Permanent-magnet helicon sources for etching, coating, and thrust

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Permanent-magnet helicon sources for etching, coating, and thrust. Francis F. Chen, UCLA. Low Temperature Plasma Teleseminar, June 14, 2013; originally prepared for (but not given at): 2013 Workshop on Radiofrequency Discharges, La Badine, La Presqu’ile de Giens, France, 29-31 May 2013.
Permanent-magnethelicon sources foretching, coating, and thrustFrancis F. Chen, UCLALow Temperature Plasma Teleseminar, June 14, 2013; originally prepared for (but not given at):2013 Workshop on Radiofrequency Discharges, La Badine, La Presqu’ile de Giens, France, 29-31 May 2013Helicons are RF plasmas in a magnetic fieldDensity increase over ICPUCLAHelicon sources usually use heavy magnetsThe MØRI source of Plasma Materials Technologies, Inc.UCLASize of the MØRI sourceUCLAThe source has been simplified to thisThis uses a commercially available 2 x 4 x 0.5 inch NeFeB magnetThe discharge is 5 cmhigh and 5 cm in diameterUCLAHow did we get here?First, the HELIC code of ArnushD. Arnush, Phys. Plasmas 7, 3042 (2000).UCLAExamples of HELIC results: Pr , PzUCLAMost important, RnB: power depositionUCLARnB results organized in matricesMatrix A: B-fieldMatrix C: pressureSimilar matrices for tube size determined the tube design.After that, there are matices for the experimental results.UCLAOptimized discharge tube: 5 x 5 cm1. Diameter: 2 inches2. Height: 2 inches3. Aluminum top4. Material: quartz5. “Skirt” to prevent eddy currents canceling the antenna currentThe antenna is a simple loop, 3 turns for 13 MHz, 1 turn for 27 MHz. The antenna must be as close to the exit aperture as possible.Antenna: 1/8” diam tube, water-cooledUCLADesign of matching circuit (1)UCLADesign of 50W matching circuit (2)Let the load be RL + jXL :R and X have first to be transformed by cable lengthk = wR0C, R0 = 50WUCLAForbidden regions of L, R, and Z (N = 8)UCLAInstead, we can use annular PMsPM  Permanent magnetNdFeB ring magnet3” ID, 5” OD, 1” highStagnation pointThe far-field is fairly uniformPut plasma hereor here, to adjust B-fieldUCLAExperimental chamberThe magnet height is set for optimum B-fieldLangmuir probes at three portsUCLAOptimization of the B-field Peak density in Port 2 vs. B and Prf @ 27 MHz30-60 G is bestUCLATypical scan of “Low-field peak”UCLADensity of ejected plasma UCLAVertical probe for inside plasmaUCLAAxial density profile inside the tubeDensity inside the tube is low (<1013 cm-3) because plasma is efficiently ejected. UCLADownstream density: 6 x 1011 cm-3Density increaseover ICPUCLAPort 2 density is higher at 13 MHzThis was a surprise and is contrary to theory.UCLACause and location of the “double layer”F.F. Chen, Phys. Plasmas 13, 034502 (2006) Maxwellian electronsBohm sheath criterionA sheath must form hereSingle layer forms where r has increased 28%Where a diffuse “double layer” would occurUCLAIon energy distribution by Impedans SEMionUCLAIEDFs vs. Prf in Port 1VsUCLAConditions at Port 1 (r = 0) at 400WPlasma potentialUCLAMach probe (in Port 2)Hutchinson:Result: This seems very low. It should be much higher in Port 1UCLAhelicon ARRAY sourcesMEDUSAMEDUSA 1UCLAThe Medusa 2 large-area arrayUCLAProbe portsAn array source for roll-to-roll processingHeight can be adjusted electrically if desiredAluminum sheetZ1Z2The source requires only 6” of vertical space above the process chamber. Two of 8 tubes are shown.UCLATop view of Medusa 2Substrate motionPossible positions shown for 8 tubes.Two arrangements of the arrayStaggered arrayCovers large area uniformly for substrates moving in the y-directionCompact arrayGives higher density, but uniformity suffers from end effects.Operation with cables and wooden magnet trayIt’s best to have at least 3200W (400W per tube) to get all tubes lit equally.Details of distributor and discharge tubeThe top gas feed did not improve operation.UCLAA rectangular 50 transmission line50-W line with ¼” diam Cu pipe for cooled center conductorOperation with rectangular transmission lineRadial profile at Z2 across rowsDensity profiles with staggered arrayStaggered configuration, 2kWBottom probe arrayArgonDensity profiles with compact arrayCompact configuration, 3kWBottom probe arrayData by Humberto Torreblanca, Ph.D. thesis, UCLA, 2008.UCLAPlans for an 8-tube array for round substratesUCLANo center tube is necessary!
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