High vacuum pumps according to Holweck principle for semiconductor production

Abstract

The production of semiconductors will require a pump system with a separate arrangement of forevacuum and high vacuum pumps. High vacuum pumps flanged to the process chamber should be very compact and should be able to deliver the compressed gas at forevacuum pressures above 10 mbar. This will permit the use of forevacuum lines of small diameters over long distances. This paper presents a pump which has two screw stages connected in-series, designed according to the Holweck principle, and a special inlet stage. This combination of stages offers not only a high pumping speed comparable to the classical turbomolecular pumps, but also a high compression ratio and a high forevacuum pressure similar to that provided by the screw-type hv pumps which were introduced in the past few years. Electrical heating of all the parts touched by the flow and the avoiding of edges and gaps decrease the deposition of particles. By applying a special coating the corrosion of aluminum parts can be prevented. The arrangement of a purge gas inlet between the second and the third stage reduces the backstreaming of oil while operating the pump at low flow rates or ultimate pressure, and enabling the pump to be cleaned with a strong nitrogen flow. The whole driving mechanism including the rotor, bearings and motor is a closed unit which can be easily disassembled while the purge gas supply is continued. This makes the cleaning and service of all parts in contact with the gas and with the particle flow very easy.