WO2025201850A1

WO2025201850A1 - Apparatus with mangin-like facet mirror

Info

Publication number: WO2025201850A1
Application number: PCT/EP2025/056343
Authority: WO
Inventors: Hedser Van Brug
Original assignee: ASML Netherlands BV
Current assignee: ASML Netherlands BV
Priority date: 2024-03-29
Filing date: 2025-03-07
Publication date: 2025-10-02
Anticipated expiration: 2026-09-29

Abstract

An apparatus of a Mangin mirror including a planar front surface and a back surface with a plurality of facets. A second mirror to direct a path of illumination and a detector, wherein the Mangin mirror to receive an a plurality of radiation beams at the planar front surface, wherein a first set of the plurality of radiation beams are partially reflected by the planar front side and directed toward the second mirror, and a second set of the plurality of radiation beams are reflected by the plurality of facets to exit the Mangin mirror through the planar front surface and directed toward the second mirror positioned to redirect the first and second set of radiation beams towards the detector, and wherein the planar front surface and the plurality of facets are coated for the first set of beams to be four times of the second set of beams.

Description

APPARATUS WITH MANGIN-LIKE FACET MIRROR

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63/571,692 which was filed on March 29, 2024 and which is incorporated herein in its entirety by reference.

FIELD

[0002] The present disclosure relates to metrology inspection systems, for example, and design of wafer alignment sensors in metrology or 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 can be a mask or a reticle, can be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiationsensitive material (photoresist or simply “resist”) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatuses include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”- direction) while synchronously scanning the target portions parallel or anti-parallel to this scanning direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

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

[0005] In order to monitor the lithographic process, parameters of the patterned substrate are measured. Parameters 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 techniques for 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] Such optical scatterometers can be used to measure parameters, such as critical dimensions of developed photosensitive resist or overlay error (OV) between two layers formed in or on the patterned substrate. Properties of the substrate can be determined by comparing the properties of an illumination beam before and after the beam has been reflected or scattered by the substrate.

[0007] As ICs become smaller and more densely packed, so too increases the number of features that must be inspected per wafer. It is desirable to improve the capabilities of metrology systems in order to keep pace with current high- volume manufacturing rates and improve production speeds beyond what is currently available.

[0008] Current metrology inspection systems can comprise a beam splitter to create two sets of four beams with intensity ratio of four to one. Then the highest intensity beams interact with a facet mirror to change their angular direction, while the lower intensity beams are reflecting by a planar mirror. The two sets of beams are combined via a polarizing beam splitter. A half- wave plate can be inserted in one of the beam paths to ensure that a high intensity beams and a lower intensity beams with the same polarization are directed towards the same image plane. However, the current system utilizes two separate paths, each having an optical component that require alignment. Such systems also require a highly achromatic half wave plate.

SUMMARY

[0009] Accordingly, a solution is desirable to reduce the alignment effort and cost of parts. The optical metrology inspection system can be improved by a single component design based on aspects described herein.

[0010] In some aspects, a metrology or lithography apparatus can comprise a Mangin mirror having a planar front surface and a back surface with a plurality of facets. The Mangin mirror is configured to receive a plurality of incident radiation beams at the planar front surface, wherein a first set of the plurality of radiation beams are partially reflected by the planar front side and directed toward the detector. A second set of the plurality of radiation beams are reflected by the plurality of facets at the back surface and exit the Mangin mirror through the planar front surface and are directed toward the detector.

[0011] In some aspects, the planar front surface can have a coating to yield a predetermined ratio and cause the second set of the plurality of radiation beams to have an intensity that is four times an intensity of the first set of the plurality of radiation beams.

[0012] In some aspects, the back surface can have two or more facets. In some aspects, the back surface can have four facets that are fully reflective. In some aspects, the Mangin mirror can be made of glass. [0013] In some aspects, the Mangin mirror itself, or the detector, or a further component disposed between the Mangin mirror and the detector, is configured to block reflections exiting the Mangin mirror other than the first and the second sets of the plurality of radiation beams.

[0014] In some aspects, the apparatus can further include a folding mirror positioned to redirect the first and second sets of the plurality of radiation beams from the Mangin mirror towards the detector.

[0015] In some aspects, a method of enhancing wafer alignment sensor measurements includes directing an illumination beam toward a target disposed on a wafer, where a portion of the illumination beam interacts with the target toward a Mangin mirror. The Mangin mirror is configured to receive a plurality of incident radiation beams at a planar front surface. A first set of the plurality of radiation beams are partially reflected by the planar front surface toward a detector. A second set of the plurality of radiation beams are reflected by a back surface and through the planar front surface toward a detector. The planar front surface and the back surface of the Mangin mirror are configured to yield a predetermined intensity ratio between the first and second sets of the plurality of radiation beams.

[0016] Further features of various aspects of the present disclosure are described in detail below with reference to the accompanying drawings. It is noted that the present disclosure is not limited to the specific aspects described herein. Such aspects are presented herein for illustrative purposes only. Additional aspects will be apparent to those skilled in the relevant art(s) based on the teachings contained herein.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

[0017] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable those skilled in the relevant art(s) to make and use aspects described herein.

[0018] FIG. 1A shows a reflective lithographic apparatus, according to some aspects.

[0019] FIG. IB shows a transmissive lithographic apparatus, according to some aspects.

[0020] FIG. 2 shows more details of a reflective lithographic apparatus, according to some aspects.

[0021] FIG. 3 shows a lithographic cell, according to some aspects.

[0022] FIG. 4 shows a schematic illustration of a metrology device, according to some aspects. [0023] FIG. 5 shows an optical setup used in the metrology device of FIG. 4, according to some aspects.

[0024] FIG. 6 shows a Mangin mirror proposed to use in the metrology device in FIG. 4 replacing the optical setup in FIG. 5, according to some aspects.

[0025] FIG. 7 shows further details an example of the Mangin mirror illustrated in FIG. 6, according to some aspects.

[0026] FIG. 8 shows a high intensity image and a lower intensity image produced by the Mangin mirror of FIGs. 6 and 7, according to some aspects.

[0027] FIG. 9 shows an illustration of a Mangin mirror with four facets on the back surface and a planer front surface, according to some aspects.

[0028] 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 left-most 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

[0029] The aspects described herein, and references in the specification to “one aspect,” “an aspect,” “an exemplary aspect,” “an example aspect,” etc., indicate that the aspects described can include a particular feature, structure, or characteristic, but every aspect may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same aspect. Further, when a particular feature, structure, or characteristic is described in connection with an aspect, it is understood that it is within the knowledge of those skilled in the art to effect such feature, structure, or characteristic in connection with other aspects whether or not explicitly described.

[0030] Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “on,” “upper” and the like, can be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein can likewise be interpreted accordingly.

[0031] The terms “about,” “approximately,” or the like can be used herein to indicate the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the terms “about,” “approximately,” or the like can indicate a value of a given quantity that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value). [0032] Aspects of the present disclosure can be implemented in hardware, firmware, software, or any combination thereof. Aspects of the disclosure can also be implemented as instructions stored on a computer-readable medium, which can be read and executed by one or more processors. A machine- readable medium can include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium can include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical 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. Furthermore, firmware, software, routines, and/or instructions can be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. The term “machine-readable medium” can be interchangeable with similar terms, for example, “computer program product,” “computer-readable medium,” “non-transitory computer- readable medium,” or the like. The term “non-transitory” can be used herein to characterize one or more forms of computer readable media except for a transitory, propagating signal.

[0033] Before describing such aspects in more detail, however, it is instructive to present an example environment in which aspects of the present disclosure can be implemented.

[0034] Example Lithographic Systems

[0035] FIGS. 1A and IB show a lithographic apparatus 100 and a lithographic apparatus 100’, respectively, in which aspects of the present disclosure can be implemented. Lithographic apparatus 100 and lithographic apparatus 100’ each include the following: an illumination system (illuminator) IL configured to condition a radiation beam B (for example, deep ultra violet or extreme ultra violet radiation); a support structure (for example, a mask table) MT configured to support a patterning device (for example, a mask, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and, a substrate table (for example, a wafer table) WT configured to hold a substrate (for example, a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. Lithographic apparatus 100 and 100’ also have a projection system PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion (for example, comprising one or more dies) C of the substrate W. In lithographic apparatus 100, the patterning device MA and the projection system PS are reflective. In lithographic apparatus 100’, the patterning device MA and the projection system PS are transmissive.

[0036] 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.

[0037] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA with respect to a reference frame, the design of at least one of the lithographic apparatus 100 and 100’, and other conditions, such as whether or not the patterning device MA is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT can be a frame or a table, for example, which can be fixed or movable. By using sensors, the support structure MT can ensure that the patterning device MA is at a desired position, for example, with respect to the projection system PS.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] The lithographic apparatus can also be of a type wherein at least a portion of the substrate can be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system and the substrate. An immersion liquid can also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid. For example, a liquid can be located between the projection system and the substrate during exposure.

[0043] 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. A radiation system can comprise the source SO, the illuminator IL, and/or the beam delivery system BD.

[0044] 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.

[0045] 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.

[0046] Referring to FIG. IB, the radiation beam B is incident on the patterning device (for example, mask MA), which is held on the support structure (for example, mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. The projection system has a pupil conjugate PPU to an illumination system pupil IPU. Portions of radiation emanate from the intensity distribution at the illumination system pupil IPU and traverse a mask pattern without being affected by diffraction at the mask pattern and create an image of the intensity distribution at the illumination system pupil IPU. [0047] 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.

[0048] The projection system PS is arranged to capture (e.g., using a lens or lens group L) the zeroth order diffracted beams, first order diffracted beams, and/or higher order diffracted beams (not shown). In some aspects, dipole illumination for imaging line patterns extending in a direction perpendicular to a line can be used to utilize the resolution enhancement effect of dipole illumination. For example, first- order diffracted beams interfere with corresponding zeroth-order diffracted beams at the level of the wafer W to create an image of the line pattern MP at highest possible resolution and process window (i.e., usable depth of focus in combination with tolerable exposure dose deviations). In some aspects, astigmatism aberration can be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. Further, in some aspects, astigmatism aberration can be reduced by blocking the zeroth order beams in the pupil conjugate PPU of the projection system associated with radiation poles in opposite quadrants. This is described in more detail in US 7,511,799 B2, issued Mar. 31, 2009, which is incorporated by reference herein in its entirety.

[0049] 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).

[0050] In general, movement of the mask table MT can be realized with the aid of a long-stroke module (coarse positioning) and a short- stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT can be realized using a long-stroke module and a short- stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT can be connected to a short-stroke actuator or can be fixed. Mask MA and substrate W can be aligned using mask alignment marks Ml, M2, and substrate alignment marks Pl, P2. Although the substrate alignment marks (as illustrated) occupy dedicated target portions, they can be located in spaces between target portions (known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks can be located between the dies.

[0051] 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 can be calibrated for a smooth transfer of any payload (e.g., mask) to a fixed kinematic mount of a transfer station.

[0052] 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- jmagnification and image reversal characteristics of the projection system PS.

3. In another mode, the support structure (for example, mask table) MT is kept substantially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO can be employed and the programmable patterning device is updated as needed after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array.

[0053] Combinations and/or variations on the described modes of use or entirely different modes of use can also be employed.

[0054] In some aspects, 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.

[0055] In some aspects, lithographic apparatus 100’ includes a deep ultraviolet (DUV) source, which is configured to generate a beam of DUV radiation for DUV lithography. In general, the DUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the DUV radiation beam of the DUV source. [0056] FIG. 2 shows the lithographic apparatus 100 in more detail, including the source collector apparatus SO, the illumination system IL, and the projection system PS. The source collector apparatus SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 220 of the source collector apparatus SO. An EUV radiation emitting plasma 210 can be formed by a discharge produced plasma source. In some aspects, a plasma of excited tin (Sn) (e.g., excited via a laser) is provided to produce EUV radiation.

[0057] The radiation emitted by the EUV radiation emitting plasma 210 is passed from a source chamber 211 into a collector chamber 212 via an optional gas barrier or contaminant trap 230 (in some cases also referred to as contaminant barrier or foil trap), which is positioned in or behind an opening in source chamber 211. The contaminant trap 230 can include a channel structure. Contamination trap 230 can also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further indicated herein at least includes a channel structure.

[0058] The collector chamber 212 can include a radiation collector CO, which can be a so-called grazing incidence collector. Radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation that traverses collector CO can be reflected off a grating spectral filter 240 to be focused in a virtual source point INTF. The virtual source point INTF is commonly referred to as the intermediate focus, and the source collector apparatus is arranged such that the intermediate focus INTF is located at or near an opening 219 in the enclosing structure 220. The virtual source point INTF is an image of the EUV radiation emitting plasma 210. Grating spectral filter 240 is used in particular for suppressing infra-red (IR) radiation.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] Example Lithographic Cell

[0063] FIG. 3 shows a lithographic cell 300, also sometimes referred to a lithocell or cluster, according to some aspects. Lithographic apparatus 100 or 100’ can form part of lithographic cell 300. Lithographic cell 300 can also include one or more apparatuses to perform pre- and post-exposure processes on a substrate. Conventionally these include spin coaters SC to deposit resist layers, developers DE to develop exposed resist, chill plates CH, and bake plates BK. A substrate handler, or robot, RO picks up substrates from input/output ports I/Ol, I/O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus 100 or 100’ . These devices, which are often collectively referred to as the track, are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0064] Example Metrology Device

[0065] 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.

[0066] FIG. 4 shows an implementation of such a metrology device. The metrology device operates somewhat like a standard microscope with a novel illumination mode. The metrology device 400 comprises an optical module (OM) 405. An illumination source 410, which may be located outside the optical module (OM) 405 and optically coupled thereto by a multimode fiber 415, provides a spatially incoherent radiation beam 420 to the optical module (OM) 405. Optical components 417 deliver the spatially incoherent radiation beam 420 to a coherent off-axis illumination generator 425. The coherent off-axis illumination generator 425 generates a plurality (e.g., four) off-axis beams 430 from the spatially incoherent radiation beam 420. The characteristics of these off-axis beams 430 will be described in detail further below. The zeroth order of the illumination generator may be blocked by an illumination zero order block element 475. This zeroth order will only be present for some of the coherent off-axis illumination generator examples described in this document (e.g., phase grating based illumination generators), and therefore may be omitted when such zeroth order illumination is not generated. The off-axis beams 430 are delivered (via optical components 435 and) a spot mirror 440 to an (e.g., high numerical aperture NA) objective lens 445. The objective lens focuses the off-axis beams 430 onto a sample (e.g., periodic structure/alignment mark) located on a substrate 450, where they scatter and diffract. The scattered higher diffraction orders 455+, 455- (e.g., +1 and -1 orders respectively), propagate back via the spot mirror 440, and are focused by optical component 460 onto a sensor or camera 465 where they interfere to form an interference pattern. A processor 480 running suitable software can then process the image(s) of the interference pattern captured by camera 465. The zeroth order diffracted (specularly reflected) radiation is blocked at a suitable location in the detection branch; e.g., by the spot mirror 440 and/or a separate detection zero-order block element. It should be noted that there is a zeroth order reflection for each of the off-axis illumination beams, i.e. in the current embodiment there are four of these zeroth order reflections in total. As such, the metrology device operates as a “dark field” metrology device.

[0067] Further example functions and devices for metrology systems are described in more detail in U.S. Patent No. 11,360,399 B2, issued June 14, 2022, which is incorporated by reference herein in its entirety.

[0068] Example Optical System for a Metrology Device

[0069] Metrology devices, such as wafer alignment sensors, can use many optical components, for example an optical system 401 as illustrated in FIG. 4. An example of the optical components 401, disposed at pupil plane P3 or pupil plane Pl, for example, is shown in FIG. 5. It may be desirable to split intensity and polarization of the illumination beams. In some aspects, an hour glass design such as 500 as shown in FIG. 5 may be used. Hour glass 500 may comprise a polarization beam splitter 504 that can be used to create two sets of four beams with intensity ratio of four to one for the incident beam 502. The highest intensity beams interact with a rooftop mirror 506 to change their angular direction. The lower intensity beams are reflected by a planar mirror 508. The two sets of beams are combined via a polarizing beam splitter (PBS) 504’. A half-wave plate (HWP) 510 is positioned in one of the beam paths to ensure that the high intensity beams and lower intensity beams pass through a glass plate 512 with the same polarization and are directed towards the same image plane. The high intensity beams and the lower intensity beams are collected by a periscope 514 (e.g., comprising four mirrors) to an output illumination beam 516. However, this hour glass design 500 requires two separate paths, each having an optical components that need very accurate alignment. This arrangement also requires a highly achromatic half waveplate 510. In some aspects, the half waveplate may rotate and output S or P polarized state of light in the hour glass that matches to the first set of the radiation beams 610 in FIG. 6, which is described in detail below. Herein the intensity and interference images are produced with hour glass system for the 4 by 1 intensity split: one set of beams being reflected by a flat mirror 508 and the other set reflected by a faceted or a rooftop mirror 506. The radiation beams are recombined with S- polarized and P- polarized into two outputs 516. Various wavelengths can be separated from output beams 516 to speed up the analysis of the wafer alignment marks.

[0070] In some aspects, a Mangin mirror having smaller overall dimensions and less complexity can replace the hour glass design 500 system. In some aspects, the Magnin mirror disclosed herein can overcome aberrations caused by the optics in system 500.

[0071] System 600 of FIG. 6 illustrates a Mangin facet mirror (MFM) 604, a folding mirror 614 (which is optional), and a detector 616. Mangin facet mirror 604 has a planar front surface 606 and a faceted back surface 608. Mangin facet mirror 604 can be made of glass or other acceptable materials with optical properties commensurate with the functions disclosed herein.

[0072] An incident beam 602 impinges the planar front surface 606, which reflects a first set of the radiation beams 610 toward the detector 616. In some aspects, the folding mirror 614 can be employed to redirect the first set of the radiation beams 610 toward the detector 616. A second set of the radiation beams 612 are reflected by the back surface 608, through the planar front surface 606, and toward the detector 616. Again, in some aspects, the folding mirror 614 can be employed to redirect the second set of the radiation beams 612 toward the detector 616.

[0073] In some embodiment, a lens can be disposed before or after a folding mirror 614, as illustrated by arrows 618. Such a lens can be employed to allow interference between the beams to achieve a desired maximum intensity and/or for matching or setting a desired intensity ratio between the first and second sets of beams 610/612.

[0074] The back surface 608 of the Mangin mirror 604 is configured with a plurality of facets (e.g., two, four, or more facets), wherein the facets can be partially or fully reflective. The first set of the radiation beams 610 in FIG. 6 correspond to the beams directing to the glass plate 512 in FIG. 5, and the second set 612 of the plurality of radiation beams in FIG. 6 can correspond to the beams directing to the half waveplate 510 in FIG. 5, for example.

[0075] In some aspects, the Mangin facet mirror 604 is configured to provide a 4: 1 intensity ratio, such that an intensity of the second set of the radiation beams 612 is four times an intensity of the first set of the radiation beams 610, in a manner similar to the two sets of beams output by the hour glass design 500.

[0076] The Mangin mirror 604 can be disposed in a pupil plane of the optical module of the metrology device of FIG. 4.

[0077] A coating can be applied to the planar front surface 606 of Mangin mirror 604, according to techniques known to persons of skill in the art. Such a coating at the front surface 606 can attenuate the first set of radiation beams 610 to achieve the 4:1 power split ratio, or any other desired ratio. In some aspects, the coating (not illustrated), or a second coating (also not illustrated) can change polarization (e.g., S and P state) or the first and second sets of radiation beams 610/612.

[0078] In some aspects, the back surface 608 of the Mangin mirror 604 can be configured with a coating to yield a predetermined intensity ratio between the first set of radiation beams 610 and the second sets of the radiation beams 612.

[0079] As noted earlier, folding mirror 614 can be positioned after the Mangin mirror 604 to redirect the first and second sets of radiation beams 610/612 from the Mangin mirror towards the detector 616. The folding mirror 614 can be used to achieve smaller overall dimensions of the optical setup of system 600 in FIG. 6.

[0080] The detector 616 is configured to detect and/or otherwise convert the first and second sets of radiation beams 610/612 to and image used to assist the metrology system to determine overly, target position, or the like. An output of the detector 616 can be sent to a sensor or a camera 465 of FIG. 4. The detector 616 can comprise a CCD camera, a photodiode, or the like, as would become apparent to persons skilled in the art.

[0081] FIG. 7 illustrates Mangin mirror 700 and a reflectivity of front surface 706 and back surface 708 to achieve the desired intensity ratio. The front surface 706 is planar and the back surface 708 is facetted and configured to be, preferably, reflective. The facetted back surface 708 can be highly reflective over a full wavelength range of the detector 616. The planar front surface 706 can be coated, as noted above, such that a predetermined ratio between high intensity beams 712 and lower intensity beams 710, can be obtained. In some aspects, the coating is engineered to provide a 4: 1 ratio. A coating that can provide about 17.2% reflectivity as the front surface 706 can yield the desired 4: 1 ratio between the high intensity beams 712 and low intensity beams 710. Persons of skill in the art can readily change the variables of coating with a reflectivity, thickness of glass, number and pitch of back facets, and incident beam angles to accomplish a desired intensity ratio.

[0082] In some aspects, the Mangin mirror 604 can be configured such that the lower intensity beams 710 comprises 17.15% of the incoming beams, while the high intensity beams 712 comprises 68.6% of the incoming beam. The remaining power of the incoming beam will comprise multiple (unwanted) higher order reflected beams (not shown in FIG. 7).

[0083] In some aspects, the higher order reflections can be blocked once they exit the Mangin mirror 604. Each of the unwanted higher order reflected beams will have an increased angular change with respect to the first and second reflected sets of beams 710/712, and will have an ever decreasing intensity with the number of reflections. The unwanted higher order beams can be blocked by the Mangin mirror 604, the detector 616, or a further component disposed between the Mangin mirror and the detector, for example.

[0084] FIG 8 illustrates an image of spots 810 that correspond to the intensity of the lower intensity beams 710 and spots 812 that correspond to the intensity of the high intensity beams 712 at an image plane of detector 616. The intensity is illustrated by the relative size of the spots in arbitrary units of intensity. FIG. 8 only illustrates two sets of images 810 and 812, which implies that any unwanted, higher order reflections generated by the Mangin facet mirror 604 were blocked prior to arrival at the detector 616 as described earlier.

[0085] Alternatively, if no blocking is performed prior to higher order beams arriving at the detector, digital signal processing (implanted by processor 480 or another system controller, for example) may be used to filter-out the higher orders based on prior knowledge of where the higher order beams are at the image plane of the detector 616, or by filtering out beam intensities of higher orders that have beam intensity less that the beam intensity of beams/images 710/810 and 712/812, for example. Implementation and programming of such digital signal processing would become apparent to persons skilled in the art based on the description of such functions herein. [0086] The angle of the high intensity images with respect to lower intensity images is determined by the desired spot size of the detector 616 in FIG. 6. This can separate the positions at detector 616 of spots 812 from the lower intensity images spots 810 with no overlap, as illustrated in FIG. 8. The Mangin facet mirror 604 is estimated to offer about 40% image size reduction compared to the original hour glass design in FIG. 5. Therefore, a smaller detector can be used with a Mangin facet mirror 604. [0087] FIG. 9 illustrates an exemplary Mangin facet mirror 904 with a front surface 906 and a back surface 908. In some aspects, back surface 908 can comprise four facets 920 that converge at a peak 922 in a center of the back surface 902. The overall thickness of the mirror 904, height of peak 922, and/or pitch of facets 920 can be selected based on the desired ratio of the output beam intensity, their exit angles, and the like, for example. FIG. 9 illustrates a convex shape, but a concave shape is also contemplated. The convex shape may be preferred for ease of manufacture. As described above, the Mangin mirror is configured to generate high intensity beams (e.g., beams 712) and lower intensity beams (e.g., beams 710).

[0088] Numerous benefits of the 904 are achieved including cost savings, ease of alignment, and optimization time reduction for integration. The earlier described setup in FIG. 5 are achieved by the elegant design of mirror 904/704/604.

[0089] The embodiments may further be described using the following clauses:

1. An apparatus comprising: a Mangin mirror having a planar front surface and a back surface, wherein the back surface comprises a plurality of facets; and a detector, wherein the Mangin mirror is configured to receive a plurality of incident radiation beams at the planar front surface, partially reflect a first set of the plurality of radiation beams by the planar front surface toward the detector, and reflect a second set of the plurality of radiation beams by the back surface and through the planar front surface toward the detector, and wherein the planar front surface and the back surface of the Mangin mirror are configured to yield a predetermined intensity ratio between the first and second sets of the plurality of radiation beams.

2. The apparatus of clause 1 , wherein the planar front surface comprises a coating to yield that predetermined ratio and cause the second set of the plurality of radiation beams to have an intensity that is four times an intensity of the first set of the plurality of radiation beams.

3. The apparatus of clause 1, wherein the back surface comprises two or more facets.

4. The apparatus of clause 3, wherein the back surface comprises four facets that are fully reflective.

5. The apparatus of clause 1, wherein the Mangin mirror comprises glass. 6. The apparatus of clause 1 , wherein the Mangin mirror, the detector, or a further component disposed between the Mangin mirror and the detector is configured to block reflections exiting the Mangin mirror other than the first and the second sets of the plurality of radiation beams.

7. The apparatus of clause 1, further comprising a folding mirror positioned to redirect the first and second sets of the plurality of radiation beams from the Mangin mirror towards the detector.

8. A method of enhancing wafer alignment sensor measurements, comprising: directing an illumination beam toward a target disposed on a wafer; directing a portion of the illumination beam that has interacted with the target toward a Mangin mirror; wherein the Mangin mirror is configured to receive a plurality of incident radiation beams at a planar front surface, and partially reflect a first set of the plurality of radiation beams by the planar front surface toward a detector, and reflect a second set of the plurality of radiation beams by a back surface and through the planar front surface toward the detector, and wherein the planar front surface and the back surface of the Mangin mirror are configured to yield a predetermined intensity ratio between the first and second sets of the plurality of radiation beams.

9. The method of clause 8, further comprising coating the planar front surface to yield that predetermined ratio and cause the second set of the plurality of radiation beams to have an intensity that is four times an intensity of the first set of the plurality of radiation beams.

10. The method of clause 8, further comprising forming the back surface with two or more facets.

11. The method of clause 8, further comprising coating the plurality of facets to be fully reflective.

12. The method of clause 8, further comprising the Mangin mirror from glass.

13. The method of clause 8, further comprising the Mangin mirror, the detector, or a further component disposed between the Mangin mirror and the detector is configured to block reflections exiting the Mangin mirror other than the first and the second sets of the plurality of radiation beams.

14. The method of clause 8, further comprising using a folding mirror to re-direct the first and second sets of the plurality of radiation beams after the Mangin mirror and prior them reaching the detector.

15. A metrology or lithography system comprising the apparatus of clause 1.

16. The metrology or lithography system of clause 15, wherein the planar front surface comprises a coating to yield that predetermined ratio and cause the second set of the plurality of radiation beams to have an intensity that is four times an intensity of the first set of the plurality of radiation beams.

17. The metrology or lithography system of clause 15, wherein the back surface comprises four facets that are fully reflective.

18. The metrology or lithography system of clause 15, wherein the Mangin mirror comprises glass. 19. The metrology or lithography system of clause 15, further comprising the Mangin mirror, the detector, or a further component disposed between the Mangin mirror and the detector is configured to block reflections exiting the Mangin mirror other than the first and the second sets of the plurality of radiation beams.

20. The metrology or lithography system of clause 15, further comprising a folding mirror positioned to redirect the first and second sets of the plurality of radiation beams from the Mangin mirror towards the detector.

[0090] The terms “radiation,” “beam,” “light,” “illumination,” or the like can be used herein to refer to one or more 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 5-100 nm such as, for example, 13.5 nm), or hard X-ray working at less than 5 nm, as well as particle beams, such as ion beams or electron beams. 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.

[0091] Although some aspects of the present disclosure are described in the context of lithographic apparatuses in the manufacture of ICs, it should be understood that lithographic apparatuses described herein can be used in other applications, for example, in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, LCDs, thin-film magnetic heads, etc. Those skilled in the art will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein can be considered as specific examples of the more general terms “substrate” or “target portion”, respectively. A substrate can be processed before or after exposure in, for example, a track unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) and/or a metrology unit. Where applicable, aspects disclosed herein can be applied to such and other substrate processing tools. Furthermore, a substrate can be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein can also refer to a substrate that already contains multiple processed layers.

[0092] Furthermore, although some aspects of the present disclosure are described in the context of optical lithography, it should be understood that aspects of the present disclosure are not limited to optical lithography. For example, 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.

[0093] 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 specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0094] 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. The foregoing description of 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 and 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.

[0095] It is to be understood 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 can set forth one or more, but not necessarily all, 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. The breadth and scope of the protected subject matter should not be limited by any of the above-described aspects, but should be defined in accordance with the following claims and their equivalents.

Claims

2. The apparatus of claim 1, wherein the planar front surface comprises a coating to yield that predetermined ratio and cause the second set of the plurality of radiation beams to have an intensity that is four times an intensity of the first set of the plurality of radiation beams.

3. The apparatus of claim 1, wherein the back surface comprises two or more facets.

4. The apparatus of claim 3, wherein the back surface comprises four facets that are fully reflective.

5. The apparatus of claim 1, wherein the Mangin mirror comprises glass.

6. The apparatus of claim 1, wherein the Mangin mirror, the detector, or a further component disposed between the Mangin mirror and the detector is configured to block reflections exiting the Mangin mirror other than the first and the second sets of the plurality of radiation beams.

7. The apparatus of claim 1 , further comprising a folding mirror positioned to redirect the first and second sets of the plurality of radiation beams from the Mangin mirror towards the detector.

8. A metrology or lithography system comprising the apparatus of claim 1.

9. The metrology or lithography system of claim 8, wherein the planar front surface comprises a coating to yield that predetermined ratio and cause the second set of the plurality of radiation beams to have an intensity that is four times an intensity of the first set of the plurality of radiation beams.

10. The metrology or lithography system of claim 8, wherein the back surface comprises four facets that are fully reflective.

11. The metrology or lithography system of claim 8, wherein the Mangin mirror comprises glass.

12. The metrology or lithography system of claim 8, further comprising the Mangin mirror, the detector, or a further component disposed between the Mangin mirror and the detector is configured to block reflections exiting the Mangin mirror other than the first and the second sets of the plurality of radiation beams.

13. The metrology or lithography system of claim 8, further comprising a folding mirror positioned to redirect the first and second sets of the plurality of radiation beams from the Mangin mirror towards the detector.