AVS 53rd International Symposium
    Vacuum Technology Tuesday Sessions
       Session VT-TuP

Paper VT-TuP14
The Small Quadrupole Mass Spectrometer for the Pressure Range Over 0.1Pa

Tuesday, November 14, 2006, 6:00 pm, Room 3rd Floor Lobby

Session: Vacuum Technology Poster Session
Presenter: Y. Matsumoto, ULVAC Inc. Japan
Authors: Y. Matsumoto, ULVAC Inc. Japan
K. Yamamuro, ULVAC Inc. Japan
N. Takahashi, ULVAC Inc. Japan
N. Mizutani, ULVAC Inc. Japan
T. Nakajima, ULVAC Inc. Japan
Correspondent: Click to Email
The quadrupole mass spectrometer (QMS) is usually used for the partial pressure measurement and the residual gas analysis of vacuum systems. However, the usual QMS, which quadrupole mass filter electrode length is about 100mm, is not available for partial pressure measurements over 10@super -2@Pa such as sputtering process etc., because of the sensitivity drop with pressure increase. This is caused by the loss of ions that arrive at an ion detector by ion-to-molecules scattering. The differential pumping system with a small orifice for gas introduction is usually used in such processes in order to maintain the pressure in the QMS less than its maximum operation pressure. But this system is relatively large and expensive. Another way to use the QMS in high pressure is down sizing of it. This presentation reports the development of the small QMS and its basic characteristics. The length and the field radius of the mass filter are 25mm and 1.8mm, respectively. The mass filter is operated with radio frequency of 7MHz. The filament and the grid of the ionizer is made of Y@sub 2@O@sub 3@ coated Ir wire and photo-etched Mo mesh, respectively. The ionizer includes an ion collector for the total pressure measurement. The ion detector for the partial pressure measurement is a Faraday cup type or a small secondary electron multiplier (SEM). The electron acceleration potential for ionization and electron emission current are 40V and 0.4mA, respectively. The sensitivity of this QMS for nitrogen was about 1x10@super -7@A/Pa with a Faraday cup type ion detector. The liner relation between ion current at mass-to-charge ratio of 28 and nitrogen pressure was obtained up to 0.1Pa. Proper correction of the sensitivity would make it possible to extend the operating pressure to 1Pa. The mass resolution, which is determined as peak width at 10% of the peak height, was less than 1 for all mass range from 1 to 50.