Hopf, C.

Jacob, W.

Schlüter, M.

Schwarz-Selinger, T.

English

MPG.PuRe

PSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 1Chemical Sputtering of Carbon Materialsdue to Combined Bombardment by Ionsand Atomic HydrogenWolfgang Jacob, C. Hopf, M. Schlüter, and T. Schwarz-SelingerMax-Planck-Institut für Plasmaphysik, 85748 Garching, GermanyContent:• Physical sputtering, chemical erosion, and chemical sputtering• The MAJESTIX experiment• Chemical Sputtering: Initial experimental results (Ar+)• Quantitative model – energy dependence• New experimental results for Ne+, He+, and N2+• SummaryMax-Planck-Institut für Plasmaphysik PSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 2Chemical sputtering• ions + neutrals• energy dependence• T dependence• very low thresholdenergy• isotope effect• ion-to-neutral ratio dep.• high erosion yieldH atomsChemical erosion• thermally activated (nothreshold energy)• no isotope effect• requires chemicallyreactive speciesPhysical sputtering• threshold energy• energy dependence(TRIM.SP)• isotope effect (kinematicfactor)• no significant Tdependence• all species (incl. inert gases)ions or energetic neutralsnon reactivereactive ionsChemical vs. physical sputteringPSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 3UHV chamberExperimental set-upH2CH3N2(CH3)2ellipsometry, infraredsubstratesubstratepreparation chamberrf plasma HWienFilterAr + 1 keVAr + 20 eVde-celerationUHV experiment with 2 radical beam sources and one ion beam sourceW. Jacob, Ch. Hopf, A. von Keudell, M. Meier, and T. Schwarz-Selinger:” Particle-beam Experiment to Study Heterogeneous Surface ReactionsRelevant to Plasma-assisted Thin Film Growth and Etching”,Review of Scientific Instruments 74, 5123-5136 (2003).PSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 4Ion | H synergismErosion of a-C:H layerscomparison of simple physical sputtering(blue symbols) due to Ar ionswitherosion due to simultaneous interactionof H and Ar+ (green symbols).Christian Hopf, PhD ThesisCh. Hopf, A. von Keudell, and W. Jacob, ”Chemical Sputtering of Hydrocarbon Films byLow-energy Ar+ Ions and H Atom Impact”, Nuclear Fusion 42, L27 (2002).Ch. Hopf, A. von Keudell, and W. Jacob, ”Chemical Sputtering of Hydrocarbon Films”,J. Appl. Phys. 94, 2373 (2003).• separation of chemical and kinematicaleffects due to use of Ar+ and H• neutral / ion ratio ≈ 400Chemical Sputtering• enhanced erosion above 200 eV forsimultaneous interaction• erosion below threshold for physicalsputtering (threshold energy forphysical sputtering ≈ 60 eV• erosion at 20 eV >> pure chemicalerosion ⇒ ‘chemical sputtering‘T = 340 K10 1000.1110erosion rate Γ (C atoms cm-2 s-1) Y (eroded carbon atoms per ion)ion energy (eV) Y(Ar+|H)   Y(Ar+)   Chemical sputtering model (a = 0.4)   TRIM.SP, Esb = 3.0 eV10121013 Γ(H) PSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 50 100 200 300 400 5000.00.51.01.52.0Eion = 200 eV  Y(Ar+ / H), jH = konst.  Y(Ar+ / H), jAr+ = konst.  model  chemical sputtering yieldR = jH / jAr+Ar+|H flux dependenceFit parameters:S       = 176Ychem = 2.86Yphys  = 0.12PSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 6Saturation requiresmuch more H than ions(R > 1000)Ar+|H flux dependence10-1 100 101 102 103 104 105 1060123  Y(Ar+ / H)R = jH / jAr+Ar+ (200 eV) + H0 → a-C:HPSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 7xvolatile speciesa-C:H film:       carbon       hydrogen2.    H° passivates broken bonds1. ions break C–C bondsRepetition of 1 and 23. volatile hydrocarbonsdiffusion to the surfacedesorptionionsH°Chemical sputtering mechanismPSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 8passivation by atomic HEnergy dependencedxexyaHionsY xbb)/()()|( λ−⋅⋅= ∫bond breaking due to ion impactdxxpxyHionsY passbb )()()|( ⋅∝ ∫Bond breaking eventsper depth intervalcalculated by TRIM.SPexponential decay,maximum range about 2 nm,known from plasma experimentsa is a fit parameter0 1 2 3 4 5051015202530ion energy (eV)                  10                  20                  50                100                200                400                800pPass(x) ydp(x) ydpC(x) [nm-1]depth x [nm]0.00.20.40.60.81.0 pPass(x) EbbC = 5 eV, λ = 0.4 nmTRIM.SP simulations for Ar ionsPSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 9101 102 10310-1100101102  Y(Ar+ / H)Ar+ energy (eV) data YCdp modelAr+/Ha = 0.4 102 10310-410-310-210-1100101  Y(H+ 2 / H)H+2 energy (eV) data YCdp model (H+2 = 2H+) model (H+2)H2+/Ha = 0.4 Energy dependencejH = 1.4×1015 cm-2 s-1, jAr+ = 3.6×1012 cm-2 s-1, R = jH/ jAr ≈ 400PSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 10New experimental results: Ne+ + H10 100 10000.1110erosion rate Γ (C atoms cm-2 s-1) Y (eroded carbon atoms per ion)ion energy (eV) Y(Ne+|H)   Y(Ne+) Chemical sputtering model TRIM.SP, Esb = 2.8 eV10121013  Γ(H) • Excellent agreementbetween model and data(same parameters as forAr, i.e., a = 0.4))• yield > 1 for  Eion >50 eVPSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 11New experimental results: He+ + H10 100 10000.010.1110erosion rate Γ (C atoms cm-2 s-1) Y (eroded carbon atoms per ion)ion energy (eV) Y(He+|H)     Chemical sputtering model (a = 0.4)    Chemical sputtering model (a = 0.6)    TRIM.SP, Esb = 2.8 eV Y(He+)101110121013 Γ(H) • Good fit of the energydependence,but only for a = 0.6(instead of 0.4)• yield ≤ 1 in whole rangePSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 12100 10000.11 N+2,      TRIM.SP Ne+,    TRIM.SP sputtering yield (eroded C per ion)ion energy (eV)Chemical sputtering by N2+• TRIM cannot describe theresults for pure N2+• yield  ≥ 1 for Eion > 50 eV• Threshold between 20and 50 eV(TRIM ca. 100 eV)• almost no energydependence in range 50to 900 eVPSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 1310 100 10000.1110erosion rate Γ (C atoms cm-2 s-1) Y (eroded carbon atoms per ion)ion energy (eV) Y(N2+|H)   Model for chemical sputtering (a=0.4) Model for chemical sputtering (a=0.6) TRIM.SP, Esb = 2.8 eV Y(N2+)10121013 Γ(H) Chemical sputtering: N2+ + H• Good fit of the energydependence,but only for a = 0.6(instead of 0.4)• yield ≥ 1 in whole range• highest chem. Sputt. yieldof all investigates species(good mass match to C, twoatoms per ion, chemicalactivity)PSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 1410 100 10000.1110  chemical sputtering yield (per ion)energy (eV)N+2Ar+Ne+He+H+2 = 2 H+Flux ratio  H/ion = 400H flux density         = 1.4 × 1015 cm-2s-1Ar ion flux density  = 3.5 × 1012 cm-2s-1Chemical sputtering: SummaryPSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 1510 100 10000.00.20.40.60.81.0a =0.4  chemical sputtering yieldion energy (eV)H+D+T+He+a =0.6Energy dependence: Modeling resultsa = 0.4R ≈ 400Fusion relevant speciesPSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 16Chemical sputtering with reactive ionsH+, D+ → graphiteC. Hopf and W. Jacob, submitted101 102 103 10410-410-310-210-1  yieldenergy (eV)models: chemical sputtering physical sputtering chem. + phys. modelD+H+July 2004Data: M. Balden, J. Roth, J. Nucl. Mater. 280, 39-44 (2000)             New weight-loss measurements of the chemical erosion yields of carbon materials under hydrogen ion bombardmentPSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 17)(d)/exp(),(),()( physCbb EYxxExnExyEY +−= ∫ λtotal yield   =                    chemical sputtering                           +  physical sputteringYphys(E)ybbC(x,E)n(x,E)exp(–x/λ)phys. sputtering yieldion induced damageimplanted hydrogendepth dependent probabilityfor outdiffusion of erosionproductsTRIM.SPEsbC = 7.4 eVEbbC = 5.0 eVλ = 0.4 nmPSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 18Summaryparticle-beam experiments• chemical sputtering: increase of yield and lowering of threshold• mechanistic model for chemical sputtering• flux dependence (rate equation model): high H fluxes required• energy dependence: bond breaking × passivation• data for Ar, Ne, He, and N2• predictions for other ions, e.g. H, D, and T• N2+ alone results in chemical sputtering of a-C:H layers• N2+ + H shows very high chemical sputtering yieldPSIF Workshop, OakRidge © Wolfgang Jacob, March 2005 19The endCollaborators:Christian HopfAchim von KeudellMichael SchlüterThomas Schwarz-Selinger

Chemical Sputtering of Carbon Materials due to Combined Bombardment by Ions and Atomic Hydrogen

http://hdl.handle.net/21.11116/0000-0000-0F2B-1

Chemical Sputtering of Carbon Materials due to Combined Bombardment by Ions and Atomic Hydrogen

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