high pressure plasma with a third electrode james roberts physics tsp 2002 supervised by dr kerrie...
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High Pressure PlasmaHigh Pressure Plasmawith a third electrodewith a third electrode
James RobertsJames Roberts
Physics TSP 2002Physics TSP 2002
Supervised by Dr Kerrie BallaSupervised by Dr Kerrie Balla
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What is a plasma?What is a plasma?
Collection of Collection of electrons, charged electrons, charged ions and neutral ions and neutral atoms and atoms and moleculesmolecules
Overall plasma is Overall plasma is neutralneutral
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How are they made?How are they made?
Charged particles result from the Charged particles result from the interaction of gas with an applied interaction of gas with an applied electric fieldelectric field
Typically confined in a reaction Typically confined in a reaction chamber at pressures < 1 mbarchamber at pressures < 1 mbar
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How are plasmas used?How are plasmas used?
Many usesMany uses SputteringSputtering
Used in making our electrodesUsed in making our electrodes Thin film depositionThin film deposition EtchingEtching
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Advantages of higher Advantages of higher pressurepressure
Improved rates in thin film processesImproved rates in thin film processes More ions More ions faster process faster process
Less expensive apparatusLess expensive apparatus At atmospheric pressure no vacuum At atmospheric pressure no vacuum
equipment neededequipment needed 100 mbar could be sustained by an 100 mbar could be sustained by an
inexpensive pumpinexpensive pump
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Vacuum systemVacuum system
Constant flow 440 sccm Constant flow 440 sccm balloon gas @ 100 mbarballoon gas @ 100 mbar
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The chamberThe chamber
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ConditionsConditions
0.1 mm gap microplanar reactor0.1 mm gap microplanar reactor Al on alumina substrateAl on alumina substrate Constant flow 440 sccm balloon gas Constant flow 440 sccm balloon gas
@ 100 mbar@ 100 mbar 320V peak to peak applied by power 320V peak to peak applied by power
supply at 1.7 kHzsupply at 1.7 kHz
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The plasmaThe plasma
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The third electrodeThe third electrode
Piece of aluminium 38x14x4 mmPiece of aluminium 38x14x4 mm Supported on two feet, 2 microscope Supported on two feet, 2 microscope
slides highslides high Negative potential applied from DC Negative potential applied from DC
supplysupply Voltage and current monitors allow VI Voltage and current monitors allow VI
characteristics to be measured on a CROcharacteristics to be measured on a CRO Langmuir probeLangmuir probe
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CRO traceCRO traceElectron current
Ion current
0 0 V applied-24 V self bias
Increase applied –ve voltage to 3rd electrode
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Ion current
No electron current
As magnitude of voltage is increased CRO trace takes this form
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VI curveVI curve
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VI curveVI curve
Graph shows relatively large ion Graph shows relatively large ion currentcurrent Potentially useful for depositionPotentially useful for deposition
Similar to that of a Langmuir probe, Similar to that of a Langmuir probe, except no maximum ion currentexcept no maximum ion current As 3As 3rdrd electrode dimensions are electrode dimensions are
comparable to the plasma itselfcomparable to the plasma itself
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ConclusionsConclusions
High pressure plasmas can be High pressure plasmas can be generated with a 1.7 kHz RF supply generated with a 1.7 kHz RF supply and microplanar reactorand microplanar reactor
Ion currents in excess of 30 mA are Ion currents in excess of 30 mA are achievedachieved
Investigation only at a preliminary Investigation only at a preliminary stage – there is much room for stage – there is much room for further studyfurther study