INFICON XTC/C Thin Film Deposition Controller - Manual (Page 125)

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XTC/C - XTC/2 Operating Manual
4.9.3 Setting Idle Power Parameters
After a deposit has completed, it may be necessary to slowly reduce the
source’s power to zero or to some non-zero value. The IDLE RAMP parameter
defines the time spent in linearly tapering the power from the value at the end
of deposit to the IDLE PWR value.
4.10 Implementing RateWatcher
It is easy to set up to automatically sample the deposition rate periodically and
then maintain the proper source power level necessary to keep the Auto Control
Rate at the set point for extended periods of time. With inherently stable
deposition sources; such as the planar magnetron, an occasional check of the
rate (with the associated automatic recomputation of the necessary power
level) is all that is needed.
This "sample and hold" type of control can supersede the fully active type of
rate control that normally limits the utility of the crystal monitor for in-line or load
locked systems.
The RateWatcher feature requires a two parameter entry.
First, the Process Engineer must decide on the SAMPLE percent. This
parameter sets the accuracy that must be maintained over the 5 second
interval.
NOTE: The minimum accuracy range settings are internally limited to 0.5 Å/sec
difference between the setpoint and the just sampled rate. This avoids
unnecessary power changes.
Second, the HOLD TIME must be programmed. This is the length of time
between the completion of the last sample period (or the achievement of rate
control) and the initiation of the next sample period. The process engineer may
set the interval up to a maximum of 99:59 for automatic operation. If longer
intervals or periodic samples are needed SAMPLE INITIATE and SAMPLE
INHIBIT inputs are available on the SYSTEM I/O connector. During HOLD
periods, thickness is accumulated at the Auto Control Rate (DEP RATE) and
power is held at the internally computed Time-Power value. During SAMPLE
periods, the power will not be changed unless two consecutive samples fall out
of the specified accuracy range (1-99%).
Entering a HOLD TIME of 00:00 disables the RateWatcher feature.
NOTE: The RateWatcher function is disabled if the sensor type is configured
for a Dual or CrystalSix sensor head. See section 4.15.1 on page 4-25 .