Patent Number: 
Section: claims

1. An extreme ultraviolet light generation apparatus used in combination with a laser system, the apparatus comprising:a chamber provided with at least one inlet port and configured for introducing a laser beam outputted from the laser system into the chamber;a target supply unit provided to the chamber and configured for supplying a target material to a predetermined region inside the chamber, where the target material is irradiated with the laser beam;a gas introduction unit configured for introducing an etching gas including hydrogen gas into the chamber;a pressure detector configured for detecting pressure inside the chamber;a mass flow controller configured for controlling a flow rate of the etching gas;an exhaust unit configured for discharging gas inside the chamber, anda controller configured for controlling at least one of the mass flow controller and the exhaust unit based on a value detected by the pressure detector. 2. The apparatus of claim 1, wherein the pressure inside the chamber is approximately at or above 0.5 Pa and is approximately at or below 13 Pa. 3. The new apparatus according to claim 2, further comprising:a magnetic field generation unit configured for generating a magnetic field around the predetermined region; andan ion collection unit disposed in a direction of a line of magnetic force of the magnetic field and configured for collecting an ion which is generated when the target material is irradiated with the laser beam and flows along the line of magnetic force. 4. The apparatus of claim 3, further comprising:a magnetic field intensity controller configured for controlling intensity of the magnetic field;a power source configured for supplying current to the magnetic field generation unit; andan ion sensor disposed close to the at least one optical element and configured for detecting an ion. 5. The apparatus of claim 3, wherein the magnetic flux density of the magnetic field is approximately at or above 0.35 tesla and is approximately at or below 2 tesla. 6. The apparatus of claim 3, further comprisingis a collector mirror configured for collecting extreme ultraviolet light emitted as the target material is irradiated with the laser beam inside the chamber. 7. The apparatus of claim 6, wherein:the magnetic field generation unit includes a coil to which current is supplied and a magnetic core which extends toward the predetermined region from the coil, anda part of the magnetic core extends into an obscuration region of the extreme ultraviolet light collected by the collector mirror. 8. The apparatus of claim 7, whereina coating film is formed on a surface of the magnetic core. 9. The apparatus of claim 7, wherein:the magnetic core is cylindrical with one end thereof being open, andthe ion collection unit is disposed at the other end of the magnetic core. 10. The apparatus of claim 9, wherein a coating film is formed on a surface of the ion collection unit. 11. An extreme ultraviolet light generation apparatus used in combination with a laser system, the apparatus comprising:a chamber provided with at least one inlet port and configured for introducing a laser beam outputted from the laser system into the chamber;a target supply unit provided to the chamber and configured for supplying a target material to a predetermined region inside the chamber, where the target material is irradiated with the laser beam;a gas introduction unit configured for introducing an etching gas mending hydrogen gas into the chamber;a pressure detector configured for detecting pressure inside the chamber;a mass flow controller configured for controlling a flow rate of the etching gas;an exhaust unit configured for discharging gas inside the chamber;a controller configured for controlling at least one of the mass flow controller and the exhaust unit based on a value detected by the pressure detector;a magnetic field generation unit configured for generating a magnetic field around the predetermined region; andan ion collection unit disposed in a direction of a line of magnetic force of the magnetic field and configured for collecting an ion which is generated when the target material is irradiated with the laser beam and flows along the line of magnetic force. 12. The apparatus of claim 11, further comprisinga free radical source configured for turning the etching gas into a free radical. 13. The apparatus of claim 12, whereinthe pressure inside the chamber is approximately at or above 0.5 Pa and is approximately at or below 13 pa.