Faceted EUV optical element

Patent metadata

Field	Value
Publication number	US-9541840-B2
Application number	US-201414575699-A
Country	US
Kind code	B2
Filing date	Dec 18, 2014
Priority date	Dec 18, 2014
Publication date	Jan 10, 2017
Grant date	Jan 10, 2017

Abstract

A reflective EUV optic such as a collector mirror configured as an array of facets that are spaced apart to form respective gaps between adjacent facets. The gaps are used as inlets for gas flow across one of the facets such that flow is introduced parallel to the optic surface. The facets can be made with offsets such that loss of reflective area of the EUV optic can be minimized. The gas facilitates removal of target material from the surface of the facets.

First claim

What is claimed is:

1. An EUV light source comprising:
a reflective EUV optic comprising a first facet comprising a first portion of a reflective surface of the reflective EUV optic and a second facet comprising a second portion of the reflective surface of the reflective EUV optic, the first facet being separated from the second facet by a gap; and
a gas supply in fluid communication with the gap.

2. An EUV light source as claimed in claim 1 wherein the first facet is separated from the second facet in a direction parallel to an optical axis of the reflective EUV optic and the first facet overlaps the second facet in a direction substantially tangential to the reflective surface where the first facet overlaps the second facet.

3. An EUV light source as claimed in claim 1 wherein the reflective EUV optic is substantially rotationally symmetric about a central optical axis, and wherein the first facet and the second facet are substantially annular.

4. A reflective EUV optic as claimed in claim 1 , further comprising a plenum in fluid communication with the gap.

5. An EUV light source as claimed in claim 4 further comprising a gas exhaust arranged to withdraw gas from the plenum to promote a uniform flow of gas through the plenum.

6. A reflective EUV optic as claimed in claim 1 comprising a plurality of additional facets separated by gaps, and wherein the first facet, the second facet, and the plurality of additional facets together make up substantially an entire reflective surface of the reflective EUV optic.

7. An EUV light source as claimed in claim 6 wherein the number of facets is about 400 facets so that the reflective EUV optic can be configured to perform the optical functions of both a collector mirror and a field facet mirror.

8. An EUV light source as claimed in claim 1 wherein the gap is configured to direct the gas from the supply in a direction tangential to a reflective surface of the EUV optic where the first facet overlaps the second facet.

9. An EUV light source as claimed in claim 1 wherein the gas supply is adapted to supply molecular hydrogen.

10. An EUV light source comprising:
a chamber;
a reflective EUV optic in the chamber, the reflective EUV optic being substantially rotationally symmetric about a central optical axis and comprising a first annular facet comprising a first portion of a reflective surface of the reflective EUV optic and a second annular facet comprising a second portion of the reflective surface of the reflective EUV optic, the first facet being separated from the second facet by an annular inlet, the reflective EUV optic further comprising a plenum in fluid communication with the annular inlet; and
a supply of gas in fluid communication with the plenum and at a pressure higher than a pressure in the chamber.

11. An EUV light source as claimed in claim 10 wherein the first annular facet is separated from the second annular facet in a direction parallel to the central optical axis of the reflective EUV optic and the first annular facet overlaps the second annular facet in a direction substantially tangential to the reflective surface where the first annular facet overlaps the second annular facet to create the annular inlet.

12. An EUV light source as claimed in claim 11 wherein the annular inlet is configured to direct the gas from the supply in a direction tangential to the reflective surface where the first annular facet overlaps the second annular facet.

13. A reflective EUV optic as claimed in claim 10 comprising a plurality of additional annular facets separated by annular inlets, and wherein the first annular facet, the second annular facet, and the plurality of additional annular facets together make up substantially the entire reflective surface of the reflective EUV optic.

14. An EUV light source as claimed in claim 13 wherein the number of facets is about 400 facets so that the reflective EUV optic can be configured to perform the optical functions of both a collector mirror and a field facet mirror.

15. An EUV light source as claimed in claim 10 wherein the gas supply is adapted to supply molecular hydrogen.

16. An EUV light source as claimed in claim 10 further comprising a gas exhaust arranged to withdraw gas from the plenum to promote a uniform flow of gas through the plenum.

17. An EUV light source comprising:
a chamber;
a reflective EUV optic in the chamber, the reflective EUV optic being substantially rotationally symmetric about a central optical axis and comprising a plurality of annular facets comprising respective portions of a reflective surface of the reflective EUV optic,
the plurality of annular facets together making up substantially the entire reflective surface,
each of the annular facets being spaced away from adjacent annular facets by a respective one of a plurality of annular inlets in a direction parallel to the central optical axis of the reflective EUV optic,
a supply of gas in fluid communication with the plurality of annular inlets and at a pressure higher than a pressure in the chamber so that gas flows from the supply and into the chamber through the annular inlets,
each of annular facets overlapping at least one adjacent annular facet in a direction substantially tangential to the reflective surface where the annular facet overlaps the adjacent annular facet to create one of the plurality of annular inlets, the plurality of annular inlets thus being configured to direct the gas from the supply in a direction tangential to the reflective surface where the annular facets overlap.

18. An EUV light source as claimed in claim 17 wherein the gas supply is adapted to supply molecular hydrogen.

19. An EUV light source as claimed in claim 17 further comprising a gas exhaust arranged to withdraw gas from the plenum to promote a uniform flow of gas through the plenum.

20. A method of generating EUV light, the method comprising the steps of:
providing a reflective EUV optic having a first facet comprising a first portion of a reflective surface of the reflective EUV optic and a second facet comprising a second portion of the reflective surface of the reflective EUV optic, the first facet being separated from the second facet by a gap;
flowing gas from a gas supply through the gap tangentially past the second portion of the reflective surface of the reflective EUV optic; and
generating a plasma which produces EUV radiation.

Assignees

• Cymer LLC
• Asml Netherlands Bv

Inventors

• Brandt David C
• Ershov Alexander I
• Fomenkov Igor V

Classifications

• G03F7/70175

  Lamphouse reflector arrangements or collector mirrors, i.e. collecting light from solid angle upstream of the light source · CPC title

• G21K1/062

  Devices having a multilayer structure · CPC title

• G02B19/0095

  for use with ultraviolet radiation · CPC title

• G03F7/70933

  Purge, e.g. exchanging fluid or gas to remove pollutants · CPC title

• G03F7/70033 Primary

  by plasma extreme ultraviolet [EUV] sources · CPC title