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EP-4740067-A1 - OBJECT HOLDER, OBJECT TABLE, OPTICAL ELEMENT AND METHOD OF CONTROLLING THE FLATNESS OF A SURFACE, AND THEIR USE IN A LITHOGRAPHIC METHOD OR APPARATUS

EP4740067A1EP 4740067 A1EP4740067 A1EP 4740067A1EP-4740067-A1

Abstract

There is provided an object holder configured to support an object, comprising a support surface having a plurality of support elements that comprise a metal-Si multilayer, metal-Ge multilayer, and/or a chromium nitride layer to provide a selectively changeable height of individual support elements via thermal treatment of the metal-Si multilayer, metal-Ge multilayer, and/or chromium nitride layer. Also provided is an object table comprising such an object holder, an apparatus for controlling the flatness of a surface comprising such an object holder, an optical element for a lithographic apparatus, an apparatus for controlling the flatness of a surface, a lithographic apparatus or tool comprising such an object holder, a method of controlling the shape of a surface, a method of manufacturing an object holder, a method of correcting the flatness of an object holder or optical element, and the use of such apparatuses or method in a lithographic apparatus or process.

Inventors

  • ALLSOP, Nicholas, Alan
  • WIGGERS, Frank, Bert

Assignees

  • ASML Netherlands B.V.

Dates

Publication Date
20260513
Application Date
20240621

Claims (16)

  1. 1. An object holder configured to support an object, the object holder comprising a support surface having a plurality of support elements, wherein the plurality of support elements comprise a metal-Si multilayer, and/or a metal-Ge multilayer, and/or a chromium nitride layer configured to provide a selectively changeable height of individual support elements via thermal treatment of the metal-Si multilayer, metal-Ge multilayer, and/or chromium nitride layer.
  2. 2. An object holder according to claim 1, wherein the metal is selected from molybdenum or titanium, or any combination thereof.
  3. 3. The object holder according to claim 1 or claim 2, wherein the plurality of support elements are burls.
  4. 4. The object holder according to any preceding claim, wherein the object holder is a wafer holder, such as a wafer clamp, preferably an electrostatic wafer clamp, or a wafer table, or wherein the object holder is a reticle holder, such as a reticle table or a reticle clamp.
  5. 5. The object holder of any preceding claim, wherein the plurality of support elements comprise a top coating material, optionally wherein the top coating material is selected from chromium nitride, diamond-like carbon, or a combination thereof.
  6. 6. The object holder of any preceding claim, wherein the thickness of the metal-Si multilayer, metal- Ge multilayer, and/or chromium nitride layer is up to around 1400 nm, up to around 1300 nm, up to around 1200 nm, up to around 1100 nm, up to around 1000 nm, up to around 900 nm, up to around 800 nm, up to around 700nm, up to around 600 nm, up to around 500 nm, up to around 400 nm, up to around 300 nm, up to around 200 nm or up to around 100 nm.
  7. 7. The object holder of any preceding claim, wherein the thickness of the layers in the multilayer or layer range from around 2 nm to around 100 nm, optionally from around 10 nm to around 20 nm.
  8. 8. An object table comprising an object holder according to any preceding claim.
  9. 9. An optical element for a lithographic apparatus, the optical element comprising a metal-Si multilayer and/or metal-Ge multilayer and/or chromium nitride layer configured to selectively change in shape via thermal treatment of the metal-Si multilayer, metal-Ge multilayer, and/or chromium nitride layer, optionally wherein the metal is selected from titanium, molybdenum, or any combination thereof, optionally wherein the optical element is a mirror block.
  10. 10. An apparatus for controlling the flatness of a surface, the apparatus comprising the object holder or optical element according to any preceding claim and a means for changing a phase configuration of the metal-Si multilayer, metal-Ge multilayer, and/or chromium nitride layer, the means comprising a heater, optionally wherein the means comprises a laser and/or an electrical heater.
  11. 11. A lithographic apparatus or tool comprising the object holder of any of claims 1 to 7, the object table of claim 8, the optical element of claim 9, or the apparatus of claim 10.
  12. 12. A method of correcting the flatness of a surface of an object holder or optical element of a lithographic apparatus, the method comprising: providing a surface comprising at least one material capable of volume change upon heating and controlling the flatness of the surface via thermal treatment of the at least one material capable of volume change upon heating, wherein the at least one material capable of volume change upon heating is a chromium nitride multilayer or a metal-Si multilayer or a metal-Ge multilayer, optionally wherein the metal is selected from titanium, molybdenum, or any combination thereof.
  13. 13. The method according to claim 12, wherein correcting the flatness of the surface is achieved by selectively heating the at least one material to a predetermined temperature and annealing, optionally by laser heating.
  14. 14. The method according to any one of claims 12 - 13, the method being of correcting the flatness of a surface of an object holder according to any one of claims 1 - 7, the surface being a support surface having a plurality of support elements, wherein said volume change is to selectively adjust the height of a support element.
  15. 15. The method according to any one of claims 12 - 14, wherein controlling the flatness of the surface takes place within a lithographic apparatus.
  16. 16. The use of an object holder according to any of claim 1 to 7, an object table according to claim 8, an optical element for a lithographic apparatus according to claim 9, an apparatus according to claim 10, a lithographic apparatus or tool according to claim 11, or a method according to any of claims 12 to 15 in a lithographic method or apparatus.

Description

OBJECT HOLDER, OBJECT TABLE, OPTICAL ELEMENT AND METHOD OF CONTROLLING THE FLATNESS OF A SURFACE, AND THEIR USE IN A LITHOGRAPHIC METHOD OR APPARATUS CROSS-REFERENCE TO RELATED APPLICATIONS [001] This application claims priority of EP application 23183500.0 which was filed on 5 July 2023, and which is incorporated herein in its entirety by reference. FIELD [002] The present disclosure relates to an object holder, an object table, an optical element, and a lithographic apparatus or tool comprising such an object holder, optical element, or object table. The present disclosure also relates to a method of controlling the flatness of a surface. Also described is the use of such an object holder, object table, lithographic apparatus or methods in a lithographic method or apparatus. The object holder may be part of an object table of a lithographic apparatus or lithographic tool. The present disclosure has particular, but not exclusive, application to EUV and DUV lithographic apparatuses and methods. BACKGROUND [003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate. [004] To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm. [005] The substrate to be exposed may be supported by a substrate holder (i.e. the object that directly supports a substrate), which in turn is supported by a substrate table. The substrate holder may have an array of projections or support elements, referred to as burls, projecting from at least one side. When the substrate rests on the top of the burls on the at least one side of the substrate holder, the substrate may be spaced apart from a main body of the substrate holder. This may aid in the prevention of a particle (i.e. a contaminating particle such as a dust particle), which may be present on the substrate holder, from distorting the substrate holder or substrate. The total surface area of the burls may only be a small fraction of the total area of the substrate or substrate holder. As such, it is more probable that any particle will lie between burls and its presence will have no effect. The tops of the burls define a plane on which objects lie when engaged therewith. [006] Due to the high accelerations that may be experienced by the substrate in use of a high- throughput lithographic apparatus, it may not be sufficient to allow the substrate simply to rest on the burls of the substrate holder. It is clamped in place. Two methods of clamping the substrate in place may be used - vacuum clamping and electrostatic clamping. In vacuum clamping, the space between the substrate holder and substrate and optionally between the substrate table and substrate holder are partially evacuated so that the substrate is held in place by the higher pressure of gas or liquid above it. Vacuum clamping, however, may not be used where the beam path and/or the environment near the substrate or substrate holder is kept at a low or very low pressure, e.g. for extreme ultraviolet (EUV) radiation lithography. In this case, it may not be possible to develop a sufficiently large pressure difference across the substrate (or substrate holder) to clamp it. Electrostatic clamping may, therefore, be used. In electrostatic clamping, a potential difference is established between the substrate and the substrate table and/or substrate holder. The potential difference may generate a clamping force. [007] It is important to control the flatness of the substrate, which may be, for example, a wafer. Whilst a substrate may have a flatness which in within specification when it is not in situ within a lithographic apparatus, the flatness may change when the substrate is held in position within a lithographic apparatus due to the forces acting upon it, such as those from electrostatic or vacuum clamping. In this way, the so-called functional flatness of the substrate, namely the flatness when in position for use, needs to be controlled as although the free substrate may be within specification, an in-situ substrate may not. Similarly, it is desirable to provide optical elements, such as mirrors, with optimised surface shapes to achieve optimal results and accuracy. [008] In use, surfaces are subject to wear and tear as well as contamination, and the flatness of surfac