| 摘要 |
PURPOSE: A stepper is provided to purify a lens portion included in a stepper by installing a purification portion at an outside of the lens portion. CONSTITUTION: A purification portion(16) includes a plurality of branch line(16a,16b) and a connection line(16c). The plural branch lines(16a,16b) are branched to an outside of a lens portion(14) as well as an inside of the lens portion(14). The connection line(16c) is connected with the plural branch lines(16a,16b). The purification portion(16) provides a purge gas to the inside of the lens portion(14) and the outside of the lens portion(14) in order to purify the lens portion(14). The purification portion(16) can be connected with additional lines as well as the plural branch lines(16a,16b). A sensor is installed at the outside of the lens portion(14) in order to sense intensity of light passing the lens portion(14). A control portion receives a sensing signal from the sensor and controls the purification portion(16).
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