EUV light source using cryogenic droplet targets in mask inspection

Patent metadata

Field	Value
Publication number	US-9295147-B2
Application number	US-201414180107-A
Country	US
Kind code	B2
Filing date	Feb 13, 2014
Priority date	Jan 30, 2013
Publication date	Mar 22, 2016
Grant date	Mar 22, 2016

Abstract

An apparatus for generating extreme ultra-violet (EUV) light, including a drive laser arranged to produce a laser pulse, a vacuum chamber, a set of focusing optics arranged to focus the laser pulse produced by the drive laser onto a target spot within the vacuum chamber, a target material generator arranged to deliver a series of droplets of a target material to the target spot by modulating a flow velocity of a supply of the target material through a nozzle tip and thereby inducing a formation process of the series of droplets which series of droplets from the nozzle tip are expelled through a triple point chamber, and a set of collector optics arranged to focus a quantity of EUV light generated when a droplet of the series of drople of the target material is exposed to the laser pulse at the target spot onto an intermediate focus spot.

First claim

What is claimed is:

1. An apparatus for generating extreme ultra-violet (EUV) light for use in a lithography mask inspection tool, comprising:
a drive laser arranged to produce a laser pulse;
a vacuum chamber;
a set of focusing optics arranged to focus the laser pulse produced by the drive laser onto a target spot within the vacuum chamber with a beam target diameter of less than 100 μm;
a target material generator arranged to deliver a series of droplets of a target material to the target spot within the vacuum chamber by modulating a flow velocity of a first supply of the target material through a nozzle tip and thereby inducing a formation process of the series of droplets of the target material which series of droplets from the nozzle tip are expelled through a triple point chamber; and,
a set of collector optics arranged to focus a quantity of EUV light generated when a droplet of the series of droplets of the target material is exposed to the laser pulse at the target spot onto an intermediate focus spot.

2. The apparatus of claim 1 , wherein the laser pulse produced by drive laser has a duration in the range of 5 ns to 50 ns.

3. The apparatus of claim 1 , wherein the laser pulse is repeatedly produced by drive laser at a frequency in the range of 5 kHz to 50 kHz.

4. The apparatus of claim 1 , wherein the laser pulse produced by drive laser comprises a plurality of short-duration pulses.

5. The apparatus of claim 4 , wherein the plurality of short-duration pulses comprises a first at least one pulse of a first intensity and a second at least one pulse of a second intensity such that the first intensity is less than the second intensity.

6. The apparatus of claim 1 , further comprising:
an at least one supplemental drive laser; and
a beam combiner arranged to combine a set of supplemental laser pulses produced by the at least one supplemental drive laser with the laser pulse produced by the drive laser into a combined laser pulse, wherein the combined laser pulse is focused by the set of focusing optics onto the target spot within the vacuum chamber.

7. The apparatus of claim 1 , further comprising:
a beam diagnostic tool arranged to receive the laser pulse and measure an at least one laser pulse characteristic and generate a beam quality signal; and
a control system arranged to receive the beam quality signal and adjust an at least one system parameter in response to the beam quality signal.

8. The apparatus of claim 1 , wherein the target material is a cryogenic liquid gas.

9. The apparatus of claim 8 , wherein the target material is delivered as a pellet of solid gas.

10. The apparatus of claim 8 , wherein the target material is delivered as a jet of cryogenic liquid gas.

11. The apparatus of claim 1 , further comprising:
a set of projection optics arranged to collect the quantity of EUV light and project the quantity of EUV light outside the apparatus.

12. The apparatus of claim 1 , wherein the drive laser is a solid state laser selected from the group consisting of Nd:YAG, Er:YAG, Yb:YAG, Ti:Sapphire, and Nd:Vanadate lasers.

13. An apparatus for generating droplets for use in a laser produced plasma extreme ultra-violet (EUV) light source, comprising:
a triple point chamber arranged to provide an environment comprising a temperature and pressure combination and having a traversal length measured axially along a central axis of the triple point chamber;
a sensor arranged within the triple point chamber and further arranged to measure the temperature and pressure combination;
an environmental control means arranged to receive a signal from the sensor and adjust the environment to conform to a predefined set of values for the temperature and pressure combination;
an exit orifice arranged at a distal end of the triple point chamber;
a source vessel arranged at a proximal end of the triple point chamber;
a nozzle tip arranged at a distal end of the source vessel;
a target material source containing a first supply of a target material arranged at the proximal end of the source vessel; and
a piezoelectric actuator arranged to modulate a flow velocity of the first supply of the target material through the nozzle tip and thereby induce a formation process of a series of droplets of the target material from the first supply of the target material from the target material source and expel the series of droplets from the nozzle tip through the triple point chamber and out the exit orifice.

14. The apparatus of claim 13 , wherein the target material from the first supply of the target material is a cryogenic liquid gas.

15. The apparatus of claim 13 , wherein each in the series of droplets comprise a plurality of droplets, with each droplet in the plurality of droplets having a velocity comprising both a speed and a direction such that the direction of each of the droplets in the plurality of droplets is equivalent and the speed of each droplet in the plurality of droplets is not equivalent to the speed of at least one other droplet in the plurality of droplets.

16. The apparatus of claim 15 , wherein the piezoelectric actuator can modulate the flow velocity of the first supply of the target material through the nozzle tip at a fundamental frequency associated with the formation process of the series of droplets and wherein the piezoelectric actuator can further be stimulated at a secondary frequency associated with the speed of each droplet in the plurality of droplets such that a magnitude associated with the secondary frequency is substantially less than a magnitude associated with the fundamental frequency.

17. The apparatus of claim 16 , wherein the relative differences in the speed of each droplet in the plurality of droplets tends to cause each of the droplets in the plurality of droplets to coalesce into a large droplet within the triple point chamber.

18. The apparatus of claim 17 , wherein the large droplet is expelled from the exit orifice.

19. The apparatus of claim 18 , wherein the traversal length is sufficient to allow each of the droplets in the plurality of droplets to coalesce into the large droplet prior to the expulsion of the large droplet from the exit orifice.

20. The apparatus of claim 13 , wherein the traversal length is in the range of 10 cm to 30 cm.

21. The apparatus of claim 13 , wherein the predefined set of values for the temperature and pressure combination are substantially similar to a triple point associated with the target material.

22. The apparatus of claim 13 , wherein the triple point chamber comprises a substantially sealed volume.

23. A channeled aperture for accelerating droplets for use in a laser produced plasma extreme ultra-violet (EUV) light source, comprising:
an entrance aperture proximal to a triple point chamber;
an exit aperture distal to a triple point chamber;
a channel arranged to connect the entrance aperture to the exit aperture and having a channel profile and a channel axis;
a gas jet having a flow from the triple point chamber to a vacuum chamber and through the channel; and
a target material droplet, wherein the channel profile is arranged to accelerate the gas jet during the flow from the triple point chamber to the vacuum chamber, which acceleration of the gas jet generally accelerates the target material droplet in a direction coincident to a direction associated with the flow from the triple point chamber to the vacuum chamber.

24. The channeled apert

Assignees

• Kla Tencor Corp

Inventors

• Bykanov Alexander
• Khodykin Oleg
• Wack Daniel Christopher

Classifications

• H10P76/00

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

• G03F1/22

  Masks or mask blanks for imaging by radiation of 100nm or shorter wavelength, e.g. X-ray masks, extreme ultraviolet [EUV] masks; Preparation thereof · CPC title

• G03F1/84

  Inspecting · CPC title

• G03F7/70033

  by plasma extreme ultraviolet [EUV] sources · CPC title

• G03F7/20

  Exposure; Apparatus therefor (photographic printing apparatus for making copies G03B27/00) · CPC title