Plasma based light source having a target material coated on a cylindrically-symmetric element

Patent metadata

Field	Value
Publication number	US-9918375-B2
Application number	US-201615268793-A
Country	US
Kind code	B2
Filing date	Sep 19, 2016
Priority date	Nov 16, 2015
Publication date	Mar 13, 2018
Grant date	Mar 13, 2018

Abstract

The present disclosure is directed to laser produced plasma light sources having a target material, such as Xenon, that is coated on the outer surface of a cylindrically-symmetric element (e.g., drum). Embodiments include a pre-pulsing arrangement which can be optimized to reduce irradiation damage to the drum and a pulse trimming unit which can be employed to reduce irradiation damage to the drum. In addition, an embodiment is disclosed wherein the surface of a cylindrically-symmetric element is formed with a plurality of grooves having a groove depth greater than 1 mm and a focusing unit focusing a laser beam and establishing an irradiation site to produce plasma from the target material, with the irradiation site distanced from a groove surface portion to protect the surface portion from irradiation damage.

First claim

What is claimed is:

1. A device comprising:
a cylindrically-symmetric element rotatable about an axis and having a surface coated with a band of plasma-forming target material having an exposed surface;
a system outputting a train of laser beam pulses, each pulse having a leading edge characterized by a rise in laser beam intensity over time; and
a pulse trimming unit receiving pulses downstream of the laser system and trimming at least a portion of the leading edge of each pulse to output a trimmed pulse for interaction with the target material to produce plasma.

2. A device as recited in claim 1 wherein the system for outputting a train of laser beam pulses is configured to generate each pulse to have a trailing edge characterized by a decline in laser beam intensity over time, wherein the pulse trimming unit trims at least a portion of the trailing edge of each pulse.

3. A device as recited in claim 1 wherein the pulse trimming unit comprises an electro-optical modulator.

4. A device as recited in claim 3 wherein the electro-optical modulator has a crystal cell having a crystal cell material selected from the group of crystal cell materials consisting of a KDP, BBO, RTP, RTA, LiNbO3.

5. A device as recited in claim 1 wherein the system outputting a train of laser beam pulses comprises a cavity dumped laser.

6. A device as recited in claim 1 wherein the system outputting a train of laser beam pulses comprises a Q-switched laser.

7. A device as recited in claim 1 wherein the pulse trimming unit is configured to trim at least some of the pulses to have a rise time less than 1 ns.

8. A device comprising:
a cylindrically-symmetric element rotatable about an axis and having a surface coated with a band of plasma-forming target material having an exposed surface and defining a surface normal at an irradiation site on the exposed surface; and
a system outputting a laser beam for interaction with the target material to produce plasma, the laser beam traveling along a laser axis at the irradiation site, with the laser axis and surface normal subtending a nonzero angle, a, at the irradiation site.

9. A device as recited in claim 8 wherein the angle, α, is greater than 10 degrees.

10. A device as recited in claim 8 wherein the laser axis is aligned normal to an axis intersecting the irradiation site and aligned parallel to the rotation axis.

11. A device as recited in claim 8 wherein the laser axis is aligned normal to an axis that intersects the irradiation site and is aligned parallel to the rotation axis.

12. A device comprising:
a cylindrically-symmetric element rotatable about an axis and having a surface coated with a band of plasma-forming target material having an exposed surface;
a system outputting a laser beam for interaction with the target material to produce plasma; and
a focusing unit focusing the laser beam to a waist at a location between the focusing unit and the exposed surface of the plasma-forming target material.

13. A device comprising:
a cylindrically-symmetric element rotatable about an axis and having a surface coated with a band of plasma-forming target material; and
a system irradiating the target material to produce plasma, the system outputting a first laser beam pulse having an intensity maximum I 1 , and pulse energy, E 1 , and a second laser beam pulse having an intensity maximum I 2 , and pulse energy, E 2 , with E 1 <E 2 , and a time delay between I 1 and I 2 selected to cause the first laser beam pulse to precondition the plasma-forming target material to reduce irradiation damage to the surface of the cylindrically-symmetric element by the second laser beam pulse.

14. A device as recited in claim 13 wherein the system irradiating the target material is configured to output the first laser beam pulse to have a longer pulse duration than the second laser beam pulse.

15. A device as recited in claim 13 wherein the system irradiating the target material is configured to output the first laser beam pulse to a shorter wavelength than the second laser beam pulse.

16. A device as recited in claim 13 wherein the system irradiating the target material is configured to output the first laser beam pulse and the second laser beam pulse, wherein the time delay between I 1 and I 2 is in the range of 10 ns to 10 μs.

17. A device as recited in claim 13 wherein the system irradiating the target material is configured to output the first laser beam pulse and the second laser beam pulse such that the intensity maximum, I 1 , of the first laser beam pulse is greater than the intensity maximum, I 2 , of the second laser beam pulse (I 1 >I 2 ).

18. A device comprising:
a cylindrically-symmetric element rotatable about an axis and having a surface coated with a band of plasma-forming target material, the surface formed with a plurality of axially aligned grooves, with each groove established by a pair of fins with each fin having a fin tip, and wherein each groove has a groove depth greater than 1 mm from a fin tip to a groove surface portion;
a system outputting a laser beam; and
a focusing unit focusing the laser beam and establishing an irradiation site to produce plasma from the target material, the irradiation site distanced from the groove surface portion to protect the surface portion from irradiation damage.

19. A device as recited in claim 18 wherein the band of plasma-forming target material has an exposed target material surface distanced from a fin tip by greater than 0.5 mm.

20. A device as recited in claim 18 wherein the groove has a root surface, and a face between the root surface and a fin tip, and wherein at least a portion of the root surface has a surface roughness, SR 1 , and at least a portion of the face has a surface roughness, SR 2 , with SR 1 <SR 2 .

21. A device as recited in claim 18 further comprising an encoder for outputting a signal indicative of a rotational position of the cylindrically-symmetric element.

22. A device as recited in claim 21 wherein the system outputting a laser beam receives the signal and is further configured to trigger a pulsed laser output to synchronize laser output with cylindrically-symmetric element rotational position based on the received signal.

23. A device as recited in claim 18 further comprising:
a drive unit to rotate the cylindrically-symmetric element about the axis and translate the cylindrically-symmetric element, back and forth, along the axis between a first end location and a second end location, the drive unit programmable to vary a rotation velocity at each end location to establish a first set of plasma-forming target material spots for irradiation on a translation from the first end location to the second end location and a second set of plasma-forming target material spots, different from the first set, for irradiation on a translation from the second end location to the first end location.

24. A device as recited in claim 18 wherein each groove has a width, normal to the axis, sized to accommodate one irradiation site.

25. A device as recited in claim 18 wherein each groove has a width, normal to the axis, sized to accommodate two irradiation sites.

Assignees

• Kla Tencor Corp

Inventors

• Kuritsyn Alexey
• Liu Ye
• Khodykin Oleg

Classifications

• H10P76/2041

  Photolithographic processes · CPC title

• H10P14/6514

  by exposure to a plasma · CPC title

• H10P95/00

  Generic processes or apparatus for manufacture or treatments not covered by the other groups of this subclass · CPC title

• H10P76/00 Primary

  Manufacture or treatment of masks on semiconductor bodies, e.g. by lithography or photolithography · CPC title

• G02F2203/26

  Pulse shaping; Apparatus or methods therefor · CPC title