System and method for compact display of optical measurement information

Abstract

A metrology device receives radiation that has interacted with a pattern on a substrate. The metrology device includes an optical module that splits the radiation into a first radiation in a first arm of the optical module and a second radiation in a second arm of the optical module. The second arm of the optical module contains an optical wedge. A first segment of the optical wedge alters an angle of travel of positive diffraction orders and a second segment of the optical wedge alters an angle of travel of negative diffraction orders, such that the positive and negative diffraction orders are spatially separated. The first and second segments of the optical wedge direct positive diffraction orders to form a first image on a detector and negative diffraction orders to form a second image on a detector.

Description

SYSTEM AND METHOD FOR COMPACT DISPLAY OF OPTICAL MEASUREMENT INFORMATIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 670,303 which was filed on July 12, 2024 and which is incorporated herein in its entirety by reference.FIELD

[0002] The present disclosure relates to metrology devices, for example, metrology devices for alignment measurements in lithographic 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 is alternatively referred to as 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 radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus 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 may require 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 may 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 may 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 techniquesfor making measurements of the microscopic structures formed in lithographic processes, including the use 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] In angle resolved scatterometry, an illumination branch irradiates the overlay target over a large band of incidence space. Diffraction orders of the light from the grating are then captured. The zero order intensity varies symmetrically as a function of overlay whereas the ±1 order intensities vary asymmetrically as a function of overlay. Overlay can be determined using the difference of intensity of the first orders. The properties measured by the scatterometer for different wavelengths and angles may include the relative intensity of differently polarized radiation. These relative intensities may be used to correct for deformed marks caused by, e.g., asymmetry.

[0007] To improve throughput, multiple types of alignment / overlay data can be measured in parallel. For example, in a camera-based system, some applications may benefit by simultaneously displaying multiple images conveying polarization-resolved measurements and / or intensity information per diffracted order.SUMMARY

[0008] Accordingly, it is desirable to design a compact metrology system capable of measuring intensity information for each diffracted order and / or polarization-resolved measurements in parallel.

[0009] In some aspects, a metrology device is arranged to receive radiation that has interacted with a pattern on a substrate. The metrology device can include an optical module configured to split the radiation into a first radiation in a first arm and a second radiation in a second arm. The second arm of the optical module can contain an optical component comprising a first segment configured to alter an angle of travel of positive diffraction orders, and a second segment configured to alter an angle of travel of negative diffraction orders. This arrangement permits spatial separation of the positive and negative diffraction orders. The first and second segments of the optical wedge can be arranged to direct the positive diffraction orders to form a first image in a first section of the detector, and direct the negative diffraction orders to form a second image in a second section of the detector.

[0010] In some aspects, a metrology device is arranged to receive radiation that has interacted with a pattern on a substrate. The metrology device can include an optical module configured to split theradiation into a first radiation in a first arm and a second radiation in a second arm. The second arm of the optical module can contain an optical component comprising a first segment configured to alter an angle of travel of positive diffraction orders, and a second segment configured to alter an angle of travel of negative diffraction orders. This arrangement permits spatial separation of the positive and negative diffraction orders. The first and second segments of the optical wedge can be arranged to direct the positive diffraction orders to form a first image in a first section of the detector and direct the negative diffraction orders to form a second image in a second section of the detector. The optical module can additionally include a polarizing beam splitter configured to receive the first radiation from the first arm, and the second radiation from the second arm and split the first and second radiation into first channel first and second radiation and second channel first and second radiation. The polarizing beam splitter can cause the first channel first and second radiation to co-propagate as combined first channel radiation, and cause the second channel first and second radiation to co-propagate as combined second channel radiation.

[0011] In some aspects, a method includes splitting radiation that has interacted with a pattern on a substrate into a first path radiation travelling through a first arm of an optical module, and a second path radiation traveling through a second arm of an optical module. The method can further include spatially separating positive diffraction orders and negative diffraction orders of the second path radiation by passing positive diffraction orders through a first segment of an optical wedge and negative diffraction orders through a second segment of an optical wedge. The method can also include detecting a first image corresponding to positive diffraction orders of the second path radiation and a second image corresponding to negative diffraction orders of the second path radiation at spatially separated regions of a detector.

[0012] Further features of the present disclosure, as well as the structure and operation of various aspects, 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 persons skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWINGS / FIGURES

[0013] 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 a person skilled in the relevant art(s) to make and use aspects described herein.FIG. 1A shows a schematic of a reflective lithographic apparatus, according to some aspects. FIG. IB shows a schematic of a transmissive lithographic apparatus, according to some aspects. FIG. 2 shows a more detailed schematic of the reflective lithographic apparatus, according to some aspects.FIG. 3 shows a schematic of a lithographic cell, according to some aspects.FIGS. 4 A and 4B show schematics of inspection apparatuses, according to some aspects.FIG. 5A, 5B, and 5C show sample metrology targets, according to some aspects.FIGS. 6A and 6B show schematics of a metrology device, according to some aspects.FIG. 7 shows a sample display field, according to some aspects.FIG. 8 shows a segmented optical wedge, according to some aspects.FIGS. 9A and 9B show sample pupils, according to some aspects.FIG. 10 shows a method, according to some aspects.

[0014] 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

[0015] This specification discloses one or more aspects that incorporate the features of the present disclosure. The disclosed embodiment! s) are provided as examples. The scope of the present disclosure is not limited to the disclosed embodiment(s). Claimed features are defined by the claims appended hereto.

[0016] The embodiment(s) described, and references in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment! s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other aspects whether or not explicitly described.

[0017] 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 may likewise be interpreted accordingly.

[0018] The term “about” as used herein indicates the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the term “about” can indicate a value of agiven quantity that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

[0019] Aspects of the disclosure can be implemented in hardware, firmware, software, or any combination thereof. Aspects of the disclosure may also be implemented as instructions stored on a machine -readable medium, which can be read and executed by one or more processors. A machine- readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, 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 in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc.

[0020] Before describing aspects in more detail, however, it is instructive to present an example environment in which aspects of the present disclosure can be implemented.

[0021] Example Lithographic Systems

[0022] FIGS. 1 A and IB show schematic illustrations of a lithographic apparatus 100 and 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.

[0023] 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.

[0024] 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 patterningdevice 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, as required. 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.

[0025] 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.

[0026] The terms “inspection apparatus,” “metrology system,” or the like may be used herein to refer to, e.g., a device or system used for measuring a property of a structure (e.g., overlay error, critical dimension parameters) or used in a lithographic apparatus to inspect an alignment of a wafer (e.g., alignment apparatus).

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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 thelithographic 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, but rather only means that liquid is located between the projection system and the substrate during exposure.

[0031] 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 source SO 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. The source SO and the illuminator IL, together with the beam delivery system BD, if required, can be referred to as a radiation system.

[0032] 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.

[0033] 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.

[0034] 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 emanatefrom 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.

[0035] 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 lens or 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.

[0036] The projection system PS is arranged to capture, by means of a lens or lens group L, not only the zeroth order diffracted beams, but also first-order or first- and 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.

[0037] 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).

[0038] 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 ashort-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 only 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.

[0039] 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, an out-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 need to be calibrated for a smooth transfer of any payload (e.g., mask) to a fixed kinematic mount of a transfer station.

[0040] 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 required 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.

[0041] Combinations and / or variations on the described modes of use or entirely different modes of use can also be employed.

[0042] In a further embodiment, 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.

[0043] 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. EUV radiation can be produced by a gas or vapor, for example Xe gas, Li vapor, or Sn vapor in which the very hot plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The very hot plasma 210 is created by, for example, an electrical discharge causing at least a partially ionized plasma. Partial pressures of, for example, 10 Pa of Xe, Li, Sn vapor, or any other suitable gas or vapor can be required for efficient generation of the radiation. In some aspects, a plasma of excited tin (Sn) is provided to produce EUV radiation.

[0044] The radiation emitted by the hot 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. The contaminant trap or contaminant barrier 230 further indicated herein at least includes a channel structure.

[0045] 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 radiation emitting plasma 210. Grating spectral filter 240 is used in particular for suppressing infra-red (IR) radiation.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] Example Lithographic Cell

[0050] 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. In some examples, 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 apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0051] Example Inspection Apparatus

[0052] 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 positioning 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 self-referencing interferometer as described in U.S. Patent No. 6,961,116 issued Nov. 1, 2005. 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. Patent No. 8,208,121 issued June 26, 2012. The full contents of both of these disclosures are incorporated herein by reference.

[0053] FIG. 4A shows a schematic of 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.

[0054] 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 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 CWL values can improve long-term stability and accuracy of alignment systems (e.g., inspection apparatus 400) compared to the current alignment apparatuses.

[0055] 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 bysimulation. 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.

[0056] 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 embodiment. Diffraction radiation beam 419 can be split into diffraction radiation sub-beams 429 and 439, as shown in FIG. 4A.

[0057] 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. It would be apparent to a person skilled in the relevant art that other optical arrangements can be used to obtain the similar result of illuminating alignment mark or target 418 on substrate 420 and detecting an image of alignment mark or target 418.

[0058] 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 embodiment, 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 embodiment, 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, but that the features of alignment mark 418 should be 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.

[0059] 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 embodiment. 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.

[0060] In a further embodiment, 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).

[0061] This data can for example be obtained with any type of alignment sensor, for example a SMASH (SMart Alignment Sensor Hybrid) sensor, as described in U.S. Patent No. 6,961,116 issued Nov. 1, 2005 that employs a self-referencing 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, issued on Oct. 10, 2001, which directs each of seven diffraction orders to a dedicated detector, which are both incorporated by reference herein in their entireties.

[0062] 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 of stage 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.

[0063] 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.

[0064] 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 processvariation-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 TM, manufactured by ASML, Veldhoven, The Netherlands, as described in U.S. Patent No. 8,706,442, issued on April 22, 2014, 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.

[0065] 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.

[0066] 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 at least all 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.

[0067] 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 beamanalyzer 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.

[0068] 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.

[0069] 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.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 432 can 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.

[0070] 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.

[0071] Briefly referring back to FIG. 4A, metrology system 400 may comprise a beam splitter 434 and a sensor 436. Sensor 436 may be referred to as a second sensor, with detector 428 being the first sensor. Beam splitter 434 may receive diffraction radiation 419. Target 418 may interact with incident radiation via reflection, refraction, diffraction, scattering, or the like to generate scattered radiation (e.g., diffraction radiation 419). For ease of discussion, and without limitation, such radiation may be termed scattered radiation throughout. Beam splitter 434 may split the radiation scattered by target 418 into first portion of radiation 441 and second portion of radiation 443. First portion of radiation 441 may continue on (e.g., as sub-beam 429 then interferometer signal) for subsequent receipt detector 428. Subsequent determination of properties of target 418 (e.g., alignment position) may be performed as described above.

[0072] Sensor 436 may be used to determine a corrections to the property determined via detector 428. Sensor 436 may work in conjunction with processor 432 to determine the correction. Though not shown in FIG. 4B, it should be understood that the structures and functions of beam splitter 434 and sensor 436 may be implemented in embodiments referencing FIG. 4B.

[0073] Example Compact Intensity Channel Metrology Device

[0074] A metrology system (e.g., inspection apparatus 400) is typically programmed with certain assumptions regarding the target it is to measure. For example, the metrology system may beprogrammed to expect diffracted radiation scattered by a grating (e.g., alignment mark). An ideal grating may generate diffraction orders in a predictable manner. Characteristics of the diffracted radiation (e.g., intensity in each diffraction order) may be analyzed by the metrology system in order to generate, for example, an alignment position of the grating. However, actual gratings on a wafer may depart from the ideal. For example, a wafer can have one or more gratings fabricated onto the wafer when undergoing a plurality of lithographic processes to form the different layers of lithographically fabricated devices. The processes may involve polishing and / or etching that distort, smear, or otherwise damage gratings that already exist on the wafer from a prior lithographic process. The damaged grating may then diffract metrology radiation in a different manner from an ideal grating, causing a metrology system to develop an error in its measurement result. For example, a damaged grating may cause an intensity imbalance between different diffraction orders, whereas the metrology system may be expecting perfectly balanced intensities based on an assumption that an ideal or near-perfect grating has been measured.

[0075] To correct for intensity imbalances, a metrology apparatus can separately measure intensities of individual diffraction orders and use said measurements to correct a non-ideal measurement. Current metrology systems can include a beam splitting element that splits scattered radiation into first and second radiation. The first radiation forms a fringe pattern on a detector, while individual diffraction orders in the second radiation are spatially separated to form an intensity image corresponding to each diffraction order on the detector. More information is provided in U.S. Patent Publication No. 2023 / 0324817 Al published on Oct. 12, 2023, which is herein incorporated by reference.

[0076] Current systems spatially separate each diffraction order onto a separate region of a pupil, and therefore a separate region of a detector. For example, if a target has both X and Y gratings, intensities of the +1 X, +1 Y, -I X and -1 Y diffraction orders are split into four separate intensity channels on the pupil and imaged as four separate images. This takes up a large amount of space on the detector. The present disclosure provides structures and functions of compact metrology systems that provide intensity information with fewer images.

[0077] FIGS. 5A, 5B, and 5C show example targets (e.g., alignment or overlay targets), according to some aspects. FIG. 5A shows a target 500. In some aspects, target 500 is an example of a pDBO overlay mark. Target 500 can comprise four sub-targets, comprising two gratings (periodic structures) 502 extending in a first direction (x-direction) and two gratings 504 extending in a second, perpendicular direction (y-direction). The pitch of the gratings may be in the range, for example, of 300-800 nm.

[0078] FIG. 5B shows a target 510. In some aspects, target 510 is an example of a bidirectional fine (“BF”) alignment mark. Target 510 can include a grating 512 arranged at an angle of +45 degrees and a grating 514 arranged at an angle of -45 degrees relative to the X and Y axes. A BF alignment mark can have typical dimensions of 160p by 40p. The use of such marks for alignment measurements may be performed using the techniques described in U.S. Patent No. 8,208,121, as referenced above.

[0079] FIG. 5C shows a target 520. In some aspects, target 520 is an example of a symmetric fine (SF) alignment mark. Target 520 can include a checkerboard mark 522. Checkerboard mark 522 can be a 180 degree symmetric mark, and can include a plurality of two types of optically different squares differentiated by pattern, reflectance (amplitude and / or phase), or some combination thereof. When rotated 180° about an axis perpendicular to the plane, checkerboard m is substantially identical and symmetrical. In some embodiments, different alignment mark patterns can be used for target 520 as long as the alignment mark patterns exhibit 180° symmetry. For example, target 520 can include parallel lines, horizontal lines, a grid pattern, or a checkerboard grating.

[0080] Other types of alignment marks, or combinations of alignment marks, can be used. For example, other ID gratings, such as combined bidirectional marks, may be used with the systems and methods disclosed herein.

[0081] FIGS. 6A and 6B show an example metrology apparatus 600, according to some aspects. In some aspects, metrology apparatus 600 is an alternative embodiment of inspection apparatus 400, as shown in FIGS. 4 A and 4B.

[0082] Metrology apparatus 600 can include an optical module 602 configured to split radiation into separate intensity channels that are captured as multiple images by detector 604. In some aspects, scattered radiation (e.g., from a target) is received by an objective 606. The radiation from objective 606 can pass through a spot mirror 608, which can partially block radiation that is not used for metrology, such as the zeroth order radiation. The radiation can then pass into optical module 602 at the objective pupil plane.

[0083] In optical module 602, the incident pupil can be split by a non-polarizing beam splitter (NPBS) 610 into a first radiation 612 in a first arm of optical module 602, and a second radiation 614 in a second arm of optical module 602. First radiation 612 can be transmitted to a mirror 613 which changes the radiations direction of travel and an optical element 616 (e.g., half-wave plate) that rotates its polarization by 90 degrees. Second radiation 614 can be transmitted towards a second arm component 618. Second arm component 618 can spatially separate the images in second radiation 614. Spatial separation in this context means that second arm component 618 gives a controlled angle to each pupil segment, causing each pupil segment to be focused at a different location in the plane at detector 604. For example, second arm component 618 can separate positive and negative diffraction orders. In some aspects, second arm component 618 can be an optical wedge comprising two segments, as described below. Second arm component 618 can be rotatable.

[0084] First radiation 612 and second radiation 614 can be directed towards mirrors 620 and 622 respectively. Mirrors 620 and 622 direct radiation from both of the first and second arms 612 and 614 towards one or more lenses 624 and folding optics 626 before reaching detector 604.

[0085] In some aspects, as shown in FIG. 6B, optical module 602 of metrology apparatus 600 additionally includes a polarizing beam splitter 628. Both of the first and second radiation 612 and 614 can be combined on polarizing beam splitter 628 or its optical equivalent, allowing for polarizationresolved measurements. The polarizing beam splitter can project the original object polarization of second radiation 614 to a defined orthogonal polarization basis, such as X or Y. In other words, the first arm radiation and the second arm radiation combine at PBS 628 which then divides the incident radiation into two channels, in this example, two polarization resolved channels, with each channel having first radiation 612 and second radiation 614. One projected polarization state channel can propagate through a lens 624 and optional folding optics 626 to detector 604. The other orthogonal projected polarization state channel has its path folded by folding mirror 620 to propagate through a lens 624 and optional folding optics 626 to detector 604. In some aspects, each polarization state channel is incident on a separate array of detector 604. Here and elsewhere, the term “array detector” has its broadest sense of any device or system capable of capturing a light distribution including a one dimensional array detector, a two dimensional array detector, e.g., a camera, and a CCD or CMOS sensor. In the example shown in FIG. 6B, detector 604 can comprise two cameras. One or more cameras in detector 604 can be rotated about an optical axis to improve the extent to which the images fill the detector sensor.

[0086] In some aspects, signals from detector 604 are provided to a processing unit, which process the signals to create a combined display. The combined display can result in camera pictures with multiple fields.

[0087] FIG. 7 shows an example of a combined display 700, according to some aspects. Display 700 can illustrate a display image resultant from radiation diffracted from target 500, described in FIG. 5A. Combined display 700 can include display fields 702, 704, and 706. In some aspects, field 702 corresponds to light traveling through the first path of optical module 602 and fields 704 and 706 correspond to light traveling through the second path of optical module 602 (i.e., spatially separated by second arm component 618). Display fields 702, 704, and 706 can be imaged on three different cameras, or three different regions of a single camera.

[0088] In some aspects, the central field 702 shows a collection of fringe patterns. Fringe patterns in field 702 can show a phase shift between diffracted orders, such as the +1 and -1 diffraction orders. In some aspects, field 702 can contain subfields 703 and 705. Subfields 703 can correspond to fringe patterns from X oriented gratings and subfields 705 can correspond to fringe patterns from Y oriented gratings. In the example shown, the fringe patterns in subfields 703 and 705 are diagonal because the diffracted orders are diagonally arranged in the pupil, although other arrangements are possible.

[0089] In some aspects, the surrounding display fields 704 and 706 include information on the intensity of individual diffraction orders. For example, display fields 704 and 706 can show intensity information for -1 and +1 diffraction orders. Images of positive and negative diffraction orders may be separated into different fields due to spatial separation by an optical element, such as second arm component 618.

[0090] In some aspects, display field 704 shows intensities of - X and -Y diffraction orders. Because X and Y gratings are spatially separated on a wafer, the resulting image will show spatial separation of the X and Y intensities (e.g., diffraction orders for each orthogonal grating are imaged by a differentpixel on a detector). Display field 704 can display intensity imbalances of a -1 X diffraction order in subfield 708 and a -1 Y diffraction order in subfield 710.

[0091] In some aspects, display field 706 show intensities of +X and +Y diffraction orders. For example, display field 706 can display a +X diffraction order on subfields 712 and a +Y diffraction order on subfields 714. In some aspects, a combined display 700 may be generated for each polarization channel as described in reference to FIG. 6B.

[0092] It can be appreciated by one of ordinary skill in the art that a similar pattern can be obtained for other target structures. For example, display field 704 can display any negative diffraction orders of a target and display field 706 can display any positive diffraction orders of a target. For example, if a bidirectional fine alignment mark, such as target 510 is imaged, display field 704 can contain images corresponding to negative diffraction orders of -45 and +45 degree gratings and display field 706 can contain images corresponding to positive diffraction orders of -45 and +45 degree gratings. In some aspects, images of higher diffraction orders (e.g., + 2, + 3, + 4. . .+ n) may be displayed.

[0093] In some aspects, the location of positive and negative diffraction orders on a detector, such as detector 604, is dependent on a shape and / or configuration of an optical element used to spatially separate the diffraction orders.

[0094] FIG. 8 shows an optical component 800 for spatially separating diffraction orders in a metrology system, according to some aspects. Optical component 800 can comprise a segmented wedge made of two wedge segments 802. In some aspects, optical component 800 can be fabricated by gluing, or otherwise bonding, the two wedge segments 802 together. Wedge segments 802 can be arranged to divide a pupil into two separate regions. For example, a first wedge segment 802 can direct negative diffraction orders to a first section of a pupil and a second wedge segment 802 can direct positive diffraction orders to a second section of a pupil. A wedge angle 804 can be chosen for each wedge segment 802 such that positive and negative diffraction orders are split on opposite sides of a pupil plane. The wedge angle 804 of each segment 802 may depend on the orientation and grating pitch of a target imaged by a metrology system. In some aspects, a rotational angle of a line that separates two wedge segments 802 can have a value between 20-35 degrees, preferably 22.5 degrees. In some aspects, optical component 800 can be transmissive. In an alternative aspect, optical component 800 can be reflective. In some aspects, optical component 800 is rotatable.

[0095] The principles described herein are not limited to systems which use two wedge segments and can be applied as well to systems using a different number and / or orientation and / or shape of segments to, for example, capture separate higher orders. In some aspects, the segments have the same dimensions and are homogeneously distributed over the pupil. It will be appreciated that this may not be necessary for some applications.

[0096] FIG. 9A and 9B show sample pupils 900 and 900’, according to some aspects. Pupils 900 and 900’ can be separated into a first intensity channel 902 and a second intensity channel 904. Dashed line 906 can show the separation between first intensity channel 902 and second intensity channel 904. Insome aspects, negative diffraction orders appear in a first intensity channel 902 of the pupil and positive diffraction orders appear in second intensity channel 904 of the pupil. In some aspects, a gratings positive and negative diffraction orders fall on opposite region of a pupil plane. In some aspects, the location of images on a pupil plane corresponds to the location of the image on a detector.

[0097] FIG. 9 A shows a pupil 900, according to some aspects. Pupil 900 can show diffraction orders resulting from scattering by a target comprising two X gratings and two Y gratings, such as target 500 in FIG. 5 A. First intensity channel 902 can contain - 1 X diffraction order 910 and - 1 Y diffraction order 912. Second intensity channel 904 can contain +1 X diffraction order 914 and +1 Y diffraction order 916. Positive diffraction orders can be located across from their corresponding negative diffraction orders on pupil 900.

[0098] FIG. 9B shows a pupil 900’, according to some aspects. In some aspects, pupil 900’ may show diffraction resulting from scattering from an X oriented target, a Y oriented target a +45 degree oriented target and a -45 degree oriented target.

[0099] First channel 902 of pupil 900’ can include negative diffraction orders corresponding to -X orders 918, -BF-45 order 920, -Y orders 922, and -BF+45 orders 924. In some aspects, first channel 902 contains multiple diffraction orders for each grating orientation. For example, - X orders 918 can include -1 X, -2 X, and -3 X diffraction orders. Diffraction orders of other grating orientations follow a similar pattern.

[0100] Second channel 904 of pupil plane 900’ can include positive diffraction orders corresponding to BF+45, BF-45, X and Y gratings. In some aspects, the positive diffraction orders on second channel 904 are opposite the corresponding negative diffraction orders on first channel 902. For example, +X diffraction orders 926, +BF-45 diffraction orders 928, +Y diffraction orders 930, and +BF+45 diffraction orders 932 are opposite their corresponding negative diffraction orders.

[0101] FIG. 10 shows a flowchart of a method 1000 of measuring radiation, according to some aspects. Method 1000 can include steps 1002, 1004, and 1006.

[0102] In some aspects, step 1002 comprises splitting radiation that has interacted with a pattern on a substrate. The radiation can be split into a first path radiation traveling through a first arm of an optical module and a second path radiation traveling through a second arm of an optical module.

[0103] In some aspects, step 1004 comprises spatially separating positive diffraction orders and negative diffraction orders of the second path radiation using an optical component. The optical component may be a segmented wedge, such that a first segment of the wedge adjusts the angle of travel of the negative diffraction orders and the second segment of the wedge adjusts the angle of travel of the positive diffraction orders. The first and second wedge segments may have an angle of about 20-35 degrees.

[0104] In some aspects, step 1006 comprises detecting a first image corresponding to the negative diffraction orders of the second path radiation and a second image corresponding to the positive diffraction orders of the second path radiation at spatially separated regions of the detector. In someaspects, the first and second images can contain intensity information of orthogonally oriented gratings. For example, the first image may contain - I X and -1 Y intensity information and the second image can contain +1 X and +1 Y intensity information.

[0105] The method steps of FIG. 10 can be performed in any conceivable order and it is not required that all steps be performed. Moreover, the method steps of FIG. 10 described above merely reflect an example of steps and are not limiting. That is, further method steps and functions may be envisioned based upon embodiments described in reference to FIGS. 1-9.

[0106] The embodiments may further be described using the following clauses:1. A metrology device arranged to receive radiation that has interacted with a pattern on a substrate, the metrology device comprising: an optical module arranged to receive at least some of the radiation, wherein the optical module is configured to split the radiation into first radiation in a first arm and second radiation a second arm, the second arm comprising an optical wedge comprising a first segment configured to alter an angle of travel of positive diffraction orders and a second segment configured to alter an angle of travel of negative diffraction orders such that the positive and negative diffraction orders are spatially separated; and a detector, wherein the first and second segments of the optical wedge are arranged to direct the positive diffraction orders to form a first image on the detector and direct the negative diffraction orders to form a second image on the detector.2. The metrology device of clause 1 , wherein the optical wedge is transmissive.3. The metrology device of clause 1, wherein the optical wedge is reflective.4. The metrology device of clause 1 , wherein the first image comprises positive diffraction orders diffracted from an X oriented target and a Y oriented target, and the second image comprises negative diffraction orders from an X oriented target and a Y oriented target.5. The metrology device of clause 4, wherein the first image additionally comprises positive diffraction orders from a +45 degree oriented target and a -45 degree oriented target, and the second image additionally comprises negative diffraction orders from a +45 degree oriented target and a -45 degree oriented target.6. The metrology device of clause 1 , wherein the first and second segments of the optical wedge have an angle between 20 and 35 degrees.7. The metrology device of clause 1, wherein the metrology device is an alignment sensor.8. The metrology device of clause 1, wherein the metrology device is an overlay sensor.9. The metrology device of clause 1, wherein the detector is a camera and the first image and the second image are simultaneously received by different pixels on the camera.10. A lithography apparatus comprising the metrology device of clause 1.11. A metrology device arranged to receive radiation that has interacted with a pattern on a substrate, the metrology device comprising:an optical module arranged to receive at least some of the radiation, wherein the optical module is configured to split the radiation into first radiation in a first arm and second radiation in a second arm, one of the first arm and the second arm comprising a polarization component adapted to rotate a polarization of a corresponding one of the first radiation and second radiation, and the second arm comprising an optical wedge comprising a first segment configured to alter the angle of travel of positive diffraction orders, and a second segment configured to alter the angle of travel of negative diffraction orders such that the positive and negative diffraction orders are spatially separated, wherein the optical module further includes a polarizing beam splitter arranged to: receive the first radiation from the first arm and the second radiation from the second arm, split the first radiation into first channel first radiation and second channel first radiation, split the separated second radiation into first channel second radiation and second channel second radiation, and cause the first channel first radiation and the first channel second radiation to co-propagate as combined first channel radiation, and cause the second channel first radiation and the second channel second radiation to co-propagate as combined second channel radiation; and a detector, wherein the first and second segments of the optical wedge are arranged to direct the positive diffraction orders to form a first image on the detector, and direct the negative diffraction orders to form a second image on the detector.12. The metrology device of clause 11, further comprising: a first lens arranged to focus the combined first channel radiation on a first portion of the detector; and a second lens arranged to focus the combined second channel radiation onto a second portion of the detector.13. The metrology device of clause 12, wherein the first portion of the detector is a first camera and the second portion of the detector is a second camera.14. The metrology device of clause 11, wherein the optical wedge is transmissive.15. The metrology device of clause 11, wherein the optical wedge is reflective.16. The metrology device of clause 11 , wherein the first image comprises positive diffraction orders diffracted from an X oriented target and a Y oriented target and the second image comprises negative diffraction orders from an X oriented target and a Y oriented target.17. The metrology device of clause 16, wherein the first image additionally comprises positive diffraction orders from a +45 degree target and a -45 degree target and the second image additionally comprises negative diffraction orders from a +45 degree target and a -45 degree target.18. The metrology device of clause 11, wherein the first and second segments of the optical wedge have an angle between 20 and 35 degrees.19. A lithography apparatus comprising the metrology device of clause 11.20. A method comprising:splitting radiation that has interacted with a pattern on a substrate into a first path radiation travelling through a first arm of an optical module and a second path radiation traveling through a second arm of an optical module; spatially separating positive diffraction orders and negative diffraction orders of the second path radiation by passing positive diffraction orders through a first segment of an optical wedge and negative diffraction orders through a second segment of an optical wedge; and detecting a first image corresponding to positive diffraction orders of the second path radiation and a second image corresponding to negative diffraction orders of the second path radiation at spatially separated regions of a detector.

[0107] 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.

[0108] 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.

[0109] The terms “radiation,” “beam of radiation” or the like as used herein may can encompass all types of electromagnetic radiation, for example, ultraviolet (UV) radiation (for example, having a wavelength I of 365, 248, 193, 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 certain wavelength band, of which at least part is in the range of 5-20 nm.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] The breadth and scope of the protected subject matter should not be limited by any of the abovedescribed example aspects, but should be defined only in accordance with the following claims and their equivalents.

Claims

CLAIMS1. A metrology device arranged to receive radiation that has interacted with a pattern on a substrate, the metrology device comprising: an optical module arranged to receive at least some of the radiation, wherein the optical module is configured to split the radiation into first radiation in a first arm and second radiation a second arm, the second arm comprising an optical wedge comprising a first segment configured to alter an angle of travel of positive diffraction orders and a second segment configured to alter an angle of travel of negative diffraction orders such that the positive and negative diffraction orders are spatially separated; and a detector, wherein the first and second segments of the optical wedge are arranged to direct the positive diffraction orders to form a first image on the detector and direct the negative diffraction orders to form a second image on the detector.

2. The metrology device of claim 1 , wherein the optical wedge is transmissive.

3. The metrology device of claim 1, wherein the optical wedge is reflective.

4. The metrology device of claim 1 , wherein the first image comprises positive diffraction orders diffracted from an X oriented target and a Y oriented target, and the second image comprises negative diffraction orders from an X oriented target and a Y oriented target.

5. The metrology device of claim 4, wherein the first image additionally comprises positive diffraction orders from a +45 degree oriented target and a -45 degree oriented target, and the second image additionally comprises negative diffraction orders from a +45 degree oriented target and a -45 degree oriented target.

6. The metrology device of claim 1 , wherein the first and second segments of the optical wedge have an angle between 20 and 35 degrees.

7. The metrology device of claim 1, wherein the metrology device is an alignment sensor.

8. The metrology device of claim 1, wherein the metrology device is an overlay sensor.

9. The metrology device of claim 1, wherein the detector is a camera and the first image and the second image are simultaneously received by different pixels on the camera.

10. A lithography apparatus comprising the metrology device of claim 1.

11. A metrology device arranged to receive radiation that has interacted with a pattern on a substrate, the metrology device comprising: an optical module arranged to receive at least some of the radiation, wherein the optical module is configured to split the radiation into first radiation in a first arm and second radiation in a second arm, one of the first arm and the second arm comprising a polarization component adapted to rotate a polarization of a corresponding one of the first radiation and second radiation, and the second arm comprising an optical wedge comprising a first segment configured to alter the angle of travel of positive diffraction orders, and a second segment configured to alter the angle of travel of negative diffraction orders such that the positive and negative diffraction orders are spatially separated, wherein the optical module further includes a polarizing beam splitter arranged to: receive the first radiation from the first arm and the second radiation from the second arm, split the first radiation into first channel first radiation and second channel first radiation, split the separated second radiation into first channel second radiation and second channel second radiation, and cause the first channel first radiation and the first channel second radiation to co-propagate as combined first channel radiation, and cause the second channel first radiation and the second channel second radiation to copropagate as combined second channel radiation; and a detector, wherein the first and second segments of the optical wedge are arranged to direct the positive diffraction orders to form a first image on the detector, and direct the negative diffraction orders to form a second image on the detector.

12. The metrology device of claim 11, further comprising: a first lens arranged to focus the combined first channel radiation on a first portion of the detector; and a second lens arranged to focus the combined second channel radiation onto a second portion of the detector.

13. The metrology device of claim 12, wherein the first portion of the detector is a first camera and the second portion of the detector is a second camera.

14. The metrology device of claim 11 , wherein the optical wedge is transmissive.

15. The metrology device of claim 11 , wherein the optical wedge is reflective.

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