UCLA Optimization of Source Modules in ICPHelicon MultiElement

UCLA 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

UCLA Conceptual multitube m=0 helicon source for large area processing

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

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 m = -1 B m = +1 m = -1

UCLA 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 RH 1/2 -helical antenna the sense of the helicity of the antenna is reversed; thus it is m = +1 helicon mode Sense of helicity “LH” “RH” LH 1/2 -helical antenna

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.

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

UCLA Radial Np profiles for 3 RH-helical antennas 1 k. W, 13. 56 MHz, 15 m. T Ar, 150 G, z=3 cm, 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 Radial Np profiles for 3 “antenna wavelengths”

UCLA Radial Np profiles for 3 RH-helical antennas 1 k. W, 13. 56 MHz, 15 m. T Ar, 150 G, z=3 cm, 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 1 k. W, 15 m. T, 150 G Half-helical m = +1 antenna Lant = 10 cm, lant = 20 cm Langmuir Probe @ z = 3 cm below mouth of source tube

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

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

UCLA 1 k. W, 10 m. T Ar, 13. 56 MHz, Lant =10 cm = lant, z=3 cm, 150 G l

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

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

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

UCLA “ 1, 2, 4, 5” 3 4 2 1 5 7 6 “ 1, 2, 4, 6” 3 4 2 1 5 7 6

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

UCLA 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.