Pulsed rf Discharges
Chemically reactive plasmas are widely used in modification of the surface
properties of materials. It is important for these technological
applications to have good control over the plasma behaviour, in particular
the flux of ions and radical species to the substrate; the ion impact
energy and angular distribution; and the electron temperature. Improved
control over some of these parameters has been obtained in low
pressure rf plasmas by turning the source voltage on and off, with pulse
lengths of the order of micro to milliseconds, which is much longer than
rf period. Pulsed rf plasmas have been used to achieve improved conditions
for processing in
both etching of semiconductors and deposition of thin films
[1-3]. However, at
the present time, the mechanisms behind this
improvement are still not well understood. In particular the temporal
behaviour of the plasma during the breakdown phase, including sheath creation
and the development of ion and electron distributions, require more
detailed study.
Pulsed plasmas are also important for studying the fundamental
physical processes taking place during non-equilibrium discharge conditions,
such as breakdown. At SP3 studies have been made of plasma
breakdown, using experimental measurements of a pulsed plasma
together with simulation results, to shed light on the evolution of
the bias voltage in asymmetric reactor geometry (see
"Charging of the blocking capacitor in an asymmetric discharge" ).
The effect of applying multiple pulses is discussed in the paper
"Pulsing a
low pressure rf plasma" .
Simulations have also
been used to study processes such as breakdown
("Simulation of plasma breakdown
in a low pressure rf plasma" ) and the multipactor effect, which up
until now have only recieved theoretical treatment [4].
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References
- R.W. Boswell, and D. Henry, Appl. Phys. Lett. 47,1095 (1985)
- L. J. Overzet, J. T. Verdeyen, and J. Beberman,
J. Appl. Phys. 66, 1622 (1989).
- Y. Watanabe, M. Shiratani, Y. Kubo, I. Ogowa, and S. Ogi,
Appl. Phys. Lett. 53, 1263 (1988).
- D. Vender, H.B. Smith, and R.W. Boswell, J. Appl.
80,4292 (1996).