IMPROVEMENT OF TURBOMOLECULAR PUMPS FOR ULTRACLEAN, LOW-PRESSURE, AND HIGH-GAS-FLOW PROCESSING

Turbomolecular pumps (TMP) have been widely used in low-pressure processing, because TMP can pump a large flow of gas as well as can exhaust the system to a suitable base pressure. A TMP, however, has the problem that its pumping speed is severely degraded at inlet pressures higher than ∼10 mTorr, where most of the low-pressure processing of semiconductor manufacturing is performed. In this study, it is confirmed that the occurrence of such a degradation in TMP performance is primarily determined by the inlet pressure of TMP and not by the outlet pressure. As the inlet pressure is increased to ∼10 mTorr, the gas flow in the front blades as well as the rear blades of the TMP goes into the transition flow, and TMP pumping speed consequently begins to decrease. Once the degradation occurs, however, the pumping speed is strongly dependent upon the pumping speed of the backing pumps, namely the foreline pressure. In order to improve the TMP performance under high gas flow, a characteristic dimension in the pum...