Support system

Abstract

Disclosed herein is a support system for an EUV lithography apparatus (LA), the support system comprising: a support structure (MT) configured to support an object (MA); a component (31) located such that the object (MA) is between the support structure (MT) and the component (31); and at least one thermal conditioner (32, 33) configured to apply a temperature gradient of at least 1,000°C / m between the object (MA) and the component (31).

Description

SUPPORT SYSTEMCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 24180071.3 which was filed on June 05, 2024 and which is incorporated herein in its entirety by reference.FIELD

[0002] The present invention relates to a support system, a lithographic apparatus, a method for supporting an object and a patterning device.BACKGROUND

[0003] 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.

[0004] 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.

[0005] Particles can contaminate the lithographic apparatus. For example, particles can contaminate the patterning device. Particles that contaminate the patterning device can cause defects.

[0006] It is therefore desirable to reduce contamination by particles. In particular, it is desirable to reduce contamination of the patterning device by particles.SUMMARY

[0007] The present invention is directed to providing a support system, a lithographic apparatus and a method for supporting an object, and a patterning device.

[0008] According to an aspect of the invention, there is provided a support system for an EUV lithography apparatus, the support system comprising: a support structure configured to support an object; a component located such that the object is between the support structure and the component; and at least one thermal conditioner configured to apply a temperature gradient of at least l,000°C / m between the object and the component.

[0009] According to another aspect of the invention, there is provided a method for supporting an object for an EUV lithography apparatus, the method comprising: supporting an object with a support structure; and applying a temperature gradient of at least l,000°C / m between the object and a component located such that the object is between the support structure and the component.

[0010] According to another aspect of the invention, there is provided a patterning device for an EUV lithography apparatus, wherein the patterning device comprises: a material that has a coefficient of thermal expansion substantially at a minimum at a temperature of at least 25 °C.

[0011] Further embodiments, features and advantages of the present invention, as well as the structure and operation of the various embodiments, features and advantages of the present invention are described in detail below with reference to the accompanying drawings.DESCRIPTION OF THE DRAWINGS

[0012] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:Figure 1 depicts a lithographic system comprising a lithographic apparatus and a radiation source;Figure 2 schematically depicts a patterning device, for example of the lithographic apparatus of Figure 1;Figure 3 is a schematic illustration of a first cross-section through a patterning device on a support structure and masking blades, for example of the lithographic apparatus of Figure 1 ; andFigure 4 is an illustration of a transport case for a patterning device.The features shown in the Figures are not necessarily to scale, and the size and / or arrangement depicted is not limiting. It will be understood that the Figures include optional features which may not be essential to the invention. Furthermore, not all of the features of the apparatus are depicted in each of the figures, and the Figures may only show some of the components relevant for describing a particular feature.DETAILED DESCRIPTION

[0013] Figure 1 shows a lithographic system comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS and a substrate table WT configured to support a substrate W.

[0014] The illumination system IL is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident upon the patterning device MA. Thereto, the illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. The faceted field mirror device 10 and faceted pupil mirror device 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to, or instead of, the faceted field mirror device 10 and faceted pupil mirror device 11.

[0015] After being thus conditioned, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B’ is generated. The projection system PS is configured to project the patterned EUV radiation beam B’ onto the substrate W. For that purpose, the projection system PS may comprise a plurality of mirrors 13,14 which are configured to project the patterned EUV radiation beam B’ onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B’, thus forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is illustrated as having only two mirrors 13,14 in Figure 1, the projection system PS may include a different number of mirrors (e.g. six or eight mirrors).

[0016] The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus LA aligns the image, formed by the patterned EUV radiation beam B’, with a pattern previously formed on the substrate W.

[0017] A relative vacuum, i.e. a small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL, and / or in the projection system PS. Also a relative vacuum may be provided around the patterning device MA and the substrate W.

[0018] The radiation source SO may be a laser produced plasma (LPP) source, a discharge produced plasma (DPP) source, a free electron laser (FEL) or any other radiation source that is capable of generating EUV radiation.

[0019] Figure 2 schematically depicts a support system (which may be referred to as a support structure system or a support system or assembly comprising a support structure). The support system is for a lithographic system, for example of the type shown in Figure 1. The support system comprises a support structure MT. For example the support structure MT may be the support structure MT shown in Figure 1. The support structure MT is configured to support an object. For example, the object may be a patterning device MA, such as the patterning device MA shown in Figure 1. Alternatively, the object may be a different component such as a reflector (e.g. mirror) or part of a sensor. For convenience, embodiments are described below in the context of the object being a patterning device MA.

[0020] As shown in Figure 2, in an embodiment the support system comprises a component 31. The component 31 is located such that the patterning device MA is between the support structure MT and the component 31. The component 31 is arranged to face at least part of the patterning device MA. The patterning device MA may face the component 31. The patterning device MA may comprise a facing surface arranged to face the component 31. The facing surface of the patterning device MA may be the surface of the patterning device MA facing away from the support structure MT. As shown in Figure 2, the component 31 is distanced from the patterning device MA. There is a gap between the patterning device MA and the component 31.

[0021] As shown in Figure 2, in an embodiment the patterning device MA is substantially planar. In an embodiment the component 31 is at least partially planar. As shown in Figure 2, in an embodiment the plane of the patterning device MA is substantially parallel to the plane of the component 31.

[0022] In an embodiment the support system comprises at least one thermal conditioner 32, 33 configured to apply a temperature gradient of at least 1000°C / m (i.e. at least 10 K / 10 mm) between the patterning device MA and the component 31. The temperature gradient may generate a thermophoretic force between the patterning device MA and the component 31.

[0023] In an embodiment the at least one thermal conditioner 32, 33 is configured such that the temperature of the patterning device MA is greater than the temperature of the component 31. The temperature gradient applied by the at least one thermal conditioner 32, 33 may be positive in the direction towards the patterning device MA. In an embodiment the temperature gradient is at least one 1000°C / m between the patterning device MA and the component 31 in a direction substantially perpendicular to the surface (e.g. the facing surface) of the patterning device MA. The temperature gradient results in a thermophoretic force substantially perpendicular to the surface of the patterning device MA down the temperature gradient. The thermophoretic force effectively pushes particles away from the patterning device MA. By pushing particles away from the patterning device MA, contamination by particles may be reduced.

[0024] In an embodiment the at least one thermal conditioner 32, 33 is configured to apply the temperature gradient of at least 1000°C / m between the facing surface of the patterning device MA and the component 31. The facing surface of the patterning device MA may be different from the average temperature of the patterning device MA. In general, the facing surface of the patterning device MA may be expected to have a higher temperature than the average temperature of the patterning device MA. In use of the lithographic system, radiation may be incident on the surface of the patterning device MA. The surface of the patterning device MA heats up. The heat may be transferred by conduction through the patterning device MA, thereby raising the average temperature of the patterning device MA. However, the surface of the patterning device MA on which the radiation is incident may be maintained at a higher temperature than the average temperature of thepatterning device MA. The temperature gradient is between the surface of the patterning device MA and the component 31.

[0025] In an embodiment the at least one thermal conditioner 32, 33 is configured to apply a temperature gradient of at least 1500°C / m, optionally at least 2000°C / m, optionally at least 2500°C / m, optionally at least 3000°C / m, optionally at least 3500°C / m and optionally at least 4000°C / m. By increasing the temperature gradient, the thermophoretic force may be increased. By increasing the thermophoretic force, the possibility of contamination of the patterning device MA by particles may be reduced. An embodiment of the invention is expected to achieve reduced contamination by particles. An embodiment of the invention is expected to achieve a reduction in imaging defects.

[0026] In an embodiment the at least one thermal conditioner 32, 33 is configured to apply a temperature difference between the patterning device MA and the component 31 of at least 10°C, optionally at least 15°C, optionally at least 20°C, optionally at least 25°C, optionally at least 30°C, optionally at least 35°C, and optionally at least 40°C. A greater temperature difference results in a greater temperature gradient for a given distance between the patterning device MA and the component 31. The temperature difference may be between the surface of the patterning device MA that faces the component 31 and the component 31.

[0027] In an embodiment the minimum distance between the patterning device MA and the component 31 is at most 50 mm, optionally at most 20 mm, optionally at most 10 mm and optionally at most 5 mm. By reducing the distance between the patterning device MA and the component 31, the temperature gradient may be increased for a given temperature difference between the patterning device MA and the component 31.

[0028] As shown in Figure 2, there may be an attractive force 36 attracting a particle 30 towards the patterning device MA. For example, the attractive force 36 may be an electrostatic force. The electrostatic force may result from an electric field which may be plasma-induced. Particles 30 may be attracted to the patterning device MA by the electrostatic force.

[0029] As shown in Figure 2, in an embodiment the temperature gradient results in a thermophoretic force 37 that is greater than the attractive force 36. There may be an overall force on the particle 30 in the direction away from the patterning device MA. It is possible that an electrostatic force might momentarily be higher than the thermophoretic force 37 when the patterning device MA is irradiated. However, the thermophoretic force 37 is expected to be higher than the attractive force 36 at least where the patterning device MA is not irradiated.

[0030] For example, the attractive force 36 may be expected to be in the region of about 5 x 1016N. In an embodiment the at least one thermal conditioner 32, 33 is configured to apply a temperature gradient that generates a thermophoretic force of greater than 5 x 1016N, optionally at least 1 x 1015N for 100 nm particles.

[0031] As shown in Figure 2, in an embodiment the support system comprises a thermal conditioner 32 for the support structure MT. The thermal conditioner 32 for the support structure MTis configured to thermally condition the patterning device MA via the support structure MT. The thermal conditioner 32 may be configured to thermally condition the support structure MT. By thermally conditioning the support structure MT, the patterning device MA may be thermally conditioned, for example through conduction between the support structure MT and the patterning device MA.

[0032] The thermal conditioner 32 may be configured to cool the support structure MT and the patterning device MA. The thermal conditioner 32 may be configured to lower the temperature of the patterning device MA compared to if the thermal conditioner 32 were not provided. The thermal conditioner, for example, comprise one or more channels within the support structure MT. A thermal conditioning fluid may pass through the one or more channels. For example, the thermal conditioning fluid may be water. The temperature of the thermal conditioning fluid may be controlled so as to control the thermal conditioning of the support structure MT and the patterning device MA.

[0033] As shown in Figure 2, in an embodiment the thermal conditioner 32 is located on the opposite side of the patterning device MA from the facing surface of the patterning device MA. The side of the patterning device MA closest to the thermal conditioner 32 may be expected to have a lower temperature compared to the facing surface of the patterning device MA. The average temperature of the patterning device may be between the temperature of the facing surface and the temperature of the side closest to the thermal conditioner 32.

[0034] In an embodiment the thermal conditioning fluid has a temperature of at least 5 °C, optionally at least 10°C, optionally at least 15°C and optionally at least 20°C. By increasing the temperature of the thermal conditioning fluid, the temperature gradient between the patterning device MA and the component 31 may be increased. The thermophoretic force may be increased.

[0035] In an embodiment the thermal conditioner 32 is configured to maintain the surface of the patterning device MA at a temperature of at least 35°C, optionally at least 40°C, optionally at least 45 °C and optionally at least 50°C. By providing a greater surface temperature of the patterning device MA, the temperature gradient and the thermophoretic force may be increased.

[0036] By increasing the temperature of the thermal conditioning fluid, less power may be required to cool the thermal conditioning fluid for the thermal conditioner 32.

[0037] By increasing the temperature at which the surface of the patterning device MA is maintained, the extent of cooling required by the thermal conditioner 32 may be reduced for a given source power (i.e. power of radiation incident on the patterning device MA). For higher radiation incident powers on the patterning device MA the temperature difference between the thermal conditioner 32 and the surface of the patterning device MA needs to be larger to remove the absorbed power. Given a temperature of the patterning device MA the cooling fluid temperature might need to be very cold even below zero requiring special fluids (at least not water), which is not desired. So, increasing the temperature of the surface of the patterning device MA can help to relax the requiredcooling fluid temperatures. By increasing the temperature at which the surface of the patterning device MA is maintained, a greater source power may be used for a given thermal conditioner 32.

[0038] In an embodiment the support system comprises at least one heater configured to heat the patterning device MA. For example, the support structure MT may comprise at least one heater. In an embodiment the support structure MT comprises a plurality of burls having distal ends within a plane for supporting the patterning device MA. In an embodiment the support structure MT comprises at least one heater on the surface of the support structure MT between the burls. For example, the heater may be a foil heater or a wire heater. The heater is configured to heat the patterning device MA. The heater may be at the same side of the support structure MT as the patterning device MA.

[0039] By providing at least one heater, the patterning device MA may be maintained at a higher temperature. The surface of the patterning device MA facing the component 31 may be maintained at a higher temperature, thereby increasing the temperature gradient and the thermophoretic force.

[0040] In an embodiment the support system comprises at least one heater external to the support structure MT. For example, the support system may comprise an infrared heater configured to irradiate the patterning device MA with infrared radiation. The infrared radiation heats up the facing surface of the patterning device MA.

[0041] By reducing the requirements of cooling by the thermal conditioner 32, the design freedom of the thermal conditioner 32 may be increased. For example, it may not be necessary to provide additives to the thermal conditioning fluid in order to enable the thermal conditioning fluid to have lower temperatures, for example lower than about 8°C. It may not be necessary to provide a cryogenic thermal conditioner.

[0042] In an embodiment the gap between the patterning device MA and the surface of the support structure MT from which the burls protrude is filled with a gas. There may be a backfill pressure, for example of the order of 10-15 mbar. The gas may be configured to increase thermal conductivity between the support structure MT and the patterning device MA. By increasing the thermal conductivity, the effectiveness of the thermal conditioner 32 in thermally conditioning the patterning device MA may be improved. By maintaining the facing surface of the patterning device MA at a higher temperature, the backfill pressure may be reduced. By reducing the backfill pressure, the effect of cooling of the patterning device MA by the thermal conditioner 32 may be reduced.

[0043] As shown in Figure 2, in an embodiment the support system comprises a thermal conditioner 33 for the component 31. The thermal conditioner 33 for the component 31 is configured to thermally condition the component 31. For example, the thermal conditioner 33 may comprise one or more channels through the component 31. A thermal conditioning fluid may pass through the one or more channels so as to thermally condition the component 31. In an embodiment the thermal conditioning fluid comprises water.

[0044] The thermal conditioner 33 for the component 31 may be configured to cool the component 31 to lower temperatures to increase the thermophoretic force. For example, in an embodiment the thermal conditioner 33 is configured to thermally condition the component 31 to a temperature of at most 20°C, optionally at most 10°C, optionally at most 5°C and optionally less than 0°C. By reducing the temperature of the component 31 , the temperature gradient and the thermophoretic force may be increased.

[0045] In an embodiment the component 31 is thermally conditioned with a thermal conditioning fluid having a temperature of at most 20°C, optionally at most 15°C, optionally at most 10°C, optionally at most 5 °C. In an embodiment the thermal conditioning fluid comprises water and at least one additive to enable lower temperatures of thermal conditioning fluid.

[0046] In an embodiment the thermal conditioner 33 is a cryogenic thermal conditioner configured to thermally condition the component 31 to a temperature below 0°C.

[0047] As shown in Figure 2, in an embodiment the support system comprises a gas supply configured to supply a gas flow 34. The gas flow 34 may be across the surface of the patterning device MA. The gas flow 34 may generate a drag force 38. The drag force 38 may be substantially parallel to the surface of the patterning device MA. The drag force 38 may reduce the possibility of particles coming into contact with the facing surface of the patterning device MA.

[0048] As shown in Figure 2, as a result of the thermophoretic force 37 and the drag force 38 on the particle 30, the particle 30 may have a trajectory 35 away from the patterning device MA. An embodiment of the invention is expected to reduce the contamination of the patterning device MA by particles 30.

[0049] In an embodiment the patterning device has a coefficient thermal expansion substantially at a minimum at a temperature of at least 25°C, optionally at least 30°C, optionally at least 35°C and optionally at least 40°C. In an embodiment the coefficient thermal expansion is substantially zero at a temperature of at least 25°C, optionally at least 30°C, optionally at least 35°C and optionally at least 40°C. By increasing the temperature at which the coefficient thermal expansion of the patterning device MA is at a minimum, the patterning device MA may be operated at a higher temperature without unduly increasing deformation of the patterning device MA by changes in temperature. Thermal deformation of the patterning device MA may be reduced around its operating temperature. The operating temperature may be the temperature of the patterning device MA during an exposure process using the EUV lithography apparatus. By reducing thermal deformation, overlay errors that can be caused by temperature variations during exposure may be reduced.

[0050] In an embodiment the patterning device MA comprises an ultra-low expansion (ULE) glass. In an embodiment the patterning device MA comprises silica and titanium dioxide. By selecting the percentage of titanium dioxide, the temperature at which the coefficient thermal expansion is at a minimum may be controlled. The titanium dioxide content of the patterning device MA may be selected to have a higher temperature at which the coefficient thermal expansion is at its minimum.When the patterning device MA is used at its operating temperature, thermal deformation may be reduced.

[0051] In an embodiment the patterning device MA comprises a pattern. The pattern may be formed on the patterning device MA in a pattern formation step. The pattern may be formed on a blank patterning device. In an embodiment the temperature of the blank patterning device is controlled during the pattern formation step. It is possible that the pattern formed on the patterning device MA may change as the temperature of the patterning device MA changes.

[0052] In an embodiment the temperature of the patterning device MA is controlled to be substantially at the operating temperature of the patterning device MA during the pattern formation step. For example, the operating temperature may be at least 25°C, optionally at least 30°C, optionally at least 35°C and optionally at least 40°C. In an embodiment the temperature of the patterning device MA during the pattern formation step is at least 25°C, optionally at least 30°C, optionally at least 35°C and optionally at least 40°C.

[0053] In an embodiment the temperature of the patterning device MA during the pattern formation step is different from the operating temperature. The pattern may be designed such that when the patterning device MA with the pattern applied to it is operated at its operating temperature, the pattern formed on the patterning device MA is the target pattern. That is, the pattern that is formed on the blank patterning device may be different from the pattern of the patterning device MA when the patterning device MA is used at its operating temperature in an exposure process. In this way, the temperature of the blank patterning device during the pattern formation step may be simulated to be at the operating temperature of the patterning device MA.

[0054] In an embodiment the lithographic apparatus is provided with four masking blades, which define the extent of the field on the patterning device MA which is illuminated, as now described with reference to Figure 3. These blades are sometimes referred to as reticle masking blades. The illumination system IL is operable to illuminate a generally rectangular region of an object (e.g. a patterning device MA) disposed on the support structure MT. This generally rectangular region may be referred to as the slit of the illumination system IL and is defined by four masking blades. The extent of the generally rectangular region in a first direction, which may be referred to as the x direction, is defined by a pair of x-masking blades 110, 112. The extent of the generally rectangular region in a second direction, which may be referred to as the y direction, is defined by a pair of y- masking blades.

[0055] Each of the masking blades 110, 112 is disposed close to, but slightly out of, the plane of a patterning device MA on the support structure MT. The x-masking blades 110, 112 are disposed in a first plane and the y-masking blades are disposed in a second plane 122.

[0056] Each of the masking blades 110, 112 defines one edge of a rectangular field region 124 in the plane of the patterning device MA which receives radiation. Each blade may be independently movable between a retracted position wherein it is not disposed in the path of the radiation beam andan inserted position wherein it at least partially blocks the radiation beam projected onto the patterning device MA. By moving the masking blades 110, 112 into the path of the radiation beam, the radiation beam B can be truncated (in the x and / or y direction) thus limiting the extent of the field region 124 which receives radiation beam B.

[0057] In an embodiment the component 31 of the support system comprises a masking blade 110, 112. The masking blade 110, 112 may be thermally conditioned in order to provide the temperature gradient that generates the thermophoretic force. In an embodiment, both the x-masking blades 110, 112 and the y-masking blades disposed in the second plane 122 are thermally conditioned so as to provide the thermal gradient.

[0058] As shown in Figure 3, the distance between the y-masking blades and the facing surface of the patterning device MA may be greater than the distance between the x-masking blades 110, 112 and the facing surface of the patterning device MA. The temperature gradient between the patterning device MA and the x-masking blades 110, 112 may be different from the temperature gradient between the patterning device MA and the y-masking blades. The thermophoretic force towards the x-masking blades 110, 112 may be different from the thermophoretic force towards the y-masking blades.

[0059] In an embodiment, the x-masking blades 110, 112 and the y-masking blades are thermally conditioned to substantially the same temperature. In an alternative embodiment, the x-masking blades 110, 112 are thermally conditioned to a temperature that is different from the temperature to which the y-masking blades are thermally conditioned. For example, the y-masking blades may be thermally conditioned to a lower temperature than the x-masking blades 110, 112. In an embodiment, the y-masking blades are provided with a thermal conditioner configured to thermally condition the y- masking blades such that the temperature gradient between the patterning device MA and the y- masking blades is substantially equal to the temperature gradient between the patterning device MA and the x-masking blades 110, 112.

[0060] It is not essential for the component 31 of the support system to comprise the masking blades. In an embodiment the component 31 comprises a body and / or plate different from the masking blades. For example, during use of the lithographic system the relative positions of the masking blades and the patterning device MA may be changed such that portions of the patterning device MA that face the masking blades during an exposure operation do not face the masking blades. In an embodiment, one or more bodies / plates are provided to function as the component 31 to face the patterning device MA in regions beyond the masking blades. The thermophoretic force away from the patterning device MA may be maintained even when the relative positions between the masking blades and the patterning device MA are changed.

[0061] In an alternative arrangement, the masking blades may be sized such that portions of the patterning device MA that face the masking blades during an exposure operation are also facing themasking blades when the relative positions between the masking blades and the patterning device MA are changed. The masking blades may be increased in size.

[0062] Figure 4 is an illustration of a transport case 60 for the patterning device MA. As shown in Figure 4 in an embodiment the transport case 60 comprises a pod 20. The pod 20 is for housing a patterning device MA. As shown in Figure 4, in an embodiment the pod 20 comprises a top member 21 and an opposing bottom member 24. In an embodiment the patterning device MA is for EUV lithography. The pod 20 houses the patterning device MA in a library, which may be kept at vacuum pressure, in the lithographic apparatus. For exposures, the pod 20 is opened and the patterning device MA is clamped into position.

[0063] In addition, the transport case 60 comprises an outer pod 61. The outer pod 61 is configured to close around the inner pod 20. As shown in Figure 4 in an embodiment the outer pod 61 comprises a top part 62 and a bottom part 63 that can enclose around the inner pod 20. The outer pod 61 is used primarily for transport and storage of the patterning device MA. The outer pod 61 is configured to shield the inner pod 20 from human touch and ambient contamination. In use, the outer pod 61 does not enter into the vacuum environment of the lithographic apparatus. The outer pod 61 is intended to be used only outside of the lithographic apparatus. In contrast, the inner pod 20 enters into the vacuum environment of the lithographic apparatus. Accordingly, there is a greater requirement for the inner pod 20 to remain clean than for the outer pod 61.

[0064] In use, the outer pod 61 may be loaded onto a patterning device loading bay. This may be done by hand. Alternatively, this may be done by an automated (overhead) delivery system. The outer pod 61 is opened. The inner pod 20 is removed from the outer pod 61. The pressure is reduced towards a vacuum pressure. The pod 20 is then stored in a vacuum library. For exposures, the top member 21 is removed from the pod 20. The top member 21 may remain in the library. The patterning device MA on the bottom member 24 is moved to an exposure clamp. The exposure clamp is configured to hold the patterning device MA in place during an exposure. When the exposure clamp holds the patterning device MA, the bottom member 24 is removed from the patterning device MA. The patterning device MA held by the clamp is then aligned, and then an exposure process is performed.

[0065] In an embodiment the patterning device MA is heated before an exposure process using the EUV lithography apparatus. For example, the patterning device MA may be preheated to its high operating temperature. The patterning device MA may be preheated such that its temperature is at or near the core temperature of the patterning device MA during an exposure process. By preheating the patterning device MA, the thermophoretic force may be provided at the beginning of the exposure process. It may not be necessary to wait for the radiation to heat the patterning device MA before the thermophoretic force reduces the possibility of particle contamination.

[0066] In an embodiment, the patterning device MA is heated before supporting the patterning device MA with the support structure MT. The patterning device MA may be preheated beforeloading it onto the support structure MT. The patterning device MA may be clamped with little or no thermal deformation with respect to its high operating temperature.

[0067] For example, the patterning device MA may be heated to substantially its operating temperature before supporting the patterning device MA with the support structure MT. An embodiment of the invention is expected to achieve a thermophoretic force that is working already before exposure starts. In an embodiment the backfill gas that generates the backfill pressure is switched off to prevent the patterning device MA from cooling down immediately after clamping, and / or during the initial measurements of alignment of the patterning device MA before the start of the exposure. This may help to maintain the pre-heated temperature.

[0068] In an embodiment the patterning device MA is heated by heating a pod housing the patterning device MA. For example, the inner pod 20 housing the patterning device MA may be heated so as to heat the patterning device MA. In an embodiment, the pod is heated while the pod is in an environment at vacuum pressure. For example, the pod 20 may be in the library when the pod 20 is heated so as to preheat the patterning device MA.

[0069] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquidcrystal displays (LCDs), thin-film magnetic heads, etc.

[0070] Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or mask (or other patterning device). These apparatuses may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non- vacuum) conditions.

[0071] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims and clauses set out below.1. A support system for an EUV lithography apparatus, the support system comprising: a support structure configured to support an object; a component located such that the object is between the support structure and the component; and at least one thermal conditioner configured to apply a temperature gradient of at least l,000°C / m between the object and the component.2. The support system of clause 1, wherein the at least one thermal conditioner is configured such that a temperature of the object is greater than a temperature of the component.3. The support system of clause 1 or 2, wherein the temperature gradient is at least l,000°C / m between the object and the component in a direction substantially perpendicular to a surface of the object.4. The support system of any preceding clause, wherein a minimum distance between the object and the component is at most 20mm.5. The support system of any preceding clause, wherein a temperature difference between the object and the component is at least 10°C.6. The support system of any preceding clause, the at least one thermal conditioner comprising: a thermal conditioner for the support structure configured to thermally condition the object via the support structure.7. The support system of any preceding clause, the at least one thermal conditioner comprising: at least one heater configured to heat the object.8. The support system of clause 7, wherein the support structure comprises the at least one heater.9. The support system of any preceding clause, the at least one thermal conditioner comprising: a thermal conditioner for the component configured to thermally condition the component.10. The support system of any preceding clause, comprising: the object.11. The support system of clause 10, wherein the object has a coefficient of thermal expansion substantially at a minimum at a temperature of at least 25 °C.12. The support system of any preceding clause, wherein the object is a patterning device.13. The support system of any preceding clause, wherein the component comprises a masking blade configured to at least partially define an extent of a field on the object which is illuminated in use.14. The support system of any preceding clause, comprising: a gas supply configured to supply a gas flow across a surface of the object.15. The support system of any preceding clause, wherein the temperature gradient induces a thermophoretic force on particles in a direction away from the object.16. A lithographic apparatus comprising: the support system of any preceding clause.17. A method for supporting an object for an EUV lithography apparatus, the method comprising: supporting an object with a support structure; and applying a temperature gradient of at least l,000°C / m between the object and a component located such that the object is between the support structure and the component.18. The method of clause 17, comprising: maintaining a surface of the object at a temperature of at least 35°C.19. The method of clause 17 or 18, comprising: thermally conditioning the support structure with a thermal conditioning fluid having a temperature of at least 10°C.20. The method of any of clauses 17-19, comprising: thermally conditioning the component with a thermal conditioning fluid having a temperature of at most 20°C.21. The method of any of clauses 17-20, comprising: heating the object before an exposure process using the EUV lithography apparatus.22. The method of clause 21, comprising: heating the object before supporting the object with the support structure.23. The method of clause 22, wherein the object is heated to substantially an operating temperature before supporting the object with the support structure, the operating temperature being the temperature of the object during an exposure process using the EUV lithography apparatus.24. The method of any of clauses 21-23, wherein the object is heated by heating a pod housing the object.25. The method of clause 24, wherein the pod is heated while the pod is in an environment at vacuum pressure.26. The method of any of clauses 17-25, comprising: applying a pattern to the object such that the object has a target pattern at a temperature of at least 25°C.27. The method of clause 26, wherein the pattern is applied while the object is maintained at a temperature of at least 25 °C.28. A patterning device for an EUV lithography apparatus, wherein the patterning device comprises: a material that has a coefficient of thermal expansion substantially at a minimum at a temperature of at least 25 °C.29. The patterning device of clause 28, wherein the material has a coefficient of thermal expansion substantially at a minimum at a temperature of at least 30°C.30. The patterning device of clause 28, wherein the material has a coefficient of thermal expansion substantially at a minimum at a temperature of at least 40°C.31. The patterning device of any of clauses 28-30, comprising: a pattern applied while the patterning device is maintained at a temperature of at least 25 °C.

Claims

CLAIMS1. A support system for an EUV lithography apparatus, the support system comprising: a support structure configured to support an object; a component located such that the object is between the support structure and the component; and at least one thermal conditioner configured to apply a temperature gradient of at least l,000°C / m between the object and the component.

2. The support system of claim 1, wherein the at least one thermal conditioner is configured such that a temperature of the object is greater than a temperature of the component.

3. The support system of claim 1 or 2, wherein the temperature gradient is at least l,000°C / m between the object and the component in a direction substantially perpendicular to a surface of the object.

4. The support system of any preceding claim, wherein a minimum distance between the object and the component is at most 20mm.

5. The support system of any preceding claim, wherein a temperature difference between the object and the component is at least 10°C.

6. The support system of any preceding claim, the at least one thermal conditioner comprising: a thermal conditioner for the support structure configured to thermally condition the object via the support structure.

7. The support system of any preceding claim, the at least one thermal conditioner comprising: at least one heater configured to heat the object.

8. The support system of claim 7, wherein the support structure comprises the at least one heater.

9. The support system of any preceding claim, the at least one thermal conditioner comprising: a thermal conditioner for the component configured to thermally condition the component.

10. The support system of claim 9, wherein the object has a coefficient of thermal expansion substantially at a minimum at a temperature of at least 25 °C.

11. The support system of any preceding claim, wherein the object is a patterning device.

12. The support system of any preceding claim, wherein the component comprises a masking blade configured to at least partially define an extent of a field on the object which is illuminated in use.

13. The support system of any preceding claim, comprising: a gas supply configured to supply a gas flow across a surface of the object.

14. The support system of any preceding claim, wherein the temperature gradient induces a thermophoretic force on particles in a direction away from the object.

15. A lithographic apparatus comprising: the support system of any preceding claim.

16. A method for supporting an object for an EUV lithography apparatus, the method comprising: supporting an object with a support structure; and applying a temperature gradient of at least l,000°C / m between the object and a component located such that the object is between the support structure and the component.

17. A patterning device for an EUV lithography apparatus, wherein the patterning device comprises:a material that has a coefficient of thermal expansion substantially at a minimum at a temperature of at least 25°C.

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