Chemistry Reference
In-Depth Information
reactive gas atmosphere (Ar/SF
6
) and its application to treatment of polymer surfaces
is reported in [135,136].
3.8.14 P
ROPERTIES OF
P
LASMA
S
OURCES FOR
P
LASMA
C
HEMISTRY
The plasma sources have to satisfy different demands depending on the various appli-
cations. A plasma reactor for research and development purposes must have many
ports for diagnostic tools as optical emission and absorption spectroscopy, mass
spectrometry, Langmuir probes. Its potential of upscaling is important. Reactors in
production lines must be matched to the selected production process. The following
microscopic and macroscopic parameters and properties are important for technolog-
ical applications (Figure 3.58), see also [137]. As already mentioned in the discussion
of the various plasma sources the input parameters for plasma chemical processes are
on one hand electrical as voltage and frequency, duty cycle, current and power for
the plasma generation, external bias voltages of the substrate, magnetic field strength
for plasma confinement, and/or ionization promotion. On the other hand nonelec-
trical parameter are important like gas pressure, gas flow, gas mixture, but also the
temperature of the reactor walls, the electrodes and the substrate.
Themagneticfieldconfigurationcanbeachievedbyvarioussolenoidsorbysingle
and several permanent magnets. The application of solenoids is power consuming
but allows an easy control and temporal variation of the magnetic field.
Plasma chemical reactors operate usually with a mixture of flowing inert carrier
gas and the reactive component. The gas control system can be positioned in different
places, upstream, into the plasma region (e.g., as a douche) or also downstream, in
the remote afterglow plasma.
The dimensions of the reactor, the flow rate, and the pumping speed determine
the residence time and the pressure regime: free fall (low-pressure ballistic movement
withoutcollisions)ordiffusiondetermined(higherpressure)withlaminarorturbulent
flow. Most of the plasma chemical reactors operate as flow reactors.
The plasma chemical reactors for material treatment are constructed for batch
or continuous operation. Examples for batch operation are the reactors of chip pro-
duction in microelectronic industry for the wafer treatment in etch and deposition
processes. Continuous operation is typical for the reactors for surface treatment of
polymer foils to improve or enable the printability in dielectric barrier discharges or
for thermal insulating coating of architectural glass by reactive sputtering in a DC
magnetron discharge.
The reactor is determined by its shape and dimensions, if it is equipped with
a single plasma source or an array, in a closed or open (e.g., in atmospheric pres-
sure) configuration. The wall temperature is also important. Various electrodes are
developed for special applications.
Concerning the substrate different types of reactors are possible. With fixed
substrate position or moving substrate across the plasma zone (in continuous opera-
tion) or also rotating substrate for improving the homogeneity. Important is also the
coupling of the substrate to the plasma [57]. A remote plasma source is a flowing
afterglow with a low concentration of charge carriers, where surface processes are
the result of long living radicals and energetic metastables. Plasma transport sources
