Patent Number: 
Section: claims

1. An extreme ultraviolet light generation apparatus comprising:a chamber in which extreme ultraviolet light is generated from plasma, the plasma being generated by irradiating a target supplied into the chamber with a laser beam;a target generator configured to supply the target into the chamber as a droplet;a droplet measurement unit configured to measure the droplet supplied from the target generator into the chamber; anda shielding member configured to shield the droplet measurement unit from electromagnetic waves emitted from the plasma,the droplet measurement unit including:a light source configured to emit continuous light to the droplet;a window provided in the chamber and configured to allow the continuous light to transmit therethrough; andan optical sensor configured to receive the continuous light via the window, andthe shielding member including a shielding body provided on the chamber side with respect to the window configured to cover an optical path of the continuous light and having a light passing opening for passing the continuous light therethrough, and the shielding member is provided within the interior of the chamber, configured separately from a wall that constitutes the chamber. 2. The extreme ultraviolet light generation apparatus according to claim 1, wherein the shielding body prevents light of the electromagnetic waves emitted from the plasma from entering the droplet measurement unit. 3. The extreme ultraviolet light generation apparatus according to claim 2, wherein the shielding member further includes a shield configured to prevent noise of the electromagnetic waves emitted from the plasma from entering the droplet measurement unit. 4. The extreme ultraviolet light generation apparatus according to claim 2, wherein the droplet measurement unit further includes a transfer optical system configured to transfer an image of the droplet irradiated with the continuous light to the optical sensor. 5. The extreme ultraviolet light generation apparatus according to claim 2, wherein:the droplet measurement unit measures the droplet passing through a predetermined position in the chamber; andthe shielding body includes:a cylinder part provided between the predetermined position and the window and configured to cover the optical path of the continuous light; andan opening formed at an end of the cylinder part on the predetermined position side. 6. The extreme ultraviolet light generation apparatus according to claim 5, further comprising a gas lock mechanism configured to supply gas into the cylinder part and discharge the gas in the cylinder part from the opening, the gas lock mechanism being provided within the interior of the chamber. 7. The extreme ultraviolet light generation apparatus according to claim 6, wherein:the shielding member further includes a shield configured to prevent noise of the electromagnetic waves emitted from the plasma from entering the droplet measurement unit; andthe shield is disposed between the window and the optical sensor. 8. The extreme ultraviolet light generation apparatus according to claim 6, wherein:the shielding member further includes a shield configured to prevent noise of the electromagnetic waves emitted from the plasma from entering the droplet measurement unit; andthe shield is disposed to close a slit provided on an end of the cylinder part on the window side. 9. The extreme ultraviolet light generation apparatus according to claim 8, further comprising a heater configured to heat the shield. 10. The extreme ultraviolet light generation apparatus according to claim 5, wherein the droplet measurement unit further includes an optical filter disposed to close the opening and configured to allow the continuous light to transmit therethrough, the optical filter and the opening are provided within the interior of the chamber. 11. The extreme ultraviolet light generation apparatus according to claim 5, wherein the droplet measurement unit further includes a spatial filter disposed between the window and the optical sensor and configured to prevent passage of light not traveling on the optical path of the continuous light. 12. The extreme ultraviolet light generation apparatus according to claim 5, wherein:the droplet measurement unit outputs a passage timing signal indicating a timing at which the droplet is passing through the predetermined position; anda line filter is provided on a signal wire through which the passage timing signal outputted from the droplet measurement unit is transmitted to attenuate noise of the electromagnetic waves. 13. An extreme ultraviolet light generation apparatus comprising:a chamber in which extreme ultraviolet light is generated from plasma, the plasma being generated by irradiating a target supplied into the chamber with a laser beam;a target generator configured to supply the target into the chamber as a droplet; anda droplet measurement unit configured to measure the droplet supplied from the target generator into the chamber,the droplet measurement unit including:a light source configured to emit continuous light to the droplet;a window provided in the chamber and configured to allow the continuous light to transmit therethrough;an optical sensor configured to receive the continuous light via the window; anda transfer optical system disposed between the window and the optical sensor and configured to transfer an image of the droplet irradiated with the continuous light to the optical sensor and prevent light of electromagnetic waves emitted from the plasma from entering the optical sensor, wherein:the droplet measurement unit measures the droplet passing through a predetermined position in the chamber and outputs a passage timing signal indicating a timing at which the droplet is passing through the predetermined position; anda line filter is provided on a signal wire through which the passage timing signal outputted from the droplet measurement unit is transmitted to attenuate noise of the electromagnetic waves emitted from the plasma, and the line filter includes an analog circuit. 14. The extreme ultraviolet light generation apparatus according to claim 3, wherein:the droplet measurement unit measures the droplet passing through a predetermined position in the chamber; and the shielding body includes:a cylinder part provided between the predetermined position and the window and configured to cover the optical path of the continuous light; andan opening formed at an end of the cylinder part on the predetermined position side. 15. The extreme ultraviolet light generation apparatus according to claim 4, wherein:the droplet measurement unit measures the droplet passing through a predetermined position in the chamber; and the shielding body includes:a cylinder part provided between the predetermined position and the window and configured to cover the optical path of the continuous light; andan opening formed at an end of the cylinder part on the predetermined position side. 16. The extreme ultraviolet light generation apparatus according to claim 6, wherein:the gas lock mechanism is configured to supply gas to the interior of the cylinder part while causing the gas to contact the surface of the window toward the side of the chamber when supplying the gas to the interior of the cylinder part. 17. The extreme ultraviolet light generation apparatus according to claim 13, wherein:the line filter is a filter circuit, which is one of a low pass filter, a band pass filter, and a band eliminating filter. 18. The extreme ultraviolet light generation apparatus according to claim 13, wherein:the line filter attenuates signal components having frequencies within a range from 12 MHz to 18 MHz. 19. The extreme ultraviolet light generation apparatus according to claim 1, wherein:a shielding surface of a portion of the shielding body at which the light passing opening is formed is inclined toward the side of the optical sensor as a distance from a region where the plasma is generated becomes greater. 20. The extreme ultraviolet light generation apparatus according to claim 1, wherein:a shielding surface of a portion of the shielding body at which the light passing opening is formed is substantially parallel to a target traveling path.