INFICON XTC/C Thin Film Deposition Controller - Manual (Page 118)

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XTC/C - XTC/2 Operating Manual
4.5.3 Setting Maximum Power
The MAX PWR parameter is generally used to ensure that no significant
damage can take place when a deposition source under rate control
experiences an unusual event. By placing a limit on the most power allowed to
be applied to the source, serious damage might be avoided if, for example,
material is depleted. Without this protection Rate Control would keep adding
power until the full 100% were applied. This is frequently catastrophic! It is
normal to set this parameter at a value that is 2-5% more than the normal power
required during deposition. Exceeding maximum power can result in a STOP or
Alarm condition; refer to
section 4.3 on page 4-9 .
4.6 Setting S&Q Parameters
(Soft Crystal Failures)
At some point during deposition the crystal may become unstable or erratic yet
continue to oscillate within the instrument’s acceptable frequency range of 6.0
MHz to 5.0 MHz. The resulting rate control will be poor and thickness
measurements may be inaccurate. By programming non-zero values for S
and/or Q, various improvements in process control can be achieved. The
instrument can be made to automatically switch to a different crystal and
continue the deposition normally, complete the run in the TIME-POWER mode
or even terminate the process whenever the programmed threshold of
instability is exceeded. As the Q and S factors are programmed to larger values
the level of instability tolerated prior to switching is lowered.