AVS 45th International Symposium
    Partial Pressure Measurements and Process Control Topical Conference Thursday Sessions
       Session PC-ThA

Paper PC-ThA6
Residual Gas Analyzer Ion Current Measurement, Calibration and Partial Pressure Detection Limits

Thursday, November 5, 1998, 3:40 pm, Room 317

Session: RGA Characteristics and Calibration
Presenter: R.E. Ellefson, Leybold Inficon, Inc.
Authors: R.E. Ellefson, Leybold Inficon, Inc.
A.J. Kubis, Leybold Inficon, Inc.
L.C. Frees, Leybold Inficon, Inc.
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Ion detection in a residual gas analyzer (RGA) is by faraday detector with electrometer and/or a secondary electron multiplier detector that use the same or separate electrometer. The minimum detectable partial pressure (MDPP) measured by these detectors is a ratio of noise(A) of the detection system to the sensitivity(A/Torr) of the RGA for each detector type. Critical to the statement of MDPP is the inclusion of the integration (dwell) time interval used to determine the noise value. Usually the MDPP reported is the longest integration time period of the RGA which produces the lowest number. However, the user normally uses integration times of the order of 0.25 s or less to rapidly get data for timely observation of the process. In this paper we present a model for predicting MDPP as a function of integration times from 8 ms to 4 s based on detector noise and ion statistics. Separately we present ion current measurements of the @super 36@Ar and @super 38@Ar minor isotopes of argon as a function of pressure to demonstrate practical detection limits of a RGA as a function of integration time. Additionally, we present data from the systematic dilution of standard gas mixtures and from a fixed composition flow standard that validate the low ppm detection limits for impurities in Ar.