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The Quadrupole mass spectrometer (QMS) equipped with a differential pumping system (DPS) has been used as a useful tool for partial pressure measurements over 0.01Pa in sputtering process etc,. The system including the orifice restricts the gas flow into the QMS chamber. The pressure in the QMS chamber is kept low enough to measure partial pressures by the QMS. However, there are some problems in the system configuration such as indirect measurements, large installation space and high cost. We have developed the small QMS for measurements of partial pressures and total pressures up to 1Pa without DPS. This paper reports the characteristics of the QMS: the pressure dependence of sensitivity, the minimum detectable partial pressure (MDPP) and the stability. The quadrupole electrodes (mass filter) are downsized for partial measurements over 0.01Pa. The length and field radius of the mass filter are 25mm and 1.8mm, respectively. The B-A type ionizer consists of the Y2O3 coated Ir wire filament, the photo-etched Mo mesh grid and the photo-etched Mo mesh ion collector for total pressure measurements. The ion detector for partial pressure measurements can be selected from two devices, a small secondary multiplier (SEM) and a Faraday cup type ion detector (FC). The acceleration voltage of electrons for ionizations was 40V. The acceleration voltage of ions to the mass filter was 10V. A radio frequency of 7MHz was applied to the mass filter. The mass resolution determined as a peak width at 10% peak height was less than 1 in all the range of the QMS, m/z = 1-50. The sensitivity and the MDPP for Ar with the SEM were 1.4×10-3A/Pa and 9.5×10-11Pa,respectively. The voltage applied to the SEM was -1.5kV. The MDPP for Ar with the FC was 4.6×10-8Pa. The sensitivity for Ar with the FC was 2.7×10-7A/Pa and was almost constant below 0.1Pa. The proper correction of the sensitivity enabled to extend the pressure range of the measurements up to 1Pa. The repeatability of the sensitivity at 0.05Pa was within 1% in 1 hour. |