Fixed parallel alignment sensors in combination with fast scanning

Abstract

An alignment system includes a substrate stage, a plurality of sensors, and a control system. The substrate stage supports and moves a substrate having a plurality of substrate alignment marks disposed thereon. The plurality of sensors are arranged on a frame. The control system scans the substrate stage with respect to the frame. The control system controls movement of the substrate stage to correct for any misalignment or pitch mismatch between the plurality of sensors and the plurality of substrate alignment marks based on a known position of individual ones of the plurality of sensors with respect to each other.

Description

FIXED PARALLEL ALIGNMENT SENSORS IN COMBINATION WITH FAST SCANNINGCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 645,547 which was filed on May 10, 2024 and which is incorporated herein in its entirety by reference.FIELD

[0002] The present disclosure relates to metrology, for example, sensors used for detecting targets on substrates in lithographic and metrology apparatuses and systems.BACKGROUND

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which can be a mask or a reticle, can be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiationsensitive material (photoresist or simply “resist”) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatuses include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”- direction) while synchronously scanning the target portions parallel or anti-parallel to this scanning direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004] During lithographic operation, different processing steps can entail different layers to be sequentially formed on the substrate. Accordingly, it can be necessary to position the substrate relative to prior patterns formed thereon with a high degree of accuracy. Generally, alignment marks are placed on the substrate to be aligned and are located with reference to a second object. A lithographic apparatus can use an alignment apparatus for detecting positions of the alignment marks and for aligning the substrate using the alignment marks to ensure accurate exposure from a mask. Misalignment between the alignment marks at two different layers is measured as overlay error.

[0005] In order to monitor the lithographic process, parameters of the patterned substrate are measured. Parameters can include, for example, the overlay error between successive layers formed in or on the patterned substrate and critical linewidth of developed photosensitive resist. This measurement can be performed on a product substrate and / or on a dedicated metrology target. There are various techniques for making measurements of the microscopic structures formed in lithographic processes, including theuse of scanning electron microscopes and various specialized tools. A fast and non-invasive form of a specialized inspection tool is a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it has been reflected or scattered by the substrate, the properties of the substrate can be determined. This can be done, for example, by comparing the reflected beam with data stored in a library of known measurements associated with known substrate properties. Spectroscopic scatterometers direct a broadband radiation beam onto the substrate and measure the spectrum (intensity as a function of wavelength) of the radiation scattered into a particular narrow angular range. By contrast, angularly resolved scatterometers use a monochromatic radiation beam and measure the intensity of the scattered radiation as a function of angle.

[0006] Such optical scatterometers can be used to measure parameters, such as critical dimensions of developed photosensitive resist or overlay error (OV) between two layers formed in or on the patterned substrate. Properties of the substrate can be determined by comparing the properties of an illumination beam before and after the beam has been reflected or scattered by the substrate.

[0007] A goal for improved wafer alignment technology is more accuracy and less sensitivity to process variations that can lead to tilted wafer alignment markers or other aberrations. Current on-axis, diffraction-based alignment sensors have improved alignment performance and enhanced process robustness. But such single alignment sensors scan over alignment markers with a certain speed. A goal is to increase scan speed by an order of magnitude or more (e.g., from about 11 mm / s to about 200 mm / s), which would achieve significant time reduction for wafer alignment.

[0008] Moveable, parallel sensors exist, which move prior to wafer alignment in order for the sensors to match a field-size. But such systems require complex mechatronics with many requirements, such as small heat generation, stiffness, complicated control of each parallel sensor, and the like. Small adjustments are necessary to accommodate on the order of about 200nm target positioning. Such systems face a risk of drift due to heat generated by movement, a risk of drift due to less stiff mechanical mounting, etc.SUMMARY

[0009] Accordingly, it is desirable to improve the efficiency of target measurements. For example, detection processes can be performed faster based on aspects described herein.

[0010] In some aspects, an alignment system can comprise a substrate stage, a plurality of sensors, and a control system. The substrate stage can be configured to support and move a substrate having a plurality of substrate alignment marks disposed thereon. The plurality of sensors can be arranged on a frame. The control system can be configured to scan the substrate stage with respect to the frame. The control system can control movement of the substrate stage to correct for any misalignment or pitch mismatch between the plurality of sensors and the substrate alignment marks based on a known position of individual ones of the plurality of sensors with respect to each other.

[0011] In some aspects, the control system can be configured to move the substrate stage in both a scan direction parallel to a length of the frame and perpendicular to the scan direction. In some aspects, each sensor of the plurality of sensors can have an optical axis orthogonal to the scan direction and can be disposed a predetermined distance apart from and parallel to any adjacent sensor’s optical axis along the frame. The predetermined distance can comprise at least a lateral spacing based on a settling distance plus a difference between a pitch of the sensors and a pitch of the substrate alignment marks.

[0012] In some aspects, the plurality of sensors can be fixed to the frame. In some aspects, the frame can comprise a thermally stable material, the thermally stable material comprising at least one of Zerodur lithium-aluminosilicate glass-ceramic, cordierite, Invar, or Ultra Low Expansion (ULE) titania- silicate glass.

[0013] In some aspects, the plurality of sensors can be moveable with respect to the frame. In some aspects, the plurality of sensors can be rotationally moveable in or perpendicular to a scan direction.

[0014] In some aspects, the plurality of sensors can be arranged in parallel on the frame. In some aspects, the plurality of sensors can be arranged in grid pattern on the frame.

[0015] In some aspects, a method is disclosed for scanning of substrate alignment marks arranged on a substrate supported by a substrate stage that is configured to move the substrate. The method comprises scanning the substrate stage with respect to a frame having a plurality of sensors disposed thereon. The method further comprises controlling movement of the substrate stage to correct for any misalignment or pitch mismatch between the plurality of sensors and the substrate alignment marks based on a position of individual ones of the plurality of sensors with respect to each other, the position determined beforehand.

[0016] In some aspects, the moving of the substrate stage can comprise moving the substrate stage in both a scan direction parallel to a length of the frame and perpendicular to the scan direction.

[0017] In some aspects, each of the plurality of sensors used in the method can have an optical axis orthogonal to a scan direction and disposed a predetermined distance apart from any adjacent sensor’s optical axis along the frame. The predetermined distance can comprise at least a lateral spacing based on a settling distance plus a difference between a pitch of the sensors and a pitch of the substrate alignment marks.

[0018] In some aspects, the method can further comprise fixing the plurality of sensors to the frame. In some aspects, the frame can comprise a thermally stable material, the thermally stable material comprising at least one of Zerodur lithium-aluminosilicate glass-ceramic, cordierite, Invar, or Ultra Low Expansion (ULE) titania-silicate glass

[0019] In some aspects, the method can further comprise moving one or more of the plurality of sensors with respect to the frame.

[0020] In some aspects, a lithographic apparatus comprises a substrate alignment system. The alignment system comprises a substrate stage, a plurality of sensors, and a control system. The substrate stage is configured to support and move a substrate having a plurality of substrate alignment marksdisposed thereon. The plurality of sensors are arranged on a frame. The control system is configured to scan the substrate stage with respect to the frame. The control system can control movement of the substrate stage to correct for any misalignment or pitch mismatch between the plurality of sensors and the substrate alignment marks based on a known position of individual ones of the plurality of sensors with respect to each other.

[0021] In some aspects, the control system can be configured to move the substrate stage to correct for any misalignment or pitch mismatch between the plurality of sensors and the substrate alignment marks based on a known position of individual ones of the plurality of sensors with respect to each other.

[0022] In some aspects, each of the plurality of sensors can have an optical axis orthogonal to a scan direction and can be disposed a predetermined distance apart from and parallel to any adjacent sensor’s optical axis along the frame. The predetermined distance can comprise at least a lateral spacing based on a settling distance plus a difference between a pitch of the sensors and a pitch of the substrate alignment marks.

[0023] In some aspects, the plurality of sensors can be fixed to the frame. In some aspects, the frame comprises a thermally stable material, the thermally stable material comprising at least one of Zerodur lithium-aluminosilicate glass-ceramic, cordierite, Invar, or Ultra Low Expansion (ULE) titania-silicate glass.

[0024] Further features of various aspects of the present disclosure are described in detail below with reference to the accompanying drawings. It is noted that the present disclosure is not limited to the specific aspects described herein. Such aspects are presented herein for illustrative purposes only. Additional aspects will be apparent to those skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWINGS / FIGURES

[0025] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable those skilled in the relevant art(s) to make and use aspects described herein.

[0026] FIG. 1A shows a reflective lithographic apparatus, according to an exemplary aspect.

[0027] FIG. IB shows a transmissive lithographic apparatus, according to an exemplary aspect.

[0028] FIG. 2 shows more details of a reflective lithographic apparatus, according to an exemplary aspect.

[0029] FIG. 3 shows a lithographic cell, according to an exemplary aspect.

[0030] FIGS. 4A and 4B show inspection apparatuses according to an exemplary aspect.

[0031] FIG. 5 shows an alignment system scanning substrate alignment marks with a plurality of sensors, according to an exemplary aspect.

[0032] FIG. 6 shows a plot illustrating performance of a fast-fixed-sequential readout versus parallel readouts, according to an exemplary aspect.

[0033] FIG. 7 shows a flowchart depicting a method of scanning wafer alignment marks with a plurality of parallel sensors, according to an exemplary aspect.

[0034] FIG. 8 shows a computer system, according to an exemplary aspect.

[0035] The features of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.DETAILED DESCRIPTION

[0036] The aspects described herein, and references in the specification to “one aspect,” “an aspect,” “an exemplary aspect,” “an example aspect,” etc., indicate that the aspects described can include a particular feature, structure, or characteristic, but every aspect may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same aspect. Further, when a particular feature, structure, or characteristic is described in connection with an aspect, it is understood that it is within the knowledge of those skilled in the art to effect such feature, structure, or characteristic in connection with other aspects whether or not explicitly described.

[0037] Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “on,” “upper” and the like, can be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein can likewise be interpreted accordingly.

[0038] The terms “about,” “approximately,” or the like can be used herein to indicate the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the terms “about,” “approximately,” or the like can indicate a value of a given quantity that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

[0039] Aspects of the present disclosure can be implemented in hardware, firmware, software, or any combination thereof. Aspects of the disclosure can also be implemented as instructions stored on a computer-readable medium, which can be read and executed by one or more processors. A machine- readable medium can 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 can include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storagemedia; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and / or instructions can be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. The term “machine -readable medium” can be interchangeable with similar terms, for example, “computer program product,” “computer-readable medium,” “non-transitory computer- readable medium,” or the like. The term “non-transitory” can be used herein to characterize one or more forms of computer readable media except for a transitory, propagating signal.

[0040] Before describing such aspects in more detail, however, it is instructive to present an example environment in which aspects of the present disclosure can be implemented.

[0041] Example Lithographic Systems

[0042] FIGS. 1A and IB show a lithographic apparatus 100 and a lithographic apparatus 100’, respectively, in which aspects of the present disclosure can be implemented. Lithographic apparatus 100 and lithographic apparatus 100’ each include the following: an illumination system (illuminator) IL configured to condition a radiation beam B (for example, deep ultra violet or extreme ultra violet radiation); a support structure (for example, a mask table) MT configured to support a patterning device (for example, a mask, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and, a substrate table (for example, a wafer table) WT configured to hold a substrate (for example, a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. Lithographic apparatus 100 and 100’ also have a projection system PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion (for example, comprising one or more dies) C of the substrate W. In lithographic apparatus 100, the patterning device MA and the projection system PS are reflective. In lithographic apparatus 100’, the patterning device MA and the projection system PS are transmissive.

[0043] The illumination system IL can include various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for directing, shaping, or controlling the radiation beam B.

[0044] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA with respect to a reference frame, the design of at least one of the lithographic apparatus 100 and 100’, and other conditions, such as whether or not the patterning device MA is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT can be a frame or a table, for example, which can be fixed or movable. By using sensors, the support structure MT can ensure that the patterning device MA is at a desired position, for example, with respect to the projection system PS.

[0045] The term “patterning device” MA should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section, such as to create a pattern in the target portion C of the substrate W. The pattern imparted to the radiation beam B can correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0046] The patterning device MA can be transmissive (as in lithographic apparatus 100’ of FIG. IB) or reflective (as in lithographic apparatus 100 of FIG. 1A). Examples of patterning devices MA include reticles, masks, programmable mirror arrays, or programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase shift, or 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 so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam B, which is reflected by a matrix of small mirrors.

[0047] The term “projection system” PS can encompass any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors, such as the use of an immersion liquid on the substrate W or the use of a vacuum. A vacuum environment can be used for EUV or electron beam radiation since other gases can absorb too much radiation or electrons. A vacuum environment can therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.

[0048] Lithographic apparatus 100 and / or lithographic apparatus 100’ can be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such “multiple stage” machines, the additional substrate tables WT can be used in parallel, or preparatory steps can be carried out on one or more tables while one or more other substrate tables WT are being used for exposure. In some situations, the additional table may not be a substrate table WT.

[0049] The lithographic apparatus can also be of a type wherein at least a portion of the substrate can be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system and the substrate. An immersion liquid can also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid. For example, a liquid can be located between the projection system and the substrate during exposure.

[0050] Referring to FIGS. 1A and IB, the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100, 100’ can be separate physical entities, for example, when the source SO is an excimer laser. In such cases, the source SO is not considered to form part of the lithographic apparatus 100 or 100’, and the radiation beam B passes from the sourceSO to the illuminator IL with the aid of a beam delivery system BD (in FIG. IB) including, for example, suitable directing mirrors and / or a beam expander. In other cases, the source SO can be an integral part of the lithographic apparatus 100, 100’ , for example, when the source SO is a mercury lamp. A radiation system can comprise the source SO, the illuminator IL, and / or the beam delivery system BD.

[0051] The illuminator IL can include an adjuster AD (in FIG. IB) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as “o-outer” and “o-inner,” respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL can comprise various other components (in FIG. IB), such as an integrator IN and a condenser CO. The illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross section.

[0052] Referring to FIG. 1A, the radiation beam B is incident on the patterning device (for example, mask) MA, which is held on the support structure (for example, mask table) MT, and is patterned by the patterning device MA. In lithographic apparatus 100, the radiation beam B is reflected from the patterning device (for example, mask) MA. After being reflected from the patterning device (for example, mask) MA, the radiation beam B passes through the projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2 (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (for example, mask) MA with respect to the path of the radiation beam B. Patterning device (for example, mask) MA and substrate W can be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2.

[0053] Referring to FIG. IB, the radiation beam B is incident on the patterning device (for example, mask MA), which is held on the support structure (for example, mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. The projection system has a pupil conjugate PPU to an illumination system pupil IPU. Portions of radiation emanate from the intensity distribution at the illumination system pupil IPU and traverse a mask pattern without being affected by diffraction at the mask pattern and create an image of the intensity distribution at the illumination system pupil IPU.

[0054] The projection system PS projects an image of the mask pattern MP, where the image is formed by diffracted beams produced from the mark pattern MP by radiation from the intensity distribution, onto a photoresist layer coated on the substrate W. For example, the mask pattern MP can include an array of lines and spaces. A diffraction of radiation at the array and different from zeroth order diffraction generates diverted diffracted beams with a change of direction in a direction perpendicular to the lines. Undiffracted beams (i.e., so-called zeroth order diffracted beams) traverse the pattern without any change in propagation direction. The zeroth order diffracted beams traverse an upper lensor upper lens group of the projection system PS, upstream of the pupil conjugate PPU of the projection system PS, to reach the pupil conjugate PPU. The portion of the intensity distribution in the plane of the pupil conjugate PPU and associated with the zeroth order diffracted beams is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. The aperture device PD, for example, is disposed at or substantially at a plane that includes the pupil conjugate PPU of the projection system PS.

[0055] The projection system PS is arranged to capture (e.g., using a lens or lens group L) the zeroth order diffracted beams, first order diffracted beams, and / or higher order diffracted beams (not shown). In some aspects, dipole illumination for imaging line patterns extending in a direction perpendicular to a line can be used to utilize the resolution enhancement effect of dipole illumination. For example, first- order diffracted beams interfere with corresponding zeroth-order diffracted beams at the level of the wafer W to create an image of the line pattern MP at highest possible resolution and process window (i.e., usable depth of focus in combination with tolerable exposure dose deviations). In some aspects, astigmatism aberration can be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. Further, in some aspects, astigmatism aberration can be reduced by blocking the zeroth order beams in the pupil conjugate PPU of the projection system associated with radiation poles in opposite quadrants. This is described in more detail in US 7,511,799 B2, issued Mar. 31, 2009, which is incorporated by reference herein in its entirety.

[0056] With the aid of the second positioner PW and position sensor IFD (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor (not shown in FIG. IB) can be used to accurately position the mask MA with respect to the path of the radiation beam B (for example, after mechanical retrieval from a mask library or during a scan).

[0057] In general, movement of the mask table MT can be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT can be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT can be connected to a short-stroke actuator or can be fixed. Mask MA and substrate W can be aligned using mask alignment marks Ml, M2, and substrate alignment marks Pl, P2. Although the substrate alignment marks (as illustrated) occupy dedicated target portions, they can be located in spaces between target portions (known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks can be located between the dies.

[0058] Mask table MT and patterning device MA can be in a vacuum chamber V, where an in-vacuum robot IVR can be used to move patterning devices such as a mask in and out of vacuum chamber. Alternatively, when mask table MT and patterning device MA are outside of the vacuum chamber, anout-of-vacuum robot can be used for various transportation operations, similar to the in-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots can be calibrated for a smooth transfer of any payload (e.g., mask) to a fixed kinematic mount of a transfer station.

[0059] The lithographic apparatus 100 and 100’ can be used in at least one of the following modes:1. In step mode, the support structure (for example, mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C at one time (i.e., a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed.2. In scan mode, the support structure (for example, mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (for example, mask table) MT can be determined by the (de-)magnification and image reversal characteristics of the projection system PS.3. In another mode, the support structure (for example, mask table) MT is kept substantially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO can be employed and the programmable patterning device is updated as needed after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array.

[0060] Combinations and / or variations on the described modes of use or entirely different modes of use can also be employed.

[0061] In a further aspect, lithographic apparatus 100 includes an extreme ultraviolet (EUV) source, which is configured to generate a beam of EUV radiation for EUV lithography. In general, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

[0062] FIG. 2 shows the lithographic apparatus 100 in more detail, including the source collector apparatus SO, the illumination system IL, and the projection system PS. The source collector apparatus SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 220 of the source collector apparatus SO. An EUV radiation emitting plasma 210 can be formed by a discharge produced plasma source. In some aspects, a plasma of excited tin (Sn) (e.g., excited via a laser) is provided to produce EUV radiation.

[0063] The radiation emitted by the EUV radiation emitting plasma 210 is passed from a source chamber 211 into a collector chamber 212 via an optional gas barrier or contaminant trap 230 (in some cases also referred to as contaminant barrier or foil trap), which is positioned in or behind an opening in source chamber 211. The contaminant trap 230 can include a channel structure. Contamination trap 230 can also include a gas barrier or a combination of a gas barrier and a channel structure. Thecontaminant trap or contaminant barrier 230 further indicated herein at least includes a channel structure.

[0064] The collector chamber 212 can include a radiation collector CO, which can be a so-called grazing incidence collector. Radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation that traverses collector CO can be reflected off a grating spectral filter 240 to be focused in a virtual source point INTF. The virtual source point INTF is commonly referred to as the intermediate focus, and the source collector apparatus is arranged such that the intermediate focus INTF is located at or near an opening 219 in the enclosing structure 220. The virtual source point INTF is an image of the EUV radiation emitting plasma 210. Grating spectral filter 240 is used in particular for suppressing infra-red (IR) radiation.

[0065] Subsequently the radiation traverses the illumination system IL, which can include a faceted field mirror device 222 and a faceted pupil mirror device 224 arranged to provide a desired angular distribution of the radiation beam 221, at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the beam of radiation 221 at the patterning device MA, held by the support structure MT, a patterned beam 226 is formed and the patterned beam 226 is imaged by the projection system PS via reflective elements 228, 229 onto a substrate W held by the wafer stage or substrate table WT.

[0066] More elements than shown can generally be present in illumination optics unit IL and projection system PS. The grating spectral filter 240 can optionally be present, depending upon the type of lithographic apparatus. Further, there can be more mirrors present than those shown in the FIG. 2, for example there can be one to six additional reflective elements present in the projection system PS than shown in FIG. 2.

[0067] Collector optic CO, as illustrated in FIG. 2, is depicted as a nested collector with grazing incidence reflectors 253, 254, and 255, just as an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254, and 255 are disposed axially symmetric around an optical axis O and a collector optic CO of this type is preferably used in combination with a discharge produced plasma source, often called a DPP source.

[0068] Example Lithographic Cell

[0069] FIG. 3 shows a lithographic cell 300, also sometimes referred to a lithocell or cluster, according to some aspects. Lithographic apparatus 100 or 100’ can form part of lithographic cell 300. Lithographic cell 300 can also include one or more apparatuses to perform pre- and post-exposure processes on a substrate. Conventionally these include spin coaters SC to deposit resist layers, developers DE to develop exposed resist, chill plates CH, and bake plates BK. A substrate handler, or robot, RO picks up substrates from input / output ports I / Ol, I / O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus 100 or 100’ . These devices, which are often collectively referred to as the track, are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which also controls the lithographic apparatusvia lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.=

[0070] Example Inspection Apparatus

[0071] In order to control the lithographic process to place device features accurately on the substrate, alignment marks are generally provided on the substrate, and the lithographic apparatus includes one or more inspection apparatuses for accurate measuring of positions of marks on a substrate. These alignment apparatuses are effectively position measuring apparatuses. Different types of marks and different types of alignment apparatuses and / or systems are known from different times and different manufacturers. A type of system widely used in current lithographic apparatus is based on a selfreferencing interferometer as described in U.S. Patent No. 6,961,116 (den Boef et al.). Generally marks are measured separately to obtain X- and Y-positions. A combined X- and Y-measurement can be performed using the techniques described in U.S. Publication No. 2009 / 195768 A (Bijnen et al.), however. The full contents of both of these disclosures are incorporated herein by reference.

[0072] FIG. 4A shows a cross-sectional view of an inspection apparatus 400 that can be implemented as a part of lithographic apparatus 100 or 100’, according to some aspects. In some aspects, inspection apparatus 400 can be configured to align a substrate (e.g., substrate W) with respect to a patterning device (e.g., patterning device MA). Inspection apparatus 400 can be further configured to detect positions of alignment marks on the substrate and to align the substrate with respect to the patterning device or other components of lithographic apparatus 100 or 100’ using the detected positions of the alignment marks. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

[0073] The terms “inspection apparatus,” “metrology system,” or the like can be used herein to refer to, e.g., a device used for measuring a property of a structure (e.g., overlay sensor, critical dimension sensor, or the like), a device or system used in a lithographic apparatus to inspect an alignment of a wafer (e.g., alignment sensor), or the like.

[0074] In some aspects, inspection apparatus 400 can include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and an overlay calculation or position calculation processor 432. Illumination system 412 can be configured to provide an electromagnetic narrow band radiation beam 413 having one or more passbands. In an example, the one or more passbands can be within a spectrum of wavelengths between about 500 nm to about 900 nm. In another example, the one or more passbands can be discrete narrow passbands within a spectrum of wavelengths between about 500 nm to about 900 nm. Illumination system 412 can be further configured to provide one or more passbands having substantially constant center wavelength (CWL) values over a long period of time (e.g., over a lifetime of illumination system 412). Such configuration of illumination system 412 can help to prevent the shift of the actual CWL values from the desired CWL values, as discussed above, in current alignment systems. And, as a result, the use of constant CWLvalues can improve long-term stability and accuracy of alignment systems (e.g., inspection apparatus 400) compared to the current alignment apparatuses.

[0075] In some aspects, beam splitter 414 can be configured to receive radiation beam 413 and split radiation beam 413 into at least two radiation sub-beams. For example, radiation beam 413 can be split into radiation sub-beams 415 and 417, as shown in FIG. 4A. Beam splitter 414 can be further configured to direct radiation sub-beam 415 onto a substrate 420 placed on a stage 422. In one example, the stage 422 is movable along direction 424. Radiation sub-beam 415 can be configured to illuminate an alignment mark or a target 418 located on substrate 420. Alignment mark or target 418 can be coated with a radiation sensitive film. In some aspects, alignment mark or target 418 can have one hundred and eighty degrees (i.e., 180°) symmetry. That is, when alignment mark or target 418 is rotated 180° about an axis of symmetry perpendicular to a plane of alignment mark or target 418, rotated alignment mark or target 418 can be substantially identical to an unrotated alignment mark or target 418. The target 418 on substrate 420 can be (a) a resist layer grating comprising bars that are formed of solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlay target structure comprising a resist grating overlaid or interleaved on a product layer grating. The bars can alternatively be etched into the substrate. This pattern is sensitive to chromatic aberrations in the lithographic projection apparatus, particularly the projection system PL, and illumination symmetry and the presence of such aberrations will manifest themselves in a variation in the printed grating. One in-line method used in device manufacturing for measurements of line width, pitch, and critical dimension makes use of a technique known as “scatterometry”. Methods of scatterometry are described in Raymond et al., “Multiparameter Grating Metrology Using Optical Scatterometry”, J. Vac. Sci. Tech. B, Vol. 15, no. 2, pp. 361-368 (1997) and Niu et al., “Specular Spectroscopic Scatterometry in DUV Lithography”, SPIE, Vol. 3677 (1999), which are both incorporated by reference herein in their entireties. In scatterometry, light is reflected by periodic structures in the target, and the resulting reflection spectrum at a given angle is detected. The structure giving rise to the reflection spectrum is reconstructed, e.g. using Rigorous Coupled- Wave Analysis (RCWA) or by comparison to a library of patterns derived by simulation. Accordingly, the scatterometry data of the printed gratings is used to reconstruct the gratings. The parameters of the grating, such as line widths and shapes, can be input to the reconstruction process, performed by processing unit PU, from knowledge of the printing step and / or other scatterometry processes.

[0076] In some aspects, beam splitter 414 can be further configured to receive diffraction radiation beam 419 and split diffraction radiation beam 419 into at least two radiation sub-beams, according to an aspect. Diffraction radiation beam 419 can be split into diffraction radiation sub-beams 429 and 439, as shown in FIG. 4A.

[0077] It should be noted that even though beam splitter 414 is shown to direct radiation sub-beam 415 towards alignment mark or target 418 and to direct diffracted radiation sub-beam 429 towards interferometer 426, the disclosure is not so limiting. Other optical arrangements can be used to obtainthe similar result of illuminating alignment mark or target 418 on substrate 420 and detecting an image of alignment mark or target 418.

[0078] As illustrated in FIG. 4A, interferometer 426 can be configured to receive radiation sub-beam 417 and diffracted radiation sub-beam 429 through beam splitter 414. In an example aspect, diffracted radiation sub-beam 429 can be at least a portion of radiation sub-beam 415 that can be reflected from alignment mark or target 418. In an example of this aspect, interferometer 426 comprises any appropriate set of optical-elements, for example, a combination of prisms that can be configured to form two images of alignment mark or target 418 based on the received diffracted radiation sub-beam 429. It should be appreciated that a good quality image need not be formed. It can be enough to have the features of alignment mark 418 resolved. Interferometer 426 can be further configured to rotate one of the two images with respect to the other of the two images 180° and recombine the rotated and unrotated images interferometrically.

[0079] In some aspects, detector 428 can be configured to receive the recombined image via interferometer signal 427 and detect interference as a result of the recombined image when alignment axis 421 of inspection apparatus 400 passes through a center of symmetry (not shown) of alignment mark or target 418. Such interference can be due to alignment mark or target 418 being 180° symmetrical, and the recombined image interfering constructively or destructively, according to an example aspect. Based on the detected interference, detector 428 can be further configured to determine a position of the center of symmetry of alignment mark or target 418 and consequently, detect a position of substrate 420. According to an example, alignment axis 421 can be aligned with an optical beam perpendicular to substrate 420 and passing through a center of image rotation interferometer 426. Detector 428 can be further configured to estimate the positions of alignment mark or target 418 by implementing sensor characteristics and interacting with wafer mark process variations.

[0080] In a further aspect, detector 428 determines the position of the center of symmetry of alignment mark or target 418 by performing one or more of the following measurements:1. measuring position variations for various wavelengths (position shift between colors);2. measuring position variations for various orders (position shift between diffraction orders); and3. measuring position variations for various polarizations (position shift between polarizations).

[0081] This data can be obtained using any type of alignment sensor, for example, a SMASH (SMart Alignment Sensor Hybrid) sensor, as described in U.S. Patent No. 6,961,116 that employs a selfreferencing interferometer with a single detector and four different wavelengths, and extracts the alignment signal in software, or Athena (Advanced Technology using High order ENhancement of Alignment), as described in U.S. Patent No. 6,297,876, which directs each of seven diffraction orders to a dedicated detector, which are both incorporated by reference herein in their entireties.

[0082] In some aspects, beam analyzer 430 can be configured to receive and determine an optical state of diffracted radiation sub-beam 439. The optical state can be a measure of beam wavelength, polarization, or beam profile. Beam analyzer 430 can be further configured to determine a position ofstage 422 and correlate the position of stage 422 with the position of the center of symmetry of alignment mark or target 418. As such, the position of alignment mark or target 418 and, consequently, the position of substrate 420 can be accurately known with reference to stage 422. Alternatively, beam analyzer 430 can be configured to determine a position of inspection apparatus 400 or any other reference element such that the center of symmetry of alignment mark or target 418 can be known with reference to inspection apparatus 400 or any other reference element. Beam analyzer 430 can be a point or an imaging polarimeter with some form of wavelength-band selectivity. In some aspects, beam analyzer 430 can be directly integrated into inspection apparatus 400, or connected via fiber optics of several types: polarization preserving single mode, multimode, or imaging, according to other aspects.

[0083] In some aspects, beam analyzer 430 can be further configured to determine the overlay data between two patterns on substrate 420. One of these patterns can be a reference pattern on a reference layer. The other pattern can be an exposed pattern on an exposed layer. The reference layer can be an etched layer already present on substrate 420. The reference layer can be generated by a reference pattern exposed on the substrate by lithographic apparatus 100 and / or 100’. The exposed layer can be a resist layer exposed adjacent to the reference layer. The exposed layer can be generated by an exposure pattern exposed on substrate 420 by lithographic apparatus 100 or 100’. The exposed pattern on substrate 420 can correspond to a movement of substrate 420 by stage 422. In some aspects, the measured overlay data can also indicate an offset between the reference pattern and the exposure pattern. The measured overlay data can be used as calibration data to calibrate the exposure pattern exposed by lithographic apparatus 100 or 100’, such that after the calibration, the offset between the exposed layer and the reference layer can be minimized.

[0084] In some aspects, beam analyzer 430 can be further configured to determine a model of the product stack profile of substrate 420, and can be configured to measure overlay, critical dimension, and focus of target 418 in a single measurement. The product stack profile contains information on the stacked product such as alignment mark, target 418, or substrate 420, and can include mark process variation-induced optical signature metrology that is a function of illumination variation. The product stack profile can also include product grating profile, mark stack profile, and mark asymmetry information. An example of beam analyzer 430 is Yieldstar™, manufactured by ASML, Veldhoven, The Netherlands, as described in U.S. Patent No. 8,706,442, which is incorporated by reference herein in its entirety. Beam analyzer 430 can be further configured to process information related to a particular property of an exposed pattern in that layer. For example, beam analyzer 430 can process an overlay parameter (an indication of the positioning accuracy of the layer with respect to a previous layer on the substrate or the positioning accuracy of the first layer with respective to marks on the substrate), a focus parameter, and / or a critical dimension parameter (e.g., line width and its variations) of the depicted image in the layer. Other parameters are image parameters relating to the quality of the depicted image of the exposed pattern.

[0085] In some aspects, an array of detectors (not shown) can be connected to beam analyzer 430, and allows the possibility of accurate stack profile detection as discussed below. For example, detector 428 can be an array of detectors. For the detector array, a number of options are possible: a bundle of multimode fibers, discrete pin detectors per channel, or CCD or CMOS (linear) arrays. The use of a bundle of multimode fibers enables any dissipating elements to be remotely located for stability reasons. Discrete PIN detectors offer a large dynamic range but each need separate pre-amps. The number of elements is therefore limited. CCD linear arrays offer many elements that can be read-out at high speed and are especially of interest if phase-stepping detection is used.

[0086] In some aspects, a second beam analyzer 430’ can be configured to receive and determine an optical state of diffracted radiation sub-beam 429, as shown in FIG. 4B. The optical state can be a measure of beam wavelength, polarization, or beam profile. Second beam analyzer 430’ can be identical to beam analyzer 430. Alternatively, second beam analyzer 430’ can be configured to perform one or more of the functions of beam analyzer 430, such as determining a position of stage 422 and correlating the position of stage 422 with the position of the center of symmetry of alignment mark or target 418. As such, the position of alignment mark or target 418 and, consequently, the position of substrate 420, can be accurately known with reference to stage 422. Second beam analyzer 430’ can also be configured to determine a position of inspection apparatus 400, or any other reference element, such that the center of symmetry of alignment mark or target 418 can be known with reference to inspection apparatus 400, or any other reference element. Second beam analyzer 430’ can be further configured to determine the overlay data between two patterns and a model of the product stack profile of substrate 420. Second beam analyzer 430’ can also be configured to measure overlay, critical dimension, and focus of target 418 in a single measurement.

[0087] In some aspects, second beam analyzer 430’ can be directly integrated into inspection apparatus 400, or it can be connected via fiber optics of several types: polarization preserving single mode, multimode, or imaging, according to other aspects. Alternatively, second beam analyzer 430’ and beam analyzer 430 can be combined to form a single analyzer (not shown) configured to receive and determine the optical states of both diffracted radiation sub-beams 429 and 439.

[0088] In some aspects, processor 432 receives information from detector 428 and beam analyzer 430. For example, processor 432 can be an overlay calculation processor. The information can comprise a model of the product stack profile constructed by beam analyzer 430. Alternatively, processor 432 can construct a model of the product mark profile using the received information about the product mark. In either case, processor 432 constructs a model of the stacked product and overlay mark profile using or incorporating a model of the product mark profile. The stack model is then used to determine the overlay offset and minimizes the spectral effect on the overlay offset measurement. Processor 432 can create a basic correction algorithm based on the information received from detector 428 and beam analyzer 430, including but not limited to the optical state of the illumination beam, the alignment signals, associated position estimates, and the optical state in the pupil, image, and additional planes.The pupil plane is the plane in which the radial position of radiation defines the angle of incidence and the angular position defines the azimuth angle of the radiation. Processor 432 can utilize the basic correction algorithm to characterize the inspection apparatus 400 with reference to wafer marks and / or alignment marks 418.

[0089] In some aspects, processor 432 can be further configured to determine printed pattern position offset error with respect to the sensor estimate for each mark based on the information received from detector 428 and beam analyzer 430. The information includes but is not limited to the product stack profile, measurements of overlay, critical dimension, and focus of each alignment marks or target 418 on substrate 420. Processor 432 can utilize a clustering algorithm to group the marks into sets of similar constant offset error, and create an alignment error offset correction table based on the information. The clustering algorithm can be based on overlay measurement, the position estimates, and additional optical stack process information associated with each set of offset errors. The overlay is calculated for a number of different marks, for example, overlay targets having a positive and a negative bias around a programmed overlay offset. The target that measures the smallest overlay is taken as reference (as it is measured with the best accuracy). From this measured small overlay, and the known programmed overlay of its corresponding target, the overlay error can be deduced. Table 1 illustrates how this can be performed. The smallest measured overlay in the example shown is -1 nm. However this is in relation to a target with a programmed overlay of -30 nm. The process may have introduced an overlay error of 29 nm.

[0090] The smallest value can be taken to be the reference point and, relative to this, the offset can be calculated between measured overlay and that expected due to the programmed overlay. This offset determines the overlay error for each mark or the sets of marks with similar offsets. Therefore, in the Table 1 example, the smallest measured overlay was -1 nm, at the target position with programmed overlay of 30 nm. The difference between the expected and measured overlay at the other targets is compared to this reference. A table such as Table 1 can also be obtained from marks and target 418 under different illumination settings, the illumination setting, which results in the smallest overlay error, and its corresponding calibration factor, can be determined and selected. Following this, processor 432can group marks into sets of similar overlay error. The criteria for grouping marks can be adjusted based on different process controls, for example, different error tolerances for different processes.

[0091] In some aspects, processor 432 can confirm that all or most members of the group have similar offset errors, and apply an individual offset correction from the clustering algorithm to each mark, based on its additional optical stack metrology. Processor 432 can determine corrections for each mark and feed the corrections back to lithographic apparatus 100 or 100’ for correcting errors in the overlay, for example, by feeding corrections into the inspection apparatus 400.

[0092] Example Alignment System and Method

[0093] In some aspects, the term “throughput” can be used to describe the rate at which a wafer clears a particular fabrication step and moves to the next step. Throughput can be a performance marker of marketability of a lithographic system. It is desirable for lithographic systems to output as many products as possible in as little time as possible. Lithographic fabrication can comprise several complex processes. Each process encompasses choices in technology that balance desired qualities (e.g., subnanometer accuracy, high yield) and drawbacks (e.g., slower fabrication, cost). Such processes can involve inspection of printed marks on a substrate. A detection system can be used in connection with a lithographic process, for example, to ascertain a conformity of a printed pattern on a substrate or to align a substrate in order to properly receive a new pattern. It should be appreciated that an inspection process can greatly enhance mass production using lithographic processes. It should also be appreciated that the inspection process can have an associated time cost, thereby reducing throughput.

[0094] Some aspects herein include devices and functions to enhance speeds of inspection processes.

[0095] FIG. 5 shows an alignment system 500 scanning substrate alignment marks with a plurality of sensors, according to some aspects. In some aspects, alignment system 500 can be implemented as a part of lithographic apparatus 100 or 100’ (as shown in and described with regard to FIGS. 1A and IB). In some aspects, alignment system 500 can be implemented as a part of inspection apparatus 400 (as shown in and described with regard to FIGS. 4A and 4B). The discussion of the components of lithographic apparatus 100 or 100’ and inspection apparatus 400 can apply to the discussion of the components and functions of alignment system 500.

[0096] In some aspects, alignment system 500 can comprise a substrate stage 502, a substrate 504, substrate alignment marks 506, a plurality of sensors 508, a frame 510, and a control system 516. In some aspects, alignment system 500 can comprise structures and functions similar to inspection apparatus 400 that were described in reference to FIGS. 4A and 4B. For example, alignment system 500 can be configured to align a substrate 504 (e.g., substrate W) with respect to a patterning device (e.g., patterning device MA shown in FIGS. 1A and IB). Alignment system 500 can be further configured to perform an alignment process based on inspections of positions of substrate alignment marks 506 on the substrate 504. Alignment system 500 can be further configured to align the substrate 504 with respect to the patterning device or other components of lithographic apparatus 100 or 100’ (as shown in and described with regard to FIG. 1A and IB) using the detected positions of the substratealignment marks 506. Such alignment of the substrate 504 can ensure accurate exposure of one or more patterns on the substrate 504. In another example, alignment system 500 can be configured to perform overlay error analysis based on inspections of substrate alignment marks 506.

[0097] In some aspects, substrate stage 502 can be configured to support and move a substrate 504 having a plurality of substrate alignment marks 506 disposed thereon. In some aspects, substrate stage 502 can comprise structures and functions similar to substrate table WT that were described in reference to FIGS. 1A and IB. Movement of substrate stage 502 can be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning). The long-stroke module and short-stroke module can form part of the second positioner PW described in reference to FIGS. 1 A and IB. As a result, substrate stage 502 can make coarse or fine movements along a scan direction. In the example aspect of FIG. 5, substrate stage 502 can move in a scan direction 518 parallel to a length of frame 510. In this example, scan direction 518 can be along a horizontal X-axis. Additionally, substrate stage 502 can make coarse or fine movements perpendicular to a scan direction. In the example aspect of FIG. 5, substrate stage 502 can move in a first perpendicular direction 526 and a second perpendicular direction 528. In this example, first perpendicular direction 526 and second perpendicular direction 528 can be along a horizontal Y-axis. In another aspect, substrate stage 502 can move in a vertical perpendicular direction along a vertical Z-axis.

[0098] In some aspects, substrate 504 can be an aspect of substrate W described in reference to FIGS. 1A and IB. Substrate 504 can include a plurality of substrate alignment marks 506. In some aspects, substrate alignment marks 506 can be an aspect of substrate alignment marks Pl, P2 described in reference to FIGS. 1A and IB. Substrate alignment marks 506 can be coated with a radiation sensitive film. Substrate alignment marks 506 can be (a) a resist layer grating comprising bars that are formed of solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlay target structure comprising a resist grating overlaid or interleaved on a product layer grating.

[0099] In some aspects, substrate alignment marks 506 can be sized with dimensions to be suitable for detection by alignment system 500. For example, substrate alignment marks 506 can have dimensions having a width of about 30 microns to about 40 microns and a length of about 40 microns to about 160 microns. In one example, a narrow one of substrate alignment marks 506 can have a width of about 40 microns and a length of about 120 microns.

[0100] In some aspects, substrate alignment marks 506 can be arranged along substrate 504 in a pattern suitable for detection by alignment system 500. Substrate alignment marks 506 can occupy dedicated target portions of substrate 504, or can be located in spaces between target portions (known as scribelane alignment marks). Substrate alignment marks 506 can be spaced apart on the substrate 504. For example, substrate alignment marks 506 can be separated by intervals of a predetermined distance. Additionally, substrate alignment marks 506 can be arranged in a scan direction in which substrate stage 502 moves. In the example aspect of FIG. 5, substrate alignment marks 506 can be arranged along scandirection 518. In some aspects, substrate alignment marks 506 can be arranged in a same direction as an array of sensors 508.

[0101] In some aspects, the plurality of sensors 508 can be configured to inspect an alignment of substrate 504 (e.g., alignment sensor). For example, sensors 508 can be configured to perform inspections of substrate alignment marks 506 on substrate 504. Each of the sensors 508 can receive scattered radiation from a plurality of substrate alignment marks 506 (e.g., as described in reference to FIGS. 4A and 4B). Though FIGS. 4A and 4B illustrate only one target (for clarity reasons) and FIG. 5 illustrates about 20 exemplary targets (arranged in a plurality of rows merely for easy description purposes), it should be appreciated that substrate 504 can include a pattern that comprises a larger plurality of substrate alignment marks 506 (e.g., several tens or hundreds of gratings used in alignment and / or overlay inspection). In some aspects, sensors 508 can generate measurement signals based on the scattered radiation from the plurality of substrate alignment marks 506.

[0102] In some aspects, the plurality of sensors 508 can be arranged on frame 510. In some aspects, frame 510 can be configured to support various components of lithographic apparatus 100 or 100’. For example, frame 510 can include position measurement devices, such as sensors 508, to inspect substrate 504 before exposure. In some aspects, sensors 508 can be distributed to match a layout of substrate alignment marks 506 on substrate 504. In some aspects, the plurality of sensors 508 can be arranged in parallel on frame 510. There can be any number of sensors 508 arranged in parallel, for example, 3 to 7 of sensors 508. In some aspects, sensors 508 can be arranged as a sequential linear array with one row and a plurality of columns. In the example aspect shown in FIG. 5, the plurality of sensors 508a-508e can be arranged as a sequential linear array with one row and five columns, for example. In some aspects, the plurality of sensors 508 can be arranged in a grid pattern on frame 510. For example, in the grid pattern, sensors 508 can be arranged in M columns and N rows, wherein M and N are integer values of 1 or more.

[0103] In some aspects, the plurality of sensors 508 can be arranged on frame 510 within a mechanical tolerance 512 for positioning. As a practical matter, it is mechanically difficult to align each one of sensors 508 relative to each other with nanometer accuracy on frame 510. Therefore, as shown in FIG. 5, each one of sensors 508 can be offset within a predetermined mechanical tolerance 512 relative to an adjacent one of sensors 508. In some aspects, mechanical tolerance 512 can account for a mechanical accuracy of about tens of microns. In some aspects, mechanical tolerance 512 can account for a mechanical accuracy of about 100 nm. As a result, mechanical tolerance 512 accounts for the mechanical realities of using alignment system 500 in practice, while still improving upon existing systems.

[0104] In some aspects, each one of sensors 508 can have an optical axis arranged approximately orthogonal to a scan direction. In the example aspect shown in FIG. 5, each one of sensors 508 can have an optical axis in the Z-axis, which is generally orthogonal to scan direction 518 in the X-axis. Each one of sensors 508 can be disposed a predetermined distance (e.g., separation 514) apart from andparallel to any adjacent sensor’s optical axis along frame 510. In some aspects, the predetermined distance (e.g., separation 514) comprises at least a lateral spacing based on a settling distance for substrate stage 502 plus a difference between a pitch of the sensors 508 and a pitch of the substrate alignment marks 506. This configuration can account for a sensor pitch that is smaller than an alignment mark pitch. This configuration can account for the time and distance it takes for substrate stage 502 to settle from rapid accelerations and decelerations between substrate alignment marks 506. Additionally, this configuration can account for actuation time for substrate stage 502 to make coarse or fine movements perpendicular to a scan direction. Also, this configuration can account for the time for sensors 508 to acquire positional data of substrate alignment marks 506. In the example aspect shown in FIG. 5, the predetermined distance can be represented by separation 514. In this example, separation 514 can be a predetermined distance greater than about 26 mm. In one example aspect, the predetermined distance (e.g., separation 514) can be greater than about 26 mm.

[0105] In some aspects, the plurality of sensors 508 can be fixed to frame 510. In some aspects, the plurality of sensors 508 can be fixed to frame 510 by fasteners such as bolts, screws, nails, clips, rotatable cams, adhesives, and the like. In some aspects, sensors 508 can use any amount of fasteners sufficient to affix sensors 508 to frame 510. In some aspects, frame 510 can comprise a thermally stable (e.g., thermally invariant) material such as, for example, Zerodur lithium-aluminosilicate glass-ceramic, cordierite, Invar, Ultra Low Expansion (ULE) titania-silicate glass, or like materials. In this example configuration, frame 510 can have a low coefficient of thermal expansion, thereby maintaining constant dimensions and, therefore, the positioning of sensors 508 fixed to frame 510. By fixing sensors 508 to frame 510, sensors 508 do not adjust to the pitch of the fields of substrate alignment marks 506. Therefore, this configuration of sensors 508 simplifies the alignment process as compared to parallel sensors using complex mechatronics to align to the field size. In this manner, fixing sensors 508 to frame 510 can enable sensors 508 to perform fast scanning of substrate alignment marks 506 up to speeds of about 200 mm / s.

[0106] In some aspects, the plurality of sensors 508 can be configured to be individually positionable. For example, each of sensors 508 can include an actuator configured to adjust a position of its respective one of sensors 508, independent of positions of other ones of sensors 508. When one of substrate alignment marks 506 is to be inspected, sensors 508 can be actuated (e.g., reoriented, redirected, or the like) so as to select an optical path. In some aspects, the plurality of sensors 508 can be moveable with respect to frame 510. In some aspects, the plurality of sensors 508 can be rotationally moveable in or perpendicular to a scan direction (e.g., scan direction 518 shown in FIG. 5). In some aspects, each of the sensors 508 can be configured to have an adjustable movement speed.

[0107] In some aspects, control system 516 can be coupled to substrate stage 502 and the plurality of sensors 508. In some aspects, during a setup calibration procedure, control system 516 can measure a position of individual ones of the plurality of sensors 508 with respect to each other. This calibration measurement can be performed with either a single sample mark or a fiducial on the substrate stage 502as a reference point to determine the relative positioning between sensors 508. The determined position of each of the individual ones of the sensors 508 can be used to determine the mismatch between the sensor pitch and alignment mark pitch, as well as any error position such as, for example, in the horizontal Y-direction. The sensor-to-sensor alignment can be determined so that control system 516 can use the known position of individual ones of the plurality of sensors 508 for more accurate sensor- to-mark alignment during a later scanning step. In some aspects, the relative positioning between individual ones of the plurality of sensors 508 can be measured with sub-nanometer accuracy.

[0108] In some aspects, the control system 516 can then scan substrate stage 502 with respect to frame 510. In response to the known position of individual ones of the plurality of sensors 508, control system 516 can control movement of substrate stage 502 to correct for any misalignment or pitch mismatch between the plurality of sensors 508 and the substrate alignment marks 506. Thus, this controlled movement of substrate stage 502 can overcome any misalignment of the sensors on the frame and relax sensor positioning parameters. For example, control system 516 can move substrate stage 502 in both a scan direction parallel to a length of frame 510 and perpendicular to the scan direction. In the example aspect shown in FIG. 5, control system 516 can move substrate stage 502 in scan direction 518 along the horizontal X-axis, in a first perpendicular direction 526 along the horizontal Y-axis in a negative Y- direction, and in a second perpendicular direction 528 along the horizontal Y-axis in a positive Y- direction. In this configuration, control system 516 can make small adjustments with substrate stage 502 to optimally position one of sensors 508 above a center of one of substrate alignment marks 506 based on the known position of each of the individual ones of sensors 508 determined during the setup calibration procedure. These small adjustments can be of a magnitude of up to about 10 pm in a horizontal Y-direction and about 5 mm in a horizontal X-direction, for example. Additionally, in the example aspect shown in FIG. 5, control system 516 can move substrate stage 502 along a vertical Z- axis to adjust a depth of substrate alignment marks 506 relative to sensors 508, thereby correcting any focus issues with sensors 508.

[0109] The above-mentioned setup calibration procedure can be performed with either a single sample mark or a fiducial on the substrate stage 502 as a reference point to determine a position of individual ones of the plurality of sensors 508 with respect to each other. After performing the setup calibration procedure, alignment system 500 can perform steps for scanning a sequence of substrate alignment marks 506 with sensors 508, as shown in the example aspect of FIG. 5. In this configuration, substrate alignment marks 506 are spaced apart on substrate 502 and arranged in a scan direction 518. Throughout Step 1, Step 2, Step 3, and further steps of the scanning procedure, substrate stage 502 can move in scan direction 518 along a horizontal X-axis to move each one of substrate alignment marks 506 under each one of sensors 508, based on the known position of each of the individual ones of the sensors 508. The known position of individual ones of the plurality of sensors 508 can be used for more accurate sensor- to-mark alignment during the scanning procedure.

[0110] In Step 1, control system 516 can control movement of substrate stage 502 to correct for any misalignment or pitch mismatch between a first one of the sensors (e.g., sensor 508a) and a respective first substrate alignment mark (e.g., first substrate alignment mark 520). As shown in FIG. 5, control system 516 does not move substrate stage 502 in a perpendicular direction to scan direction 518 because sensor 508a is already aligned over a center of first substrate alignment mark 520. Therefore, the first one of the plurality of sensors (e.g., sensor 508a) can be arranged to perform a first scan of the first one of the plurality of substrate alignment marks (e.g., first substrate alignment mark 520).

[0111] In Step 2, control system 516 can control movement of substrate stage 502 to correct for any misalignment or pitch mismatch between a second one of the sensors (e.g., sensor 508b) and a respective second substrate alignment mark (e.g., second substrate alignment mark 522), based on the previously measured position of each of the individual ones of the sensors 508. As shown in FIG. 5, control system 516 can move substrate stage 502 in a first perpendicular direction 526 along the horizontal Y-axis in a negative Y-direction to align second substrate alignment mark 522 with sensor 508b. Therefore, the second one of the plurality of sensors (e.g., sensor 508b) can be arranged to perform a second scan of the second one of the plurality of substrate alignment marks (e.g., second substrate alignment mark 522).

[0112] In Step 3, control system 516 can control movement of substrate stage 502 to correct for any misalignment or pitch mismatch between a third one of the sensors (e.g., sensor 508c) and a respective third substrate alignment mark (e.g., third substrate alignment mark 524), based on the previously measured position of each of the individual ones of the sensors 508. As shown in FIG. 5, control system 516 can move substrate stage 502 in a second perpendicular direction 528 along the horizontal Y-axis in a positive Y-direction to align third substrate alignment mark 524 with sensor 508c. Therefore, the third one of the plurality of sensors (e.g., sensor 508c) can be arranged to perform a third scan of the third one of the plurality of substrate alignment marks (e.g., third substrate alignment mark 524).

[0113] After Step 3, alignment system 500 can perform a plurality of subsequent steps according to the number of substrate alignment marks 506 to be scanned. In the example aspect shown in FIG. 5, the plurality of sensors 508 can comprise at least two further sensors (e.g., sensor 508d and sensor 508e) arranged in parallel on frame 510 to scan further substrate alignment marks 506.

[0114] The aspects discussed in regard to FIG. 5 improve on existing systems by using substrate stage 502 to correct for misalignments of the plurality of sensors 508 relative to the plurality of substrate alignment marks 506. In this configuration, alignment system 500 can remove the use of complicated mechanics to correct positioning of sensors 508. This simplified design can improve the efficiency of alignment system 500, thereby enabling alignment system 500 to scan more of substrate alignment marks 506 in less time.

[0115] FIG. 6 shows a plot 600 illustrating performance of a fast-fixed-sequential readout range 610 versus parallel readouts, according to an exemplary aspect. Plot 600 shows the relationship between an arbitrary number of alignment marks 604 that can be scanned by a number of sensor heads 602, depending on the readout configuration for alignment system 500 for a fixed fine wafer alignment(FIWA) time of an arbitrary time period. The number of sensor heads 602 can represent the plurality of sensors 508 used in the aspects described with regard to FIG. 5. In the example aspect shown in FIG. 6, alignment system 500 can include a number of sensor heads 602 within a range of 1 to 6, for example. The arbitrary number of alignment marks 604 can represent the plurality of substrate alignment marks 506 used in the aspects described with regard to FIG. 5. In the example aspect shown in FIG. 6, alignment system 500 can include an arbitrary number of alignment marks 604 within a range of about 0 to about 100. In some aspects, alignment system 500 can include a lesser or greater number of sensor heads 602 and a lesser or greater number of alignment marks 604 — plot 600 only shows these numerical ranges for illustrative purposes.

[0116] In the example aspect shown in FIG. 6, plot 600 indicates a normal-parallel readout 606, in which an alignment system uses sensors arranged in parallel at a normal scan speed. The normal-parallel readout 606 can indicate a standard benchmark of throughput performance of an existing alignment system using parallel sensors. In this example aspect, normal-parallel readout 606 illustrates that 5 sensor heads 602 can scan an arbitrary number of about 60 alignment marks 604 within the arbitrary time period.

[0117] In the example aspect shown in FIG. 6, plot 600 indicates a fast-parallel readout 608, in which an alignment system uses sensors arranged in parallel at a fast scan speed. The fast-parallel readout 608 can indicate an idealized, if impractical, visualization of throughput performance of an alignment system using parallel sensors that quickly calibrate with complex mechatronics. In this example aspect, fast-parallel readout 608 illustrates that 5 sensor heads 602 can scan an arbitrary number of about 75 alignment marks 604 within the arbitrary time period.

[0118] In the example aspect shown in FIG. 6, plot 600 indicates a fast-fixed-sequential readout range 610, in which an alignment system uses sensors, sequentially arranged on a frame, at a fast scan speed. The fast-fixed-sequential readout range 610 can indicate a visualization of a range of throughput performance values for aspects of alignment system 500 described with regard to FIG. 5. Fast-fixed- sequential readout range 610 can depend on a field size variation 612, such that a smaller field size results in a smaller arbitrary number of alignment marks 604 scanned and a larger field size results in a larger arbitrary number of alignment marks 604 scanned. This dependency relationship can result from the wafer stage traveling a distance to move an alignment mark to a sensor. If the pitch of the fields (e.g., alignment marks) is N mm and the pitch of the sensors is M mm, the distance traveled can be |N — M| mm, where N and M are positive non-zero integers. When the traveled distance increases, the time to move to the next sensor also can increase. In the example aspect shown in FIG. 6, fast-fixed- sequential readout range 610 can have a fast-fixed-sequential readout sample 614 that represents a sample readout by sensor heads 602 falling either within or slightly outside the depicted fast-fixed- sequential readout range 610. In the example aspect shown in FIG. 6, fast-fixed-sequential readout sample 614 illustrates that 5 sensor heads 602 can scan up to an arbitrary number of about 60 alignmentmarks 604 within the arbitrary time period when the field size is optimized for the upper bound of field size variation 612.

[0119] In the example aspect shown in FIG. 6, in the context of an optimal configuration of a sensor pitch approximately equal to an alignment mark pitch for 6 or fewer sensors, a comparison of normalparallel readout 606, fast-parallel readout 608, and fast-fixed-sequential readout sample 614 (as an example of fast-fixed-sequential readout range 610) can illustrate the improvement that aspects of alignment system 500 provide over existing alignment systems. For example, the performance indicated by fast-fixed-sequential readout sample 614 can be relatively equivalent to the performance indicated by normal-parallel readout 606. Referring to the above-mentioned sample data point of 5 sensor heads 602, both fast-fixed-sequential readout sample 614 and normal-parallel readout 606 indicate about the same arbitrary number of about 60 alignment marks 604 scanned. Therefore, fast-fixed-sequential readout sample 614 indicates that aspects of alignment system 500 can provide comparable performance to existing parallel sensor systems, while also providing the benefit of a more cost-effective, simplified design. Even though fast-parallel readout 608 indicates the comparatively highest performance, it is impractical for its use of complex mechatronics. As a result, fast-fixed-sequential readout range 610 provided by aspects of alignment system 500 can be an improvement over existing alignment systems because of its use of fine-adjustment by substrate stage 502 and its lack of lateral scan offset problems of fully parallel sensors.

[0120] FIG. 7 shows method steps (e.g., using one or more processors) for performing a method 700 including functions described herein, according to some aspects. The method 700 of FIG. 7 can be performed in any conceivable order and it is not required that all steps be performed. Moreover, the method steps of FIG. 7 described above merely reflect an example of steps and are not limiting.

[0121] In some aspects, method 700 illustrates a method for scanning of substrate alignment marks (e.g., substrate alignment marks 506) arranged on a substrate (e.g., substrate 504) supported by a substrate stage (e.g., substrate stage 502) that is configured to move the substrate.

[0122] In some aspects, in step 702 a plurality of sensors can be arranged in parallel on a frame (e.g., frame 510). This can facilitate more rapid scanning of substrate alignment marks, wherein the marks are arranged in a scan direction (e.g., scan direction 518) on the substrate supported by the substrate stage.

[0123] In some aspects, in step 704 a control system (e.g., control system 516) can measure a position of individual ones of the plurality of the sensors with respect to each other. The relative positioning between individual ones of the plurality of sensors can be measured with sub-nanometer accuracy.

[0124] In some aspects, in step 706 a first scan of a first substrate alignment mark (e.g., first substrate alignment mark 520) can be performed using a first one of the sensors (e.g., sensor 508a).

[0125] In some aspects, in step 708 the substrate stage can be moved / positioned by the control system based on the measured position(s) to correct misalignments or pitch mismatch between the plurality of sensors and the substrate alignment marks. In some aspects, the moving of the substrate stage cancomprise moving the substrate stage in both a scan direction parallel to a length of the frame and perpendicular to the scan direction.

[0126] In some aspects, in step 710 control system can determine whether there are more substrate alignment marks to scan with the plurality of sensors.

[0127] In some aspects, in step 712, optionally if there are more substrate alignment marks to be scanned, a next scan of a next substrate alignment mark can be performed using a next one of the sensors. After performing the next scan, step 706 can be performed again based on the next scan. A recursive cycle of steps 712, 706, 708, and 710 can be repeated until control system determines at step 710 that there are no more substrate alignment marks to scan with the plurality of sensors.

[0128] In some aspects, in step 714, if there are no more substrate alignment marks to be scanned, the performance of scans can be stopped by the control system.

[0129] Various aspects may be implemented, for example, using one or more well-known computer systems, such as computer system 800 shown in FIG. 8. One or more computer systems 800 can be used, for example, to implement any aspect of the disclosure discussed herein, as well as combinations and sub-combinations thereof.

[0130] Computer system 800 can include one or more processors (also called central processing units, or CPUs), such as a processor 804. Processor 804 can be connected to a communication infrastructure or bus 806.

[0131] Computer system 800 can also include customer input / output device(s) 803, such as monitors, keyboards, pointing devices, etc., which may communicate with communication infrastructure 806 through customer input / output interface(s) 802.

[0132] One or more of processors 804 can be a graphics processing unit (GPU). In an aspect, a GPU may be a processor that is a specialized electronic circuit designed to process mathematically intensive applications. The GPU may have a parallel structure that is efficient for parallel processing of large blocks of data, such as mathematically intensive data common to computer graphics applications, images, videos, etc.

[0133] Computer system 800 can also include a main or primary memory 808, such as random access memory (RAM). Main memory 808 can include one or more levels of cache. Main memory 808 can have stored therein control logic (i.e., computer software) and / or data.

[0134] Computer system 800 can also include one or more secondary storage devices or memory 810. Secondary memory 810 can include, for example, a hard disk drive 812 and / or a removable storage device or drive 814. Removable storage drive 814 can be a floppy disk drive, a magnetic tape drive, a compact disk drive, an optical storage device, tape backup device, and / or any other storage device / drive.

[0135] Removable storage drive 814 can interact with a removable storage unit 818. Removable storage unit 818 can include a computer usable or readable storage device having stored thereon computer software (control logic) and / or data. Removable storage unit 818 can be a floppy disk,magnetic tape, compact disk, DVD, optical storage disk, and / any other computer data storage device. Removable storage drive 814 can read from and / or write to removable storage unit 818.

[0136] Secondary memory 810 can include other means, devices, components, instrumentalities or other approaches for allowing computer programs and / or other instructions and / or data to be accessed by computer system 800. Such means, devices, components, instrumentalities or other approaches may include, for example, a removable storage unit 822 and an interface 820. Examples of the removable storage unit 822 and the interface 820 can include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM or PROM) and associated socket, a memory stick and USB port, a memory card and associated memory card slot, and / or any other removable storage unit and associated interface.

[0137] Computer system 800 can further include a communication or network interface 824. Communication interface 824 can enable computer system 800 to communicate and interact with any combination of external devices, external networks, external entities, etc. (individually and collectively referenced by reference number 828). For example, communication interface 824 can allow computer system 800 to communicate with external or remote devices 828 over communications path 826, which may be wired and / or wireless (or a combination thereof), and which may include any combination of LANs, WANs, the Internet, etc. Control logic and / or data may be transmitted to and from computer system 800 via communication path 826.

[0138] Computer system 800 can also be any of a personal digital assistant (PDA), desktop workstation, laptop or notebook computer, netbook, tablet, smart phone, smart watch or other wearable, appliance, part of the Internet-of-Things, and / or embedded system, to name a few non-limiting examples, or any combination thereof.

[0139] Computer system 800 can be a client or server, accessing or hosting any applications and / or data through any delivery paradigm, including but not limited to remote or distributed cloud computing solutions; local or on-premises software (“on-premise” cloud-based solutions); “as a service” models (e.g., content as a service (CaaS), digital content as a service (DCaaS), software as a service (SaaS), managed software as a service (MSaaS), platform as a service (PaaS), desktop as a service (DaaS), framework as a service (FaaS), backend as a service (BaaS), mobile backend as a service (MBaaS), infrastructure as a service (laaS), etc.); and / or a hybrid model including any combination of the foregoing examples or other services or delivery paradigms.

[0140] Any applicable data structures, file formats, and schemas in computer system 800 can be derived from standards including but not limited to JavaScript Object Notation (JSON), Extensible Markup Language (XML), Yet Another Markup Language (YAML), Extensible Hypertext Markup Language (XHTML), Wireless Markup Language (WML), MessagePack, XML User Interface Language (XUL), or any other functionally similar representations alone or in combination. Alternatively, proprietary data structures, formats or schemas may be used, either exclusively or in combination with known or open standards.

[0141] In some aspects, a tangible, non-transitory apparatus or article of manufacture comprising a tangible, non-transitory computer useable or readable medium having control logic (software) stored thereon may also be referred to herein as a computer program product or program storage device. This includes, but is not limited to, computer system 800, main memory 808, secondary memory 810, and removable storage units 818 and 822, as well as tangible articles of manufacture embodying any combination of the foregoing. Such control logic, when executed by one or more data processing devices (such as computer system 800), may cause such data processing devices to operate as described herein.

[0142] Based on the teachings contained in this disclosure, it will be apparent to persons skilled in the relevant art(s) how to make and use aspects of this disclosure using data processing devices, computer systems and / or computer architectures other than that shown in FIG. 8. In particular, aspects can operate with software, hardware, and / or operating system implementations other than those described herein.

[0143] The embodiments may further be described using the following clauses:1. An alignment system comprising: a substrate stage configured to support and move a substrate having a plurality of substrate alignment marks disposed thereon; a plurality of sensors arranged on a frame; and a control system configured to: scan the substrate stage with respect to the frame; and control movement of the substrate stage to correct for any misalignment or pitch mismatch between the plurality of sensors and the plurality of substrate alignment marks based on a known position of individual ones of the plurality of sensors with respect to each other.2. The alignment system of clause 1 , wherein: a first one of the plurality of sensors is arranged to perform a first scan of a first one of the plurality of substrate alignment marks, a second one of the plurality of sensors is arranged to perform a second scan of a second one of the plurality of substrate alignment marks, a third one of the plurality of sensors is arranged to perform a third scan of a third one of the plurality of substrate alignment marks, and the substrate alignment marks are spaced apart on the substrate and arranged in a scan direction, and the control system controls movement of the substrate stage to correct for any misalignment or pitch mismatch between the plurality of sensors and the plurality of substrate alignment marks based on the known position of individual ones of the plurality of sensors with respect to each other.3. The alignment system of clause 2, wherein the plurality of sensors comprises at least two further sensors arranged in parallel on the frame to scan further alignment marks.4. The alignment system of clause 1, wherein the control system is configured to move the substrate stage in both a scan direction parallel to a length of the frame and perpendicular to the scan direction.5. The alignment system of clause 4, wherein: each sensor of the plurality of sensors has an optical axis orthogonal to the scan direction and disposed a predetermined distance apart from and parallel to any adjacent sensor’s optical axis along the frame, and the predetermined distance comprises at least a lateral spacing based on a settling distance plus a difference between a pitch of the sensors and a pitch of the substrate alignment marks.6. The alignment system of clause 1, wherein the plurality of sensors are fixed to the frame.7. The alignment system of clause 6, wherein the frame comprises a thermally stable material, the thermally stable material comprising at least one of Zerodur lithium-aluminosilicate glass-ceramic, cordierite, Invar, or Ultra Low Expansion (ULE) titania-silicate glass.8. The alignment system of clause 1, wherein the plurality of sensors are moveable with respect to the frame.9. The alignment system of clause 1, wherein the plurality of sensors are rotationally moveable in or perpendicular to a scan direction.10. The alignment system of clause 1, wherein the plurality of sensors are arranged in parallel on the frame.11. The alignment system of clause 1 , wherein the plurality of sensors are arranged in grid pattern on the frame.12. A method for scanning of substrate alignment marks arranged on a substrate supported by a substrate stage that is configured to move the substrate, the method comprising: scanning the substrate stage with respect to a frame having a plurality of sensors disposed thereon; and controlling movement of the substrate stage to correct for any misalignment or pitch mismatch between the plurality of sensors and the substrate alignment marks based on a position of individual ones of the plurality of sensors with respect to each other, the position determined beforehand.13. The method of clause 12, further comprising: performing a first scan of a first substrate alignment mark using a first one of the sensors; performing a second scan of a second substrate alignment mark using a second one of the sensors; performing a third scan of a third substrate alignment mark using a third one of the sensors; and moving the substrate stage to correct for any misalignment or pitch mismatch between the plurality of sensors and the substrate alignment marks based on the position determined beforehand.14. The method of clause 12, wherein the moving of the substrate stage comprises moving the substrate stage in both a scan direction parallel to a length of the frame and perpendicular to the scan direction.15. The method of clause 12, wherein:each of the plurality of sensors has an optical axis orthogonal to a scan direction and disposed a predetermined distance apart from any adjacent sensor’s optical axis along the frame, and the predetermined distance comprises at least a lateral spacing based on a settling distance plus a difference between a pitch of the sensors and a pitch of the substrate alignment marks.16. The method of clause 12, further comprising fixing the plurality of sensors to the frame.17. The method of clause 16, wherein the frame comprises a thermally stable material, the thermally stable material comprising at least one of Zerodur lithium-aluminosilicate glass-ceramic, cordierite, Invar, or Ultra Low Expansion (ULE) titania-silicate glass.18. The method of clause 12, further comprising moving one or more of the plurality of sensors with respect to the frame.19. A lithographic apparatus comprising the alignment system of clause 1.20. The lithographic apparatus of clause 19, wherein the control system is configured to move the substrate stage to correct for any misalignment or pitch mismatch between the plurality of sensors and the substrate alignment marks based on a known position of individual ones of the plurality of sensors with respect to each other.21. The lithographic apparatus of clause 19, wherein: each of the plurality of sensors has an optical axis orthogonal to a scan direction and disposed a predetermined distance apart from and parallel to any adjacent sensor’s optical axis along the frame, and the predetermined distance comprises at least a lateral spacing based on a settling distance plus a difference between a pitch of the sensors and a pitch of the substrate alignment marks.22. The lithographic apparatus of clause 21, wherein the plurality of sensors are fixed to the frame.23. The alignment system of clause 22, wherein the frame comprises a thermally stable material, the thermally stable material comprising at least one of Zerodur lithium-aluminosilicate glass-ceramic, cordierite, Invar, or Ultra Low Expansion (ULE) titania-silicate glass.

[0144] Although specific reference can be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, LCDs, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein can be considered as specific examples of the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein can be processed, before or after exposure, in for example a track unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) and / or a metrology unit. Where applicable, the disclosure herein can be applied to such and other substrate processing tools. Further, the substrate can be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

[0145] Although specific reference may have been made above to the use of aspects of the present disclosure in the context of optical lithography, it will be appreciated that the present disclosure can be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device can be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.

[0146] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present disclosure is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0147] The terms “radiation,” “beam of radiation” or the like as used herein can encompass all types of electromagnetic radiation, for example, ultraviolet (UV) radiation (for example, having a wavelength I of 365, 248, 183, 157 or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (for example, having a wavelength in the range of 5-20 nm such as, for example, 13.5 nm), or hard X-ray working at less than 5 nm, as well as matter beams, such as ion beams or electron beams. The terms “light,” “illumination,” or the like can refer to non-matter radiation (e.g., photons, UV, X-ray, or the like). Generally, radiation having wavelengths between about 400 to about 700 nm is considered visible radiation; radiation having wavelengths between about 780-3000 nm (or larger) is considered IR radiation. UV refers to radiation with wavelengths of approximately 100-400 nm. Within lithography, the term “UV” also applies to the wavelengths that can be produced by a mercury discharge lamp: G- line 436 nm; H-line 405 nm; and / or, I-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by gas), refers to radiation having a wavelength of approximately 100-200 nm. Deep UV (DUV) generally refers to radiation having wavelengths ranging from 126 nm to 428 nm, and in some aspects, an excimer laser can generate DUV radiation used within a lithographic apparatus. It should be appreciated that radiation having a wavelength in the range of, for example, 5-20 nm relates to radiation with a desired wavelength band, of which at least part is in the range of 5-20 nm.

[0148] It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary aspects of the present disclosure as contemplated by the inventor(s), and thus, are not intended to limit the present disclosure and the appended claims in any way.

[0149] The present disclosure has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.

[0150] While specific aspects of the disclosure have been described above, it will be appreciated that aspects of the present disclosure may be practiced otherwise than as described. The descriptions are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the disclosure as described without departing from the scope of the claims set out below.

[0151] The foregoing description of the specific aspects will so fully reveal the general nature of the present disclosure that others can, by applying knowledge within the skill of the art, readily modify and / or adapt for various applications such specific aspects, without undue experimentation, without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed aspects, based on the teaching and guidance presented herein.

[0152] The breadth and scope of the protected subject matter should not be limited by any of the abovedescribed exemplary aspects, but should be defined only in accordance with the following claims and their equivalents.

Claims

CLAIMS1. An alignment system comprising: a substrate stage configured to support and move a substrate having a plurality of substrate alignment marks disposed thereon; a plurality of sensors arranged on a frame; and a control system configured to: scan the substrate stage with respect to the frame; and control movement of the substrate stage to correct for any misalignment or pitch mismatch between the plurality of sensors and the plurality of substrate alignment marks based on a known position of individual ones of the plurality of sensors with respect to each other.

2. The alignment system of claim 1, wherein: a first one of the plurality of sensors is arranged to perform a first scan of a first one of the plurality of substrate alignment marks, a second one of the plurality of sensors is arranged to perform a second scan of a second one of the plurality of substrate alignment marks, a third one of the plurality of sensors is arranged to perform a third scan of a third one of the plurality of substrate alignment marks, and the substrate alignment marks are spaced apart on the substrate and arranged in a scan direction, and the control system controls movement of the substrate stage to correct for any misalignment or pitch mismatch between the plurality of sensors and the plurality of substrate alignment marks based on the known position of individual ones of the plurality of sensors with respect to each other.

3. The alignment system of claim 2, wherein the plurality of sensors comprises at least two further sensors arranged in parallel on the frame to scan further alignment marks.

4. The alignment system of claim 1 , wherein the control system is configured to move the substrate stage in both a scan direction parallel to a length of the frame and perpendicular to the scan direction.

5. The alignment system of claim 4, wherein: each sensor of the plurality of sensors has an optical axis orthogonal to the scan direction and disposed a predetermined distance apart from and parallel to any adjacent sensor’s optical axis along the frame, and the predetermined distance comprises at least a lateral spacing based on a settling distance plus a difference between a pitch of the sensors and a pitch of the substrate alignment marks.

6. The alignment system of claim 1 , wherein the plurality of sensors are fixed to the frame.

7. The alignment system of claim 6, wherein the frame comprises a thermally stable material, the thermally stable material comprising at least one of Zerodur lithium-aluminosilicate glassceramic, cordierite, Invar, or Ultra Low Expansion (ULE) titania-silicate glass.

8. The alignment system of claim 1, wherein the plurality of sensors are moveable with respect to the frame.

9. The alignment system of claim 1, wherein the plurality of sensors are rotationally moveable in or perpendicular to a scan direction.

10. The alignment system of claim 1, wherein the plurality of sensors are arranged in parallel on the frame.

11. The alignment system of claim 1 , wherein the plurality of sensors are arranged in grid pattern on the frame.

12. A method for scanning of substrate alignment marks arranged on a substrate supported by a substrate stage that is configured to move the substrate, the method comprising: scanning the substrate stage with respect to a frame having a plurality of sensors disposed thereon; and controlling movement of the substrate stage to correct for any misalignment or pitch mismatch between the plurality of sensors and the substrate alignment marks based on a position of individual ones of the plurality of sensors with respect to each other, the position determined beforehand.

13. The method of claim 12, further comprising: performing a first scan of a first substrate alignment mark using a first one of the sensors; performing a second scan of a second substrate alignment mark using a second one of the sensors; performing a third scan of a third substrate alignment mark using a third one of the sensors; and moving the substrate stage to correct for any misalignment or pitch mismatch between the plurality of sensors and the substrate alignment marks based on the position determined beforehand.

14. The method of claim 12, wherein the moving of the substrate stage comprises moving the substrate stage in both a scan direction parallel to a length of the frame and perpendicular to the scan direction.

15. The method of claim 12, wherein: each of the plurality of sensors has an optical axis orthogonal to a scan direction and disposed a predetermined distance apart from any adjacent sensor’s optical axis along the frame, and the predetermined distance comprises at least a lateral spacing based on a settling distance plus a difference between a pitch of the sensors and a pitch of the substrate alignment marks.

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