Advanced turbomolecular pumps used to pump reactive and abrasive media

Abstract

This paper will give a review on problems encountered when using standard turbomolecular pumps for pumping corrosive or abrasive media. It is shown how turbomolecular pumps have been modified in order to meet the specific requirements of applications such as CVD and metallizing processes. The critical parts within the pump with respect to corrosive attack are described in detail. In some cases special fluids such as polyfluorinated polyethers have been used as lubricant for the turbomolecular pump with only little improvement in performance compared with unmodified pumps. The introduction of the purge gas method into the pump design has improved the reliability of the pump considerably. Corrosive gases can no more attack the ball bearings of this special turbomolecular pump while unmodified pumps are failing already after a few days operation. Reactive ion etching processes require an increasingly high throughput of the turbomolecular pump for extended periods. It is described how a turbomolecular pump has to be modified in order to provide optimum performance in the interesting pressure range of Knudsen flow and laminar flow. By modification of the geometry of the rotor/stator configuration the throughput of the pump in that pressure range is increased considerably. It is not necessary to use larger backing pumps compared with other applications. Performance data for several turbomolecular pumps in the pressure range between 10−4 and 10 mbar are given.