AVS 47th International Symposium
    Vacuum Technology Thursday Sessions
       Session VT-ThA

Paper VT-ThA6
Performance of the Axial-symmetric Transmission Gauge Improved for the Measurement of Wide Pressure Range

Thursday, October 5, 2000, 3:40 pm, Room 201

Session: Pressure and Flow Measurements
Presenter: H. Akimichi, ULVAC Japan, Ltd.
Authors: H. Akimichi, ULVAC Japan, Ltd.
N. Takahashi, ULVAC Japan, Ltd.
T. Hayashi, ULVAC Japan, Ltd.
Y. Tuzi, ULVAC Japan, Ltd.
Correspondent: Click to Email
The axial-symmetric transmission gauge (AT gauge) is originally developed for the pressure measurement in extreme high vacuum . The Bessel-Box type energy analyzer is placed between the ionizer and the ion collector with a secondary electron multiplier (SEM). The analyzer prevents the SEM from the effects of soft x-rays and electron stimulated desorption (ESD) ions produced in the ionizer. The lower limit of the pressure measurement was estimated to be about 10 @super -12@ Pa. The higher limit, however, was restricted to about 10 @super -6@ Pa due to the limit of pulse resolution of the SEM. In order to expand the pressure measurement up to high vacuum range (~ 10 @super -2@ Pa), the SEM was replaced by a Faraday cup type ion collector. The sensitivity factors of the gauge calibrated by the Conductance Modulation Method through the pressure range of 10 @super -10@ to 10 @super -6@ Pa were (6.7 ± 0.2) x 10 @super -3@ Pa @super -1@ for nitrogen and (2.3 ± 0.04) x 10 @super -3@ Pa @super -1@ for hydrogen, respectively. Comparison of the AT gauge to the extractor gauge (EG) and the spinning rotor gauge also gave the sensitivity factor of (5.8 ± 0.1) x 10 @super -3@ Pa @super -1@ for nitrogen in the pressure range of 10 @super -8@ to 10 @super -2@ Pa. When oxygen was introduced into the system with an AT gauge and a conventional EG, the nominal pressure readings of the EG showed higher values than those of the AT gauge. The difference increased with the increment of oxygen pressure and exposure, and decreased to zero by the bake-out of the system during the pumping process. The results show that the ESD ions, originated from the oxygen adsorbed on the grid surface of ionizer, are effectively separated from the gas phase ions by the energy analyzer in AT gauge.