AVS 51st International Symposium
    Vacuum Technology Wednesday Sessions
       Session VT-WeA

Paper VT-WeA9
Ultra-sensitive Leak Detection during UHV Evacuation by QMS under Accumulate Mode

Wednesday, November 17, 2004, 4:40 pm, Room 303D

Session: Vacuum Measurement, Sensors and Control
Presenter: T. Huang, Tsinghua University, China
Authors: X. Chen, Tsinghua University, China
L. Wang, Tsinghua University, China
T. Huang, Tsinghua University, China
Q. Jin, Tsinghua University, China
L. Cha, Tsinghua University, China
Correspondent: Click to Email
Tightness is extremely important to guarantee the longevity of the sealed vacuum devices with smaller volume, especially if it has to maintain high vacuum or even ultra high vacuum (UHV). As the structure of such minimized UHV devices is developed to be more complicated, it becomes a serious challenge to the leak detection technology. According to the basic concepts of the modern leak detection engineering, each part of the device and their whole assembly should be passed leak detection strictly before UHV evacuation. However, the long term baking during the UHV evacuation may cause formerly plugged mini leakage reopen or produce some new mini leakages. In order to improve the tightness reliability of such devices, it is necessary to carry out ultra-sensitive leak detection during the UHV evacuation, especially just before the device be sealed off from the vacuum system. The quadrupole mass spectrometer (QMS) in the UHV evacuation system can be used under accumulate mode to solve this problem. After the long term baking, the UHV will be achieved and the background will be very low if there are no large leaks. Under such condition, the leak detection sensitivity of QMS is high enough to detect small leaks. By closing the all-metal valve in front of the tested device to accumulate helium for a period, a peak can be observed by QMS when the valve reopen if there are mini leakages. The ultra-sensitive leak detection can be achieved by this way. It is found that the open action of the metal valve always severely affects the height of the peak indicated by QMS to bring considerable errors. If denote the mini leakage by the peak area instead of the peak height, the situation will be much improved. It has been proven that this method is quite useful to ensure the tightness quality for the complex sealed UHV devices with small and mini volume.