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MVT 94X Sputtering System
Operators Manual
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Auto-Regen

V1.02 — 04 Jan 07

One of the routine maintenance issues with cryo pumps is the occassional pump regeneration. Since cryo pumps are effectively molecular traps, the accumulated gasses need to be released from the pump for the pump to continue opimal operation. The Auto-Regen feature completely automates this tedious manual operation. The operator simply initiates the sequence and the rest of the operations continue automatically. The Auto-Regen process can take several hours, and is normally initiated at the end of a shift and left to run overnight. The system cannot sputter while Auto-Regen is in process.

Some systems only have chamber cryo pumps while others have both Load Lock and chamber cryo pumps. On dual pump systems only one pump can be regenerated at a time. This limitation is not normally a problem as the Load Lock cryo's tend to need regeration relatively frequently as compared to the chamber cryo pumps. This is because the Load Lock gets pumped down repeatedly while the chamber only has residual sputter gasses to contend with.

Prior to starting the Auto-Regen process certain conditions have to be met. These include:
  • Mech Pump on
  • Master Key in Enabled Position
  • PLC in Valve Master Override (indicated by the Cryo Power LED(s) blinking slowly)
  • Sufficient N2 Vent gas
Without these conditions, Auto-Regen will not start/operate.

Red Cryo power LED's Blink slowly in valve Master Override mode and then rapidly during Auto-Regen.
Auto-Regen can only be initiated from the rack mounted DMP (Diagnostic Maintenace Panel). It cannot be started from the VB GUI program on the PC. Having met the aforementioned preconditions, Auto-Regen is initiated by pressing and holding the GTG button and the momentarily pressing the appropriate Cryo Regen Close valve switch (presuming that you have a dual cryo system). Once the associated red Cryo Power LED starts rapidly blinking both switches can be released. The process will continue to completion automatically.

The cryo regeneration sequence follows the pump manufactures suggested procedure and the following actions will occur as the process runs:
  1. The cryo pump is stopped and the gate, rough, vent, and cryo regen valves are all closed.
  2. When the gate valve is confirmed closed, the N2 purge gas valve is opened.
  3. The N2 purge gas rapidly warms the cryo and continues to flow for a preset interval once the cryo high temp setpoint (ambient ~270° K) is met.
  4. Having acheived the temperature setpoint the N2 purge valve is closed and the regen valve is opened.
  5. The regen valve remains open until the cryo internal pressure drops below the convectron gauge lower setpoint (normally 30mT).
  6. The system then conducts a Rate Of Rise (ROR) test. The ROR test consists of closing the regen valve for a fixed interval (two minutes) and seeing if the upper setpoint (normally 50mT) is met. The ROR test will repeat up to a specified maximum number of times or until the ROR is under 10mT per minute. If the maximum number of retries is exceeded the system will generate an error #8 indicating regen failure. This will illuminate the ERROR LED on the DMP and the LED will blink the error code until acknowledged. Failure of the ROR test also aborts the Auto-Regen process. The operator should reset the PLC once the problem is corrected to insure continued proper operation.
  7. Having successfully passed the ROR test the cryo is again pumped down to until the lower convectron gauge setpoint is met for a specifed time and then it is pumped for an additional interval before the regen valve is closed and the pump contactor is energized.
  8. The cryo pump should start it's cool down process. If, during the cool down the upper convectron setpoint is met for a certain time, the regen valve will open to allow the mech pump to assist. Once the lower convectron setpoint is made, the regen valve will automatically close. This prevents backstreaming from the mech pump into the cryo.
  9. The system will wait until the cryo low temperature setpoint is met (typically 20° K) or until the maximum cool down time is exceeded (usually 3 hours). If the maximum cool down time is exceeded the system will generate an error #9 indicating regen failure. This will illuminate the ERROR LED on the DMP and the LED will blink the error code until acknowledged. Failure of the cool down also aborts the Auto-Regen process. The operator should reset the PLC once the problem is corrected to insure continued proper operation.


Cryo Temp and Convectron Gauges
Click for larger image
See: REGEN Routine Ladder Logic for complete details.

While the Auto-Regen process is running, a status screen will be displayed at the lower right of the normal program screen. This status screen has special indicators for the pump temperature and pressure setpoints and a graph area showing a histogram of the Rate of Rise (ROR) test.


The system is configured to automatically repeat the regeneration process until the specified ROR is met. In this case the ROR criteria is not to exceed 10mT per minute. For each iteration of the regen process the time for the system to rise from 30mT to 50mT is noted and plotted. When this time reaches or exceeds 120 seconds for a 20mT rise, the ROR criteria is met and the pump begins cool down. The cool down period has mechanical assist so that every time the pump internal pressure rises above 50mT for 10 seconds the mechanical pump is used to pull the pressure back down to under 30mT. Under normal operation the mechanical assist will only need to cycle a few times before the cyro 'catches' and begins cooling. Typically cool down occurs in one to two hours and if it does and error will be generated. As the cryo cools from the upper setpoint of 270° K to the lower setpoint of 20°K the time will increment in the Cool Down Time field.

The Auto-Regen screen will appear and disappear automatically as the regen process runs. No other processing can occur while the Auto-Regen process is running.
Fin



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