| 摘要 |
PURPOSE:To prevent fly-up phenomenon of dust in a vacuum chamber as well as adhesion of dust to a specimen by a method wherein an evacuating path and a leak path are constituted so that the evacuating pressure and the leak pressure thereof are capable of being switched in a plurality of steps. CONSTITUTION:A main evacuating pump system 5 and a preliminary evacuating pump system 7 are connected to a vacuum vessel 1. The leak path, connected with pressure regulating valves 12, 13, 14 having different set pressures in parallel, is connected to the vacuum vessel 1. In the case of evacuating, the evacuating is effected at first by the preliminary evacuating pump system 7 slowly, thereafter, the system is switched to the main evacuating pump system 5 to evacuate quickly when a vacuum has arrived at a predetermined vacuum pressure. On the other hand, the pressure regulating valve 12, provided with a lower leak pressure, is opened in the case of leak and the leaking is effected slowly at first, then, it is effected more quickly sequentially.
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