System and method for pumping laser sustained plasma with an illumination source having modified pupil power distribution

Patent metadata

Field	Value
Publication number	US-11262591-B2
Application number	US-201816186320-A
Country	US
Kind code	B2
Filing date	Nov 9, 2018
Priority date	Nov 9, 2018
Publication date	Mar 1, 2022
Grant date	Mar 1, 2022

Abstract

A system for generating pump illumination for laser sustained plasma (LSP) is disclosed. In embodiments, the system includes an illumination source and a beam shaper. The illumination source can be configured to output illumination having a first pupil power distribution. In embodiments, the beam shaper is configured to receive the illumination having the first pupil power distribution from the illumination source and is further configured to output pump illumination having a second pupil power distribution that is different from the first pupil power distribution.

First claim

What is claimed:

1. A system for generating pump illumination for a laser sustained plasma, comprising:
an illumination source configured to output illumination having a first beam profile with a central peak and decreasing intensity along a transverse direction perpendicular to a propagation direction;
a focusing lens; and
a beam shaper configured to receive the illumination having the first beam profile from the illumination source and configured to output pump illumination having a second beam profile that is different from the first beam profile, wherein the second beam profile is selected to provide a distribution of the output pump illumination through a focal region around a focal plane when focused with the focusing lens, wherein the distribution of the output pump illumination maintains a plasma in at least a portion of the focal region around the focal plane when focused with the focusing lens, wherein the plasma emits broadband light, wherein the second beam profile and a power of the output pump illumination are selected to increase at least one of a radiance or a temperature of the plasma relative to a plasma generated with the first beam profile by decreasing a peak intensity of the output pump illumination in locations prior to the focal plane in order to decrease a length of the plasma along the propagation direction in the locations prior to the focal plane, decrease associated absorption of the output pump illumination by the plasma in the locations prior to the focal plane, and increase absorption of the output pump illumination by the plasma in locations proximate to the focal plane relative to the plasma generated with the first beam profile.

2. The system of claim 1 , wherein the first beam profile comprises at least one of a bell-shaped distribution, a gaussian distribution, or a near-gaussian distribution.

3. The system of claim 1 , wherein the second beam profile comprises an inverted profile with a center-to-edge intensity ratio of less than one.

4. The system of claim 1 , wherein the second beam profile comprises a truncated version of the first pupil power distribution.

5. The system of claim 1 , wherein the beam shaper comprises one or more diffractive optical elements.

6. The system of claim 1 , wherein the beam shaper comprises one or more axicons.

7. The system of claim 1 , wherein the beam shaper comprises a delivery fiber imaged on a pupil plane of one or more focusing elements.

8. The system of claim 1 , wherein the beam shaper comprises a delivery fiber with selectively populated high-order transverse modes.

9. The system of claim 1 , wherein the beam shaper comprises a limiting aperture.

10. The system of claim 1 , wherein the beam shaper is configured to output the pump illumination from the illumination source onto a pupil plane such that the pump illumination having the second pupil power distribution uniformly fills an available solid angle of the illumination beam.

11. The system of claim 1 , wherein the second beam profile comprises:
a flat-top profile.

12. A system for generating broadband illumination, comprising:
a plasma forming material;
one or more pump modules, each pump module including:
an illumination source configured to output illumination having a first beam profile with a central peak and decreasing intensity along a transverse direction perpendicular to a propagation direction;
a focusing lens; and
a beam shaper configured to receive the illumination having the first beam profile from the illumination source and configured to output pump illumination having a second beam profile that is different from the first beam profile, wherein the second beam profile is selected to provide a distribution of the output pump illumination through a focal region around a focal plane when focused with the focusing lens, wherein the distribution of the output pump illumination maintains a plasma in at least a portion of the focal region around the focal plane when focused with the focusing lens, wherein the plasma emits broadband light, wherein the second beam profile and a power of the output pump illumination are selected to increase at least one of a radiance or a temperature of the plasma relative to a plasma generated with the first beam profile by decreasing a peak intensity of the output pump illumination in locations prior to the focal plane to decrease a length of the plasma along the propagation direction in the locations prior to the focal plane, decrease associated absorption of the output pump illumination by the plasma in the locations prior to the focal plane, and increase absorption of the output pump illumination by the plasma in locations proximate to the focal plane relative to the plasma generated with the first beam profile.

13. The system of claim 12 , wherein the first beam profile comprises at least one of a bell-shaped distribution, a gaussian distribution, or a near-gaussian distribution.

14. The system of claim 12 , wherein the second beam profile comprises an inverted profile with a center-to-edge intensity ratio of less than one.

15. The system of claim 12 , wherein the second beam profile comprises a truncated version of the first pupil power distribution.

16. The system of claim 12 , wherein the beam shaper comprises one or more diffractive optical elements.

17. The system of claim 12 , wherein the beam shaper comprises one or more axicons.

18. The system of claim 12 , wherein the beam shaper comprises a delivery fiber imaged on a pupil plane of one or more focusing elements.

19. The system of claim 12 , wherein the beam shaper comprises a delivery fiber with selectively populated high-order transverse modes.

20. The system of claim 12 , wherein the beam shaper comprises a limiting aperture.

21. The system of claim 12 , wherein the beam shaper is configured to output the pump illumination from the illumination source onto a pupil plane such that the pump illumination having the second pupil power distribution uniformly fills an available solid angle.

22. The system of claim 12 , wherein the second beam profile comprises:
a flat-top profile.

23. A method of generating broadband illumination, comprising:
generating illumination having a first beam profile with an illumination source, wherein the first beam profile includes a central peak and decreasing intensity along a transverse direction perpendicular to a propagation direction;
reshaping the illumination having the first beam profile into pump illumination having a second beam profile that is different from the first beam profile; and
directing the pump illumination to a plasma forming material, wherein the second beam profile is selected to provide a distribution of the output pump illumination through a focal region around a focal plane when focused with a focusing lens, wherein the distribution maintains a plasma in at least a portion of the focal region around the focal plane when focused with the focusing lens, wherein the plasma emits broadband light, wherein the second beam profile and a power of the output pump illumination are selected to increase at least one of a radiance or a temperature of the plasma relative to a plasma generated with the first beam profile by decreasing a peak intensity of the output pump illumination in the locations prior to focal plane to decrease a length of the plasma along the propagation direction in the locations prior to the focal plane, decrease associated absorption of the output pump illu

Assignees

• Kla Tencor Corp
• Kla Corp

Inventors

• Bezel Ilya
• Derstine Matthew
• Stepanov Andrey
• Sherbak Nikolay

Classifications

• H05H1/0043 Primary

  by using infrared or ultraviolet radiation · CPC title

• H05G2/0086

  Optical arrangements for conveying the laser beam to the plasma generation location · CPC title

• G02B27/0955

  Lenses (lenses per se G02B3/00) · CPC title

• G02B27/0944

  Diffractive optical elements, e.g. gratings, holograms (gratings per se G02B5/18; holograms used as optical elements per se G02B5/32) · CPC title

• H05H1/0037

  by spectrometry · CPC title