LH”

“RH”

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 thedirection 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

slide6

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

slide8

UCLA

Left Hand (LH) Helical Antenna Nomenclature Defined

Lant = Physical length of active antenna element

lant = Antenna Wavelength - pitch ofhelical straps

l

Half Helix

slide9

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

slide11

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

slide12

UCLA

1kW, 15mT, 150G

Half-helical m = +1 antenna

Lant = 10cm, lant = 20cm

Langmuir Probe @ z = 3 cm

below mouth of source tube

slide13

l

UCLA

Full-helical m = +1 antenna

Lant = 10cm, lant = 10cm

Langmuir Probe @ z = 3 cm

below mouth of source tube

slide14

UCLA

Double-helical m = +1 antenna

Lant = 10cm, lant = 5 cm

Langmuir Probe @ z = 3 cm

below mouth of source tube

slide15

l

UCLA

1kW, 10mT Ar, 13.56MHz, Lant =10cm = lant, z=3cm, 150G

slide16

M = 0 radial profiles

4 equispaced source tubes,

Enough for uniform plasma?

YES, for axial distance z > 10cm from source tubes

slide17

Pyrex

antenna

Schematic of multi-turn loop “m=0” source element

slide18

“1,2,4,6”

3

3

4

4

2

2

1

1

5

5

7

7

6

6

Numerical label convention: 7 tube source, aerial view

“w,x,y,z” = Antennas # W, X, Y, Z “ON”, others “OFF”

“1,2,4,5”

slide19

“1,2,4,5”

“1,2,4,6”

3

4

3

4

2

1

5

2

1

5

6

7

7

6

slide20

“1,2,4,5”

3

4

2

1

5

7

6

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

slide22

CONCLUSIONS

4 equispaced source tubes good enough,

due to Helicon-enhanced uniformity

Multitube concept appears to be

applicable to arbitrarily large area.