INFICON STC-2000A Thin Film Deposition Controller Operating Manual - Manual (Page 115)

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STC-2000A DEPOSITION CONTROLLER
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SECTION 3.17 STC-2000A Crystal Failure Processing
The STC-2000A instrument gives the user many options in the event of a crystal or sensor failure.
This failure may be a hard sensor failure or caused by tripping over the crystal stability(S) or the control
loop quality(Q) thresholds. Improper setting of the S & Q film parameters may trigger an apparent early
sensor failure. It is possible to switch to other sensors and/or continue operation in a time power fashion,
or abort the process. These options are available on a per film basis and are programmable in each film
parameter list. The REVIEW SS MAP menu parameters specify starting crystal[s], backup crystal[s], active
crystal[s], channel [1-2] start mode, channel [1-2] fail action and channel [1-2] backup list. The specific ss
map that defines these parameters is called out by a Film parameter, thus providing the linkage between the
film and its associated ss map. In addition to being physically installed, the utilized source sensor cards
must be enabled on the SYSTEM CONFIGURATION menu (set to ON) before its sensors can be used as
an option in a film program. This is a global system enable and indicates that proper hardware is installed
on the system.
Measurement Fail Parameter
Time Power Mode
The SS Map parameter, Channel [1-2] Fail Action, can provide no action or abort film. The Film
parameter, Film Fail Mode, determines what the instrument will do when all crystal processing options
have been exhausted and there is still no valid sensor data available for processing. The options are 1: to
abort the run or 2: to complete the run in a Time Power Mode. If option 1 is selected, the unit will stop with
the last valid thickness showing on the display and the control power will be set to zero. If option 2 is
selected, the unit will continue to run using the average deposition power for the 5 second period previous
to the sensor failure, and will simulate the continued accumulation of material on the sensor using the
present rate setpoint value. Simulated accumulation will continue until the final thickness setpoint is
reached. The unit will then do the post deposition sequence as programmed and indicate to the user that a
time power completion was achieved.
Using Crystal Switching
If a crystal sensor has been provided with a backup capability by menu programming with the
Film and Map parameters, a sensor failure on the primary sensor will cause a switch to a backup sensor.
Each crystal in succession that fails can have a backup or follow processing as programmed otherwise.
Crystal Switching Function Description
The crystal switching function within the STC-2000A allows for either manual or automatic
switching from one sensor crystal to an alternate sensor crystal. This switch over is done without
introducing rate control transients into the system and also will maintain all valid thickness information
accumulated. The availability of this function can provide an extra measure of safety in insuring proper
deposition completion if the primary sensing crystal should fail or become erratic for some reason.
Crystal Stability Terms
Crystal
failures can be of three types. During a hard failure the crystal just stops oscillating. The
other modes of failure are types of erratic operation. When sensor crystals begin to approach the end of
their useful life, they begin to exhibit small positive frequency jumps. These positive jumps can cause
large instantaneous rate error signals to be seen by the control loop. The loop tries to correct for these
false signals and significant short-term rate control errors may occur. These positive frequency jumps also
cause an apparent loss of accumulated thickness on the sensor. Therefore, the final thickness setpoint may
be reached with more material deposited on the substrates than desired. By internally monitoring these
frequency jumps along with the control loop deviation from the desired control value, an automatic switch
over to a new or fresh sensor crystal can be made to occur. This is done by placing setpoint limits on
sustained control deviation error and the number and magnitude of positive frequency jumps allowed.
SECTION 3.XX page 115 of 292