AVS 60th International Symposium and Exhibition
    Vacuum Technology Tuesday Sessions
       Session VT-TuP

Paper VT-TuP8
Measurement of Low Outgassing Rates using Quadrupole Mass Spectrometers

Tuesday, October 29, 2013, 6:00 pm, Room Hall B

Session: Vacuum Technology Poster Session and Student-Built Vacuum System Poster Competition
Presenter: D.L. Seymour, Hiden Analytical
Authors: D.L. Seymour, Hiden Analytical
S. Davies, Hiden Analytical
J.A. Rees, Hiden Analytical
Correspondent: Click to Email
Measurements of the total outgassing rates of UHV chambers are often limited to around 1x10E-13 Torr-litres per sec by the outgassing rates of the vacuum gauges used to monitor the behaviour of the vacuum chamber and by possible thermal desorption caused by heating of the chamber walls by the gauges. The use of quadrupole mass spectrometer instruments to monitor the outgassing of vacuum chambers, including those used in plasma processing systems, is of interest both because the minimum measureable outgassing rate may be lower and because the mass spectrometer data provides partial outgassing rates for individual gas components. This more detailed description of the outgassing process gives a better historical record of the behaviour of a particular system, and can readily follow, for example, changes from outgassing dominated by water vapour to a regime where the dominant outgassing gas is hydrogen. Increased sophistication may be added to the mass spectrometric measurements by adopting threshold ionisation techniques in which the use of electron energies well below those normally employed in QMS instruments can be used to distinguish between gases , such as nitrogen and carbon monoxide, that have nominally the same mass peak at m/q =28. New measurements carried out using a high sensitivity instrument are reported which illustrate the power of such procedures and, in particular, help resolve outstanding problems such as the identity and origins of the mass peak at m/q =19 in RGA data for UHV systems.