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HU Berlin Plasmaphysik

HU Berlin Plasmaphysik. The Scavenger Effect - does it work?. W. Bohmeyer* a ,d , F.L. Tabares b , M. Baudach a,g , A. Cwiklinski e , T. Schwarz-Selinger g , A. Markin c , J.A. Ferreira b , G. Fussmann a,d and A. Loarte f

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HU Berlin Plasmaphysik

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  1. HU Berlin Plasmaphysik The Scavenger Effect - does it work? W. Bohmeyer*a,d, F.L. Tabaresb, M. Baudacha,g, A. Cwiklinskie, T. Schwarz-Selingerg , A. Markinc , J.A. Ferreirab, G. Fussmanna,d and A. Loartef a  AG Plasmaphysik der Humboldt Universität, Newtonstr. 15, D-12489 Berlin, Germanyb Euratom  Ciemat Association, 28040 Madrid , Spainc Institute of Physical Chemistry, Russian Academy of Sciences, Moscow, Russiad Max-Planck-Institut für Plasmaphysik, EURATOM Ass. Wendelsteinstr. 1, 17491 Greifswald, e Fachbereich für Physik, FU Berlin, Arnimallee 14, D-14159 Berlinf EFDA closed support unit,D-85748  Garching,Boltzmannstr.2  Germanyg Max-Planck-Institut für Plasmaphysik, EURATOM Ass.Boltzmannstr.2 D-85748 GarchingThis work has been carried out within the research programme of the European Task Force on Plasma Wall Interaction and was partially supported by TW4-TPP-TRIDEP.

  2. The Scavenger Effect - does it work? Introduction Experimental set up and results for the pump duct Experimental set up and results for the main chamber Summary

  3. CxHy NX Scavanger technique gas phase reactions of nitrogen or nitrogen containing species with the growth precursors. Formation of non-reactive species that can be pumped away + stable non-reactive species F.L.Tabarés, V. Rohde and the AUG Team Nucl. Fusion 45 (2005) L27-L31.

  4. Experimental setup Thickness measurement Langmuir probe QMS window Si wafer CH4 /N2 1.5 m no uncontrolled CxHy losses at cold walls the behavior of re-eroded species is studied ions can not reach the collector plates QMS turbopump

  5. pump duct deposition profile highly sticking species QMS: CH4:C2H2:C2H6

  6. Pump duct / nitrogen • strong influence of nitrogen during methane injection • no influence of nitrogen for clean plasma (not enhanced erosion by nitrogen) +0.02nm/min - - Scavenger effect: yes, it works !

  7. Pump duct: Collector temperature 310 and 330 K nitrogen effect: -reduction of deposition -shift to from deposition to erosion

  8. Pump duct : deposition profile ex situ thickness measurement (Tcoll not fixed , about 320 K) strong influence of nitrogen

  9. Nitrogen injection at different positions 6 hot tube .5 .2 pump duct 2 1 .5 4 ΦN2 [sccm] nm 2 0 0 50 100 150 min 1. into the pump duct: weak effect 2. into the hot tube: strong effect

  10. Neon injection Neon has no influence !

  11. Si collector Optical system: in-situ film thickness H2/D2/Ar plasma vacuum chamber wall Main chamber: Experimental setup QMS Injection of CH4/N2/H2 Protection of the collector area against ions by an additional limiter Ions are not included in the deposition process

  12. Main chamber, He-plasma no atomic hydrogen → no HCN and NHx Deposition is not influenced → no volume process No erosion → no surface effect

  13. Main chamber, H2 discharge, methane, nitrogen reduced deposition surface and volume process enhanced erosion surface reaction

  14. Main chamber, He-discharge Bayessian data analysis HCN CH3CN CH3 NH2 NH3

  15. 4 important reactions (Bayessian data analysis) 1.CH3+ NH2->CH3NH2 (Methylamine) not stable surface reaction volume reaction 2. CH3+ HCN->CH3CN (Acetonitrile)+H -> C2H2 + H2 + XN bzw.->C2H4 + XN volume reaction s <<1 3. C2H+ HCN->C2HCN (Cyanoacetylene)+H volume reaction s ≈ 1 4. C2H3+ NH2->C2H3NH2(Ethenamine) <->C2H4NH(Ethylenimine)<->C2H4+NH volume reaction , s≈1 [M.Baudach, thesis, HU Berlin, 2008]

  16. Summary Nitrogen molecules are stable and dont influence film formation, but they are decomposed in the plasma. Close to the plasma- where energetic neutrals are included- enhanced erosion is detected (surface process) as well as a reduction of the depositionrate by a volume process. Far away from the plasma we detected only a volume effect, the conversion of (high sticking) hydrocarbons to inert ones, the so called scavenger effect. Enhanced erosion was not found. .

  17. PSI-2 Thank you!

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