INFICON MDC-360 Thin Film Deposition Controller - Manual (Page 92)

MDC-360 DEPOSITION CONTROLLER
6-4 Tuning the MDC-360 Control Loop
The following table lists some recommended PID values for different types of
ent a good starting point and in some
ed.
Suggested PID Starting Values for Different Sources
Parameter Electron
Beam Gun
Filament
Boat
Proportional gain 2000 600
Integral time constant,
sec.
99.9 99.9
Derivative time constant
sec.
25.0 75.0
In the MDC-360, the PID parameters are defined at the material level because
different materials often require different PID settings even though they may be
deposited from the same source. Therefore it is usually necessary to establish the
PID parameters for every each material and deposition source.
The first step in setting the PID parameters for a new material or source is to enter
the recommended starting values listed above. Be sure and choose the PID values
for the type of source you're using. Next, create a dummy process with the first
layer set for the new material. Start and abort the dummy process to load the new
material as the active material. You should now see the material's name in the top
line of any Status Screen. Next, open the shutter and put the 360 in the manual
power mode and adjust the source power using the remote handset to establish the
power ramp parameters. Set the Predeposit Power level at or slightly below the
power needed to get the desired deposition rate.
With the power ramp parameters defined, the next step is to start the dummy
process to see how well the 360 controls the rate. If the rate is too high or low
when the shutter opens then make a note to go back and adjust the Predeposit
Power level. Watch the rate graph and the power display. If the rate is different
from the target rate then you should see the 360 adjust the power attempting to
achieve the target rate. If the rate is close to the target, then you should
temporarily change the rate to see how the 360 reacts. Ideally the 360 will adjust
the power so that the rate goes right to the target rate without overshooting it. If it
does then no further adjustments are necessary.
If it seems like the 360 is reacting too slowly, press the Program key to get back
to the material screen and increase the Proportional Gain parameter. Begin with
changes of about 10 to 20%. Changes of this magnitude are a good starting point
because they are large enough to show the effect of the parameter and small
enough that you won't greatly overshoot the ideal setting. Remember that too
much Proportional Gain will make the system unstable and too little will make the
360 slow to react. An unstable system is evident by the rate oscillating around the
target value. A general rule of thumb is the faster the source, the larger the
Proportional Gain. And conversely, the slower the source the smaller the
Proportional Gain.
deposition sources. These values repres
cases may not need to be further modifi