Substrate support assembly

Abstract

A substrate support assembly for a lithographic apparatus comprises: a substrate supporting area configured to support a substrate; and a cover plate positioned radially outwards of and surrounding the substrate supporting area, and configured to provide a surface adjacent to a surface of the substrate, wherein: the cover plate has an inner edge facing the substrate supporting area and an outer edge opposite to the inner edge, and the outer edge is slanted with respect to the surface of the cover plate; the surface of the substrate has a first height with respect to a surface of the substrate support assembly when supported on the substrate supporting area; and the surface of the cover plate has a second height with respect to the surface of the substrate support assembly that is less than the first height.

Description

SUBSTRATE SUPPORT ASSEMBLYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 24186077.4 which was filed on 2 July 2024 and which is incorporated herein in its entirety by reference.FIELD

[0002] The present invention relates to a substrate support assembly and a lithographic apparatus.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 (also often referred to as “design layout” or “design”) of a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., a wafer).

[0004] 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 which are patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm and 13.5 nm.

[0005] A lithographic apparatus may include an illumination system for providing a projection beam of radiation, and a support structure for supporting a patterning device. The patterning device may serve to impart the projection beam with a pattern in its cross-section. The apparatus may also include a projection system for projecting the patterned beam onto a target portion of a substrate.

[0006] In a lithographic apparatus, the substrate to be exposed (which may be referred to as a production substrate) may be held on a substrate supporting area (for example of a wafer table).

[0007] It is desirable for the hardware to be as light as possible so as to make high precision movements quicker. It is also desirable to reduce factors such as temperature variations and contaminations of the projection system, particularly its final lens.SUMMARY

[0008] An object of the present invention is to provide a substrate support assembly configured to support a substrate.

[0009] In accordance with the present invention is a substrate support assembly for a lithographic apparatus comprising: a substrate supporting area configured to support a substrate; and a cover plate positioned radially outwards of and surrounding the substrate supporting area, and configured to provide a surface adjacent to a surface of the substrate, wherein: the cover plate has an inner edge facing the substrate supporting area and an outer edge opposite to the inner edge, and the outer edge is slanted with respect to the surface of the cover plate; the surface of the substrate has a first height with respect to a surface of the substrate support assembly when supported on the substrate supporting area; and the surface of the cover plate has a second height with respect to the surface of the substrate support assembly that is less than the first height.

[0010] In accordance with another aspect of the present invention is a substrate support assembly for a lithographic apparatus comprising: a substrate supporting area configured to support a substrate; and a cover plate positioned radially outwards of and surrounding the substrate supporting area, and configured to provide a surface adjacent to a surface of the substrate, wherein: the cover plate has an inner edge facing the substrate supporting area and an outer edge opposite to the inner edge, and the outer edge is slanted with respect to the surface of the cover plate; and the cover plate is configured to cover at most 95% of an area of the substrate support assembly in plan view radially outwards of the substrate supporting area.

[0011] In accordance with another aspect of the present invention is a substrate support assembly for a lithographic apparatus comprising: a substrate supporting area configured to support a substrate; and a cover plate positioned radially outwards of and surrounding the substrate supporting area, and configured to provide a surface adjacent to a surface of the substrate, wherein: the cover plate has an inner edge facing the substrate supporting area and an outer edge opposite to the inner edge, and the outer edge is slanted with respect to the surface of the cover plate; and at least one opening is defined in a surface of the substrate support assembly facing the outer edge, the opening configured to extract fluid guided by the outer edge.

[0012] Also in accordance with the present invention is a lithographic apparatus comprising the substrate support assembly.

[0013] 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, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Embodiments of the invention will now be described by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:Figure 1 schematically depicts an overview of a lithographic apparatus;Figure 2 schematically depicts a cross-section of part of a substrate support assembly, for example of the lithographic apparatus of Figure 1 ;Figure 3 schematically depicts in plan view a substrate support assembly, for example of the type shown in Figure 2;Figures 4-6 schematically depict different stages of movement of a substrate under a projection system;Figure 7 schematically depicts part of a cover plate of a substrate support assembly;Figure 8 schematically depicts a substrate support assembly, for example of the lithographic apparatus of Figure 1 ;Figure 9 schematically depicts part of a substrate support assembly, for example of the lithographic apparatus of Figure 1 ;Figure 10 schematically depicts in plan view a substrate support assembly, for example of the type shown in Figure 2; andFigure 11 schematically depicts a cross-section of part of a cover plate of a substrate support assembly.

[0015] 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 substrate support 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

[0016] In the present document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g. with a wavelength of 436, 405, 365, 248, 193, 157, 126 or 13.5 nm).

[0017] The term “reticle”, “mask” or “patterning device” as employed in this text may be broadly interpreted as referring to a generic patterning device that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate. The term “light valve” can also be used in this context. Besides the classic mask (transmissive or reflective, binary, phase-shifting, hybrid, etc.), examples of other such patterning devices include a programmable mirror array and a programmable LCD array.

[0018] Figure 1 schematically depicts a lithographic apparatus LA. The lithographic apparatus includes an illumination system (also referred to as illuminator) IL configured to condition a radiation beam B (e.g., EUV radiation or DUV radiation), a mask support (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA in accordance with certain parameters, a substrate table (e.g., a support table or a substrate support) WT constructed to hold a substrate (e.g., a resist coatedwafer) W and connected to a second positioner PW configured to accurately position the substrate table WT in accordance with certain parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0019] In operation, the illumination system IL receives the radiation beam B from a radiation source SO, e.g. via a beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and / or other types of optical components, or any combination thereof, for directing, shaping, and / or controlling radiation. The illuminator IL may be used to condition the radiation beam B to have a desired spatial and angular intensity distribution in its cross section at a plane of the patterning device MA.

[0020] The term “projection system” PS used herein should be broadly interpreted as encompassing various types of projection system, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, and / or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system” PS.

[0021] The lithographic apparatus may be of a type having two or more substrate tables WT (also named “dual stage”). In such “multiple stage” machine, the substrate supports WT may be used in parallel, and / or steps in preparation of a subsequent exposure of the substrate W may be carried out on the substrate W located on one of the substrate table WT while another substrate W on the other substrate table WT is being used for exposing a pattern on the other substrate W.

[0022] In addition to the substrate table WT, the lithographic apparatus may comprise a measurement stage (not depicted in Figure 1). The measurement stage is arranged to hold a sensor and / or a cleaning device. The sensor may be arranged to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold multiple sensors. The cleaning device may be arranged to clean part of the lithographic apparatus, for example a part of the projection system PS or a part of a system that provides the immersion liquid. The measurement stage may move beneath the projection system PS when the substrate able WT is away from the projection system PS.

[0023] In operation, the radiation beam B is incident on the patterning device, e.g. mask, MA which is held on the mask support MT, and is patterned by the pattern (design layout) present on patterning device MA. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and a position measurement system PMS, the substrate table WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B at a focused and aligned position. Similarly, the first positioner PM and possibly another position sensor(which is not explicitly depicted in Figure 1) may be used to accurately position the patterning device MA with respect to the path of the radiation beam B. Patterning device MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks Pl, P2 as illustrated occupy dedicated target portions, they may be located in spaces between target portions. Substrate alignment marks Pl, P2 are known as scribe -lane alignment marks when these are located between the target portions C.

[0024] In this specification, a Cartesian coordinate system is used. The Cartesian coordinate system has three axis, i.e., an x-axis, a y-axis and a z-axis. Each of the three axes is orthogonal to the other two axes. A rotation around the x-axis is referred to as an Rx-rotation. A rotation around the y- axis is referred to as an Ry -rotation. A rotation around about the z-axis is referred to as an Rz- rotation. The x-axis and the y-axis define a horizontal plane, whereas the z-axis is in a vertical direction. The Cartesian coordinate system is not limiting the invention and is used for clarification only. Instead, another coordinate system, such as a cylindrical coordinate system, may be used to clarify the invention. The orientation of the Cartesian coordinate system may be different, for example, such that the z-axis has a component along the horizontal plane.

[0025] Figure 2 schematically depicts a cross-section of part of a substrate support assembly 10. As shown in Figure 2, in an embodiment the substrate support assembly 10 comprises a substrate table WT. The substrate support assembly 10 may be part of a lithographic apparatus LA such as the lithographic apparatus LA shown in Figure 1, for example. Figure 1 shows the substrate table WT of the lithographic apparatus LA. The substrate table WT shown in Figure 1 may be part of the substrate support assembly 10 shown in Figure 2, for example.

[0026] As shown in Figure 2, in an embodiment the substrate support assembly 10 comprises a substrate supporting area 20. The substrate supporting area 20 is configured to support a substrate W.

[0027] As shown in Figure 2, in an embodiment the substrate support assembly 10 comprises a substrate support 51 corresponding to the substrate supporting area 20. In a lithographic apparatus it is necessary to position with great accuracy the upper surface of a substrate W to be exposed in the plane of best focus of the aerial image of the pattern projected by the projection system PS. To achieve this, the substrate W can be held on a substrate support 51. The surface of the substrate support 51 that supports the substrate W can be provided with a plurality of burls 52 whose distal ends can be coplanar in a nominal support plane. The burls 52, though numerous, may be small in cross- sectional area parallel to the support plane so that the total cross-sectional area of their distal ends is a few percent, e.g. less than 5%, of the surface area of the substrate W. The gas pressure in the space between the substrate support 51 and the substrate W may be reduced relative to the pressure above the substrate W to create a force clamping the substrate W to the substrate support 51.

[0028] However, it is not essential for the substrate support assembly 10 to comprise a substrate support 51 of the type shown in Figure 2. In an alternative embodiment, the substrate support 51 maybe omited. The substrate supporting area 20 corresponds to the area on which the substrate W is supported.

[0029] As shown in Figure 2, in an embodiment the substrate table WT comprises a block 50. The block 50 may be configured to support the substrate support 51. In an alternative embodiment, the block 50 and the substrate support 51 may be formed integrally. For example the block 50 may be formed with a step, the substrate W being supported on the step.

[0030] During use of the lithographic apparatus LA, sometimes the substrate support assembly 10 supports a substrate W. At other times the substrate support assembly 10 may not have a substrate W supported on it.

[0031] As shown in Figure 2, in an embodiment the substrate support assembly 10 comprises a cover plate 11. The cover plate 11 may be positioned radially outwards of the substrate supporting area 20. Figure 2 shows only part of the substrate support assembly 10. In particular, Figure 2 shows the cover plate 11 on the left hand side of the substrate supporting area 20. The cover plate 11 may also be provided on the right hand side of the substrate supporting area 20, although this is not shown in Figure 2.

[0032] Figure 3 schematically depicts in plan view the substrate support assembly 10. The substrate support assembly 10 shown in Figure 3 may be the substrate support assembly 10 shown in Figure 2, for example. Figure 3 shows the cover plate 11 positioned radially outwards of the substrate supporting area 20.

[0033] As shown in Figure 3, for example, in an embodiment the cover plate 11 surrounds the substrate supporting area 20. For example, the cover plate 11 may be provided on opposing sides of the substrate supporting area 20. Figure 3 shows a substrate support assembly 10 which is substantially rectilinear. The substrate support assembly 10 may be considered to have four sides. As shown in Figure 3, in an embodiment the cover plate 11 is provided on all four sides of the substrate supporting area 20 with respect to the shape of the substrate support assembly 10. In an alternative arrangement, the cover plate 11 may be provided on two opposing sides or on three sides of the substrate supporting area 20.

[0034] As shown in Figure 2, in an embodiment the cover plate 11 is configured to provide a cover plate surface 12 adjacent to a substrate surface 22 of the substrate W. The cover plate surface 12 may face substantially the same direction as the substrate surface 22. For example in the orientation shown in Figure 2, the cover plate surface 12 and the substrate surface 22 face upwards. The cover plate surface 12 may be an upper surface of the cover plate 11. However, it is not essential for the cover plate surface 12 to face vertically upwards. For example, the substrate support assembly 10 may be oriented differently to how it is shown in Figure 2, in which case the cover plate surface 12 may face a different direction.

[0035] As shown in Figure 2 and Figure 3, the cover plate surface 12 is proximal to the substrate surface 22. As shown in Figure 3, in an embodiment a gap 15 is between the cover plate surface 12and the substrate surface 22. For example, as shown in Figure 2, the cover plate 11 may be distanced from (i.e. separated from) the substrate supporting area 20. When a substrate support 51 is present as shown in Figure 2, the cover plate 11 may be distanced from the substrate support 51. In plan view the cover plate 11 may be distanced from the outer edge of the substrate W. However, it is not essential for the gap 15 to be provided. In an alternative embodiment, in plan view the cover plate 11 is substantially contiguous with the outer edge of the substrate W. The cover plate 11 may be in physical contact with the outer edge of a substrate support 51 when the substrate support 51 is present.

[0036] As shown in Figure 2 and Figure 3, in an embodiment the cover plate 11 has an inner edge 13. The inner edge 13 is at the radially inward side of the cover plate 11. The inner edge 13 faces the substrate supporting area 20. The cover plate 11 has an outer edge 14. The outer edge 14 is at the radially outward side of the cover plate 11. The outer edge 14 is opposite to the inner edge 13. The outer edge 14 faces away from the substrate supporting area 20.

[0037] As shown in Figure 2, in an embodiment the outer edge 14 is slanted with respect to the surface 12 of the cover plate 11. This means that the outer edge 14 does not make a right angle with the surface 12 in a cross-section of the substrate support assembly 10, for example as shown in Figure 2.

[0038] By providing that the outer edge 14 is slanted, undesirable unconditioned factors affecting the projection system PS may be reduced. An embodiment of the invention is expected to reduce unconditioned factors, thereby improving the accuracy of lithographic processes performed by the lithographic apparatus LA.

[0039] Figures 4-6 schematically depict different stages of a substrate W moving relative to the projection system PS.

[0040] As shown in Figures 4-6, in an embodiment the lithographic apparatus LA comprises a purger configured to generate a gas flow 45. The gas flow 45 is between the projection system PS and the substrate support assembly 10. The gas flow 45 is for protecting the projection system PS from contaminants, for example. The part of the projection system PS that is labelled in Figures 4-6 is the bottom surface of the final lens of the projection system PS.

[0041] As shown in Figure 4, in an embodiment the purger comprises a purger supply 41. The purger supply 41 is configured to output the gas flow 45. For example the purger supply 41 may be a gas blower. The purger supply 41 may be configured to blow the gas flow 45 across the surface of the final lens of the projection system PS.

[0042] As shown in Figures 4-6, in an embodiment the purger comprises a purger extraction 46. The purger extraction 46 is configured to extract the gas flow 45 from the region between the projection system PS and the substrate support assembly 10. The purger extraction 46 may be configured to make the gas flow 45 more laminar.

[0043] In an embodiment the purger supply 41 and the purger extraction 46 are shaped such that the gas flow 45 has a trapezoid shape. The trapezoid is wider at the projection system side and narrowerat the substrate support assembly side. The purger supply 41 may be diagonally inclined facing towards the projection system PS and away from the substrate support assembly 10. The purger extraction 46 may be diagonally inclined facing towards the projection system PS and away from the substrate support assembly 10.

[0044] Figure 4 shows the substrate W at a first time. Figure 5 shows the substrate W at a second, later time. Figure 6 shows the substrate W at a third, later time. Figure 4 schematically shows a volume 40 between the substrate support assembly 10 and the projection system PS. As shown in the sequence of Figures 4-6, the volume 40 is contracted to a contracted volume 44. The contracted volume 44 is smaller than the volume 40 shown in Figure 4. The contraction of the volume 40 to the contracted volume 44 is caused at least partly by the upward protrusions, for example the substrate W and part of the substrate table WT such as the substrate support 51.

[0045] It is possible for the upward flow 42, i.e. the contraction of the volume 40, to carry unconditioned and / or contaminated gas (e.g. air) into the gas flow 45 of the purger.

[0046] The direction of motion of the substrate table WT relative to the projection system PS is shown by the big arrow in Figures 4-6. The small arrows show the flow of unconditioned and / or contaminated gas. The spark shapes represent unconditioned factors 43 such as temperature disturbance, variation of gas species and contamination (e.g. contaminant particles). As shown in Figures 4-6, the upward flow 42 can cause such unconditioned factors 43 to undesirably affect the gas flow 45 of the purger and the projection system PS.

[0047] By providing the cover plate 11 radially outward of the substrate supporting area 20, the cover plate 11 may act as a shielding mechanism. The cover plate 11 may be configured to reduce the extent to which unconditioned gas undesirably reaches the gas flow 45 of the purger. The cover plate 11 may function as a mechanical shield. By providing that the cover plate 11 is radially outwards of the substrate supporting area 20, the upward flow 42 shown in Figures 4-6 may occur further from the substrate W. This may help to reduce the extent to which the unconditioned factors undesirably affect exposure of the substrate W by the lithographic apparatus LA. By relocating the step profile further away from the substrate supporting area 20, the actual impact on the gas flow 45 of the purger may be reduced.

[0048] By providing that the outer edge 14 of the cover plate 11 is a slanted leading edge, the outer edge 14 may be configured to redirect the unconditioned gas away from the gas flow 45 of the purger. For example, the outer edge 14 may be configured to redirect any unconditioned gas downwards towards the substrate table WT instead of going upwards to the final lens of the projection system PS and the purger. An embodiment of the invention is expected to reduce the influence of unconditioned gas on the projection system PS and the purger.

[0049] As shown in Figure 2, in an embodiment the outer edge 14 is slanted such that an angle defined between the outer edge 14 and the cover plate surface 12 is acute. By providing that the angle is acute, the unconditioned gas may be more readily redirected away from the projection system PS.Of course, it is possible for some flow to be in the direction of the projection system PS. However, the extent of such upward flow may be reduced.

[0050] In an embodiment the angle is at most 85 degrees, optionally at most 80 degrees, optionally at most 70 degrees, optionally at most 50 degrees and optionally at most 40 degrees. By reducing the angle, the outer edge 14 may more effectively redirect unconditioned gas downwards towards the substrate table WT and away from the projection system PS. In an embodiment the angle is at least 10 degrees, optionally at least 20 degrees, optionally at least 40 degrees and optionally at least 50 degrees. By increasing the angle, the size of the cover plate 11 for a given vertical extent of the cover plate 11 may be reduced. By reducing the size of the cover plate 11, the mass of the substrate support assembly 10 may be desirably reduced. In an embodiment the angle varies among different parts of the cover ring 11.

[0051] As shown in Figure 2, in an embodiment the substrate surface 22 has a first height hl with respect to a surface 21 of the substrate support assembly 10. The surface 21 of the substrate support assembly 10 may be the surface on which the cover plate 11 is positioned. The surface 21 of the substrate support assembly 10 may be a surface of the block 50 on which the substrate support 51 is positioned. The substrate surface 22 has the first height hl when the substrate W is supported by the substrate support assembly 10, i.e. when the substrate W is supported on the substrate supporting area 20.

[0052] As shown in Figure 2, in an embodiment the cover plate surface 12 has a second height h2 with respect to the surface 21 of the substrate support assembly 10. As shown in Figure 2, in an embodiment the second height h2 is less than the first height hl . The cover plate surface 12 may be lower than the substrate surface 22. By providing that the cover plate surface 12 is lower than the substrate surface 22, there is more space for mechanically handling the substrate W. Additionally, by providing that the cover plate surface 12 is lower than the substrate surface 22, the maximum step change as the substrate table WT is moved relative to the projection system PS is reduced.

[0053] However, it is not essential for the second height h2 to be less than the first height hl . For example, in an alternative embodiment the second height h2 is substantially equal to the first height hl. The cover plate surface 12 may be substantially coplanar with the substrate surface 22.

[0054] The substrate support 51 may be referred to as a burl plate. The substrate support 51 corresponds to the substrate supporting area 20. As shown in Figure 2, the substrate support 51 may comprise a plurality of burls 52 with distal ends in a support plane for supporting the substrate W. As shown in Figure 2, in an embodiment the support plane has a third height h3 with respect to the surface 21 of the substrate support assembly 10. As shown in Figure 2, in an embodiment the second height h2 is less than the third height h3. The third height h3 corresponds to the height of the lower surface of the substrate W. The substrate W may be thinner than the difference in height between the cover plate surface 12 and the substrate surface 22. By providing a greater difference in height between the cover plate surface 12 and the substrate surface 22, the step size from the surface 21 ofthe substrate support assembly 10 to the cover plate surface 12 may be closer to the step size from the cover plate surface 12 to the substrate surface 22.

[0055] As shown in Figure 2, in an embodiment the burls 52 protrude from a base surface 53 of the substrate support 51. The base surface 53 may have a fourth height h4 with respect to the surface 21 of the substrate support assembly 10. As shown in Figure 2, in an embodiment the second height h2 is less than the fourth height h4. By providing two more evenly distributed steps, the extent of upward flow of unconditioned gas towards the projection system PS may be reduced when the substrate table WT is moved relative to the projection system PS.

[0056] As shown in Figure 2, there may be a distance between the inner edge 13 of the cover plate 11 and the substrate W. This gap 15 is shown in plan view in Figure 3. In an embodiment the difference between the first height hl and the second height h2 is greater than the distance between the inner edge 13 and the substrate W (in plan view).

[0057] Figure 11 schematically depicts an optional feature of the cover plate 11. As shown in Figure 11, in an embodiment the cover plate 11 comprises a tip 60. The tip 60 is at the outer edge 14 of the cover plate 11. As shown in Figure 11, in an embodiment the tip 60 has a fifth height h5 with respect to the surface 21 of the substrate support assembly 10. In an embodiment the fifth height h5 is greater than the second height h2. The fifth height h5 is measured from the top 61 of the tip 60. By providing the tip 60, the length of the outer edge 14 may be increased, while still providing the cover plate surface 12 at the second height h2. The tip 60 may help to redirect unconditioned gas downwards away from the projection system PS. The tip 60 may significantly add to the length of the outer edge 14 without unduly increasing the mass of the cover plate 11. By providing that the tip 60 is elevated relative to the second height h2, the tip 60 provides an additional restriction for pressure build-up, thereby reducing the occurrence of upward flow. In an embodiment the fifth height h5 is less than the first height hl . In an embodiment the fifth height h5 is substantially equal to the first height hl . By providing that the fifth height h5 is less than or equal to the first height hl, there is space available for mechanical handling of the substrate W.

[0058] As shown in Figure 11, in an embodiment the tip 60 is rounded in a plane perpendicular to the cover plate surface 12. Figure 11 is a cross-sectional view in a plane perpendicular to the cover plate surface 12. The rounded surface 62 of the tip 60 is shown in Figure 11. By providing the rounded surface 62, the possibility of undesirable turbulent flow as the substrate table WT moves relative to the projection system PS may be reduced. However, it is not essential for the tip 60 to be rounded. In an alternative embodiment the tip 60 is sharp. A sharp tip 60 may make manufacture of the cover plate 11 easier.

[0059] In an embodiment the cover plate 11 is configured to protect the substrate support assembly 10 from radiation, for example from ultraviolet (UV) radiation. Such UV radiation may undesirably damage the substrate support assembly 10. By providing the cover plate 11, the lifetime of the substrate support assembly 10 may be increased.

[0060] In an embodiment the substrate support assembly 10 comprises a UV protective layer on or at the cover plate surface 12. In an embodiment the UV protective layer comprises a metal such as titanium.

[0061] Figure 3 shows the substrate support assembly 10 with the cover plate 11 in plan view. As shown in Figure 3, the cover plate 11 is configured to partly cover the area of the substrate support assembly 10 in plan view radially outwards of the substrate supporting area 20. The substrate supporting area 20 corresponds to the position of the substrate W when the substrate W is supported on the substrate support assembly 10. As shown in Figure 3, the substrate supporting area 20 may be substantially shaped the same as the substrate W, for example a circle (although other shapes are equally possible). Part of the area in plan view of the substrate support assembly 10 is taken up by the substrate supporting area 20. There is another part of the area of the substrate support assembly 10 that is radially outwards of the substrate supporting area 20. The cover plate 11 is radially outwards of the substrate supporting area 20. The cover plate 11 partly covers the area 23 of the substrate support assembly 10 that is radially outwards of the substrate supporting area 20.

[0062] In an embodiment the cover plate 11 is configured to cover at least 10%, optionally at least 20%, optionally at least 25% and optionally at least 50% of the area 23 of the substrate support assembly 10 in plan view radially outwards of the substrate supporting area 20. By increasing the area covered by the cover plate 11, the extent of UV protection provided by the cover plate 11 may be increased. This may help to reduce undesirable damage of the substrate support assembly 10 and / or increase the lifetime of the substrate support assembly 10.

[0063] In an embodiment the cover plate 11 is configured to cover at most 95%, optionally at most 90%, optionally at most 80%, optionally at most 70% and optionally at most 50% of the area 23 of the substrate support assembly 10 in plan view radially outwards of the substrate supporting area 20. By reducing the area covered by the cover plate 11, the mass of the cover plate 11 may be reduced, thereby reducing the mass of the substrate support assembly 10. By reducing the mass of the substrate support assembly 10, the substrate W may be moved relative to the projection system PS at higher speed and / or acceleration for a given input power. The power consumption for moving the substrate W relative to the projection system PS may be reduced for a given speed and / or acceleration of motion. An embodiment of the invention is expected to achieve more rapid relative motion between the projection system PS and the substrate W. An embodiment of the invention is expected to reduce power consumption.

[0064] As shown in Figure 2, in an embodiment at least one opening 65 is defined in a surface of the substrate support assembly 10 facing the outer edge 14. The surface may be at least partly below the outer edge 14 of the cover plate 11. In an embodiment the opening 65 is configured to extract fluid guided by the outer edge 14. For example, as mentioned elsewhere the outer edge 14 may be configured to redirect unconditioned gas downwards towards the substrate table WT rather than upwards towards the projection system PS. The opening 65 may allow the redirected unconditionedgas to flow away from the region between the substrate support assembly 10 and the projection system PS. The opening 65 may help to reduce the possibility of unconditioned gas reaching the purger and / or the projection system PS.

[0065] In an embodiment a plurality of openings 65 are provided in the substrate support assembly 10. The opening 65 may be the opening to a cavity in the substrate support assembly 10. The opening may allow gas to be retained away from the projection system PS. The opening 65 may allow gas to flow through and away from the substrate support assembly 10.

[0066] As shown in Figure 2, in an embodiment the surface 21 of the substrate support assembly 10 in which the opening 65 is defined may comprise a slanted portion slanting downwards towards the opening 65. This may effectively increase the size of the opening 65 so as to encourage the flow of gas away from the projection system PS. An embodiment of the invention is expected to reduce unconditioned factors at the projection system PS and / or at the purger.

[0067] In an embodiment the substrate support assembly 10 comprises a source of underpressure. The source of underpressure may be in fluid communication with the opening 65 so as to extract fluid guided by the outer edge 14 through the opening 65. The underpressure may be a pressure lower than the pressure in the region between the projection system PS and the substrate support assembly 10. For example the underpressure may be lower than ambient pressure. By providing the underpressure, the unconditioned gas may flow more rapidly and / or a greater volume of unconditioned gas may be redirected away from the projection system PS.

[0068] Figure 7 schematically depicts part of a cover plate 11 of a substrate support assembly 10. Figure 7 shows part of the substrate support assembly 10 in the vicinity of a sensor pad 24. A sensor pad 24 may comprise a sensor. The sensor may be configured to sense one or more properties. For example, the sensor pad 24 may be configured to measure a position and / or orientation of a component of the lithographic apparatus LA.

[0069] As shown in Figure 3, in an embodiment a plurality of sensor pads 24 are provided to the substrate support assembly 10. The sensor pad 24 may protrude in the same direction that the substrate W protrudes. For example the sensor pads 24 may be provided at the upper surface of the substrate support assembly 10.

[0070] As shown in Figure 7, in an embodiment the outer edge 14 of the cover plate 11 comprises a convex rounded comer 17 in a plane parallel to the cover plate surface 12. The convex rounded comer 17 may help to reduce the possibility of undesirable turbulent gas flow.

[0071] In an embodiment the cover plate surface 12 may be no higher than the height of the upper surface of the sensor pad 24. The cover plate 11 may be configured to accommodate the sensor pad 24. For example, as shown in Figure 7 the substrate support assembly 10 may comprise at least one sensor pad 24 physically separate from the substrate supporting area 20. The sensor pad 24 is positioned radially outwards of the substrate supporting area 20. The cover plate 11 may comprise at least one concave rounded comer 18. The concave rounded comer 18 is for accommodating thesensor pad 24. By providing rounded comers, sharp edges may be reduced, thereby reducing undesirable turbulent gas flow. In an embodiment the cover plate 11 is aerodynamic.

[0072] Figure 10 schematically depicts an alternative arrangement of a substrate support assembly 10. As shown in Figure 10, in an embodiment the cover plate 11 comprises a plurality of segments 19. For example, Figure 10 schematically shows four segments 19. One segment 19 may be provided for each side of the substrate support assembly 10. For example the substrate support assembly 10 may have a rectilinear shape. Each segment 19 of the cover plate 11 may be located between the substrate supporting area 20 and a respective side of the substrate support assembly 10.

[0073] By providing that the cover plate 11 comprises a plurality of segments 19, the cover plate 11 may be easier to manufacture. By providing a plurality of segments 19, the tolerances for manufacturing the cover plate 11 and locating the cover plate 11 in the substrate support assembly 10 may be increased. As shown in Figure 10, gaps 16 may be provided between the segments 19 of the cover plate 11. By providing the gaps 16, the mass of the cover plate 11 may be reduced.

[0074] However, it is not essential for the cover plate 11 to comprise a plurality of segments 19. In the alternative arrangement shown in Figure 3, the cover plate 11 is formed as a single piece. As shown in Figure 3, a gap 16 may be provided so as to increase the tolerance for fitting the cover plate 11 when the substrate support assembly 10 is assembled. However, it is not essential for the gap 16 to be provided. In an alternative arrangement, the cover plate 11 may form substantially an annulus.

[0075] As shown in Figure 2, for example, in an embodiment the cover plate surface 12 is substantially flat. The cover plate surface 12 may be flat so as to avoid protrusions that could redirect gas flow upwards towards the projection system PS. Of course, there may be a tip 60 provided to the outer edge of the cover plate 11. The tip 60 may protrude above the cover plate surface 12. However, the tip 60 is positioned radially outward of the cover plate surface 12 such that the protrusion provided by the tip 60 is further from the substrate supporting area 20.

[0076] As shown in Figure 2, for example, in an embodiment the cover plate surface 12 is substantially flat. The cover plate surface 12 may be flat so as to avoid protrusions that could redirect gas flow upwards towards the projection system PS. Of course, there may be a tip 60 provided to the outer edge of the cover plate 11. The tip 60 may protrude above the cover plate surface 12. However, the tip 60 is positioned radially outward of the cover plate surface 12 such that the protrusion provided by the tip 60 is further from the substrate supporting area 20.

[0077] In an embodiment the substrate support assembly 10 comprises an adhesive (not shown). The adhesive is for securing the cover plate 11 to the substrate support assembly 10. For example, the adhesive may be for securing the cover plate 11 to the surface 21 of the substrate support assembly 10 on which the cover plate 11 is provided. In an alternative arrangement, the cover plate 11 may be secured by a mechanical fixing mechanism such as one or more screws or other suitable fasteners.Additionally or alternatively, the cover plate 11 may be secured at its inner edge 13 to the substrate table WT, for example to the substrate support 51.

[0078] In an embodiment the cover plate 11 is at least partly hollow. By providing that the cover plate 11 is at least partly hollow, the mass of the cover plate 11 may be reduced, thereby reducing the mass of the substrate support assembly 10.

[0079] Figure 8 schematically depicts a substrate support assembly 10, for example of the lithographic apparatus LA shown in Figure 1. As shown in Figure 8, in an embodiment the substrate table WT comprises at least one gas opening 80 at an outer edge (i.e. an outwardly facing edge). For example, in the arrangement shown in Figure 8 the substrate table WT comprises at least one gas opening 80 configured to supply gas 81. The gas opening 80 may be configured as a gas blower. The at least one gas opening 80 is configured to supply a flow of gas 81 radially outwards away from the substrate table WT.

[0080] In the arrangement shown in Figure 8, the substrate table WT may comprise the block 50 and the substrate support 51. The substrate support 51 may comprise the at least one gas opening 80 at its outer edge. In an alternative arrangement, the substrate table WT may be formed substantially integrally with a step. The at least one gas opening 80 may be provided at the radially outward facing edge of the step.

[0081] By providing the at least one gas opening 80, the gas opening 80 providing the flow of gas 81 may function as a flow shield. The flow shield may be configured to keep the unconditioned gas from the gas flow 45 of the purger and / or from the projection system PS. As shown in Figure 8, the gas 81 from the at least one gas opening 80 may move the unconditioned factor 43 away from the projection system PS and / or the gas flow 45 of the purger.

[0082] Figure 9 schematically depicts an alternative embodiment in which the at least one gas opening 90 is configured to extract gas 91. For example, the at least one gas opening 90 shown in Figure 9 may be configured to induce the flow of gas 91 such that the unconditioned factor 43 is removed from the region between the projection system PS and the substrate support assembly 10. By providing the extraction of the gas 91, the possibility of the unconditioned factor 43 undesirably affecting the gas flow 45 of the purger and / or the projection system PS may be reduced.

[0083] The different features described in this specification may be combined in ways that are not shown in the Figures. Merely as an example, at least one gas opening 80 configured to supply gas 81 or at least one gas opening 90 configured to extract gas 91 may be provided at the outer edge 14 of the cover plate 11. Accordingly, the slanted edge shown in Figure 2 may be combined with the at least one gas opening 80, 90 shown in Figure 8 or Figure 9, for example. Other combinations of features are also possible because they are compatible with each other.

[0084] It will also be appreciated that the principles of the present invention can be applied to metrology or lithographic tools.

[0085] Although specific reference may be made in this text to the use of a metrology system in the context of the manufacture of ICs, it should be understood that the metrology system described herein may have other applications, such as in the manufacture of integrated optical systems, guidance anddetection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin fdm magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion", respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and / or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains one or multiple processed layers.

[0086] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications.

[0087] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0088] 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 set out below.

Claims

CLAIMS1. A substrate support assembly for a lithographic apparatus comprising: a substrate supporting area configured to support a substrate; and a cover plate positioned radially outwards of and surrounding the substrate supporting area, and configured to provide a surface adjacent to a surface of the substrate, wherein: the cover plate has an inner edge facing the substrate supporting area and an outer edge opposite to the inner edge, and the outer edge is slanted with respect to the surface of the cover plate; the surface of the substrate has a first height with respect to a surface of the substrate support assembly when supported on the substrate supporting area; and the surface of the cover plate has a second height with respect to the surface of the substrate support assembly that is less than the first height.

2. A substrate support assembly for a lithographic apparatus comprising: a substrate supporting area configured to support a substrate; and a cover plate positioned radially outwards of and surrounding the substrate supporting area, and configured to provide a surface adjacent to a surface of the substrate, wherein: the cover plate has an inner edge facing the substrate supporting area and an outer edge opposite to the inner edge, and the outer edge is slanted with respect to the surface of the cover plate; and the cover plate is configured to cover at most 95% of an area of the substrate support assembly in plan view radially outwards of the substrate supporting area.

3. A substrate support assembly for a lithographic apparatus comprising: a substrate supporting area configured to support a substrate; and a cover plate positioned radially outwards of and surrounding the substrate supporting area, and configured to provide a surface adjacent to a surface of the substrate, wherein: the cover plate has an inner edge facing the substrate supporting area and an outer edge opposite to the inner edge, and the outer edge is slanted with respect to the surface of the cover plate; and at least one opening is defined in a surface of the substrate support assembly facing the outer edge, the opening configured to extract fluid guided by the outer edge.

4. The substrate support assembly of claim 1, wherein the cover plate is configured to cover at most 95% of an area of the substrate support assembly in plan view radially outwards of the substrate supporting area or wherein at least one opening is defined in a surface of the substrate support assembly facing the outer edge, the opening configured to extract fluid guided by the outer edge, desirably wherein at least one opening is defined in a surface of the substrate support assembly facing the outer edge, the opening configured to extract fluid guided by the outer edge.

5. The substrate support assembly of claim 2, wherein at least one opening is defined in a surface of the substrate support assembly facing the outer edge, the opening configured to extract fluid guided by the outer edge.

6. The substrate support assembly of claim 1 or 4, comprising: a substrate support corresponding to the substrate supporting area and comprising a plurality of burls with distal ends in a support plane for supporting the substrate, wherein: the support plane has a third height with respect to the surface of the substrate support assembly; and the second height is less than the third height, desirably wherein: the burls protrude from a base surface of the substrate support; the base surface has a fourth height with respect to the surface of the substrate support assembly; and the second height is less than the fourth height.

7. The substrate support assembly of any of claims 1, 4 and 6, wherein a difference between the first height and the second height is greater than any distance between the inner edge and the substrate, and / or wherein the cover plate comprises a tip at the outer edge having a fifth height with respect to the surface of the substrate support assembly that is greater than the second height, desirably wherein the tip is rounded in a plane perpendicular to the surface of the cover plate.

8. The substrate support assembly of any of claims 2, 4 and 5, wherein the cover plate is configured to cover at most 70% of the area of the substrate support assembly in plan view radially outwards of the substrate supporting area, desirably wherein the cover plate is configured to cover at most 50% of the area of the substrate support assembly in plan view radially outwards of the substrate supporting area.

9. The substrate support assembly of any of claims 3-5, comprising: a source of underpressure in fluid communication with the opening so as extract fluid guided by the outer edge through the opening.

10. The substrate support assembly of any preceding claim, wherein the cover plate is configured to cover at least 10% of the area of the substrate support assembly in plan view radially outwards of the substrate supporting area, desirably wherein the cover plate is configured to cover at least 25% of the area of the substrate support assembly in plan view radially outwards of the substrate supporting area.

11. The substrate support assembly of any preceding claim, wherein the outer edge is slanted such that an angle defined between the outer edge and the surface of the cover plate is acute, and / or wherein the cover plate comprises a plurality of segments, and / or wherein the outer edge comprises a convex rounded comer in a plane parallel to the surface of the cover plate, and / or comprising: at least one sensor pad, physically separate from the substrate supporting area, positioned radially outwards of the substrate supporting area, wherein the cover plate comprises at least one concave rounded comer for accommodating the sensor pad.

12. The substrate support assembly of any preceding claim, wherein the surface of the cover plate is substantially flat, and / or comprising: a UV protective layer on the surface of the cover plate, and / or comprising: an adhesive securing the cover plate to the surface of the substrate support assembly, and / or wherein the cover plate is at least partly hollow, and / or wherein the cover plate comprises at least one gas opening at the outer edge configured to induce gas flow substantially parallel to the surface of the cover plate, and / or wherein the cover plate is physically separate from the substrate supporting area.

13. The substrate support assembly of claim 12, wherein the at least one gas opening is configured to extract gas, and / or wherein the at least one gas opening is configured to supply gas.

14. A lithographic apparatus comprising the substrate support assembly of any preceding claim.

15. The lithographic apparatus of claim 14, comprising: a projection system configured to project a radiation beam onto the substrate; anda purger configured to generate a gas flow between the projection system and the substrate support assembly for protecting the projection system from contaminants.

Images