INFICON XTC/C Thin Film Deposition Controller User Manual
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XTC/C - XTC/2 Operating Manual
accumulator does not retain its values, but rather, builds up when the rate
deviation exceeds its set tolerance and counts down to zero when the rate
deviation is within its programmed tolerance band.
The S accumulator shows the total magnitude of only the positive frequency
shifts (in Hz) from the moment the start button is pushed until that film is
completed and the next film layer is started. When the S value exceeds the set
point, the crystal is disabled. Unlike the Q accumulator, the S values are
retained and added to the accumulator whenever the positive frequency shift is
greater than 25 Hz. Table 4.4 shows the accumulated frequency shift required
to trigger the switch.
One problem is E-B gun arcing. If the S value constantly increments during arcs
it usually indicates poor grounding and the S factor should be disabled until this
problem is corrected.
Improved rate and thickness information results from programming non-zero
values for Q and S. The trade off is between improved process control and
lower crystal utilization. By observing the behavior on the operating display a
determination can be made, after several runs, whether or not the programmed
values provide a desirable compromise.
INFICON’s laboratory experiments have shown the following values to be
useful and they can serve as general guidelines.
If the process/crystal behavior is unknown and you want to employ the Q and
S factors, start with S = Q = 5 and watch their behavior on the display by
pressing the LIFE switch. Monitor and fine tune these parameters until the
desired level of rate control is ensured.
Often during process setup, the initial settings of the Q factor may soft fail the
crystal sensor. This can be caused by process delays in getting the system
under control (i.e., slow response sources or SOAK2 power levels poorly set).
The crystal sensor’s state of soft failure can be cleared or reset by changing or
re-entering the value of the Q or S factor parameter.
Table 4-5 Representative S and Q Factor Values
SOURCE
MATERIAL
S-FACTOR
Q-FACTOR
2" E-B gun w/liner
Cu
7
7
2" E-B gun
Cu
5
7
1-1/8" E-B gun
Al
4
4
1-1/8" E-B gun
Ni
4
3
Integral W-Al
2
O
3
Cu
6
7