VALIDITY OF MASS-SPECTROMETRIC MEASUREMENTS AT PRESSURES EXCEEDING 10-4 MBAR

In modern thin-film processes the working pressures often exceed the high or ultrahigh vacuum range. For sputtering, ion plating, etc. , pressures go up to the 10** minus **2 mbar region. The knowledge of impurities and reaction products is of importance. With differentially pumped mass spectrometers the question arises whether all information can be retained. Comparative measurements have been performed with a quadrupole mass spectrometer pumped differentially in two alternative ways: (1) The whole QMS is pumped differentially but with the ion source arranged favorably with respect to the sample gas flow. (2) A special high-pressure ion source is directly exposed to the process environment and only the rod system is pumped differentially. Results are given. Advantages and drawbacks of the two systems will be discussed.