For extreme ultraviolet light source reflector contamination preventing method and an exposure apparatus

Reducing the pressure of the multilayer mirror 12 to the vacuum chamber 11 disposed, introduced during the EUV light on the multilayer film reflecting mirror 12 is irradiated, the organic gas in the gas and the like ethanol vacuum chamber 11. The partial pressure of organic gas is 1% to 200% of the pressure in the vacuum chamber prior to introduction of this gas. Alternatively, to measure the amount of the amount and water of the organic substance in the vacuum chamber 11 (steam) using a mass spectrometer 16, the amount of organic gas such that the amount of the organic matter of 0.1% to 3% of the amount of water vapor it may be adjusted. Thus, the surface of the multilayer mirror 12 by steam that remains to be prevented from being oxidized in the vacuum chamber 11, and carbon can be prevented from adhering to the surface of the multilayer mirror 12, thereby it is possible to prevent the lowering of reflectivity of the multilayer mirror 12. Similarly, already can be removed contamination by organic substances and oxide adhering to the multilayer mirror 12.