US-12619165-B2 - Electrostatic holder, object table and lithographic apparatus

US12619165B2US 12619165 B2US12619165 B2US 12619165B2US-12619165-B2

Abstract

The invention relates to an electrostatic holder comprising: a body, and a clamping element attached to the body, said clamping element comprising an electrode for applying an attractive force between the clamping element and a first to be clamped object, wherein an outer edge of the body is configured to provide a gap between the outer edge of the body and the first to be clamped object, which gap is configured for outputting a fluid for reducing dust particles reaching the first to be clamped object or a second to be clamped object on an opposite side of the holder.

Inventors

Tiannan GUAN
Richard Joseph Bruls
Frits Van Der Meulen
Zhuangxiong Huang
Johannes Bernardus Charles ENGELEN
Güneş Nakiboǧlu
Matthias KRUIZINGA
Petrus Jacobus Maria Van Gils
Aldo Tralli
Sjoerd Frans DE VRIES
Marcel Maria Cornelius Franciscus TEUNISSEN

Assignees

ASML NETHERLANDS B.V.

Dates

Publication Date: 20260505
Application Date: 20220713
Priority Date: 20210812

Claims (13)

1 . An object table comprising: a positioning device configured to move the object table in at least one direction; an electrostatic holder comprising: a body comprising a recess and an outer edge that defines a gap between the outer edge and the positioning device; a clamping element arranged in the recess and attached to the body such that there is a first space between the clamping element and the body, the clamping element comprising an electrode configured to apply an attractive force between the clamping element and the positioning device to clamp the positioning device on a side of the body; and a seal arranged between a bottom of the recess and the clamping element and comprising one or more holes opposite to the outer edge, the seal configured to provide a gas barrier at a circumference of the first space; and a gas supply system configured to provide a fluid to the first space and through the one or more holes in the seal such that the gap outputs the fluid.
2 . The object table of claim 1 , wherein the electrostatic holder further comprises: a pressure equalizing chamber arranged between the gap and the gas supply system, and wherein the gap is configured to act as a flow restriction of the pressure equalizing chamber.
3 . The object table of claim 2 , wherein the pressure equalizing chamber is arranged between the one or more holes in the seal and the gap.
4 . The object table of claim 1 , wherein a gap distance between the outer edge of the body and the positioning device varies over the gap as determined by a shape of the outer edge.
5 . The object table of claim 4 , wherein the gap distance over the gap has a wave pattern, a sine wave pattern, or a square wave pattern, with one or more portions of the outer edge defining a minimal gap distance being alternated by one or more portions of the outer edge defining a maximum gap distance.
6 . The object table of claim 5 , wherein the one or more portions of the outer edge defining the minimal gap distance are arranged opposite corresponding ones of the one or more holes in the seal.
7 . The object table of claim 1 , wherein: an inner valve is provided between each of the one or more holes in the seal and the first space, an outer valve is provided between each of the one or more holes in the seal and the gap, and the inner and outer valves are configured such that with an increasing pressure the inner valve is urged towards a closed position and the outer valve is urged towards an open position.
8 . The object table of claim 1 , wherein: the first space comprises a high-pressure subspace and a high-flow subspace, the seal is further configured to provide a gas barrier between the high-pressure subspace and the high-flow subspace, the high-pressure subspace and the high-flow subspace are both connectable to the gas supply system, and the gap is in fluid communication with the high-flow subspace.
9 . The object table of claim 8 , further comprising: one or more pressure connections to connect the gas supply system to the high-pressure subspace and one or more flow connections to connect the gas supply system to the high-flow subspace, and the one or more pressure connections are provided with removable flow restrictor devices to set a flow resistance in the one or more pressure connections at a larger value than a flow resistance of the one or more flow connections.
10 . The object table of claim 1 , wherein the positioning device has a flat surface opposite the outer edge of the body.
11 . The object table of claim 1 , wherein: an output of the fluid has a flow rate in a range between 2 mbar/s and 100 mbar/s or between 5 mbar/s and 50 mbar/s, or/and the gap has a maximum height in a range between 20 um and 500 um or between 50 um and 200 um.
12 . The object table of claim 1 , further comprising: a first sensor configured to measure a position change of the clamping element with respect to the body; or/and a second sensor configured to measure a position change of a second clamping element with respect to the body, wherein the second clamping element is configured to hold an object on an opposite side of the body from the side with the positioning device.
13 . A lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a support structure constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; and a projection system configured to project the patterned radiation beam onto the substrate, wherein the substrate table comprises the object table according to claim 1 , or/and wherein the support structure comprises the object table according claim 1 .

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority of EP application Ser. No. 21191135.9 which was filed on 12 Aug. 2021 and 21202475.6 which was filed on 13 Oct. 2021 and which are incorporated herein in their entirety by reference. FIELD The present invention relates to an electrostatic holder, an object table comprising such an electrostatic holder, and a lithographic apparatus comprising such an object table. 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. 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. EUV radiation may easily be absorbed by a gas, so that illumination of a substrate or reticle with EUV radiation is typically carried out in an environment with a gaseous pressure much less than atmospheric pressure, which may be referred to as a vacuum or under vacuum conditions. A drawback of these conditions is that a perfect vacuum cannot be reached and dust particles coming from elsewhere in the lithographic apparatus may reach a substrate or reticle illuminated by the EUV radiation causing defects in the transferred pattern. This may even result in a non-functional integrated circuit on the substrate. SUMMARY Considering the above, it is an object of the invention to provide a lithographic apparatus in which dust particles coming from elsewhere in the lithographic apparatus cause less problems during illumination of a substrate or reticle with EUV radiation. According to an embodiment of the invention, there is provided an electrostatic holder comprising: a body, and a clamping element attached to the body, said clamping element comprising an electrode for applying an attractive force between the clamping element and a first to be clamped object, wherein an outer edge of the body is configured to provide a gap between the outer edge of the body and the first to be clamped object, which gap is configured for outputting a fluid for reducing dust particles reaching the first to be clamped object or a second to be clamped object on an opposite side of the holder. According to another embodiment of the invention, there is provided an object table for holding and/or positioning an object, comprising a positioning device for moving the object table in at least one direction, and an electrostatic holder for holding an object, wherein the holder is attachable to the positioning device using attractive forces, wherein the electrostatic holder comprises: a body, and a clamping element attached to the body, said clamping element comprising an electrode for applying the attractive force between the clamping element and the positioning device, wherein an outer edge of the body is configured to provide a gap between the outer edge of the body and the positioning device, which gap is configured for outputting a fluid for reducing dust particles reaching the object on the holder. According to a further embodiment of the invention, there is provided a lithographic apparatus comprising: an illumination system configured to condition a radiation beam, a support structure constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam, a substrate table constructed to hold a substrate, and a projection system configured to project the patterned radiation beam onto the substrate, wherein the substrate table is an object table according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: FIG. 1 depicts a lithographic system comprising a lithographic apparatus and a radiation source; FIG. 2 schematically depicts a first cross-section of an object table according to an embodiment of the invention; FIG. 3 schematically depicts a second cross-section of the object table of FIG. 2; FIG. 4 schematically depicts a third cross-section of the object table of FIG. 2; FIG. 5 schematically depicts a side view of a gap between the outer edge of the electrostatic holder and the positioning device of the object table of FIG. 2; FIG. 6 schematically depicts a cross-section of an obje