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High Pressure Plasma with a third electrode

High Pressure Plasma with a third electrode. James Roberts Physics TSP 2002 Supervised by Dr Kerrie Balla. What is a plasma?. Collection of electrons, charged ions and neutral atoms and molecules Overall plasma is neutral. -. +. +. -. +. +. -. -. -. +. -. -. +. +. +. -. -.

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High Pressure Plasma with a third electrode

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  1. High Pressure Plasmawith a third electrode James Roberts Physics TSP 2002 Supervised by Dr Kerrie Balla

  2. What is a plasma? • Collection of electrons, charged ions and neutral atoms and molecules • Overall plasma is neutral - + + - + + - - - + - - + + + - - + - - - + - + + + - - + - - + + + + + - - - - + +

  3. How are they made? • Charged particles result from the interaction of gas with an applied electric field • Typically confined in a reaction chamber at pressures < 1 mbar

  4. How are plasmas used? • Many uses • Sputtering • Used in making our electrodes • Thin film deposition • Etching

  5. Advantages of higher pressure • Improved rates in thin film processes • More ions  faster process • Less expensive apparatus • At atmospheric pressure no vacuum equipment needed • 100 mbar could be sustained by an inexpensive pump

  6. Vacuum system • Constant flow 440 sccm balloon gas @ 100 mbar

  7. The chamber

  8. Conditions • 0.1 mm gap microplanar reactor • Al on alumina substrate • Constant flow 440 sccm balloon gas @ 100 mbar • 320V peak to peak applied by power supply at 1.7 kHz

  9. The plasma

  10. The third electrode • Piece of aluminium 38x14x4 mm • Supported on two feet, 2 microscope slides high • Negative potential applied from DC supply • Voltage and current monitors allow VI characteristics to be measured on a CRO • Langmuir probe

  11. CRO trace Electron current 0 V applied -24 V self bias 0 Ion current Increase applied –ve voltage to 3rd electrode No electron current 0 As magnitude of voltage is increased CRO trace takes this form Ion current

  12. VI curve

  13. VI curve • Graph shows relatively large ion current • Potentially useful for deposition • Similar to that of a Langmuir probe, except no maximum ion current • As 3rd electrode dimensions are comparable to the plasma itself

  14. Conclusions • High pressure plasmas can be generated with a 1.7 kHz RF supply and microplanar reactor • Ion currents in excess of 30 mA are achieved • Investigation only at a preliminary stage – there is much room for further study

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