Rotating shutter for laser-produced plasma debris mitigation

• US 7,302,043 B2
• Filed: 07/27/2005
• Issued: 11/27/2007
• Est. Priority Date: 07/27/2004
• Status: Active Grant

• Current Assignee: Gatan Incorporated (Ametek Incorporated)
• Original Assignee: Gatan Incorporated (Ametek Incorporated)
• Inventors: Alwan, James J., Rieger, Harry, Bloom, Scott H.
• Primary Examiner(s): SONG, HOON K
• Application Number:
  US11/161,237
• Publication Number:
  US 20060067476A1
• Time in Patent Office: 853 Days
• Field of Search: 378/34, 378/160, 378/119, 378/143, 378145-162, 378/10, 378/120, 250/504.R, 250/517.21, 250/518.1, 250/503.1, 250/498.1
• US Class Current: 378/143
• CPC Class Codes: G03F 7/70916 Pollution mitigation, i.e. mitigating effect of contamination or debris, e.g. foil traps

Abstract

A laser produced plasma device comprises a shutter assembly for mitigating the contaminating effects of debris generated by the plasma. In one embodiment, the shutter assembly includes a rotatable shutter having at least one aperture that provides a line-of-sight between a radiation source and an exit of the device during a first period of rotation of the shutter, and obstructs the line-of-sight between the radiation source and the exit during a second period of rotation. The shutter assembly in this embodiment also includes a motor configured to rotate the shutter to permit passage of the X-rays through the at least one aperture during the first period of rotation, and to thereafter rotate the shutter to obstruct passage of the debris through the at least one aperture during the second period of rotation.

Claims

1. A shutter assembly for mitigating debris in a laser-produced plasma device, the shutter assembly comprising:

a rotatable shutter having at least one aperture that provides a line-of sight between a radiation source and an exit of the device during a first period of rotation of the shutter, and wherein the shutter obstructs the line-of-sight between the radiation source and the exit during a second period of rotation; and

a motor configured to rotate the shutter to permit passage of radiation through the at least one aperture during the first period of rotation, and to obstruct the passage of debris generated at the radiation source through the at least one aperture during the second period of rotation, wherein the shutter further comprises a plurality of vanes arranged in parallel defining a plurality of parallel apertures.

2. A shutter assembly according to claim 1, wherein the shutter further comprises a plurality of apertures radially extending from a center of the shutter.

3. A shutter assembly according to claim 1, further comprising a synchronization device configured to synchronize the first period of rotation with a radiation generation event at the radiation source.

4. A shutter assembly according to claim 3, wherein the synchronization device comprises an encoded motor configured to generate a synchronization signal.

5. A shutter assembly according to claim 3, wherein the synchronization device comprises a blade coupled to the shutter, wherein the blade is configured to synchronize the first period of rotation with the radiation generating event by blocking a laser beam during the first or second period of rotation.

6. A shutter assembly according to claim 1, wherein the motor is further configured to rotate the shutter at about 300 RPM when the radiation source generates X-rays and the debris generated at the radiation source has a velocity of about 10⁵ cm/sec or slower.

7. A shutter assembly according to claim 1, wherein the motor is further configured to rotate the shutter at about 3000 RPM when the radiation source generates X-rays and the debris generated at the radiation source has a velocity of about 10⁶ cm/sec or slower.

8. A method for mitigating debris in a laser-produced plasma device, the method comprising:

providing a rotatable shutter having at least one aperture;

rotating the shutter to provide a line-of-sight between a radiation source and an exit of the device through the at least one aperture during a first period of rotation;

rotating the shutter to obstruct the line-of-sight between the radiation source and the exit during the second period of rotation; and

whereby rotating the shutter during the first period of rotation permits the passage of radiation generated at the radiation source through the at least one aperture to the exit, and obstructs the passage of debris generated at the radiation source through the at least one aperture during the second period of rotation,

wherein the shutter further comprises a plurality of vanes arranged in parallel defining a plurality of parallel apertures.

9. A method according to claim 8, wherein the shutter further comprises a plurality of apertures radially extending from a center of the shutter.

10. A method according to claim 8, further comprising synchronizing the first period of rotation with a radiation generating event at the radiation source.

11. A method according to claim 10, wherein synchronizing the first period of rotation further comprises generating a synchronization signal with an encoded motor configured to rotate the shutter.

12. A method according to claim 10, wherein synchronizing the first period of rotation further comprises obstructing a laser beam during the first or second portion of the rotation with a blade coupled to the shutter, the obstruction configured to synchronize the first period of rotation with the radiation generating event.

13. A method according to claim 8, wherein the shutter is rotated at about 300 RPM wherein the radiation source generates X-rays and the debris generated at the radiation source has a velocity of about 10⁵ cm/sec or slower.

14. A method according to claim 8, wherein the shutter is rotated at about 3000 RPM and wherein the radiation source generates X-rays and the debris generated at the radiation source has a velocity of about 10⁶ cm/sec or slower.

15. A laser-produced plasma device, comprising:

a laser source for laser irradiation of a target;

a radiation source comprising a target that forms a plasma that generates short-wavelength radiation and generates debris when irradiated by the laser; and

a shutter assembly for obstructing the passage of debris through an exit, the shutter assembly comprising;

a rotatable shutter having at least on aperture that provides a line-of-sight between the radiation source and the exit of the device during a first period of rotation of the shutter, and obstructs a line-of-sight between the radiation source and the exit during a second period of rotation, and

a motor configured to rotate the shutter to permit passage of the radiation through the at least one aperture during the first period of rotation, and to obstruct the passage of the debris through the at least one aperture during the second period of rotation, wherein the shutter further comprises a plurality of vanes arranged in parallel defining a plurality of parallel apertures.

16. A laser-produced plasma device according to claim 15, wherein the shutter further comprises a plurality of apertures radially extending from a center of the shutter.

17. A shutter assembly according to claim 15, further comprising a synchronization device configured to synchronize the first period of rotation with the radiation generating event.