INFICON XTC/C Thin Film Deposition Controller - Manual (Page 126)

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XTC/C - XTC/2 Operating Manual
4.11 Crystal Fail
Whenever the ModeLock measurement system is unable to effectively identify
and drive a monitor crystal, a special set of sweep and find instructions are
executed. This sequence takes up to five seconds as it is repeated a number of
times. This sequence of events is depicted in the "Measurement and Control
Processing Loop" flow chart,
Figure 4-5 on page 4-5 .
If the measurement system is unable to recover, the message XTAL FAIL is
displayed. The action next taken by the instrument is dependent on the value
of the TIME-POWER parameter as described in
section 4.12 on page 4-22 .
Sometimes a monitor crystal will spontaneously recover if its temperature is
reduced or sufficient time passes and the stress induced by the coating is
naturally relieved. Even with the XTAL FAIL message displayed the
measurement system will continue to attempt to find the fundamental resonant
mode’s frequency. This message will disappear when the crystal recovers or is
replaced.
Additional information on crystal failures is presented in section 6.3.2 on page
6-4 . The ModeLock oscillator is more fully explained in section 5.5.5 on page
5-9 and section 5.5.6 on page 5-11 .
4.12 Completing on TIME-POWER
When used as a controller this instrument has the ability to complete a
deposition normally if a crystal fails during the deposit phase. Depending on the
setting of the TIME-PWR parameter, the unit will either complete on
TIME-POWER (Y), or STOP (N) on crystal fail. When set up to complete on
TIME-POWER and a crystal fail is encountered the instrument will establish an
average power-based on the values output to the source prior to the crystal
failure. This average power is used while thickness is accumulated at the DEP
RATE. The deposition will terminate normally. The thickness accuracy will
depend on the duration of the TIME-POWER phase. A shorter duration of
TIME-POWER will increase the Final Thickness accuracy; longer durations will
decrease accuracy. This feature has no utility when used in a monitor only
situation.