| 摘要 |
PURPOSE: A level keeping device is to maintain an optimum condition of overlay and focus upon exposing by reducing vibration from exterior and keeping high accuracy leveling. CONSTITUTION: A damper is arranged at four lower corners of a main body. A stage(13) moves a wafer in a step. A position detecting sensor(14) is provided at a periphery of the stage. The position detecting sensor supplies air to the body of the stage by an air pressure controller(15) and operates a linear motor(17) by a linear motor controller(16) to control vibration. An active damper actively controls a power of the linear motor and a pressure in an air tank. A pressure detecting sensor(20) is arranged within the active damper. The damper driven by supply of power exhibits high vibrating capacity against a floor vibration by actively controlling the power of the linear motor in the air tank. Amount of primarily supplied air is continuously and minutely adjusted depending on a value sensed by the pressure detecting sensor to reduce the vibration from exterior and to keep a highly accurate leveling.
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