Investigation of ion mass diagnostics for plasma processing
Hayden, Chanel (2009) Investigation of ion mass diagnostics for plasma processing. PhD thesis, Dublin City University.
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Plasma properties can be characterised with a multitude of diagnostic techniques which are as varied as the many industrial applications that employ
them, from etching microchips to surface treatment and cleaning. A particular manufacturing technique may require a certain plasma characteristic
at a given condition. In order to get the necessary properties, other characteristics must be fine tuned and monitored. In some cases there is an
offset in the degree of control and what can be measured accurately without disturbing the overall process, thus the ability to monitor and control
these parameters is crucial. Of these parameters, the plasma density, n0,
the electron temperature, Te, the ion bombarding energy, Ei, and the ion
current density, Ji, are the most important quantities for processing plasma
applications. Monitoring plasma parameters is often difficult due to poor
access or operating condition limitations and so there is an ever-increasing
need for improved techniques. Electrical properties of plasmas can be measured relatively easily over a broad range of conditions however ion mass on
the other hand is generally only measured using mass-spectrometry. A novel
electrostatic probe, arranged so that a cylindrical probe is oriented normal
to a planar probe with a retarding potential applied to the normal and a
dc pulse to the other is investigated with a view to inferring ion mass. A
Retarding Field Energy Analyser (RFEA) is used to investigate Ion Energy
Distributions (IED's) and to indicate the average ion mass in gas mixtures.
The goal of this thesis is to investigate methods for measuring mass and to
use this as feedback for process control.
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