Residual Gas Analyzer (RGA)

 

We have permanently installed a residual gas analyzer on our secondary ion source chamber. This small quadrupole mass spectrometer can measure the partial pressure of vacuum contaminants with a detection limit below e-13 Torr. The model which we have installed is:

 

• Balzers QMA 200 quadrupole mass spectrometer
• Tungsten Cathode with open ion source
• Faraday and Channeltron Detectors

Installation required the machining of a adapter with an elbow which replaces a blanking flange present on the chamber (adapter technical diagram in pdf format). This adapter was welded to a commercially purchased half tube which terminates with a DN40 CF (2.75 inch conflat) rotatable flange. The RGA housing seals directly onto this conflat flange. This configuration allows the ion source of the RGA to be located very close to the SIMS source chamber.

During a study of the dependence of our vacuum quality on pumping times and contents of our source chamber, we have collected the following three spectra. As expected, our primary vacuum contaminants were found to be water and hydrogen. The introduction of an epoxy bearing sample obviously introduces a large amount of water into our system, and this problem is only partially ameliorated by the use of the liquid nitrogen trap within the sample chamber.