Gas exhaust pump system and gas exhaust method

A gas exhaust pump system having a main pump and a sub pump, the main pump comprising:

• a rotor;
• a rotating shaft fixed to the rotor or formed integrally with the rotor and rotatably engaging with a rotation driving unit so as to rotate the rotor;
• a holding unit configured to rotatably hold the rotating shaft;
• a lubricating oil supply path having an oil ejection port for supplying a lubricating oil to the holding unit at one end;
• a seal housing configured to cover a periphery of a portion that is not held by the holding unit of the rotating shaft, with a predetermined gap formed with an outer periphery of the rotating shaft;
• a seal member interposed between the rotating shaft and the seal housing all around the rotating shaft, for suppressing entry of the lubricating oil supplied to the holding unit into an exhaust system space in the main pump through the gap;
• a seal gas supply path having a supply port for supplying a seal gas to the gap;
• and
• a seal gas exhaust path having a seal gas suction port for exhausting the seal gas supplied to the gap from the gap to the outside of the main pump, wherein
• the sub pump is configured to reduce a pressure in the seal gas exhaust path, and
• at least one of the outer periphery of the rotating shaft and an inner periphery of the seal housing is provided with a film of perfluoro alkoxy alkane of the formula:
• where Rf is a perfluoro alkyl group and m and n are both positive integers.

A gas exhaust method using a gas exhaust pump system having a main pump and a sub pump, the main pump being in connection relation with a process chamber so as to reduce a pressure in the process chamber to a pressure equal to or less than atmospheric pressure and comprising:

• a screw rotor;
• a rotating shaft fixed to the screw rotor or formed integrally with the screw rotor and rotatably engaging with a rotation driving unit so as to rotate the screw rotor;
• a holding unit configured to rotatably hold the rotating shaft;
• a lubricating oil supply path having an oil ejection port for supplying a lubricating oil to the holding unit at one end;
• a seal housing configured to cover a periphery of a portion that is not held by the holding unit of the rotating shaft, with a predetermined gap formed with an outer periphery of the rotating shaft;
• a seal member interposed between the rotating shaft and the seal housing all around the rotating shaft, for suppressing entry of the lubricating oil supplied to the holding unit into an exhaust system space in the main pump through the gap;
• a seal gas supply path having a supply port for supplying a seal gas to the gap, upstream from the seal member;
• and
• a seal gas exhaust path having a seal gas suction port for exhausting the seal gas supplied to the gap from the gap to the outside of the main pump, downstream from the seal member, wherein
• the sub pump is in connection relation with the seal gas exhaust path so as to reduce a pressure in the seal gas exhaust path,
• at least one of the outer periphery of the rotating shaft and an inner periphery of the seal housing is provided with a film of perfluoro alkoxy alkane of the formula:
• where Rf is a perfluoro alkyl group and m and n are both positive integers, and
• the gas exhaust method comprises associating an exhaust operation of the main pump with a pressure reducing operation of the sub pump in operating the gas exhaust pump system.