| 摘要 |
<p>PURPOSE:To detect the speed of rotation of a placing stage support pillar in a closed vessel in a state that the sealing performance of the closed vessel is held. CONSTITUTION:A placing stage 3 placed with a wafer 2 and a placing stage support pillar 4 bonded firmly to this placing stage 3 are respectively housed in a closed vessel 1. A magnetic fluid seal 6 couples a motor 7 with the pillar 4 in a noncontact state in a state that the sealing performance of the vessel 1 is held. A through hole 8 is perforated in the pillar 4 and a luminous flux from a light-emitting device 14 passes through the hole 8 via a window 14, transmits a window 12 and is made incicident to a photodetector 15. A detection output of the photodetector 15 shows the speed of rotation of the pillar 4. A control device 16 controls the speed of rotation of the motor 7 on the basis of the detection output so that the speed of rotation of the pillar 4 reaches a desired value.</p> |
