AVS 47th International Symposium
    Vacuum Technology Wednesday Sessions
       Session VT-WeP

Paper VT-WeP2
Development of the Quadrupole Mass Spectrometer with the Bessel-Box Type Energy Analyzer : Function of the Energy Analyzer in the Partial Pressure Measurements

Wednesday, October 4, 2000, 11:00 am, Room Exhibit Hall C & D

Session: Poster Session
Presenter: N. Takahashi, ULVAC Japan, Ltd.
Authors: N. Takahashi, ULVAC Japan, Ltd.
H. Akimichi, ULVAC Japan, Ltd.
T. Hayashi, ULVAC Japan, Ltd.
Y. Tuzi, ULVAC Corporation, Japan
Correspondent: Click to Email
We have obtained several advantages of the newly developed quadrupole mass spectrometer (QMS) with the Bessel-Box type energy analyzer for the accurate measurement of partial pressures in high to extreme high vacuum. The analyzer is placed between the ionizer and the quadrupole assembly of QMS. The gas phase ions and the electron stimulated desorption (ESD) ions generated in the ionizer are separated by the analyzer, because of the difference of kinetic energies between them. As the overlapping of the gas phase ions and ESD ions gives the complex mass spectra, the elimination of ESD ions by the energy analyzer improves the spectra to simpler ones. The accurate measurement of partial pressures was made use of the simple mass spectra of gas phase ions which were given by the new QMS. The sensitivity of new QMS for the very small amount of impurities in the atmosphere of relatively higher pressure was also improved down to 10ppb of the total pressure owing to the reduction of background signal. The background signal is much reduced by the geometrical structure of the energy analyzer which prevents the ion collector with secondary electron multiplier from the irradiations of vacuum ultraviolet rays and soft x-rays generated in the ionizer. The discrimination between the non-dissociative molecular ions and the fragment ions with same mass to charge ratio (m/z) is also the important factor for the accurate measurement of partial pressures. The energy spectra of those ions are determined by the mechanism of ion formation such as ionization process, fragmentation process, etc. Thus, the spectra of each m/z ions are expected to apply for the discrimination mentioned above.