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 for introducing a laser beam outputted from the laser system into the chamber;a target supply unit provided to the chamber for supplying a target material to a predetermined region inside the chamber, where the target material is irradiated with the laser beam;at least one optical element disposed inside the chamber;a magnetic field generation unit for generating a magnetic field around the predetermined region;an ion collection unit disposed in a direction of a line of magnetic force of the magnetic field for collection an ion which is generated when the target material is irradiated with the laser beam and flows along the line of magnetic force; anda gas introduction unit for introducing an etching gas into the chamber. 2. The extreme ultraviolet light generation apparatus of claim 1, further comprising:a pressure detector for detecting pressure inside the chamber;a mass flow meter for detecting a flow rate of the etching gas;a gas flow controller for controlling the flow rate of the etching gas such that a value detected by the mass flow meter is a value at which a desired etching rate is achieved;an exhaust unit for discharging gas inside the chamber; andan ion sensor disposed close to the at least one optical element for detecting an ion. 3. The extreme ultraviolet light generation apparatus of claim 2, wherein the pressure inside the chamber is approximately at or above 0.5 Pa and is approximately at or below 13 Pa. 4. The extreme ultraviolet light generation apparatus of claim 2, wherein the flow rate of the etching gas is approximately at or above 25 sccm and is approximately at or below 100 sccm. 5. The extreme ultraviolet light generation apparatus of claim 2, wherein the gas flow controller controls the flow rate of the etching gas introduced into the chamber from the gas introduction unit based at least on one of the pressure detected by the pressure detector and the value detected by the ion sensor. 6. The extreme ultraviolet light generation apparatus of claim 1, further comprising:a magnetic field intensity controller for controlling intensity of the magnetic field;a power source for supplying current to the magnetic field generation unit; andan ion sensor disposed close to the at least one optical element for detecting an ion. 7. The extreme ultraviolet light generation apparatus of claim 1, further comprising:a magnet sensor for detecting a magnetic flux density of the magnetic field;a magnetic field intensity controller for controlling intensity of the magnetic field;a power source for supplying current to the magnetic field generation unit; andan ion sensor disposed close to the at least one optical element for detecting an ion. 8. The extreme ultraviolet light generation apparatus of claim 6, 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. 9. The extreme ultraviolet light generation apparatus of claim 7, 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. 10. The extreme ultraviolet light generation apparatus of claim 7, wherein the magnetic field intensity controller controls current supplied to the magnetic field generation unit based at least on one of the magnetic flux density detected by the magnet sensor and the value detected by the ion sensor. 11. The extreme ultraviolet light generation apparatus of claim 1, whereinthe ion flowing along the line of magnetic force forms an ion flow having a predetermined diffusion width, andthe at least one optical element is disposed substantially off an edge of the ion flow. 12. The extreme ultraviolet light generation apparatus of claim 1, whereinthe ion flowing along the line of magnetic force forms an ion flow having a predetermined diffusion width, andthe target supply unit has a tip thereof disposed substantially off an edge of the ion flow. 13. The extreme ultraviolet light generation apparatus of claim 1, whereinthe ion flowing along the line of magnetic force forms an ion flow having a predetermined diffusion width, andthe gas introduction unit has a tip thereof disposed substantially off an edge of the ion flow. 14. The extreme ultraviolet light generation apparatus of claim 11, wherein the predetermined diffusion width is determined by intensity distribution of the magnetic field, the pressure inside the chamber, and energy of the ion. 15. The extreme ultraviolet light generation apparatus of claim 12, wherein the predetermined diffusion width is determined by intensity distribution of the magnetic field, the pressure inside the chamber, and energy of the ion. 16. The extreme ultraviolet light generation apparatus of claim 13, wherein the predetermined diffusion width is determined by intensity distribution of the magnetic field, the pressure inside the chamber, and energy of the ion. 17. The extreme ultraviolet light generation apparatus of claim 1, further comprising a free radical source for turning the etching gas into a free radical. 18. The extreme ultraviolet light generation apparatus of claim 1, wherein the etching gas is hydrogen gas. 19. The extreme ultraviolet light generation apparatus of claim 1, wherein the etching gas is hydrogen radical gas. 20. The extreme ultraviolet light generation apparatus of claim 1, wherein the at least one optical element is a collector mirror for collecting extreme ultraviolet light emitted as the target material is irradiated with the laser beam inside the chamber. 21. The extreme ultraviolet light generation apparatus of claim 20, whereinthe 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. 22. The extreme ultraviolet light generation apparatus of claim 21, wherein a coating film is formed on a surface of the magnetic core. 23. The extreme ultraviolet light generation apparatus of claim 21, whereinthe magnetic core is cylindrical with one end thereof being open, andthe ion collection unit is disposed at the other end of the magnetic core. 24. The extreme ultraviolet light generation apparatus of claim 23, wherein a coating film is formed on a surface of the ion collection unit. 25. The extreme ultraviolet light generation apparatus of claim 1, wherein the at least one optical element is a measuring unit for measuring extreme ultraviolet light emitted as the target material is irradiated with the laser beam inside the chamber.