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US-20260126615-A1 - HOLDING DEVICE, OPTICAL ASSEMBLY AND OPTICAL SYSTEM

US20260126615A1US 20260126615 A1US20260126615 A1US 20260126615A1US-20260126615-A1

Abstract

A holding device ( 28 ) for a mirror element, in particular for a mirror element ( 19 ) for reflecting EUV radiation ( 16 ), having a ratio of length (L) to width (B) of more than 2:1, preferably of more than 3:1, particularly preferably of more than 4:1f, or even more than 10:1. The holding device ( 28 ) has a mount ( 29 ) with a plurality of holding elements ( 30 ) laterally clamping the mirror element ( 19 ). The holding elements ( 30 ) have projecting, resilient portions ( 32 ) for the resilient mounting of the mirror element ( 19 ). Also disclosed are an optical assembly ( 27 ) having such a mirror element ( 19 ) and holding device ( 28 ) configured to hold the mirror element ( 19 ), as well as an EUV lithography system having at least one such optical assembly ( 27 ).

Inventors

  • Erik Loopstra
  • Semih Oeztuerk

Assignees

  • CARL ZEISS SMT GMBH

Dates

Publication Date
20260507
Application Date
20251219
Priority Date
20230620

Claims (20)

  1. 1 . A holding device for a mirror element, having a ratio of length to width of more than 2:1, the holding device comprising a mount with a plurality of holding elements configured to laterally clamp the mirror element, wherein the holding elements have projecting, resilient portions configured to mount the mirror element.
  2. 2 . The holding device as claimed in claim 1 , wherein the ratio of the length to the width is more than 4:1.
  3. 3 . The holding device as claimed in claim 2 , wherein the ratio of the length to the width is more than 10:1.
  4. 4 . The holding device as claimed in claim 1 , wherein the mount is formed from a material having a coefficient of linear thermal expansion which is 2 ppm/K or less.
  5. 5 . The holding device as claimed in claim 4 , wherein the material has a coefficient of linear thermal expansion which is 1 ppm/K or less.
  6. 6 . The holding device as claimed in claim 1 , wherein the mount is formed from Invar.
  7. 7 . The holding device as claimed in claim 1 , wherein the holding elements are secured to the mount.
  8. 8 . The holding device as claimed in claim 1 , wherein the projecting portions of the holding elements have respective securing surfaces configured to secure the mirror element.
  9. 9 . The holding device as claimed in claim 8 , wherein the securing surfaces of ones of the holding elements which are mounted along a longitudinal side of the mirror element are each arranged at mutually equal distances, and/or wherein the securing surfaces of ones of the holding elements which are mounted along a width side of the mirror element are each arranged at mutually equal distances.
  10. 10 . The holding device as claimed in claim 1 , wherein the respective holding elements are formed at least in the projecting portions, respectively, from a material having a tensile strength of more than 800 MPa.
  11. 11 . The holding device as claimed in claim 10 , wherein the holding elements are formed entirely from the material having a tensile strength of more than 800 MPa.
  12. 12 . The holding device as claimed in claim 1 , wherein the holding elements are formed at least in the projecting portion from a tool steel.
  13. 13 . The holding device as claimed in claim 12 , wherein the holding elements are formed completely from a tool steel.
  14. 14 . An optical assembly, comprising: a mirror element having a ratio of length to width which is greater than 2:1 and a holding device as claimed in claim 1 for holding the mirror element.
  15. 15 . The optical assembly as claimed in claim 14 , wherein the mirror element is configured for reflecting extreme ultraviolet (EUV) radiation.
  16. 16 . The optical assembly as claimed in claim 14 , wherein the ratio of the length to the width is greater than 10:1.
  17. 17 . The optical assembly as claimed in claim 14 , wherein a ratio between a coefficient of linear thermal expansion of a material of the mount and a coefficient of linear thermal expansion of a material of a substrate of the mirror element is between 0.5 and 2.
  18. 18 . The optical assembly as claimed in claim 17 , wherein the ratio between the coefficient of linear thermal expansion of the material of the mount and the coefficient of linear thermal expansion of the material of the substrate of the mirror element is between 0.8 and 1.25.
  19. 19 . The optical assembly as claimed in claim 14 , wherein the projecting portions of the holding elements bridge an interspace between the substrate of the mirror element and the mount.
  20. 20 . The optical assembly as claimed in claim 14 , wherein the substrate of the mirror element is secured to securing surfaces of the holding elements through a materially bonded connection.

Description

CROSS-REFERENCE TO RELATED APPLICATION This is a Continuation of International Application PCT/EP2024/066103, which has an international filing date of Jun. 11, 2024, and the disclosure of which is incorporated in its entirety into the present Continuation by reference. This Continuation also claims foreign priority under 35 U.S.C. § 119(a)-(d) to and also incorporates by reference, in its entirety, German Patent Application DE 10 2023 205 748.4 filed Jun. 20, 2023. FIELD The invention relates to a holding device for a mirror element, in particular for a mirror element for reflecting EUV radiation, having a ratio of length to width of more than 2:1, preferably of more than 3:1, particularly preferably of more than 4:1, in particular of more than 10:1. The invention also relates to an optical assembly having such a holding device and such a mirror element. The invention additionally relates to an optical system, in particular an EUV lithography system, comprising at least one such optical assembly. BACKGROUND The EUV lithography system can be an EUV lithography apparatus for exposing a wafer or some other optical arrangement used for EUV lithography, for example an inspection system, e.g. an arrangement for measuring or inspecting masks, wafers or the like that are used in EUV lithography. The EUV lithography system is configured for operation with radiation in the extreme ultraviolet (EUV) wavelength range. In the context of this application, the EUV wavelength range is understood to be a wavelength range between approximately 5 nm and approximately 30 nm. The mirror element described further above, more precisely the substrate of such a mirror element, is typically rectangular or cuboid. Mirror elements for EUV lithography or for x-ray optics are typically exposed to high radiation loads during operation, whereas this is not the case during breaks in operation. This may lead to temperature fluctuations of the mirror elements on the order of magnitude of e.g. ΔT=±40 K. Temperature fluctuations on the order of magnitude of ΔT=±10 K may also occur during the transport of such mirror elements. In general, mirror elements, more precisely substrates of mirror elements, for EUV lithography are produced from a so-called zero expansion material, i.e. from a material that has a very low coefficient of linear thermal expansion (referred to as coefficient of thermal expansion, CTE) which has a minimum at a temperature, the so-called zero crossing temperature. The material of the holding device is typically not formed from a zero expansion material, which is why its coefficient of linear thermal expansion differs from the coefficient of linear thermal expansion of the material of the mirror element. The difference between the coefficients of thermal expansion of the substrate of the mirror element and the material of the holding device may lead to impermissible deformations, stresses and possibly breakage. The holding of mirror elements for EUV lithography apparatuses is typically not effected by accommodating them in a mount, as is generally the case with lens elements, but rather with the aid of a three-point support, in which the mirror element, more precisely the substrate of the mirror element, is supported by a holding device at three support points. However, this kind of holding likewise leads to generally intolerable deformations in mirror elements having a large aspect ratio, i.e. a large difference between their length and their width. Another problem concerning the holding of such mirror elements, especially if replacement parts are involved, is the fact that the optical assembly consisting of the mirror element and the holding device, in the event that this has high natural frequencies of e.g. more than approx. 100 Hz, may need to absorb a shock load or g-forces of possibly up to 10 g during handling and transport, without being damaged in the process. SUMMARY One object of the invention is to provide a holding device, an optical assembly and an EUV lithography system which enable the holding of mirror elements having a large aspect ratio with the smallest possible deformations and stresses. This and other objects are achieved according to a first aspect by a holding device of the type mentioned initially which has a mount with a plurality of holding elements for laterally clamping the mirror element. The holding elements typically have resilient portions projecting beyond the mount for the resilient mounting of the mirror element. In this aspect of the invention, it is proposed to use a mount for the holding of a generally rectangular mirror element having a large aspect ratio, which mount clamps the mirror element, more precisely the substrate of the mirror element, laterally at a plurality of holding elements, typically at more than ten or more than twenty holding elements, and thus introduces lower local stresses into the mirror element than is the case with a three-point support. For clamping, the hold