Exposure apparatus and exposure method

Abstract

An exposure apparatus comprises a first object support configured to support a first object (e.g. a reticle) and a second object support configured to support a second object (e.g. a reticle). The first and second object supports are movable relative to an illumination region. In some embodiments, imaging optics of the exposure apparatus may be anamorphic (i.e. having a reduction factor of the image(s) that is different in two different directions. In some embodiments, a gap between the first object support and the second object support may be sufficiently small that a single object may be partially supported by the first object support and partially supported by the second object support. An exposure method is disclosed in which an image is formed of each of two objects (reticles) during a single scanning exposure process.

Description

EXPOSURE APPARATUS AND EXPOSURE METHODCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 24191697.2 which was filed on 30 July 2024 and EP application 24204137.4 which was filed on 02 October 2024 and which are incorporated herein in its entirety by reference.FIELD

[0002] The present invention relates to an exposure apparatus. The exposure apparatus may comprise a lithographic apparatus. In particular, the lithographic apparatus may comprise an extreme ultraviolet (EUV) lithographic apparatus. The exposure apparatus may be a scanning exposure apparatus. The present invention also relates to an exposure method (which may be carried out using the exposure 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 at a patterning device (e.g., a mask or a reticle) onto a layer of radiation-sensitive material (resist) provided on a substrate.

[0004] To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.

[0005] In general, a lithographic apparatus may be used to form a pattern on a plurality of target regions of a substrate . For example, a lithographic apparatus may be used to form the same pattern on a plurality of target regions (also referred to as fields) of a resist-coated silicon wafer. The pattern is typically defined by a patterning device (also referred to as a reticle or mask). Radiation is patterned by the reticle and then imaging optics are used to form an image of the pattern on the wafer. EUV lithographic reticles are typically reflective optical elements provided with a patterned coating that absorbs EUV radiation. The wafer may then be moved and the image can be formed on another field of the wafer and so on. The pattern may be transferred to the wafer during a scanning exposure in which the reticle is scanned through an illumination region (also referred to as a slit) while the wafer is also moved such that the image of the reticle is stationary with respect to the wafer.

[0006] It may be desirable to provide new exposure apparatus and / or exposure methods that improve existing arrangements. For example, it may be desirable to provide new exposure apparatus and / orexposure methods that improves throughput and / or accuracy relative to such existing arrangements. Additionally or alternatively, it may be desirable to provide new exposure apparatus and / or exposure methods that at least partially address one or more problems associated with existing arrangements whether such problems are identified herein or otherwise.SUMMARY

[0007] According to a first aspect of the present disclosure there is provided an exposure apparatus comprising: a main support; a first object support configured to support a first object and movable relative to the main support so that the first object is movable relative to a first illumination region; a second object support configured to support a second object and movable relative to the main support so that the second object is movable relative to the first illumination region; and imaging optics configured to form an image of the first illumination region in a second illumination region; wherein the first object support is movable relative to the second object support and / or the second object support is movable relative to the first object support; wherein the first object support is offset from the second object support in a first direction; and wherein the imaging optics is anamorphic such that a reduction factor of the image in the first direction is greater than a reduction factor of the image in a second direction that is generally perpendicular to the first direction.

[0008] The first object support and / or the second object support may be configured to support any type of patterning device (also referred to as a reticle or mask). The first object support and / or the second object support may comprise any type of reticle stage.

[0009] The exposure apparatus may comprise a lithographic apparatus (for example an EUV lithographic apparatus). The exposure apparatus may be a scanning exposure apparatus. A lithographic apparatus may be used to form a pattern on a plurality of target regions of a substrate. For example, a lithographic apparatus may be used to form the same pattern on a plurality of target regions (also referred to as fields) of a resist-coated silicon wafer. The pattern is typically defined by a patterning device (also referred to as a reticle or mask). Radiation is patterned by the reticle and then imaging optics are used to form an image of the pattern on the wafer. EUV lithographic reticles are reflective optical elements provided with a patterned coating that absorbs EUV radiation. The wafer may then be moved and the image can be formed on another field of the wafer and so on.

[0010] The pattern may be transferred to the wafer during a scanning exposure in which the reticle is scanned through an illumination region (also referred to as a slit) while the wafer is also moved such that the image of the reticle is stationary with respect to the wafer.

[0011] Within the lithographic field, reticles are expensive to manufacture. Reticles are typically formed from a reticle blank and reticle blanks are typically of a standard size (referred to as a 6” reticle blank). A first generation of EUV lithographic apparatus (also referred to as scanners) used spherical imaging optics with a reduction factor of 4 to form an image of a reticle (formed from a standard 6” reticle blank) that was reduced in both dimensions by the factor of 4. In order to increase the resolutionof EUV lithography, the imaging optics of the next generation of EUV lithographic apparatus will have an increased numerical aperture (NA). Since EUV reticles are reflective, the EUV radiation is not normal to the reticle but rather is incident at a non-zero angle to a normal of the reticle in one direction (so that the incoming cone of radiation that is incident on the reticle is separate from the outgoing cone of radiation scattered by the reticle and which is accepted by the imaging optics). This direction is typically the scanning direction of the lithographic apparatus. In this direction, there is a limit the extent to which the cone of radiation of the incoming radiation can be enlarged without overlapping the scattered cone of radiation (unless the angle of incidence of the chief ray of the incoming radiation is increased). However, it is undesirable to increase the angle of incidence of the chief ray of the incoming radiation as this will increase 3D effects of the reticle, reducing contrast. Therefore, it has been proposed to use anamorphic imaging optics in the next generation of EUV lithographic apparatus such that, in the scanning direction, the reduction factor of the imaging optics is 8 whereas in the nonscanning direction the reduction factor remains 4 and the cone of light is enlarged only in the nonscanning direction.

[0012] However, one consequence of the increased reduction factor is that the field of view that can be imaged with a standard 6” reticle is now halved.

[0013] It may be desirable to form a pattern that is larger than the size of existing reticles (especially in the next generation of EUV lithographic apparatus using anamorphic imaging optics). Therefore, in some systems, each target region (field) may be exposed using two reticles, each of which defines the pattern of half of the field. However, such a half-field design increases the number of field-steps that need to be taken in order to expose the entire wafer and therefore reduces the throughput of the lithographic apparatus as compared to a full-field system (in which the pattern of the entire field is defined by a single reticle). By default, the wafer is exposed in two steps and a (slow) reticle swap is performed in between. This further reduces throughput of the system. The second exposure with the second reticle can be done in at least two different ways. A first method involves keeping the wafer on a wafer stage once each field has been exposure using the first reticle, exchanging the reticle and exposing the wafer for the second time. However, this is very slow. A second method involves exposing a whole lot of wafers (e.g. 25 wafers) with one reticle, exchanging the reticle and then involves exposing the whole lot of wafers again. This can increase the throughput relative to the first method, however, it also has some disadvantages. For example, since the wafer is clamped to the wafer stage twice there is some additional time overhead in the time taken to swap wafers and, once a new wafer has been positioned on the wafer stage, the time taken to align the wafer. In addition, with the second method the wafer is clamped on the wafer stage for less time each time, which can limit the available time for measurements to be made once the wafer has been clamped and before it is exposed (without again negatively impacting the lithographic throughout). For example, the available measurement time may be reduced by a factor of 2 since only half the amount of fields are exposed per wafer pass. As a consequence, the number of alignment marks that can be measured is halved. In addition, a buffer (alsoreferred to as a stacker) may be required to temporarily store the entire lot of wafers in between the first and second exposures.

[0014] Advantageously, by providing both a first object support and a second object support two objects (reticles) may be provided in the lithographic apparatus at the same time. This can allow for the reticle to be effectively swapped very quickly by simply moving the first object support and the second object support so as to position a different reticle in the illumination region (slit). Furthermore, this allows for each wafer to be exposed using both reticles with no (or a negligible) loss of throughput whilst the same amount of time is available for measurements of the wafer once the wafer has been clamped and before it is exposed as would be available for a full -field system.

[0015] Furthermore, allowing the first object support to be movable relative to the second object support is particularly advantageous as it allows for two objects (reticles) to be accommodated while minimizing the volume required for the two object supports, as now discussed.

[0016] It will be appreciated that in order to accurately print features on a wafer of a desired critical dimension (for example of the order of 10 nm) the position of the wafer needs to controlled with greater precision than said critical dimension. A similar accuracy is required for the position of the reticle (although the accuracy may be relaxed by a factor equal to a reduction factor of the imaging optics). However, the accuracy with which a reticle can be positioned and orientated relative to a reticle stage may be significantly less that the desired critical dimension. For example, the accuracy with which a reticle can be positioned and orientated relative to a reticle stage may be of the order of 10-100 pm. Therefore, the reticle stage itself should be accurately controlled to allow for any inaccuracy of the position or orientation of the reticle.

[0017] When two reticles are provided in a lithographic apparatus, the position and orientation of each reticle relative to a stage to which it is clamped will, in general, be different. Allowing the first object support to be movable relative to the second object support allows for the reticles to be moved relative to each other once each one is clamped to a different one of the object supports. Advantageously, this may provide the adjustability to allow the position and / or the orientation of the two reticles to be controlled with sufficient accuracy that, for at least part of the exposure process, the two reticles can both partially overlap the illumination region simultaneously. This allows the two reticles to be provided arbitrarily close to each other (for example in a scanning direction of the lithographic apparatus). This is advantageous as the available volume for reticle stages in lithographic apparatus (especially an EUV lithographic apparatus which uses reflective reticles) may be limited.

[0018] The first object support may be movable relative to the second object support and / or the second object support may be movable relative to the first object support such that a relative position of the first and second object supports is controllable in 6 degrees of freedom.

[0019] For example, these 6 degrees of freedom may comprise three translational degrees of freedom (x, y and z) and three rotational degrees of freedom (Rx, Ry, Rz).

[0020] According to a second aspect of the present disclosure there is provided an exposure apparatus comprising: a main support; a first object support configured to support a first object and movable relative to the main support; and a second object support configured to support a second object and movable relative to the main support; wherein a gap between the first object support and the second object support is sufficiently small that a single object may be partially supported by the first object support and partially supported by the second object support.

[0021] The first object support and / or the second object support may be configured to support any type of patterning device (also referred to as a reticle or mask). The first object support and / or the second object support may comprise any type of reticle stage.

[0022] The exposure apparatus may comprise a lithographic apparatus (for example an EUV lithographic apparatus). The exposure apparatus may be a scanning exposure apparatus. A lithographic apparatus may be used to form a pattern on a plurality of target regions of a substrate. For example, a lithographic apparatus may be used to form the same pattern on a plurality of target regions (also referred to as fields) of a resist-coated silicon wafer. The pattern is typically defined by a patterning device (also referred to as a reticle or mask). Radiation is patterned by the reticle and then imaging optics are used to form an image of the pattern on the wafer. EUV lithographic reticles are reflective optical elements provided with a patterned coating that absorbs EUV radiation. The wafer may then be moved and the image can be formed on another field of the wafer and so on. The pattern may be transferred to the wafer during a scanning exposure in which the reticle is scanned through an illumination region (also referred to as a slit) while the wafer is also moved such that the image of the reticle is stationary with respect to the wafer.

[0023] The exposure apparatus according to the second aspect of the present disclosure is advantageous since to allows (a) for two separate objects (reticles) to be supported, one by each of the first and second object supports or (b) a single object (for example a larger than standard reticle) to be supported by the two object supports together. Therefore, the exposure apparatus according to the second aspect of the present disclosure provides a particularly versatile arrangement.

[0024] As with the exposure apparatus of the first aspect, the first object support may be offset from the second object support in a first direction. As with the exposure apparatus of the first aspect, the exposure apparatus of the second aspect may comprise imaging optics configured to form an image of the first illumination region in a second illumination region. The imaging optics may be anamorphic such that a reduction factor of the image in the first direction may be greater than a reduction factor of the image in a second direction that is generally perpendicular to the first direction.

[0025] The first object support of the exposure apparatus according to the second aspect of the present disclosure may be movable relative to the second object support and / or the second object support may be movable relative to the first object support.

[0026] A gap between the first object support and the second object support of the exposure apparatus according to the second aspect of the present disclosure being “sufficiently small that a single objectmay be partially supported by the first object support and partially supported by the second object support” may mean that the first object support and the second object support of the exposure apparatus according to the second aspect are suitable for supporting a reflective lithography reticle such that it is partially supported by the first object support and partially supported by the second object support.

[0027] A gap between the first object support and the second object support of the exposure apparatus according to the second aspect of the present disclosure is sufficiently small that a single object may be partially supported by the first object support and partially supported by the second object support. How this may be interpreted by the skilled person is now discussed.

[0028] Within the field of lithography, it is desirable to form a (usually diffraction-limited) image of a pattern defined by a mask or reticle on a substrate (for example a resist-coated silicon wafer). It will be appreciated by the skilled person that any deformation of the reticle will give rise to a deformation of the (aerial) image of the reticle formed on the substrate. The larger the deformation of the reticle is, the larger a deviation of the image formed on the substrate from a desired image will be. Eventually, the deviation of the image formed on the substrate from a desired image may be sufficiently large so as to result in printing errors, which is undesirable. The skilled person will be aware that deformation of the reticle should be carefully limited so as to avoid such printing errors.

[0029] As will be appreciated by the skilled person, a reflective reticle within an EUV lithographic apparatus is typically clamped to a reticle stage using an electrostatic clamp and is typically supported by a plurality of protrusions (known in the art as “burls”). The plurality of protrusions reduces a contact area between a rear surface of the reticle and the reticle stage, which is advantageous as this can reduce distortion of the reticle as it is clamped to the reticle stage. The plurality of protrusions may each extend from a common support substrate and the distal ends of the plurality of protrusions may define a support plane.

[0030] The reticle may be distorted if a distal end of one or more of the protrusions, or burls, becomes contaminated such that a foreign object or contaminant is disposed between those protrusions, or burls, and the reticle.

[0031] The skilled person will also be aware that a spacing between adjacent protrusions, or burls, is important in order to control a deformation of the reticle. For example, if a spacing between the protrusions, or burls becomes too large then the reticle will be distorted as it is clamped to the reticle stage.

[0032] In some embodiments, the first object support may define a first set of protrusions having a first pitch or spacing, distal ends of the first set of protrusions defining a first support plane, and second object support may define a second set of protrusions having a second pitch or spacing, distal ends of the second set of protrusions defining a second support plane. For example, in order to provide sufficient support for a reflective reticle, the first pitch or spacing and the second pitch or spacing may be of the order of 1 mm.

[0033] For such embodiments, the gap between the first object support and the second object support of the exposure apparatus according to the second aspect of the present disclosure in a direction in which the first object support is offset from the second object support may be less than the first pitch or spacing and the second pitch or spacing. Advantageously, this may ensure that said gap is sufficiently small that a single reflective reticle may be partially supported by the first object support and partially supported by the second object support.

[0034] In some embodiments a gap between the first object support and the second object support in a direction in which the first object support is offset from the second object support may be sufficiently small that when a single object is partially supported by the first object support and partially supported by the second object support a central portion of the single object that extends between the first object support and the second object support is subject to no more distortion than: a first side portion of the single object supported by the first object support and / or a second side portion of the single object supported by the second object support. In particular, it may be that when the single object is partially supported by the first object support and partially supported by the second object support and is clamped to both the first object support and the second object support, the central portion of the single object (that extends between the first object support and the second object support) is subject to no more distortion than: a first side portion of the single object (supported by the first object support) and / or a second side portion of the single object (supported by the second object support).

[0035] In some embodiments, the exposure apparatus may comprise a lithographic apparatus, the first object support may be configured to support a first reflective reticle, and the second object support may be configured to support a second reflective reticle.

[0036] In some embodiments, the first object support may define a first set of protrusions having a first pitch or spacing, distal ends of the first set of protrusions defining a first support plane; the second object support may define a second set of protrusions having a second pitch or spacing, distal ends of the second set of protrusions defining a second support plane. For such embodiments, a gap between the first object support and the second object support in a direction in which the first object support is offset from the second object support may be less than the first pitch or spacing and the second pitch or spacing.

[0037] The first object support and the second object support of the exposure apparatus according to the first or second aspects of the present disclosure may be provided such that a gap between them in a direction in which the first object support is offset from the second object support is less than 400 pm.

[0038] In some embodiments, the first object support and the second object support may be provided such that, in use, a gap between an imaging portion of a first object supported by the first object support and an imaging portion of a second object supported by the second object support in a direction in which the first object support is offset from the second object support is less than 400 pm.

[0039] Typically the scribe lanes in a silicon wafer that separate adjacent fields or target regions have a dimension of the order of 50 pm on the wafer. Therefore, with a reduction factor of 8 in the directionin which the first object support is offset from the second object support, at reticle level the scribe lane between two adjacent fields in this direction will be of the order of 400 pm. Therefore, by ensuring that the first object and the second object are provided such that a gap between them in the direction in which the first object support is offset from the second object support is less than 400 pm, the gap between the first and second objects can fall within a scribe lane.

[0040] The first object support and / or the second object support of the exposure apparatus according to the first or second aspect of the present disclosure may comprise an electrostatic clamp. In some embodiments, the exposure apparatus may comprise a single electrostatic clamp, which may form part of the first object support and part of the second object support.

[0041] The exposure apparatus according to the first or second aspect of the present disclosure may comprise a long stroke assembly comprising a first portion that is fixed relative to the main support and a second portion that is movable relative to the first portion and which supports the first object support and the second object support.

[0042] The long stroke assembly may allow for the first and second object supports to be moved relative to the first illumination region over distances of the order of 10s or 100s of millimetres.

[0043] The long stroke assembly may further comprise a balance mass. The balance mass may be movable relative to the first portion of the long stroke assembly. In use, the balance mass and the first portion of the long stroke assembly may move in an opposite sense to each other.

[0044] The exposure apparatus according to the first or second aspects of the present disclosure may further comprising at least one short stroke assembly comprising a first portion that is fixed relative to second portion of the long stroke assembly and a second portion that is movable relative to the first portion and which supports the first object support and / or the second object support.

[0045] Some embodiments may comprise two short stroke assemblies; a first short stroke assembly may support the first object support and a second short stroke assembly may support the second object support. Alternatively, in some embodiments, two reticles may be supported by a single short stroke assembly (but via separate reticle clamps). For such embodiments, at least one of the clamps may comprise actuators (for example piezoelectric actuators) configured to allow the first object support to be movable relative to the second object support (for example in 6 degrees of freedom).

[0046] The exposure apparatus according to the second aspect of the present disclosure may further comprise imaging optics configured to form an image of a first illumination region in a second illumination region. Said imaging optics may be anamorphic such that a reduction factor of the image in the first direction is greater than a reduction factor of the image in a second direction that is generally perpendicular to the first direction.

[0047] In some embodiments of the exposure apparatus according to the second aspect of the present disclosure the first object support and second object support may be movable relative to the first illumination region. The first object support and the second object support may be configured such that a single object may be partially supported by the first object support and partially supported by thesecond object support such that the imaging optics can form an image of the single object in the second illumination region.

[0048] In particular, in some embodiments, when a single object is partially supported by the first object support and partially supported by the second object support the imaging optics can form an image of a central portion of the single object that extends between the first object support and the second object support.

[0049] A reduction factor of the image formed by the imaging optics of the exposure apparatus according to the first or second aspect of the present disclosure in the direction in which the first object support is offset from the second object support may be 8 and a reduction factor of said image in a second direction that is generally perpendicular to the first direction may be 4.

[0050] The exposure apparatus according to the first or second aspect of the present disclosure may further comprise illumination optics configured to illuminate with radiation a first illumination region through which an object supported by the first object support and / or the second object support can be moved.

[0051] The exposure apparatus according to the first or second aspect of the present disclosure may further comprise a radiation source operable to produce the radiation.

[0052] The radiation may comprise EUV radiation. The radiation source may comprise a laser- produced plasma (LPP) radiation source.

[0053] The exposure apparatus according to the first or second aspect of the present disclosure may further comprise a coating provided conformally over an edge of the first object and / or an edge of the second object, wherein the coating is configured to absorb radiation incident on the edge of the first object and / or the edge of the second object. The coating is for example made of a material having an extinction coefficient of at least 0.03 and a refraction index of at least 0.90. The coating may be at least partially provided on the first object support and / or the second object support.

[0054] The exposure apparatus according to the first or second aspect of the present disclosure may further comprise a controller operable to carry out the exposure method according to the third aspect of the present disclosure.

[0055] According to a third aspect of the present disclosure there is provided an exposure method for forming a pattern on a plurality of target regions of a substrate, the exposure method comprising: providing a first object defining a first portion of the pattern and a second object defining a second portion of the pattern, such that the first object is adjacent to, and generally coplanar with, the second object, the first object offset from the second object in a first direction; and at least one scanning exposure, the or each scanning exposure comprising: moving the first object and the second object in the first direction such that they sequentially scan through a first illumination region while providing radiation to the first illumination region; and capturing radiation scattered by the first and second objects and using it to form an image of the first and second objects in a second illumination region while moving the substrate through the second illumination region such that an image of the first object isformed on a first target region of the substrate and an image of the second object is formed on a second target region of the substrate, the first and second target regions being mutually adjacent.

[0056] The exposure method according to the third aspect may be carried out using the exposure apparatus of the first or second aspects of the present disclosure.

[0057] The exposure method according to the third aspect of the present disclosure may comprise a lithographic exposure method. The first object and the second object may comprise any type of patterning device (also referred to as a reticle or mask). The first illumination region may be disposed in an object plane (which may also referred to as a reticle-level illumination region). The second illumination region may be disposed in an image plane (which may also referred to as a wafer-level illumination region). The first and / or second illumination region may be referred to as a slit (or exposure slit).

[0058] Instead of exposing two half-fields separately as two different steps, with the exposure method of the third aspect both reticles are exposed in a single stroke. An image of the first object (reticle) is formed on a first target region (field) of the substrate and an image of the second object (reticle) is formed on a second target region (field) of the substrate, the first and second target regions being mutually adjacent. The area in-between these two images is matched to fall within the scribe line area of the wafer.

[0059] The first object and the second object may be provided such that a gap between them in the first direction is less than an extent of the first illumination region in the first direction.

[0060] The first object and the second object may be provided such that for at least a portion of the or each scanning exposure the first and second objects are both partially disposed in the first illumination region in the first direction.

[0061] The first object and the second object may be provided such that a gap between them in the first direction is less than 400 pm.

[0062] The method may comprise a plurality of scanning exposures and the plurality of scanning exposures may be performed as a meander scan.

[0063] The method may comprise a plurality of scanning exposures and the image of the first object formed on a target region of the substrate during one scanning exposure may be stitched to the image of the second object formed on that target region of the substrate during another scanning exposure.

[0064] The images of the first object and the second object that are stitched may be mutually adjacent in the first direction.

[0065] That is, the two images that are stitched are mutually adjacent in the scanning direction. Put differently, a join line between the two images that are stitched extends in a second direction (a nonscanning direction).

[0066] Another benefit of the embodiments of the present disclosure is that they will, in general, result in less reticle heating than prior art arrangements. This is because the reticle heating load is divided between two reticles and therefore the heat load is divided by a factor of 2. Furthermore, theembodiments of the present disclosure will, in general, result in less particle defectivity as the wafers are not stored in a stacker (since the wafers are only exposed once).

[0067] According to a fourth aspect of the present disclosure there is provided an exposure apparatus comprising: a main support; a first object support configured to support a first object and movable relative to the main support; and a second object support configured to support a second object and movable relative to the main support; wherein when projected into an image plane of the exposure apparatus, an image of a gap between the first object support and the second object support is smaller than a dimension of a scribe lane of the exposure apparatus between two adjacent fields.

[0068] The exposure apparatus according to the fourth aspect of the present disclosure may comprise any combination of features of the exposure apparatus according to the second aspect of the present disclosure.

[0069] According to a fifth aspect of the present disclosure there is provided an exposure method for forming a pattern on each of a plurality or target regions of a substrate, the exposure method comprising: providing a first object defining a first pattern and providing a second object defining a second pattern; forming an image on each of a first set of the plurality of target regions using the first object, wherein the first set of the plurality of target regions have been determined to, or are expected to, have a first imaging performance; and forming an image on each of a second, different set of the plurality of target regions using the second object or a combination of the first object and the second object, wherein the second set of the plurality of target regions have been determined to, or are expected to, have a second imaging performance.

[0070] The exposure method according to the fifth aspect may be carried out using the exposure apparatus of the first, second or fourth aspects of the present disclosure.

[0071] The exposure method according to the fifth aspect of the present disclosure may comprise a lithographic exposure method. The first object and the second object may comprise any type of patterning device (also referred to as a reticle or mask).

[0072] The method according to the fifth aspect of the present disclosure is advantageous, as now discussed. During a lithographic exposure method, typically an image of a single reticle is formed in each of a plurality of target regions (also referred to as fields). Furthermore, as discussed above in relation to the first, second, third and fourth aspects of the present disclosure, if a lithographic apparatus is provided with two reticles then in each target region or field an image may be formed of each the first reticle and the second reticle thus effectively doubling the size of the fields and increasing lithographic throughput. However, for some lithographic processes, it may be that the additional reticle clamp does not increase throughput. This may be the case for in DRAM (dynamic random access memory) processes or for processes with small product sizes.

[0073] The method according to the fifth aspect of the present disclosure provides a way of utilizing the second object support (reticle clamp) for such processes, as now explained.

[0074] It may be the case that some regions of a substrate (for example a lithography wafer) suffer from poorer than average imaging performance. For example, some fields may suffer increased overlay and / or edge placement errors (EPE) and / or some fields may suffer from reduced contrast and / or some fields may suffer from increased defocus. Furthermore, it is possible to predict that some images on the wafer will have a reduced performance or yield. Examples of regions of a wafer that may suffer from reduced imaging performance include bonding fingerprints, edge fields and regions or a wafer stage or clamp that have become contaminated (referred to as chuck spots).

[0075] There are a number of advanced imaging techniques that can be used to improve lithographic imaging performance, however, typically these significantly increase lithographic throughput.

[0076] The method according to the fifth aspect is able to (for example using two object supports within an exposure apparatus) expose a substrate such that the first and second sets of target regions are exposed differently. Advantageously, this allows advanced imaging techniques to be used to selectively improve lithographic imaging performance of some target regions (for example the second set of target regions). The first set of the plurality of target regions may, for example, be target regions where a nominal or baseline imaging performance can be expected. The second, different set of the plurality of target regions may, for example, be target regions where a reduced imaging performance can be expected. This allows a first object (for example loaded on a first object support) to be used to expose the first set of target regions (which may, for example, constitute a majority of the target regions) using a standard exposure technique and a second object (for example loaded on a second object support) to be used to expose the second set of target regions (which may, for example, constitute a minority of the target regions) using an advanced imaging technique. Advantageously, this improves the imaging performance in the second set of target regions whilst maintaining a faster, standard exposure technique for the first set of target regions.

[0077] The exposure method according to the fifth aspect of the present disclosure may further comprise: determining the first set of the plurality of target regions and the second, different set of the plurality of target regions, wherein the first and second sets of the plurality of target regions are determined based on a determined or expected imaging performance of each of the plurality of target regions.

[0078] It will be appreciated that it may be that the determination of the first and second sets of target regions is not made for each substrate. For example, it may be that such a determination can be made once, or periodically, for example at the start of a process of exposing a plurality (or “lot”) of wafers.

[0079] The determination of the first and second sets of target regions may be made according to any selection criterion based on imaging performance. For example, selection criterion may be based on an overlay and / or a contrast and / or a focus related parameter.

[0080] The first set of the plurality of target regions may be target regions where a nominal or baseline imaging performance can be expected; and the second set of the plurality of target regions may be target regions where a reduced imaging performance can be expected.

[0081] The first set of target regions may constitute a majority of the plurality of target regions and the second set of target regions may constitute a minority of the plurality of target regions.

[0082] Forming an image on each of a first set of the plurality of target regions may comprise using a standard exposure technique; and forming an image on each of a second set of the plurality of target regions may comprise using an advanced imaging technique.

[0083] It will be appreciated that the first and second sets of target regions can be exposed in various different orders.

[0084] For example, in some embodiments, the images may be formed first in all target regions belonging to one set (either the first set or the second set) and then subsequently be formed in all target regions belonging to the other set. For such embodiments, the exposure of each set of target regions may be achieved using a modified meander scan (in which the substrate may be moved as for a meander scan but not all fields or target regions are exposed to the patterned radiation).

[0085] Alternatively, in some embodiments, the steps of forming the images in the first and second sets of target regions may at least partially overlap temporally. For example, images may be formed all of the plurality of target regions on the substrate in single meander scan wherein: (a) when the meander scan reaches a target region belonging to the first set an image may be formed using the first object; and (b) when the meander scan reaches a target region belonging to the second set an image may be formed using the second object or a combination of the first object and the second object.

[0086] Providing the first object and providing the second object may comprise providing the first object on a first object support and providing the second object on a second object support.

[0087] The first object may define a main pattern to be applied to the plurality of target regions; the second object may define a second pattern comprising one or more enhancement or optical proximity correction (OPC) features; and an image may be formed on each of the second set of the plurality of target regions using a combination of the first object and the second object.

[0088] With such embodiments, the enhancement or optical proximity correction (OPC) features on the second object (reticle) can be used to enhance a contrast of the image of the first object (reticle). For such embodiments, the enhancement or optical proximity correction (OPC) features may be designed as taught in W02021043519A1, which is incorporated herein in its entirety by reference.

[0089] For such embodiments, an image of the first pattern formed on each of the second set of target regions may be formed with a lower dose of radiation than an image of the first pattern formed on each of the first set of target regions.

[0090] It will be appreciated that, in general, it is important to control the dose of radiation used in a lithographic exposure method. When using an additional exposure of the second pattern, for example to enhance a contrast of an image of the first pattern, additional exposure of the second pattern delivers additional radiation to the substrate. It may be that, for such target regions a dose of the image of the first pattern is reduced slightly so that a nominal or target total dose is still supplied across the two exposures.

[0091] The first object may define a main pattern to be applied to the plurality of target regions; the second object may define the same main pattern that has been split into at least two portions separated by an absorbing or non-reflective material; and an image may be formed on each of the second set of the plurality of target regions using the second object using a plurality of exposures, each one of the plurality of exposures forming an image of a different one of the at least two portions of the main pattern.

[0092] Such a split exposure allows for a higher order correction to be applied for overlay across the target regions belonging to the second set, especially in a non-scanning direction of the exposure method.

[0093] The image of the main pattern and the images of the at least two portions of the main pattern may be formed as scanning exposures by: scanning the first object or the second object through a radiation beam so as to pattern the radiation beam; and simultaneously scanning the substrate such that an aerial image of the first or second object is stationary with respect to the substrate. The at least two portions of the main pattern may be separated in a direction that is perpendicular to the scanning direction.

[0094] The direction that is perpendicular to the scanning direction may be referred to as a nonscanning direction.

[0095] For each of the plurality of exposures of each target region belonging to the second set, an aerial image of the portion of the main pattern being imaged may be adjusted in dependence of a deformation of a portion of that target region that is being exposed.

[0096] For each of the plurality of exposures of each target region belonging to the second set, radiation used for the exposure(s) may be controlled such that the portion(s) of the main pattern not being imaged are not illuminated by radiation.

[0097] Controlling the radiation such that the portion(s) of the main pattern not being imaged are not illuminated by radiation may comprise adjusting a position of one or more masking blades of a masking device to reduce an extent of an illumination region.

[0098] Controlling the radiation such that the portion(s) of the main pattern not being imaged are not illuminated by radiation may comprise adjusting a configuration of a MEMS illuminator.BRIEF DESCRIPTION OF THE DRAWINGS

[0099] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:Figure 1 depicts a lithographic system comprising a lithographic apparatus and a radiation source;Figure 2A is a schematic representation of a single target region of a wafer, showing both: (a) a shape of the target region; and (b) a shape of a wafer-level illumination region;Figure 2B schematically shows two adjacent target regions of a wafer which are exposed sequentially using two opposite scan directions; these two consecutive exposures may form part of a meander scan, for example a meander scan of the type shown in Figure 3;Figure 3 is a schematic plan view representation of a (generally circular) substrate comprising a plurality of (generally rectangular) target regions or dies; also shown is a standard meander scan pattern in which each row of target regions (extending in a non-scanning direction) is exposed in turn, with the order of the exposure of the target regions indicated by a number on each target region, the scanning direction of the exposure of each target region is indicated by a solid arrow and the movement of the substrate in between exposure of two consecutive target regions is indicated by dashed lines;Figure 4 is a schematic representation of a first new exposure apparatus according to the present disclosure;Figure 5 A is a schematic representation of a second new exposure apparatus according to the present disclosure supporting two objects;Figure 5B is a schematic representation of the second new exposure apparatus according to the present disclosure as shown in Figure 5A but supporting a single object;Figure 6A schematically shows a first arrangement, which may form part of the first new exposure apparatus shown in Figures 4 or the second new exposure apparatus shown in Figures 5A and 5B, comprising a long stroke assembly and two short stroke assemblies;Figure 6B schematically shows a second arrangement, which may form part of the first new exposure apparatus shown in Figures 4 or the second new exposure apparatus shown in Figures 5 A and 5B, comprising a long stroke assembly and a single short stroke assembly;Figure 7A shows a possible actuation pattern for the electrodes of the arrangements shown in Figures 6A and 6B when the first and second object supports are each supporting a different object (reticle);Figure 7B shows a possible actuation pattern for the electrodes of the arrangements shown in Figures 6A and 6B when only one of the first and second object supports is supporting an object (reticle);Figure 7C shows a first possible actuation pattern for the electrodes of the arrangements shown in Figures 6A and 6B when the first and second object supports are together supporting a single object (reticle);Figure 7D shows a second possible actuation pattern for the electrodes of the arrangements shown in Figures 6A and 6B when the first and second object supports are together supporting a single object (reticle);Figure 8 shows an arrangement wherein, for at least part of an exposure process using the first new exposure apparatus shown in Figures 4 or the second new exposure apparatus shown in Figures 5 A and 5B, two objects (reticles) both partially overlap the a first illumination region simultaneously;Figure 9 schematically illustrates an example exposure method and shows six target regions (solid line rectangles) arranged in a two-dimensional array of two rows (extending in the non-scanning or x- direction) and three columns (extending in the scanning or y-direction); each target region comprises two portions: a first portion (labelled A and on a lower half of the target regions as shown in Figure 8); and a second portion (labelled B and on an upper half of the target regions as shown in Figure 8);Figure 10 is a schematic representation of a new exposure method according to an embodiment of the present disclosure for forming a pattern on a plurality of target regions of a substrate;Figure 11 is a schematic representation of a second new exposure method according to an embodiment of the present disclosure for forming a pattern on a plurality of target regions of a substrate;Figure 12 schematically depicts a cross-section of a patterned radiation beam in a scanning movement with respect to an exposure field;Figure 13 schematically depicts an overlay error related parameter in slit direction and an overlay correction to at least partially correct the overlay error related parameter;Figures 14A and 14B schematically depict an adapted patterned radiation beam that is exposed in two separate scanning movements to partial exposure fields;Figure 15 schematically depicts an overlay error related parameter in slit direction and two overlay corrections values to at least partially correct the overlay error related parameter during the separate scanning movements of Figure 14A and 14B;Figure 16 schematically depicts a radiation intensity received by the partial exposure fields during the two scanning movements of Figs. 4 A and 4B;Figure 17A is a schematic representation of a first object (reticle) for use in an embodiment of the second exposure method shown in Figure 11, which selectively uses split fields (using the second object shown in Figure 17B);Figure 17B is a schematic representation of a second object (reticle) for use in an embodiment of the second exposure method shown in Figure 11, which selectively uses split fields (using this second object); andFigure 18 is a schematic plan view representation of a (generally circular) substrate comprising a plurality of (generally rectangular) target regions or fields; also shown is that the plurality of target regions comprises a first set of target regions and a second, different set of a target regions.DETAILED DESCRIPTION

[0100] Figure 1 shows a lithographic system comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS and a substrate table WT configured to support a substrateW. The support structure MT may also be referred to as the reticle stage MT. The substrate table WT may also be referred to as the wafer stage WT.

[0101] The illumination system IL is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident upon the patterning device MA. Thereto, the illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. The faceted field mirror device 10 and faceted pupil mirror device 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to, or instead of, the faceted field mirror device 10 and faceted pupil mirror device 11 .

[0102] After being thus conditioned, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B’ is generated. The projection system PS is configured to project the patterned EUV radiation beam B’ onto the substrate W. For that purpose, the projection system PS may comprise a plurality of mirrors 13, 14 which are configured to project the patterned EUV radiation beam B’ onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B’, thus forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is illustrated as having only two mirrors 13, 14 in Figure 1, the projection system PS may include a different number of mirrors (e.g., six or eight mirrors).

[0103] The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus LA may be operable to align the image formed by the patterned EUV radiation beam B’ with a pattern previously formed on the substrate W.

[0104] A relative vacuum, i.e. a small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL, and / or in the projection system PS.

[0105] The radiation source SO shown in Figure 1 is, for example, of a type which may be referred to as a laser produced plasma (LPP) source. A laser system 1, which may, for example, include a CO2 laser, is arranged to deposit energy via a laser beam 2 into a fuel, such as tin (Sn) which is provided from, e.g., a fuel emitter 3. Although tin is referred to in the following description, any suitable fuel may be used. The fuel may, for example, be in liquid form, and may, for example, be a metal or alloy. The fuel emitter 3 may comprise a nozzle configured to direct tin, e.g. in the form of droplets, along a trajectory towards a plasma formation region 4. The laser beam 2 is incident upon the tin at the plasma formation region 4. The deposition of laser energy into the tin creates a tin plasma 7 at the plasma formation region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during deexcitation and recombination of electrons with ions of the plasma.

[0106] The EUV radiation from the plasma is collected and focused by a collector 5. Collector 5 comprises, for example, a near-normal incidence radiation collector 5 (sometimes referred to moregenerally as a normal -incidence radiation collector). The collector 5 may have a multilayer mirror structure which is arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may have an ellipsoidal configuration, having two focal points. A first one of the focal points may be at the plasma formation region 4, and a second one of the focal points may be at an intermediate focus 6, as discussed below.

[0107] The laser system 1 may be spatially separated from the radiation source SO. Where this is the case, the laser beam 2 may be passed from the laser system 1 to the radiation source SO with the aid of a beam delivery system (not shown) comprising, for example, suitable directing mirrors and / or a beam expander, and / or other optics. The laser system 1 , the radiation source SO and the beam delivery system may together be considered to be a radiation system.

[0108] Radiation that is reflected by the collector 5 forms the EUV radiation beam B. The EUV radiation beam B is focused at intermediate focus 6 to form an image at the intermediate focus 6 of the plasma present at the plasma formation region 4. The image at the intermediate focus 6 acts as a virtual radiation source for the illumination system IL. The radiation source SO is arranged such that the intermediate focus 6 is located at or near to an opening 8 in an enclosing structure 9 of the radiation source SO.

[0109] Although Figure 1 depicts the radiation source SO as a laser produced plasma (LPP) source, any suitable source such as a discharge produced plasma (DPP) source or a free electron laser (FEL) may be used to generate EUV radiation.

[0110] The faceted field mirror device 10 and the faceted pupil mirror device 11 are arranged to provide a desired angular distribution of the radiation beam B, at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. The illumination system IL may be arranged to provide Kohler illumination of an illumination region IR (that the patterning device MA may be moved through during exposure of a substrate W) such that the plasma at the plasma formation region 4 is out of focus (and therefore does not influence properties of the radiation beam) at the patterning device MA and in the conjugate plane of the substrate W. As used herein, the illumination region IR may also be referred to as the illumination slit or the slit.

[0111] The illumination region IR is in a field plane in which the reticle MA is disposed during a lithographic exposure. Therefore, the illumination region IR may be referred to as a reticle-level or object-level illumination region IR. The reticle-level illumination region IR may be referred to as a first illumination region IR. It will be appreciated that projection system PS forms an image IR’ of the illumination region IR in the plane of the substrate W. The image IR’ of the illumination region IR in the plane of the substrate W may be referred to as a wafer-level or image-level illumination region IR’ . As used herein, the wafer-level illumination region IR’ may also be referred to as the slit. The waferlevel illumination region IR’ may be referred to as a second illumination region IR.

[0112] The lithographic apparatus LA may be a scanning lithographic apparatus (also referred to as a scanner) and the image (of a reticle MA) may be formed during a scanning exposure. In such anexposure, the reticle MA may be moved in a scanning direction through the reticle-level illumination region IR. It will be appreciated that, as a result of this movement of the reticle MA, the image of the reticle MA will move at wafer level. Therefore, during the scanning exposure, the wafer W is also moved through the wafer-level illumination region IR’ . In particular, the wafer W is moved so that the image of reticle MA is substantially static with respect to the wafer W. The movement of the reticle MA and the substrate W are therefore synchronized. The movement (speed and direction) of the substrate W will be dependent on the movement of the reticle and the imaging performed by the projection system PS. In some embodiments, the projection system PS may form an inverted image of the reticle MA and therefore the substrate W may be moved in an opposite direction to the reticle MA. In some embodiments, the projection system PS may apply a reduction factor to the patterned EUV radiation beam B’ in the scanning direction and therefore the substrate W may move at a speed that is smaller than the speed of the reticle MA by this reduction factor.

[0113] The lithographic apparatus LA may be of a type having two or more substrate supports WT (also named “dual stage” or “multiple stage” machines). 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 support WT while another substrate W, on the other substrate support WT, is being used for exposing a pattern on the other substrate W.

[0114] For example in a dual stage machine, while an nth wafer is being exposed on one of the stages, an (n + l)th wafer is disposed on the other stage and various measurements are made in order to improve the accuracy of the lithographic process. Such measurements may be referred to generally as a metrology step or stage. Such measurements include, for example, measurements of the positions of alignments marks (used to help ensure the image formed in the lithographic process is well aligned to previously formed process layers). Another example of such a measurement includes a measurement of a shape of the wafer W, for example, measured using a level-sensor (used dynamically during the subsequent exposure of that wafer to keep the surface of the wafer as close to a plane of best focus as possible).

[0115] In general, for the accuracy of the subsequent lithographic exposure, it is desirable to increase the number of measurements taken during the metrology stage. On the other hand, it is desirable to increase the throughput of the lithographic apparatus LA (i.e. the speed at which wafers are exposed, for example number of wafers per hour). In practice, in order to maximize throughput, the time available for the metrology stage is limited to the time taken to expose the previous wafer such that as soon as one wafer has been exposed the next wafer has already been measured and is ready to be exposed.

[0116] Figure 2A shows schematically a single target region 20 of a wafer W. A shape of the target region 20 is generally rectangular. Also shown in Figure 2A is the wafer-level illumination region IR’ and a direction in which the wafer-level illumination region IR’ effectively scans over the target region20 is indicated by arrow 22. It will be appreciated that, in practice this may be achieved by scanning the target region 20 through the wafer-level illumination region IR’ in a direction opposite to the arrow 22.

[0117] As shown in Figure 2B, in some known arrangements two adjacent target regions 20 may be exposed sequentially, as an nth exposure and an (n + l)th exposure. The wafer W may be moved such that a direction in which the wafer-level illumination region IR’ effectively scans over the target region 20 (indicated by dotted arrow 22) is in a first direction for the nth exposure and in an opposite direction for the (n + l)th exposure. Such an arrangement may improve the throughput of the lithographic apparatus as this may minimize movements of the wafer W.

[0118] The arrangement shown in Figure 2B may form part of a meander scan, which is now described with reference to Figure 3. Figure 3 is a schematic plan view representation of a (generally circular) substrate W comprising a plurality of (generally rectangular) target regions 20 or fields. In the embodiment shown in Figure 15 the substrate W comprises 110 target regions 20. Each field may comprise a single die or multiple dies. For example, in some embodiments each field may comprise of the order of 4 to 25 dies.

[0119] Forming an image of a reticle MA on a substrate a plurality of times may comprise forming an image of the reticle MA on a plurality of target regions 20 of the substrate W. Each of the plurality of target regions 20 may be generally rectangular. The plurality of target regions 20 may be arranged as a two-dimensional array.

[0120] In some embodiments, the two-dimensional array of target regions 20 may be exposed using a standard meander scan pattern in which each row of target regions 20 (extending in a non-scanning direction; the x-direction in Figure 3) is exposed in turn. Such a standard meander scan pattern is illustrated in Figure 3, with the order of the exposure of the target regions 20 indicated by a number on each target region. The scanning direction 22 of the exposure of each target region 20 is indicated by a solid arrow and the movement of the substrate W in between exposure of two consecutive target regions 20 is indicated by dashed lines.

[0121] It will be appreciated by the skilled person that the speed and / or acceleration at which objects can be moved (for example the reticle MA and / or the wafer W) within the lithographic apparatus LA is determined by the mass and / or force and deformation limits of a support that supports them (for example a reticle stage MT or a wafer stage WT). Note that, in general, the reticle stage MT does not move in the non-scanning direction and only moves in the scanning direction whereas the wafer stage WT moves in both the scanning and non-scanning directions. Therefore, the reticle stage may be easier to design than the safer stage WT. It will also be appreciated that since the projection system PS may apply a reduction factor, in order for the reticle MA and the wafer W to move synchronously the reticle MA will, in general, experience greater speeds and accelerations that the wafer W.

[0122] In general, movement of a reticle MA is accomplished with a long stroke assembly and a short stroke assembly. The long stroke assembly allows the reticle to move (relative to a fixed frame) overdistances of the order of 10s or 100s of millimetres. The short stroke assembly allows the reticle MA to be moved over small distance scales.

[0123] As used herein a short stroke assembly may comprise a chuck and a carrier. The chuck may house a clamp (for example an electrostatic clamp), encoders (position sensors) and the fiducials (marks that may be used for various measurements within the lithographic apparatus LA).

[0124] The clamp may comprise a glass structure (formed, for example, from ultra-low expansion glass or Zerodur glass), which supports the encoders and the fiducials. The glass structure may comprise three plates or layers. A first plate of the clamp faces the rear surface of the reticle (and may be provided with a plurality of protrusions or burls with the rear surface of the reticle contacting the distal ends of these burls). Between the first plate and a second plate are the electrodes. Between the second plate and a third plate may be water cooling. The third plate of the clamp may directly contact the chuck.

[0125] Some embodiments of the present disclosure relate to exposure apparatus (for example EUV lithography apparatus LA of the type shown in Figure 1 and described above) which can support two objects (for example reticles or patterning devices MA) simultaneously. For example, an EUV lithography apparatus LA may comprise a reticle stage that can support two reticles in series (i.e. side by side or adjacent each other). Alternatively, an EUV lithography apparatus LA may comprise two reticle stages that can each support a reticle such that the two reticles are adjacent each other and which can move synchronously. Some embodiments may comprise two short stroke assemblies: a first short stroke assembly arranged to support a first object support and a second short stroke assembly arranged to support a second object support. Alternatively, in some other embodiments, two reticles may be supported by a single short stroke assembly (via either one reticle clamp or two separate reticle clamps) . For such embodiments, at least one of the clamps may comprise actuators (for example piezoelectric actuators) configured to allow first object support to be movable relative to the second object support (for example in 6 degrees of freedom).

[0126] Figure 4 is a schematic representation of an exposure apparatus 100 according to an embodiment of the present disclosure. The exposure apparatus 100 comprises: a main support 110; a first object support 120; a second object support 130; and imaging optics 140. The exposure apparatus 100 may comprise a lithographic apparatus LA of the type shown in Figure 1 or a part or sub-component of such a lithographic apparatus LA.

[0127] The main support 110 may be considered to be a static portion of the exposure apparatus. For example, the main support 110 may comprise a frame which static parts of the exposure apparatus 100 are connected to. Alternatively, the main support 110 may comprise a body which is connected to such a frame.

[0128] The first object support 120 is configured to support a first object 122. As indicated by arrow 124, the first object support 120 is movable relative to the main support 110 so that the first object 122 is movable relative to a first illumination region 150. The first object 122 may comprise a reticle or mask MA. The first object support 120 may be generally of the form of a support structure MT (i.e. areticle stage) of the type shown in Figure 1. The first illumination region 150 maybe generally equivalent to the reticle-level or object-level illumination region IR described above with reference to Figure 1.

[0129] The second object support 130 is configured to support a second object 132. As indicated by arrow 134, the second object support 130 is movable relative to the main support 110 so that the second object is movable relative to the first illumination region 150. The second object 132 may comprise a reticle or mask MA. The second object support 130 may be generally of the form of a support structure MT (i.e. a reticle stage) of the type shown in Figure 1.

[0130] The first object support 120 is offset from the second object support 130 in a first direction. In Figure 4 the first direction is labelled as the y-direction. As discussed further below, the first direction (y-direction) is a scanning direction of the exposure apparatus 100. Note that, as indicated by arrows 124, 134, the first object support 120 and second object support 130 are each movable relative to the main support 110 in the first direction (y-direction). The first object support 120 and second object support 130 may also be movable relative to the main support 110 in a second direction that is perpendicular the first direction (y-direction).

[0131] The imaging optics 140 is configured to form an image of the first illumination region 150 in a second illumination region 160. The imaging optics 140 may be generally analogous to the projection system PS shown in Figure 1 and as described above. The imaging optics 140 is anamorphic such that a reduction factor of the image in the first direction is greater than a reduction factor of the image in a second direction that is generally perpendicular to the first direction. In Figure 4 the second direction is into the page (and may be referred to as the x-direction).

[0132] The first object support 120 is movable relative to the second object support 130 and / or the second object support 130 is movable relative to the first object support 120. As discussed below, this has a number of advantages.

[0133] The first object support 120 and / or the second object support 130 may be configured to support any type of patterning device MA (also referred to as a reticle or mask). The first object support 120 and / or the second object support 130 may comprise any type of reticle stage MT.

[0134] The exposure apparatus 100 may comprise a lithographic apparatus (for example an EUV lithographic apparatus LA of the type shown in Figure 1). The exposure apparatus 100 may be a scanning exposure apparatus. A lithographic apparatus LA may be used to form a pattern on a plurality of target regions of a substrate. For example, a lithographic apparatus LA may be used to form the same pattern on a plurality of target regions (also referred to as fields) of a resist-coated silicon wafer W. The pattern is typically defined by a patterning device MA (also referred to as a reticle or mask). Radiation is patterned by the reticle MA and then imaging optics PS are used to form an image of the pattern on the wafer W. EUV lithographic reticles MA are reflective optical elements provided with a patterned coating that absorbs EUV radiation. The wafer W may then be moved and the image can be formed on another field of the wafer W and so on. As discussed above, the pattern may be transferredto the wafer W during a scanning exposure in which the reticle MA is scanned through an illumination region IR (also referred to as a slit) while the wafer W is also moved such that the image of the reticle is stationary with respect to the wafer W.

[0135] Within the lithographic field, reticles MA are expensive to manufacture. Reticles MA are typically formed from a reticle blank and reticle blanks are typically of a standard size (referred to as a 6” reticle blank). A first generation of EUV lithographic apparatus (also referred to as scanners) used spherical imaging optics PS with a reduction factor of 4 to form an image of a reticle (formed from a standard 6” reticle blank) that was reduced in both dimensions by the factor of 4.

[0136] In order to increase the resolution of EUV lithography, the imaging optics PS of the next generation of EUV lithographic apparatus will have an increased numerical aperture (NA). Since EUV reticles are reflective, the EUV radiation is not normal to the reticle MA but rather is incident at a nonzero angle to a normal of the reticle MA in one direction (so that the incoming cone of radiation B that is incident on the reticle MA is separate from the outgoing cone of radiation B’ scattered by the reticle MA and which is accepted by the imaging optics PS). This direction is typically the scanning direction of the lithographic apparatus LA. In this direction, there is a limit the extent to which the cone of radiation of the incoming radiation B can be enlarged without overlapping the scattered cone of radiation B’ (unless the angle of incidence of the chief ray of the incoming radiation B is increased). However, it is undesirable to increase the angle of incidence of the chief ray of the incoming radiation B as this will increase 3D effects of the reticle, reducing contrast and transmission. Therefore, it has been proposed to use anamorphic imaging optics PS in the next generation of EUV lithographic apparatus LA such that, in the scanning direction (e.g. the y-direction in Figure 1), the reduction factor of the imaging optics PS is 8 whereas in the non-scanning direction (e.g. the x-direction in Figure 1) the reduction factor remains 4 and the cone of light is enlarged only in the non-scanning direction.

[0137] However, one consequence of the increased reduction factor is that the field of view that can be imaged on the substrate W with a standard 6” reticle is now halved. That is, a single reticle can now only image half of the target region 20 shown, for example, in Figure 2A.

[0138] It may be desirable to form a pattern that is larger than the size of existing reticles (especially in the next generation of EUV lithographic apparatus using anamorphic imaging optics). Therefore, in some systems, each target region 20 (field) may be exposed using two reticles, each of which defines the pattern of half of the field. However, such a half-field design increases the number of field-steps that need to be taken in order to expose the entire wafer W and therefore reduces the throughput of the lithographic apparatus LA as compared to a full-field system (in which the pattern of the entire field 20 is defined by a single reticle). Such a full-field exposure process is described above with reference to Figures 2B and 3. With half-field exposures, by default, the wafer W is exposed in two steps and a (slow) reticle swap is performed in between. This further reduces throughput of the system. The second exposure with the second reticle can be done in at least two different ways. A first method involves keeping the wafer W on a wafer stage WT once each field 20 has been exposure using the first reticle,exchanging the reticle and exposing the wafer for the second time. However, this is very slow as it takes a significant amount of time to swap the reticles and align the new reticle. A second method involves exposing a whole lot of wafers (e.g. 25 wafers) with one reticle, exchanging the reticle and then involves exposing the whole lot of wafers again using a second reticle. This can increase the throughput relative to the first method, however, it also has some disadvantages. For example, since the wafer is clamped to the wafer stage twice there is some additional time overhead in the time taken to swap wafers and, once a new wafer has been positioned on the wafer stage, the time taken to align the wafer. In addition, with the second method the wafer is clamped on the wafer stage for less time each time, which can limit the available time for measurements to be made once the wafer has been clamped and before it is exposed (without again negatively impacting the lithographic throughout). For example, the available measurement time (for example for the next wafer that is clamped to another wafer stage) may be reduced by a factor of 2 since only half the amount of fields are exposed per wafer pass. As a consequence, the number of alignment marks that can be measured is halved. In addition, a buffer (also referred to as a stocker) may be required to temporarily store the entire lot of wafers in between the first and second exposures.

[0139] Advantageously, by providing both a first object support 120 and a second object support 130 two objects (reticles MA) may be provided in the lithographic apparatus LA at the same time. This can allow for the reticle MA to be effectively swapped very quickly by simply moving the first object support 120 and the second object support 130 so as to position a different reticle in the illumination region 150 (slit). Furthermore, this allows for each wafer W to be exposed using both reticles MA with no (or a negligible) loss of throughput whilst the same amount of time is available for measurements of the wafer W once the wafer W has been clamped and before it is exposed as would be available for a full-field system. As discussed above, in a dual stage machine, while an nth wafer is being exposed on one of the stages, an (n + l)th wafer is disposed on the other stage and various measurements are made in order to improve the accuracy of the (subsequent) lithographic process. Such measurements may be referred to generally as a metrology step or stage. With the exposure apparatus 100 shown in Figure 4, the only additional time penalty relative to a full-field system is the (relatively small) additional time required to align two objects 122, 132 rather than just one.

[0140] Furthermore, allowing the first object support 120 to be movable relative to the second object support 130 is particularly advantageous as it allows for two objects (reticles MA) to be accommodated while minimizing the volume required for the two object supports 120, 130, as now discussed.

[0141] It will be appreciated that in order to accurately print features on a wafer of a desired critical dimension (for example of the order of 10 nm) the position of the wafer W needs to controlled with greater precision than said critical dimension. A similar accuracy is required for the position of the reticle MA (although the accuracy may be relaxed by a factor equal to a reduction factor of the imaging optics PS). However, the accuracy with which a reticle MA can be positioned and orientated relative to a reticle stage MT may be significantly less that the desired critical dimension. For example, theaccuracy with which a reticle MA can be positioned and orientated relative to a reticle MT stage may be of the order of 10-100 pm. Therefore, the reticle stage MT itself should be accurately controlled to allow for any inaccuracy of the position or orientation of the reticle MA.

[0142] When two reticles MA are provided in a lithographic apparatus LA, the position and orientation of each reticle MA relative to a stage to which it is clamped will, in general, be different. Allowing the first object support 120 to be movable relative to the second object support 130 allows for the objects 122, 132 (reticles MA) to be moved relative to each other once each one is clamped to a different one of the object supports 120, 130. Advantageously, this may provide the adjustability to allow the position and / or the orientation ofthe two objects 122, 132 (reticles MA) to be controlled with sufficient accuracy that, for at least part of the exposure process, the two objects 122, 132 (reticles MA) can both partially overlap the illumination region 150 simultaneously. This allows the two objects 122, 132 (reticles MA) to be provided arbitrarily close to each other (for example in a scanning direction of the lithographic apparatus LA). This is advantageous as the available volume for reticle stages in lithographic apparatus (especially an EUV lithographic apparatus which uses reflective reticles) may be limited.

[0143] In some embodiments, the first object support 120 may be movable relative to the second object support 130 and / or the second object support 130 may be movable relative to the first object support 120 such that a relative position of the first and second object supports 120, 130 is controllable in 6 degrees of freedom. For example, these 6 degrees of freedom may comprise three translational degrees of freedom (x, y and z) and three rotational degrees of freedom (Rx, Ry, Rz).

[0144] Figures 5A and 5B are schematic representations of a second exposure apparatus 200 according to an embodiment of the present disclosure. The second exposure apparatus 200 comprises: a main support 210; a first object support 220; and a second object support 230. The second exposure apparatus 200 comprises features that may be similar or identical to corresponding features of the exposure apparatus 100 shown in Figure 4. Features of the second exposure apparatus 200 which are generally equivalent to, or play a similar role to, features of the exposure apparatus 100 shown in Figure 4 have a reference numeral that is incremented by 100 relative to the reference numeral of the features of the exposure apparatus 100 shown in Figure 4. The second exposure apparatus 200 may comprise a lithographic apparatus LA of the type shown in Figure 1 or a part or sub-component of such a lithographic apparatus LA.

[0145] The main support 210 may be considered to be a static portion ofthe second exposure apparatus 200. For example, the main support 210 may comprise a frame which static parts of the second exposure apparatus 200 are connected to. Alternatively, the main support 210 may comprise a body which is connected to such a frame.

[0146] The first object support 220 is configured to support a first object 222 (see Figure 5A). As indicated by arrow 224, the first object support 220 is movable relative to the main support 210 so that the first object 222 is movable relative to a first illumination region 250. The first object 222 may comprise a reticle or mask MA. The first object support 220 may be generally of the form of a supportstructure MT (i.e. a reticle stage) of the type shown in Figure 1. The first illumination region 250 may be generally equivalent to the reticle-level or object-level illumination region IR described above with reference to Figure 1.

[0147] The second object support 230 is configured to support a second object 232 (see Figure 5B). As indicated by arrow 234, the second object support 230 is movable relative to the main support 210 so that the second object is movable relative to the first illumination region 250. The second object 232 may comprise a reticle or mask MA. The second object support 230 may be generally of the form of a support structure MT (i.e. a reticle stage) of the type shown in Figure 1.

[0148] The first object support 220 is offset from the second object support 230 in a first direction. In Figures 5A and 5B the first direction is labelled as the y-direction. As discussed further below, the first direction (y-direction) may be a scanning direction of the exposure apparatus 200. Note that, as indicated by arrows 124, 134, the first object support 220 and second object support 230 are each movable relative to the main support 110 in the first direction (y-direction). The first object support 220 and second object support 230 may also be movable relative to the main support 210 in a second direction that is perpendicular the first direction (y-direction).

[0149] A gap 270 between the first object support 220 and the second object support 230 is sufficiently small that a single object 226 (e.g. a single reticle MA) can be partially supported by the first object support 220 and partially supported by the second object support 230. Such an arrangement is shown in Figure 5B. For example, the single object 226 may have a dimension of the order of a factor of 2 greater than a dimension of existing reticles. For example, as opposed to a known 6”x6” reticle, the single object 226 may comprise a reticle having dimensions of the order of 12”x6”.

[0150] The first object support 220 and / or the second object support 230 may be configured to support any type of patterning device MA (also referred to as a reticle or mask). The first object support 220 and / or the second object support 230 may comprise any type of reticle stage.

[0151] The second exposure apparatus 200 may comprise a lithographic apparatus (for example an EUV lithographic apparatus LA of the type shown in Figure 1). The second exposure apparatus 200 may be a scanning exposure apparatus. A lithographic apparatus LA may be used to form a pattern on a plurality of target regions 20 of a substrate W. For example, a lithographic apparatus LA may be used to form the same pattern on a plurality of target regions 20 (also referred to as fields) of a resist-coated silicon wafer W. The pattern is typically defined by a patterning device MA (also referred to as a reticle or mask). Radiation is patterned by the reticle MA and then imaging optics are used to form an image of the pattern on the wafer W. EUV lithographic reticles MA are reflective optical elements provided with a patterned coating that absorbs EUV radiation. The wafer W may then be moved and the image can be formed on another field 20 of the wafer W and so on. The pattern may be transferred to the wafer W during a scanning exposure in which the reticle MA is scanned through an illumination region IR (also referred to as a slit) while the wafer W is also moved such that the image of the reticle is stationary with respect to the wafer W.

[0152] The second exposure apparatus 200 is advantageous since it allows (a) for two separate objects 222, 233 (reticles) to be supported, one by each of the first and second object supports 220, 230 (see Figure 5 A) or (b) a single object 226 (for example a larger than standard reticle) to be supported by the two object supports 220, 230 together (see Figure 5B). Therefore, the second exposure apparatus 200 provides a particularly versatile arrangement.

[0153] As with the exposure apparatus 100 shown in Figure 4, the first object support 220 may be offset from the second object support in a first direction (the y-direction in Figures 5A and 5B). As with the exposure apparatus 100 shown in Figure 4, the second exposure apparatus 200 may comprise imaging optics configured to form an image of the first illumination region 150 in a second illumination region. The imaging optics may be anamorphic such that a reduction factor of the image in the first direction may be greater than a reduction factor of the image in a second direction that is generally perpendicular to the first direction.

[0154] In some embodiments, the first object support 220 is movable relative to the second object support 230 and / or the second object support 230 is movable relative to the first object support 220 (similar to the functionality of the exposure apparatus 100 shown in Figure 4).

[0155] It will be appreciated that the exposure apparatus 100 shown in Figure 4 and the second exposure apparatus 200 shown in Figures 5A and 5B can be combined together. It will also be appreciated that optionally the exposure apparatus 100 shown in Figure 4 and / or the second exposure apparatus 200 shown in Figures 5A and 5B may comprise one or more optional features, as now discussed. In general, any features shown in dotted lines in Figures 4, 5A and 5B are optional features.

[0156] Optionally, as with the exposure apparatus 100 shown in Figure 4, the second exposure apparatus 200 may comprise imaging optics 240, which may be configured to form an image of the first illumination region 250 in a second illumination region 260. The imaging optics 240 may be generally analogous to the projection system PS shown in Figure 1 and as described above. The imaging optics 240 may also be anamorphic such that a reduction factor of the image in the first direction is greater than a reduction factor of the image in a second direction that is generally perpendicular to the first direction. In Figure 4 the second direction is into the page (and may be referred to as the x-direction).

[0157] In some embodiments of the second exposure apparatus 200, the first object support 220 and second object support 230 may be movable relative to the first illumination region 250. The first object support 220 and the second object support 230 may be configured such that a single object 228 may be partially supported by the first object support 220 and partially supported by the second object support 230 such that the imaging optics 240 can form an image of the single object 228 in the second illumination region 260. In particular, in some embodiments, when a single object 228 is partially supported by the first object support 220 and partially supported by the second object support 230 the imaging optics 240 can form an image of a central portion of the single object 228 that extends between the first object support 220 and the second object support 230.

[0158] The first object support 120, 220 and the second object support 130, 230 of the exposure apparatus 100, 200 may be provided such that a gap 170, 270 between them in a direction in which the first object support 120, 220 is offset from the second object support 130, 230 is less than 400 pm.

[0159] In some embodiments, the first object support 120, 220 and the second object support 130, 230 may be provided such that, in use, a gap between an imaging portion of a first object 122, 222 supported by the first object support 120, 220 and an imaging portion of a second object 132, 232 supported by the second object support 130, 230 in a direction in which the first object support 120, 220 is offset from the second object support 130, 230 is less than 400 pm.

[0160] The first and second objects 122, 222, 132, 232 define patterns that may contribute towards a device formed in the lithographic process. In addition to these patterns, the first object 122, 222 may also define some other features that are imaged by the lithographic process and, similarly, the second object 132, 232 may also define some other features that are imaged by the lithographic process. For example, the first and second objects 122, 222, 132, 232 may each also define various metrology marks and targets (for example overlay marks, electrical test structures etc.) which may be imaged onto the scribe lanes of the wafer W. The scribe lanes are the regions of the wafer that will be cut when the wafer W is divided into individual dies.

[0161] Typically the scribe lanes in a silicon wafer W that separate adjacent fields or target regions 20 have a dimension of the order of 50 pm on the wafer W. Therefore, with a reduction factor of 8 in the direction in which the first object support 120, 220 is offset from the second object support 130, 230, at reticle level the scribe lane between two adjacent fields 20 in this direction will be of the order of 400 pm. Therefore, by ensuring that an imaging portion of the first object 122, 222 and an imaging portion of the second object 132, 232 are provided such that a gap between them in the direction in which the first object support 120, 220 is offset from the second object support 130, 230 is less than 400 pm, the gap between the first and second objects can fall within a scribe lane.

[0162] The first object support 120, 220 may comprise an electrostatic clamp 128, 228. Similarly, the second object support 130, 230 comprises an electrostatic clamp 138, 238.

[0163] Optionally, the imaging optics 140, 240 may be configured such that a reduction factor of the image in the direction in which the first object support 120, 220 is offset from the second object support 130, 230 is 8 and a reduction factor of the image in a second direction that is generally perpendicular to the first direction is 4.

[0164] The exposure apparatus 100 and / or second exposure apparatus 200 may comprise illumination optics 180, 280 configured to illuminate with radiation 182, 282 the first illumination region 150, 250 through which an object supported by the first object support 120, 220 and / or the second object support 130, 230 can be moved. The illumination optics 140, 240 may be generally analogous to the illumination system IL shown in Figure 1 and as described above.

[0165] The exposure apparatus 100 and / or second exposure apparatus 200 may further comprise a radiation source 190, 290 operable to produce the radiation. For example, the radiation source 190, 290may be operable to produce radiation 192, 292 which is received by the illumination optics 180, 280. The illumination optics 180, 280 may be operable to receive the radiation beam 192, 292 produced by the radiation source 190, 290 and to produce therefrom the radiation 182, 282 which illuminates the first illumination region 150, 250.

[0166] The radiation 192, 292 may comprise EUV radiation. The radiation source 190, 290 may comprise a laser-produced plasma (LPP) radiation source. For example, the radiation source 190, 290 may be generally of the form of to the radiation source SO shown in Figure 1 and as described above.

[0167] A gap 270 between the first object support 220 and the second object support 230 of the second exposure apparatus 200 being “sufficiently small that a single object 226 may be partially supported by the first object support 220 and partially supported by the second object support 230” may mean that the first object support 220 and the second object 230 support of the second exposure apparatus 200 are suitable for supporting a reflective lithography reticle 226 such that it is partially supported by the first object support 220 and partially supported by the second object support 230.

[0168] A gap 270 between the first object support 220 and the second object support 230 of the second exposure apparatus 200 is sufficiently small that a single object 226 may be partially supported by the first object support 220 and partially supported by the second object support 230. How this may be interpreted by the skilled person is now discussed.

[0169] Within the field of lithography, it is desirable to form a (usually diffraction-limited) image of a pattern defined by a mask or reticle on a substrate W (for example a resist-coated silicon wafer). It will be appreciated by the skilled person that any deformation of the reticle will give rise to a deformation of the (aerial) image of the reticle formed on the substrate W. The larger the deformation of the reticle is, the larger a deviation of the image formed on the substrate W from a desired image will be. Eventually, the deviation of the image formed on the substrate W from a desired image may be sufficiently large so as to result in printing errors, which is undesirable. The skilled person will be aware that deformation of the reticle should be carefully limited so as to avoid such printing errors.

[0170] As will be appreciated by the skilled person, a reflective reticle within an EUV lithographic apparatus is typically clamped to a reticle stage 220, 230 using an electrostatic clamp 228, 238 and is typically supported by a plurality of protrusions (known in the art as “burls”). The plurality of protrusions reduces a contact area between a rear surface of the reticle and the reticle stage, which is advantageous as this can reduce distortion of the reticle as it is clamped to the reticle stage. The plurality of protrusions may each extend from a common support substrate and the distal ends of the plurality of protrusions may define a support plane.

[0171] The reticle may be distorted if a distal end of one or more of the protrusions, or burls, becomes contaminated such that a foreign object or contaminant is disposed between those protrusions, or burls, and the reticle.

[0172] The skilled person will also be aware that a spacing between adjacent protrusions, or burls, is important in order to control a deformation of the reticle. For example, if a spacing between theprotrusions, or burls becomes too large then the reticle will be distorted as it is clamped to the reticle stage.

[0173] In some embodiments, the first object support 220 may define a first set of protrusions having a first pitch or spacing, distal ends of the first set of protrusions defining a first support plane, and second object support 230 may define a second set of protrusions having a second pitch or spacing, distal ends of the second set of protrusions defining a second support plane. For example, in order to provide sufficient support for a reflective reticle, the first pitch or spacing and the second pitch or spacing may be of the order of 1 mm.

[0174] For such embodiments, the gap 270 between the first object support and the second object support of the exposure apparatus according to the second aspect of the present disclosure in a direction in which the first object support is offset from the second object support may be less than the first pitch or spacing and the second pitch or spacing. Advantageously, this may ensure that said gap 270 is sufficiently small that a single reflective reticle may be partially supported by the first object support and partially supported by the second object support.

[0175] In some embodiments a gap 270 between the first object support 220 and the second object support 230 in a direction in which the first object support 220 is offset from the second object support 230 may be sufficiently small that when a single object 226 is partially supported by the first object support 220 and partially supported by the second object support 230 a central portion of the single object 228 that extends between the first object support 220 and the second object support 230 is subject to no more distortion than: a first side portion of the single object 228 supported by the first object support 220 and / or a second side portion of the single object 228 supported by the second object support 230. In particular, it may be that when the single object 228 is partially supported by the first object support 220 and partially supported by the second object support 230 and is clamped to both the first object support 220 and the second object support 230, the central portion of the single object 228 (that extends between the first object support 220 and the second object support 230) is subject to no more distortion than: a first side portion of the single object 228 (supported by the first object support 220) and / or a second side portion of the single object 228 (supported by the second object support 230).

[0176] In some embodiments, the exposure apparatus 200 may comprise a lithographic apparatus, the first object support 220 may be configured to support a first reflective reticle 222, and the second object support 230 may be configured to support a second reflective reticle 232.

[0177] In some embodiments, the first object support 230 may define a first set of protrusions having a first pitch or spacing, distal ends of the first set of protrusions defining a first support plane; the second object support 230 may define a second set of protrusions having a second pitch or spacing, distal ends of the second set of protrusions defining a second support plane. For such embodiments, a gap 270 between the first object support 220 and the second object support 230 in a direction in which the first object support 220 is offset from the second object support 230 may be less than the first pitch or spacing and the second pitch or spacing.

[0178] Above, the second exposure apparatus 200 is described such that the gap 270 between the first object support 220 and the second object support 230 of the second exposure apparatus 200 is “sufficiently small that a single object 226 may be partially supported by the first object support 220 and partially supported by the second object support 230”. Additionally or alternatively, the gap 270 may be such that when projected into an image plane of the exposure apparatus 200 (for example in the second illumination region 260), an image of a gap 270 between the first object support 220 and the second object support 230 is smaller than a dimension of a scribe lane of the exposure apparatus 200 between two adjacent fields.

[0179] The exposure apparatus 100 and / or second exposure apparatus 200 may further comprise a controller 195, 295 operable to carry out any of the exposures methods described herein with reference to any one of Figures 7 to 9. The controller may, for example, be able to send one or more control signals si, S2 so as to control, for example, a position of the first and second object supports 120, 130.

[0180] The exposure apparatus 100 and / or second exposure apparatus 200 may further comprise a substrate table WT configured to support a substrate W such that it is disposed in, and movable through, the second illumination region 160.

[0181] The exposure apparatus 100 and / or second exposure apparatus 200 may comprise a long stroke assembly 400 and / or at least one short stroke assembly 450, 450a, 450b, as now discussed with reference to Figures 6A and 6B. An embodiment comprising two short stroke assemblies 450a, 450b is shown in Figure 6A. An embodiment comprising one short stroke assembly 450 is shown in Figure 6B.

[0182] The long stroke assembly 400 may comprise a first portion 410 that is fixed relative to the main support 110, 210 and a second portion 420 that is movable relative to the first portion 410 (as indicated by arrow 422). The first portion 410 of the long stroke assembly 400 may comprise the main support 110, 210, a part of the main support 110, 210, or a member that is fixed to the main support 110, 210. The second portion 420 supports the first object support 120, 220 and the second object support 130, 230.

[0183] The coupling between the first and second portions 410, 420 of the long stroke assembly 400 (not shown) may comprise any suitable coupling which allows the second portion 420 to be movable relative to the first portion 410. For example, the coupling between the first and second portions 410, 420 of the long stroke assembly 400 may comprise a track and a motor operable to move the second portion 420 along the track and relative to the first portion 410, as is known in the art. The long stroke assembly 400 may allow for the first and second object supports 120, 220, 130, 230 to be moved relative to the first illumination region over distances of the order of 10s or 100s of millimetres.

[0184] The long stroke assembly 400 may further comprise at least one balance mass 440. The or each balance mass 440 may be movable relative to the first portion 410 of the long stroke assembly 400 (as indicated by arrow 442). In use, the or each balance mass 440 may move in an opposite sense to the first portion 410 of the long stroke assembly 400. When the second portion 420 of the long stroke assembly 400 accelerates relative to the first portion 410 of the long stroke assembly 400 it will exertreaction forces on the second portion 420 via the coupling between the first and second portions 410, 420 of the long stroke assembly 400. Although not shown there will be a coupling between the first portion of the long stroke assembly 400 and the or each balance mass 440. The or each balance mass 440 may be arranged and moved in such a way so as to also create reaction forces on the first portion 410 that at least partially cancel out the forces exerted by the second portion 420.

[0185] Each short stroke assembly 450, 450a, 450b comprises a first portion that is fixed relative to second portion 420 of the long stroke assembly 400 and a second portion that is movable relative to the first portion and which supports the first object support 120, 220 and / or the second object support 130, 230. That is, the second portion short stroke assembly 450, 450a, 450b is movable relative to the second portion 420 of the long stroke assembly 400, as indicated by arrows 452, 452a, 452b.

[0186] The coupling between the first portion and the second portion of each short stroke assembly 450, 450a, 450b (not shown) may comprise any suitable coupling which allows the second portion to be movable relative to the first portion. For example, the coupling may comprise any arrangement known in the art.

[0187] As shown in Figure 6A, some embodiments may comprise two short stroke assemblies 450a, 450b; a first short stroke 450a assembly may support the first object support 120, 220 and a second short stroke assembly 450b may support the second object support 130, 230. Such embodiments may comprise two clamps, each on a separate one of two short stroke assemblies 450a, 450b. The relative movement of the two clamps (for example in 6 degrees of freedom) may be achieved suing the two short stroke assemblies 450a, 450b, to achieve nanometer accurate positioning of one reticle with respect to the other. A gap between the two reticles can be made smaller than 400 pm. Such arrangements can support a single, larger (for example 12”) reticle.

[0188] Alternatively, as shown in Figure 6B, in some other embodiments, two reticles may be supported by a single short stroke assembly 450 (either via the same or separate reticle clamps).

[0189] For embodiments of the type shown in Figure 6B and comprising two reticle clamps, at least one of the clamps may comprise actuators (for example piezoelectric actuators) configured to allow the first object support 120, 220 to be movable relative to the second object support 130, 230 (for example in 6 degrees of freedom). For such embodiments comprising two clamps on one short stroke 450 assembly, at least one of the two clamps can be adjusted (for example in 6 degrees of freedom) with respect to the other, to achieve nanometer accurate positioning of one reticle with respect to the other.

[0190] For embodiments of the type shown in Figure 6B and comprising one reticle clamp, a single glass structure may support the reticle(s). As explained above, this single glass structure may comprise a plurality of glass layers or plates, and a set of electrodes sandwiched between these glass layers. In particular, it may comprise a single plate or layer of glass (for example ultra-low expansion glass), which may define a plurality of protrusions or burls. For embodiments comprising a single reticle clamp, one set of burls and / or electrodes may be considered to form part of the first object support 120, 220 and another set of burls and / or electrodes may be considered to form part of the second objectsupport 130, 230. For such embodiments, at least some of the burls may be provided with piezoelectric actuators in order to allow the first object support 120, 220 to be movable relative to the second object support 130, 230 (for example in 6 degrees of freedom). In principle the piezoelectric actuators could be provided on the burls. Alternatively, in one embodiment, the glass structure of the single clamp may comprise an additional layer, which could function as a piezoelectric layer to provide the adjustability to allow the first object support 120, 220 to be movable relative to the second object support 130, 230 (for example in 6 degrees of freedom). Alternatively, the clamp may comprise a flexure associated with the clamp which can allow for the first object support 120, 220 to be movable relative to the second object support 130, 230 (for example in 6 degrees of freedom).

[0191] It will be appreciated by the skilled person that the above mentioned description of the piezoelectric actuators in the burls or as an additional layer on the clamp and the clamp comprising a flexure for in 6 degrees of freedom is not limited alone to embodiment of Figure 6B but equally applicable to all the embodiments where 6 degrees of freedom control is required to move and align the first object with respect to the second object or vice versa.

[0192] With all of the above-described embodiments of the type shown in Figure 6B, a gap between the two reticles can be made smaller than 400 pm. Such arrangements can support a single, larger (for example 12”) reticle.

[0193] Each of the first object support 120, 220 and the second object support 130, 230 may, in general, comprise an electrostatic clamp 128, 228, 138, 238. In both Figure 6A and 6B, each the first object support 120, 220 and the second object support 130, 230 are shown schematically as comprising four electrodes 460 (only some are labelled to improve the clarity of the Figures). It will be appreciated that other arrangements of electrodes may alternatively be used and this is merely an example. In general, to clamp a reticle typically a number of electrodes at a positive voltage is equal to a number of electrodes at a negative voltage.

[0194] Some examples of how these eight electrodes may be actuated for different arrangements of reticles are now discussed with reference to Figures 7A to 7D. It will be appreciated that different electrode configurations, and different polarity configurations, are also possible.

[0195] Figure 7A shows a possible actuation pattern for the electrodes of the arrangements shown in Figures 6A and 6B when the first and second object supports 120, 220, 130, 230 are each supporting a different object. Each set of four electrodes may be actuated as a pattern of positive, negative, negative, positive (+ - - +) or vice versa (- + + -). With such an arrangement the electrode from the first object support 120, 220 that is adjacent to the electrode from the second object support 130, 230 has the same polarity.

[0196] Figure 7B shows a possible actuation pattern for the electrodes of the arrangements shown in Figures 6A and 6B when only one of the first and second object supports 120, 220, 130, 230 is supporting an object (reticle). The arrangement is similar to that shown in Figure 7A although the voltage of all of the four electrodes of the object support that is not supporting an object are set to 0.

[0197] Figure 7C shows a first possible actuation pattern for the electrodes of the arrangements shown in Figures 6A and 6B when the first and second object supports 120, 220, 130, 230 are together supporting a single object (reticle). The arrangement is the same as that shown in Figure 7A.

[0198] Figure 7D shows a second possible actuation pattern for the electrodes of the arrangements shown in Figures 6A and 6B when the first and second object supports 120, 220, 130, 230 are together supporting a single object (reticle). The arrangement alternates between positive and negative polarities (i.e. either + - + - + - + - or - + - + - + - +).

[0199] Various new exposure methods and uses of the exposure apparatus 100 and / or second exposure apparatus 200 are now discussed.

[0200] The exposure apparatus 100 and / or second exposure apparatus 200 allow for two different objects 122, 222, 132, 232 (reticles) to be provided within the exposure apparatus 100, 200. Furthermore, they allow for an arrangement wherein, for at least part of an exposure process, the two objects 122, 222, 132, 232 (reticles) can both partially overlap the first illumination region 150, 250 simultaneously. This is shown schematically in Figure 8, wherein the first illumination region 150, 250 is of a similar form to the reticle-level illumination region IR described above with reference to Figures 2A and 2B. A direction in which the first (reticle -level) illumination region 150, 250 effectively scans over the two objects 122, 222, 132, 232 is indicated by arrow C. It will be appreciated that, in practice this may be achieved by scanning the two objects 122, 222, 132, 232 through the first (reticle-level) illumination region 150, 250 in a direction opposite to the arrow C.

[0201] Therefore, with the exposure apparatus 100 and / or second exposure apparatus 200, rather than exposing two individual half fields during two different scans over the wafer W (with two different objects or reticles) two different objects 122, 222, 132, 232 (reticles) can be exposed during a single scanning exposure. One object 122, 222 is supported by the first object support 120, 220 and the other object 132, 232 is supported by the second object support 130, 230. One of the objects 122, 222 (reticles) is used to expose half of a first target region 20 or field and the other object 132, 232 (reticle) is used to expose half of an adjacent target region 20 or field. The two adjacent target regions 20 that are exposed are adjacent in the scanning direction of the exposure apparatus 100, 200 (i.e. the y- direction). The gap between the image regions of the two objects 122, 222, 132, 232 is matched to fall within a scribe line area of the wafer W between the two adjacent target regions 20. Therefore part of the scribe line areas that separate adjacent target regions 20 that are separated in the scanning direction (i.e. scribe lines that extend in a non-scanning direction or x-direction) may be provided with an exclusion zone which corresponds to the gap between the image portions of the two objects 122, 222, 132, 232 (reticles).

[0202] In some embodiments, an optional thin mask may be provided to control the radiation which is incident on the two objects 122, 222, 132, 232. The optional thin mask may take any convenient form. For example, the optional thin mask may comprise anything (for example reticle masking blades,opaque tape or a thin material made of a mask) that is arranged to shield the gap between the image regions of the two objects 122, 222, 132, 232 from the radiation.

[0203] Any flare impact of the edge of the two objects 122, 222, 132, 232 can be modelled in a software package.

[0204] The exposure apparatus 100 and / or the second exposure apparatus may further comprise a coating provided conformally over the edge of the first object 122, 222 and / or the edge of the second object 132, 232. In this respect, conformally means that the coating is applied very smooth without roughness over the respective edge. Ideally, the coating is plane and symmetric. The coating is configured to absorb radiation incident on the edge of the first object 122, 222 and / or the edge of the second object 132, 232. Without the coating at the edge, radiation at the edge of the first object 122, 222 or second object 132, 232 could diffract the incident radiation, e.g. EUV radiation, resulting in imaging artefacts which are difficult or even impossible to correct for. The conformal coating over the edge of the first object 122, 222 and / or the second object 132, 232 prevent diffraction of the incident radiation. The coating is made of a material having an extinction coefficient of at least 0.03, preferably above 0.04, and a refraction index of at least 0.90. The coating is for example made of Tungsten. The coating has a thickness in the range of 50-100 nm, preferably 60-80 nm. The coating may be provided by a sputtering method. Additionally or alternatively, the coating is at least partially provided on the first object support 120, 220 and / or the second object support 130, 230. Optionally, when the coating is provided conformably over the edge of the first object 122, 222 and / or the edge of the second object 132, 232, a protective layer is provided over the remaining surface of the reticle not being covered by the coating. The protective layer is a layer of radiation-sensitive material (resist). The protective layer is configured to mask the remaining surface of the reticle.

[0205] An example exposure method is shown schematically in Figure 9, which shows six target regions 20 (solid line rectangles) arranged in a two-dimensional array of two rows 30A, 30B (extending in the non-scanning or x-direction) and three columns 32A, 32B, 32C (extending in the scanning or y- direction). Each target region 20 comprises two portions: a first portion (labelled A and on a lower half of the target regions 20 as shown in Figure 9); and a second portion (labelled B and on an upper half of the target regions 20 as shown in Figure 9).

[0206] Figure 9 illustrates a method during which, one object 122, 222 (reticles) is used to expose the first portion A of target regions from a first row 30A of target regions and another object 132, 232 (reticle) is used to expose the second portion B of target regions from a second row 30B of target regions 20. Within each column 32A, 32B, 32C of target regions, the first portion A from the first row 30A and the second portion B from the second row 30B are exposed during a single scanning exposure. Pairs of adjacent target regions 20 that are exposed during a single scanning exposure are adjacent in the scanning direction of the exposure apparatus 100, 200 (i.e. the y-direction). A path that the second (wafer-level) illumination region 160, 260, IR’ scans over the wafer W is indicated by a dotted line (although it will be appreciated that in practice this scanning may be achieved by moving the waferrelative to the second illumination region 160, 260). The portions of the target regions that are being exposed as the second (wafer-level) illumination region 160, 260, IR’ scans over the wafer W along the dotted line are shaded.

[0207] As shown in Figure 9, the exposure pattern may be similar to known meander scans except instead of a single target region 20, during each scanning exposure two portions of two adjacent target regions are exposed. As with known meander scans, two sequential exposures (which are exposing parts of the same two rows 30A, 30B of target regions) may use substantially opposite scan directions.

[0208] The arrangement shown in Figure 9 may form part of a meander scan which is similar to that shown Figure 3 and described above except, in general, instead of a single target region 20, during each scanning exposure two portions of two adjacent target regions are exposed. It will be appreciated that target regions adjacent to the edges of the wafer W exposures may be partially exposed by a scanning exposure using only one of the two objects 122, 222, 132, 232 (reticles).

[0209] Optionally the two images A, B formed on each target region 20 can be stitched together in the middle for dies with dimensions that exceed those of a half-field or to simply enhance the maximum field size used.

[0210] Optionally, the exposure apparatus 100 or second exposure apparatus 200 can be used to expose a single object 122, 222 to expose half fields at reduced throughput. This may be a particularly relevant option for small product sizes where the reticle cost dominates the total cost to produce dies. When operating in this way, the exposure apparatus 100 or second exposure apparatus 200 has an additional advantage in that in-between lot transitions, the object (reticle) for a new lot can be pre-loaded if its full field capability is not used, which can save some reticle exchange time.

[0211] Some embodiments of the present disclosure relate to new exposure methods for forming a pattern on a plurality of target regions of a substrate W. Such new exposure methods may comprise any of the features discussed above with reference to Figures 8 and 9. An example, of such a new exposure method 500 forming a pattern on a plurality of target regions of a substrate W is now discussed with reference to Figure 10.

[0212] The exposure method 500 comprises a step 510 of providing a first object 122, 222 defining a first portion A of the pattern and a second object 132, 232 defining a second portion B of the pattern, such that the first object 122, 222 is adjacent to, and generally coplanar with, the second object 132, 232 and the first object 122, 222 is offset from the second object 132, 232 in a first direction (e.g. the y-direction or scanning direction).

[0213] The exposure method 500 further comprises at least one scanning exposure 520.

[0214] In turn, the or each scanning exposure 520 comprises a step 522 of moving the first object 122, 222 and the second object 132, 232 in the first direction such that they sequentially scan through a first illumination region IR, 150, 250 while providing radiation B, 182, 282 to the first illumination region IR, 150, 250.

[0215] The or each scanning exposure 520 further comprises a step 524 of capturing radiation scattered by the first and second objects 122, 222, 132, 232 and using it to form an image of the first and second objects 122, 222, 132, 232 in a second illumination region IR’, 160, 260 while moving the substrate W through the second illumination region IR’, 160, 260 such that an image of the first object 122, 222 is formed on a first target region of the substrate W and an image of the second object 132, 232 is formed on a second target region of the substrate W, the first and second target regions being mutually adjacent.

[0216] Note that although steps 522 and 524 are shown as separate steps it will be appreciated that in practice they will be performed substantially simultaneously. As will be appreciated by the skilled person, the first object 122, 222 and the second object 132, 232 are moved through the first illumination region IR, 150, 250 at the same time as the substrate W is moved through the second illumination region IR’, 160, 260.

[0217] The exposure method 500 shown schematically in Figure 10 may be carried out using the exposure apparatus 100 shown in Figure 4 or the second exposure apparatus 200 shown in Figures 5 A and 5B.

[0218] The exposure method 500 shown in Figure 10 may comprise a lithographic exposure method. The first object 122, 222 and the second object 132, 232 may comprise any type of patterning device MA (also referred to as a reticle or mask). The first illumination region IR, 150, 250 may be disposed in an object plane (which may also referred to as a reticle-level illumination region). The second illumination region IR’, 160, 260 may be disposed in an image plane (which may also referred to as a wafer-level illumination region). The first and / or second illumination region may be referred to as a slit (or exposure slit).

[0219] Instead of exposing two half-fields separately as two different steps, with the exposure method 500 shown schematically in Figure 10 both reticles are exposed in a single stroke or scanning exposure. An image of the first object 122, 222 (reticle) is formed on a first target region (field) of the substrate W and an image of the second object 132, 232 (reticle) is formed on a second target region (field) of the substrate W, the first and second target regions being mutually adjacent. The area in-between these two images is matched to fall within the scribe line area of the wafer W.

[0220] In some embodiments of the method 500, the first object 122, 222 and the second object 132, 232 are provided such that a gap between them in the first direction is less than an extent of the first illumination region IR, 150, 250 in the first direction.

[0221] In some embodiments of the method 500, the first object 122, 222 and the second object 132, 232 are provided such that for at least a portion of the or each scanning exposure 520 the first and second objects 122, 222, 132, 232 are both partially disposed in the first illumination region IR, 150, 250 in the first direction.

[0222] In some embodiments of the method 500, the first object 122, 222 and the second object 132, 232 are provided such that a gap between them in the first direction is less than 400 pm.

[0223] In some embodiments of the method 500, the method 500 comprises a plurality of scanning exposures 520 and wherein the plurality of scanning exposures 520 are performed as a meander scan. For such embodiments, the method 500 may comprise a step 530 of moving the wafer W in between successive scanning exposures 520.

[0224] In some embodiments of the method 500, the method 500 may comprise a plurality of scanning exposures 520 and wherein the image A of the first object 122, 222 formed on a target region of the substrate W during one scanning exposure 520 is stitched to the image B of the second object 132, 232 formed on that target region of the substrate W during another scanning exposure 520.

[0225] In such embodiments of the method 500, the images A, B of the first object 122, 222 and the second object 132, 232 that are stitched may be mutually adjacent in the first direction. That is, the two images A, B that are stitched may be mutually adjacent in the scanning direction (y-direction). Put differently, a join line between the two images A, B that are stitched may extend in a second direction (a non-scanning direction or x-direction).

[0226] Some embodiments of the present disclosure relate to a second new exposure method for forming a pattern on a plurality of target regions of a substrate W. An example, of such a second new exposure method 600 forming a pattern on a plurality of target regions of a substrate W is now discussed with reference to Figure 11.

[0227] The exposure method 600 shown in Figure 11 for is forming a pattern on each of a plurality or target regions of a substrate W. The exposure method 600 shown in Figure 11 comprises a step 610 of providing a first object 122, 222 defining a first pattern and providing a second object 132, 232 defining a second pattern.

[0228] The exposure method 600 shown in Figure 11 further comprises a step 620a of forming an image on each of a first set of the plurality of target regions using the first object 122, 222, wherein the first set of the plurality of target regions have been determined to, or are expected to, have a first imaging performance.

[0229] The exposure method 600 shown in Figure 11 further comprises a step 620b of forming an image on each of a second, different set of the plurality of target regions using the second object 132, 232 or a combination of the first object 122, 222 and the second object 132, 232, wherein the second set of the plurality of target regions have been determined to, or are expected to, have a second imaging performance.

[0230] The exposure method 600 shown in Figure 11 may be carried out using the exposure apparatus 100 shown in Figure 4 or the second exposure apparatus 200 shown in Figures 5 A and 5B.

[0231] The exposure method 600 shown in Figure 11 may comprise a lithographic exposure method. The first object 122, 222 and the second object 132, 232 may comprise any type of patterning device (also referred to as a reticle or mask).

[0232] The method 600 shown in Figure 11 is advantageous, as now discussed. During a lithographic exposure method, typically an image of a single reticle is formed in each of a plurality of target regions(also referred to as fields). Furthermore, as discussed above in relation to the exposure apparatus 100 shown in Figure 4, the second exposure apparatus 200 shown in Figures 5 A and 5B and the exposure method 500 shown in Figure 10, if a lithographic apparatus is provided with two reticles then in each target region or field an image may be formed of each the first reticle and the second reticle thus effectively doubling the size of the fields and increasing lithographic throughput. However, for some lithographic processes, it may be that the additional reticle clamp does not increase throughput. This may be the case for in DRAM (dynamic random access memory) processes or for processes with small product sizes.

[0233] The method 600 shown in Figure 11 provides a way of utilizing the second object support (reticle clamp) 130, 230 for such processes, as now explained.

[0234] It may be the case that some regions of a substrate W (for example a lithography wafer) suffer from poorer than average imaging performance. For example, some fields may suffer increased overlay and / or edge placement errors (EPE) and / or some fields may suffer from reduced contrast and / or some fields may suffer from increased defocus. Furthermore, it is possible to predict that some images on the wafer will have a reduced performance or yield. Examples of regions of a wafer that may suffer from reduced imaging performance include bonding fingerprints, edge fields and regions or a wafer stage or clamp that have become contaminated (referred to as chuck spots).

[0235] There are a number of advanced imaging techniques that can be used to improve lithographic imaging performance, however, typically these significantly increase lithographic throughput.

[0236] The method 600 shown in Figure 11 is able to (for example using two object supports within an exposure apparatus 100, 200) expose a substrate W such that the first and second sets of target regions are exposed differently. Advantageously, this allows advanced imaging techniques to be used to selectively improve lithographic imaging performance of some target regions (for example the second set of target regions). The first set of the plurality of target regions may, for example, be target regions where a nominal or baseline imaging performance can be expected. The second, different set of the plurality of target regions may, for example, be target regions where a reduced imaging performance can be expected. This allows a first object 122, 222 (for example loaded on a first object support 120, 220) to be used to expose the first set of target regions (which may, for example, constitute a majority of the target regions) using a standard exposure technique and a second object 132, 232 (for example loaded on a second object support 130, 230) to be used to expose the second set of target regions (which may, for example, constitute a minority of the target regions) using an advanced imaging technique. Advantageously, this improves the imaging performance in the second set of target regions whilst maintaining a faster, standard exposure technique for the first set of target regions.

[0237] Optionally, the exposure method 600 shown in Figure 11 may further comprise a step 602 of determining the first set of the plurality of target regions and the second, different set of the plurality of target regions, wherein the first and second sets of the plurality of target regions are determined based on a determined or expected imaging performance of each of the plurality of target regions.

[0238] It will be appreciated that it may be that the determination of the first and second sets of target regions is not made for each substrate W. For example, it may be that such a determination can be made once, or periodically, for example at the start of a process of exposing a plurality (or “lot”) of wafers W.

[0239] The determination of the first and second sets of target regions may be made according to any selection criterion based on imaging performance. For example, selection criterion may be based on an overlay and / or a contrast and / or a focus related parameter.

[0240] The first set of the plurality of target regions may be target regions where a nominal or baseline imaging performance can be expected; and the second set of the plurality of target regions may be target regions where a reduced imaging performance can be expected.

[0241] The first set of target regions may constitute a majority of the plurality of target regions and the second set of target regions may constitute a minority of the plurality of target regions.

[0242] Forming an image on each of a first set of the plurality of target regions (at step 620a) may comprise using a standard exposure technique. Forming an image on each of a second set of the plurality of target regions (at step 620b) may comprise using an advanced imaging technique.

[0243] It will be appreciated that the first and second sets of target regions can be exposed in various different orders.

[0244] For example, in some embodiments, the images may be formed first in all target regions belonging to one set (either the first set or the second set) and then subsequently be formed in all target regions belonging to the other set. For such embodiments, the exposure of each set of target regions may be achieved using a modified meander scan (in which the substrate may be moved as for a meander scan but not all fields or target regions are exposed to the patterned radiation).

[0245] Alternatively, in some embodiments, the steps 620a, 620b of forming the images in the first and second sets of target regions may at least partially overlap temporally. For example, images may be formed all of the plurality of target regions on the substrate in single meander scan wherein: (a) when the meander scan reaches a target region belonging to the first set an image may be formed using the first object 122, 222; and (b) when the meander scan reaches atarget region belonging to the second set an image may be formed using the second object 132, 232 or a combination of the first object 122, 222 and the second object 132, 232.

[0246] The step 610 of providing the first object 122, 222 and providing the second object 132, 232 may comprise providing the first object 122, 222 on a first object support 120, 220 and providing the second object 132, 232 on a second object support 130, 230.

[0247] In some embodiments, the first object 122, 222 defines a main pattern to be applied to the plurality of target regions; the second object 132, 232 defines a second pattern comprising one or more enhancement or optical proximity correction (OPC) features. For such embodiments an image may be formed on each of the second set of the plurality of target regions using a combination of the first object 122, 222 and the second object 132, 232.

[0248] With such embodiments, the enhancement or optical proximity correction (OPC) features on the second object 132, 232 (reticle) can be used to enhance a contrast of the image of the first object 122, 222 (reticle). For such embodiments, the enhancement or optical proximity correction (OPC) features may be designed as taught in WO2021043519A1, which is incorporated herein in its entirety by reference, or as otherwise known in the art.

[0249] With such embodiments, an image of the first pattern 122, 222 formed on each of the second set of target regions may be formed with a lower dose of radiation than an image of the first pattern 122, 222 formed on each of the first set of target regions.

[0250] It will be appreciated that, in general, it is important to control the dose of radiation used in a lithographic exposure method. When using an additional exposure of the second pattern 132, 232, for example to enhance a contrast of an image of the first pattern 122, 222, additional exposure of the second pattern 132, 232 delivers additional radiation to the substrate. It may be that, for such target regions a dose of the image of the first pattern 122, 222 is reduced slightly so that a nominal or target total dose is still supplied across the two exposures.

[0251] The lithographic apparatus LA of Figure 1 may be a scanner-type lithographic apparatus. In such scanner-type lithographic apparatus the illumination beam is guided through a masking device REMA to the patterning device MA. The masking device REMA defines the reticle-level illumination region (also referred to as an exposure slit) which the radiation beam illuminates. As discussed above, the illumination region IR may be curved or rectangular and mainly extends in a slit direction (or x- direction of non-scanning direction).

[0252] During projection of the patterned radiation beam on exposure fields on the substrate W, the patterning device MA is moved with a scanning movement in a scanning direction with respect to the illumination region IR. The scanning direction (y-direction) is perpendicular to the slit direction (x- direction). Simultaneously with the scanning movement of the patterning device MA, the substrate W is moved with a scanning movement with respect to the projection system PS such that the patterned radiation beam having a cross-section defined by the wafer-level illumination region IR’ will be scanned along the substrate W to project the patterned radiation beam B’ on the respective exposure field. The length of the illumination region IR, e .g . its dimension in slit direction, is adapted by the masking device REMA to the width of the exposure field on which the patterned radiation beam B’ is projected. The width of the illumination region IR, i.e. its dimension in the scanning direction, is substantially smaller than the length of the illumination region IR. To folly cover the full exposure field the reticle and the wafer are synchronously scanned in the scanning direction.

[0253] In some embodiments the first object 122, 222 may define a main pattern to be applied to the plurality of target regions; and the second object 132, 232 may define the same main pattern that has been split into at least two portions separated by an absorbing or non-reflective material. An image may be formed on each of the second set of the plurality of target regions using the second object 132,232 by using a plurality of exposures, each one of the plurality of exposures forming an image of a different one of the at least two portions of the main pattern.

[0254] Such a split exposure allows for a higher order correction to be applied for overlay across the target regions belonging to the second set, especially in a non-scanning direction of the exposure method, as discussed further below with reference to Figures 12 to 18.

[0255] For such split exposure embodiments, the image of the main pattern and the images of the at least two portions of the main pattern may be formed as scanning exposures by: scanning the first object 122, 222 or the second object 132, 232 through a radiation beam B so as to pattern the radiation beam B’; and simultaneously scanning the substrate W such that an aerial image of the first or second object is stationary with respect to the substrate W. The at least two portions of the main pattern (on the second object 132, 232) may be separated in a direction that is perpendicular to the scanning direction. The direction that is perpendicular to the scanning direction may be referred to as a non-scanning direction.

[0256] For such split exposure embodiments, for each of the plurality of exposures of each target region belonging to the second set, an aerial image of the portion of the main pattern being imaged is adjusted in dependence of a deformation of a portion of that target region that is being exposed. That is, dynamically during the scan corrections may be made to reduce overlay caused by deformation of the wafer W.

[0257] For such split exposure embodiments, for each of the plurality of exposures of each target region belonging to the second set, radiation used for the exposure(s) is controlled such that the portion(s) of the main pattern not being imaged are not illuminated by radiation B.

[0258] In some embodiments, controlling the radiation such that the portion(s) of the main pattern not being imaged are not illuminated by radiation B may comprise adjusting a position of one or more masking blades of a masking device REMA to reduce an extent of an illumination region.

[0259] In some embodiments, controlling the radiation such that the portion(s) of the main pattern not being imaged are not illuminated by radiation comprises adjusting a configuration of a MEMS illuminator IL.

[0260] Some features and advantages of such split exposure embodiments, are now discussed with reference to Figures 12 to 18.

[0261] Figure 12 schematically depicts a cross-section of a patterned radiation beam PRB as dimensioned by the masking device REMA in a scanning movement with respect to an exposure field EXF. The shape of the cross-section of the patterned radiation beam substantially corresponds with the shape of the illumination region IR. The length of the cross-section of the patterned radiation beam PRB (in x-direction) as projected on the exposure field EXF is substantially the same as the width of the exposure field EXF. The width of the cross-section of the patterned radiation beam PRB (in y-direction) is smaller than the length of the exposure field EXF.

[0262] Figure 12 shows only one exposure field EXF. In practice, a substrate W may have a multitude of exposure fields, each exposure field being designed to be exposed to a pattern of a patterning device.

[0263] Deformation of a substrate W, in particular in-plane deformation may lead to overlay errors due to mis-alignment of the patterned radiation beam PRB with respect to the exposure field EXF. This deformation may for example be caused by clamping a warped substrate W on a substrate support WT. To reduce these overlay errors, a position of an aerial image of the patterned radiation beam projected on the exposure field may be adjusted in dependence of a deformation of the exposure field on which the patterned radiation beam is projected.

[0264] The position of this aerial image can be adjusted by adjusting positions of the patterning device and / or positions of reflective surfaces in the projection system PS of the lithographic apparatus. The flexibility to apply these corrections may be limited due to the hardware used. For example, the corrections provided by adjusting positions of the reflective surfaces in the projection system PS may be limited to second order corrections.

[0265] In the scanning direction, the width of the cross-section of the patterned radiation beam PRB is relatively small with respect to the exposure field EXF and the dimension of the illumination region IR in slit direction. The overlay errors in this scanning direction may therefore be relatively small compared to the overlay errors that may occur in the slit direction of the patterned radiation beam PRB. During the scanning movement of the exposure field EXF in the scanning direction, e.g. y-direction, with respect to the patterned radiation beam, the correction in scanning direction may be continuously adjusted to the part of the exposure field EXF that is aligned with the patterned radiation beam PRB.

[0266] The cross-section of the patterned radiation beam in slit direction, e.g. x-direction, extends over the complete width of the exposure field EXF. Due to this relatively large dimension in the slit direction, it may be more difficult to correct for overlay errors in this direction.

[0267] Figure 13 shows a graph with an overlay error related parameter ORP in relation to a position P of the exposure field EXF in the slit direction for a specific position of the patterned radiation beam PRB in the scanning direction, for example the position shown in Figure 12. The overlay error related parameter ORP may be determined by measurement of the substrate W and is typically related to deformation of the substrate W, such as in-plane deformation of the substrate W. Figure 13 also shows an overlay correction OCO to at least partially correct the overlay error related parameter ORP. The overlay correction OCO is a second order correction.

[0268] By comparison of the overlay error related parameter ORP and the overlay correction OCO, it can be concluded that the overlay error related parameter ORP and the overlay correction do not completely match. In other words a substantial error residue remains. As a result, the overlay error cannot be folly corrected. For some exposure fields EXF the error residue and associated overlay error may even be too large to be acceptable. These exposure fields EXF may be classified as non-correctable. This is generally undesirable.

[0269] The present disclosure proposes to split in the slit direction, e.g. x-direction, at least one of the multiple exposure fields in two or more partial exposure fields. The patterned radiation beam PRB may be projected on the two or more partial exposure fields in two or more separate scanning movements ofthe patterning device in the scanning direction. This may improve available overlay correction capacity for deformation of the substrate W, since for each scanning movement its own overlay correction may be applied.

[0270] In such approach, the cross-section of the patterned radiation beam has to be adapted to the width of the respective partial exposure field. This can be done by using the masking device REMA to mask the part of the radiation beam that should not be projected on the exposure field. The masking device REMA comprises masking blades that are arranged to delimit the length of the illumination region IR in the slit direction. By movement of these masking blades in the slit direction the position and length of the illumination region IR in slit direction and therewith the position and length of the cross-section of the patterned radiation beam projected on the exposure field can be adjusted.

[0271] In an alternative embodiment a MEMS illuminator may be provided, which MEMS illuminator is arranged to provide the radiation beam only in that part of the illumination region IR associated with the respective one of the two or more partial exposure fields to be exposed.

[0272] Figures 14A and 14B show an example of two separate scanning movements over two partial exposure fields. The exposure field EXF on the substrate W is split in slit direction in a first partial exposure field EF-1 and a second partial exposure field EF-2, i.e. each of the first partial exposure field EF-1 and the second partial exposure field EF-2 extend over a part of the width of the exposure field EXF in x-direction. Both the first partial exposure field EF-1 and the second partial exposure field EF- 2 extend over the complete length of the exposure field EXF in the scanning direction.

[0273] Figure 14A shows a first scanning movement during which the patterned radiation beam PRB is projected on the first exposure field EF-1. The part of the exposure field EXF that has already been exposed to the patterned radiation beam PRB is indicated by a horizontally hatched area. The patterned radiation beam PRB is thus adapted to only project the patterned radiation beam on the first partial exposure field EF-1. The masking device REMA (see Figure 1) is used to mask the part of the radiation beam that would be projected after being imparted with a pattern on the second partial exposure field EF-2.

[0274] Figure 14B shows a second scanning movement during which the patterned radiation beam PRB is projected on the second exposure field EF-2. The part of the exposure field EXF that has already been exposed to the patterned radiation beam PRB is indicated by a horizontally hatched area. It can be seen that the first partial exposure field EF-1 has already been completely exposed to the patterned beam of radiation PRB. In the second scanning movement, the patterned radiation beam PRB is thus adapted to only project the patterned radiation beam PRB on the second partial exposure field EF-2. The masking device REMA (see Figure 1) is used in the second scanning movement to mask the part of the radiation beam that would be projected after being imparted with a pattern on the first partial exposure field EF-1.

[0275] Figure 15 shows a graph with an overlay error related parameter ORP in relation to a position P of the exposure field EXF in the slit direction for a specific position of the patterned radiation beamPRB in the scanning direction. As this overlay error related parameter ORP relates to the same position on the exposure field EXF in scanning direction as shown in Figure 13, the overlay error related parameter ORP of Figures 13 and 15 are the same.

[0276] As a result of splitting the exposure field EXF in slit direction in a first partial exposure field EF-1 and a second partial exposure field EF-2, the overlay correction can be determined for each scanning movement. This means that a first overlay correction OCO-1 can be determined to compensate the overlay error related parameter ORP in the first partial exposure field EF-1 and a second overlay correction OCO-2 can be determined to compensate the overlay error related parameter ORP in the second partial exposure field EF-2. Figure 15 shows the first overlay correction OCO-1 and the second overlay correction OCO-2. Both the first overlay correction OCO-1 and the second overlay correction OCO-2 are second order corrections. It can be seen that the difference between the overlay error related parameter ORP and the combination of the first overlay correction OCO-1 and the second overlay correction OCO-2 is substantially smaller than the difference between the overlay error related parameter ORP and the overlay correction OCO in Figure 13. The error residue is thus also substantially smaller resulting in a better overlay performance.

[0277] Similarly, the focus performance can be improved by splitting the exposure field EXF in slit direction in a first partial exposure field EF-1 and a second partial exposure field EF-2, and determining a focus correction for each respective scanning movement with respect to the first partial exposure field EF-1 and the second partial exposure field EF-2, respectively. This means that a first focus correction can be determined to compensate an focus error related parameter in the first partial exposure field EF- 1 and a second focus correction can be determined to compensate a focus error related parameter in the second partial exposure field EF-2.

[0278] Although the split of the exposure field EXF in two or more partial exposure fields to be exposed in separate scanning movements has substantial advantage with respect to reducing focus and / or overlay errors, the required separate scanning movements negatively influence the throughput capacity of the lithographic process. Therefore, it may be desirable to apply the split of the exposure field EXF only at locations of the substrate W where the deformation of the substrate W, in particular in-plane deformation of the substrate W, is substantial enough to accept the loss of throughput. The selection criterion to determine whether an exposure field EXP should be split in two or more partial exposure fields for exposure during two or more separate scanning movements, or not, is for example a residual of a deformation of the substrate W after deformation correction.

[0279] The lithographic apparatus LA may be arranged, for example in a processing device, to select, based on a selection criterion, at least one of the multiple exposure fields to be split in the slit direction in two or more partial exposure fields, wherein the two or more partial exposure fields are exposed to the patterned radiation beam in two or more separate scanning movements of the patterning device. The exposure fields that do not fulfil the selection criterion may be exposed to the patterned radiation beam over the whole width of the respective exposure field in slit direction during a single scanningmovement. The selection criterion may be based on an overlay and / or focus related parameter. The selection criterion is for example the error residue between the overlay error related parameter ORP and the overlay correction OCO as shown in Figure 13.

[0280] By using such selection criterion only the exposure fields having deformations that cannot be sufficiently compensated by second order corrections, may be split in multiple partial exposure fields. In this way, a proper balance between overlay and throughput performance can be obtained in the lithographic process.

[0281] Again referring to Figures 14A and 14B, the location of the splitting line between the first partial exposure field EF-1 and the second partial exposure field EF-2 of Figure 14A and 14B does not have to be predetermined in the pattern of the patterning device. There may be continuous features of the pattern running between the partial exposure fields. It may not be required to create a pattern with subfields with a black border between them.

[0282] As discussed above, masking blades of the masking device REMA may be used to adapt the size of the patterned radiation beam PRB. The masking blades may however not provide a perfect separation between the first partial exposure field EF-1 and the second partial exposure field EF-2. In practice, the masking blades may create overlapping half-shadows around the splitting line between the first partial exposure field EF-1 and the second partial exposure field EF-2.

[0283] Figure 16 shows the radiation intensity 1-1 of the first exposure during the first scanning movement and the radiation intensity 1-2 of the second exposure during the second scanning movement in dependence of the position P in slit direction. It is desirable that the combined radiation intensity CI of the first exposure and the second exposure is about 100% over the whole width of the exposure field, i.e. equal to the desired radiation intensity.

[0284] When positioning the masking blades of the masking device during the two or more separate scanning movements, the half-shadows resulting from the masking blades should therefore be taken into account. The positions of the masking blades should be selected such that the combined radiation intensity CI received by the exposure field during the two or more scanning movements is substantially the same over the width of the exposure field in slit direction.

[0285] An advantage of the half-shadows resulting from the masking blade edges is that there is no strict separation between the first and second exposure. The half-shadows may provide a smooth transition between projected patterns of the first exposure and the second exposure, i.e. stitching. This smooth transition may be beneficial for continuous features of the pattern running between the partial exposure fields and take away the need to create a pattern with subfields with a black border between them at the location of the splitting line between the two partial exposure fields.

[0286] In the shown example of Figure 14, the exposure field EXF is split into a first partial exposure field EF-1 and a second partial exposure field EF-2 having an equal width in the slit direction, e.g. the x-direction. In other embodiments, the first partial exposure field EF-1 and the second partial exposure field EF-2 may not have an equal width. For example, the width of the first partial exposure field EF-1and the second partial exposure field EF-2 may be selected such that the error residue in both the first partial exposure field EF-1 and the second partial exposure field EF-2 is the same or substantially the same over the length of the exposure field EXF. In the example of Figure 15, this could result in that the first partial exposure field EF-1 would have a larger width than the second partial exposure field EF-2 in order to obtain the same error residue in the first partial exposure field EF-1 and the second partial exposure field EF-2, assuming that the overlay error related parameter ORP will be substantially the same over the length of the exposure field EXF.

[0287] In other embodiments, in order to further increase the correction potential in slit direction, the exposure field may be split in three or more partial exposure fields having equal or different widths in slit direction, wherein for each of the three or more partial exposure fields a separate scanning movement is carried out to project the patterned radiation beam on the respective part of the exposure field.

[0288] Figure 17A is a schematic representation of a first object 122, 222 (reticle) for use in an embodiment of the second exposure method shown in Figure 11, which selectively uses split fields (using the second object 132, 232 shown in Figure 17B). The first object 122, 222 defines a main pattern 602 to be applied to the plurality of target regions. In this example, the main pattern 602 is shown as comprising an image AB. Figure 17B is a schematic representation of a second object 132, 232 (reticle) for use in an embodiment of the second exposure method shown in Figure 11, which selectively uses split fields (using this second object 132, 232). The second object 132, 232 also defines the same main pattern that has been split into two portions 704a, 704b separated by an absorbing or non-reflective material 706. In this example, a first portion 704a of the main pattern 602 is shown as comprising an image A and a second portion 704b of the main pattern 602 is shown as comprising an image B. An image may be formed on each of the second set of the plurality of target regions (at step 620b) using the second object 132, 232 by using two exposures, each forming an image of a different one of the two portions 704a, 704b of the main pattern 702. Such a split exposure may be used to pattern the second set of target regions, as discussed above with reference to Figures 11 to 16. Such a split exposure allows for a higher order correction to be applied for overlay across the target regions belonging to the second set, especially in a non-scanning direction of the exposure method 600.

[0289] Figure 18 is a schematic plan view representation of a (generally circular) substrate W comprising a plurality of (generally rectangular) target regions or fields 20. Also shown in Figure 18 is that the plurality of target regions comprises a first set of target regions and a second, different set of a target regions. As discussed above, the second set oftarget regions ofthe method 600 shown in Figure 11 may: (i) comprise target regions where a reduced imaging performance can be expected; (ii) be determined according to criterion based that may be based on an overlay and / or a contrast and / or a focus related parameter; and (iii) constitute a minority of the plurality of target regions.

[0290] It may be the case that some regions of a substrate W (for example a lithography wafer) suffer from poorer than average imaging performance. For example, some fields may suffer increased overlayand / or edge placement errors (EPE) and / or some fields may suffer from reduced contrast and / or some fields may suffer from increased defocus. Furthermore, it is possible to predict that some images on the wafer will have a reduced performance or yield. Examples of regions of a wafer W that may suffer from reduced imaging performance include: (a) bonding fingerprints and regions or a wafer stage or clamp that have become contaminated (referred to as chuck spots), which are indicated schematically in Figure 18 by label 708; and (b) edge fields, which are indicated schematically in Figure 18 by label 710.

[0291] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thinfilm magnetic heads, etc.

[0292] Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or mask (or other patterning device). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non-vacuum) conditions.

[0293] 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, where the context allows, is not limited to optical lithography and may be used in other applications, for example imprint lithography.

[0294] Where the context allows, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the 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, acoustical or other forms of propagated signals (e.g. carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. and in doing that may cause actuators or other devices to interact with the physical world.

[0295] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended tobe 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. An exposure apparatus comprising: a main support; a first object support configured to support a first object and movable relative to the main support so that the first object is movable relative to a first illumination region; a second object support configured to support a second object and movable relative to the main support so that the second object is movable relative to the first illumination region; and imaging optics configured to form an image of the first illumination region in a second illumination region; wherein the first object support is movable relative to the second object support and / or the second object support is movable relative to the first object support; wherein the first object support is offset from the second object support in a first direction; and wherein the imaging optics is anamorphic such that a reduction factor of the image in the first direction is greater than a reduction factor of the image in a second direction that is generally perpendicular to the first direction.

2. The exposure apparatus of claim 1 wherein the first object support is movable relative to the second object support and / or the second object support is movable relative to the first object support such that a relative position of the first and second object supports is controllable in 6 degrees of freedom.

3. An exposure apparatus comprising: a main support; a first object support configured to support a first object and movable relative to the main support; and a second object support configured to support a second object and movable relative to the main support; wherein a gap between the first object support and the second object support is sufficiently small that a single object may be partially supported by the first object support and partially supported by the second object support.

4. The exposure apparatus of claim 3 wherein the first object support is movable relative to the second object support and / or the second object support is movable relative to the first object support.

5. The exposure apparatus of claim 3 or claim 4 wherein a gap between the first object support and the second object support in a direction in which the first object support is offset from the second object support is sufficiently small that when a single object is partially supported by the first object support and partially supported by the second object support a central portion of the single object that extends between the first object support and the second object support is subject to no more distortion than: a first side portion of the single object supported by the first object support and / or a second side portion of the single object supported by the second object support.

6. The exposure apparatus of any one of claims 3 to 5 wherein the exposure apparatus comprises a lithographic apparatus, the first object support is configured to support a first reflective reticle, and the second object support is configured to support a second reflective reticle.

7. The exposure apparatus of any preceding claim wherein the first object support defines a first set of protrusions having a first pitch or spacing, distal ends of the first set of protrusions defining a first support plane; the second object support defines a second set of protrusions having a second pitch or spacing, distal ends of the second set of protrusions defining a second support plane; and a gap between the first object support and the second object support in a direction in which the first object support is offset from the second object support is less than the first pitch or spacing and the second pitch or spacing.

8. The exposure apparatus of any preceding claim wherein the first object support and the second object support are provided such that a gap between them in a direction in which the first object support is offset from the second object support is less than 400 pm.

9. The exposure apparatus of any preceding claim wherein the first object support and / or the second object support comprises an electrostatic clamp.

10. The exposure apparatus of any preceding claim comprising a long stroke assembly comprising a first portion that is fixed relative to the main support and a second portion that is movable relative to the first portion and which supports the first object support and the second object support.

11. The exposure apparatus of claim 10 further comprising at least one short stroke assembly comprising a first portion that is fixed relative to second portion of the long stroke assembly and a second portion that is movable relative to the first portion which supports the first object support and / or the second object support.

12. The exposure apparatus of any preceding claim when not dependent either directly or indirectly on claim 1 further comprising imaging optics configured to form an image of a first illumination region in a second illumination region.

13. The exposure apparatus of claim 12 wherein the first object support and second object support are movable relative to the first illumination region and wherein the first object support and the second object support are configured such that a single object may be partially supported by the first object support and partially supported by the second object support such that the imaging optics can form an image of the single object in the second illumination region.

14. The exposure apparatus of any preceding claim when dependent either directly or indirectly on claim 1 or claim 12 wherein a reduction factor of the image in the direction in which the first object support is offset from the second object support is 8 and a reduction factor of the image in a second direction that is generally perpendicular to the first direction is 4.

15. The exposure apparatus of any preceding claim further comprising illumination optics configured to illuminate with radiation a first illumination region through which an object supported by the first object support and / or the second object support can be moved.

16. The exposure apparatus of claim 15 further comprising a radiation source operable to produce the radiation.

17. The exposure apparatus of any preceding claim, wherein a coating is provided conformally over an edge of the first object and / or an edge of the second object, wherein the coating is configured to absorb radiation incident on the edge of the first object and / or the edge of the second object.

18. The exposure apparatus of claim 17, wherein the coating is made of a material having an extinction coefficient of at least 0.03 and a refraction index of at least 0.90.

19. The exposure apparatus of claim 17 or claim 18, wherein the coating is at least partially provided on the first object support and / or the second object support.

20. The exposure apparatus of any preceding claim further comprising a controller operable to carry out the exposure method of any one of claims 21 to 41.

21. An exposure method for forming a pattern on a plurality of target regions of a substrate, the exposure method comprising:providing a first object defining a first portion of the pattern and a second object defining a second portion of the pattern, such that the first object is adjacent to, and generally coplanar with, the second object, the first object offset from the second object in a first direction; and at least one scanning exposure, the or each scanning exposure comprising: moving the first object and the second object in the first direction such that they sequentially scan through a first illumination region while providing radiation to the first illumination region; and capturing radiation scattered by the first and second objects and using it to form an image of the first and second objects in a second illumination region while moving the substrate through the second illumination region such that an image of the first object is formed on a first target region of the substrate and an image of the second object is formed on a second target region of the substrate, the first and second target regions being mutually adjacent.

22. The exposure method of claim 21 wherein the first object and the second object are provided such that a gap between them in the first direction is less than an extent of the first illumination region in the first direction.

23. The exposure method of claim 21 or claim 22 wherein the first object and the second object are provided such that for at least a portion of the or each scanning exposure the first and second objects are both partially disposed in the first illumination region in the first direction.

24. The exposure method of any one of claims 21 to 23 wherein the first object and the second object are provided such that a gap between them in the first direction is less than 400 pm.

25. The exposure method of any one of claims 21 to 24 wherein the method comprises a plurality of scanning exposures and wherein the plurality of scanning exposures are performed as a meander scan.

26. The exposure method of any one of claims 21 to 25 wherein the method comprises a plurality of scanning exposures and wherein the image of the first object formed on a target region of the substrate during one scanning exposure is stitched to the image of the second object formed on that target region of the substrate during another scanning exposure.

27. The exposure method of claim 26 wherein images of the first object and the second object that are stitched are mutually adjacent in the first direction.

28. An exposure method for forming a pattern on each of a plurality or target regions of a substrate, the exposure method comprising: providing a first object defining a first pattern and providing a second object defining a second pattern; forming an image on each of a first set of the plurality of target regions using the first object, wherein the first set of the plurality of target regions have been determined to, or are expected to, have a first imaging performance; and forming an image on each of a second, different set of the plurality of target regions using the second object or a combination of the first object and the second object, wherein the second set of the plurality of target regions have been determined to, or are expected to, have a second imaging performance.

29. The exposure method of claim 28 further comprising: determining the first set of the plurality of target regions and the second, different set of the plurality of target regions, wherein the first and second sets of the plurality of target regions are determined based on a determined or expected imaging performance of each of the plurality of target regions.

30. The exposure method of claim 28 or claim 29 wherein the first set of the plurality of target regions are target regions where a nominal or baseline imaging performance can be expected; and wherein the second set of the plurality of target regions are target regions where a reduced imaging performance can be expected.

31. The exposure method of any one of claims 28 to 30 wherein the first set of target regions constitute a majority of the plurality of target regions and wherein the second set of target regions constitute a minority of the plurality of target regions.

32. The exposure method of any one of claims 28 to 31 wherein forming an image on each of a first set of the plurality of target regions comprises using a standard exposure technique; and wherein forming an image on each of a second set of the plurality of target regions comprises using an advanced imaging technique.

33. The exposure method of any one of claims 28 to 32 wherein providing the first object and providing the second object comprises providing the first object on a first object support and providing the second object on a second object support.

34. The exposure method of any one of claims 28 to 32 wherein: the first object defines a main pattern to be applied to the plurality of target regions; the second object defines a second pattern comprising one or more enhancement or optical proximity correction (OPC) features; and wherein an image is formed on each of the second set of the plurality of target regions using a combination of the first object and the second object.

35. The exposure method of claim 34 wherein an image of the first pattern formed on each of the second set of target regions is formed with a lower dose of radiation than an image of the first pattern formed on each of the first set of target regions.

36. The exposure method of any one of claims 28 to 32 wherein: the first object defines a main pattern to be applied to the plurality of target regions; the second object defines the same main pattern that has been split into at least two portions separated by an absorbing or non-reflective material; and wherein an image is formed on each of the second set of the plurality of target regions using the second object using a plurality of exposures, each one of the plurality of exposures forming an image of a different one of the at least two portions of the main pattern.

37. The exposure method of claim 36 wherein: the image of the main pattern and the images of the at least two portions of the main pattern are formed as scanning exposures by: scanning the first object or the second object through a radiation beam so as to pattern the radiation beam; and simultaneously scanning the substrate such that an aerial image of the first or second object is stationary with respect to the substrate; and wherein the at least two portions of the main pattern are separated in a direction that is perpendicular to the scanning direction.

38. The exposure method of claim 36 or claim 37 wherein, for each of the plurality of exposures of each target region belonging to the second set, an aerial image of the portion of the main pattern being imaged is adjusted in dependence of a deformation of a portion of that target region that is being exposed.

39. The exposure method of any one of claims 36 to 38 wherein for each of the plurality of exposures of each target region belonging to the second set, radiation used for the exposure(s) is controlled such that the portion(s) of the main pattern not being imaged are not illuminated by radiation.

40. The exposure method of claim 39 wherein controlling the radiation such that the portion(s) of the main pattern not being imaged are not illuminated by radiation comprises adjusting a position of one or more masking blades of a masking device to reduce an extent of an illumination region.

41. The exposure method of claim 39 wherein controlling the radiation such that the portion(s) of the main pattern not being imaged are not illuminated by radiation comprises adjusting a configuration of a MEMS illuminator.

Images