The present invention relates to a vacuum pump capable of evacuating gaseous body from the atmospheric pressure to a high-vacuum and relates more particularly to a vacuum pump suitable for making a clean vacuum in semiconductor manufacturing apparatus.
Sputter ion pumps, turbomolecular pumps, cryo pumps, etc. have been known as conventional types of vacuum pumps. Any type of these pumps requires a roughing pump or a backing pump in order to evacuate air from the atmospheric pressure to a high-vacuum and they necessitate complicated controllers and the like for controlling the operation of both pumps, thus enlarging the size of the system using vacuum and the installation space for accommodating the system.
One known type of pump for enabling evacuation to be carried out from the atmospheric pressure to a high-vacuum has been proposed in U.S. Pat. No. 3,969,039 wherein pump is bilaterally symmetrical and is provided, in the housing, with a turbomolecular pump stage, a spiral molecular drag pump stage, a centrifugal compressor stage and a vortex diode pump stage located one after another from the side of a suction opening to the side of exhaust opening.
The turbomolecular pump stage is composed of alternate combinations of fixed plates attached to an inner wall of the housing and rotating disc plates attached to the rotating shaft. The spiral molecular drag pump stage is composed of alternate combinations of fixed plates attached to an inner wall of the housing and impellers in the form of disc plates attached to the rotating shaft. The centrifugal compressor stage is composed of alternate combinations of fixed plates with a diffuser attached to an inner wall of the housing and impellers attached to the rotating shaft. The vortex diode pump stage is composed of alternate combinations of fixed disc plates attached to an inner wall of the housing and rotating disc plates attached to the rotating shaft.
The rotating shaft is driven through the medium of a turbine which is connected to air inlet and air outlet ports formed in a side wall of the housing.
A vacuum pump arranged as described above can effect satisfactory compressing work when it reaches a steady state, the pressure at the suction opening, that is, the ultimate pressure thereby being sufficiently lowered. However, at the initial stage of the operation of the pump, that is a transient condition, the ppmp does not work at a sufficient pumping speed. In such a transient condition, the turbomolecular pump stage and the spiral molecular drag pump stage which are effective for the molecular flow air or the transition flow air do not substantially effect the compressing work because of the high pressure in the pump. The flow passage of the spiral molecular pump stage has an especially small sectional area so as to have higher pressure ratio, thereby causing high pressure loss while at a high flow rate.
The object of the present invention is to provide a vacuum pump which is capable of evacuating air from the atmospheric pressure to a high vacuum so as to obtain a clean vacuum and which can work at a high pumping speed under a transient condition at the initial stage of the pump operation.
To this end, the present invention provides a pump comprising a housing having suction and exhaust openings, a rotating shaft rotatably supported in this housing, a plurality of fixed members attached to an inner wall of the housing, and a plurality of rotating members attached to the rotating shaft, the fixed members and the rotating members being alternately disposed so as to constitute pump stages in which a centrifugal compressor stage is constituted on the side of the suction opening and a circumferential flow pump stage is constituted on the side of the exhaust opening, with the rotating member of the centrifugal compressor stage being composed of an open-form impeller having a plurality of backward vanes. This pump is designed to work as a Siegbahn molecular pump in a steady state, and to work as a centrifugal compressor under a transient condition of the initial pump operation, thus obtaining a high pumping speed under the transient condition.