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David J. Hilton, Busch Semiconductor Vacuum Group, Morgan Hill, CA, USA

ABSTRACT

In times past, semiconductor vacuum processing was typically done with “oilsealed” wet rotary vane, or rotary piston-type vacuum pumps. Variations of the actual operation of these types of pumps were not so great that substitution from one manufacturer to the next was not difficult. With today’s modern dry vacuum pumps, this is no longer the case. Over the past decade or so, there have been several different types of these dry vacuum pumps, designed and manufactured, which have very striking differences in mechanical design. Within 300mm processing, these differences create a unique situation of having each pump design affecting the long-term operational conditions, and throughput capability. Variations in the type of design have been commonly placed into two categories, multi-stage compression, and single-stage screw. Within each of these categories there are variations as well. Each of these variations has unique qualities that create different positives and negatives with regard to supporting 300mm processes along with cost of ownership impacts. Within the semiconductor industry there appears to be a lack of understanding of each of these types, and what their physical differences can amount to in operational reliability and cost. The purpose of this article is to give some further insight as to the operational differences within the dry vacuum pump designs and allow the industry decision makers to make more informed choices when it comes to selecting vacuum pumps for given processes conditions. Of the types described above, the rotary lobe, rotary claw, as well as the roots claw combination, are all considered multi-stage compression pumps. This definition is termed so because of their having multiple pumping stages in which compression of the pumped gas occurs. Even though all of the described vacuum pump designs have similar methods of creating vacuum, through positive displacement, subtle differences cause changes in the mechanical tolerances, as well as temperature and pressure profiles within each stage, which can create variable issues with regard to process effluent buildups and gas-load support.