Advanced Energy Industries RFX 600 Manuel de l'utilisateur - Page 16
Parcourez en ligne ou téléchargez le pdf Manuel de l'utilisateur pour {nom_de_la_catégorie} Advanced Energy Industries RFX 600. Advanced Energy Industries RFX 600 20 pages. Advanced energy generator
Imprimer la page
Dc
Bias
"Dc bias" refers to the dc component of the RF power that is
developed between the cathode and the anode of a typical RF
plasma vacuum system. This dc component is blocked from the
RF generator by the capacitors that are used in the
impedance-matching networks.
Thedc potential is a controllable parameter. It is also a
valuable indicator that changes in response to changes in
other process parameters. Some of the parameters that affect
dc bias are molecular densities and ratios of process gases,
cathode/anode surface area ratios, pressure regimes and
stability, and RF power densities. While some of these
parameters are controllable, others are fixed and so must be
worked around.
The amount of dc bias that is developed within a process
system depends upon the system design or the process being
run. Although a systems manufacturer can use modeling or
empirical data to predict the dc bias that should be expected
with a specific system or process, a power supply
manufacturer cannot.
In any case, you can determine dc bias by measuring it
yourself with a high-voltage probe.
DANGER!
Lethal high-voltage and high-current potentials
are present during the measurement of dc bias.
Extreme caution is required to ensure the
safety of yourself and of those working with
you. Carelessness can cause severe burns,
paralysis, or instant death.
Measure dc bias at the RF feedthrough. The farther the probe
is from the feedthrough, the less accurate the measurement.
This is because dc bias decreases with distance from the
feedthrough due to electrical loss. A convenient point for
taking this measurement is inside the impedance- matChing
network, at the output of the series capacitor.
Dc bias can be regulated in two ways, the choice of which
depends upon the process or application. The mutually
exclusive choices result in either maximum range or maximum
resolution.
If you choose maximum range, run the RF generator at maximum
power when you measure dc bias. In the more advanced,
microprocessor- controlled RF generators, a normalization
(calibration) function makes it possible to tailor the
17
~.'