4883. Pumping of corrosive or hazardous gases with turbomolecular and oil-filled rotary vane backing pumps: K Fischer et al, J Vac Sci Technol, 18 (3), 1981, 1026–1029

Abstract

A novel high performance cryopumped throttling device, whose mechanism remains frost-free in operation is described. It consists of an ambient temperature louvre valve situated above a cryopump and heat sunk to the pump body. This is mounted in conjunction with cryopump panels which extend above the valve. The unit offers excellent pumping speeds for volatile contaminants (especially water vapour which is pumped at over 3700 I s−1), irrespective of valve position, whilst maintaining low consumption of process gases such as argon over the normal sputtering pressure range up to 10−2 mbar. Regeneration intervals are thus extended, but pumpdown times remain short due to the high conductance of the Iouvre valve/cryopanel combination, when the valve is fully open. The design process was aided by Monte Carlo techniques to maximize conductances, consistent with the sufficiently low radiant load to the second stage cryopanels necessary to provide an operating regime extending to high pressure. A description of modelling methods used and a comparison with alternative upstream and downstream approaches to throttling is also given.