Test substrate for use in substrate support manufacturing and / or reconditioning

Abstract

A test substrate is provided. The test substrate includes a substrate, and a plurality of projections formed on one of the major surfaces of the substrate. A method of determining the condition of the main body of a substrate support of a substrate clamp of a lithographic apparatus is provided. The method includes obtaining a main body of a substrate support, wherein the main body is for forming projections on to thereby form the substrate support; clamping a test substrate to the main body; and measuring a property of the test substrate when clamped to the main body.

Description

TEST SUBSTRATE FOR USE IN SUBSTRATE SUPPORT MANUFACTURING AND / OR RECONDITIONINGCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 716,467 which was filed on 5 November 2024 and which is incorporated herein in its entirety by reference.FIELD

[0002] The present invention relates to the process of manufacturing and / or reconditioning clamps of substrates in a lithographic apparatus. A test substrate that includes projections is used to test the condition of a main body of a substrate support prior to projections being formed on the main body.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). To project a pattern on the substrate the 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. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within a range of 4 nm to 20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on the substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.

[0004] The lithographic apparatus comprises a substrate table with a clamp. The clamp holds, i.e. clamps, the substrate on a substrate support of the substrate table when the substrate is illuminated with light, that is patterned by the patterning device, in a lithographic process. A substrate support conventionally has a plurality of projections extending in a first (z) direction (called burls) to support the substrate. The total area of terminal surfaces of the projections that contact the substrate thereby to support the substrate is small compared to the total area of a substrate. Therefore, the chance that a contaminant particle randomly located on the surface of the substrate or the substrate support is trapped between a projection and the substrate is small. Also, in manufacture of the substrate support, the tops of the projections can be made more accurately coplanar than a large surface can be made accurately flat.

[0005] When a substrate is first loaded onto the substrate support in preparation for exposure, the substrate is supported by so-called e-pins which hold the substrate at multiple positions. To load thesubstrate onto the substrate support, the e-pins are retracted so that the substrate is supported by projections of the substrate support.

[0006] The flatness of the terminal surfaces of the projections (i.e., how close to being in the same plane all of the terminal surfaces of the projections are) is important. This is because any variation in the flatness of the projections is transmitted to the top surface of the substrate which is subjected to irradiation. The roughness of the terminal surfaces of the projections is also important because the substrate may stick to the terminal surfaces of the projections if they are too smooth. There are also other factors that affect the performance of a clamp, such as the stiffness of the projections.

[0007] Clamps need to be periodically reconditioned so that they continue to meet the required performance specifications. A problem with the reconditioning process of clamps is that it is slow and expensive.

[0008] There is a general need to improve on known techniques for reconditioning and manufacturing clamps.SUMMARY

[0009] There is a general need to improve the manufacturing of clamps of substrates. There is also a general need to improve the reconditioning of clamps of substrates that no longer meet the required performance specifications.

[0010] According to a first aspect of the invention, there is provided a test substrate that includes a substrate, and a plurality of projections formed on one of the major surfaces of the substrate.

[0011] According to a second aspect of the invention, there is provided a method of determining the condition of the main body of a substrate support of a substrate clamp of a lithographic apparatus. The method includes obtaining a main body of a substrate support, wherein the main body is for forming projections on to thereby form the substrate support; clamping a test substrate to the main body; and measuring a property of the test substrate when clamped to the main body.BRIEF 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 corresponding reference symbols indicate corresponding parts, and in which:

[0013] Figure 1 schematically depicts a lithographic apparatus;

[0014] Figure 2 depicts in plan a substrate support and a superimposed treatment tool;

[0015] Figure 3A schematically shows in cross-section part of a clamp prior to a reconditioning process being performed;

[0016] Figure 3B schematically shows in cross-section a polished main body of a clamp;

[0017] Figure 3C schematically shows in cross-section the polished main body of the clamp after new projections have been formed on the main body;

[0018] Figure 4 schematically shows in cross section part of a test substrate according to embodiments; and

[0019] Figure 5 schematically shows in cross-section the test substrate according to embodiments when clamped to a polished main body.DETAILED DESCRIPTION

[0020] 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 365, 248, 193, 157 or 126 nm).

[0021] 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.

[0022] Figure 1 schematically depicts a lithographic apparatus of an embodiment. The apparatus comprises: optionally, an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., UV radiation or DUV radiation); a support structure (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 support table, e.g., a sensor table to support one or more sensors or a substrate table or wafer table WT constructed to hold a substrate (e.g., a resist-coated production substrate) W, connected to a second positioner PW configured to accurately position the surface of the table, for example of a substrate W, 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 part of, one, or more dies) of the substrate W.

[0023] The lithographic apparatus may be of a type wherein at least a portion of the substrate W may be covered by an immersion liquid having a relatively high refractive index, e.g., water such as ultrapure water (UPW), so as to fill an immersion space between the projection system PS and the substrate W. An immersion liquid may also be applied to other spaces in the lithography apparatus, for example, between the patterning device MA and the projection system PS. Immersion techniques can be used toincrease the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate W, must be submerged in immersion liquid; rather “immersion” only means that an immersion liquid is located between the projection system PS and the substrate W during exposure. The path of the patterned radiation beam B from the projection system PS to the substrate W is entirely through immersion liquid. In an arrangement for providing immersion liquid between a final optical element of the projection system PS and the substrate W a liquid confinement structure extends along at least a part of a boundary of an immersion space between the final optical element of the projection system PS and the facing surface of the stage or table facing the projection system PS.

[0024] In operation, the illuminator IL receives a radiation beam 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.

[0025] 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.”

[0026] The lithographic apparatus may be of a type having two or more support tables, e.g., two or more support tables or a combination of one or more support tables and one or more cleaning, sensor or measurement tables. For example, the lithographic apparatus is a multi-stage apparatus comprising two or more tables located at the exposure side of the projection system, each table comprising and / or holding one or more objects. In an example, one or more of the tables may hold a radiation-sensitive substrate. In an example, one or more of the tables may hold a sensor to measure radiation from the projection system. In an example, the multi-stage apparatus comprises a first table configured to hold a radiation-sensitive substrate (i.e., a support table) and a second table not configured to hold a radiationsensitive substrate (referred to hereinafter generally, and without limitation, as a measurement, sensor and / or cleaning table). The second table may comprise and / or may hold one or more objects, other than a radiation-sensitive substrate. Such one or more objects may include one or more selected from the following: a sensor to measure radiation from the projection system, one or more alignment marks, and / or a cleaning device (to clean, e.g., the liquid confinement structure).

[0027] In operation, the radiation beam B is incident on the pattern (design layout) present on patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device MA. Having traversed the patterning device 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 position sensor IF (e.g., an interferometric device, linear encoder, 2-D encoder or capacitive sensor), 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 another position sensor (which is not explicitly depicted in Figure 1) can 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 patterning device 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 C (these are known as scribe-lane alignment marks). A controller 500 controls the overall operations of the lithographic apparatus and in particular performs an operation process described further below. Controller 500 can be embodied as a suitably -programmed general purpose computer comprising a central processing unit, volatile and non-volatile storage means, one or more input and output devices such as a keyboard and screen, one or more network connections and one or more interfaces to the various parts of the lithographic apparatus. It will be appreciated that a one-to-one relationship between controlling computer and lithographic apparatus is not necessary. One computer can control multiple lithographic apparatuses. Multiple networked computers can be used to control one lithographic apparatus. The controller 500 may also be configured to control one or more associated process devices and substrate handling devices in a lithocell or cluster of which the lithographic apparatus forms a part. The controller 500 can also be configured to be subordinate to a supervisory control system of a lithocell or cluster and / or an overall control system of a fab.

[0028] Figure 2 schematically shows a substrate support 60 that is comprised by the substrate table WT. The substrate W is conventionally clamped to the substrate support 60 during exposures. Two clamping techniques are commonly used. In vacuum-clamping a pressure differential across the substrate W is established, e.g., by connecting the space between the substrate support 60 and the substrate W to an under-pressure that is lower than a higher pressure above the substrate W. The pressure difference gives rise to a force holding the substrate W to the substrate support 60. In electrostatic clamping, electrostatic forces are used to exert a force between the substrate W and the substrate support 60. Several different arrangements are known to achieve this. In one arrangement a first electrode is provide on the lower surface of the substrate W and a second electrode on the upper surface of the substrate support 60. A potential difference is established between the first and second electrodes. In another arrangement two semi-circular electrodes are provided on the substrate support 60 and a conductive layer is provided on the substrate W. A potential difference is applied between the two semi-circular electrodes so that the two semi-circular electrodes and the conductive layer on the substrate W act like two capacitors in series.

[0029] To load a substrate W onto the substrate support 60 for exposures, the substrate W is pickedup by a substrate handler robot and lowered onto a set of e-pins. The e-pins project through the substrate support 60. The e-pins are actuated so that they can extend and retract. The e-pins may be provided with suction openings at their tips to grip the substrate W. The e-pins may comprise six e-pins spaced around the center of the substrate support 60. Once the substrate W has settled on the e-pins, the e-pins are retracted so that the substrate W is supported by projections 20 of the substrate support 60.

[0030] Figure 2 depicts a substrate support 60 for use in a lithographic apparatus. The substrate support 60 supports a substrate W. The substrate support 60 comprises a main body 21. The main body 21 has a main body surface 22. A plurality of projections 20 are provided projecting from the main body surface 22 in a first (z) direction. A terminal surface of each projection 20 engages (contacts) with the substrate W. The terminal surfaces of the projections 20 substantially conform to a support plane and support the substrate W. Main body 21 and projections 20 may be formed of SiSiC, a ceramic material having silicon carbide (SiC) grains in a silicon matrix. Alternatively, main body 21 and projections 20 may be formed of SiC or other materials known in the art.

[0031] A plurality of through-holes 89 may be formed in the main body 21. Through-holes 89 allow the e-pins to project through the substrate support 60 to receive the substrate W. Through-holes 89 may allow the space between a substrate W and the substrate support 60 to be evacuated. Evacuation of the space between a substrate W and the substrate support 60 can provide a clamping force, if the space above the substrate W is not also evacuated. The clamping force holds the substrate W in place. If the space above the substrate W is also evacuated, as would be the case in a lithographic apparatus using EUV radiation, electrodes can be provided to form an electrostatic clamp according to known techniques.

[0032] Further through-holes 79 are illustrated in Figure 2. Such through-holes may be present, for example, to allow the substrate support 60 to be fixed to the substrate table WT, for example using bolts. Alternatively the substrate support 60 can be fixed to substrate table WT by vacuum clamping.

[0033] The flatness of the terminal surfaces of the projections 20 (i.e., how close to being in the same plane all of the terminal surfaces of the projections 20 are) is important. This is because any variation in the flatness of the projections 20 is transmitted to the top surface of the substrate W which is subjected to irradiation. There is a flatness specification that all of the terminal surfaces of the projections 20 are required to meet otherwise unacceptable errors may be caused by the flatness variation.

[0034] The roughness of the terminal surfaces of the projections 20 is also important. There is a roughness specification that all of the terminal surfaces of the projections 20 are required to meet because the substrate W may stick to the terminal surfaces of the projections 20 if the terminal surfaces are not rough enough.

[0035] Another property of the substrate support is the stiffness of the projections 20 in the z- direction, i.e., a direction perpendicular to the plane on the substrate support. The stiffness in the z- direction may be affected by the coating properties of the projections 20, the diameter of the projections20, the thickness of the main body 21 of the substrate support 60 and other factors. The actual height of the projections 20 when used to clamp a substrate is dependent on the stiffness of the projections 20 in the z-direction. This is because the same clamping force will compress projections 20 with a lower stiffness more than projections 20 with a larger stiffness.

[0036] The clamp of the substrate W comprises the substrate support 60 as well as the required apparatuses for generating the clamping force that holds the substrate to the substrate support 60. In particular, an electrostatic claim further comprises the electrodes and electrical connections required to generate the clamping force.

[0037] Figure 3A schematically shows in cross-section part of a clamp 300. The clamp 300 comprises a substrate support 60 and an electrode 301. The electrode 301 may be one of a plurality of electrodes 301 that are arranged to clamp a substrate W to the substrate support 60 in an electrostatic clamping process.

[0038] The substrate support 60 comprises a main body 21 and projections 20 that extend from the main body 21. The leftmost projection 20a shown in Figure 3 A is in good condition. The rightmost projection 20b shown in Figure 3A is damaged and it includes a crack 302. Due to the damage to the rightmost projection 20b, a substantial reconditioning process needs to be performed on the substrate support 60 of the clamp 300.

[0039] The substantial reconditioning of the clamp first requires disassembling the clamp into its constituent parts. Stripping and polishing processes are then performed on the substrate support 60 to remove all of the existing projections 20. The stripping and polishing processes may take about two weeks. Processes that form new projections 20 on the main body 21 are then performed and these may take about two weeks. The clamp 300 then needs to be reassembled. The reassembly of a clamp is a complicated process that may take about four weeks. A number of ion / ionic beam figuring (IBF) processes may then be performed so that the clamp meets the required flatness specification. Each IBF process may take about one week and four or five IBF processes may be required.

[0040] Figure 3 A schematically shows in cross-section part of a clamp 300 prior to a substantial reconditioning process being performed. Figure 3B schematically shows in cross-section the part of the clamp 300 after the stripping and polishing processes have been performed for removing all of the existing projections 20, as is required in a reconditioning process.

[0041] The condition of the polished main body 21 is determined before the processes that form new projections 20 on the main body 21 are performed. The time required to reassemble a clamp 300 from a polished main body 21 that is in a good condition may be substantially less than that required to reassemble a clamp 300 from a polished main body 21 that is in a bad condition. A main body 21 may also be in such a bad condition that a reassembled clamp that uses the main body 21 is unlikely to meet the required performance specifications. By prioritizing performing further processes on polished main bodies 21 that are in a good condition over those that are in a bad condition, the number of availablereconditioned clamps 300 for use is increased. For main bodies 21 that are in such a bad condition that they are unlikely to meet the required performance specifications, no further processes may be performed.

[0042] When the condition of the polished main body 21 is inspected, damage to the surface of the main body may be detected. An example of such damage is the crack 302 shown in Figure 3B. The damage to the main body 21 may be reduced by performing further polishing processes that remove the layers of material that contain cracks. However, there is a minimum thickness requirement of the main body 21 that limits the extent that such further polishing processes may be performed. Accordingly, the main body 21 may include cracks 302 that are not removable. If it is known that a crack 302 is present, but a determination is also made that the main body 21 is still usable despite the crack 302, then the further processes for forming a reassembled clamp 300 may still be performed despite the presence of the crack 302. There may also be cracks, or other faults, present in the main body 21 that are difficult to detect and therefore not detected when the condition of the polished main body 21 is inspected.

[0043] Figure 3C schematically shows in cross-section the part of clamp 300 after the processes that form new projections 20 on the main body 21 have been performed and the clamp 300 has been reassembled. The processes that form new projections 20 has been performed despite presence of the crack 302. The crack 302 may have an adverse effect on the performance of the reassembled clamp 300. With known techniques, further processes, such as time consuming IBF processes, may need to be performed to reduce the adverse effects of the crack 302 so that the clamp 300 meets the required performance specifications. If the adverse effects of the crack 300 are severe, the clamp may need to be scrapped and the time and expense of reassembling the clamp 300 will have been wasted.

[0044] Embodiments provide a new technique for improving the determination of the condition of a polished main body 21 before new projections 20 are formed on the polished main body 21.

[0045] Embodiments secure a test substrate to the polished main body 21. The test substrate 400 provides the polished main body 21 with temporary projections and a temporary substrate, in a substantially equivalent way to how an actual substrate W would be clamped to an assembled clamp 300 with the polished main body 21. Measurements of the temporary substrate may then be made to determine the effects of cracks, and other faults, on an assembled clamp 300 with the polished main body 21.

[0046] Figure 4 schematically shows in cross section part of a test substrate 400 according to embodiments. The test substrate 400 includes a substrate 401 that is a main body of the test substrate 400. There are projections 402 on only one of the major surfaces of the main body of the test substrate 400.

[0047] The substrate 401 of the test substrate 400 may be substantially the same as a normal substrate W for use in lithographic processes. The projections 402 of the test substrate 400 may be substantiallythe same as the new projections 20 that are formed on a main body 21. Accordingly, they may be formed on the substrate 401 in substantially the same way using the same materials. Each projection 402 of the test substrate may have the same diameter as the intended diameter of a corresponding projection 20 that may be formed on a main body 21 of a substrate support 60. The pattern of the projections 402 on the test substrate 400 may be the mirror image of the pattern of the projections 20 that may be formed on a main body 21 of a substrate support 60.

[0048] The test substrate 400 includes any features that are required for it to be clamped to the polished main body 21 of a substrate support 60. For example, the test substrate may include one or more metal plates so it is usable in an electrostatic clamping process.

[0049] Figure 5 schematically shows in cross-section a test substrate 400 according to embodiments when clamped to a polished main body 21 of a substrate support 60. On the opposite side of the substrate support 60 to the test substrate there are electrodes 301, 501. The electrodes 301, 501 are connected to an electrical power supply 502 that applies a voltage to the electrodes 301, 501 so that the test substrate 400 is clamped to the polished main body 21 by an electrostatic clamping process.

[0050] Measurements may be made of the test substrate 400 when the test substrate 400 is clamped to the polished main body 21 of the substrate support 60. In particular, on the major surface of the test substrate 400 that is equivalent to the major surface of an actual substrate W that features are formed on, the flatness may be measured.

[0051] As shown in Figure 5, the polished main body 21 of the substrate support 60 may include a crack 302. The polished main body 21 may also include other faults, some of which may not have been detected by an inspection of the main body 21. The crack 302, and any other faults, of the polished main body 21, may change the flatness of the substrate 401 of the test substrate 400. The flatness measurement of the test substrate 400 may determine the effect of the crack 302, and any other faults, of the polished main body 21.

[0052] Advantageously, the flatness measurement provides further information on the condition of a polished main body 21 of the substrate support 60 that is not obtainable with known techniques for inspecting the condition of a polished main body 21. A limitation of known techniques for inspecting the condition of a polished main body 21 is that the effects of faults in the main body 21 on the flatness of a substrate W may only be determinable after the processes of forming projections 20 on the main body 21 and assembling an actual clamp have been performed. Embodiments solve this problem because they allow a determination to be made of the performance of a polished main body 21 during the clamping of a substrate 401 without first performing the processes of forming projections 20 on the main body 21 and assembling an actual clamp.

[0053] Due to manufacturing constraints, it may not be possible to form projections 20 on a main body of a substrate support 60 with a desired diameter to a high level of accuracy. The possible range of diameters of the projections 20 may therefore be quite large. The variation of diameters of theprojections 20 may cause a variation in the stiffness of the projections 20 in the z-direction. The variation in the stiffness of the projections 20 may cause a variation in the heights of the projections 20 when they are clamped. For example, a projection 20 with an intended diameter of 210pm may have an actual diameter in the range 180pm to 240pm. A projection with a diameter of 240pm may have a stiffness in the z-direction that is over twice that of a projection with a diameter of 180pm. The unclamped heights of projections with diameters of 180 pm and 240pm may be the same. However, the clamped height of the projection with a diameter of 240pm may be about 10% higher than that of the projection with a diameter of 180pm.

[0054] Other manufacturing variables of the projections 20 that influence the actual clamped height of the projections 20 include the thickness of the coating of the projections 20, the uniformity of the coating of the projections 20, and variations in the properties of the coating of the projections 20. The actual clamped height of the projections 20 may also be dependent on properties of the polished main body 21 of the substrate support 60, such as the thickness variation of the polished main body 21.

[0055] Embodiments include performing a plurality of measurements on a polished main body 21 with a plurality of different test substrates 400. The projections 402 of the test substrates 400 may have different properties so that the manufacturing variables of projections 20 may be tested. In particular, the test substrates 400 may differ by some, or all, of the projections 20 having different diameters, coating thicknesses, coating uniformities, and / or variations in coating properties.

[0056] Advantageously, the measurements with a plurality of different test substrates 400 allow the effects of the manufacturing variables of the projections 20 to be measured across their range. This may provide determinations of the effects of any faults in the polished main body 21 across the entire range of properties of the projections 20 given the uncertainties in their manufacturing processes.

[0057] Embodiments provide an improved determination of the condition of a polished main body 21 before projections 20 are formed on the polished main body 21. The further process may be prioritized so that they are performed on the polished main bodies 21 that are in the best condition. Furthermore, in response to the determination of the condition of a polished main body 21, processes may be performed on the polished main body 21 to improve its condition prior to forming projections 20 on the polished main body 21. There are more options for improving the condition of a polished main body 21 before projections 20 are formed on the polished main body 21.

[0058] Embodiments include a number of modifications and variations to the above-described techniques.

[0059] Embodiments are not restricted to determining the conditions of polished main bodies 21 in electrostatic clamps. The techniques of embodiments may be used to determine the conditions of polished main bodies 21 in vacuum clamps, or any other type of clamp for a substrate W.

[0060] Embodiments may also be used to improve the manufacturing processes of new clamps for substrates W. Embodiments improve the determination of the condition of a new polished main body21 prior to projections 20 being formed of the new polished main body 21.

[0061] Embodiments are not restricted to only measuring the flatness of the test substrate 400 when the test substrate 400 is clamped to the polished main body 21. Embodiments may measure any property of the test substrate 400 when the test substrate 400 is clamped to the polished main body 21.

[0062] 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, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin film 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.

[0063] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0064] Any controllers described herein may each or in combination be operable when the one or more computer programs are read by one or more computer processors located within at least one component of the lithographic apparatus. The controllers may each or in combination have any suitable configuration for receiving, processing, and sending signals. One or more processors are configured to communicate with the at least one of the controllers. For example, each controller may include one or more processors for executing the computer programs that include machine-readable instructions for the methods described above. The controllers may include data storage media for storing such computer programs, and / or hardware to receive such media. So the controller(s) may operate according the machine readable instructions of one or more computer programs.

[0065] Embodiment include the following numbered clauses:1. A test substrate comprising: a substrate; and a plurality of projections formed on one of the major surfaces of the substrate.2. The test substrate according to clause 1, wherein the test substrate is for use in determining the condition of the main body of a substrate support of a substrate clamp of a lithographic apparatus.3. The test substrate according to clause 1 or 2, wherein the projections are formed on only one of the major surfaces of the substrate.4. The test substrate according to any preceding clause, wherein the test substrate is configured so that it is clampable to a main body of a substrate support of a clamp.5. The test substrate according to any preceding clause, wherein the projections on the major surface have a pattern that is the mirror image of an intended pattern of projections on a substrate support.6. A method of determining the condition of the main body of a substrate support of a substrate clamp of a lithographic apparatus, the method comprising: obtaining a main body of a substrate support, wherein the main body is for forming projections on to thereby form the substrate support; clamping a test substrate to the main body; and measuring a property of the test substrate when clamped to the main body.7. The method according to clause 6, wherein the main body does not have any projections formed on it when the test substrate is clamped to the main body.8. The method according to clause 6 or 7, wherein the measured property of the test substrate is the flatness of the test substrate.9. The method according to any of clauses 6 to 8, wherein the test substrate is according to any of clauses 1 to 5.10. The method according to any of clauses 6 to 9, wherein the method is used in a process for manufacturing or reconditioning a substrate support.11. The method according to any of clauses 6 to 10, further comprising repeating the processes of clamping a test substrate to the main body and measuring a property of the test substrate when clamped to the main body with a plurality of different test substrates.12. The method according to clause 11, wherein the plurality of test substrates have projections with different diameters, coating thicknesses, coating uniformities, and / or coating properties.

[0066] 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 test substrate comprising: a substrate; and a plurality of projections formed on one of the major surfaces of the substrate.

2. The test substrate according to claim 1, wherein the test substrate is for use in determining the condition of the main body of a substrate support of a substrate clamp of a lithographic apparatus.

3. The test substrate according to claim 1 or 2, wherein the projections are formed on only one of the major surfaces of the substrate.

4. The test substrate according to any preceding claim, wherein the test substrate is configured so that it is clampable to a main body of a substrate support of a clamp.

5. The test substrate according to any preceding claim, wherein the projections on the major surface have a pattern that is the mirror image of an intended pattern of projections on a substrate support.

6. A method of determining the condition of the main body of a substrate support of a substrate clamp of a lithographic apparatus, the method comprising: obtaining a main body of a substrate support, wherein the main body is for forming projections on to thereby form the substrate support; clamping a test substrate to the main body; and measuring a property of the test substrate when clamped to the main body.

7. The method according to claim 6, wherein the main body does not have any projections formed on it when the test substrate is clamped to the main body.

8. The method according to claim 6 or 7, wherein the measured property of the test substrate is the flatness of the test substrate.

9. The method according to any of claims 6 to 8, wherein the test substrate is according to any of claims 1 to 5.

10. The method according to any of claims 6 to 9, wherein the method is used in a process for manufacturing or reconditioning a substrate support.

11. The method according to any of claims 6 to 10, further comprising repeating the processes of clamping a test substrate to the main body and measuring a property of the test substrate when clamped to the main body with a plurality of different test substrates.

12. The method according to claim 11, wherein the plurality of test substrates have projections with different diameters, coating thicknesses, coating uniformities, and / or coating properties.

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