1. 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

2. Conceptual multitube m=0 helicon source for large area processing

3. UCLA Single source tube with individual solenoidal Bo
One-tube configuration
using large-area Bo-field
coils and radially scannable
Langmuir probes
COIL
Single source tube with
individual solenoidal Bo

4. UCLA B B 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 B
m = +1
m = -1 B
m = -1
m = +1

5. Sense of helicity “LH” “RH”
Experimental evidence: Half-helical antennas launch m = +1
Helicon mode from source tube when “low field peak” is present.
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
RH 1/2-helical antenna
Sense of helicity
“LH”
“RH”
LH 1/2-helical antenna

6. 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

7. Low-field peak increases, broadens and shifts to higher B at higher Po.

8. UCLA Left Hand (LH) Helical Antenna Nomenclature Defined l Half Helix
Lant = Physical length of active antenna element
lant = Antenna Wavelength - pitch of helical straps l
Half Helix

9. 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

10. Radial Np profiles for 3 “antenna wavelengths”

11. 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

12. below mouth of source tube
UCLA
1kW, 15mT, 150G
Half-helical m = +1 antenna
Lant = 10cm, lant = 20cm
Langmuir z = 3 cm
below mouth of source tube

13. below mouth of source tube
UCLA
Full-helical m = +1 antenna
Lant = 10cm, lant = 10cm
Langmuir z = 3 cm
below mouth of source tube

14. below mouth of source tube
UCLA
Double-helical m = +1 antenna
Lant = 10cm, lant = 5 cm
Langmuir z = 3 cm
below mouth of source tube

15. 1kW, 10mT Ar, 13.56MHz, Lant =10cm = lant, z=3cm, 150G
UCLA
1kW, 10mT Ar, 13.56MHz, Lant =10cm = lant, z=3cm, 150G

16. YES, for axial distance z > 10cm from source tubes
M = 0 radial profiles
4 equispaced source tubes,
Enough for uniform plasma?
YES, for axial distance z > 10cm from source tubes

17. Schematic of multi-turn loop “m=0” source element
antenna
Pyrex

18. Numerical label convention: 7 tube source, aerial view
“w,x,y,z” = Antennas # W, X, Y, Z “ON”, others “OFF” 1 2 3 4 5 6 7
“1,2,4,6”
“1,2,4,5” 1 2 3 4 5 6 7

19. 1 2 3 4 5 6 7
“1,2,4,5” 1 2 3 4 5 6 7
“1,2,4,6”

20. Np radial nonuniformity vs axial distance z from source tubes1 2 3 4 5 6 7
“1,2,4,5”
Broad/flat cannot be explained by streaming
of plasma along B-lines and normal diffusion

21. N(R) vs Z for 3-turn loops, 4 symmetric (1,2,4,6)

22. Multitube concept appears to be applicable to arbitrarily large area.
CONCLUSIONS
4 equispaced source tubes good enough,
due to Helicon-enhanced uniformity
Multitube concept appears to be
applicable to arbitrarily large area.