| 摘要 |
PURPOSE:To enable early detection of dielectric breakdown of an electrostatic chuck and the foreseeing of its life, by detecting a current flowing through a light emitting diode owing to the dielectric breakdown of the electrostatic chuck by a detection circuit. CONSTITUTION:The photocouplers 13 and 14 of the photocouplers 11-14 lose their sensitivity by bypass resistors 15 and 16 to be used for the big current detection at the time of generating a big spark. That is, a park current of about some mA due to the dielectric breakdown of an electrostatic chuck is detected separately from a high tension circuit, using the photocoupler to operate an alarm circuit. Further, the number of times of the big sparks requiring the replacement of the electrostatic chuck and of the small sparks foreseeing a life of the electrostatic chuck can be detected by using two photocouplers having different sensitivities. |
