System and method for alignment with a tunable light source

Abstract

A metrology system includes a radiation source, one or more intensity adjustors, an optical system, a detector, and a processor. The radiation source generates one or more wavelengths of light. The one or more intensity adjustors adjust intensities of the wavelengths of light such that a signal-to-noise ratio is set at or above a target threshold for selected wavelengths of the one or more wavelengths of light. The optical system combines the one or more wavelengths of light into a beam, directs the beam toward a target, and receives the beam after it interacts with the target. The detector receives the beam from the optical system after the beam interacts with the target and measures the intensities of the one or more wavelengths of the beam after its target interaction. The processor generates metrology data as a function of the one or more wavelengths of the beam.

Description

SYSTEM AND METHOD FOR ALIGNMENT WITH A TUNABLE LIGHT SOURCECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 762,978 which was filed on February 25, 2025 and which is incorporated herein in its entirety by reference.FIELD

[0002] The present disclosure relates to metrology systems, for example, an alignment system for measuring alignment mark positions in lithographic apparatuses and systems.BACKGROUND

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which 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 may be necessary to position the substrate relative to prior patterns formed thereon with a high degree of accuracy. Generally, alignment marks are placed on the substrate to be aligned and are located with reference to a second object. A lithographic apparatus can use an alignment apparatus for detecting positions of the alignment marks and for aligning the substrate using the alignment marks to ensure accurate exposure from a mask. Misalignment between the alignment marks at two different layers is measured as overlay error.

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

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

[0007] When radiation interacts with the layers formed in or on the patterned substrate, the alignment apparatus may measure various intensity responses depending on the wavelengths (i.e., colors) of the radiation. Based on the intensity response of each color, one or more colors may be selected for the alignment signal. A signal-to-noise ratio (SNR) for the alignment signal can indicate how much uncertainty exists for the detected position of an alignment mark. A low SNR can mean that the alignment apparatus is receiving a low amount of photons relative to electronic interference, thereby resulting in a high uncertainty of the detected position. Colors with a low SNR may be selected for the alignment process due to such colors’ insensitivity to process variations, but these colors present the drawback of increased uncertainty of the detected position. However, it is difficult to reduce the uncertainty in current alignment processes by merely increasing the light source’s power because light intensities beyond a certain threshold can damage the resist layer.SUMMARY

[0008] Accordingly, it is desirable to have an alignment system with an optimized power distribution across wavelengths that produces an alignment signal with a high signal-to-noise ratio (SNR), while still allowing for measurements of various colors for process monitoring.

[0009] In some embodiments, a system or a metrology system can include a radiation source, one or more intensity adjustors, an optical system, a detector, and a processor. The radiation source can be configured to generate one or more wavelengths of light. The one or more intensity adjustors can be configured to adjust intensities of the one or more wavelengths of light such that a signal-to-noise ratio is set at or above a target threshold for selected wavelengths of the one or more wavelengths of light. The optical system can be configured to combine the one or more wavelengths of light into a beam, direct the beam toward a target, and receive the beam after it interacts with the target. The detector canbe configured to receive the beam from the optical system after the beam interacts with the target and measure the intensities of the one or more wavelengths of the beam after interacting with the target. The processor can be configured to generate metrology data as a function of the one or more wavelengths of the beam.

[0010] In some embodiments, a lithographic apparatus can include an illumination system, a patterning system, a projection system, and a metrology system. The illumination system can be configured to condition a radiation beam. The patterning system can be configured to impart a pattern onto the radiation beam to form a patterned beam. The projection system can be configured to project the patterned beam onto a substrate. The metrology system can include a radiation source, one or more intensity adjustors, an optical system, a detector, and a processor. The radiation source can be configured to generate one or more wavelengths of light. The one or more intensity adjustors can be configured to adjust intensities of the one or more wavelengths of light such that a signal-to-noise ratio is set at or above a target threshold for selected wavelengths of the one or more wavelengths of light. The optical system can be configured to combine the one or more wavelengths of light into a beam, direct the beam toward a target, and receive the beam after it interacts with the target. The detector can be configured to receive the beam from the optical system after the beam interacts with the target and measure the intensities of the one or more wavelengths of the beam after interacting with the target. The processor can be configured to generate metrology data as a function of the one or more wavelengths of the beam.

[0011] In some embodiments, a method can include generating, with a radiation source, one or more wavelengths of light. The method can further include adjusting, with one or more intensity adjustors, intensities of the one or more wavelengths of light such that a signal-to-noise ratio is set at or above a target threshold for selected wavelengths of the one or more wavelengths of light. The method can further include combining, with an optical system, the one or more wavelengths of light into a beam. The method can further include directing, with the optical system, the beam toward a target. The method can further include receiving, with the optical system, the beam after it interacts with the target. The method can further include receiving, at a detector, the beam from the optical system after the beam interacts with the target. The method can further include measuring, with the detector, intensities of the one or more wavelengths of the beam after interacting with the target. The method can further include generating, with a processor, metrology data as a function of the one or more wavelengths of the beam based on the measuring.

[0012] Further features of various embodiments 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 embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to those skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWINGS / FIGURES

[0013] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable those skilled in the relevant art(s) to make and use embodiments described herein.

[0014] FIG. 1A shows a reflective lithographic apparatus, according to some embodiments.

[0015] FIG. IB shows a transmissive lithographic apparatus, according to some embodiments.

[0016] FIG. 2 shows more details of a reflective lithographic apparatus, according to some embodiments.

[0017] FIG. 3 shows a lithographic cell, according to some embodiments.

[0018] FIGS. 4 A and 4B show inspection apparatuses, according to some embodiments.

[0019] FIGS. 5A and 5B show a metrology system, according to some embodiments.

[0020] FIG. 6 shows a schematic plot of metrology data as a function of wavelengths, according to some embodiments.

[0021] FIG. 7 shows a method for performing an alignment process with an optimized signal-to-noise ratio for one or more wavelengths, according to some embodiments.

[0022] The features of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.DETAILED DESCRIPTION

[0023] The embodiments described herein, and references in the specification to “one embodiment,” “an embodiment,” “an exemplary embodiment,” “an example embodiment,” etc., indicate that the embodiments described can include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of those skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0024] 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 toencompass 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.

[0025] 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).

[0026] Embodiments of the present disclosure can be implemented in hardware, firmware, software, or any combination thereof. Embodiments 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.

[0027] Before describing such embodiments in more detail, however, it is instructive to present an example environment in which embodiments of the present disclosure can be implemented.

[0028] Example Lithographic Systems

[0029] FIGS. 1A and IB show a lithographic apparatus 100 and a lithographic apparatus 100’, respectively, in which embodiments of the present disclosure can be implemented. Eithographic 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 deviceMA and the projection system PS are reflective. In lithographic apparatus 100’, the patterning device MA and the projection system PS are transmissive.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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 carriedout 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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 embodiments, 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 embodiments, astigmatism aberration can be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. Further, in some embodiments, 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.

[0043] 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 usedto 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).

[0044] 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.

[0045] 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.

[0046] The lithographic apparatus 100 and 100’ can be used in at least one of the following modes: 1. In step mode, the support structure (for example, mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C at one time (i.e., a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed.2. In scan mode, the support structure (for example, mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (for example, mask table) MT can be determined by the (de)magnification and image reversal characteristics of the projection system PS.3. In another mode, the support structure (for example, mask table) MT is kept substantially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO can be employed and the programmable patterning device is updated as needed after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array.

[0047] Combinations and / or variations on the described modes of use or entirely different modes of use can also be employed.

[0048] In some embodiments, 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.

[0049] In some embodiments, 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.

[0050] FIG. 2 shows the lithographic apparatus 100 in more detail, including the source collector apparatus SO, the illumination system IL, and the projection system PS. The source collector apparatus SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 220 of the source collector apparatus SO. An EUV radiation emitting plasma 210 can be formed by a discharge produced plasma source. EUV radiation can be produced by a gas or vapor, for example Xe gas, Li vapor, or Sn vapor in which EUV radiation emitting plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The EUV radiation emitting plasma 210 is created by, for example, an electrical discharge causing at least a partially ionized plasma. Partial pressures of, for example, 10 Pa of Xe, Li, Sn vapor, or any other suitable gas or vapor can be used for efficient generation of the radiation. In some embodiments, a plasma of excited tin (Sn) (e.g., excited via a laser) is provided to produce EUV radiation.

[0051] 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.

[0052] 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.

[0053] 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 ofradiation 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.

[0054] 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.

[0055] 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.

[0056] Example Lithographic Cell

[0057] FIG. 3 shows a lithographic cell 300, also sometimes referred to a lithocell or cluster, according to some embodiments. 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.

[0058] Example Inspection Apparatus

[0059] In order to control the lithographic process to place device features accurately on the substrate, alignment marks are generally provided on the substrate, and the lithographic apparatus includes one or more inspection apparatuses for accurate positioning of marks on a substrate. These alignment apparatuses are effectively position measuring apparatuses. Different types of marks and different types of alignment apparatuses and / or systems are known from different times and different manufacturers. A type of system widely used in current lithographic apparatus is based on a self-referencing interferometer as described in U.S. Patent No. 6,961,116 (den Boef et al.). Generally marks are measured separately to obtain X- and Y-positions. A combined X- and Y-measurement can be performed using the techniques described in U.S. Publication No. 2009 / 195768 A (Bijnen et al.), however. The full contents of both of these disclosures are incorporated herein by reference.

[0060] FIG. 4A shows a cross-sectional view of an inspection apparatus 400 that can be implemented as a part of lithographic apparatus 100 or 100’, according to some embodiments. In some embodiments, inspection apparatus 400 can be configured to align a substrate (e.g., substrate W) with respect to a patterning device (e.g., patterning device MA). Inspection apparatus 400 can be further configured to detect positions of alignment marks on the substrate and to align the substrate with respect to the patterning device or other components of lithographic apparatus 100 or 100’ using the detected positions of the alignment marks. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

[0061] The terms “inspection apparatus,” “metrology system,” or the like can be used herein to refer to, e.g., a device used for measuring a property of a structure (e.g., overlay sensor, critical dimension sensor, or the like), a device or system used in a lithographic apparatus to inspect an alignment of a wafer (e.g., alignment sensor), or the like.

[0062] In some embodiments, inspection apparatus 400 can include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and a processor 432. Illumination system 412 can be configured to provide an electromagnetic narrow band radiation beam 413 having one or more passbands. In an example, the one or more passbands can be within a spectrum of wavelengths between about 500 nm to about 900 nm. In another example, the one or more passbands can be discrete narrow passbands within a spectrum of wavelengths between about 500 nm to about 900 nm. Illumination system 412 can be further configured to provide one or more passbands having substantially constant center wavelength (CWL) values over a long period of time (e.g., over a lifetime of illumination system 412). Such configuration of illumination system 412 can help to prevent the shift of the actual CWL values from the desired CWL values, as discussed above, in current alignment systems. And, as a result, the use of constant CWL values can improve long-term stability and accuracy of alignment systems (e.g., inspection apparatus 400) compared to the current alignment apparatuses.

[0063] In some embodiments, beam splitter 414 can be configured to receive radiation beam 413 and split radiation beam 413 into at least two radiation sub-beams. For example, radiation beam 413 can be split into radiation sub-beams 415 and 417, as shown in FIG. 4A. Beam splitter 414 can be further configured to direct radiation sub-beam 415 onto a substrate 420 placed on a stage 422. In one example, the stage 422 is movable along direction 424. Radiation sub-beam 415 can be configured to illuminate an alignment mark or a target 418 located on substrate 420. Alignment mark or target 418 can be coated with a radiation sensitive film. In some embodiments, alignment mark or target 418 can have one hundred and eighty degrees (i.e., 180°) symmetry. That is, when alignment mark or target 418 is rotated 180° about an axis of symmetry perpendicular to a plane of alignment mark or target 418, rotated alignment mark or target 418 can be substantially identical to an unrotated alignment mark or target 418. The target 418 on substrate 420 can be (a) a resist layer grating comprising bars that are formed of solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlay target structure comprising a resist grating overlaid or interleaved on a product layer grating. The bars canalternatively be etched into the substrate. This pattern is sensitive to chromatic aberrations in the lithographic projection apparatus, particularly the projection system PL, and illumination symmetry and the presence of such aberrations will manifest themselves in a variation in the printed grating. One inline method used in device manufacturing for measurements of line width, pitch, and critical dimension makes use of a technique known as “scatterometry”. Methods of scatterometry are described in Raymond et al., “Multiparameter Grating Metrology Using Optical Scatterometry”, J. Vac. Sci. Tech. B, Vol. 15, no. 2, pp. 361-368 (1997) and Niu et al., “Specular Spectroscopic Scatterometry in DUV Lithography”, SPIE, Vol. 3677 (1999), which are both incorporated by reference herein in their entireties. In scatterometry, light is reflected by periodic structures in the target, and the resulting reflection spectrum at a given angle is detected. The structure giving rise to the reflection spectrum is reconstructed, e.g. using Rigorous Coupled-Wave Analysis (RCWA) or by comparison to a library of patterns derived by simulation. Accordingly, the scatterometry data of the printed gratings is used to reconstruct the gratings. The parameters of the grating, such as line widths and shapes, can be input to the reconstruction process, performed by processing unit PU, from knowledge of the printing step and / or other scatterometry processes.

[0064] In some embodiments, beam splitter 414 can be further configured to receive diffraction radiation beam 419 and split diffraction radiation beam 419 into at least two radiation sub-beams, according to an embodiment. Diffraction radiation beam 419 can be split into diffraction radiation subbeams 429 and 439, as shown in FIG. 4A.

[0065] It should be noted that even though beam splitter 414 is shown to direct radiation sub-beam 415 towards alignment mark or target 418 and to direct diffracted radiation sub-beam 429 towards interferometer 426, the disclosure is not so limiting. Other optical arrangements can be used to obtain the similar result of illuminating alignment mark or target 418 on substrate 420 and detecting an image of alignment mark or target 418.

[0066] As illustrated in FIG. 4A, interferometer 426 can be configured to receive radiation sub-beam 417 and diffracted radiation sub-beam 429 through beam splitter 414. In an example embodiment, diffracted radiation sub-beam 429 can be at least a portion of radiation sub-beam 415 that can be reflected from alignment mark or target 418. In an example of this embodiment, interferometer 426 comprises any appropriate set of optical-elements, for example, a combination of prisms that can be configured to form two images of alignment mark or target 418 based on the received diffracted radiation sub-beam 429. It should be appreciated that a good quality image need not be formed. It can be enough to have the features of alignment mark 418 resolved. Interferometer 426 can be further configured to rotate one of the two images with respect to the other of the two images 180° and recombine the rotated and unrotated images interferometrically.

[0067] In some embodiments, detector 428 can be configured to receive the recombined image via interferometer signal 427 and detect interference as a result of the recombined image when alignment axis 421 of inspection apparatus 400 passes through a center of symmetry (not shown) of alignmentmark or target 418. Such interference can be due to alignment mark or target 418 being 180° symmetrical, and the recombined image interfering constructively or destructively, according to an example embodiment. Based on the detected interference, detector 428 can be further configured to determine a position of the center of symmetry of alignment mark or target 418 and consequently, detect a position of substrate 420. According to an example, alignment axis 421 can be aligned with an optical beam perpendicular to substrate 420 and passing through a center of image rotation interferometer 426. Detector 428 can be further configured to estimate the positions of alignment mark or target 418 by implementing sensor characteristics and interacting with wafer mark process variations.

[0068] In a further embodiment, detector 428 determines the position of the center of symmetry of alignment mark or target 418 by performing one or more of the following measurements:1. measuring position variations for various wavelengths (position shift between colors);2. measuring position variations for various orders (position shift between diffraction orders);3. measuring position variations for various polarizations (position shift between polarizations); and

[0069] 4. measuring intensity difference between opposite orders of a diffraction order pair (e.g., to characterize and correct for asymmetry).

[0070] This data can be obtained using any type of alignment sensor, for example, a SMASH (SMart Alignment Sensor Hybrid) sensor, as described in U.S. Patent No. 6,961,116 that employs a selfreferencing interferometer with a single detector and four different wavelengths, and extracts the alignment signal in software, or Athena (Advanced Technology using High order ENhancement of Alignment), as described in U.S. Patent No. 6,297,876, which directs each of seven diffraction orders to a dedicated detector, which are both incorporated by reference herein in their entireties.

[0071] In some embodiments, beam analyzer 430 can be configured to receive and determine an optical state of diffracted radiation sub-beam 439. The optical state can be a measure of beam wavelength, polarization, or beam profile. Beam analyzer 430 can be further configured to determine a position of stage 422 and correlate the position of stage 422 with the position of the center of symmetry of alignment mark or target 418. As such, the position of alignment mark or target 418 and, consequently, the position of substrate 420 can be accurately known with reference to stage 422. Alternatively, beam analyzer 430 can be configured to determine a position of inspection apparatus 400 or any other reference element such that the center of symmetry of alignment mark or target 418 can be known with reference to inspection apparatus 400 or any other reference element. Beam analyzer 430 can be a point or an imaging polarimeter with some form of wavelength-band selectivity. In some embodiments, beam analyzer 430 can be directly integrated into inspection apparatus 400, or connected via fiber optics of several types: polarization preserving single mode, multimode, or imaging, according to other embodiments.

[0072] In some embodiments, beam analyzer 430 can be further configured to determine the overlay data between two patterns on substrate 420. One of these patterns can be a reference pattern on a reference layer. The other pattern can be an exposed pattern on an exposed layer. The reference layercan be an etched layer already present on substrate 420. The reference layer can be generated by a reference pattern exposed on the substrate by lithographic apparatus 100 and / or 100’. The exposed layer can be a resist layer exposed adjacent to the reference layer. The exposed layer can be generated by an exposure pattern exposed on substrate 420 by lithographic apparatus 100 or 100’. The exposed pattern on substrate 420 can correspond to a movement of substrate 420 by stage 422. In some embodiments, the measured overlay data can also indicate an offset between the reference pattern and the exposure pattern. The measured overlay data can be used as calibration data to calibrate the exposure pattern exposed by lithographic apparatus 100 or 100’, such that after the calibration, the offset between the exposed layer and the reference layer can be minimized.

[0073] In some embodiments, beam analyzer 430 can be further configured to determine a model of the product stack profile of substrate 420, and can be configured to measure overlay, critical dimension, and focus of target 418 in a single measurement. The product stack profile contains information on the stacked product such as alignment mark, target 418, or substrate 420, and can include mark process variation-induced optical signature metrology that is a function of illumination variation. The product stack profile can also include product grating profile, mark stack profile, and mark asymmetry information. An example of beam analyzer 430 is Yieldstar™, manufactured by ASML, Veldhoven, The Netherlands, as described in U.S. Patent No. 8,706,442, which is incorporated by reference herein in its entirety. Beam analyzer 430 can be further configured to process information related to a particular property of an exposed pattern in that layer. For example, beam analyzer 430 can process an overlay parameter (an indication of the positioning accuracy of the layer with respect to a previous layer on the substrate or the positioning accuracy of the first layer with respective to marks on the substrate), a focus parameter, and / or a critical dimension parameter (e.g., line width and its variations) of the depicted image in the layer. Other parameters are image parameters relating to the quality of the depicted image of the exposed pattern.

[0074] In some embodiments, an array of detectors (not shown) can be connected to beam analyzer 430, and allows the possibility of accurate stack profile detection as discussed below. For example, detector 428 can be an array of detectors. For the detector array, a number of options are possible: a bundle of multimode fibers, discrete pin detectors per channel, or CCD or CMOS (linear) arrays. The use of a bundle of multimode fibers enables any dissipating elements to be remotely located for stability reasons. Discrete PIN detectors offer a large dynamic range but each need separate pre-amps. The number of elements is therefore limited. CCD linear arrays offer many elements that can be read-out at high speed and are especially of interest if phase-stepping detection is used.

[0075] In some embodiments, a second beam analyzer 430’ can be configured to receive and determine an optical state of diffracted radiation sub-beam 429, as shown in FIG. 4B. The optical state can be a measure of beam wavelength, polarization, or beam profile. Second beam analyzer 430’ can be identical to beam analyzer 430. Alternatively, second beam analyzer 430’ can be configured to perform one or more of the functions of beam analyzer 430, such as determining a position of stage 422 and correlatingthe position of stage 422 with the position of the center of symmetry of alignment mark or target 418. As such, the position of alignment mark or target 418 and, consequently, the position of substrate 420, can be accurately known with reference to stage 422. Second beam analyzer 430’ can also be configured to determine a position of inspection apparatus 400, or any other reference element, such that the center of symmetry of alignment mark or target 418 can be known with reference to inspection apparatus 400, or any other reference element.

[0076] In some embodiments, second beam analyzer 430’ can be directly integrated into inspection apparatus 400, or it can be connected via fiber optics of several types: polarization preserving single mode, multimode, or imaging, according to other embodiments. Alternatively, second beam analyzer 430’ and beam analyzer 430 can be combined to form a single analyzer (not shown) configured to receive and determine the optical states of both diffracted radiation sub-beams 429 and 439.

[0077] In some embodiments, processor 432 receives information from detector 428 and beam analyzer 430. Processor 432 can create a basic correction algorithm based on the information received from detector 428 and beam analyzer 430, including but not limited to the optical state of the illumination beam, the alignment signals, associated position estimates, and the optical state in the pupil, image, and additional planes. The pupil plane is the plane in which the radial position of radiation defines the angle of incidence and the angular position defines the azimuth angle of the radiation. Processor 432 can utilize the basic correction algorithm to characterize the inspection apparatus 400 with reference to wafer marks and / or alignment marks 418.

[0078] Example Metrology System Using a Tunable Light Source

[0079] A metrology system can operate with a light source capable of emitting various light recipes depending on the manufacturing purpose. Typically, a research phase can be conducted to determine a light recipe by testing one or more wavelengths on a fiducial alignment mark. One indicator of performance of the one or more wavelengths is, for example, a detected signal-to-noise ratio of the one or more wavelengths returning as an alignment signal from the fiducial alignment mark. Based on data collected during the research phase, a set of wavelengths can be selected for use in a high-volume manufacturing phase. The detected signal-to-noise ratio of the selected wavelengths may be noted as being too low during the research phase. As a result, a target threshold can be set for the signal-to-noise ratio that would generate an alignment signal having a sufficient certainty in an alignment position of an alignment mark during the manufacturing phase. To meet or exceed the target threshold for the signal-to-noise ratio of the selected wavelengths, it is useful for a light source to have adjustable power across wavelengths.

[0080] Accordingly, the disclosed system, sub-system, or metrology system can perform an alignment process with a light source having adjustable power across wavelengths for optimized power distribution. The intensities of a selected set of wavelengths useful for the alignment process can be increased to produce an alignment signal with an optimized signal-to-noise ratio without damaging the resist layer. These intensities can be selectively adjusted such that comparatively more light at theselected wavelengths is used with respect to any undesirable noise, thereby resulting in an increased or maximized signal-to-noise ratio. Specifically, for example, the signal-to-noise ratio for the selected wavelengths can be set at or above the target threshold determined during the research phase. As a result, the tunable adjustment of the intensities of the selected wavelengths means the corresponding signal-to-noise ratio can be set to produce an easily detectable alignment signal having a sufficient certainty in an alignment position of an alignment mark. Meanwhile, the intensities of other wavelengths not as useful for the alignment process can be reduced or turned off to produce a low signal-to-noise ratio for these other wavelengths, while still enabling process monitoring for some or all wavelengths. As a result, the disclosed metrology system can provide an improved accuracy for wavelengths useful for high precision measurements while offering a way to monitor performance of some or all wavelengths during the alignment process.

[0081] FIG. 5A shows a system, sub-system, or a metrology system 560, according to some embodiments. Metrology system 560 (referenced “metrology” for convenience and not by limitation) can be configured to measure a position of an alignment target. In some embodiments, metrology system 560 can represent a detailed view of inspection apparatus 400 (as shown in a described with reference to FIGS. 4A and 4B). Metrology system 560 can be built as a part of lithographic apparatus 100 or 100', or can be an independent metrology device in communication with lithographic apparatus 100 or 100'. In one example, metrology system 560 can be a stand-alone unit in lithographic cell 300 and work together with other apparatuses during operation. In some embodiments, metrology system 560 can include a radiation source 562, one or more intensity adjustors 564a-564n, an optical system 566, a detector 568, and a processor 570.

[0082] In some embodiments, radiation source 562 can be configured to generate one or more wavelengths of light 572a-572n. Radiation source 562 can include one or more light sources and optical elements for generating the one or more wavelengths of light 572a-572n. In some embodiments, as shown in the example of FIG. 5A, radiation source 562 can include a supercontinuum light source 574 and a color separator 576. Radiation source 562 can be configured to direct each of the one or more wavelengths of light 572a-572n toward corresponding ones of the one or more intensity adjustors 564a-564n. Radiation source 562 can use a medium such as, for example, an optical fiber, air, a vacuum, or the like to direct the one or more wavelengths of light 572a-572n toward corresponding ones of one or more intensity adjustors 564a-564n.

[0083] In some embodiments, supercontinuum light source 574 can be configured to generate a multicolor light beam 578. Supercontinuum light source 574 can be interchangeably called a white light source. Supercontinuum light source 574 can be configured to simultaneously generate a broad spectrum of wavelengths can be ultraviolet light, visible light, or infrared light within in a range between about 5 nm to about 2 pm. Supercontinuum light source 574 can be configured to direct multi-color light beam 578 toward color separator 576. Supercontinuum light source 574 can use a medium suchas, for example, an optical fiber, air, a vacuum, or the like to direct multi-color light beam 578 toward color separator 576.

[0084] In some embodiments, multi-color light beam 578 can be spatially coherent radiation or spatially incoherent radiation. Multi-color light beam 578 can have an electromagnetic narrow band with one or more passbands and can have substantially continuous wavelengths. In some embodiments, multi-color light beam 578 can be ultraviolet light, visible light, or infrared light having a plurality of wavelengths in a range between about 5 nm to about 2 pm.

[0085] In some embodiments, color separator 576 can be configured to separate multi-color light beam 578 into a plurality of single-color light beams each corresponding to individual ones of the one or more wavelengths of light 572a-572n. Color separator 576 can include optical elements for separating multicolor light beam 578 into individual single-color light beams such as, for example, at least a diffraction grating, an optical filter assembly including one or more optical filters, or the like. From the spectrum of wavelengths of multi-color light beam 578, color separator 576 can select a predetermined amount of wavelengths for use in the alignment process with detector 568. For example, the selected wavelengths can be within a range of about 500 nm to about 900 nm, where the bandwidth is in the order of about 5 nm for a shortest wavelength and about 10 nm for a longest wavelength. Color separator 576 can be configured to direct each of the single-color light beams that correspond to individual ones of the one or more wavelengths of light 572a-572n toward corresponding ones of the one or more intensity adjustors 564a-564n. Color separator 576 can use a medium such as, for example, an optical fiber, air, a vacuum, or the like to direct one or more wavelengths of light 572a-572n toward corresponding ones of one or more intensity adjustors 564a-564n.

[0086] In some embodiments, one or more intensity adjustors 564a-564n can correspond to the amount of the one or more wavelengths of light 572a-572n supplied by radiation source 562. The one or more intensity adjustors 564a-564n can be configured to adjust intensities of the one or more wavelengths of light 572a-572n to produce a corresponding one or more attenuated wavelengths of light 573a-573n. The one or more intensity adjustors 564a-564n can adjust the intensities of the one or more wavelengths of light 572a-572n such that there is comparatively more light for selected wavelengths of the one or more wavelengths of light 572a-572n with respect to noise caused by electronic interference in the alignment process. For example, the one or more intensity adjustors 564a-564n can adjust the intensities of the one or more wavelengths of light 572a-572n to overcome the noise and therefore optimize the signal-to-noise ratio by increasing the signal-to-noise ratio to meet or exceed a target threshold. As a result, the one or more intensity adjustors 564a-564n can set a signal-to-noise ratio at or above the target threshold for the selected wavelengths of the one or more wavelengths of light 572a-572n to produce an easily detectable alignment signal having a sufficient certainty in an alignment position of an alignment mark. Accordingly, one or more intensity adjustors 564a-564n can be configured to produce a selected power distribution among the one or more wavelengths of light 572a-572n by attenuating the intensities of the one or more wavelengths of light 572a-572n into the one or more attenuatedwavelengths of light 573a-573n. Each of the one or more intensity adjustors 564a-564n can be configured to direct corresponding ones of the one or more attenuated wavelengths of light 573a-573n toward optical system 566. The one or more intensity adjustors 564a-564n can use a medium such as, for example, an optical fiber, air, a vacuum, or the like to direct the one or more attenuated wavelengths of light 573a-573n toward optical system 566.

[0087] In some embodiments, the one or more intensity adjustors 564a-564n can include optical devices for attenuating intensities (e.g., power tuning) of the one or more wavelengths of light 572a-572n to produce the corresponding one or more attenuated wavelengths of light 573a-573n. For example, the one or more intensity adjustors 564a-564n can include at least one of a microelectromechanical systems (MEMS) array, a digital micro-mirror device (DMD), a mechanical finger device, an adjustable aperture, a polarizer, a spatial light modulator, or an optical filter.

[0088] In one example, the one or more intensity adjustors 564a-564n can include at least one of MEMS array and / or a DMD. A micromirror array, which can include an array of hundreds or thousands of micromirrors (often referred to below simply as “mirrors”), can alter the intensity distribution of the one or more wavelengths of light 572a-572n to produce the corresponding one or more attenuated wavelengths of light 573a-573n. In operation, each micromirror reflects a corresponding one of the one or more wavelengths of light 572a-572n. By tuning the angle of each micromirror independently, the position of the light moves and causes the light distribution at the output to change spatially and spectrally, thus producing the corresponding one or more attenuated wavelengths of light 573a-573n having an adjusted intensity. MEMS technology can be used to manufacture and control the mirrors. For example, electrostatic or piezoelectric actuators can be used to angle the mirrors.

[0089] In one example, the one or more intensity adjustors 564a-564n can include at least one of a mechanical finger device and / or an adjustable aperture. The mechanical finger device can have one or more mechanical fingers, orthogonal to the propagation direction, that are configured to partially insert into the light path to block user-selected ones of the one or more wavelengths of light 572a-572n by variable amounts. An adjustable aperture can alter the size of the aperture to change the amount of that one or more wavelengths of light 572a-572n that passes through the aperture. In operation of either the mechanical finger device and the adjustable aperture, the intensity of the light increases when more light passes through the light path and the intensity of the light decreases when more light is blocked by the mechanical finger(s) or the aperture border. Accordingly, the mechanical finger device and / or the adjustable aperture can adjust the intensities of the one or more wavelengths of light 572a-572n to produce the corresponding one or more attenuated wavelengths of light 573a-573n.

[0090] In one example, the one or more intensity adjustors 564a-564n can include at least one polarizer. A polarizer can filter out any light waves except for specific light waves that propagate along a predetermined plane of a polarizing axis, thereby altering the intensity of incident light. The amount of the intensity adjustment can depend on a relative angle between an angle of the polarizing axis and an angle of incident light. As such, a polarizer can block certain ones of the one or more wavelengths oflight 572a-572n that are not propagating along the polarizing axis to produce the corresponding one or more attenuated wavelengths of light 573a-573n.

[0091] In one example, the one or more intensity adjustors 564a-564n can include at least one spatial light modulator (SLM). A SLM can modulate the intensity of a light beam in a spatially varying manner, and can also modulate the polarization and / or phase of the light beam as well. Therefore, a SLM can modulate intensities of the one or more wavelengths of light 572a-572n to produce the corresponding one or more attenuated wavelengths of light 573a-573n.

[0092] In one example, the one or more intensity adjustors 564a-564n can include an optical filter. An optical filter can alter intensities of the one or more wavelengths of light 572a-572n by selectively transmitting certain ones as the corresponding one or more attenuated wavelengths of light 573a-573n while simultaneously blocking, absorbing, and / or reflecting transmission of other ones of the one or more wavelengths of light 572a-572n. A particular type of optical filter called a Neutral Density (ND) filter can reduce the intensity of each of the one or more wavelengths of light 572a-572n by approximately the same amount across the spectrum.

[0093] In some embodiments, optical system 566 can be configured to combine the one or more attenuated wavelengths of light 573a-573n into a beam 580 and direct the beam 580 toward a target 582 disposed on a substrate (e.g., target 418 on substrate 420 as shown in and described with reference to FIGS. 4A and 4B). Optical system 566 can include one or more optical elements such as, for example, at least one of a beam splitter, mirrors, prisms, focusing elements, or the like, to direct or condition the one or more attenuated wavelengths of light 573a-573n into a beam 580 (e.g., focus, collimate, and the like). In some embodiments, target 582 can comprise a diffractive structure (e.g., one or more gratings). Target 582 can reflect, refract, diffract, scatter, or the like, the beam 580. In some embodiments, optical system 566 can be configured to receive the beam 580 after it interacts with the target 582 and direct beam 580 toward detector 568.

[0094] In some embodiments, detector 568 can be a sensor configured to receive beam 580 from optical system 566 after beam 580 interacts with target 582. Detector 568 can be configured to measure the intensities of the one or more wavelengths of the beam 580 after interacting with the target 582. Detector 568 can generate a detection signal based on the measured intensities of the one or more wavelengths of the beam 580 and can transmit the detection signal to processor 570.

[0095] In some embodiments, processor 570 can be a processing device or computing device configured to receive the detection signal from detector 568. Processor 570 can be configured to generate metrology data as a function of the one or more wavelengths of the beam 580 that was measured by detector 568. The metrology data can include data based on the measurements by detector 568 such as, for example, the measured intensities of the one or more wavelengths of the beam 580. The metrology data can be graphically represented as a line graph, a scatter plot, a bar graph, a table, or the like. The metrology data can include key performance indicators (KPIs) such as light intensity, resolution, alignment position, measurement accuracy, feature uniformity, or the like to enable processmonitoring of the measurements by detector 568. Processor 570 can be configured to monitor the metrology data for data that deviates from the KPIs. Accordingly, processor 570 can be configured to generate an alert signal when a KPI threshold is exceeded for the metrology data. For example, an measured intensity value for a certain wavelength may exceed a KPI threshold for monitoring intensities that can damage the resist layer; as a result, processor 570 can generate an alert indicating that either the power for radiation source 562 should be reduced or the one or more intensity adjustors 564a-564n should perform greater attenuation of the one or more wavelengths of light 572a-572n. In some embodiments, processor 570 can autonomously adjust the power of radiation source 562 or attenuation performed by the one or more intensity adjustors 564a-564n in response to the alert signal.

[0096] FIG. 5B shows a metrology system 560’, according to some embodiments. In some embodiments, metrology system 560’ can be an alternative embodiment of metrology system 560 as shown in and described with reference to FIG. 5A. The elements of metrology system 560’ shown in FIG. 5B and the elements of metrology system 560 shown in FIG. 5A may be similar. Accordingly, the above discussion of metrology system 560 can apply to metrology system 560’ shown in FIG. 5B. In some embodiments, metrology system 560’ can include a radiation source 562’, one or more intensity adjustors 564a-564n, an optical system 566, a detector 568, and a processor 570. The numbered elements previously discussed with regard to metrology system 560 can have the same structure and functions in metrology system 560’ and the detailed description related to those elements is incorporated in this section.

[0097] In some embodiments, radiation source 562’ can be an alternative embodiment of radiation source 562 shown in and described with reference to FIG. 5A. Radiation source 562 can include one or more light sources and optical elements for generating the one or more wavelengths of light 572a-572n. In some embodiments, as shown in the example of FIG. 5B, radiation source 562’ can include a plurality of single-color light sources 575a-575n each configured to generate a corresponding one of the one or more wavelengths of light 572a-572n. Each of the single-color light sources 575a-575n can be configured to produce a monochromatic wavelength of ultraviolet light, visible light, or infrared light from a range between about 5 nm to about 2 pm. Each of the single-color light sources 575a-575n can generate spatially coherent radiation or spatially incoherent radiation. In one example, each of the single-color light sources 575a-575n can be a laser diode. Radiation source 562’ can be configured to direct each of the one or more wavelengths of light 572a-572n from the corresponding single-color light sources 575a-575n toward corresponding ones of the one or more intensity adjustors 564a-564n. Radiation source 562’ can use a medium such as, for example, an optical fiber, air, a vacuum, or the like to direct the one or more wavelengths of light 572a-572n toward corresponding ones of one or more intensity adjustors 564a-564n.

[0098] Example Plot

[0099] FIG. 6 shows a schematic plot 684 of metrology data as a function of wavelengths, according to some embodiments. The metrology data can be graphically represented as a line graph, a scatter plot,a bar graph, a table, or the like. In the example of FIG. 6, the metrology data of plot 684 is represented as a line graph showing intensity 685 (arbitrary units) as a function of wavelength 686 (arbitrary units). For example, intensity 685 and wavelength 686 can be measured values of the alignment signal from target 582 as detected by detector 568 described with reference to FIGS. 5A and 5B. The relationship between intensity 685 and wavelength 686 can be depicted as curve 687. Plot 684 can be generated by processor 570 based on the detection signal as described with reference to FIGS. 5A and 5B.

[0100] In some embodiments, plot 684 can indicate which values of wavelength 686 produce comparatively strong or weak intensity 685 responses when beam 580 diffracts and / or reflects from target 582. Curve 687 can be useful for monitoring the performance of any wavelengths 686 during the alignment process, even if the alignment signal has a low signal-to-noise ratio. Accordingly, the shape of curve 687 can be informative of the performance of the wavelengths 686. For example, if a certain wavelength 686 is expected to produce a high intensity 685 but instead produces a low intensity 685, then it can determined that a process error exists. In another example, a certain wavelength 686 can produce an inordinately high intensity 685 that risks damage to the resist layer. Processor 570 can monitor the shape of curve 687 and / or values of intensity 685 and wavelength 686 for data that deviates from predetermined KPIs. Accordingly, processor 570 can be configured to generate an alert signal when a KPI threshold is exceeded for the metrology data of curve 687.

[0101] Example Method

[0102] FIG. 7 shows a method 790 for performing an alignment process with an optimized signal-to-noise ratio for one or more wavelengths, according to some embodiments.

[0103] In some embodiments, at step 791, a radiation source (e.g., radiation source 562 and 562’ as shown in and described with reference to FIGS. 5 A and 5B, respectively) can generate one or more wavelengths of light (e.g., one or more wavelengths of light 572a-572n as shown in and described with reference to FIGS. 5A and 5B). In some embodiments, the radiation source (e.g., radiation source 562 as shown in and described with reference to FIG. 5A) can include a supercontinuum light source (e.g., supercontinuum light source 574 as shown in and described with reference to FIG. 5A) that generates a multi-color light beam (e.g., multi-color light beam 578 as shown in and described with reference to FIG. 5A) and a color separator (e.g., color separator 576 as shown in and described with reference to FIG. 5A) that separates the multi-color light beam into a plurality of single-color light beams each corresponding to individual ones of the one or more wavelengths of light. In some embodiments, the radiation source (e.g., radiation source 562’ as shown in and described with reference to FIG. 5B) can include a plurality of single-color light sources (e.g., single-color light sources 575a-575n as shown in and described with reference to FIG. 5B) that generate individual corresponding ones of the one or more wavelengths of light.

[0104] In some embodiments, at step 792, one or more intensity adjustors (e.g., one or more intensity adjustors 564a-564n as shown in and described with reference to FIGS. 5A and 5B) can adjust intensities of the one or more wavelengths of light such that a signal-to-noise ratio is set at or above atarget threshold for selected wavelengths of the one or more wavelengths of light. For example, the one or more intensity adjustors can adjust the intensities of the one or more wavelengths of light to optimize the signal-to-noise ratio by increasing the signal-to-noise ratio to meet or exceed the target threshold. The one or more intensity adjustors can produce a selected power distribution among the one or more wavelengths of light by attenuating the intensities of the one or more wavelengths of light. The one or more intensity adjustors can adjust the intensities of the one or more wavelengths of light with at least one of a microelectromechanical systems (MEMS) array, a digital micro-mirror device (DMD), a mechanical finger device, an adjustable aperture, a polarizer, a spatial light modulator, or an optical filter.

[0105] In some embodiments, at step 793, an optical system (e.g., optical system 566 as shown in and described with reference to FIGS. 5 A and 5B) can combine the one or more wavelengths of light into a beam (e.g., beam 580 as shown in and described with reference to FIGS. 5A and 5B).

[0106] In some embodiments, at step 794, the optical system can direct the beam toward a target (e.g., target 582 as shown in and described with reference to FIGS. 5A and 5B).

[0107] In some embodiments, at step 795, the optical system can receive the beam after it interacts with the target.

[0108] In some embodiments, at step 796, a detector (e.g., detector 568 as shown in and described with reference to FIGS. 5A and 5B) can receive the beam from the optical system after the beam interacts with the target.

[0109] In some embodiments, at step 797, the detector can measure intensities of the one or more wavelengths of the beam after interacting with the target.

[0110] In some embodiments, at step 798, a processor (e.g., processor 570 as shown in and described with reference to FIGS. 5A and 5B) can generate metrology data as a function of the one or more wavelengths of the beam based on the measuring.

[0111] In some embodiments, the method 790 can further include generating, with the processor, an alert signal when a key performance indicator (KPI) threshold is exceeded for the metrology data.

[0112] The method steps of FIG. 7 can be performed in any conceivable order and it is not required that all steps be performed. Moreover, the method steps of FIG. 7 described above merely reflect an example of steps and are not limiting. That is, further method steps and functions are envisaged based embodiments described in reference to FIGS. 1A-6.

[0113] In the following, further features, characteristics, and exemplary technicalsolutions of the present disclosure will be described in terms of clauses that may be optionally claimed in any combination:1. A metrology system comprising:a radiation source configured to generate one or more wavelengths of light;one or more intensity adjustors configured to adjust intensities of the one or more wavelengths of light such that a signal-to-noise ratio is set at or above a target threshold for selected wavelengths of the one or more wavelengths of light;an optical system configured to combine the one or more wavelengths of light into a beam, direct the beam toward a target, and receive the beam after it interacts with the target;a detector configured to receive the beam from the optical system after the beam interacts with the target and measure the intensities of the one or more wavelengths of the beam after interacting with the target; anda processor configured to generate metrology data as a function of the one or more wavelengths of the beam.2. The metrology system of clause 1, wherein the radiation source comprises:a supercontinuum light source configured to generate a multi-color light beam; and a color separator configured to separate the multi-color light beam into a plurality of singlecolor light beams each corresponding to individual ones of the one or more wavelengths of light. 3. The metrology system of clause 2, wherein the color separator comprises at least a diffraction grating or an optical filter assembly.4. The metrology system of clause 1 , wherein the radiation source comprises a plurality of singlecolor light sources each configured to generate a corresponding one of the one or more wavelengths of light.5. The metrology system of clause 1, wherein the one or more intensity adjustors are configured to produce a selected power distribution among the one or more wavelengths of light by attenuating the intensities of the one or more wavelengths of light.6. The metrology system of clause 1 , wherein the one or more intensity adjustors comprise at least one of a microelectromechanical systems (MEMS) array, a digital micro-mirror device (DMD), a mechanical finger device, an adjustable aperture, a polarizer, a spatial light modulator, or an optical filter.7. The metrology system of clause 1, wherein the processor is configured to generate an alert signal when a key performance indicator (KPI) threshold is exceeded for the metrology data.8. A lithographic apparatus comprising:an illumination system configured to condition a radiation beam;a patterning system configured to impart a pattern onto the radiation beam to form a patterned beam;a projection system configured to project the patterned beam onto a substrate; anda metrology system comprising:a radiation source configured to generate one or more wavelengths of light;one or more intensity adjustors configured to adjust intensities of the one or more wavelengths of light such that a signal-to-noise ratio is set at or above a target threshold for selected wavelengths of the one or more wavelengths of light;an optical system configured to combine the one or more wavelengths of light into a beam, direct the beam toward a target, and receive the beam after it interacts with the target;a detector configured to receive the beam from the optical system after the beam interacts with the target and measure the intensities of the one or more wavelengths of the beam after interacting with the target; anda processor configured to generate metrology data as a function of the one or more wavelengths of the beam.9. The lithographic apparatus of clause 8, wherein the radiation source comprises:a supercontinuum light source configured to generate a multi-color light beam; and a color separator configured to separate the multi-color light beam into a plurality of singlecolor light beams each corresponding to individual ones of the one or more wavelengths of light. 10. The lithographic apparatus of clause 9, wherein the color separator comprises at least a diffraction grating or an optical filter assembly.11. The lithographic apparatus of clause 8, wherein the radiation source comprises a plurality of single-color light sources each configured to generate a corresponding one of the one or more wavelengths of light.12. The lithographic apparatus of clause 8, wherein the one or more intensity adjustors are configured to produce a selected power distribution among the one or more wavelengths of light by attenuating the intensities of the one or more wavelengths of light.13. The lithographic apparatus of clause 8, wherein the one or more intensity adjustors comprise at least one of a microelectromechanical systems (MEMS) array, a digital micro-mirror device (DMD), a mechanical finger device, an adjustable aperture, a polarizer, a spatial light modulator, or an optical filter.14. The lithographic apparatus of clause 8, wherein the processor is configured to generate an alert signal when a key performance indicator (KPI) threshold is exceeded for the metrology data.15. A method comprising:generating, with a radiation source, one or more wavelengths of light;adjusting, with one or more intensity adjustors, intensities of the one or more wavelengths of light such that a signal-to-noise ratio is set at or above a target threshold for selected wavelengths of the one or more wavelengths of light;combining, with an optical system, the one or more wavelengths of light into a beam; directing, with the optical system, the beam toward a target;receiving, with the optical system, the beam after it interacts with the target;receiving, at a detector, the beam from the optical system after the beam interacts with the target;measuring, with the detector, intensities of the one or more wavelengths of the beam after interacting with the target; andgenerating, with a processor, metrology data as a function of the one or more wavelengths of the beam based on the measuring.16. The method of clause 15, wherein the generating the one or more wavelengths of light comprises:generating, with a supercontinuum light source, a multi-color light beam; and separating, with a color separator, the multi-color light beam into a plurality of single-color light beams each corresponding to individual ones of the one or more wavelengths of light.17. The method of clause 15, wherein the generating the one or more wavelengths of light comprises generating individual ones of the one or more wavelengths of light at corresponding ones of a plurality of single-color light sources.18. The method of clause 15, wherein the adjusting the intensities of the one or more wavelengths of light comprises producing a selected power distribution among the one or more wavelengths of light by attenuating the intensities of the one or more wavelengths of light.19. The method of clause 15, wherein the adjusting the intensities of the one or more wavelengths of light comprises adjusting the intensities of the one or more wavelengths of light with at least one of a microelectromechanical systems (MEMS) array, a digital micro-mirror device (DMD), a mechanical finger device, an adjustable aperture, a polarizer, a spatial light modulator, or an optical filter.20. The method of clause 15, further comprising generating, with the processor, an alert signal when a key performance indicator (KPI) threshold is exceeded for the metrology data.21. A system comprising :a radiation source configured to generate one or more wavelengths of light;one or more intensity adjustors configured to adjust intensities of the one or more wavelengths of light such that a signal-to-noise ratio is set at or above a target threshold for selected wavelengths of the one or more wavelengths of light;an optical system configured to combine the one or more wavelengths of light into a beam, direct the beam toward a target, and receive the beam after it interacts with the target;a detector configured to receive the beam from the optical system after the beam interacts with the target and measure the intensities of the one or more wavelengths of the beam after interacting with the target; anda processor configured to generate metrology data as a function of the one or more wavelengths of the beam.

[0114] 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, visible radiation (for example, havinga wavelength X in the range of 400 to 780 nm), ultraviolet (UV) radiation (for example, having a wavelength X 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 embodiments, 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.

[0115] Although some embodiments 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, embodiments 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.

[0116] Furthermore, although some embodiments of the present disclosure are described in the context of optical lithography, it should be understood that embodiments 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.

[0117] 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.

[0118] 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 embodiments 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 embodiments, 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 embodiments, based on the teaching and guidance presented herein.

[0119] 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, embodiments 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 abovedescribed embodiments, but should be defined in accordance with the following claims and their equivalents.

Claims

CLAIMS1. A metrology system comprising:a radiation source configured to generate one or more wavelengths of light;one or more intensity adjustors configured to adjust intensities of the one or more wavelengths of light such that a signal-to-noise ratio is set at or above a target threshold for selected wavelengths of the one or more wavelengths of light;an optical system configured to combine the one or more wavelengths of light into a beam, direct the beam toward a target, and receive the beam after it interacts with the target;a detector configured to receive the beam from the optical system after the beam interacts with the target and measure the intensities of the one or more wavelengths of the beam after interacting with the target; anda processor configured to generate metrology data as a function of the one or more wavelengths of the beam.

2. The metrology system of claim 1, wherein the radiation source comprises:a supercontinuum light source configured to generate a multi-color light beam; and a color separator configured to separate the multi-color light beam into a plurality of singlecolor light beams each corresponding to individual ones of the one or more wavelengths of light.

3. The metrology system of claim 2, wherein the color separator comprises at least a diffraction grating or an optical filter assembly.

4. The metrology system of claim 1 , wherein the radiation source comprises a plurality of singlecolor light sources each configured to generate a corresponding one of the one or more wavelengths of light.

5. The metrology system of claim 1, wherein the one or more intensity adjustors are configured to produce a selected power distribution among the one or more wavelengths of light by attenuating the intensities of the one or more wavelengths of light.

6. The metrology system of claim 1 , wherein the one or more intensity adjustors comprise at least one of a microelectromechanical systems (MEMS) array, a digital micro-mirror device (DMD), a mechanical finger device, an adjustable aperture, a polarizer, a spatial light modulator, or an optical filter.

7. The metrology system of claim 1 , wherein the processor is configured to generate an alert signal when a key performance indicator (KPI) threshold is exceeded for the metrology data.

8. A lithographic apparatus comprising:an illumination system configured to condition a radiation beam;a patterning system configured to impart a pattern onto the radiation beam to form a patterned beam;a projection system configured to project the patterned beam onto a substrate; anda metrology system comprising:a radiation source configured to generate one or more wavelengths of light;one or more intensity adjustors configured to adjust intensities of the one or more wavelengths of light such that a signal-to-noise ratio is set at or above a target threshold for selected wavelengths of the one or more wavelengths of light;an optical system configured to combine the one or more wavelengths of light into a beam, direct the beam toward a target, and receive the beam after it interacts with the target;a detector configured to receive the beam from the optical system after the beam interacts with the target and measure the intensities of the one or more wavelengths of the beam after interacting with the target; anda processor configured to generate metrology data as a function of the one or more wavelengths of the beam.

9. The lithographic apparatus of claim 8, wherein the radiation source comprises:a supercontinuum light source configured to generate a multi-color light beam; and a color separator configured to separate the multi-color light beam into a plurality of singlecolor light beams each corresponding to individual ones of the one or more wavelengths of light.

10. The lithographic apparatus of claim 9, wherein the color separator comprises at least a diffraction grating or an optical filter assembly.

11. The lithographic apparatus of claim 8, wherein the radiation source comprises a plurality of single-color light sources each configured to generate a corresponding one of the one or more wavelengths of light.

12. The lithographic apparatus of claim 8, wherein the one or more intensity adjustors are configured to produce a selected power distribution among the one or more wavelengths of light by attenuating the intensities of the one or more wavelengths of light.

13. The lithographic apparatus of claim 8, wherein the one or more intensity adjustors comprise at least one of a microelectromechanical systems (MEMS) array, a digital micro-mirror device (DMD), a mechanical finger device, an adjustable aperture, a polarizer, a spatial light modulator, or an optical filter.

14. The lithographic apparatus of claim 8, wherein the processor is configured to generate an alert signal when a key performance indicator (KPI) threshold is exceeded for the metrology data.

15. A method comprising:generating, with a radiation source, one or more wavelengths of light;adjusting, with one or more intensity adjustors, intensities of the one or more wavelengths of light such that a signal-to-noise ratio is set at or above a target threshold for selected wavelengths of the one or more wavelengths of light;combining, with an optical system, the one or more wavelengths of light into a beam; directing, with the optical system, the beam toward a target;receiving, with the optical system, the beam after it interacts with the target;receiving, at a detector, the beam from the optical system after the beam interacts with the target;measuring, with the detector, intensities of the one or more wavelengths of the beam after interacting with the target; andgenerating, with a processor, metrology data as a function of the one or more wavelengths of the beam based on the measuring.

Images