| 摘要 |
PURPOSE:To prevent faults due to back diffusion phenomenon of oil vapor, by performing treatment in a treatment chamber, which is evacuated into a vacuum state by an oil free vacuum pump. CONSTITUTION:An inner chamber in a process tube 1 forms a treatment chamber 2. An exhausting port 12 is provided at another end of the process tube 1. An evacuating device 13 is connected to the exhausting port 12. An oil free vacuum pump 14 is connected to the evacuating device 13. In the vacuum pump, a centrifugal compressor pump stage 23, which is provided on the side of air inlet port, serves the two roles of a centrifugal compressor in the excessive state and a siegbahn molecular drag pump under the steady state. Therefore, the pressure at the exhaust port is kept in the vicinity of atmospheric pressure, and a large exhausting speed is obtained at the transient state of the initial period of the pump operation. Since a sucking medium such as oil and mercury is not used in the vacuum pump, the clean vacuum state can be provided. Thus the back diffusion phenomenon of oil vapor into the treatment chamber can be prevented.
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