EXHAUST SYSTEM FOR PARTICLE BEAM DEVICE

PURPOSE:To enable stable operation of an exhaust system to be maintained by judging whether current changes during a short time are caused by electric discharge occuring within the pump or a practical decrease in the vacuum degree and causing the exhaust system not to operated for pulse-like changes. CONSTITUTION:In a field-discharge-type scanning electron microscope, an electron gun 1 and lens system 4a and 4b are exhausted by ion pumps 11-13 before the vacuum degrees of the electron gun 1 and the lens systems 4a and 4b are determined by discharge currents during the exhaustion. At the same time, a sample chamber 5 is exhausted by a cryo-pump 14 and the vacuum degree of the chamber 5 is measured by a vacuum meter 17. In order to prevent a high-voltage power supply 32, lens power supplies 33 and 34 and a detection-circuit power supply 35 from being influenced by a puls- like signal, the power supplies 32, 33, 34 and 35 are driven after whether each measured signal is pulse signal of short duration or not is determined by entering the signal in a safety circuit 31. The water supply suspention of the pump 14 is protected by a protection circuit 28 and instantaneous service interruption is protected by a protective circuit 29. Owing to the above constitution, it is possible to increase the reliability of a particle ray device by constantly operating it stably by totally protecting changes caused during a short time.