Lithographic apparatus and method for detecting a radiation beam

Abstract

A substrate table configured to hold a substrate, comprising: a plurality of sensor elements configured to detect a radiation beam from a projection system, the radiation beam forming an illumination area having an elongated shape at substrate level, the elongated shape having a long edge and a short edge and defining a longitudinal direction and a transverse direction perpendicular to the longitudinal direction, the sensor elements being arranged along the longitudinal direction, wherein the plurality of sensor elements are arranged at different distances from one of the long edges of the elongated shape in the transverse direction.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP application 19202357.0, filed on October 10, 2019, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to a lithographic apparatus and a method of detecting a radiation beam in a lithographic apparatus. Background Art

[0004] Lithographic equipment is a machine that applies a desired pattern to a substrate (usually applied to a target portion of a substrate). Lithographic equipment can be used in the manufacture of, for example, integrated circuits (ICs). In this example, a pattern forming device (alternatively referred to as a mask or reticle) can be used to generate a circuit pattern to be formed on a single layer of the IC. The pattern can be transferred to a target portion (e.g., comprising a portion of a die, one or more dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is typically via imaging onto a radiation-sensitive material (resist) layer provided on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are continuously patterned.

[0005] Photolithography is widely recognized as one of the key steps in the manufacture of ICs and other devices and / or structures. However, as the feature sizes manufactured using photolithography become smaller, photolithography is becoming a more critical factor in enabling the manufacture of miniature ICs and other devices and / or structures.

[0006] A theoretical estimate of the pattern printing limit can be given by the Rayleigh criterion for resolution shown in equation (1):

[0007]

[0008] where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection system used to print the pattern, k1 is a process-dependent adjustment factor also known as the Rayleigh constant, and CD is the characteristic size (or critical dimension) of the printed feature. From equation (1), it can be inferred that a reduction in the minimum printable size of the feature can be obtained in three ways: by shortening the exposure wavelength λ, by increasing the numerical aperture NA, or by reducing the value of k1.

[0009] In order to shorten the exposure wavelength and thus reduce the minimum printable size, it has been proposed to use a deep ultraviolet (DUV) radiation source or an extreme ultraviolet (EUV) radiation source. EUV radiation is electromagnetic radiation with a wavelength in the range of 10 to 20 nm, for example in the range of 13 to 14 nm. It has also been proposed that EUV radiation with a wavelength of less than 10 nm can be used, for example in the range of 5 to 10 nm, such as 6.7 nm or 6.8 nm. Such radiation is known as extreme ultraviolet radiation or soft x-ray radiation. Possible sources include, for example, laser-generated plasma sources, discharge plasma sources or sources based on synchrotron radiation provided by electron storage rings.

[0010] EUV radiation can be generated using a plasma. A radiation system for generating EUV radiation may include a laser for exciting a fuel to provide a plasma and a source collector module for containing the plasma. For example, a plasma can be created by directing a laser beam with a fuel, such as particles of a suitable material (e.g., tin) or a stream of a suitable gas or vapor (such as xenon or lithium vapor). The resulting plasma emits output radiation, such as EUV radiation, which is collected using a radiation collector. The radiation collector may be a mirrored normal incidence radiation collector that receives radiation and focuses the radiation into a beam. The source collector module may include an enclosed structure or chamber arranged to provide a vacuum environment to support the plasma. Such a radiation system is generally referred to as a laser produced plasma (LPP) source.

[0011] A sensor may be provided for detecting characteristics of the radiation beam. The radiation beam may be a patterned radiation beam, i.e., a radiation beam having a pattern imparted by a patterning device. For example, the difference between a measured radiation beam and a nominal (e.g., ideal) radiation beam may be measured. This may allow for the possibility of compensating for the difference.

[0012] In order to measure how the patterned radiation beam varies over the illuminated area at substrate level, it may be necessary to perform multiple measurements. Performing multiple measurements increases the measurement time.

[0013] It is desirable to provide a substrate apparatus and method of detecting a radiation beam that may allow the overall measurement time to be reduced. Summary of the Invention

[0014] According to one aspect of the present invention, there is provided a lithographic apparatus comprising: a substrate table configured to hold a substrate; and a projection system configured to project a radiation beam to form an illumination area having an elongated shape at substrate level, the elongated shape having a long edge and a short edge and defining a longitudinal direction and a lateral direction perpendicular to the longitudinal direction; wherein the substrate table comprises a plurality of sensor elements configured to detect the radiation beam, the sensor elements being arranged along the longitudinal direction, wherein the plurality of sensor elements are arranged at different distances from one of the long edges of the elongated shape in the lateral direction.

[0015] According to one aspect of the present invention, a method for detecting a radiation beam in a lithography device is provided, the method comprising: providing a projection radiation beam; projecting the projection beam to form an irradiation area having an elongated shape at a substrate level, the elongated shape having a long edge and a short edge and defining a longitudinal direction and a lateral direction perpendicular to the longitudinal direction; detecting the radiation beam at the substrate level using a plurality of sensor elements, the sensor elements being arranged along the longitudinal direction, wherein the plurality of sensor elements are arranged at different distances from one of the long edges of the elongated shape in the lateral direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which corresponding reference characters indicate corresponding parts, and in which:

[0017] Figure 1 depicts a lithographic apparatus according to an embodiment of the present invention;

[0018] Figure 2 is a more detailed view of the lithography equipment;

[0019] Figure 3 yes Figure 1 and 2 A more detailed view of the source collector module SO of the device;

[0020] Figure 4 is a schematic diagram of a radiation sensor;

[0021] Figure 5 is a schematic diagram of the irradiation area on the substrate;

[0022] Figure 6 is a close-up view of the irradiated area;

[0023] Figure 7 is a schematic diagram of an arrangement of sensor elements according to an embodiment of the present invention;

[0024] Figure 8 is a schematic diagram of an alternative arrangement of sensor elements according to an embodiment of the present invention;

[0025] Figure 9 is a schematic diagram of an arrangement of sensor elements according to a comparative example; and

[0026] Figure 10 is a graph illustrating the relationship between the lateral position of an illuminated area and the intensity of a patterned radiation beam.

[0027] The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the accompanying drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. DETAILED DESCRIPTION

[0028] Figure 1 A lithographic apparatus 100 including a source collector module SO according to an embodiment of the present invention is schematically depicted. The apparatus comprises an illumination system (also referred to as illuminator) IL configured to condition a radiation beam B (e.g., EUV radiation); a support structure (e.g., mask table) MT configured to support a patterning device (e.g., a mask or reticle) MA and connected to a first positioner PM (configured to accurately position the patterning device); a substrate table (e.g., wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW (configured to accurately position the substrate); and a projection system (e.g., refractive projection system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0029] The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping or controlling the radiation.

[0030] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions such as, for example, whether the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device. The support structure can be a frame or a table, for example, which can be fixed or movable as desired. The support structure can ensure that the patterning device is located at a desired position, for example relative to the projection system.

[0031] The term "patterning device" should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section, such as to create a pattern in a target portion of a substrate. The pattern imparted to the radiation beam can correspond to a specific functional layer in a device (such as an integrated circuit) created in the target portion.

[0032] The patterning device can be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam that is reflected by the mirror array.

[0033] As with the illumination system, the projection system can include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, as appropriate for the exposure radiation used or other factors, such as the use of a vacuum. It may be desirable to use a vacuum for EUV radiation because other gases may absorb too much radiation. Therefore, a vacuum environment can be provided to the entire optical path with the aid of vacuum walls and vacuum pumps.

[0034] As depicted here, the device is reflective (eg, employing a reflective mask).

[0035] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and / or two or more mask tables). In such a "multi-stage" machine, the additional tables may be used in parallel, or preparatory steps may be performed on one or more tables while one or more other tables are being used for exposure.

[0036] Reference Figure 1 , the illuminator IL receives a beam of extreme ultraviolet radiation from a source collector module SO. Methods of generating EUV light include, but are not necessarily limited to, converting a material into a plasma state having at least one element (e.g., xenon, lithium, or tin) having one or more emission lines in the EUV range. In one such method, often referred to as laser produced plasma ("LPP"), the desired plasma can be generated by irradiating a fuel (such as a droplet, stream, or cluster of material having the desired line-emitting element) with a laser beam. The source collector module SO can be part of an EUV radiation system that includes a device not provided in the EUV radiation system. Figure 1 The laser shown in FIG. 1 is used to provide a laser beam for excitation of the fuel. The resulting plasma emits output radiation, such as EUV radiation, which is collected using a radiation collector disposed in a source collector module. The laser and source collector module can be separate entities, such as when a CO2 laser is used to provide the laser beam for fuel excitation.

[0037] In this case, the laser is not considered to form part of the lithographic apparatus, and the radiation beam is passed from the laser to the source collector module with the aid of a beam delivery system comprising, for example, suitable guide mirrors and / or a beam expander. In other cases, the source may be an integrated part of the source collector module, for example when the source is a discharge produced plasma EUV generator, often referred to as a DPP source.

[0038] The illuminator IL may include an adjuster for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer and / or inner radial extent of the intensity distribution in a pupil plane of the illuminator (commonly referred to as σouter and σinner, respectively) may be adjusted. In addition, the illuminator IL may include various other components, such as a facet field and pupil mirror arrangement. The illuminator may be used to condition the radiation beam to have a desired uniformity and intensity distribution in its cross-section.

[0039] A radiation beam B is incident on a patterning device (e.g., mask) MA, which is held on a support structure (e.g., mask table) MT, and is patterned by the patterning device. After reflection from the patterning device (e.g., mask) MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor PS2 (e.g., an interferometer device, a linear encoder, or a capacitive sensor), the substrate table WT can be accurately moved, for example, to position a different target portion C in the path of the radiation beam B. Similarly, a first positioner PM and a further position sensor PS1 can be used to accurately position the patterning device (e.g., mask) MA relative to the path of the radiation beam B. The patterning device (e.g., mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0040] The depicted device can be used in at least one of the following modes:

[0041] 1. In step mode, the support structure (e.g. mask table) MT and substrate table WT are held substantially stationary while the entire pattern imparted to the radiation beam is projected at one time (i.e. a single static exposure) onto a target portion C. The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed.

[0042] 2. In scan mode, the support structure (e.g., mask table) MT and substrate table WT are scanned synchronously as a pattern imparted to the radiation beam is projected onto a target portion C (i.e., a single dynamic exposure). The speed and direction of the substrate table WT relative to the support structure (e.g., mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0043] 3. In another mode, the support structure (e.g., mask table) MT remains essentially stationary, thereby holding the programmable patterning device, and the substrate table WT is moved or scanned, while a pattern imparted to the radiation beam is projected onto the target portion C. In this mode, typically a pulsed radiation source is employed, and the programmable patterning device is updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation can readily be applied to maskless lithography, which utilizes a programmable patterning device (such as a programmable mirror array of the type referenced above).

[0044] Combinations and / or variations on the above-described modes of use or entirely different modes of use may also be employed.

[0045] Figure 2 The apparatus 100 is shown in more detail and comprises a source collector module SO, an illumination system IL and a projection system PS. The source collector module SO is constructed and arranged so that a vacuum environment can be maintained in an enclosed structure 220 of the source collector module SO. The EUV radiation emitting plasma 210 can be formed by a plasma source produced by a discharge. EUV radiation can be generated by a gas or vapor, such as xenon, lithium vapor or tin vapor, wherein a very hot plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The very hot plasma 210 is formed by, for example, a discharge that causes a plasma that is at least partially ionized. In order to effectively generate radiation, a partial pressure of, for example, 10 Pa of Xe, Li, Sn vapor or any other suitable gas or vapor may be required. In an embodiment, a plasma that excites tin (Sn) is provided to generate EUV radiation.

[0046] Radiation emitted by the hot plasma 210 is transferred from the source chamber 211 to the collector chamber 212 via an optional gas barrier or contaminant trap 230 (also referred to in some cases as a contaminant barrier or fin trap) positioned in or behind an opening in the source chamber 211. The contaminant trap 230 may include a channel structure. The contaminant trap 230 may also include a gas barrier or a combination of a gas barrier and a channel structure. As is known in the art, the contaminant trap or contaminant barrier 230, further indicated herein, includes at least a channel structure.

[0047] The collector chamber 211 may include a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation traversing the collector CO may be reflected from the grating spectral filter 240 to be focused in a virtual source point IF. The virtual source point IF is generally referred to as an intermediate focus, and the source collector module is arranged such that the intermediate focus IF is located at or near an opening 221 in the enclosure 220. The virtual source point IF is an image of the radiation-emitting plasma 210.

[0048] The radiation then traverses illumination system IL, which may include a faceted field mirror arrangement 22 and a faceted pupil mirror arrangement 24, which are arranged to provide a desired angular distribution of radiation beam 21 at patterning device MA, and a desired uniformity of radiation intensity at patterning device MA. Upon reflection of radiation beam 21 at patterning device MA, held by support structure MT, a patterned radiation beam 26 is formed, and patterned radiation beam 26 is imaged by projection system PS via reflective elements 28, 30 onto a substrate W held by the wafer stage of substrate table WT.

[0049] More elements than shown may typically be present in the illumination optics unit IL and the projection system PS. Depending on the type of lithographic apparatus, a grating spectral filter 240 may optionally be present. Further, there may be more mirrors than shown in the figures, for example with Figure 2 Compared to what is shown, there may be 1 to 6 additional reflective elements in the projection system PS.

[0050] like Figure 2 As illustrated, the collector optics CO is depicted as a nested collector with grazing incidence reflectors 253, 254 and 255, merely as an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254 and 255 are arranged axially symmetrically around the optical axis O, and preferably, this type of collector optics CO is used in combination with a discharge produced plasma source, commonly referred to as a DPP source.

[0051] Alternatively, the source collector module SO can be Figure 3 Part of an LPP radiation system is shown. Laser LA is arranged to deposit laser energy into a fuel such as xenon (Xe), tin (Sn), or lithium (Li), thereby creating a highly ionized plasma 210 with an electron temperature of tens of eV. Energetic radiation generated during the deexcitation and recombination of these ions is emitted from the plasma, collected by collector optics CO at near normal incidence, and focused onto an opening 221 in an enclosure structure 220.

[0052] Figure 4is a schematic diagram of a radiation sensor 10 of a lithographic apparatus 100 . Figure 4 There is shown a substrate table WT of the lithographic apparatus 100. The substrate table WT is configured to hold a substrate W.

[0053] like Figure 1 and 2 As shown, the lithographic apparatus 100 comprises a projection system PS. The projection system PS is configured to project a radiation beam B to form an illumination area 11 (eg, Figure 5 shown).

[0054] like Figure 4 As shown, in an embodiment the substrate table WT comprises a radiation sensor 10. The radiation sensor 10 is configured to detect a radiation beam B. The radiation sensor 10 is configured to detect characteristics of the radiation beam B at substrate level.

[0055] For example, in an embodiment, the radiation sensor 10 is configured to measure how the intensity of the radiation beam B varies across the illumination area 11. In an embodiment, the radiation sensor 10 is configured to measure the wavefront of the radiation beam B at the substrate level. For example, the radiation sensor 10 can be configured to measure Zernike aberrations. In an embodiment, the radiation sensor 10 is configured to measure high-order Zernike aberrations and / or low-order Zernike aberrations.

[0056] As mentioned above, the radiation beam B may be EUV radiation. Figure 1 and 2 As shown, the patterning device MA held by the support structure MT may be configured to reflect the radiation beam B. Alternatively, the radiation beam B conditioned by the illumination system IL may be DUV (deep ultraviolet) radiation. Figure 4 As shown, in an embodiment, the patterning device MA is transmissive. The patterning device MA is configured to transmit the radiation beam B while imparting a pattern to the radiation beam B. The present invention is applicable to the lithographic apparatus 100 regardless of whether it uses EUV radiation or DUV radiation. The present invention is compatible with either a transmissive patterning device MA or a reflective patterning device MA.

[0057] As mentioned above, the projection system PS is configured to project a radiation beam B to form an illumination area 11 at substrate level. The illumination area 11 has an elongated shape. Figure 5 is a schematic diagram of the irradiation area 11 relative to the substrate W. In an embodiment, the shape of the radiation sensor 10 in a plan view substantially matches the shape of the irradiation area 11. Figure 5 As shown, in the embodiment shown, the illuminated area 11 has a long edge 12 and a short edge 13. The illuminated area 11 defines a longitudinal direction 15 and a transverse direction 16 perpendicular to the longitudinal direction.

[0058] Figure 6 yes Figure 5A close-up view of the illuminated area 11 is shown. Figure 6 , longitudinal direction 15 and transverse direction 16 are shown. In an embodiment, irradiation area 11 has a curved shape. When irradiation area 11 has a curved shape, transverse direction 16 at one point along the elongated shape may not be parallel to the transverse direction at another point along the elongated shape. Longitudinal direction 15 follows a curve. Figure 6 Also shown is a center line 14 along the middle of the illuminated area 11. The center line 14 is formed by the locus of midpoints between the long edges 12 in the transverse direction 16.

[0059] The radiation sensor 10 is configured to measure how the radiation beam B varies along the length of the illumination area 11. The radiation sensor 10 comprises a plurality of sensor elements 17 configured to detect the radiation beam B. The sensor elements 17 are arranged along the longitudinal direction 15. This allows the sensor elements 17 of the radiation sensor 10 to measure how the radiation beam B varies along the illumination area 11.

[0060] The sensor elements may be arranged to follow the centre line 14 or one of the long edges 12 of the illumination area 11. When the illumination area has a curved elongated shape, then the sensor elements may be arranged to follow the same curve.

[0061] like Figure 5 and 6 As shown, in an embodiment the elongated shape is curved. In an alternative embodiment, the projection system PS is configured to project the radiation beam B to form an illumination area 11 having an elongated rectangular shape. For example, when the radiation beam B is DUV radiation, a rectangular illumination area 11 may be provided.

[0062] Figure 7 is a schematic diagram showing the arrangement of the sensor elements 17 of the radiation sensor 10 according to the present invention, Figure 7 It is also shown how the arrangement of the elements 17 compares to a comparative example. Figure 7 , comparison point 27 shows the position of the sensor element according to the comparative example. In the comparative example, the sensor elements are arranged to closely follow the curve of the elongated shape of the illumination area 11.

[0063] like Figure 7 As shown, in the embodiment, the plurality of sensor elements 17 are arranged at different distances from one of the long edges 12 of the elongated shape of the irradiation area 11 in the lateral direction 16. The plurality of sensor elements 17 are offset (in the lateral direction) from the positions shown in the comparative example. Figure 7 In FIG. 1 , arrows 18 show how the position of each sensor element 17 changes relative to comparison point 27 .

[0064] Embodiments of the present invention are expected to reduce the time spent measuring how the radiation beam B varies across the illumination area 11. It is desirable to measure how the radiation beam B varies along a transverse direction 16 (i.e., in the width direction) of the illumination area 11. This requires measurements to be taken at a plurality of different positions along the transverse direction 16. By providing sensor elements 17 at different transverse positions, the radiation beam B is measured at the different transverse positions simultaneously. Conversely, Figure 7 The comparative example shown would require more measurements, wherein the entire radiation sensor 10 is displaced in a lateral direction relative to the illumination area 11. A greater number of measurements would take longer.

[0065] It is desirable to measure the decay of the radiation beam B. The decay of the radiation beam B is related to how the radiation beam varies (e.g. in intensity or other characteristics) along a lateral direction of the illumination area 11. Figure 7 In the layout shown in the comparative example in , fading measurements require two or more scans at different lateral positions in the illumination area 11. This results in a loss of throughput. It is contemplated that embodiments of the present invention capture fading with a smaller number of measurements (e.g., using only a single scan).

[0066] like Figure 7 As shown, in the embodiment, at least one of the sensor elements 17 is offset in the transverse direction 16 towards the concave side of the elongated shape. Figure 7 In the embodiment shown, the first sensor element 17, the fourth sensor element 17 and the seventh sensor element 17 (in Figure 7 This is indicated by the downward arrow 18. Figure 7 As shown, in the embodiment, at least one of the sensor elements 17 is offset in the transverse direction 16 towards the convex side of the elongated shape. Figure 7 In the embodiment shown, the second sensor element 17, the third sensor element 17, the fifth sensor element 17 and the seventh sensor element 17 (in Figure 7 from left to right in the middle) is offset towards the convex side. This is caused by Figure 7 The offset is relative to a comparative example which follows the center line 14 of the irradiation area 11 .

[0067] By providing offsets towards the concave and convex sides, a single scan includes measurements from at least three lateral positions in the illumination area 11 .

[0068] exist Figure 7In the example shown, measurements are made at two different transverse positions. The second, third, fifth, and sixth sensor elements 17, 17 correspond to the first transverse position. The first, fourth, and seventh sensor elements 17, 17 correspond to the second transverse position. Rather than measuring seven different longitudinal positions at a single transverse position, at least one measurement is made at multiple different transverse positions. In an embodiment, at least one sensor element 17 is not offset. This allows for simultaneous measurement of three different transverse positions.

[0069] The measurement values ​​corresponding to different sensor elements 17 may be interpolated in order to provide information about variations of the radiation beam B in the longitudinal and transverse directions of the illumination shape 11 .

[0070] Figure 8 The arrangement of sensor elements 17 of radiation sensor 10 is shown. Figure 8 The arrangement shown is Figure 7 Alternative to the arrangement shown. Figure 8 Also shown is a comparison point 27 which illustrates the arrangement of the sensor elements in a comparative example.

[0071] Figure 7 and 8 The arrangements shown differ from each other in that Figure 7 The arrangement shown is symmetrical, and Figure 8 The arrangement shown is sparse or asymmetric. Figure 7 As shown, in the exemplary embodiment, the sensor elements 17 are arranged symmetrically about an axis of symmetry extending in the transverse direction 16. Figure 7 In the example shown, the axis of symmetry cuts through the central (fourth) sensor element 17 in the transverse direction, as shown in FIG. Figure 7 shown.

[0072] Alternatively, as Figure 8 As shown, in the embodiment, the sensor elements 17 are arranged asymmetrically around an axis extending in the transverse direction along half of the sensor element 17 in the longitudinal direction. For example, the third sensor element 17 is offset toward the convex side, while the fifth sensor element 17 is not offset.

[0073] Figure 7 and 8 The arrangement shown is an example of how the sensor elements 17 may be arranged. However, other arrangements are possible while providing the advantage of measuring the radiation beam B at multiple lateral positions simultaneously.

[0074] In an embodiment, the sensor elements 17 are arranged in a zigzag pattern. For example, when the elongated shape is a rectangle, the sensor elements 17 may be arranged in a simple zigzag pattern in order to perform measurements at two different lateral positions simultaneously.

[0075] Figure 9 The radiation sensor 10 is shown with comparison points 27 corresponding to the sensor elements. Figure 9 The comparative example shown may be a sensor for an illumination area 11 having a rectangular shape. The sensor elements are all located at the same lateral position. This makes it necessary to perform multiple measurements to measure multiple lateral positions.

[0076] In contrast, providing sensor elements 17 arranged in a zigzag pattern allows multiple lateral positions to be measured simultaneously.

[0077] In an embodiment, the central sensor element 17 is either not offset or offset towards the concave side. In an embodiment, one of the plurality of sensor elements 17 positioned centrally in the longitudinal direction is offset further from the one of the long edges 12 in the transverse direction along the concave side of the elongated shape than another sensor element 17 of the plurality of sensor elements 17. Figure 7 Shown towards the concave side (at Figure 7 The central sensor element 17 is deflected downwards. Figure 8 The central sensor element 17 is shown without offset. By providing the central sensor element 17 with no offset or an offset towards the concave side, the lateral extent of the sensor element 17 (at Figure 7 and 8 It is expected that embodiments of the present invention will reduce the lateral extent of the radiation sensor 10.

[0078] However, in alternative embodiments, the central sensor element 17 may be offset towards the convex side.

[0079] As mentioned above, in an embodiment, the lithographic apparatus comprises an illuminator IL. The illuminator IL is configured to provide a projection radiation beam. In an embodiment, the illuminator IL is configured to provide the radiation beam B such that its intensity varies nominally trapezoidally in a lateral direction 16 of the elongated shape. Figure 10 is a graph showing the relationship between lateral position and radiation beam intensity. The x-axis corresponds to the position of the irradiated area 11 along the lateral direction 16. The y-axis represents the intensity of the radiation beam B. The lateral position of the long edge 12 of the elongated shape is as follows: Figure 10 shown. Figure 10 The trapezoidal shape of the radiation beam B is shown.

[0080] Figure 10An intensity plateau 18 is shown for the radiation beam B in the lateral direction 16. A central region 19 of the illumination area 11 corresponds to the intensity plateau 18. In an embodiment, the sensor elements 17 are arranged so that they are all arranged in a trapezoidal nominal intensity plateau 18. It is contemplated that embodiments of the present invention simultaneously improve the accuracy of measurements made at different lateral positions.

[0081] Of course, radiation beam B may not have a perfect trapezoidal shape in the lateral direction. In an embodiment, radiation beam B has a Gaussian distribution in the lateral direction. Radiation beam B may have a target shape corresponding to a nominal trapezoidal shape. Deviations from the nominal trapezoidal shape may be detected by measurements taken by radiation sensor 10. Lithographic apparatus 100 may be adjusted to compensate for the deviations from the nominal shape of radiation beam B. For example, the position and / or orientation of optical elements may be adjusted based on measurements taken by radiation sensor 10. In an embodiment, projection system PS is configured to correct for wavefront aberrations measured by radiation sensor 10.

[0082] It is not necessary that the radiation beam B has a trapezoidal shape in the transverse direction. Some other shapes of beams are also possible. In an embodiment, the radiation beam B has an intensity plateau in the transverse direction.

[0083] exist Figure 7 and Figure 8 In the example shown, some sensor elements 17 are offset in one direction, while other sensor elements 17 are offset in the opposite direction. In an embodiment, the offset is the same for all sensor elements 17 that are offset. Figure 7 In the example shown, all sensor elements except the central sensor element 17 are offset. In an embodiment, the offset size of each of the offset sensor elements 17 is the same. In other words, the distance between the sensor element 17 and the comparison point 27 is the same for the first sensor element 17, the second sensor element 17, the third sensor element 17, the fifth sensor element 17, the sixth sensor element 17, and the seventh sensor element 17.

[0084] exist Figure 8In the example shown, each of the first, second, third, fourth, sixth, and seventh sensor elements 17, ...

[0085] like Figure 7 and Figure 8 As shown, in the embodiment, the sensor elements 17 are evenly spaced along the longitudinal direction 15. It is expected that embodiments of the present invention achieve better fitting quality and / or reduce sensitivity to sensor noise. However, this is not necessarily the case. The sensor elements 17 can be spaced at different intervals along the longitudinal direction.

[0086] In an embodiment, radiation sensor 10 includes an imaging device. The imaging device can be, for example, a charge-coupled device (CCD). A single imaging device can be used for multiple sensor elements 17. Sensor elements 17 correspond to different locations that can be measured simultaneously. In an embodiment, radiation sensor 10 includes one or more gratings. In an embodiment, each sensor element 17 corresponds to a separate grating. In an embodiment, each sensor element corresponds to a separate opening in the cover of radiation sensor 10. Each opening allows radiation beam B to reach the grating and subsequently reach the imaging device.

[0087] Although specific reference may be made herein to the use of lithographic apparatus in the manufacture of ICs, it will be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like. Those skilled in the art will appreciate that in the context of such alternative applications, any use of the terms "wafer" or "die" herein may be considered synonymous with the more general terms "substrate" or "target portion," respectively. The substrates referenced herein may be processed before or after exposure, for example in a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where applicable, the present disclosure herein may be applied to such and other substrate processing tools. Further, a substrate may be processed more than once, for example to create a multi-layer IC, such that the term substrate as used herein may also refer to a substrate that already contains multiple processed layers.

[0088] The term "lens," where the context permits, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components.

[0089] Although specific embodiments of the present invention have been described above, it will be appreciated that the present invention may be practiced in other ways than those described. For example, the arrangement of the sensor element 17 may be different from that described. Figure 7 and 8 Different as shown.

[0090] Item:

[0091] Item 1. A lithographic device comprising: a substrate table configured to hold a substrate; and a projection system configured to project a radiation beam to form an irradiation area having an elongated shape at the substrate level, the elongated shape having a long edge and a short edge and defining a longitudinal direction and a lateral direction perpendicular to the longitudinal direction; the substrate table comprising a plurality of sensor elements configured to detect the radiation beam, the sensor elements being arranged along the longitudinal direction, the plurality of sensor elements being arranged at different distances from one of the long edges of the elongated shape in the lateral direction.

[0092] Clause 2. The lithographic apparatus of clause 1 , wherein the elongated shape is rectangular.

[0093] Clause 3. The lithographic apparatus of clause 1, wherein the elongated shape is curved.

[0094] Clause 4. The lithographic apparatus of clause 3, wherein one of the sensor elements centrally located along the longitudinal direction is offset in a lateral direction from the one of the long edges more towards the concave side of the elongated shape than another of the sensor elements.

[0095] Clause 5. A lithographic apparatus according to clause 3 or 4, wherein at least one of the sensor elements is offset in a lateral direction towards a concave side of the elongated shape, and at least one of the sensor elements is offset in a lateral direction from said one of the long edges of the elongated shape towards a convex side.

[0096] Clause 6. The lithographic apparatus of any preceding clause, wherein at least one of the sensor elements is offset in a lateral direction differently than another of the sensor elements relative to a locus of midpoints between the long edges of the elongated shape.

[0097] Clause 7. The lithographic apparatus of any preceding clause, wherein the sensor elements are arranged in a zigzag pattern.

[0098] Clause 8. The lithographic apparatus of any preceding clause, wherein the sensor elements are arranged asymmetrically about an axis extending in the transverse direction along half of the sensor elements in the longitudinal direction.

[0099] Clause 9. The lithographic apparatus of any one of Clauses 1 to 7, wherein the sensor elements are arranged symmetrically about an axis of symmetry, the axis of symmetry extending in a lateral direction.

[0100] Clause 10. The lithographic apparatus of any preceding clause, wherein each of the sensor elements is offset by substantially the same amount, each sensor element being offset in a lateral direction from the one of the long edges of the elongated shape.

[0101] Clause 11. The lithographic apparatus of any preceding clause, wherein the sensor elements are equidistant along the longitudinal direction.

[0102] Clause 12. The lithographic apparatus of any preceding clause, comprising: an illuminator configured to provide a projection radiation beam, wherein the projection beam is a radiation beam projected by the projection system.

[0103] Clause 13. The lithographic apparatus of clause 12, wherein the illuminator is configured to provide the projection beam such that its intensity varies nominally trapezoidally in a lateral direction of the elongated shape.

[0104] Clause 14. The lithographic apparatus of clause 13, wherein the sensor elements are arranged such that they are all arranged within a trapezoidal nominal intensity plateau.

[0105] Clause 15. The lithographic apparatus of any preceding clause, comprising: a support structure configured to support a patterning device that patterns a radiation beam according to a desired pattern, wherein the patterned beam is a radiation beam projected by the projection system.

[0106] Clause 16. A substrate table of a lithographic apparatus according to any preceding clause.

[0107] Item 17. A method for detecting a radiation beam in a lithographic device, the method comprising: providing a projection radiation beam; projecting the projection beam to form an irradiation area having an elongated shape at a substrate level, the elongated shape having a long edge and a short edge and defining a longitudinal direction and a lateral direction perpendicular to the longitudinal direction; detecting the radiation beam at the substrate level using a plurality of sensor elements, the sensor elements being arranged along the longitudinal direction, wherein the plurality of sensor elements are arranged at different distances from one of the long edges of the elongated shape in the lateral direction.

Claims

1. A substrate stage configured to hold a substrate, the substrate stage comprising: a plurality of sensor elements configured to detect a radiation beam coming from a projection system, the radiation beam forming an illumination area having an elongated shape at the level of the substrate, the elongated shape having a long edge and a short edge and defining a longitudinal direction and a transverse direction perpendicular to the longitudinal direction, the sensor elements being arranged along the longitudinal direction, wherein said plurality of said sensor elements are arranged at different distances from one of said long edges of said elongated shape in said transverse direction; wherein at least one of the sensor elements is offset in the lateral direction from the one of the long edges of the elongated shape toward a first side, and at least one of the sensor elements is offset in the lateral direction from the one of the long edges of the elongated shape toward a second side, the second side and the first side being opposite sides of the one of the long edges.

2. The substrate table according to claim 1, wherein the elongated shape is rectangular or curved. The substrate table according to claim 1 , wherein the elongated shape is curved.

4. A substrate table according to claim 3, wherein one of the sensor elements positioned centrally along the longitudinal direction is offset more from the one of the long edges towards the concave side of the elongated shape in the transverse direction than another of the sensor elements.

5. A substrate table according to claim 3 or 4, wherein at least one of the sensor elements is offset in the lateral direction toward a concave side of the one of the long edges of the slender shape, and at least one of the sensor elements is offset in the lateral direction toward a convex side of the one of the long edges of the slender shape.

6. A substrate table according to any of the preceding claims, wherein at least one of the sensor elements is offset in the lateral direction differently than another of the sensor elements relative to a locus of midpoints between the long edges of the elongated shape.

7. A substrate table according to any of the preceding claims, wherein the sensor elements are arranged in a zigzag pattern and / or wherein the sensor elements are arranged asymmetrically around an axis, the axis extending in the transverse direction along a middle position of the sensor elements in the longitudinal direction.

8. The substrate table according to any one of claims 1 to 6, wherein the sensor elements are arranged symmetrically around an axis of symmetry, the axis of symmetry extending in the lateral direction.

9. A substrate table according to any preceding claim, wherein each of the sensor elements is offset by substantially the same amount, each sensor element being offset in the lateral direction from the one of the long edges of the elongated shape.

10. A substrate table according to any preceding claim, wherein the sensor elements are equispaced along the longitudinal direction.

11. A lithographic apparatus comprising a substrate table according to any preceding claim.

12. The lithographic apparatus according to claim 11, comprising: an illuminator configured to provide a projection radiation beam, wherein the projection radiation beam is the radiation beam projected by the projection system.

13. The lithographic apparatus of claim 12, wherein the illuminator is configured to provide the projection radiation beam such that its intensity varies nominally trapezoidally in the lateral direction of the elongated shape.

14. The lithographic apparatus of claim 13, wherein the sensor elements are arranged such that they are all arranged within the nominal intensity plateau of the trapezoid.

15. A method of detecting a radiation beam in a lithographic apparatus, the method comprising: providing a projected radiation beam; projecting the projection radiation beam to form an illumination area having an elongated shape at substrate level, the elongated shape having long and short edges and defining a longitudinal direction and a lateral direction perpendicular to the longitudinal direction; detecting the radiation beam at the substrate level with a plurality of sensor elements, the sensor elements being arranged along the longitudinal direction, wherein a plurality of said sensor elements are arranged at different distances from one of said long edges of said elongated shape in said transverse direction; wherein at least one of the sensor elements is offset in the lateral direction from the one of the long edges of the elongated shape toward a first side, and at least one of the sensor elements is offset in the lateral direction from the one of the long edges of the elongated shape toward a second side, the second side and the first side being opposite sides of the one of the long edges.

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