CONTROLLED OXIDATION OF ORGANIC COMPOUNDS IN OXYGEN PLASMA

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Chemical cleaning with neutral oxygen or
nitrogen atoms
Miran Mozetic
Jozef Stefan Institute Plasma laboratory Ljubljana
, Slovenia
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Mednarodna podiplomska ola Joefa Stefana
Fast removal of HC deposits Benign to CFC No
oksidation of metals

Application of neutral atoms (O or N)
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Remote O atom source
Tokamak
Connection tube
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O atom source is inductively coupled RF plasma
1.2 kW
We are building 15 kW source
5kW
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O atom density at 500W
These values are measured in a side tube. The
density in the major discharge tube is 2x larger
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• The transmission of the tube depends on
• the recombination coefficient
• gas drift velocity
• length of the tube

Connection tube is made from material with a low
coefficient for heterogeneous surface
recombination ? lt 10-4
Drift velocity is close to sound velocity (300m/s)
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FLUID simulations
Connection tube
plasma
To pump
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Experiment fits the theory
Oxygen atom density
Tube length m
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Influence of effective pumping speed
8 m3/h 16m3/h
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3m long tube Schott 8250
Setup under construction
n 4x1022m-3
plasma
Experimental chamber
n gt 1x1021m-3
Roots 500m3/h
Rotary 100m3/h
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Experimental chamber
O atom inlet

• Oxidation probability depends on
• type of CH
• temperature

Heatable sample holder
To pumps
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HC film prepared by magnetron sputtering in Ar
H2 (pretty hard coating)
nO 1021 m-3
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Mednarodna podiplomska ola Joefa Stefana
Introduction to reactive plasma
Plasma is created in many gaseous discharges, but

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but only inductively coupled RF plasma is cold
and extremely reactive
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Surface effects depend on plasma parameters
Discharge parameters
Surface effects
Plasma parameters

• gas mixture
• pressure
• gas flow
• type of discharge
• voltage
• current
• magnetic field
• reactor

• composition
• structure
• morphology
• wettability
• compatibility

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Plasma parameters may change without changing
discharge parameters
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Mednarodna podiplomska ola Joefa Stefana
Example H density in a pyrex reactor
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Mednarodna podiplomska ola Joefa Stefana
It pays to measure the neutral atom density
during plasma processing of materials
Recommended tool
catalytic probe
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• Catalytic probes operation principles
• There is a flux of O atoms on catalytic surface
• O atoms recombine on the surface O O ? O2
  5.2 eV
• Power dissipated on the surface P ½ g Wd jO
• The catalyst is heating at dT/dt P/mcp (often
  over 10K/s)

Optical fibre
Probe tip
O
Surface recombination g x 5.2 eV
O2
Catalyst material
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A typical probe temperature in H rich atmosphere
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A catalytic probe
Probe tip
Catalytic probes (FOCP version)
The right choice of catalytic material depends on
particular requirements
Our choice copper with ? 0.18
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Warning
The temperature of the probe tip can be too high
if plasma is fully dissociated
We have destroyed many probes
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O atom density in a MW plasma
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O atom density during titration with NO
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If your plasma is too aggressive
place the probe in a side - vessel
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Experimental chamber Pyrex tube with diameter
11 cm
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Schematic of the discharge chamber
Sample holder
O2 inlet
sample
Catalytic probe
To pump
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Rotatable nickel plate
probe
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CONCLUSION RF plasma at about 100 Pa is an
excellent source of O atoms Values over 1x1022
m-3 are obtained Catalytic probes are suitable
for real time measuring of O atom density