Patent Number: 
Section: claims

1. A target supply unit to be used in an extreme ultraviolet light source apparatus for generating extreme ultraviolet light by irradiating a target material with a laser beam to turn the target material into plasma, said target supply unit comprising:a target container configured to accommodate the target material;a target nozzle configured to inject the target material supplied from said target container;a reducing gas supply unit configured to supply a reducing gas into said target container;an exhaust pipe configured to exhaust a gas within said target container;a gas analysis unit configured to measure concentration of a reaction product of the reducing gas in said exhaust pipe to output a signal representing the concentration of the reaction product of the reducing gas; anda control unit configured to control said reducing as supply unit to stop supply of the reducing gas when the concentration of the reaction product of the reducing gas becomes not more than a predetermined value according to the signal outputted from said gas analysis unit. 2. The target supply unit according to claim 1, further comprising:a heater attached to said target container and electrically connected to said control unit. 3. The target supply unit according to claim 1, wherein said reducing gas contains at least one of hydrogen gas, hydrogen radical, and carbon monoxide gas. 4. The target supply unit according to claim 3, further comprising:a radicalizing unit configured to radicalize the hydrogen gas contained in said reducing gas. 5. The target supply unit according to claim 1, further comprising:a gasifying unit configured to gasify a reducing agent, which is in a liquid state at room temperature, to generate said reducing gas. 6. The target supply unit according to claim 5, wherein said reducing agent, which is in a liquid state at room temperature, contains an acid solution. 7. The target supply unit according to claim 1, further comprising:a pressurization gas supply unit configured to supply a pressurization gas for adjusting pressure within said target container and diluting said reducing gas. 8. The target supply unit according to claim 1, further comprising:a pressure container configured to accommodate the target material supplied from said target container,wherein said target nozzle injects the target material supplied from said target container via said pressure container. 9. The target supply unit according to claim 1, wherein said reducing gas supply unit includes at least one mass flow controller electrically connected to said control unit. 10. The target supply unit according to claim 1, further comprising:a heater provided to a pipe connected to said target container. 11. The target supply unit according to claim 1, further comprising:a temperature sensor provided to said target container. 12. The target supply unit according to claim 1, further comprising:a pressure sensor configured to measure pressure within said target container. 13. The target supply unit according to claim 1, wherein said gas analysis unit includes one of a dew-point meter and a Fourier transform infrared spectrophotometer. 14. The target supply unit according to claim 4, wherein said radicalizing unit includes one of a microwave plasma unit and a high-temperature heating unit using a filament. 15. The target supply unit according to claim 6, wherein said reducing agent contains one of formic acid, acetic acid, and hydrochloric acid.