AGS - Service Notes
To help our Semi-Group/IPE/PME/1700 users, we provide quick service notes to give you important information about how to maximize uptime on your system.
Service Note No: 12
To: Maintenance staff
Subject: Leak Checking Process Gas lines
Problem: Whenever you have to change a gas bottle, install a new MFC, or suspect a process gas line may be leaking, you will need to verify the gas line is leak tight. The best way is to use a Helium leak checking unit. However, one may not be available.
Solution: You can use the pump-down method to verify, with a high degree of confidence, that a non-hazardous gas line is leak tight to approximately the 10-6 scale.
WARNING: This technique is only to be used by a technicians qualified to perform service tasks on the System 1000/1700 by A.G.Services. We do not advise that you attempt to service plasma systems unless you are qualified to do so. Finally, A.G.Services assumes no liability for the use of this procedure. It is presented only as guideline and for informational purposes only. If you need expert assistance to solve problems with your system, feel free to call A.G.Services.
Preventive maintenance: Check MFC zero weekly, Check bottle pressure every 2 weeks, Check MFC operation monthly
- Close the gas line supply valves for the gas lines you wish to check (either the valve on the gas bottle or any in-line valve that will close the far end of the line you wish to check). Make sure that there are no other outlets that are open (to other systems, etc.)
- Manually rough down the process chamber to at least 150mT. If you have a turbo pump on your system, use it for the remainder of the procedure. (on systems with separate turbo foreline and hivac valves, close the rough and open the foreline and hivac valves in that order).
- Once the system is pumped down, record the MFC readings and use this number as your zero flow reference. Next, open the gas line isolation valve(s) that you want to test.
- Enter the maximum setpoint for the MFC so that it will allow 100% of the residual gas to be pumped through the MFC.
- Wait. It can take between 5 minutes to 12 hours to pump all the residual gas out of a gas line. Observe the decrease in the chamber pressure, the MFC flow, and the source gas pressure gauge to monitor the progress of the pump-down. If the MFC reading falls to the zero reference reading that you took in step 3, your gas line is probably leak tight.
- To verify the quality of your gas line once you are satisfied with the pump down, record the MFC flow and the pressure gauge readings. Then, close the gas line isolation valve(s) that you want to check.
- Wait five minutes. Again, record the pressure gauge readings. Compare these with the readings from step 6. No change is indicative that there is not a significant leak present. This test is sometimes called a "rate-of-rise" test. If you wait for 12 hours before recording the change in gauge pressure you can be assured of a very accurate measure of the gas line integrity.
- Finally, record the MFC flow readings. Now, reopen the gas line isolation valve(s) that you want to test. If the MFC reading raises more than 5%, your gas line may be leaking. This is because an increased flow reading would tend to indicate that somehow a gas has entered into the pumped-out gas line: probably due to a leak. If the MFC flow reading does not increase you can assume that the gas line is leak tight.
- To end this procedure: Close off each gas isolation valve and reset the MFC setpoints to 0. Reset the gas bottle regulators and gas source valves to their normal positions. Vent the system or place it into standby as your requirements dictate.
Note: This method will not be usable if the MFC is not functioning correctly.
Expert Tips: Do not leave unused gas lines under vacuum. Small leaks are always present and if the line is not pressurized air and moisture will contaminate the line. We recommend cycle purging with dry N2 and leaving idle lines under pressure to prevent vacuum based contamination.
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Last update made on: 6 September, 2002 by Webmaster