Substrate support system, lithographic apparatus

Abstract

Provided is a substrate support system comprising: a support portion configured to support a bottom surface of a substrate on a support surface; a movable portion movable between a retracted position where an upper end of the movable portion is below the support surface and an extended position where the upper end of the movable portion is above the support surface, the movable portion supporting the bottom surface of the substrate above the support surface when in the extended position; and a measurement system configured to measure the time it takes for the movable portion to move from the retracted position to the extended position, compare the measured time with a reference time, and generate a signal when the measured time deviates from the reference time by more than a predetermined amount.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to European Application No. 20174973.6, filed May 15, 2020, and International Application No. PCT / CN2021 / 076817, filed February 19, 2021, which are incorporated by reference in their entireties.

[0002] The present invention relates to a substrate support system, a lithographic apparatus and a method for exposing a substrate, and particularly, although not exclusively, to a system, apparatus and method for measuring the unload time of a substrate from a support and comparing it to a reference value. [Background technology]

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern (often referred to as a "design layout" or "design") in a patterning device (e.g., mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., wafer).

[0004] As semiconductor manufacturing processes continue to advance, following a trend commonly referred to as "Moore's Law," the dimensions of circuit elements are continually shrinking, and the amount of functional elements, such as transistors, per device has steadily increased for decades. To keep up with Moore's Law, the semiconductor industry is seeking technologies that allow it to create smaller and smaller features. To project patterns onto a substrate, lithography equipment can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm.

[0005] Immersion technology has been introduced into lithography apparatus to improve the resolution of smaller features. In an immersion lithography apparatus, a layer of immersion liquid, having a relatively high refractive index, is interposed in the space between the apparatus's projection system (through which a patterned beam is projected towards the substrate) and the substrate. This immersion liquid ultimately covers the portion of the substrate that is under the final element of the projection system. In this way, at least a portion of the substrate that will be exposed to light is immersed in liquid. The effect of the immersion liquid is that the wavelength of the exposure radiation is shorter in the immersion liquid than in a gas, allowing for the imaging of smaller features (the effect of the liquid can also be thought of as increasing the effective numerical aperture (NA) of the system, increasing the depth of focus).

[0006] In commercial immersion lithography, the immersion liquid is water. This water is typically high-purity distilled water, such as ultrapure water (UPW), commonly used in semiconductor manufacturing facilities. In immersion systems, UPW is often purified and may undergo additional processing steps before being supplied to the space as the immersion liquid. High-refractive-index liquids other than water can also be used, such as hydrocarbons, e.g., fluorocarbons, and / or aqueous solutions. Furthermore, other fluids than liquids are also contemplated for use in immersion lithography. References herein to localized immersion, where in use the immersion liquid is confined to a space between a final element and a surface facing the final element, can be the surface of the substrate or a surface of a support table (or substrate support) that is coplanar with the surface of the substrate. (Note that references to the surface of the substrate in the following text can additionally or alternatively refer to the surface of the substrate support, and vice versa, unless explicitly stated otherwise.) Fluid handling structures present between the projection system and the stage are used to confine the immersion liquid to the space. The space filled by the immersion liquid is smaller in plan than the top surface of the substrate, and this space remains substantially stationary relative to the projection system while the substrate and substrate stage move underneath.

[0007] In lithography systems, the substrate is clamped onto the substrate table. Seals are present near the edge of the substrate to ensure that a negative pressure is created to hold the substrate in place and "clamp" the wafer onto the substrate table. The substrate rests on a number of protrusions, or burls, on the substrate table. During loading of the substrate onto the substrate table, friction of the burls close to the substrate's edge has a significant effect on substrate deformation. This is particularly important for so-called "umbrella-shaped" substrates, where the burls closest to the edge (e.g., the outer burls) make contact first. In immersion systems, the area on the substrate table close to the outer burls is usually wet and remains wet when the substrate is loaded.

[0008] Changes in the frictional properties of the burls can cause irreparable deformation of the substrate during loading of the substrate onto the substrate table.

[0009] It is an object of the present invention to provide a system and method that allows for the identification of substrates that may have experienced significant deformation during clamping, preferably without requiring inspection of the substrate itself. Summary of the Invention

[0010] A first aspect of the present invention provides a substrate support system comprising: a support portion configured to support a bottom surface of a substrate on a support surface; a movable portion movable between a retracted position where an upper end of the movable portion is below the support surface and an extended position where the upper end of the movable portion is above the support surface, the movable portion contacting the bottom surface of the substrate supported by the support portion when moving between the retracted position and the extended position and supporting the bottom surface of the substrate above the support surface in the extended position; and a measurement system configured to measure the time it takes for the movable portion to move from the retracted position to the extended position, compare the measured time with a reference time, and generate a signal when the measured time deviates from the reference time by more than a predetermined amount.

[0011] A second aspect of the present invention provides a stage positioning system comprising: a substrate support system configured to support a substrate; a clamping system configured to hold the substrate to the substrate support as the substrate is exposed to radiation; and a processor; (a) a sensor configured to measure the time it takes for the substrate to be removed from the substrate support, the processor being configured to compare the time measured by the sensor to a reference time and generate a signal when the measured time deviates from the reference time by more than a predetermined amount; or (b) a sensor configured to measure a change in pressure used by the clamping system to clamp the substrate to the substrate support, the processor being configured to compare the measured pressure change with the reference and generate a signal based on the comparison.

[0012] A third aspect of the present invention provides a method of exposing a substrate in a lithographic process, the method comprising the steps of clamping the substrate to a support structure, exposing the clamped substrate to radiation, and removing the substrate from the support structure, and further comprising the steps of: (a) measuring the time it takes to remove the substrate from the support structure, comparing the measured time to a predetermined reference time, and generating a signal if the measured time deviates from the reference time by more than a predetermined amount; or (b) measuring a change in pressure used to clamp the substrate to the support structure during the clamping step, comparing the measured pressure change to a predetermined reference, and generating a signal based on the comparison.

[0013] A further aspect of the present invention provides a computer program comprising computer readable instructions which, when executed on a suitable computing device, cause the computing device to carry out the method of the above-mentioned aspect, and a computer readable medium having stored such a computer program. [Brief explanation of the drawings]

[0014] Some embodiments of the present invention are now described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0015] [Figure 1] 1 depicts a lithographic apparatus according to an embodiment of the invention;

[0016] [Figure 2] 1 shows an outer part of a substrate table of a lithographic apparatus;

[0017] [Figure 3] 2 illustrates schematically the interaction between a substrate and a substrate table;

[0018] [Figure 4] A comparison is shown between a dry and wet outer portion of the substrate table.

[0019] [Figure 5a] 1 shows a clamp fingerprint for a substrate unloaded from a wet substrate table. [Figure 5b] 1 shows a clamp fingerprint for a substrate unloaded from a dry substrate table.

[0020] [Figure 6] 10 shows the substrate unload time from the substrate table for substrates with different degrees of wetness.

[0021] [Figure 7] 1 shows the movement of the e-pins over time during unloading of the substrate from the substrate table.

[0022] [Figure 8] The variation in observed marker positions from the expected positions is shown as a function of placement within the lot for three substrate lots.

[0023] [Figure 9]The overall variation in observed marker positions from the expected positions is shown as a function of placement within the lot for one set of substrate lots.

[0024] [Figure 10] 1 shows the pre-clamp pressure profile over time for multiple substrates. DETAILED DESCRIPTION OF THE INVENTION

[0025] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (eg, having wavelengths of 365, 248, 193, or 126 nm).

[0026] The terms "reticle," "mask," or "patterning device," as used in this text, may be broadly interpreted to refer to any general patterning device that can be used to impart an incident radiation beam with a patterned cross section that corresponds to the pattern to be created in a target portion of a substrate. The term "light valve" can also be used in this context. In addition to traditional masks (transmissive or reflective; binary, phase-shifting, hybrid, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0027] Figure 1 shows a schematic diagram of a lithographic apparatus. a. optionally an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., UV radiation or DUV radiation); b. a support structure (e.g., mask table) MT constructed to support a patterning device (e.g., mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters; c. a support table (e.g., a sensor table supporting one or more sensors) or substrate table WT constructed to hold a substrate (e.g., a resist-covered substrate) W and connected to a second positioner PW configured to accurately position the surface of the table (e.g., substrate W) according to certain parameters; d. A projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C of the substrate (e.g. comprising one or more dies).

[0028] In operation, the illumination system IL receives a radiation beam from the source SO, or radiation, for example via the 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, to direct, shape and / or control the radiation. The illuminator IL may be used to condition the radiation beam B so that it has a desired spatial and angular intensity distribution in its cross-section in the plane of the patterning device MA.

[0029] The term "projection system" PS as used herein should be interpreted broadly to encompass various types of projection systems that are appropriate for the exposure radiation used and / or for other factors such as the use of an immersion liquid, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems, or any combination thereof. Any use of the term "projection lens" herein can be considered as synonymous with the more general term "projection system".

[0030] The lithographic apparatus may be of a type in which at least part of the substrate W may be covered by an immersion liquid having a relatively high refractive index, e.g. water, so as to fill an immersion space between the projection system PS and the substrate W, which is also known as immersion lithography. Details of immersion techniques are described in US6952253, which is incorporated herein by reference.

[0031] The lithographic apparatus may be of a type having two or more substrate tables WT (also known as "dual stage"). In such a "multiple stage" machine, the substrate tables WT may be used in parallel and / or may be used to expose a pattern onto a substrate W placed on one of the substrate tables WT while preparatory steps for a subsequent exposure are being performed on the other substrate table WT.

[0032] In addition to the substrate table WT, the lithographic apparatus may also include a measurement stage (not shown in Figure 1). The measurement stage is configured to hold a sensor and / or a cleaning device. The sensor is configured 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 is configured to clean part of the lithographic apparatus, for example part of the projection system PS or part of a system for providing immersion liquid. The measurement stage may be moved below the projection system PS when the substrate table WT is spaced apart from the projection system PS.

[0033] In operation, radiation beam B is incident on patterning device MA, e.g., a mask, held on mask support MT, and is patterned by a pattern (design layout) present on patterning device MA. After passing through mask MA, radiation beam B passes through projection system PS, which focuses the beam onto target portions C of substrate W. With the aid of second positioner PW and position measurement system IF (e.g., an interferometer arrangement, linear encoders, two-dimensional encoders, or capacitive sensors), substrate table WT can be precisely moved, e.g., to position various target portions C in the path of radiation beam B at focused and aligned positions. Similarly, first positioner PM and possibly further position sensors (not explicitly shown in FIG. 1 ) can be used to accurately position patterning device MA with respect to the path of radiation beam B. Patterning device MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. As shown, substrate alignment marks P1, P2 occupy dedicated target portions, although they may also be located in spaces between the target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are known as scribe-lane alignment marks.

[0034] A Cartesian coordinate system is used herein. The Cartesian coordinate system has three axes: X, Y, and Z. Each of the three axes is orthogonal to the other two. Rotation about the X axis is called Rx rotation. Rotation about the Y axis is called Ry rotation. Rotation about the Z axis is called Rz rotation. The X and Y axes define the horizontal plane, and the Z axis defines the vertical direction. The Cartesian coordinate system is not a limitation of the present invention and is used for illustration purposes only. Alternatively, another coordinate system, such as a cylindrical coordinate system, can be used to clarify the present invention. The orientation of the Cartesian coordinate system may be different, for example, the Z axis has a component along the horizontal plane.

[0035] A localized liquid supply or fluid handling system is provided between the projection system PS and the substrate W. The liquid supply system comprises a fluid handling structure IH (or liquid confinement structure) that extends along at least part of the boundary of the space between the final element of the projection system PS and the substrate table WT or substrate W. The fluid handling structure IH is substantially stationary relative to the projection system PS in the XY plane, although there may be some relative movement in the Z direction (along the optical axis). In one example, a seal is formed between the fluid handling structure IH and the surface of the substrate W, and this may be a contactless seal such as a gas seal (such a system having a gas seal is disclosed in EP 1,420,298) or a liquid seal.

[0036] The fluid handling structure IH at least partly confines immersion liquid to a space between the final element of the projection system PS and the substrate W. The space is at least partly formed by the fluid handling structure IH positioned below and surrounding the final element of the projection system PS. Immersion liquid is brought into the space below the projection system PS and within the fluid handling structure IH by one of the liquid openings. Immersion liquid may be removed by another of the liquid openings.

[0037] The immersion liquid may be confined in a space by a contactless seal, such as a gas seal formed by gas that, in use, forms between the bottom of the fluid handling structure IH and the surface of the substrate W. Gas in the gas seal is supplied under pressure to the gap between the fluid handling structure IH and the substrate W via an inlet. The gas is removed via an outlet. The overpressure at the gas inlet, the vacuum at the outlet, and the shape of the gap are arranged so that there is a high velocity gas flow inside that confines the immersion liquid. Such a system is disclosed in US 2004 / 0207824, which is incorporated herein by reference in its entirety. In one example, the fluid handling structure IH does not have a gas seal.

[0038] Another example of a liquid supply system is disclosed in US 2010 / 0045949 A1, which is incorporated herein by reference in its entirety.

[0039] Figure 2 shows part of a lithographic apparatus according to an embodiment of the present invention. The arrangement depicted in Figure 2 and described below may be applied to the lithographic apparatus described above and shown in Figure 1. Figure 2 shows a cross-section through a substrate table WT and a substrate W. A gap 5 exists between the edge of the substrate W and the edge of the substrate table WT. When the edge of the substrate W is being imaged, or when the substrate W initially moves under the projection system PS (described above), etc., an immersion space filled with liquid by a liquid confinement structure IH (for example) will at least partly pass through the gap 5 between the edge of the substrate W and the edge of the substrate table WT. As a result, liquid from the immersion space may enter the gap 5.

[0040] The substrate W is held by supports 30 (e.g. a pimple table or burl table) which have one or more protrusions 32 (i.e. burls). The supports 30 are an example of an object holder. Another example of an object holder is a mask holder. Negative pressure applied between the substrate W and the substrate table WT helps to ensure that the substrate W is held firmly in place. However, problems can arise if immersion liquid gets between the substrate W and the supports 30, particularly when unloading the substrate W.

[0041] To deal with immersion liquid entering the gap 5, at least one drain 10, 20 is provided at the edge of the substrate W to remove the immersion liquid that has entered the gap 5. In the embodiment of Figure 2, two drains 10, 20 are shown, but there may be only one drain, or there may be three or more drains. In one embodiment, each drain 10, 20 is annular so as to surround the entire periphery of the substrate W.

[0042] The primary function of the first drain 10 (radially outward from the edge of the substrate W / support 30) is to help prevent gas bubbles from entering the immersion space where the liquid in the liquid confinement structure IH is present. Such bubbles could adversely affect imaging of the substrate W. The first drain 10 is present to help prevent gas in the gap 5 from escaping into the immersion space in the liquid confinement structure IH. If gas were to escape into the immersion space, it could result in the creation of air bubbles floating in the immersion space. Such bubbles could lead to imaging errors if they are in the path of the projection beam. The first drain 10 is configured to remove gas from the gap 5 between the edge of the substrate W and the edge of a recess in the substrate table WT on which the substrate W rests. The edge of the recess in the substrate table WT may be defined by a cover ring 130 (optionally separate from the support 30 for the substrate table WT). The cover ring 130 may be ring-shaped in plan and surround the outer edge of the substrate W. The first drain 10 extracts mainly gas and only a small amount of immersion liquid.

[0043] The second drain 20 (radially inward from the edge of the substrate W / support 30) is provided to help prevent liquid from seeping through the gap 5 into the space below the substrate W which could prevent the substrate W from efficiently leaving the substrate table WT after imaging. The provision of the second drain 20 reduces or eliminates problems that can arise from liquid getting under the substrate W.

[0044] As depicted in FIG. 2 , in one embodiment, the lithographic apparatus includes a channel 46 for passing two-phase flow therethrough. The channel 46 is formed in a block. The first and second drains 10, 20 include openings 42, 22 and channels 46, 26, respectively. The channels 46, 26 are in fluid communication with the respective openings 42, 22 via passages 44, 24. One or more outer protrusions 32 a may be provided in the same region as the second drain 20. The openings 22 of the second drain 20 may be blocked at the locations of the outer protrusions 32 a, or the openings 22 may include a plurality of individual openings alternating with the outer protrusions 32 a, or may be arranged in other repeating or non-repeating patterns.

[0045] As depicted in Figure 2, the cover ring 130 has a top surface. The top surface extends circumferentially around the substrate W on the support 30. In use of the lithographic apparatus, the substrate table WT moves relative to the liquid confinement structure IH. During this relative movement, the liquid confinement structure IH may be positioned across the gap 5 between the cover ring 130 and the substrate W. In an embodiment, the relative movement is caused by the substrate table WT moving under the liquid confinement structure IH. In an alternative embodiment, the relative movement is caused by the liquid confinement structure IH moving over the substrate table WT. In a further alternative embodiment, the relative movement is caused by movement of the substrate table WT under the liquid confinement structure IH and movement of the substrate W. table In the following description, movement of the liquid confinement structure IH will be used to mean movement of the substrate table WT relative to the liquid confinement structure IH.

[0046] A plurality of pins (or e-pins) 38 protrude through holes 39 in the substrate table WT. The e-pins 38 are shown in Figure 2 in a retracted position. In the retracted position, the top surfaces of the e-pins 38 are below a support surface P. The support surface P is defined by the end surfaces of the protrusions 32 and outer protrusions 32a and coincides with the bottom surface of the substrate W when the substrate W rests on the protrusions 32 and outer protrusions 32a. The e-pins 38 are used to unload the substrate W from the substrate table WT when exposure to patterning radiation is complete. To unload the substrate W, the e-pins 38 are moved upward to an extended position, so that the top surfaces of the e-pins 38 first contact the bottom surface of the substrate W and lift the substrate W from the protrusions 32 and outer protrusions 32a. Once the substrate W has been lifted from the protrusions 32 and outer protrusions 32a, the substrate W can be picked up and repositioned by other mechanisms within the lithographic apparatus.

[0047] The substrate W may be deformed as a result of handling within the lithographic apparatus. Such deformation is generally undesirable as it may cause problems with the subsequent alignment of the substrate W with the applied patterning. While some deformations can be measured and adjusted for in subsequent steps in the lithographic process, excessive and / or abnormal deformations may not be adjustable, which may result in inaccurate results in subsequent processes. It is therefore desirable to identify substrates W that have undergone or may have undergone excessive and / or abnormal deformation as early as possible in the lithographic process after such deformations have occurred or may have occurred.

[0048] Deformations resulting from various operations within a lithography process may be referred to as "fingerprints." For example, deformations resulting from the process of loading, clamping, and unloading a substrate W by a stage positioning system comprising a substrate support system including a substrate table WT and a clamping system may be referred to as a "substrate clamp fingerprint." During loading of the substrate W onto the substrate table WT, friction of the protrusions 32 near the edges of the substrate W determines to a large extent the substrate clamp fingerprint. In particular, abrupt changes in the frictional characteristics of the protrusions 32, especially those near the edges of the substrate table WT, may result in an uncorrectable substrate clamp fingerprint.

[0049] This is particularly important for so-called "umbrella-shaped substrates" which have a dome-shaped structure that is generally concave relative to the substrate table WT and therefore first contact protrusions 32, e.g. outer protrusions 32a, near the edge of the substrate table WT as shown on the left side of Figure 3. The right side of Figure 3 shows an outer region of the substrate W supported on the support surface P by protrusions 32, e.g. outer protrusions 32a, on the substrate table WT.

[0050] In an immersion system, the area near the protrusions 32 on the edge of the substrate table WT (and the substrate W when placed on the substrate table WT) is wet and remains wet when the substrate W is loaded. Liquid is slowly removed through the extraction opening 22.

[0051] The inventors have realised that the presence of different amounts of liquid between the inner or first seal and the outer or second seal will result in a significant change in the frictional properties of the protrusions, e.g. the second protrusions, in this area. This is illustrated in the photographs of the substrate table in Figure 4, where the top photograph shows the substrate table WT dry in the area of ​​the outer protrusion 32a or second protrusion formed between the inner seal 34 and the outer seal 36 and the removal opening 22. The bottom photograph of Figure 4 shows the same area when the substrate table WT is wet, which is indicated by the darker colouring of this area.

[0052] The inventors have also determined that when the area of ​​the outer protrusion 32a dries out, for example due to a delay in the operation of the system, the friction between the substrate table WT and the substrate W changes, and as a result a substrate W loaded onto a dry substrate table WT (for example immediately after a delay) may exhibit a large clamping fingerprint.

[0053] Figure 5a (top) shows a typical clamp fingerprint of a substrate W loaded during normal operation, with the edge regions of the substrate table WT remaining completely wet, while Figure 5b (bottom) shows the fingerprint after loading the same substrate W onto a substrate table WT that has been intentionally dried locally, particularly in the region where the portion of the substrate W that is in contact with the substrate table WT can be seen in the upper right corner of Figure 5b.

[0054] In the clump fingerprint, arrows indicate the position of the alignment markers relative to their expected undeformed positions. The origin of each arrow is the expected position of the alignment marker, and the length of each arrow represents the degree of displacement of the alignment marker from the expected position.

[0055] The locally dried substrate experiences much larger deformations across a significant portion of the substrate W, with an average 3-sigma change of 11.9 nm for all observed positions of the markers from their expected positions. In contrast, the fully wet fingerprint exhibits only minimal and localized deformation, with an average 3-sigma change of 0.8 nm.

[0056] As a result, a substrate W that has experienced localized (or complete) dry contact with the substrate table WT is likely to be significantly deformed and may need to be rejected from the lithographic process. The ability to identify and / or reject such substrates W in time after experiencing deformation, and in particular before they are subjected to further processing, would be beneficial for the entire lithographic process.

[0057] The inventors have discovered a relationship between the amount of liquid near the edge of the substrate table WT and the unload time of the substrate W. Figure 6 shows the substrate unload times for three experiments in which two substrates W were each unloaded from the substrate tables WT (e.g., "wafer table chuck 1" and "wafer table chuck 2"). Experiment 1 simulated a "normal" configuration in which the edges of both substrate tables WT were fully wet, and a long unload time of over 0.6 seconds was recorded. In Experiment 2, a different movement profile of the fluid handling structure IH over the substrate table WT was used. The edges of the substrate table WT at wafer table chuck 2 remained fully wet, and again an unload time of over 0.6 seconds was recorded. Meanwhile, the edge of the substrate table WT at wafer table chuck 1 was partially dry, and a short unload time of approximately 0.56 seconds was recorded. In Experiment 3, the control of the fluid handling structure IH was intentionally adjusted to ensure that no immersion liquid (e.g., UPW) was present. This left both substrate tables WT completely dry and a fast unload time of just over 0.4 seconds was recorded, thus showing that the unload time for a substrate W loaded onto a partially dry substrate table WT is shorter than the unload time for a substrate W loaded onto a completely wet substrate table WT.

[0058] The unload time of the substrate W can therefore be used as an indicator of whether the substrate table WT was completely wet or at least partially dry. This approach may have the advantage of identifying potential problems immediately when the substrate W is unloaded, and is particularly likely to be more accurate than, for example, measuring substrate alignment residuals, which may miss deformations resulting from clamping due to under-sampling of the substrate alignment marks and generally cannot distinguish between different potential causes of alignment residuals. Substrate alignment residuals also cannot be used to detect problems in zero-coupling layers, because no substrate alignment has been performed in those layers and no alignment markers have yet been formed.

[0059] In some embodiments, the unload time of the substrate W can be accurately measured by the measurement system 500 using the movement of a movable part of the substrate table WT relative to the support 30. In one embodiment, the e-pins 38 are used to lift the substrate W off the surface of the substrate table WT and thus can form movable parts. The movement of the e-pins 38 in the lithographic apparatus is already highly controlled and measured and can therefore provide a reliable indication of the substrate unload time. Because the movement of the e-pins 38 is already measured, no additional physical components or sensors need to be added to an existing lithographic apparatus to measure the substrate unload time in this manner.

[0060] 7 shows the relative height z (y-axis) of the e-pins 38 during substrate unloading. The substrate unloading time is the time from when the e-pins 38 start to move upward from their retracted position below the support surface P (t s ), the time (t) when the upper end of the pin 38 reaches a predetermined height from the storage position or an extended position at a predetermined height above the support surface P, and the substrate W is supported above the protrusions 32 and the outer protrusions 32a but is no longer in contact with them. e ) The predetermined height in the example of FIG. 7 is 6 mm.

[0061] In an alternative embodiment, the substrate W is unloaded from the substrate table WT by another mechanism, such as a gripper (not shown) or vortex gripper that engages the side and / or top surface of the substrate W. In such an arrangement, the time taken to unload each substrate W using this different mechanism can similarly be determined by measuring the movement and / or position of this mechanism.

[0062] The substrate unload time may alternatively or additionally be derived from signals from other sensors used in the lithographic apparatus, examples of which include pressure sensors and / or temperature sensors.

[0063] Alternatively or additionally, dedicated additional sensors can be provided to measure substrate unload time, but these may be difficult to implement in existing systems.

[0064] The substrate unload time determined by either of the above approaches, or by further alternative approaches, can be compared to a reference time determined to be useful for distinguishing between wet and dry substrate tables WT during unloading. For example, in the apparatus tested in the experiment shown in Figure 6, 0.6 seconds can be selected as the reference time. If a substrate unload time is measured or calculated to be less than the reference time by more than a predetermined amount, a warning signal can be generated.

[0065] The exact selection of the reference time and predetermined amount will depend on one or more of the lithographic apparatus, the substrate W, the unload mechanism, the desired accuracy and tolerances, and other factors. It will be appreciated that selecting a reference time and / or predetermined amount such that even small variations from the observed or predicted normal unload time will cause a warning signal will result in a high rate of false positive results. Conversely, selecting a reference time and / or predetermined amount that is too far from the observed or predicted normal unload time may result in a low rate of detection of potentially deformed substrates W.

[0066] The inventors have also determined that monitoring the clamping pressure (negative pressure below the substrate W held on the substrate table WT during the lithography process) can be used to detect a substrate W that may be deformed.

[0067] It has been found that localized drying of the outer protrusions 32a and the resulting changes in friction can be particularly important for the substrate table WT, where changes in water management and / or changes in clamping pressure design between the inner or first seal 34 and the outer or second seal 36 can significantly speed up drying times. During normal operation, even in the absence of long delays, localized effects can become noticeable in the alignment / overlay of the substrate W.

[0068] Figures 8 and 9 show example performance from a series of tests on initial substrates on the substrate table WT. In Figures 8 and 9, the y-axis plots the variation of the observed marker position from the expected position for each substrate at sequential positions shown on the x-axis. Figure 8 shows the alignment performance of three lots. Figure 9 shows the average alignment performance of multiple lots of initial substrates. The crosses represent individual measurements, the horizontal lines represent the average, and the boxes represent the 3-sigma variation of the measurements.

[0069] Both Figures 8 and 9 show clear performance degradation for substrates in positions 1 through 3 within a single lot. The extra operations required to start the lot, such as handling the closing substrate, introduce timing delays of approximately several seconds, likely resulting in overlay effects. For example, a delay of approximately 6 seconds occurred before substrate 3 was loaded, again resulting in performance degradation.

[0070] The pre-clamping pressure of the substrate table WT for several lots was analyzed and compared to subsequent lots during the production lithography process. Figure 10 shows the recorded pre-clamping pressure profiles (i.e., the change in negative pressure before clamping at approximately 3.1 Pa) over time for substrates W that were found to suffer from alignment issues and the remaining substrates (substrates that were not). Substrates 1 and 3 of each lot were loaded onto chuck 2 (graph on the right in Figure 10), and substrate 2 of each lot was loaded onto chuck 1 (graph on the left in Figure 10). The three lots whose pressure profiles were analyzed in Figure 10 are the same three lots with the alignment errors shown in Figure 8.

[0071] From the recorded pressure profiles shown in Figure 10, it can be seen that substrates W that had alignment problems exhibited different pressure profiles in the build up to clamping pressure.

[0072] Therefore, in a further embodiment, measurements of the clamping pressure or clamping pressure change are used to determine whether the substrate W may have undergone deformation due to clamping.

[0073] In such a first embodiment, a cut-off time value is measured for the clamping pressure build-up. This is defined as the time it takes for the clamping pressure to reach 95% of the final clamping pressure, and is shown by the "95%" dotted line in Figure 10. As can be seen from Figure 10, the misaligned substrate reaches the 95% value sooner than a good substrate, so the measured cut-off time can be compared to a reference threshold value to determine whether the substrate W may have been deformed by clamping. In the example shown in Figure 10, this threshold value may be, for example, 1 second.

[0074] It will be understood that alternative definitions of cutoff time may be used. From the recorded pressure profile shown in Figure 10, it can be seen that the profile deviates between about 70% of the final clamp pressure and 100% of the final clamp pressure, but the deviation is more substantial between about 85% and 100% of the final clamp pressure.

[0075] The appropriate choice of reference threshold value for the cut-off time will likely need to be determined empirically for different types of lithographic apparatus (and possibly for different substrates W) and will also depend on the definition of the cut-off time.

[0076] In such a second embodiment, pressure build-up profiles for known good and problematic substrates W may be empirically determined for a particular combination of lithographic apparatus and substrate W and stored as reference profiles. These stored reference profiles may be compared to profiles measured during operation of the lithographic apparatus, and depending on whether the measured profile better matches the stored profile for the problematic substrate or the good substrate.

[0077] If it is determined that a substrate W may have been deformed by clamping (e.g. because the measured substrate unload time is some defined percentage less than the expected unload time, or because the clamping pressure deviates from an expected profile), a substrate rejection strategy may be implemented that prevents such substrate W from being used further in the lithographic process. The specific threshold for rejection may be set for each user and may be selected depending on the desired accuracy and / or characteristics of the substrate W and / or the lithographic apparatus.

[0078] Alternatively or additionally, a system rewetting process may be initiated to ensure that the substrate table WT is fully wet for future substrate loading and unloading. This may involve reloading the substrate W that has been determined to have suffered deformation, or a substitute substrate. The substitute substrate may be a closure substrate or a dummy substrate, which is already used in many lithographic apparatus, for example to protect the substrate table WT when the system is idle, or in other functions when no production substrates W are present. Once such a substrate has been reloaded, a standard exposure process can be performed (including wetting the substrate table WT), after which the substrate is unloaded and a subsequent substrate W can be loaded as normal for exposure with patterning radiation.

[0079] Alternatively or additionally, the apparatus may be configured to use an alignment approach that differs from the standard approach for any substrate W identified as possibly having been deformed. This may involve changing the alignment strategy or measuring with an enhanced layout of markers to better capture the overlay / alignment fingerprint. It may also involve changing one or more parameters or settings in the alignment process.

[0080] It will be understood that any of the features described above can be used with any other feature, and it is not just the combinations expressly described that are encompassed by this application.

[0081] Although specific reference is made in this document 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 in the manufacture of components with microscale or even nanoscale features, such as the manufacture of integrated optical systems, guide and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0082] Where the context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM); random-access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), among others. Furthermore, firmware, software, routines, and instructions may be described herein as performing certain operations. However, it should be understood that such description is merely for convenience and that such operations may, in fact, result from a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc., which may cause actuators or other devices to interact with the physical world.

[0083] While specific embodiments of the present invention have been described above, it should be understood that the invention may be practiced otherwise than as described. The above description is intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications can be made to the invention as described without departing from the scope of the claims set forth below.

Claims

1. a support portion configured to support a bottom surface of the substrate on a support surface; a movable part movable between a retracted position where an upper end of the movable part is below the support surface and an extended position where the upper end of the movable part is above the support surface, the movable part contacting the bottom surface of a substrate supported by the support part when the upper end is moving between the retracted position and the extended position, and supporting the bottom surface of the substrate above the support surface in the extended position; a measurement system configured to measure the time it takes for the movable part to move from the retracted position to the extended position, compare the measured time to a reference time, and generate a warning signal when the measured time is less than the reference time by more than a predetermined amount.

2. The substrate support system of claim 1 , wherein the support portion comprises a support, and the movable portion comprises a plurality of pins movable through the support.

3. The substrate support system of claim 2 , wherein the support portion has a plurality of first protrusions extending from the support to form the support surface and configured to support the bottom surface of the substrate.

4. 4. The substrate support system of claim 3, further comprising: a first seal member extending from the support at an end region of the support portion, the first seal member surrounding the plurality of first protrusions; and a second seal member extending from the support at the end region of the support portion, the second seal member surrounding the first seal member.

5. 5. The substrate support system of claim 4, further comprising a plurality of second protrusions extending from the support and disposed between the first seal member and the second seal member, the plurality of second protrusions configured to support the substrate on the support surface.

6. The substrate support system of claim 4 or 5, further comprising a plurality of extraction openings formed in the support for extracting fluid from between the support portion and the substrate to a space.

7. The substrate support system of claim 6 , wherein the plurality of extraction openings are disposed between the first seal member and the second seal member.

8. a substrate support system configured to support a substrate; a clamping system configured to hold the substrate on the substrate support system while the substrate is being exposed to radiation; a processor, (a) a sensor configured to measure the time it takes for a substrate to be removed from the substrate support system; the processor is configured to compare the time measured by the sensor with a reference time and generate a warning signal when the measured time is less than the reference time by more than a predetermined amount; or (b) a sensor configured to measure a change in pressure used by the clamping system to clamp the substrate to the substrate support system; The processor is configured to compare the measured pressure change with a reference and generate a warning signal when a clamping pressure buildup of the measured pressure change is faster than the reference.

9. 9. The stage positioning system of claim 8, wherein the processor is configured to compare the measured times, the clamping system is configured to hold the substrate on a support surface, and the sensor is configured to measure the time it takes for the substrate to be moved from the support surface to a position away from the support surface.

10. 10. The stage positioning system of claim 8 or 9, wherein the processor is configured to compare the measurement times, the substrate support system is the substrate support system of any one of claims 1 to 7, and the measurement system is provided with the sensor and the processor of the stage positioning system.

11. 10. The stage positioning system of claim 8 or 9, wherein the sensor configured to measure the time it takes for a substrate to be removed from the substrate support system is a pressure sensor or a temperature sensor.

12. The processor is configured to compare the measured pressure changes, and further measuring the time it takes for the measured pressure change to reach a predetermined pressure threshold; comparing the measured time to a predetermined time threshold; The stage positioning system of claim 8 , configured to generate the warning signal if the measured time falls below the time threshold.

13. The processor is configured to compare the measured pressure changes, and further Recording the pressure change over time to generate a pressure profile; comparing the recorded pressure profile with a stored profile of pressure changes; 9. The stage positioning system of claim 8, configured to generate the warning signal if the recorded pressure profile does not match a stored profile.

14. 14. A stage positioning system according to any of claims 8 to 13, wherein the stage positioning system is further configured to remove the substrate from the stage positioning system when the warning signal is generated.

15. A lithographic apparatus comprising a stage positioning system according to any one of claims 8 to 14.

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