US-12619166-B2 - Clamp for holding an object and method

Abstract

The disclosure provides a clamp comprising a dielectric member; a conductive element disposed on the dielectric member and comprised of a first conductive material; and a number of burls arranged on the conductive element for supporting the object, each burl comprising a second conductive material, wherein the clamp comprises a stack of alternating layers of etch resistant material and a third conductive material arranged between the conductive element and the number of burls.

Inventors

• Thomas POIESZ
• René Adrianus Van Rooij
• Alexander Stein

Assignees

• ASML NETHERLANDS B.V.

Dates

Publication Date

20260505

Application Date

20221014

Priority Date

20211029

Claims (20)

1. 1 . A clamp for holding an object, the clamp comprising: a plurality of burls arranged and configured to support the object, each burl comprising a first conductive material, wherein the plurality of burls is on top of a stack of alternating layers of a layer comprising etch resistant material and a layer comprising a second conductive material, the etch resistant material has a lower removal rate than the removal rate of the first conductive material when the plurality of burls is being removed, and wherein bottom parts of the plurality of burls are formed from the stack of alternating layers.
2. 2 . The clamp of claim 1 , wherein the stack is configured to connect at least two burls of the plurality of burls.
3. 3 . The clamp of claim 1 , wherein the removal rate of the etch resistant material is between 1/10 and 1/10000 of the removal rate of the first conducting material when the plurality of burls is being removed.
4. 4 . The clamp of claim 1 , further comprising a conductive element comprising a third conductive material below the stack, which conductive element is configured to conductively connect at least two burls of the plurality of burls.
5. 5 . The clamp of claim 4 , wherein the etch resistant material protects the conductive element when the plurality of burls is being removed.
6. 6 . The clamp of claim 4 , wherein the first, second, and third conductive materials are the same materials.
7. 7 . The clamp of claim 4 , wherein the stack comprises at least four layers comprising etch resistant material and at least three layers comprising the third conductive material.
8. 8 . The clamp of claim 4 , wherein the first second, and third conductive materials comprise CrN.
9. 9 . The clamp of claim 1 , wherein the etch resistant material comprises Si.
10. 10 . The clamp of claim 1 , wherein the stack has a total thickness between 0.2 and 20 mm.
11. 11 . The clamp of claim 1 , wherein the stack comprises at least two layers of the etch resistant material.
12. 12 . The clamp of claim 1 , wherein the clamp is an electrostatic wafer clamp.
13. 13 . The clamp of claim 1 , wherein the layer comprising etch resistant material and the layer comprising the second conductive material have about the same area seen from a top view of the clamp.
14. 14 . A lithographic system comprising a clamp according to claim 1 .
15. 15 . The clamp of claim 1 , wherein each layer of the stack has a thickness between 50 nm and 1 mm.
16. 16 . The clamp of claim 1 , wherein the burls define a plane configured to support the object.
17. 17 . The clamp of claim 1 , wherein the stack is configured to electrically connect the burls.
18. 18 . A method of making a clamp for holding an object, the method comprising the steps of: disposing a conductive element comprising a first conductive material on a dielectric member; arranging a number of burls, configured to support the object, on the conductive element, wherein each burl comprises a top part comprising a second conductive material and a bottom part comprising a stack of alternating layers of etch resistant material and a third conductive material.
19. 19 . A method of making a clamp for holding an object, the method comprising: arranging a number of burls for supporting the object, each burl comprising a first conductive material, wherein arranging the number of burls comprises: depositing a stack of alternating layers of a layer comprising etch resistant material and a layer comprising a second conductive material on top of an electrically conductive element, depositing the first conductive material on the stack; removing the first conductive material not covered by a mask and removing part of the stack not covered by the first conductive material to thereby form the burl from the first conductive material and a remaining part of the stack.
20. 20 . A method of refurbishing a clamp for holding an object, wherein the clamp comprises a plurality of burls, each burl comprising a first conductive material, on top of a stack of alternating layers of a layer comprising etch resistant material and a layer comprising a second conductive material, the stack is arranged above a dielectric member, the method comprising: removing the first conductive material of each of the plurality of burls to form an intermediate structure; depositing a layer comprising the first conductive material on the intermediate structure; depositing a layer comprising the etch resistant material on the layer of the first conductive material; patterning the layer comprising the etch resistant material for forming another plurality of burls; and removing the first conductive material by etching for forming the another plurality of burls; and removing the layer comprising the etch resistant material.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This applications claims priority of EP application 21205594.1 which was filed on 29 Oct. 2021 and which is incorporated herein in its entirety by reference. FIELD The present invention relates to a clamp for holding an object and a method. The clamp may be an electrostatic clamp. The clamp is for instance part of a wafer support system. The object may be, for instance, a wafer, substrate or reticle in a lithographic apparatus. BACKGROUND 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. As semiconductor manufacturing processes continue to advance, the dimensions of circuit elements have continually been reduced while the amount of functional elements, such as transistors, per device has been steadily increasing over decades, following a trend commonly referred to as ‘Moore's law’. To keep up with Moore's law the semiconductor industry is chasing technologies that enable to create increasingly smaller features. 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 that are patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm (KrF), 193 nm (ArF) and 13.5 nm (EUV). A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within a range of 4 nm to 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 n. At such short wavelengths, precise positioning of the patterning device and/or substrate within the lithographic apparatus is essential. Such lithographic apparatuses may be provided with one or more clamps to clamp the patterning device and/or substrate to an object support, such as a mask table or a wafer table respectively. The clamp may be, for example, a mechanical clamp, a vacuum clamp, or an electrostatic clamp. Electrostatic clamps may be particularly suited to operating at EUV wavelengths, since regions of an EUV lithographic apparatus necessarily operate under near vacuum conditions. Near vacuum herein may refer to pressures in the range of 5 kPa and below, or in the range of 1 to 10 Pa. At such short wavelengths, precise positioning of the patterning device and/or substrate within the lithographic apparatus is essential. Such lithographic apparatuses may be provided with one or more clamps to clamp the patterning device and/or substrate to an object support, such as a mask table or a wafer table respectively. The clamp may be, for example, a mechanical clamp, a vacuum clamp, or an electrostatic clamp. Electrostatic clamps may be particularly suited to operating at EUV wavelengths, since regions of an EUV lithographic apparatus necessarily operate under near vacuum conditions. Some electrostatic wafer clamps have a dielectric surface comprising (equally spaced) metallic lines, known in the art as ‘Manhattan lines’, which electrically conductively connect protrusions or ‘burls’ defining a plane for holding the patterning device and/or substrate. As a result of extensive use, wherein for instance thousands or even tens of thousands of wafers are produced per day, an initial relative roughness of top surfaces of the protrusions is reduced over time. As the top surfaces smoothen, they start to stick to the wafers, which are also relatively smooth. The stickiness slows down the lithography process, and eventually involves a risk of damaging the wafers. To obviate this problem, the wafer clamp is typically refurbished at some point. Refurbishing involves etching or stripping the protrusions. The etching step removes all metallic or conductive material. Subsequently, the structures are deposited anew. This process however is relatively time intensive and costly. It is an object of at least one embodiment of at least one aspect of the present invention to obviate or at least mitigate at least one of the above identified shortcomings of the prior art. SUMMARY A clamp for holding an object, the clamp comprising: a dielectric member;a conductive element disposed on the dielectric member and comprised of a first conductive material; anda number of burls arranged on the conductive element for supporting the object, each burl comprising a second conductive material,wherein the clamp comprises a stack of alternating layers of etch resistant material and a third conductive material arranged between the conductive element and the number of burls. In an embodiment, the first, second, third conductive material are the same. In an embodiment, the first,