Lithographic apparatus, inspection system and method for implementing parallel sensor head with common radiation source

Abstract

A lithographic apparatus includes an illumination system, a projection system, and an inspection system. The inspection system includes a broadband radiation system, an optical system, a wavelength splitter system, and a detector system. The broadband radiation system generates source radiation having a first set of narrowband wavelengths distributed within an operating bandwidth of the inspection system and a second set of narrowband wavelengths distributed within the operating bandwidth. The narrowband wavelengths of the first set are close to the narrowband wavelengths of the second set. The optical system directs the first and second portions of the source radiation toward the first and second targets to produce first and second scattered radiation. The wavelength separator system separates a narrowband wavelength of the first scattered radiation and the second scattered radiation. The detector system receives the first scattered radiation and the second scattered radiation to generate a first measurement signal and a second measurement signal based on the first scattered radiation and the second scattered radiation.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to US application 63 / 486,584, filed February 23, 2023, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to metrology equipment, such as alignment sensors for measuring wafer alignment in lithographic equipment and lithographic systems. Background Art

[0004] A lithographic apparatus is a machine that applies a desired pattern to a substrate (typically onto a target portion of the substrate). Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In this case, a patterning device (which can be a mask or reticle) is used to produce the circuit patterns to be formed on individual layers of the IC. This pattern can be transferred to a target portion (e.g., a portion of a die, a die, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern typically occurs by imaging onto a layer of radiation-sensitive material (photoresist, or simply "resist") provided on the substrate. Typically, a single substrate will contain a network of adjacent, sequentially patterned target portions. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern to the target portion at once; and so-called scanners, in which each target portion is irradiated by simultaneously scanning a radiation beam across the pattern in a given direction (the "scanning" direction) while simultaneously scanning the target portion parallel or antiparallel to the scan direction. It is also possible to transfer the pattern from the patterning device to the substrate by printing the pattern onto the substrate.

[0005] During a lithography operation, different processing steps may require different layers to be sequentially formed on a substrate. Therefore, the substrate may need to be positioned with high accuracy relative to an existing pattern formed on the substrate. Typically, alignment marks are placed on the substrate to be aligned and positioned with reference to a second object. The lithography equipment can use alignment equipment to detect the position of the alignment marks and use them to align the substrate to ensure accurate exposure from the mask. Misalignment between alignment marks at two different layers is measured as overlay error.

[0006] To monitor the photolithography process, parameters of the patterned substrate are measured. For example, these parameters may include the overlay error between successive layers formed in or on the patterned substrate and the critical linewidth of the developed photoresist. These measurements can be performed on production substrates and / or specialized metrology targets. Various techniques exist for measuring the microstructures formed during the photolithography process, including the use of scanning electron microscopes and various specialized tools. One rapid and non-invasive specialized inspection tool is a scatterometer, in which a radiation beam is directed onto a target on the substrate's surface and the properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it is reflected or scattered by the substrate, the properties of the substrate can be determined. This can be achieved, for example, by comparing the reflected beam with data stored in a library of known measurements associated with known substrate properties. Spectral 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 specific narrow angular range. In contrast, angle-resolved scatterometers use a monochromatic radiation beam and measure the intensity of the scattered radiation as a function of angle.

[0007] Such optical scatterometers can be used to measure parameters such as the critical dimension of developed photoresist or the overlay error (OV) between two layers formed in or on a patterned substrate. By comparing the properties of the illumination beam before and after it is reflected or scattered by the substrate, the properties of the substrate can be determined.

[0008] Photolithography systems can only output a limited number of fabricated devices in a given timeframe. The fabrication process can include multiple complex and time-consuming steps to ensure sub-nanometer accuracy. Summary of the Invention

[0009] Therefore, it is desirable to increase manufacturing speed and throughput without sacrificing accurate photolithographic pattern transfer.To increase throughput, inspection operations can be performed more quickly based on the aspects described herein.

[0010] In some aspects, a lithographic apparatus may include an illumination system, a projection system, and an inspection system. The illumination system may illuminate a pattern on a patterning device. The projection system may project an image of the pattern onto a substrate to form a plurality of targets on the substrate. The inspection system may inspect the plurality of targets. The inspection system may include a broadband radiation system, an optical system, a wavelength separator system, and a detector system. The broadband radiation system may generate source radiation. The source radiation may have a first set of narrowband wavelengths distributed within an operating bandwidth of the inspection system. The source radiation may also have a second set of narrowband wavelengths distributed within the operating bandwidth. The narrowband wavelengths of the first set may be close to the narrowband wavelengths of the second set. The optical system may direct a first portion of the source radiation toward a first target among the plurality of targets to generate first scattered radiation. The optical system may also direct a second portion of the source radiation toward a second target among the plurality of targets to generate second scattered radiation. The wavelength separator system may separate the narrowband wavelengths of the first and second scattered radiation. The detector system may receive the first and second scattered radiation. The detector system may also generate first and second measurement signals based on the first and second scattered radiation, respectively.

[0011] In some aspects, an inspection system may include a broadband radiation system, an optical system, a wavelength separator system, and a detector system. The broadband radiation system may generate source radiation. The source radiation may have a first set of narrowband wavelengths distributed within an operating bandwidth of the inspection system. The source radiation may also have a second set of narrowband wavelengths distributed within the operating bandwidth. The narrowband wavelengths of the first set are close to the narrowband wavelengths of the second set. The optical system may direct a first portion of the source radiation toward a first target among the plurality of targets to generate first scattered radiation. The optical system may also direct a second portion of the source radiation toward a second target among the plurality of targets to generate second scattered radiation. The wavelength separator system may separate the narrowband wavelengths of the first scattered radiation and the second scattered radiation. The detector system may receive the first scattered radiation and the second scattered radiation. The detector system may also generate a first measurement signal and a second measurement signal based on the first scattered radiation and the second scattered radiation, respectively.

[0012] In some aspects, a method may include one or more of the following operations. The method may include generating source radiation using a broadband radiation system. The source radiation may have a first set of narrowband wavelengths distributed within an operating bandwidth of the inspection system. The source radiation may also have a second set of narrowband wavelengths distributed within the operating bandwidth. The narrowband wavelengths of the first set may be close to the narrowband wavelengths of the second set. The method may also include directing a first portion of the source radiation toward a first target among a plurality of targets to generate first scattered radiation. The method may also include directing a second portion of the source radiation toward a second target among the plurality of targets to generate second scattered radiation. The method may also include separating the narrowband wavelengths of the first and second scattered radiation using a wavelength separator system. The method may also include receiving the first scattered radiation at a detector system. The method may also include generating a first measurement signal based on the first scattered radiation using the detector system. The method may also include receiving the second scattered radiation at the detector system. The method may also include generating a second measurement signal based on the second scattered radiation using the detector system.

[0013] Other features of various aspects of the present disclosure are described in detail below with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the specific aspects described herein. These aspects are presented herein for illustrative purposes only. Based on the teachings contained herein, (multiple) persons skilled in the relevant art will understand additional aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings, which are now incorporated herein and form a part of the specification, illustrate the present disclosure and, together with the description, serve to explain the principles of the present disclosure and to enable one skilled in the relevant art(s) to make and use the aspects described herein.

[0015] Figure 1A A reflective lithographic apparatus according to some aspects is shown.

[0016] Figure 1B A transmissive lithographic apparatus according to some aspects is shown.

[0017] Figure 2 Shown are further details of a reflective lithographic apparatus according to some aspects.

[0018] Figure 3 A lithographic cell is shown in accordance with some aspects.

[0019] Figure 4A 、 Figure 4B and Figure 5 An inspection apparatus according to some aspects is shown.

[0020] Figure 6A graph illustrating wavelengths resulting from a broadband radiation system according to some aspects.

[0021] Figure 7 A flow chart illustrating a method according to some aspects is shown.

[0022] Features of the present disclosure will become more apparent from the following detailed description, which is set forth in conjunction with the accompanying drawings, in which like reference numerals identify corresponding elements throughout. In the drawings, like reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, the leftmost digit(s) of a reference numeral generally identifies the drawing in which the reference numeral first appears. Unless otherwise indicated, the drawings provided throughout this disclosure should not be construed as being drawn to scale. DETAILED DESCRIPTION

[0023] The aspects described herein and references in the specification to "an aspect," "an aspect," "an exemplary aspect," "an example aspect," etc., indicate that the aspects described may include a particular feature, structure, or characteristic, but not every aspect necessarily includes the particular feature, structure, or characteristic. Moreover, these words or phrases do not necessarily refer to the same aspect. In addition, when a particular feature, structure, or characteristic is described in conjunction with an aspect, it should be understood that it is within the knowledge of those skilled in the art to implement such feature, structure, or characteristic in conjunction with other embodiments, regardless of whether the other aspects are explicitly described.

[0024] For ease of description, spatially relative terms, such as "below," "beneath," "above," "over," and the like, may be used herein to describe the relationship of one element or feature to other element(s) or feature(s) in the drawings. Spatially relative terms are intended to encompass different orientations of the device or component in use or operation in addition to the orientation depicted in the drawings. The device may be otherwise oriented (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein should be interpreted accordingly.

[0025] The terms "about," "approximately," and the like may be used herein to indicate a value for a given quantity that may vary based on the particular technology. Depending on the particular technology, the terms "about," "approximately," and the like may indicate a value for a given quantity that varies, for example, by 10% to 30% above or below the stated value (e.g., ±10%, ±20%, or ±30% of the stated value).

[0026] Aspects of the present disclosure can be implemented in hardware, firmware, software, or any combination thereof. Aspects of the present 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 may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM); random-access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), etc. Furthermore, firmware, software, routines, and / or instructions may be described herein as performing specific actions. However, it should be understood that such descriptions are for convenience only, and that such actions result from the computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc. The term "machine-readable medium" may be used interchangeably with similar terms such as "computer program product," "computer-readable medium," "non-transitory computer-readable medium," and the like. The term "non-transitory" may be used herein to characterize one or more forms of computer-readable media other than transitory propagated signals.

[0027] Before describing these aspects in further detail, however, it is instructive to present an example environment in which aspects of the disclosure may be implemented.

[0028] Exemplary lithography systems

[0029] Figure 1A and Figure 1B A lithographic apparatus 100 and a lithographic apparatus 100' are respectively shown, in which aspects of the present disclosure may be implemented. The lithographic apparatus 100 and the lithographic apparatus 100' each include an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., deep ultraviolet radiation or extreme ultraviolet radiation); a support structure (e.g., a mask table) MT configured to support a patterning device (e.g., a mask, reticle, or dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and a substrate table (e.g., a wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. The lithographic apparatus 100 and the lithographic apparatus 100' further have a projection system PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W. In lithographic apparatus 100, patterning device MA and projection system PS are reflective.In lithographic apparatus 100', patterning device MA and projection system PS are transmissive.

[0030] The illumination system IL may include various types of optical components for directing, shaping or controlling the radiation beam B, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof.

[0031] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA relative to the reference frame, the design of at least one of the lithographic apparatuses 100 and 100', and other conditions, such as whether 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, for example, a frame or table, which can be fixed or movable. Using sensors, the support structure MT can ensure that the patterning device MA is in a desired position, for example, relative 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 so as to create a pattern in a target portion C of the substrate W. The pattern imparted to the radiation beam B may correspond to a specific functional layer in the target portion C to be created for forming a device in an integrated circuit.

[0033] The patterning device MA may be of the transmissive type (e.g. Figure 1B lithographic apparatus 100 ′) or reflective (as in Figure 1A lithographic apparatus 100). 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 uses a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incident radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam B that is reflected by the matrix of small mirrors.

[0034] The term "projection system" PS may encompass any type of projection system suitable for the exposure radiation used or for other factors, such as the use of an immersion liquid on the substrate W or the use of a vacuum, including refractive, reflective, catadioptric, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof. Because other gases may absorb excessive radiation or electrons, a vacuum environment may be used for EUV or electron beam radiation. Thus, a vacuum environment can be maintained throughout the beam path using vacuum walls and a vacuum pump.

[0035] The lithographic apparatus 100 and / or the lithographic apparatus 100 ′ may be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such a “multi-stage” machine, the additional substrate tables WT may be used in parallel, or one or more other substrate tables WT may be used for exposure while preparatory steps are being performed on one or more tables. In some cases, the additional tables may not be substrate tables WT.

[0036] The lithographic apparatus may also be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index (e.g., water) so as to fill the space between the projection system and the substrate. Immersion liquid may also be applied to other spaces in the lithographic apparatus, such as the space between the mask and the projection system. Immersion techniques for increasing the numerical aperture of a projection system are well known in the art. The term "immersion," as used herein, does not necessarily mean that structures such as the substrate are submerged in the liquid. For example, the liquid may be located between the projection system and the substrate during exposure.

[0037] refer to Figure 1A and Figure 1B , the illuminator IL receives a radiation beam from a radiation source SO. For example, when the source SO is an excimer laser, the source SO and the lithographic apparatus 100, 100' may be separate physical entities. In such a case, the source SO is not considered to form part of the lithographic apparatus 100 or 100', and the radiation beam B is delivered to the lithographic apparatus 100 or 100' by means of a beam delivery system BD ( Figure 1B The radiation system may comprise the source SO, the illuminator IL and / or the beam delivery system BD.

[0038] The illuminator IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam ( Figure 1B In general, at least the outer radial extent and / or the inner radial extent (commonly referred to as "σ-outer" and "σ-inner", respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components ( Figure 1B ), 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] refer to Figure 1A, a radiation beam B is incident on a patterning device (e.g., a mask) MA, which is held on a support structure (e.g., a mask table) MT, and is patterned by the patterning device MA. In the lithographic apparatus 100, the radiation beam B is reflected from the patterning device (e.g., a mask) MA. After reflecting from the patterning device (e.g., a mask) MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor IF2 (e.g., an interferometry device, a linear encoder, or a capacitive sensor), the substrate table WT can be accurately moved (e.g., to position a different target portion C in the path of the radiation beam B). Similarly, a first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (e.g., a mask) MA relative to the path of the radiation beam B. Mask alignment marks M1, M2 and substrate alignment marks P1, P2 can be used to align the patterning device (e.g., a mask) MA and the substrate W.

[0040] refer to Figure 1B , radiation beam B is incident on a patterning device (e.g., mask MA) held on a support structure (e.g., mask table MT) and patterned by the patterning device. After passing through mask MA, radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. The projection system has a conjugate pupil PPU relative to an illumination system pupil IPU. Components of the radiation emanate from the intensity distribution at illumination system pupil IPU and pass through the mask pattern without being affected by diffraction at the mask pattern, producing an image of the intensity distribution at illumination system pupil IPU.

[0041] The projection system PS projects an image of a mask pattern MP onto a photoresist layer applied to a substrate W, wherein the image is formed by a diffraction beam generated by the mask pattern MP caused by radiation having an intensity distribution. For example, the mask pattern MP may include an array of lines and spaces. Diffraction of radiation at the array, other than the zeroth order diffraction, produces a diffraction beam that is deflected, having a change of direction in a direction perpendicular to the lines. The undiffracted beam (i.e., the so-called zeroth order diffraction beam) passes through the pattern without any change in propagation direction. The zeroth order diffraction beam passes through an upper lens or an upper lens group of the projection system PS, which is located upstream of the conjugate pupil or conjugate pupil PPU of the projection system PS, to reach the conjugate pupil PPU. The portion of the intensity distribution in the plane of the conjugate pupil PPU and associated with the zeroth order diffraction beam is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. The aperture device PD is, for example, arranged at or approximately at a plane including the conjugate pupil PPU of the projection system PS.

[0042] The projection system PS is arranged (e.g., using a lens or lens group L) to capture a zeroth-order diffraction beam, a first-order diffraction beam, and / or higher-order diffraction beams (not shown). In some aspects, dipole illumination for imaging a line pattern extending perpendicular to the line can be used to exploit the resolution-enhancing effect of dipole illumination. For example, at the level of wafer W, the first-order diffraction beam interferes with the corresponding zeroth-order diffraction beam to produce an image of the line pattern MP with the highest possible resolution and process window (i.e., usable depth of focus and tolerable exposure dose deviation). In some aspects, astigmatic aberrations can be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. Additionally, in some aspects, astigmatic aberrations can be reduced by blocking the zeroth-order beam in the projection system's conjugate pupil PPU, associated with the radiation pole in the opposite quadrant. This is described in more detail in US Pat. No. 7,511,799 B2, issued Mar. 31, 2009, the entire contents of which are incorporated herein by reference.

[0043] With the help of a second positioner PW and a position sensor IFD (e.g. an interferometry device, a linear encoder, or a capacitive sensor), the substrate table WT can be accurately moved (e.g., to position a different target portion C in the path of the radiation beam B). Similarly, the substrate table WT can be accurately moved using a first positioner PM and another position sensor ( Figure 1B ) to accurately position the mask MA relative to the path of the radiation beam B (eg after mechanical retrieval from a mask library or during scanning).

[0044] Typically, movement of the mask table MT may 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 may 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 may be connected to a short-stroke actuator, or may be fixed. Mask alignment marks M1, M2 and substrate alignment marks P1, P2 may be used to align the mask MA with the substrate W. Although the substrate alignment marks (as shown) occupy dedicated target portions, these marks may be located in the spaces between target portions (called scribe line alignment marks). Similarly, in the case where more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.

[0045] The mask table MT and patterning device MA can be located in a vacuum chamber V, where an in-vacuum robot (IVR) can be used to move the patterning device (such as a mask) into and out of the vacuum chamber. Alternatively, when the mask table MT and patterning device MA are outside the vacuum chamber, an out-of-vacuum robot similar to the in-vacuum robot (IVR) can be used to perform various transport operations. Both the in-vacuum and out-of-vacuum robots can be calibrated to smoothly transfer any payload (e.g., a mask) to the fixed kinematic support of the transfer station.

[0046] The lithographic apparatuses 100 and 100 ′ may be used in at least one of the following modes:

[0047] 1. In step mode, the support structure (e.g. mask table) MT and substrate table WT are held substantially stationary (i.e. a single static exposure) while the entire pattern imparted to the radiation beam B is projected at once onto a target portion C. The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed.

[0048] 2. In scan mode, the support structure (e.g. mask table) MT and substrate table WT are scanned synchronously (i.e. single dynamic exposure) as a pattern imparted to the radiation beam B is projected onto a target portion C. The velocity and direction of the substrate table WT relative to the support structure (e.g. mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0049] 3. In another mode, the support structure (e.g., mask table) MT is held substantially stationary, thereby holding the 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 may be used, with the programmable patterning device updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation may be readily applicable to maskless lithography utilizing a programmable patterning device, such as a programmable mirror array.

[0050] Combinations and / or variations on the described modes of use or entirely different modes of use may also be employed.

[0051] In some aspects, the lithographic apparatus 100 includes an extreme ultraviolet (EUV) source configured to generate an EUV radiation beam for EUV lithography. Typically, 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.

[0052] In some aspects, the lithographic apparatus 100' includes a deep ultraviolet (DUV) source configured to generate a DUV radiation beam for DUV lithography. Typically, 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.

[0053] Figure 2 The lithographic apparatus 100 is shown in greater detail and includes a source collector apparatus SO, an illumination system IL, and a projection system PS. The source collector apparatus SO is constructed and arranged such that a vacuum environment can be maintained within the enclosed structure 220 of the source collector apparatus SO. An EUV radiation-emitting plasma 210 can be formed by a discharge-generated plasma source. EUV radiation can be generated by a gas or vapor (e.g., Xe gas, Li vapor, or Sn vapor), wherein the EUV radiation-emitting plasma 210 is generated to emit radiation in the EUV range of the electromagnetic spectrum. The EUV radiation-emitting plasma 210 is generated, for example, by a discharge, which results in an at least partially ionized plasma. Radiation can be effectively generated using, for example, a partial pressure of 10 Pa of Xe, Li, Sn vapor, or any other suitable gas or vapor. In some aspects, an excited (e.g., laser-excited) tin (Sn) plasma is provided to generate the EUV radiation.

[0054] Radiation emitted by EUV radiation-emitting plasma 210 passes from source chamber 11 into collector chamber 212 via an optional gas barrier or contamination trap 230 (also referred to as a contamination barrier or fin trap in some cases) positioned in or behind an opening in source chamber 211. Contamination 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. Herein, contamination trap or contamination barrier 230 is further referred to as including at least a channel structure.

[0055] The collector chamber 212 may include a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation passing through the collector CO may be reflected by a grating spectral filter 240 to be focused at a virtual source point INTF. The virtual source point INTF is often referred to as an intermediate focus, and the source collector apparatus is arranged such that the intermediate focus INTF is positioned at or near an opening 219 in the enclosure 220. The virtual source point INTF is an image of the EUV radiation emitting plasma 210. The grating spectral filter 240 is used, in particular, to suppress infrared (IR) radiation.

[0056] The radiation then passes through the illumination system IL, which may include a faceted field mirror arrangement 222 and a faceted pupil mirror arrangement 224 arranged to provide a desired angular distribution of the radiation beam 21 at the patterning device MA, and a desired uniformity of radiation intensity at the patterning device MA. When the radiation beam 221 reflects at the patterning device MA, which is 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 a wafer stage or substrate table WT.

[0057] Typically, more elements than shown may be present in the illumination optics unit IL and the projection system PS. A grating spectral filter 240 may optionally be present depending on the type of lithographic apparatus. Additionally, more than Figure 2 The reflectors shown in FIG are more reflectors, for example, compared to Figure 2 In addition to the reflective elements shown in FIG, there may be one to six additional reflective elements in projection system PS.

[0058] like Figure 2 The collector optics CO illustrated in FIG2 is depicted as a nested collector with grazing incidence reflectors 253, 254, and 255, which is merely an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254, and 255 are arranged to be axially symmetric about the optical axis O, and this type of collector optics CO is preferably used in conjunction with a discharge produced plasma source, commonly referred to as a DPP source.

[0059] Exemplary Lithography Cell

[0060] Figure 3A lithography cell 300, sometimes also referred to as a lithocell or cluster, is shown according to some aspects. The lithography apparatus 100 or 100' may form part of the lithography cell 300. The lithography cell 300 may also include one or more devices that perform pre-exposure and post-exposure processes on the substrate. Conventionally, these devices include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chill plate CH, and a bake plate BK. A substrate transport device or robot RO picks up substrates from input / output ports I / O1 and I / O2, moves substrates between various process devices, and delivers them to a loading station LB of the lithography apparatus 100 or 100'. These devices, often collectively referred to as a track or coating and development control system, are under the control of a track or coating and development control system control unit TCU, which is itself controlled by a supervisory control system SCS, which also controls the lithography apparatus via a lithography control unit LACU. Thus, the various devices can be operated to maximize throughput and processing efficiency.

[0061] Exemplary inspection equipment

[0062] To control the lithography process and accurately place device features on the substrate, alignment marks are typically provided on the substrate, and the lithography apparatus includes one or more inspection devices for accurately locating the marks on the substrate. These alignment devices are essentially position measurement devices. Different types of marks and alignment devices and / or systems are known from different eras and manufacturers. One system currently widely used in lithography apparatuses is based on the self-referencing interferometer described in U.S. Patent No. 6,961,116 (den Boef et al.). Typically, the marks are measured separately to obtain the X and Y positions. However, combined X and Y measurements can be performed using the techniques described in U.S. Publication No. 2009 / 195768 A (Bijnen et al.). The entire contents of both publications are incorporated herein by reference.

[0063] Figure 4A A cross-sectional view of an inspection apparatus 400, which can be implemented as part of a lithographic apparatus 100 or 100', according to some aspects, is shown. In some aspects, the inspection apparatus 400 can be configured to align a substrate (e.g., substrate W) relative to a patterning device (e.g., patterning device MA). The inspection apparatus 400 can also be configured to detect the positions of alignment marks on the substrate and use the detected positions of the alignment marks to align the substrate relative to the patterning device or other components of the lithographic apparatus 100 or 100'. This alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

[0064] The terms "inspection equipment," "measurement system," etc. may be used herein to refer to, for example, a device for measuring properties of a structure (e.g., an overlay sensor, a critical dimension sensor, etc.), a device or system used in a lithography device to check the alignment of a wafer (e.g., an alignment sensor), etc.

[0065] In some aspects, inspection device 400 may include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and an overlap calculation processor 432. Illumination system 412 may be configured to provide an electromagnetic narrowband radiation beam 413 having one or more passbands. In one example, the one or more passbands may be within a spectrum of wavelengths between approximately 500 nm and approximately 900 nm. In another example, the one or more passbands may be discrete narrow passbands within a spectrum of wavelengths between approximately 500 nm and approximately 900 nm. Illumination system 412 may also be configured to provide the one or more passbands with a substantially constant center wavelength (CWL) value over an extended period of time (e.g., over the lifetime of illumination system 412). This configuration of illumination system 412 may help prevent drift between the actual CWL value and the desired CWL value in current alignment systems, as described above. Thus, using a constant CWL value may improve the long-term stability and accuracy of an alignment system (e.g., inspection device 400) compared to current alignment devices.

[0066] In some aspects, beam splitter 414 can be configured to receive radiation beam 413 and split radiation beam 413 into at least two radiation sub-beams. Figure 4AAs shown, radiation beam 413 can be split into radiation sub-beams 415 and 417. Beam splitter 414 can also be configured to direct radiation sub-beam 415 onto substrate 420 placed on stage 422. In one example, stage 422 can be moved along direction 424. Radiation sub-beam 415 can be configured to illuminate alignment mark or target 418 located on substrate 420. Alignment mark or target 418 can be coated with a radiation-sensitive film. In some aspects, alignment mark or target 418 can have one hundred and eighty degrees (i.e., 180°) symmetry. That is, when alignment mark or target 418 is rotated 180° about an axis of symmetry perpendicular to the plane of alignment mark or target 418, the rotated alignment mark or target 418 can be substantially identical to the unrotated alignment mark or target 418. The target 418 on the substrate 420 can be (a) a resist layer grating comprising stripes formed from solid resist lines, or (b) a product layer grating, or (c) a composite grating stack comprising a resist grating superimposed or interleaved on the product layer grating in an overlay target structure. Alternatively, the stripes can be etched into the substrate. The pattern is sensitive to chromatic aberrations in the lithographic projection equipment (particularly the projection system PL), and illumination symmetry and the presence of such aberrations will manifest themselves in variations in the printed grating. One in-line method for measuring line width, pitch, and critical dimensions in device manufacturing uses a technique known as "scatterometry." Scatterometry methods 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), both of which are incorporated herein by reference in their entirety. In scatterometry, light is reflected by periodic structures in a target, and the resulting reflection spectrum at a given angle is detected. The structure that produced the reflection spectrum is reconstructed, for example, using rigorous coupled wave analysis (RCWA) or by comparison with a library of simulated patterns. Scatterometry data of the printed grating is thus used to reconstruct the grating. The parameters of the grating, such as line width and shape, can be input into the reconstruction process performed by the processing unit PU based on knowledge of the printing step and / or other scatterometry processes.

[0067] In some aspects, the beam splitter 414 can also be configured to receive the diffracted radiation beam 419 and, according to one aspect, can split the diffracted radiation beam 419 into at least two radiation sub-beams. The diffracted radiation beam 419 can be split into diffracted radiation sub-beams 429 and 439, as shown in FIG. Figure 4A shown.

[0068] It should be noted that although beam splitter 414 is shown as directing radiation sub-beam 415 toward alignment mark or target 418 and directing diffracted radiation sub-beam 429 toward interferometer 426, the present disclosure is not limited thereto. Other optical arrangements may be used to achieve similar results of illuminating an alignment mark or target 418 on substrate 420 and detecting an image of the alignment mark or target 418.

[0069] like Figure 4A As shown, interferometer 426 can be configured to receive radiation sub-beam 417 and diffracted radiation sub-beam 429 via beam splitter 414. In an example aspect, diffracted radiation sub-beam 429 can be at least a portion of radiation sub-beam 415 that can be reflected from alignment mark or target 418. In examples of this aspect, interferometer 426 includes any suitable set of optical elements, such as a prismatic combination 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 understood that high-quality images need not be formed. Having resolved features of alignment mark 418 is sufficient. Interferometer 426 can also be configured to rotate one of the two images 180° relative to the other of the two images and recombining the rotated image and the unrotated image in an interferometric manner.

[0070] In some aspects, detector 428 can be configured to receive the recombined image via interferometer signal 427 when an alignment axis 421 of inspection apparatus 400 passes through the center of symmetry (not shown) of alignment mark or target 418, and detect interference resulting from the recombined image. According to one example aspect, this interference can be caused by alignment mark or target 418 being 180° symmetrical and the recombined image interfering constructively or destructively. Based on the detected interference, detector 428 can also be configured to determine the location of the center of symmetry of alignment mark or target 418 and, thereby, detect the position of substrate 420. According to one example, alignment axis 421 can be aligned with a light beam perpendicular to substrate 420 and passing through the center of image rotation interferometer 426. Detector 428 can also be configured to estimate the position of alignment mark or target 418 by implementing sensor characteristics and interacting with wafer marking process variations.

[0071] In other aspects, the detector 428 determines the location of the center of symmetry of the alignment mark or target 418 by performing one or more of the following measurements:

[0072] 1. Measure the positional shift of multiple wavelengths (the positional shift between colors);

[0073] 2. Measure the positional shift of multiple orders (positional offset between diffraction orders);

[0074] 3. Measuring the positional changes of multiple polarizations (positional shifts between polarizations); and

[0075] 4. Measuring the intensity difference between opposite orders of a diffraction order pair (e.g., to characterize and correct for asymmetries).

[0076] This data can be obtained using any type of alignment sensor, such as a SMASH sensor (SMART Alignment Sensor Hybrid) as described in U.S. Patent No. 6,961,116, which uses a self-referencing interferometer with a single detector and four different wavelengths and extracts the alignment signal in software, or Athena (Advanced Technology using High order ENhancement of Alignment) as described in U.S. Patent No. 6,297,876, which directs each of the seven diffraction orders to a dedicated detector, both of which are incorporated herein by reference in their entirety.

[0077] In some aspects, the beam analyzer 430 can be configured to receive and determine the optical state of the diffracted radiation sub-beam 439. The optical state can be a measure of the beam wavelength, polarization, or beam profile. The beam analyzer 430 can also be configured to determine the position of the stage 422 and relate the position of the stage 420 to the position of the center of symmetry of the alignment mark or target 418. Thus, the position of the alignment mark or target 418, and therefore the position of the substrate 420, can be accurately known with reference to the stage 422. Alternatively, the beam analyzer 430 can be configured to determine the position of the inspection device 400 or any other reference element so that the center of symmetry of the alignment mark or target 418 can be known with reference to the inspection device 400 or any other reference element. The beam analyzer 430 can be a point or imaging polarimeter with some form of wavelength-band selectivity. In some aspects, beam analyzer 430 can be integrated directly into inspection device 400, or according to other aspects, beam analyzer 430 can be connected to inspection device 400 via several types of optical fibers: polarization-maintaining single-mode fiber, multimode fiber, or imaging fiber.

[0078] In some aspects, beam analyzer 430 may also be configured to determine overlay data between two patterns on substrate 420. One of these patterns may be a reference pattern on a reference layer. The other pattern may be an exposure pattern on an exposure layer. The reference layer may be an etch layer already present on substrate 420. The reference layer may be generated by exposing the reference pattern on the substrate using lithography apparatus 100 and / or 100'. The exposure layer may be a resist layer exposed adjacent to the reference layer. The exposure layer may be generated by exposing the exposure pattern on substrate 420 using lithography apparatus 100 or 100'. The exposure pattern on substrate 420 may correspond to movement of substrate 420 by stage 422. In some aspects, the measured overlay data may also indicate an offset between the reference pattern and the exposure pattern. The measured overlay data may be used as calibration data to calibrate the exposure pattern exposed by lithography apparatus 100 or 100', so that after calibration, the offset between the exposure layer and the reference layer can be minimized.

[0079] In some aspects, the beam analyzer 430 can also be configured to determine a model of the product stack profile of the substrate 420 and can be configured to measure the overlay, critical dimension, and focal length of the target 418 in a single measurement. The product stack profile contains information about the stacked product (such as, alignment marks, target 418, or substrate 420) and can include optical signal measurements caused by variations in the marking process as a function of illumination variations. The product stack profile can also include product raster profiles, mark stack profiles, and mark asymmetry information. An example of a beam analyzer 430 is the Yieldstar™ manufactured by ASML of Wilhoven, The Netherlands, as described in U.S. Patent No. 8,706,442, which is incorporated herein by reference in its entirety. The beam analyzer 430 can also be configured to process information related to specific properties of the exposure pattern in the layer. For example, the beam analyzer 430 may process overlay parameters (indicative of the accuracy of positioning of the layer relative to the previous layer on the substrate or the accuracy of positioning of the first layer relative to a mark on the substrate), focus parameters, and / or critical dimension parameters (e.g., line width and line width variation) of the depicted image in the layer. Other parameters are image parameters related to the quality of the depicted image of the exposure pattern.

[0080] In some aspects, a detector array (not shown) can be connected to the beam analyzer 430 and allow accurate stack profile detection to be performed, as described below. For example, the detector 428 can be a detector array. For the detector array, there are several options: a bundle of multimode fiber, discrete pin detectors per channel, or a CCD or CMOS (linear) array. For stability reasons, using a bundle of multimode fiber allows any dissipative elements to be located further away. Discrete pin detectors provide a larger dynamic range, but each discrete pin detector requires a separate preamplifier. Therefore, the number of elements is limited. CCD linear arrays provide many elements that can be read out at high speed and are particularly interesting if phase-stepped detection is used.

[0081] In some aspects, the second beam analyzer 430' can be configured to receive and determine the optical state of the diffracted radiation sub-beam 429, such as Figure 4B As shown. The optical state can be a measure of the beam wavelength, polarization, or beam profile. The second beam analyzer 430' can be identical to the beam analyzer 430. Alternatively, the second beam analyzer 430' can be configured to perform one or more functions of the beam analyzer 430, such as determining the position of the stage 422 and correlating the position of the stage 420 with the position of the center of symmetry of the alignment mark or target 418. Thus, the position of the alignment mark or target 418, and therefore the position of the substrate 420, can be accurately known with reference to the stage 422. The second beam analyzer 430' can also be configured to determine the position of the inspection device 400 or any other reference element, so that the center of symmetry of the alignment mark or target 418 can be known with reference to the inspection device 400 or any other reference element. The second beam analyzer 430' can also be configured to determine overlay data between two patterns and a model of the product stack profile of the substrate 420. The second beam analyzer 430' can also be configured to measure the overlay, critical dimension, and focal length of the target 418 in a single measurement.

[0082] In some aspects, second beam analyzer 430' can be integrated directly into inspection device 400, or according to other aspects, second beam analyzer 430' can be connected to inspection device 400 via one of several types of optical fibers: polarization-maintaining single-mode fiber, multimode fiber, or imaging fiber. 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 state of both diffracted radiation sub-beams 429 and 439.

[0083] In some aspects, processor 432 receives information from detector 428 and beam analyzer 430. For example, processor 432 may be an overlay calculation processor. This information may include a model of the product stack profile constructed by beam analyzer 430. Alternatively, processor 432 may use the received information about product markings to construct a model of the product marking profile. In either case, processor 432 may use or combine the model of the product marking profile to construct a model of the stacked product and the overlay marking profile. The overlay model is then used to determine the overlay offset and minimize the spectral effects on the overlay offset measurement. Processor 432 may create a basic correction algorithm based on information received from detector 428 and beam analyzer 430, including, but not limited to, the optical state of the illumination beam, alignment signals, associated position estimates, and optical states in pupil, image, and additional planes. The pupil plane is a plane in which the radial position of the radiation defines the angle of incidence and the angular position of the radiation defines the azimuthal angle of the radiation. Processor 432 may utilize the basic correction algorithm to characterize inspection apparatus 400 with reference to wafer marks and / or alignment marks 418.

[0084] In some aspects, processor 432 can also be configured to determine the printed pattern position offset error relative to the sensor estimate for each mark based on information received from detector 428 and beam analyzer 430. This information includes, but is not limited to, product stack profile, overlay measurements, critical dimensions, and focus for each alignment mark or target 418 on substrate 420. Processor 432 can utilize a clustering algorithm to group marks into sets with similar constant offset errors and create an alignment error offset correction table based on this information. The clustering algorithm can be based on overlay measurements, position estimates, and additional optical stack process information associated with each offset error set. Overlay is calculated for multiple different marks, such as overlay targets with positive and negative deviations offset near the planned overlay. The target with the minimum overlap is considered a reference (because the target with the minimum overlap is measured with the best accuracy). Based on this measured minimum overlap and the known planned overlay of its corresponding target, the overlay error can be inferred. Table 1 illustrates how this is performed. The measured minimum overlap in the example shown is -1 nm. However, this is relative to the target of having a planned overlay of -30 nm. The process may have introduced an overlay error of 29 nm.

[0085]

[0086] A minimum value can be taken as a reference point, and relative to this reference point, the offset between the measured overlap and the expected overlap due to the planned overlap can be calculated. This offset determines the overlay error for each marker or a set of markers with similar offsets. Thus, in the example of Table 1, the minimum measured overlap is -1 nm, with a planned overlap of 30 nm at that target location. The difference between the expected and measured overlap at other targets is compared to this reference. A table such as Table 1 can also be obtained from markers and targets 418 at different illumination settings, and the illumination setting that produces the minimum overlay error and the corresponding calibration factor for that illumination setting can be determined and selected. Thereafter, the processor 432 can group the markers into sets with similar overlay errors. The criteria used to group the markers can be adjusted based on different process controls (e.g., different error tolerances for different processes).

[0087] In some aspects, the processor 432 can confirm, based on its additional optical stack metrology, that all or most members of the group have similar offset errors and apply a single offset correction to each mark based on a clustering algorithm. The processor 432 can determine the correction for each mark and feed the correction back to the lithographic apparatus 100 or 100' to correct the error in overlay, for example, by feeding the correction back to the inspection apparatus 400 to correct the error in overlay.

[0088] Example Illumination Arrangement for Parallelizing Sensors

[0089] In some aspects, the term "throughput" can be used to refer to the rate at which a certain amount of material or item moves through a system or process. For example, throughput can be used to characterize the rate of photolithographic fabrication. As another example, throughput can refer to the rate at which photolithographic fabrication is completed on a wafer, the rate at which a wafer clears a particular fabrication step and moves on to the next step, and so on. Yield can be a performance indicator of photolithographic equipment. It is desirable for a photolithographic system to output as many products as possible in the shortest possible time. Photolithographic fabrication can include several complex processes. Each part of the process may involve a trade-off between quality (e.g., sub-nanometer accuracy, high yield) and drawbacks (e.g., slower manufacturing, cost). For example, to improve pattern transfer accuracy, photolithography can include inspection of printed marks on a substrate. Inspection performed by inspection equipment 400 can determine the consistency or accuracy of the printed pattern on the substrate or the alignment of the substrate to ensure proper acceptance of new patterns. However, the increased time required for inspection operations can adversely impact yield.

[0090] In some aspects, a wafer substrate may include tens, hundreds, thousands, or even more inspection targets. A single inspection device 400 can inspect multiple inspection targets continuously (one at a time). Between inspections, the mark-to-mark movement of the inspection device 400 can sometimes occupy a significant portion of the time dedicated to metrology. In other words, if this mark-to-mark movement time could be reduced or eliminated, the result would be a significant increase in throughput. In some aspects, the inspection solution can be scaled (e.g., by parallelizing multiple inspection devices). However, scaling may be difficult to achieve due to practical limitations. For example, scaling multiple iterations of the inspection device 400 would mean deploying multiple illumination systems 412. The individual power requirements may be prohibitive. On the other hand, using a single illumination system to power multiple inspection devices may be prohibitive for other reasons (e.g., insufficient power to flow). Without sufficient power / photons, the inspection operation may lack the signal-to-noise ratio (SNR) required for accurate measurements.

[0091] In some aspects, a broadband source (e.g., a white light source) can produce a powerful radiation beam with photon wavelengths covering a broad spectrum. Inspection device 400 may not need to use the entire broad spectrum (e.g., it can use selected wavelengths). In this case, inspection device 400 uses a given wavelength, while additional photons at other wavelengths are discarded. In other words, the wasted photons are not fully utilized.

[0092] In some aspects, the apparatus and functionality described herein can be used in multi-sensor head implementations using a shared radiation source.

[0093] Figure 5 An inspection system 500 is shown according to some aspects. In some aspects, unless otherwise indicated, the above references to the inspection device 400 ( Figure 4A and 4B ) can also be performed using the inspection system 500 (e.g., interferometry, signal processing, alignment position calculation, overlay calculation, etc.). Figure 5 The can be different from Figure 4A and 4B One way is to use a single illumination source to facilitate more than one sensor head.

[0094] In some aspects, inspection system 500 can include broadband radiation system 502, optical system 504, wavelength separator system 506, and detector system 508. Broadband radiation system 502 can be configured to generate source radiation 510.

[0095] In some aspects, optical inspection of targets on a wafer can be performed using illumination of multiple colors (or wavelengths). A given wavelength can provide information about the target that is not readily apparent at another wavelength. Terms such as "multiple wavelengths," "multiple photon frequencies," and "multiple parameter values" may be used to refer to a collection of discrete narrow bands within a wider range (a broadband). In a non-limiting example of a wavelength parameter, a first wavelength may be characterized as comprising a narrow band of wavelengths centered around a first central wavelength. Similarly, a second wavelength may be characterized as comprising a narrow band of wavelengths centered around a second central wavelength. Characterizing the first wavelength as different from the second wavelength may be interpreted as meaning that the first central wavelength is different from the second central wavelength.

[0096] In some aspects, source radiation 510 can have a first set of narrowband wavelengths distributed within the operating bandwidth of inspection system 500 and a second set of narrowband wavelengths distributed within the operating bandwidth. As non-limiting examples, the operating bandwidth can be in the visible range (e.g., wavelengths of approximately 400-700 nm), infrared (near infrared and / or far infrared), ultraviolet, far ultraviolet, or a combination thereof. In the visible range example, the first wavelength can be red, while the second wavelength can be green. In another example, the narrowband wavelengths of the first set can be close to the narrowband wavelengths of the second set (e.g., both are red wavelengths, but offset by approximately 20 nm, 15 nm, 10 nm, 5 nm, or within a range such as 5 nm to 10 nm, 5 nm to 15 nm, 5 nm to 20 nm, 10 nm to 15 nm, 10 nm to 20 nm, etc.). For example, the operating bandwidth of the inspection system 500 can be approximately 2000 nm or less, 1600 nm or less, 1500 nm or less, 1200 nm or less, 1000 nm or less, 700 nm or less, 500 nm or less, 300 nm or less, etc.

[0097] In some aspects, enumerable adjectives (e.g., "first," "second," "third," etc.) can be used to distinguish similar elements without establishing an order, hierarchy, quantity, or permanent numerical assignment (unless otherwise specified). For example, the terms "first target" and "second target" can be used in a manner similar to "i-th target" and "j-th target" to distinguish two targets without specifying a particular order, hierarchy, quantity, or immutable numerical correspondence.

[0098] In some aspects, targets 514-a and 514-b may be fabricated via photolithographic operations (e.g., as described in reference Figure 1A 、 Figure 1B 、 Figure 2 and Figure 3 Alignment marks are produced by transferring a pattern onto substrate 518 as described above.

[0099] In some aspects, optical system 504 can be configured to direct portion 512-a (e.g., a first portion) of source radiation toward target 514-a (e.g., a first target) among the plurality of targets to produce scattered radiation 516-a (e.g., a first scattered radiation), and to direct portion 512-b (e.g., a second portion) of source radiation 510 toward target 514-b (e.g., a second target) among the plurality of targets to produce scattered radiation 516-b (e.g., a second scattered radiation). It should be understood that the designations "a" and "b" can be generalized to designations "n" that can represent two or more quantities. Figure 5 The scalability shown is a non-limiting example, where "n" represents two quantities (it is contemplated that Figure 5 The features in may be scaled to an amount of three or more, five or more, ten or more, etc.).

[0100] In some aspects, each of the scattered radiation 516-a and 516-b can have multiple wavelengths. For example, the scattered radiation 516-a can have a first set of narrowband wavelengths, while the scattered radiation 516-b can have a second set of narrowband wavelengths. In another example, the scattered radiation 516-a can have one or more wavelengths from the first set of narrowband wavelengths and one or more wavelengths from the second set of narrowband wavelengths. Other combinations and / or permutations are contemplated. The wavelength distribution across multiple sensor heads is described in more detail below (see Figure 6 The term “sensor head” may be used herein to refer to the portion of the inspection system 500 downstream from the substrate 518 (eg, the hardware responsible for collecting scattered radiation and / or detection).

[0101] In some aspects, wavelength separator system 506 can be configured to separate narrowband wavelengths of first and second scattered radiation. Detector system 508 can be configured to receive the first and second scattered radiation. Detector system 508 can also be configured to generate measurement signals based on scattered radiation 516-a and 516-b (e.g., generate first and second measurement signals). In the context of wavelength separation, different wavelengths are not limited to physical separation (e.g., diffusing light into different colors). Wavelength "separation" can refer to an implementation that allows an inspection technique to account for the use of two or more discrete wavelengths in a manner that produces additional or alternative measurement information compared to implementations that ignore discretized wavelengths. For example, wavelength separation can be achieved through time separation (e.g., wavelength-dependent delay), wavelength modulation via a carrier signal, wavelength filters, etc.

[0102] In some aspects, broadband radiation system 502 can include a broadband source (e.g., a white light laser for generating white light) and a filter system 522. Source radiation 510 can include coherent radiation, incoherent radiation, or a combination of both. Filter system 522 can include a multiplexer system (e.g., a device that combines two or more narrowband wavelengths into a single channel or beam). Filter system 522 can be configured to filter radiation such that portion 512-a of source radiation 510 has a first set of narrowband wavelengths and portion 512-b of source radiation 510 has a second set of narrowband wavelengths. The first set of narrowband wavelengths and the second set of narrowband wavelengths can be the same or different.

[0103] In some aspects, optical system 504 can include optical structures 524-n (e.g., optical structures 524-a and 524-b; e.g., a first optical structure and a second optical structure). For example, the optical structures can include wedges, prisms, reflectors, beam splitters, refraction devices, etc. Optical structure 524-a can be configured to direct portion 512-a of source radiation 510 toward target 514-a. Optical structure 524-b can be configured to direct portion 512-b of source radiation 510 toward target 514-b. Via optical system 504, filter system 522 can transmit a first set of narrowband wavelengths toward a first target and a second set of narrowband wavelengths toward a second target (and, by extension, transmit an nth set of narrowband wavelengths toward an nth target).

[0104] In some aspects, the wavelength separator system 506 can include a demultiplexer system that includes wavelength separator devices 526-n (e.g., wavelength separator devices 526-a and 526-b; a first wavelength separator device and a second wavelength separator device). For example, the wavelength separator devices can include dispersive devices, dichroic mirrors, refractive devices, gratings, filters (e.g., color filters), etc.

[0105] In some aspects, detector system 508 may include detectors 528-n (e.g., detectors 528-a and 528-b; a first detector and a second detector). In some aspects, the detectors may include a single element detector (e.g., a single-pixel photodiode), a two-dimensional detector array (e.g., a multi-pixel camera), etc. Each detector may generate a measurement signal corresponding to the detected scattered radiation. The measurement signal may include data corresponding to different narrowband wavelengths included in the detected scattered radiation. The measurement signal may be analyzed to infer information about properties of the target (e.g., alignment position, overlay error, etc.). Analysis of the measurement radiation may be performed by a processor, a computing device, etc. (e.g., processor 432 ( FIG. 4 )).

[0106] In some aspects, the inspection system 500 may further include a fiber optic system including optical fibers 530-n (eg, optical fibers 530-a and 530-b; a first optical fiber and a second optical fiber). The optical fibers 530-n may allow for a reduced footprint of sensor head components near the target. Figure 5 In a specific non-limiting example, the wavelength separator system 506 and / or the detector system 508 can be implemented at a more distant location (e.g., remotely), with the optical fibers 530-n used to direct the collected scattered radiation to the remote wavelength separator system 506 and / or detector system 508. Alternatively or additionally, other optical hardware can be used to direct the scattered radiation (e.g., wedges, prisms, reflectors, beam splitters, refraction devices, etc.).

[0107] Figure 6 Graph 600 shows a set of wavelengths that can be generated by a broadband radiation system according to some aspects. In some aspects, reference Figure 5 Describe the structure and function to achieve the Figure 6 Disclosed features. When broadband source 520 is in an "on" state (e.g., generating radiation), it can simultaneously generate all wavelengths within its operating spectrum. In other words, broadband radiation system 502 can simultaneously generate a collection of narrowband wavelengths.

[0108] In some aspects, the horizontal axis of graph 600 can represent the wavelength of radiation generated by the broadband radiation system (alternatively, a measure of photon frequency or energy can serve the same purpose). The vertical axis of graph 600 can represent an intensity measure (e.g., energy, flux, power, etc.). Graph 600 shows sets 602, 612, and 622 of narrowband wavelengths (e.g., a first set, a second set, and a third set of narrowband wavelengths) that can span the operating bandwidth of inspection system 500. While three sets are shown, as few as two sets can be implemented in sensor head parallelization. It should be understood that additional sets can be implemented by using appropriate wavelength offsets to distinguish them from existing sets.

[0109] In some aspects, using filter system 522, set 602 of narrowband wavelengths can be selected for portion 512-a of source radiation 510. Similarly, set 604 of narrowband wavelengths can be selected for portion 512-b of source radiation 510. Set 622 of narrowband wavelengths can be used for another parallel sensor head.

[0110] In some aspects, set 602 of narrowband wavelengths may include narrowband wavelengths 604 and 606. Set 612 of narrowband wavelengths may include narrowband wavelengths 614 and 616. Set 622 of narrowband wavelengths may include narrowband wavelengths 624 and 626. As a non-limiting example, narrowband wavelength 604 may be within a range that may be considered "blue" (e.g., approximately 400 nm to 490 nm). For the purposes of this non-limiting example, assume that narrowband wavelength 604 is approximately 440 nm.

[0111] In some aspects, broadband source 520 may impose limits on the amount of radiant power it can generate. When implementing two sensor heads, for example, both sensor heads may operate at the same wavelength (i.e., portions 512-a and 512-b of source radiation 510 may have the same wavelength). While splitting the photon counts for the same wavelength in this manner may be acceptable when only a few sensor heads are involved, splitting the photon counts too many times may result in slower measurement times (e.g., longer detector integration times may compensate for the reduction in photon counts). This is contrary to the goal of increasing throughput in photolithographic manufacturing. Therefore, because broadband source 520 can generate the full spectrum of photons within its operating bandwidth, and because the sensor heads use a subset of that range (e.g., using set 602 of narrowband wavelengths), it is more efficient to use the photons that would otherwise be discarded.

[0112] Referring back to the non-limiting example of narrowband wavelength 604 being approximately 440 nm, narrowband wavelength 614 may also be within the blue range (e.g., close to but not equal to narrowband wavelength 604 (440 nm)). As a non-limiting example, narrowband wavelength 614 may be 445 nm (e.g., offset by +5 nm). It should be understood that in a single sensor head implementation, a set of narrowband wavelengths would be used, while photons with wavelengths outside of that set would be discarded. Now, in a multi-sensor head implementation, more of the spectrum can be used without waste. The magnitude of the wavelength offset may be approximately 20 nm, 15 nm, 10 nm, 5 nm, etc. (or may be expressed as a range, e.g., 5 nm to 10 nm, 5 nm to 15 nm, 5 nm to 20 nm, 10 nm to 15 nm, 10 nm to 20 nm, etc.).

[0113] In some aspects, the next set of wavelengths toward the right (e.g., narrowband wavelengths 606, 616, and 626) are contemplated to have a similar wavelength arrangement to that previously described with reference to narrowband wavelengths 604, 614, and 624 (e.g., with a smaller offset from one another). Figure 6Three sets of narrowband wavelengths are explicitly shown, each set having ten narrowband wavelengths, but it should be understood that fewer or more sets (and fewer or more narrowband wavelengths in each set) may be implemented depending on the requirements of the inspection to be performed (e.g., alignment, overlay) and the number of sensor heads to be implemented.

[0114] In this manner, in some aspects, multiple sensor heads can be powered by a common broadband source 520 without compromising photon counting and increasing measurement speed. This can increase measurement speed by avoiding situations where a single sensor head must travel long distances when traveling from mark to mark. For example, after inspecting target 514-a using an element with label "a" of inspection system 500, an inspection element with label "b" may already be near or at target 514-b for immediate inspection, thereby reducing the amount of time inspection system 500 needs to move from one mark to the next. One of the most time-consuming steps in an inspection operation can be moving a sensor head from one mark to another.

[0115] In some aspects, other distributions of narrowband wavelengths across multiple sensor heads are contemplated. For example, a portion of set 602 of narrowband wavelengths may be emitted toward target 514-a, while another portion of set 602 of narrowband wavelengths may be emitted toward target 514-b. In the event that additional wavelengths remain unused, it is contemplated that the unused wavelengths may be used at additional sensor heads. For example, at least a portion of set 612 (or 622) of narrowband wavelengths may be emitted toward another target (e.g., a third target, a fourth target, or more) to generate additional scattered radiation (e.g., a third scattered radiation, a fourth scattered radiation, or more). In this case, detector system 508 may receive the additional scattered radiation and generate additional measurement signals (e.g., a third measurement signal) based on the additional scattered radiation. The additional measurement signals may be analyzed to determine properties of the additional targets (e.g., alignment position, overlap, etc.). In this manner, it is contemplated that multiple sensor heads may be scaled to cover tens or even hundreds of targets while using a common broadband source, thereby reducing costs by eliminating the need for additional radiation sources and increasing throughput by reducing the amount of mark-to-mark movement in inspection system 500.

[0116] Figure 7 A method 700 is shown according to some aspects.

[0117] In some aspects, at step S702, source radiation 510 can be generated using broadband radiation system 502. Source radiation 510 can have a first set of narrowband wavelengths (e.g., set of narrowband wavelengths 602) distributed within the operating bandwidth of inspection system 500. Source radiation 510 can also have a second set of narrowband wavelengths (e.g., set of narrowband wavelengths 612) distributed within the operating bandwidth. The first set of narrowband wavelengths (e.g., narrowband wavelengths 604) can be close to the second set of narrowband wavelengths (e.g., narrowband wavelengths 614). The second set of narrowband wavelengths, which would be discarded in conventional approaches (if the broadband source were multiplied and scaled), is instead used in parallel sensor heads.

[0118] In some aspects, at step S704 , a first portion (eg, 512 - a ) of source radiation 510 may be directed toward a first target (eg, 514 - a ) of the plurality of targets to produce first scattered radiation (eg, 516 - a ).

[0119] In some aspects, at step S706 , a second portion (eg, 512 - b ) of source radiation 510 can be directed toward a second target (eg, 514 - b ) of the plurality of targets to produce second scattered radiation (eg, 516 - b ).

[0120] In some aspects, at step S708 , the wavelength separator system 506 can be used to separate the narrowband wavelengths of the first scattered radiation and the second scattered radiation.

[0121] In some aspects, at step S710 , first scattered radiation can be received at the detector system 508 .

[0122] In some aspects, at step S712 , using the detector system 508 , a first measurement signal can be generated based on the first scattered radiation.

[0123] In some aspects, at step S714 , second scattered radiation can be received at the detector system 508 .

[0124] In some aspects, at step S716 , using the detector system 508 , a second measurement signal can be generated based on the second scattered radiation.

[0125] Figure 7 The method steps may be performed in any conceivable order, and it is not necessary to perform all steps. Figure 7 The method steps are merely examples of the steps and are not restrictive. Figure 6The described aspects contemplate other method steps and functionality. The following is a non-exhaustive list of example steps contemplated based on the description of the aspects disclosed herein. Other steps may include transmitting a portion of the first set of narrowband wavelengths toward a first target. Other steps may include transmitting another portion of the first set of narrowband wavelengths toward a second target. Other steps may include transmitting at least a portion of the second set of narrowband wavelengths toward a third target to produce third scattered radiation. Other steps may include receiving the third scattered radiation at detector system 508. Other steps may include generating a third measurement signal based on the third scattered radiation using detector system 508.

[0126] The embodiments may be further described using the following terms:

[0127] 1. A lithographic apparatus comprising:

[0128] an illumination system configured to illuminate a pattern on the patterning device;

[0129] a projection system configured to project an image of the pattern onto a substrate to form a plurality of targets on the substrate; and

[0130] an inspection system configured to inspect the plurality of targets, the inspection system comprising:

[0131] a broadband radiation system configured to generate source radiation having a first set of narrowband wavelengths distributed within an operating bandwidth of the inspection system and a second set of narrowband wavelengths distributed within the operating bandwidth, wherein the narrowband wavelengths of the first set are proximate to the narrowband wavelengths of the second set;

[0132] an optical system configured to direct a first portion of the source radiation toward a first target of the plurality of targets to produce first scattered radiation, and to direct a second portion of the source radiation toward a second target of the plurality of targets to produce second scattered radiation;

[0133] a wavelength separator system configured to separate narrowband wavelengths of the first scattered radiation and the second scattered radiation; and

[0134] A detector system is configured to receive the first scattered radiation and the second scattered radiation and to generate a first measurement signal and a second measurement signal based on the first scattered radiation and the second scattered radiation, respectively.

[0135] 2. A lithographic apparatus according to clause 1, wherein the broadband radiation system comprises a filter system configured to emit a first set of the narrowband wavelengths towards the first target and to transmit a second set of the narrowband wavelengths towards the second target.

[0136] 3. The lithographic apparatus of clause 1, wherein:

[0137] The plurality of targets includes a third target configured to generate third scattered radiation; and

[0138] The broadband radiation system includes a filter system configured to:

[0139] transmitting a portion of the first set of narrowband wavelengths toward the first target,

[0140] transmitting another portion of the first set of narrowband wavelengths toward the second target, and

[0141] transmitting at least a portion of the second set of narrowband wavelengths toward the third target to produce third scattered radiation; and

[0142] The detector system is further configured to receive the third scattered radiation and to generate a third measurement signal based on the third scattered radiation.

[0143] 4. The lithographic apparatus of clause 1 , wherein the operating bandwidth is approximately 1600 nm or less.

[0144] 5. The lithographic apparatus of clause 1 , wherein the first set of narrowband wavelengths is offset from the second set of narrowband wavelengths by approximately 5 nm to 15 nm.

[0145] 6. The lithographic apparatus of clause 1 , wherein the wavelength separator comprises a demultiplexer system comprising a dispersion device, a grating, a dichroic mirror and / or a filter.

[0146] 7. The lithographic apparatus of clause 1 , wherein the inspection system further comprises an optical fiber system configured to direct the first scattered radiation and the second scattered radiation towards the detector system.

[0147] 8. The lithographic apparatus of clause 1 , wherein the source radiation comprises coherent radiation.

[0148] 9. The lithographic apparatus of clause 1 , wherein the first set of narrowband wavelengths and the second set of narrowband wavelengths are generated simultaneously by the broadband radiation system.

[0149] 10. An inspection system comprising:

[0150] a broadband radiation system configured to generate source radiation having a first set of narrowband wavelengths distributed within an operating bandwidth of the inspection system and a second set of narrowband wavelengths distributed within the operating bandwidth, wherein the first set of narrowband wavelengths is proximate to the second set of narrowband wavelengths;

[0151] an optical system configured to direct a first portion of the source radiation toward a first target of the plurality of targets to produce first scattered radiation, and to direct a second portion of the source radiation toward a second target of the plurality of targets to produce second scattered radiation;

[0152] a wavelength separator system configured to separate narrowband wavelengths of the first scattered radiation and the second scattered radiation; and

[0153] A detector system is configured to receive the first scattered radiation and the second scattered radiation and to generate a first measurement signal and a second measurement signal based on the first scattered radiation and the second scattered radiation, respectively.

[0154] 11. An inspection system according to clause 10, wherein the broadband radiation system includes a filter system, the filter system being configured to transmit a first set of the narrowband wavelengths toward the first target and to transmit a second set of the narrowband wavelengths toward the second target.

[0155] 12. The inspection system of clause 10, wherein:

[0156] The plurality of targets includes a third target configured to generate third scattered radiation; and

[0157] The broadband radiation system includes a filter system configured to:

[0158] transmitting a portion of the first set of narrowband wavelengths toward the first target,

[0159] transmitting another portion of the first set of narrowband wavelengths toward the second target, and

[0160] transmitting at least a portion of the second set of narrowband wavelengths toward the third target to produce third scattered radiation; and

[0161] The detector system is further configured to receive the third scattered radiation and to generate a third measurement signal based on the third scattered radiation.

[0162] 13. The inspection system of clause 10, wherein the operating bandwidth is approximately 1600 nm or less.

[0163] 14. The inspection system of clause 10, wherein the first set of narrowband wavelengths and the second set of narrowband wavelengths are offset by approximately 5 nm to 15 nm.

[0164] 15. The inspection system of clause 10, wherein the wavelength separator comprises a demultiplexer system comprising a dispersion device, a grating, a dichroic mirror, and / or a filter.

[0165] 16. The inspection system of clause 10, wherein the inspection system further comprises a fiber optic system configured to direct the first scattered radiation and the second scattered radiation toward the detector system.

[0166] 17. The inspection system of clause 10, wherein the source radiation comprises coherent radiation.

[0167] 18. The inspection system of clause 10, wherein the first set of narrowband wavelengths and the second set of narrowband wavelengths are generated simultaneously by the broadband radiation system.

[0168] 19. A method of operating an inspection system, the method comprising:

[0169] generating source radiation using a broadband radiation system, the source radiation having a first set of narrowband wavelengths distributed within an operating bandwidth of the inspection system and a second set of narrowband wavelengths distributed within the operating bandwidth, wherein the narrowband wavelengths of the first set are proximate to the narrowband wavelengths of the second set;

[0170] directing a first portion of the source radiation toward a first target of a plurality of targets to produce first scattered radiation;

[0171] directing a second portion of the source radiation toward a second target in the plurality of targets to produce second scattered radiation;

[0172] separating the narrowband wavelengths of the first scattered radiation and the second scattered radiation using a wavelength separator system;

[0173] receiving the first scattered radiation at a detector system;

[0174] generating a first measurement signal based on the first scattered radiation using the detector system;

[0175] receiving the second scattered radiation at the detector system; and

[0176] A second measurement signal is generated based on the second scattered radiation using the detector system.

[0177] 20. The method of clause 19, further comprising:

[0178] transmitting a portion of the first set of narrowband wavelengths toward the first target,

[0179] transmitting another portion of the first set of narrowband wavelengths toward the second target, and

[0180] transmitting at least a portion of the second set of narrowband wavelengths toward a third target to produce third scattered radiation;

[0181] receiving the second scattered radiation at the detector system; and

[0182] A third measurement signal is generated based on the third scattered radiation using the detector system.

[0183] The terms "radiation," "beam," "light," "irradiation," and the like may be used herein to refer to one or more types of electromagnetic radiation, such as ultraviolet (UV) radiation (e.g., having a wavelength λ of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (e.g., having a wavelength in the range of 5 nm to 100 nm, such as, for example, 13.5 nm), or hard X-rays operating at less than 5 nm, and particle beams (such as ion beams or electron beams). Generally, radiation having a wavelength between about 400 nm and about 700 nm is considered visible radiation; radiation having a wavelength between about 780 nm and 3000 nm (or greater) is considered IR radiation. UV refers to radiation having a wavelength between about 100 nm and 400 nm. In photolithography, the term "UV" also applies to wavelengths that can be produced by mercury discharge lamps: G-line 436 nm; H-line 405 nm; and / or I-line 365 nm. Vacuum UV or VUV (i.e., UV absorbed by gases) refers to radiation having a wavelength of approximately 100 nm to 200 nm. Deep UV (DUV) generally refers to radiation having a wavelength in the range of 126 nm to 428 nm, and in some aspects, excimer lasers can generate DUV radiation for use within lithographic equipment. It should be understood that radiation having a wavelength in the range of, for example, 5 nm to 20 nm refers to radiation having a specific wavelength band, at least a portion of which is within the range of 5 nm to 20 nm.

[0184] Although some aspects of the present disclosure are described in the context of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, LCDs, thin film magnetic heads, and the like. Those skilled in the art will understand that, in the context of such alternative applications, any use of the terms "wafer" or "die" herein may be considered a specific example of the more general terms "substrate" or "target portion," respectively. The substrate may be processed, for example, in a track or coater / developer control system unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) and / or a metrology unit, either before or after exposure. Where applicable, the aspects disclosed herein may be applied to such and other substrate processing tools. Furthermore, a substrate may be processed more than once, for example to produce a multi-layer IC, so that the term "substrate" as used herein may also refer to a substrate that has already included multiple processed layers.

[0185] Furthermore, while some aspects of the present disclosure are described in the context of optical lithography, it should be understood that aspects of the present disclosure are not limited to optical lithography. For example, in imprint lithography, the topography in the patterning device defines the pattern formed on the substrate. The topography of the patterning device can be pressed into a resist layer supplied to the substrate, and the resist is then cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterning device is removed from the resist, leaving a pattern in the resist.

[0186] It will be understood that the phraseology or terminology herein is for the purpose of description and not limitation, so that the phraseology or terminology of this application document will be interpreted by those skilled in the relevant art(s) based on the teachings herein.

[0187] The present disclosure has been described above with the aid of functional building blocks, which illustrate the implementation of specific functions and their relationships. For ease of description, the boundaries of these functional building blocks have been arbitrarily defined in this article. As long as specific functions and their relationships are properly performed, alternative boundaries can be defined. The above description of specific aspects will fully reveal the general nature of the present disclosure, so that others can easily modify and / or adjust the various applications of these specific aspects by applying the knowledge in the art without excessive experimentation and without departing from the general concept of the present disclosure. Therefore, based on the teachings and guidance presented herein, such modifications and adjustments are intended to fall within the meaning and scope of equivalents of the disclosed aspects.

[0188] It should be understood that the "Detailed Description" section, rather than the "Summary" and "Abstract" sections, is intended to be used to interpret the claims. The "Summary" and "Abstract" sections may set forth one or more, but not necessarily all, aspects of the disclosure as contemplated by the inventor(s), and thus are not intended to limit the disclosure and the appended claims in any way. The breadth and scope of the claimed subject matter should not be limited by any of the aforementioned aspects, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A lithographic apparatus comprising: an illumination system configured to illuminate a pattern on the patterning device; a projection system configured to project an image of the pattern onto a substrate to form a plurality of targets on the substrate; and an inspection system configured to inspect the plurality of targets, the inspection system comprising: a broadband radiation system configured to generate source radiation having a first set of narrowband wavelengths distributed within an operating bandwidth of the inspection system and a second set of narrowband wavelengths distributed within the operating bandwidth, wherein the narrowband wavelengths of the first set are proximate to the narrowband wavelengths of the second set; an optical system configured to direct a first portion of the source radiation toward a first target of the plurality of targets to produce first scattered radiation, and to direct a second portion of the source radiation toward a second target of the plurality of targets to produce second scattered radiation; a wavelength separator system configured to separate narrowband wavelengths of the first scattered radiation and the second scattered radiation; and A detector system is configured to receive the first scattered radiation and the second scattered radiation and to generate a first measurement signal and a second measurement signal based on the first scattered radiation and the second scattered radiation, respectively.

2. The lithographic apparatus of claim 1 , wherein the broadband radiation system comprises a filter system configured to transmit a first set of the narrowband wavelengths toward the first target and a second set of the narrowband wavelengths toward the second target.

3. The lithographic apparatus according to claim 1 , wherein: The plurality of targets includes a third target configured to generate third scattered radiation; and The broadband radiation system includes a filter system configured to: transmitting a portion of the first set of narrowband wavelengths toward the first target, transmitting another portion of the first set of narrowband wavelengths toward the second target, and transmitting at least a portion of the second set of narrowband wavelengths toward the third target to produce third scattered radiation; as well as The detector system is further configured to receive the third scattered radiation and to generate a third measurement signal based on the third scattered radiation. The lithographic apparatus of claim 1 , wherein the operating bandwidth is approximately 1600 nm or less. 5 . The lithographic apparatus of claim 1 , wherein the first set of narrowband wavelengths is offset from the second set of narrowband wavelengths by approximately 5 nm to 15 nm.

6. The lithographic apparatus of claim 1, wherein the wavelength separator comprises a demultiplexer system comprising a dispersion device, a grating, a dichroic mirror and / or a filter.

7. The lithographic apparatus of claim 1, wherein the inspection system further comprises an optical fiber system configured to direct the first scattered radiation and the second scattered radiation towards the detector system.

8. The lithographic apparatus of claim 1, wherein the source radiation comprises coherent radiation.

9. The lithographic apparatus of claim 1, wherein the first set of narrowband wavelengths and the second set of narrowband wavelengths are generated simultaneously by the broadband radiation system.

10. An inspection system comprising: a broadband radiation system configured to generate source radiation having a first set of narrowband wavelengths distributed within an operating bandwidth of the inspection system and a second set of narrowband wavelengths distributed within the operating bandwidth, wherein the narrowband wavelengths of the first set are proximate to the narrowband wavelengths of the second set; an optical system configured to direct a first portion of the source radiation toward a first target of the plurality of targets to produce first scattered radiation, and to direct a second portion of the source radiation toward a second target of the plurality of targets to produce second scattered radiation; a wavelength separator system configured to separate narrowband wavelengths of the first scattered radiation and the second scattered radiation; and A detector system is configured to receive the first scattered radiation and the second scattered radiation and to generate a first measurement signal and a second measurement signal based on the first scattered radiation and the second scattered radiation, respectively.

11. The inspection system of claim 10, wherein the broadband radiation system comprises a filter system configured to transmit a first set of the narrowband wavelengths toward the first target and a second set of the narrowband wavelengths toward the second target.

12. The inspection system of claim 10, wherein: The plurality of targets includes a third target configured to generate third scattered radiation; and The broadband radiation system includes a filter system configured to: transmitting a portion of the first set of narrowband wavelengths toward the first target, transmitting another portion of the first set of narrowband wavelengths toward the second target, and transmitting at least a portion of the second set of narrowband wavelengths toward the third target to produce third scattered radiation; as well as The detector system is further configured to receive the third scattered radiation and to generate a third measurement signal based on the third scattered radiation.

13. The inspection system of claim 10, wherein the operating bandwidth is approximately 1600 nm or less.

14. The inspection system of claim 10, wherein the first set of narrowband wavelengths and the second set of narrowband wavelengths are offset by approximately 5 nm to 15 nm.

15. The inspection system of claim 10, wherein the wavelength separator comprises a demultiplexer system comprising a dispersion device, a grating, a dichroic mirror, and / or a filter.

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