System Manual
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they begin to click again and change LK2 (corresponding to RV1) or LK102
(corresponding to RV101) to position ‘a’ and begin turning the potentiometers anti-
clockwise again until the oscillations stop.
15) Confirm the automatching behaviour, increasing the RF power to maximum in small
steps, repeating Steps 10 to 13 if necessary.
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WARNING
THE FOLLOWING ADJUSTMENT INVOLVES WORKING ON THE SYSTEM WITH
PANELS/COVERS REMOVED. IT SHOULD ONLY BE CARRIED OUT BY TRAINED
PERSONNEL WHO ARE AWARE OF THE HAZARDS INVOLVED.
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The
DC bias / Peak-to-peak
switch is located on the outer case of the AMU, adjacent to RV1
(null adjustment potentiometer). See Fig 1, page 3.
This switch selects one of two sensing output signals from the AMU:
DC bias:
This switch setting is the default position. The output is a SCALED dc
voltage proportional to the RF-induced self-bias on the electrode,
sometimes called the 'DC bias'. This is a negative offset voltage on the
electrode with respect to ground, which is inverted and conventionally
referred to as a positive value, typically 100 - 600 Vdc. Normal scaling can
read up to 1000 Vdc. This signal is read by the front-end software with
correct scaling on OIPT tools.
Peak-to-peak:
The output is an UNSCALED dc voltage related to the peak-to-peak value
of the RF signal at the output of the automatch. This can be useful when
the scaled dc bias is inaccessible, for example if the electrode has no dc
contact to the plasma because a quartz carrier plate masks the whole
electrode. The value displayed on the PC screen will be an arbitrary value,
not a true peak-to-peak value, but can still be a useful monitor.
Note that the software has no knowledge of the switch setting, and is scaled only for the dc
bias setting.
OIPT Automatch Unit
Printed: 16-Nov-07, 9:26
Page 13 of 20
Issue 6: September 05
Summary of Contents for OpAL
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