Apparatus and method for combined display of optical measurement information

Abstract

Devices and methods are disclosed for simultaneously acquiring and presenting multiple types of alignment information in which a pupil is divided and radiation from the pupil is spatially separated. In some versions, the alignment information is first order diffraction information and polarization channel intensity information simultaneously presented in an image-based system.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority of U.S. Application No. 63 / 428,762, filed on November 30, 2022, and the entire content of this U.S. application is incorporated herein by reference. Technical field

[0003] The subject matter of the present disclosure relates to devices and methods for obtaining and displaying measurement information in lithographic apparatuses and processes. Background art

[0004] A lithographic apparatus applies a desired pattern onto a substrate, typically onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device (which is alternatively referred to as a mask or reticle) can be used to generate a circuit pattern to be formed on a single layer of the IC. Such a pattern can be transferred onto a target portion (e.g., a portion of a die, one die, or several dice) on the substrate (e.g., a silicon wafer).

[0005] Pattern transfer is typically achieved by imaging onto a layer of radiation - sensitive material (resist) provided on the substrate. Usually, a single substrate will include a network of adjacent target portions that are successively patterned.

[0006] ICs are created layer - by - layer, and modern ICs can have many layers. Successive layers or multiple processes on the same layer must be accurately aligned with the previous layer. Otherwise, the electrical contacts between structures will be poor and the resulting device will not perform to specification. Overlay (OPO) on the product is a measure of the ability of the system to print these layers accurately on top of each other. Good overlay improves device yield and enables the printing of smaller product patterns.

[0007] One or more patterns, such as overlay marks, are typically provided on the substrate to control the lithographic process to accurately place device features on the substrate. It is known that different types of marks and different types of systems are from different times and different manufacturers. Types of overlay marks include bidirectional fine (BF) wafer overlay marks and smaller format marks, such as micro - diffraction - based overlay (µDBO) overlay marks (e.g., C16 or C10 marks). These marks are configured as patterns of lines, for example.

[0008] Typically, these marks are printed on top of each other, i.e., one mark is printed on one layer and later a second mark is printed on another layer at a target location relative to the first mark, i.e., above the first mark. If the two marks are perfectly registered, the overlay error is zero and it can be assumed that the features on the second layer have been printed in the proper location. If the two marks are not perfectly registered, there is a non-zero overlay error indicating the degree of misalignment between the two layers. The lack of registration is encoded in the diffraction order intensity in the interference pattern of the light scattered from the overlaid marks.

[0009] Specifically, one type of alignment tool is a scatterometer, in which a radiation beam is directed onto a target on the surface of a substrate and the properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it has interacted with the substrate (e.g., reflected or scattered by the substrate), the properties of the substrate can be determined. For example, this determination can be achieved by comparing the reflected beam with data stored in a known measurement database associated with known substrate properties. A spectroscopic scatterometer directs a broadband radiation beam onto the substrate and measures the spectrum (intensity as a function of wavelength) of the radiation scattered into a specific narrow angular range. In contrast, an angular-resolved scatterometer uses a monochromatic radiation beam and measures the intensity of the scattered radiation as a function of angle.

[0010] In angular-resolved scatterometry, the illumination branch irradiates the overlapping target within a large range of incident space. Then the diffraction orders of the light from the grating are acquired. The zero-order intensity varies symmetrically with respect to the overlay, while the + / -1-order intensities vary asymmetrically with respect to the overlay. The first-order intensity difference can be used to determine the overlay.

[0011] The properties measured by the scatterometer at different wavelengths and angles can include the relative intensities of different polarized radiations. These relative intensities can be used to correct for distorted marks caused, for example, by asymmetry.

[0012] Known lithographic apparatuses use multiple alignment systems to align a substrate relative to the lithographic apparatus. Data can be obtained, for example, using any type of alignment sensor, such as a Smart Mix Alignment Sensor Hybrid (SMASH) sensor, as described in U.S. Patent No. 6,961,116, issued November 1, 2005, and entitled "Lithographic Apparatus, Device Manufacturing Method, and Device Manufactured Thereby", which alignment sensor employs a self-referencing interferometer with a single detector and four different wavelengths and extracts alignment signals in software. Another system is the Advanced Technology with High-Order Alignment (ATHENA), as described in U.S. Patent No. 6,297,876, issued October 2, 2001, and entitled "Lithographic Projection Apparatus with an Alignment System for Aligning Substrate on Mask", which directs each of seven diffraction orders to a dedicated detector or an ORION sensor, which uses multiple polarizations for each available signal (color).

[0013] All patent applications, patents, and printed publications cited herein are incorporated herein by reference in their entirety, where, except for any definitions, disclaimers of subject matter, or denials and except to the extent that the material contained therein is inconsistent with the expressly disclosed content herein, in which case the language herein shall govern.

[0014] Another known alignment system is described in WIPO International Publication No. WO 2020 / 057900, published March 26, 2020, and entitled "Metrology Sensor for Position Metrology". One of the systems described therein uses multiple spatially incoherent illumination beams and multiple pupil points in the illumination pupil of the metrology device.

[0015] To improve the benefits of throughput, alignment information needs to be made available in a way that facilitates and accelerates measurements. This need can be addressed at least in part by concurrently (i.e., simultaneously) displaying multiple types of data. Thus, in a camera-based system, being able to concurrently display, for example, images representing polarization-resolved measurements and intensity information per diffraction order would be beneficial for some applications. In such a context, a need for the subject matter disclosed herein arises. SUMMARY OF THE INVENTION

[0016] A brief summary of one or more embodiments is presented below to provide a basic understanding of the present invention. This summary is not intended as an extensive overview of all the covered embodiments, nor does it identify the key or decisive elements of all possible embodiments, or delimit the scope of any or all possible embodiments. Its sole purpose is to present some concepts related to one or more embodiments in a concise form as a prelude to the more detailed description presented later.

[0017] According to one aspect of an embodiment, a metrology device is disclosed, the metrology device being configured to collect radiation that has interacted with a pattern on a substrate. The metrology device includes: an objective lens arranged to collect the radiation; and an optical module arranged to receive at least some of the radiation and adapted to split the radiation into first-path radiation traveling in a first arm and second-path radiation traveling in a second arm. One of the first arm and the second arm may include a polarization component adapted to rotate the polarization of the first-path radiation and a corresponding one of the polarization intensity information, and the second arm may include a second-arm component adapted to spatially separate the second-path radiation.

[0018] The optical module further includes a polarization beam splitter arranged to: receive the first path from the first arm and the second path radiation from the second arm, and split the first-path radiation into first-channel first-path radiation and second-channel first-path radiation and split the separated second path into first-channel second-path radiation and second-channel second-path radiation, and cause the first-channel first-path radiation and the first-channel second-path radiation to propagate together as combined first-channel radiation and cause the second-channel first-path radiation and the second-channel second-path radiation to propagate together as combined second-channel radiation.

[0019] The metrology device may be part of an alignment sensor or an alignment sensing system. The metrology device may be part of an overlay sensor or an overlay sensing system. The second-arm component adapted to spatially separate the second-path radiation may be configurable. The second-arm component adapted to be adjusted to spatially separate the second-path radiation may include a rotatable optical wedge.

[0020] The measurement device may further include: a first lens arranged to receive and focus the first channel radiation; a first array detector arranged at the focal plane of the first lens; a second lens arranged to receive and focus the second channel radiation; and a second array detector arranged at the focal plane of the second lens. The first array detector may include a first camera, and the second array detector may include a second camera. The first array detector may have a first optical axis and may be rotatable relative to the first optical axis to improve the filling of the first channel radiation on the first array detector. The polarization component may include a half-wave plate. The first arm may include the polarization component adapted to rotate the polarization of the image information radiation. The polarization component may include a half-wave plate.

[0021] The second arm component may include a segmented optical wedge arranged to spatially separate the second path radiation. The segmented optical wedge may be transmissive. The segmented optical wedge may be reflective. The second arm component may include a split-aperture wavefront (PAW) imaging lens.

[0022] According to another aspect of an embodiment, a measurement device is disclosed that is configured to collect radiation that has interacted with a pattern on a substrate. The measurement device includes: an objective lens arranged to collect the radiation; and an optical module arranged to receive at least some of the radiation and adapted to split the radiation into image information radiation traveling in a first arm and second path radiation traveling in a second arm.

[0023] The first arm includes a half-wave plate adapted to rotate the polarization of the image information radiation, and the second arm includes a segmented optical wedge arranged to spatially separate the second path radiation. The optical module further includes a polarization beam splitter arranged to: receive the image information from the first arm and the second path radiation from the second arm, split the image information radiation into first channel image information radiation and second channel image information radiation and split the separated second path radiation into first channel second path radiation and second channel second path radiation, and cause the first channel image information radiation and the first channel second path radiation to propagate together as combined first channel radiation and cause the second channel image information radiation and the second channel second path radiation to propagate together as combined second channel radiation.

[0024] The device further includes: a first lens arranged to receive and focus the first channel radiation; a first array detector arranged at the focal plane of the first lens; a second lens arranged to receive and focus the second channel radiation; and a second array detector arranged at the focal plane of the second lens.

[0025] The measuring device can be an alignment sensor or part of an alignment sensing system. The measuring device can be an overlay sensor or part of an overlay sensing system.

[0026] The first array detector can include a first camera, and the second array detector can include a second camera. The first array detector can have a first optical axis, and wherein the first array detector can be rotatable relative to the first optical axis to improve or enhance the filling of the first channel radiation on the first array detector. The segmented optical wedge can be rotatable.

[0027] According to another aspect of the embodiment, an optical module is disclosed, including: a first arm including a half-wave plate; a second arm including a segmented optical wedge; a neutral beam splitter arranged to split an incident radiation beam into a first component traveling in the first arm and a second component traveling in the second arm; and a polarization beam splitter arranged to receive the first component after the first component has traveled through the first arm and to receive the second component after the second component has traveled through the second arm.

[0028] The half-wave plate can rotate the polarization of the first component by ninety degrees. The segmented optical wedge can separate the second component into a plurality of spatially separated components. The polarization beam splitter can cause a first part of the first component to propagate together with a first part of the second component. The polarization beam splitter can cause a second part of the first component to propagate together with a second part of the second component.

[0029] The optical module can be an alignment sensor or part of an alignment sensing system. The optical module can be an overlay sensor or part of an overlay sensing system. The segmented optical wedge can be rotatable.

[0030] According to another aspect of the embodiment, an optical module is disclosed, comprising: a first optical component including a neutral beam splitter arranged to split an incident radiation beam into a first sub-beam traveling in a first arm and a second sub-beam traveling in a second arm, the first arm including a second optical component including a half-wave plate, and the second arm including a third optical component including a segmented optical wedge; and a fourth optical component including a polarization beam splitter arranged to receive the first sub-beam after the first sub-beam may have traveled through the first arm and to receive the second sub-beam after the second sub-beam may have traveled through the second arm. The optical module further includes: a first transparent element attached to and connecting the first optical component and the second optical component; a second transparent element attached to and connecting the second optical component and the fourth optical component; a third transparent element attached to and connecting the first optical component and the third optical component; and a fourth transparent element attached to and connecting the third optical component and the fourth optical component, such that the optical module can be configured as an integral block.

[0031] The half-wave plate may rotate the polarization of the first sub-beam by ninety degrees. The segmented optical wedge may separate the second sub-beam into a plurality of spatially separated components. The polarization beam splitter may cause a first portion of the first sub-beam to propagate together with a first portion of the second sub-beam. The polarization beam splitter may cause a second portion of the first sub-beam to propagate together with a second portion of the second sub-beam.

[0032] The optical module may be an alignment sensor or part of an alignment sensing system. The optical module may be an overlap sensor or part of an overlap sensing system. The segmented optical wedge may be rotatable.

[0033] According to another aspect of an embodiment, a measurement method is disclosed, including: collecting radiation that has interacted with a pattern on a substrate; splitting at least a portion of the radiation into image information radiation and second path radiation; rotating the polarization of one of the second path radiation and the image information radiation, and the second arm includes a second arm component adapted to spatially separate the second path radiation; and splitting the image information radiation into first channel image information radiation and second channel image information radiation and simultaneously splitting the separated second path into first channel second path radiation and second channel second path radiation, and causing the first channel image information radiation and the first channel second path radiation to propagate together as combined first channel radiation and causing the second channel image information radiation and the second channel second path radiation to propagate together as combined second channel radiation.

[0034] The measurement method may further include focusing the first channel radiation on a first array detector and focusing the second channel radiation on a second array detector.

[0035] Other embodiments, features, and advantages of the subject matter of the present disclosure, as well as the structure and operation of each embodiment, are described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic diagram, not drawn to scale, showing the general broad concept of a lithography system.

[0037] Figure 2A is an example of an overlay mark such as may be used in accordance with aspects of some embodiments.

[0038] Figure 2B is such as may be Figure 2A an image of a diffraction order generated by interaction of an incident beam with an overlay mark.

[0039] Figure 3A is a pupil representation corresponding to the resulting radiation after scattering of an off-axis illumination beam.

[0040] Figure 3B shows the resulting pupil (only the acquired orders) generated by four off-axis beams.

[0041] Figure 4 is a schematic diagram of a system for simultaneously displaying a diffraction pattern and polarization channel intensity information according to aspects of an embodiment.

[0042] Figure 5A is such as may be Figure 4 a representation of an example of a simultaneous display generated by a system.

[0043] Figure 5B is such as inFigure 4 Schematic diagram of the relative angular orientation of the point mirror and segmented wedge in a system like the one shown in .

[0044] Figure 6A is a schematic diagram of another system for simultaneously displaying diffraction patterns and polarization channel intensity information according to another aspect of the embodiment.

[0045] Figure 6B is a schematic diagram of another system for simultaneously displaying diffraction patterns and polarization channel intensity information according to another aspect of the embodiment.

[0046] Figure 6C is a schematic diagram of another system for simultaneously displaying diffraction patterns and polarization channel intensity information according to another aspect of the embodiment.

[0047] Figure 7 is a schematic diagram of another system for simultaneously displaying diffraction patterns and polarization channel intensity information according to another aspect of the embodiment.

[0048] Figure 8A is a perspective view of an example of a segmented optical wedge such as may be used in various embodiments.

[0049] Figure 8B is a perspective view of an example of a segmented lens array such as may be used in various embodiments.

[0050] Figure 9 is a graphical representation of an arrangement of fields in a combined display according to aspects of an embodiment.

[0051] Figure 10 is a graphical representation of an arrangement of fields in a combined display according to aspects of an embodiment.

[0052] Figure 11 is a graphical representation of an arrangement of fields in a combined display according to aspects of an embodiment.

[0053] Figure 12 is a schematic diagram of a system for simultaneously displaying diffraction patterns and polarization channel intensity information according to aspects of an embodiment.

[0054] Figure 13A , Figure 13B and Figure 13C is a schematic diagram of a portion of a system for simultaneously displaying diffraction patterns and polarization channel intensity information according to aspects of an embodiment.

[0055] Figure 14 is a schematic diagram of a portion of a system for simultaneously displaying diffraction patterns and polarization channel intensity information according to aspects of an embodiment.

[0056] Figure 15Schematic diagram of a part of a system for simultaneously displaying a diffraction pattern and polarization channel intensity information according to an aspect of an embodiment.

[0057] The following describes in detail other features and advantages of the disclosed subject matter, as well as the structure and operation of various embodiments of the disclosed subject matter, with reference to the accompanying drawings. It should be noted that the applicability of the disclosed subject matter is not limited to the specific embodiments described herein. These embodiments are presented herein for illustrative purposes only. Based on the teachings included herein, those skilled in the relevant art will appreciate additional embodiments. Detailed Description

[0058] Various embodiments are now described with reference to the drawings, wherein like reference numerals are always used to refer to like elements. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. However, it is apparent that in some or all instances, any of the embodiments described below may be practiced or carried out without the specific design details described below. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate the description of one or more embodiments.

[0059] Embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include: read-only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; propagated signals in electrical, optical, acoustic, or other forms (e.g., carrier waves, infrared signals, digital signals, etc.); and the like.

[0060] As an introduction, Figure 1 An embodiment of a lithographic apparatus LA that may be associated with the present system is schematically depicted. The lithographic apparatus LA includes an illumination system (illuminator) IL configured to condition a radiation beam B. As used herein, the terms “radiation” and “beam” encompass all types of electromagnetic radiation, including ultraviolet (UV) or deep ultraviolet (DUV) radiation (e.g., having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range of 5 nm to 20 nm), as well as particle beams, such as ion beams or electron beams.

[0061] The lithographic apparatus LA also includes a support structure (e.g., a mask table) MT configured to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device according to certain parameters; one or more substrate tables (e.g., wafer tables) WT (in the example, two wafer tables WTa and WTb), the one or more substrate tables being configured to hold a substrate (e.g., a wafer coated with resist) W. Each wafer table is mechanically connected to a corresponding positioner PW configured to accurately position the substrate on the wafer support surface WSS according to certain parameters.

[0062] The lithographic apparatus LA also includes a projection system (e.g., a refractive projection lens system) PS configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., including one or more dies and commonly referred to as a field) of the substrate W. The projection system is supported on a reference frame RF.

[0063] As depicted, the apparatus is of the transmissive type (e.g., using a transmissive mask). Alternatively, the apparatus may be of the reflective type (e.g., using a programmable mirror array of the type mentioned above, or using a reflective mask).

[0064] The illuminator IL receives a radiation beam from a radiation source SO. For example, when the radiation source is an excimer laser, the radiation source and the lithographic apparatus may be separate entities. In such a case, the radiation beam is transferred from the source SO to the illuminator IL by means of a beam delivery system BD, which includes, for example, suitable directing mirrors and / or beam expanders. In other cases, for example when the source is a mercury lamp, the source may be an integral part of the apparatus. The source SO and the illuminator IL together with the beam delivery system BD may be referred to as the radiation system when required. If the radiation source is of the type that generates EUV radiation, reflective optics will generally be used.

[0065] The illuminator IL may include an adjuster AD configured to adjust the (angular / spatial) intensity distribution of the beam. Additionally, the illuminator IL generally includes various other components, such as an integrator IN and a condenser CO. The illumination system may include various types of optical components for guiding, shaping, or controlling the radiation. Thus, the illuminator IL provides a conditioned radiation beam B having a desired uniformity and intensity distribution in the cross-section of the conditioned radiation beam B.

[0066] The support structure MT holds the patterning device using mechanical, vacuum, electrostatic or other clamping techniques to maintain the patterning device. The term "patterning device" as used herein should be construed broadly as referring to any device that can be used to impart a pattern in a target portion of a substrate. The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels.

[0067] The lithographic apparatus may be of the type having two (dual stage) or more stages (e.g., two or more substrate stages WTa, WTb, two or more patterning device stages, a substrate stage WTa and a stage WTb under the projection system without a dedicated substrate for, e.g., facilitating measurement and / or cleaning). In these "multi-stage" machines, additional stages may be used in parallel, or preparatory steps may be carried out on one or more stages while one or more other stages are used for exposure. For example, alignment measurements using an alignment sensor AS and / or leveling (height, tilt, etc.) measurements using a leveling sensor LS may be performed.

[0068] The lithographic apparatus may also be of the type in which at least a portion of the substrate is covered by a liquid (e.g., water) having a relatively high refractive index to fill the space between the projection system and the substrate.

[0069] In operation of the lithographic apparatus LA, the radiation beam B is conditioned and provided by the illumination system IL. The radiation beam B is incident on a patterning device (e.g., a mask) MA held on a support structure (e.g., a mask table) MT and is patterned by the patterning device. After having traversed the patterning device MA, the patterned radiation beam B passes through the projection system PS which focuses the beam onto a target portion C of the substrate W. By means of corresponding positioners PW and position sensors IF (e.g., interferometric devices, linear encoders, 2-D encoders or capacitive sensors) of the wafer stage WTa or WTb, the wafer stage WTa or WTb can be accurately moved, e.g., to position different target portions C in the path of the patterned radiation beam B. Similarly, another positioner and another position sensor (which are not explicitly depicted in Figure 1 can be used to accurately position the patterning device MA relative to the path of the radiation beam B, e.g., after mechanical retrieval from a mask library or during scanning.

[0070] Patterning device marks M1, M2 and marks P1, P2 may be used to align the patterning device MA with the substrate W. Although the illustrated marks occupy dedicated target portions, the marks may be located in the space between the target portions. Similarly, in the case where more than one die is provided on the patterning device MA, the patterning device marks may be located between the dies.

[0071] The substrates mentioned herein can be processed in an automated resist coating and development system (a tool that typically applies a resist layer to a substrate and develops the exposed resist), or a metrology or inspection tool, for example, before or after exposure. In appropriate cases, the disclosures herein can be applied to these and other substrate processing tools. Additionally, the substrate can be processed more than once, for example, to produce a multi-layer IC, such that the term "substrate" as used herein can also refer to a substrate that already includes one or more processed layers.

[0072] Figure 2A and Figure 2B illustrate some aspects of an example of an alignment mark for determining alignment parameters. Figure 2A Illustrate target 310, which is an example of a µDBO overlap mark that can be used as an overlap mark in some embodiments. Target 310 includes four sub-targets, including two gratings (periodic structures) 315a extending in a first direction (x-direction) and two gratings 315b extending in a perpendicular second direction (y-direction). The pitch of the gratings can be in the range of, for example, 300 nm to 800 nm.

[0073] In a manner similar to other metrology devices that can be used for alignment sensing, a shift in the position of the target gratings causes a phase shift between the diffraction orders in each direction (such as the +1 and -1 diffraction orders). The diffraction orders are caused to interfere on a camera. The phase shift between the diffraction orders causes a corresponding shift in the interference fringes on the camera. Thus, the alignment position can be determined from the position of the interference fringes on the camera.

[0074] Specifically, in this example, the acquired orders include the -1 x-direction diffraction order, the +1 x-direction diffraction order, the -1 y-direction diffraction order, and the +1 y-direction diffraction order. These diffraction orders are imaged on a camera, where they interfere to form a fringe pattern 350 such as Figure 2B shown in, having fields 316a and 316b corresponding to gratings 315a and 315b, respectively. In the example shown, since the diffraction orders are arranged diagonally in the pupil, the fringe pattern is diagonal, but other arrangements with different resulting fringe pattern orientations are possible.

[0075] Figure 3A and Figure 3B illustrate the working principle of a metrology system. Figure 3Ais a pupil representation corresponding to the radiation obtained after scattering of a single off-axis illumination beam 420. The zero-order diffracted beam is shown as 420'. The shaded region 422 corresponds to the blocking (i.e., reflecting or absorbing) region of a specific point mirror design, where white represents the transmission region, which can be used in an embodiment. This point mirror design is just one example of a pupil block that ensures that unwanted light (such as the light around the zero-order and the zero-order) is not detected. Other point mirror profiles (or substantially zero-order blocks) can be used. As used herein, the term "point mirror" refers to any optical element for zero-order blocking.

[0076] As Figure 3A can be seen, only one of the higher diffraction orders is acquired, more specifically, the -1 X-direction diffraction order 425. The +1 X-direction diffraction order 430, the -1 Y-direction diffraction order 435, and the +1 Y-direction diffraction order 440 fall outside the pupil (the detection NA represented by the extent of the point mirror 422) and are not acquired. Any higher orders (not shown) also fall outside the detection NA. The zero-order 420 is shown for illustration purposes, but in reality, the zero-order 420 will be blocked by the point mirror or the zero-order block 422.

[0077] Figure 3B shows the resulting pupil (only the acquired orders) generated by four off-axis beams. The acquired orders include the -1 X-direction diffraction order 425', the +1 X-direction diffraction order 430', the -1 Y-direction diffraction order 435', and the +1 Y-direction diffraction order 440'. These diffraction orders are imaged on a camera, where they interfere to form the fringe pattern shown in Figure 2B . Again, in the example shown, the fringe pattern is diagonal when the diffraction orders are diagonally arranged in the pupil, but other arrangements with different resulting fringe pattern orientations are possible. The original off-axis illumination beam 420 is at least partially coherent for the x illumination order and at least partially coherent for the y illumination order to allow the corresponding diffraction orders to interfere.

[0078] As mentioned, some applications desire the ability to present multiple images in a coordinated unified format, each image expressing its own alignment data, e.g., an image representing information related to a series of diffraction orders of a specific polarization of the radiation that has interacted with the image. According to aspects of an embodiment, this is achieved by using a system that can be implemented as a compact optical building block without switchable optical elements.

[0079] According to aspects of an embodiment, an optical arrangement includes at least two paths for radiation that has interacted with a pattern on a substrate. A first path conveys a first portion of the radiation (first path radiation), and a second path conveys a second portion of the radiation (second path radiation). The first path and the second path include different optical elements such that the first path produces a first image including first image information and the second path produces a second image including second image information. The images can then be presented together for simultaneous synthesis to display the first image and the second image.

[0080] As an example, the first image can be an interference image and the second image can be an intensity image. As another example, in the case where the second path includes an optical device that crops a portion of the pupil and images the cropped radiation, the first image can be characterized as a full image and the second image can be characterized as a partial pupil image. As another example, the first path can produce a conventional bright field image and the other path can convey a “dark field imaging mode” image. In such an embodiment, a partial pupil block can be placed together with an image separation element (e.g., a prism or a tilted mirror or a tilted beam splitter) to separate the images in the synthesized image. As another example, one of the paths can implement a “phase contrast imaging mode”. Such an arrangement will use a phase plate in a portion of the pupil that shifts the phase in that portion of the pupil relative to the rest of the pupil. As yet another example, there can be an arrangement in which a focused image comes from one path and a defocused image comes from the other path. This can be achieved, for example, by adding a weak lens in the second path. If spatially coherent light is used, such an arrangement is substantially capable of obtaining both the phase and the amplitude of the light from a single image.

[0081] Specifically, in Figure 4 the illustrated embodiment, the objective lens 500 receives radiation that has interacted with a pattern (e.g., an overlapping mark such as the overlapping mark 310 described above). The radiation from the objective lens 500 passes through the point mirror 510, which partially blocks radiation not used for measurement, such as the zero order. The radiation then enters the module 520 at the objective pupil plane.

[0082] The entrance pupil is split into two arms, namely a first arm 535 and a second arm 537, by a non-polarizing beam splitter (NPBS) 530. This entrance pupil will include some polarization state information collected from the target 310. When the entrance pupil is projected based on orthogonal polarizations (e.g., X polarization and Y polarization), the system presents information related to the alignment response of the target 310. The first arm 535 transmits a first light beam to an optical element 550, such as a half-wave plate (HWP), which rotates the polarization of the first beam by 90 degrees. The second arm 537 uses a second arm component 560 to achieve spatial separation of the image in the lower light beam. The second arm component 560 can be a prism or a partitioned aperture wavefront (PAW) imaging lens as described below. Spatial separation in this context means that the second arm component 560 provides a controlled angle to each pupil segment such that each pupil segment is focused at a different position in the plane at the first array detector 610 and the second array detector 640. Each pupil segment can include a single diffraction order or a series of diffraction orders. In some embodiments, the second arm component 560 is configurable. For example, in the case where the second arm component 560 is implemented as a prism, the prism can be rotatable.

[0083] Both the first arm 535 and the second arm 537 are combined on a polarization beam splitter (PBS) 570 or its optical equivalent, allowing polarization-resolved measurements. The PBS 570 projects the original objective polarization in the second arm 537 onto a defined orthogonal polarization reference (such as X or Y). In other words, the first arm radiation and the second arm radiation are combined at the PBS 570, which then divides the incident radiation into two channels, in this example two polarization-resolved channels, where each channel has first arm radiation and second arm radiation. Optionally, mirrors 540 and 580 are provided to fold the beam path as needed to allow a physically compact configuration. One projected polarization state channel propagates through a lens 590 and optional folding optics 600 to the first array detector 610. The other orthogonally projected polarization state channel has its path folded by a folding mirror 650 to propagate through a lens 620 and optional folding optics 630 to the second array detector 640. Here and elsewhere, the term "array detector" has its broadest meaning and refers to any device or system capable of acquiring a light distribution, including one-dimensional array detectors, two-dimensional array detectors (e.g., cameras), and CCD or CMOS sensors. In the example shown, the array detectors 610 and 640 are cameras. The first array detector 610 or the second array detector 640 or both can be rotated about their optical axes 612 and 642 respectively to improve or enhance the degree to which the image fills the array detector sensor.

[0084] Signals from array detectors 610, 640 are provided to a processing unit 670 which processes the signals in a known manner to produce a combined display 700 that simultaneously displays fields 710, 720, 730, 740, and 750 that together include information from two channels. As described more fully below, the arrangement and selection of optical components can be chosen to obtain any of a number of relative positions of these fields in the combined display 700.

[0085] The combined output can produce a camera image that includes multiple fields. An example of such a combined display of the results is shown as combined display 700 in Figure 5A The central field 710 corresponds to a set of fringe patterns 350 from Figure 2B The surrounding fields 720, 730, 740, and 750 include images with separate polarization intensity information. In other words, the diffraction pattern and the intensity pattern of the same polarization projection state are imaged on the same array detector. Specifically, field 720 includes intensity information of the target field for one diffraction order (e.g., -1 X order) of the displayed polarization channel. Field 730 includes intensity information of the target field for another diffraction order (e.g., +1 X order) of the displayed polarization channel. Field 740 includes intensity information of the target field for another diffraction order (e.g., -1 Y order) of the displayed polarization channel. Field 750 includes intensity information of the target field for another diffraction order (e.g., +1 Y order) of the displayed polarization channel.

[0086] The orientation, arrangement, and content of the fields depend on the optical wedge orientation and design. Here, “content” refers to which diffraction orders are imaged at which positions on the displayed combined image. In the illustrated embodiment, the second arm member 560 is a four-fold optical wedge oriented relative to the point mirror 510 indicated in Figure 5B However, it should be understood that other relative orientations and different numbers of optical wedge segments can be used. The concepts set forth herein can be extended to different numbers and / or orientations and / or shapes of segments, such as for separating higher orders.

[0087] In this embodiment, the path defined by the object NPBS 530 - mirror 540 - HWP 550 - PBS 570 is traversed by radiation forming an alignment pattern. The path defined by NPBS 530 - optical wedge 560 - mirror 580 - PBS 570 is traversed by radiation forming a surrounding field, each field representing a series of diffraction orders. Since the two image paths recombine on PBS 570, the transmitted output has orthogonal polarization. The system is configured to allow the polarization state of the radiation to be analyzed by projecting the radiation onto a desired polarization reference when the radiation reaches NPBS 530. This means that for a specific polarization state at NPBS 530, the two resulting image paths corresponding to this specific polarization state are directed to the same focal plane. This is achieved by introducing HWP 550, which rotates the polarization state of the image by 90°.

[0088] Instead of using HWP 550 placed in the image path NPBS 530 - mirror 540 - HWP 550 - PBS 570 to rotate the polarization state, polarization rotation can also be achieved by placing the HWP in the path of the image forming the surrounding structure NPBS 530 - optical wedge 560 - mirror 580 - PBS 570. This is shown in Figure 6A where HWP 550 is located in the second arm 537. In another embodiment, in addition to a specific optical wedge geometry adapted to change the direction of the beam in each pupil section, the optical wedge is also made of a material that rotates polarization, so no separate element is required to perform this function. This is shown in Figure 6B where the optical wedge 560’ serves as both an optical wedge and a polarization rotation element.

[0089] For embodiments that utilize dispersion, for example, a grating can be used to perform the function of the optical wedge, such that the deflection angle exhibits a strong dependence on wavelength. This is shown in Figure 6C where the second arm component 560 of the Figure 6A embodiment is implemented as a deflection element 565, which can be a grating or any other element that spatially separates the radiation passing through it.

[0090] According to another aspect of the embodiment, a potential advantage of the embodiment just described is that the components can be fabricated as an integral block having components of a transparent material such as glass, with the components attached to each other using, for example, an adhesive. Figure 7 An example of such an arrangement is shown in Figure 4configured with the optical components of the embodiments, where the optical components are attached to the transparent components 541, 551, 561, 571, and 581. Alternatively, an air gap may be present in at least a portion of the optical path between separate optical components. The use of these air gaps can be utilized to minimize the optical path length.

[0091] Simultaneously accessing polarization channel and intensity information may improve process stability. Some applications desire that the diffraction order alignment information in the field 710 (FIG. 5) and the intensity information of the same polarization state of the diffraction orders shown in the fields 720, 730, 740, and 750 be projected onto the same array detector. As mentioned, projecting information regarding the same polarization state can be achieved by placing the HWP 550 or its equivalent in the arm 535. If an element such as the HWP 550 is not placed in the arm 535, the images in the field 710 on the array detectors 610 and 640 will be from a polarization state orthogonal to the polarization state of the intensity information being displayed. This may be suitable for some applications. However, there will be arrangements where this will not be preferred because orthogonal polarization states may have an uncorrelated dynamic range difference between two different types of patterns.

[0092] All folding optical devices including the mirrors 540, 680, and 650 and the folding optics 600 and 630 are optionally provided to allow for a more compact arrangement. Depending on the design considerations of a particular implementation, more or fewer such folding optical devices may be used. Additionally, either or both of the array detectors 610 and 640 can be rotated about the z-axis (where the plane of the figure is the xy plane) to provide better frame filling on the array detector.

[0093] The above embodiments use segmented optical wedges to produce a spatial separation of the image in the pupil. The use of segmented optical wedges provides the following advantages: optical wedges typically introduce only a small amount of dispersion. A possible implementation of such a segmented optical wedge is shown in Figure 8A . As shown, the segmented optical wedge 1100 is composed of four identical segments 1110 that are symmetrically arranged to divide the pupil into four separate regions. Such a segmented optical wedge 1100 can be manufactured, for example, by gluing the four segments together. The application of the principles set forth herein is not limited to systems using four segments or four identical segments, and can also be applied to systems using different numbers and / or orientations and / or shapes of segments to, for example, obtain separate higher orders.

[0094] For some embodiments, the segments have the same size and shape and are evenly distributed above the pupil. It will be appreciated that this may not be necessary for some applications.

[0095] In the above description, the optical wedge used in the exemplary embodiments is of the transmissive type. It should be understood that, alternatively, a reflective optical wedge can be used, wherein the ray path is appropriately modified and other components are placed.

[0096] While the above examples use polarization filtering to produce separate channels, it will be appreciated that color filtering can also be used to produce channels.

[0097] Another advantage of the exemplary embodiments described above is that they can be implemented using a relatively small number of demultiplexer modules.

[0098] As another alternative to the use of a combination of an optical wedge and a lens, it will be appreciated that a segmented lens array can be used. Figure 8B A segmented lens array 1150 implemented as a 2×2 lens array is shown, such as can be used as a split-aperture wavefront (PAW) imaging lens. In the example shown, the segmented lens array 1150 is a four-leaf lens formed by four lenses 1160 that are cut off-axis and glued together. An image of each quadrant is obtained from a portion 1170 of the lens 1160 that is close to its intersection with the other lenses.

[0099] Figure 5A A possible arrangement of the fields of the combined display 700 is shown. As mentioned, the combined display 700 includes a central field 710, which includes a set of Figure 2B fringe patterns 350. The surrounding fields 720, 730, 740, and 750 include separate polarization intensity information. Figure 9 is a graphical representation of the arrangement of the five fields 710, 720, 730, 740, and 750 of FIG. 5. The central field 710 is located at or near the center of the combined display 700, where the intensity fields 720, 730, 740, and 750 are set at the corners of a square centered around the central field 710. This arrangement is produced by the operation of an optical wedge (e.g., Figure 4 the optical wedge 560 of the arrangement), which shifts the peripheral fields relative to the center of the combined image 710. Thus, in order to shift the field 750 in the direction of arrow A from the center of the combined image 700, the optical wedge has a wedge angle that is proportional to the desired image displacement by a proportionality constant k, where the image displacement is at least twice the radius r of the field. The proportionality constant k will generally depend in a known manner on the focal length of the lens used and the optical properties of the optical wedge, such as its refractive index.

[0100] Figure 9 The field arrangement of Figure 10 is one of many possible such arrangements. For some embodiments, other arrangements may provide advantages. For example, the arrangement shown in Figure 9 may be more compact than the arrangement shown in Figure 10In the arrangement shown, the net displacement shown by the dashed arrow can be caused by using a first optical wedge with a wedge angle A to cause a first displacement A and a second optical wedge with a wedge angle E to cause a second displacement E. In Figure 10 the arrangement, generally, the image displacement should be greater than , where k is the proportionality constant mentioned above and r is the field radius.

[0101] Figure 11 Another arrangement is shown where the centers of the peripheral fields 720, 730, 740, and 750 do not lie at the vertices of a square but at the vertices of a rectangle. This combination display 700 is thus compressed in the vertical dimension of the figure. Again, this is more compact and allows a greater magnification of the field.

[0102] There are several different arrangements of optical elements that can be used to obtain Figure 9 , Figure 10 and Figure 11 the field arrangements shown in Figure 12 One such arrangement is shown where an additional optical wedge 562 is placed in one of the arms of the arrangement to introduce the additional field image displacement described above. Figure 13A FIG. is a close-up view of the optical wedges 560 and the additional optical wedge 562 in the combination 563. The same displacement can be obtained by using Figure 13B the single optical wedge 564 shown in Figure 13B In the embodiment shown in Figure 13C the angle θ between the face of the bottom portion of the optical wedge 564 and the waist of the combined optical wedge 564 is such that the face extends to the left in the figure, i.e., such that the angle θ has the opposite sign to the sign of the angle δ. As

[0103] shown in Figure 14 it is also possible to have an arrangement 565 where the angle θ of the face of the bottom portion of the optical wedge 566 is such that the face extends to the right in the figure, i.e., such that the angle θ has the same sign as the sign of the angle δ. Figure 15 FIG. shows an example of such an arrangement. Thus, in Figure 15 the embodiment of

[0104] According to another aspect of the embodiment, instead of using or modifying one or more optical wedges to achieve a desired image displacement, one or more of the mirrors 540 or 580 or the beam splitters 530 or 570 are also tilted to achieve a desired displacement of the field in the combined display 700. Achieving the displacement in these ways has the advantage of requiring fewer optical elements. In addition, tilting the mirror to cause image displacement can have less dispersion (achromatic) effect compared to the effect caused by adding transmissive optical wedges.

[0105] In addition, according to another aspect of the embodiment, in some arrangements, the wedge angles of the optical wedges A, B, C, and D can be made relative to Figure 5A and Figure 9 the arrangement of is reduced by a factor of

[0106] The embodiments described above are examples of configurations with two optical paths, where the complete image comes from one path and one or more (e.g., four) partial images (corresponding to a quarter pupil) come from the other path. However, those of ordinary skill in the art will readily understand that alternative configurations are possible in principle. For example, as mentioned, in one embodiment, the first path that can be configured as above can transmit a conventional bright-field image, and the other path can transmit a "dark-field imaging mode" image. In such an embodiment, the partial pupil blocks can be placed together with an image separation element (e.g., an optical wedge or a tilted mirror or a tilted beam splitter) to separate the images on the camera.

[0107] As another example, one of the paths can implement a "phase contrast imaging mode". Such an arrangement will use a phase plate in a part of the pupil, which shifts the phase in that part of the pupil relative to the rest of the pupil.

[0108] As yet another example, there can be an arrangement where the focused image comes from one path and the defocused image comes from the other path. This can be achieved, for example, by adding a weak lens in the second path. Such an arrangement is essentially capable of obtaining both the phase and amplitude of light from a single image (at least in the case of using spatially coherent light).

[0109] The above description includes examples of multiple embodiments. Of course, it is not possible to describe every conceivable combination of components or methods for the purpose of describing the foregoing embodiments, but one of ordinary skill in the art will recognize that many other combinations and permutations of the various embodiments are possible. Accordingly, the described embodiments are intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims. Additionally, to the extent that the term "comprising" is used in the specification or claims, such term is intended to be inclusive in a manner similar to the term "including" as interpreted when "including" is used as a transitional word in a claim. Further, while the elements of the described aspects and / or embodiments may be described or claimed in the singular, the plural is also contemplated unless expressly stated to be a singular limitation. Additionally, unless otherwise illustrated, all or a portion of any aspect and / or embodiment may be utilized in conjunction with all or a portion of any other aspect and / or embodiment.

[0110] It will be appreciated that the detailed description section, rather than the summary of the invention and abstract sections, is intended to be used to interpret the claims. The summary of the invention and abstract sections may set forth one or more, but not all, exemplary embodiments contemplated by the inventors of the present invention, and as such, are not intended to limit the present invention and the appended claims in any way.

[0111] The present invention has been described above by means of functional building blocks of embodiments that illustrate specific functions and the relationships of the described functions. For ease of description, the boundaries of these functional building blocks have been arbitrarily defined herein. Alternative boundaries may be defined as long as the specified functions and their relationships are appropriately performed.

[0112] The embodiments can be further described using the following aspects.

[0113] 1. A measuring device, the measuring device being arranged to receive radiation that has interacted with a pattern on a substrate, the measuring device comprising:

[0114] An optical module, the optical module being arranged to receive at least some of the radiation and adapted to split the radiation into first-path radiation traveling in a first arm and second-path radiation traveling in a second arm,

[0115] One of the first arm and the second arm includes a polarization component, the polarization component being adapted to rotate the polarization of a respective one of the first-path radiation and the second-path radiation, and

[0116] The second arm includes a second-arm component, the second-arm component being adapted to spatially separate the second-path radiation,

[0117] The optical module further includes a polarization beam splitter, which is arranged to: receive the first path radiation from the first arm and the second path radiation from the second arm, split the first path radiation into a first channel first path radiation and a second channel first path radiation and split the separated second path radiation into a first channel second path radiation and a second channel second path radiation, and cause the first channel first path radiation and the first channel second path radiation to propagate together as a combined first channel radiation and cause the second channel first path radiation and the second channel second path radiation to propagate together as a combined second channel radiation.

[0118] 2. The measuring device according to aspect 1, wherein the measuring device is an alignment sensor.

[0119] 3. The measuring device according to aspect 1, wherein the measuring device is an overlap sensor.

[0120] 4. The measuring device according to aspect 1, wherein the second arm component adapted to spatially separate the second path radiation is configurable.

[0121] 5. The measuring device according to aspect 1, wherein the second arm component adapted to spatially separate the second path radiation includes a rotatable optical wedge.

[0122] 6. The measuring device according to aspect 1 further includes:

[0123] a first lens arranged to focus the combined first channel radiation;

[0124] a first array detector arranged at the focal plane of the first lens;

[0125] a second lens arranged to focus the combined second channel radiation; and

[0126] a second array detector arranged at the focal plane of the second lens.

[0127] 7. The measuring device according to aspect 6, wherein the first array detector includes a first camera and the second array detector includes a second camera.

[0128] 8. The measuring device according to aspect 6, wherein the first array detector has a first optical axis, and wherein the first array detector is rotatable relative to the first optical axis to improve the filling of the first array detector by the first channel radiation.

[0129] 9. The measuring device according to aspect 1, wherein the polarization component includes a half-wave plate.

[0130] 10. The measuring device according to aspect 1, wherein the first arm includes the polarization component, and the polarization component is adapted to rotate the polarization of the first path radiation.

[0131] 11. The measuring device according to aspect 10, wherein the polarization component includes a half-wave plate.

[0132] 12. The measuring device according to aspect 1, wherein the second arm component includes a segmented optical wedge, and the segmented optical wedge is arranged to spatially separate the second path radiation.

[0133] 13. The measuring device according to aspect 12, wherein the segmented optical wedge is of the transmissive type.

[0134] 14. The measuring device according to aspect 12, wherein the segmented optical wedge is of the reflective type.

[0135] 15. The measuring device according to aspect 1, wherein the second arm component includes a segmented aperture wavefront imaging lens.

[0136] 16. The measuring device according to aspect 1, further comprising:

[0137] at least one camera, the at least one camera being arranged to receive the combined first channel radiation; and

[0138] a display, the display being arranged to show a first image based on the combined first channel radiation.

[0139] 17. The measuring device according to aspect 16, wherein the second arm component is arranged such that the first image includes a central image and four displacement images arranged around the first image.

[0140] 18. The measuring device according to aspect 16, wherein the first image includes a central image and four displacement images, and wherein the second arm includes an additional second arm component, the additional second arm component being arranged to laterally shift the four displacement images such that the display shows the four displacement images laterally shifted from the central image.

[0141] 19. The measuring device according to aspect 1, wherein the second arm component includes a tiltable beam splitter.

[0142] 20. The measuring device according to aspect 1, wherein the second arm component includes a tiltable folding mirror.

[0143] 21. A measuring device configured to collect radiation that has interacted with a pattern on a substrate, the measuring device comprising:

[0144] an optical module arranged to receive at least some of the radiation and adapted to split the radiation into first-path radiation traveling in a first arm and second-path radiation traveling in a second arm,

[0145] the first arm including a half-wave plate adapted to rotate the polarization of the first-path radiation,

[0146] the second arm including a segmented optical wedge arranged to spatially separate the second-path radiation, and

[0147] the optical module further including a polarization beam splitter arranged to: receive the first-path radiation from the first arm and the second-path radiation from the second arm, and split the first-path radiation into first-channel first-path radiation and second-channel first-path radiation and split the separated second-path radiation into first-channel second-path radiation and second-channel second-path radiation, and cause the first-channel first-path radiation and the first-channel second-path radiation to propagate together as combined first-channel radiation and cause the second-channel first-path radiation and the second-channel second-path radiation to propagate together as combined second-channel radiation;

[0148] a first lens arranged to receive and focus the combined first-channel radiation;

[0149] a first array detector arranged at the focal plane of the first lens;

[0150] a second lens arranged to receive and focus the combined second-channel radiation; and

[0151] a second array detector arranged at the focal plane of the second lens.

[0152] 22. The measuring device according to aspect 21, wherein the measuring device is an alignment sensor.

[0153] 23. The measuring device according to aspect 21, wherein the measuring device is an overlay sensor.

[0154] 24. The measuring device according to aspect 21, wherein the first array detector includes a first camera and the second array detector includes a second camera.

[0155] 25. The measuring device according to aspect 21, wherein the first array detector has a first optical axis, and wherein the first array detector is rotatable relative to the first optical axis to improve the filling of the first channel radiation on the first array detector.

[0156] 26. The measuring device according to aspect 21, wherein the segmented optical wedge is rotatable.

[0157] 27. The measuring device according to aspect 21, further comprising:

[0158] at least one camera arranged to receive the first path radiation and the spatially separated second path radiation, and

[0159] a display arranged to simultaneously show a first image based on the first path radiation and at least one image based on the spatially separated second path radiation.

[0160] 28. The measuring device according to aspect 27, wherein the second arm member is arranged such that the display simultaneously shows the first image in a central portion, and wherein the at least one image includes four images arranged around the first image.

[0161] 29. The measuring device according to aspect 27, wherein the at least one image includes four images, and wherein the second arm includes an additional second arm member arranged to laterally shift the four images such that the display shows the four images laterally shifted from the first image.

[0162] 30. The measuring device according to aspect 21, wherein the second arm member includes a beam splitter that can be tilted.

[0163] 31. The measuring device according to aspect 21, wherein the second arm member includes a foldable mirror that can be tilted.

[0164] 32. An optical module, comprising:

[0165] a first arm including a half-wave plate;

[0166] a second arm, the second arm including a segmented optical wedge;

[0167] a neutral beam splitter arranged to split an incident radiation beam into a first branch traveling in the first arm and a second branch traveling in the second arm; and

[0168] A polarization beam splitter, the polarization beam splitter being arranged to receive the first portion after the first portion has traveled through the first arm and to receive the second portion after the second portion has traveled through the second arm.

[0169] 33. The optical module according to aspect 32, wherein the half-wave plate rotates the polarization of the first portion by ninety degrees.

[0170] 34. The optical module according to aspect 32, wherein the segmented optical wedge separates the second portion into a plurality of spatially separated components.

[0171] 35. The optical module according to aspect 32, wherein the polarization beam splitter causes a first part of the first portion to propagate together with a first part of the second portion.

[0172] 36. The optical module according to aspect 35, wherein the polarization beam splitter causes a second part of the first portion to propagate together with a second part of the second portion.

[0173] 37. The optical module according to aspect 32, wherein the optical module is an alignment sensor.

[0174] 38. The optical module according to aspect 32, wherein the optical module is an overlap sensor.

[0175] 39. The optical module according to aspect 32, wherein the segmented optical wedge is rotatable.

[0176] 40. An optical module, comprising:

[0177] A first optical component, the first optical component including a neutral beam splitter, the neutral beam splitter being arranged to split an incident radiation beam into a first portion traveling in a first arm and a second portion traveling in a second arm,

[0178] The first arm includes a second optical component, the second optical component including a half-wave plate, and

[0179] The second arm includes a third optical component, the third optical component including a segmented optical wedge; and

[0180] A fourth optical component, the fourth optical component including a polarization beam splitter, the polarization beam splitter being arranged to receive the first portion after the first portion has traveled through the first arm and to receive the second portion after the second portion has traveled through the second arm,

[0181] And, the optical module further includes:

[0182] A first transparent element, the first transparent element being attached to the first optical component and the second optical component and connecting the first optical component and the second optical component,

[0183] A second transparent element, the second transparent element being attached to the second optical component and the fourth optical component and connecting the second optical component and the fourth optical component,

[0184] A third transparent element, the third transparent element being attached to the first optical component and the third optical component and connecting the first optical component and the third optical component, and

[0185] A fourth transparent element, the fourth transparent element being attached to the third optical component and the fourth optical component and connecting the third optical component and the fourth optical component,

[0186] such that the optical module is configured as an integral block.

[0187] 41. The optical module according to aspect 40, wherein the half-wave plate rotates the polarization of the first portion by ninety degrees.

[0188] 42. The optical module according to aspect 40, wherein the segmented optical wedge separates the second portion into a plurality of spatially separated components.

[0189] 43. The optical module according to aspect 40, wherein the polarization beam splitter causes a first part of the first portion to propagate together with a first part of the second portion.

[0190] 44. The optical module according to aspect 43, wherein the polarization beam splitter causes a second part of the first portion to propagate together with a second part of the second portion.

[0191] 45. The optical module according to aspect 40, wherein the optical module is an alignment sensor.

[0192] 46. The optical module according to aspect 40, wherein the optical module is an overlap sensor.

[0193] 47. The optical module according to aspect 40, wherein the segmented optical wedge is rotatable.

[0194] 48. A measurement method, comprising:

[0195] Collecting radiation that has interacted with a pattern on a substrate;

[0196] Splitting at least a portion of the radiation into first-path radiation and second-path radiation,

[0197] Rotate the polarization of one of the first-path radiation and the second-path radiation, and

[0198] Split the first-path radiation into a first-channel first-path radiation and a second-channel first-path radiation and split the separated second-path radiation into a first-channel second-path radiation and a second-channel second-path radiation, and cause the first-channel first-path radiation and the first-channel second-path radiation to propagate together as a combined first-channel radiation and cause the second-channel first-path radiation and the second-channel second-path radiation to propagate together as a combined second-channel radiation.

[0199] 49. The measurement method according to aspect 48, further comprising focusing the combined first-channel radiation on a first array detector and focusing the combined second-channel radiation on a second array detector.

[0200] 50. A measurement device configured to collect radiation that has interacted with a pattern on a substrate, the measurement device comprising:

[0201] An optical module arranged to receive at least some of the radiation and adapted to split the radiation into a first radiation portion propagating in a first arm and a second radiation portion propagating in the second arm, the first arm having a first optical configuration, and the second arm having a second optical configuration different from the first optical configuration; and

[0202] An optical element arranged to receive the first radiation portion after the first radiation portion has passed through the first arm and to receive the second radiation portion after the second radiation portion has passed through the second arm, and to produce a composite image of the first radiation portion and the second radiation portion.

[0203] 51. The measurement device according to aspect 50, wherein one of the first arm and the second arm includes a polarization component adapted to rotate the polarization of the first-path radiation, and wherein the second arm includes a second-arm module adapted to spatially separate the second radiation portion into spatially separated components.

[0204] The above embodiments and other embodiments are within the scope of the following claims.

Claims

1. A measuring device, the measuring device being arranged to receive radiation that has interacted with a pattern on a substrate, the measuring device comprising: an optical module, the optical module being arranged to receive at least some of the radiation and adapted to split the radiation into first-path radiation traveling in a first arm and second-path radiation traveling in a second arm, one of the first arm and the second arm includes a polarization component, the polarization component being adapted to rotate the polarization of a corresponding one of the first-path radiation and the second-path radiation, and the second arm includes a second-arm component, the second-arm component being adapted to spatially separate the second-path radiation, the optical module further includes a polarization beam splitter, the polarization beam splitter being arranged to: receive the first-path radiation from the first arm and the second-path radiation from the second arm, and split the first-path radiation into first-channel first-path radiation and second-channel first-path radiation, and split the separated second-path radiation into first-channel second-path radiation and second-channel second-path radiation, and cause the first-channel first-path radiation and the first-channel second-path radiation to propagate together as combined first-channel radiation and cause the second-channel first-path radiation and the second-channel second-path radiation to propagate together as combined second-channel radiation.

2. The measuring device according to claim 1, wherein The measuring device is an alignment sensor.

3. The measuring device according to claim 1, wherein, The measuring device is an overlay sensor.

4. The measuring device according to claim 1, wherein, The second-arm component adapted to spatially separate the second-path radiation is configurable.

5. The measuring device according to claim 1, wherein, The second-arm component adapted to spatially separate the second-path radiation includes a rotatable optical wedge.

6. The measuring device according to claim 1, further comprising: a first lens, the first lens being arranged to focus the combined first-channel radiation; a first array detector, the first array detector being arranged at the focal plane of the first lens; a second lens, the second lens being arranged to focus the combined second-channel radiation; and a second array detector, the second array detector being arranged at the focal plane of the second lens.

7. The measuring device according to claim 6, wherein, The first array detector includes a first camera, and the second array detector includes a second camera.

8. The measuring device according to claim 6, wherein, The first array detector has a first optical axis, and wherein the first array detector is rotatable relative to the first optical axis to improve the filling of the first array detector by the first-channel radiation.

9. The measuring device according to claim 1, wherein, The polarization component includes a half-wave plate.

10. The measuring device according to claim 1, wherein, The first arm includes the polarization component, the polarization component being adapted to rotate the polarization of the first-path radiation.

11. The measuring device according to claim 10, wherein, The polarization component includes a half-wave plate.

12. The measuring device according to claim 1, wherein, The second-arm component includes a segmented optical wedge, the segmented optical wedge being arranged to spatially separate the second-path radiation.

13. The measuring device according to claim 12, wherein, The segmented optical wedge is transmissive.

14. The measuring device according to claim 12, wherein, The segmented optical wedge is reflective.

15. The measuring device according to claim 1, wherein, The second-arm component includes a split-aperture wavefront imaging lens.

Images