PURPOSE: To prevent the attachment of reaction products in a gas to be evacuated to the inside of a housing by making flow a gas to prevent the attachment of foreign matters other than the gas to be evacuated, to an oil-free pump.
CONSTITUTION: This vacuum evacuation device has an oil-free pump, which furnishes a housing 21 with a suction port 21A and an exhaust port 21B, a rotary shaft 22 held inside the housing 21 through a bearing 25, and centrifugal compression pump steps 23 and circumferential flow compression pump steps 24 arranged in order in the housing 21. In this case, a feeding passage 41 to feed nitrogen gas as a preventive gas of foreign matter attachment is connected to the suction port 21A, while the feeding passage 41 is connected to a nitrogen gas feeding source 42. Moreover, on the way of the feeding passage 41, a gas heater 43 to preheat the nitrogen gas is furnished. In such a composition, nitrogen gas is fed to the inside of the housing 21, and reaction products in the exhaust gas is prevented from attaching to the inner wall of the housing.
UEYAMA KEIJI
FUJIWARA KAZUAKI
KOBAYASHI KAICHIRO
HITACHI TOKYO ELECTRONICS