CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Application No. 63/191,584, filed May 21, 2021, titled METROLOGY SYSTEM FOR EXTREME ULTRAVIOLET LIGHT SOURCE, which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

[0002] The disclosed subject matter relates to a metrology system for determining position information of a target traveling along a target axial path.

BACKGROUND

[0003] Extreme ultraviolet (EUV) light, for example, electromagnetic radiation having wavelengths of around 50 nm or less (also sometimes referred to as soft x-rays), and including light at a wavelength of about 13 nm, can be used in photolithography processes to produce extremely small features in substrates, for example, silicon wafers.

[0004] Methods to produce EUV light include, but are not necessarily limited to, converting a material that has an element, for example, xenon, lithium, or tin, with an emission line in the EUV range in a plasma state. In one such method, often termed laser produced plasma (“LPP”), the required plasma can be produced by irradiating a target material, for example, in the form of a droplet, plate, tape, stream, or cluster of material, with an amplified light beam that can be referred to as a drive laser. For this process, the plasma is typically produced in a sealed vessel, for example, a vacuum chamber, and monitored using various types of metrology equipment.

[0005] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is interchangeably referred to as a mask or a reticle, can be used to generate a circuit pattern to be formed on an individual layer of the IC being formed. This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (e.g., resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Traditional lithographic apparatuses include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the target portions parallel or anti-parallel to this scanning direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. [0006] Extreme ultraviolet (EUV) light, for example, electromagnetic radiation having wavelengths of around 50 nanometers (nm) or less (also sometimes referred to as soft x-rays), and including light at a wavelength of about 13 nm, can be used in or with a lithographic apparatus to produce extremely small features in substrates, for example, silicon wafers. Methods to produce EUV light include, but are not necessarily limited to, converting a material that has an element, for example, xenon (Xe), lithium (Li), or tin (Sn), with an emission line in the EUV range to a plasma state. For example, in one such method called laser produced plasma (LPP), the plasma can be produced by irradiating a target material, which is interchangeably referred to as fuel in the context of LPP sources, for example, in the form of a droplet, plate, tape, stream, or cluster of material, with an amplified light beam that can be referred to as a drive laser. For this process, the plasma is typically produced in a sealed vessel, for example, a vacuum chamber, and monitored using various types of metrology equipment.

SUMMARY

[0007] In some general aspects, a metrology system includes: a light apparatus, a detection apparatus, and a control apparatus in communication with the detection apparatus. The light apparatus is configured to generate an optical probe that includes light of a plurality of distinct wavelengths. The optical probe includes the distinct wavelengths of the light propagating along a probe optical axis that intersects a target axial path at a probe region. The detection apparatus is configured to detect produced light at the plurality of distinct wavelengths. The produced light is produced from an interaction in the probe region between the optical probe and a target traveling along the target axial path. The control apparatus is configured to analyze the detected light and adjust, based on the analysis, one or more characteristics relating to one or more of the target and the target axial path. [0008] Implementations can include one or more of the following features. For example, the control apparatus can also be in communication with the light apparatus.

[0009] The light apparatus can include one or more optical sources configured to generate a plurality of probing light beams as the optical probe, each probing light beam propagating along the probe optical axis that intersects the target axial path and each probing light beam having a distinct center wavelength. Each probing light beam can have a distinct center wavelength that is focused at a distinct location along the probe optical axis and within the probe region. The light apparatus can include one or more optical sources configured to generate a probing light beam as the optical probe, the probing light beam propagating along the probe optical axis that intersects the target axial path and the probing light beam defined by a continuous spectrum of center wavelengths.

[0010] The optical probe can have a distinct focus along the probe optical axis and within the probe region. The metrology system can also include a cylindrical focusing optic in the path of the optical probe, the cylindrical focusing optic configured to form the distinct focus as an optical curtain of the optical probe along a direction perpendicular to the probe optical axis. [0011] The optical probe can be collimated along the probe optical axis or can be imaged at the probe region.

[0012] The detection apparatus can include a plurality of detectors, each detector configured to detect produced light from the interaction between a respective probing light beam of the optical probe and the target. Each detector can be configured to detect a portion of the respective probing light beam incident on the target. Each detector being configured to detect the portion of the respective probing light beam incident on the target can include each detector being configured to detect a portion of the respective probing light beam reflected from or scattered from the target. Each detector can be configured to detect produced light having a wavelength that is distinct from the wavelength of the produced light detected by the other detectors. The detection apparatus can be configured to distinguish produced light between each of the distinct wavelengths.

[0013] The produced light can travel along a path that is distinct from the probe optical axis and also distinct from the target axial path.

[0014] The produced light can travel along a path that is parallel with an operational axis, the operational axis defined by a direction along which one or more operational light beams travel, the one or more operational light beams interacting with the target in a target region that is downstream of the probe region. The produced light can be or include a portion of the probe light beam that is reflected from the target back along the operational axis. The produced light can interact with at least some of the same optics with which the one or more operational light beams interact.

[0015] Along the target axial path, the probe region can be upstream of a target region in which the target interacts with one or more operational light beams. The target axial path can extend at least along an X axis and the probe optical axis can be not parallel with the X axis. The control apparatus can be configured to determine a position of the target along a Y direction that is perpendicular to the X axis. The probe optical axis can be parallel with a Y axis, and the operational light beams can generally travel along a Z axis. The light of the plurality of wavelengths can have an extent such that the wavelength of the light changes along the Y axis. The probe optical axis can be perpendicular to the Y axis. The light of the plurality of wavelengths can extend such that the wavelength of the light changes along the Y axis.

[0016] The one or more operational light beams can include a first amplified light beam configured to interact with the target to modify the shape and movement of the target to thereby form a modified target and a second amplified light beam configured to interact with the modified target to thereby convert the modified target to plasma that emits extreme ultraviolet light.

[0017] The control apparatus being configured to adjust one or more characteristics relating to one or more of the target and the target axial path can include one or more of: the control apparatus being configured to instruct a target material supply to adjust one or more aspects relating to production of the target; and the control apparatus being configured to instruct an operational light source to adjust one or more aspects relating to production of one or more operational light beams that interact with the target in a target region downstream of the probe region.

[0018] The detection apparatus can be configured to detect produced light at the plurality of distinct wavelengths at a rate that is as fast as or faster than the rate at which targets pass the probe region. The control apparatus can be configured to effect the adjustment to the one or more characteristics relating to the target upon which the analysis for the target is based. The control apparatus being configured to adjust one or more characteristics relating to the target can include the control apparatus being configured to instruct an operational light source to adjust a pointing of one or more operational light beams that interact with the target in a target region downstream of the probe region, the adjustment of the pointing being relative to a Z axis of an X, Y, Z coordinate system, in which the target axial path extends mostly along an X axis, and the probe optical axis is either aligned with the Y axis or aligned with the Z axis.

[0019] In other general aspects, an extreme ultraviolet (EUV) light system includes a target supply apparatus configured to form a stream of targets directed to a target region, each target traveling along a target axial path that extends primarily along an X axis of an X, Y, Z coordinate system; an operational optical source configured to produce one or more operational light beams directed to the target region, at least one operational light beam configured to interact with the target to form a modified target; and a metrology system. The metrology system includes a light apparatus, a detection apparatus, and a control apparatus in communication with the detection apparatus. The light apparatus is configured to generate an optical probe propagating along a probe optical axis that intersects the target axial path at a probe region. The detection apparatus is configured to detect produced light at the plurality of distinct wavelengths, each wavelength associated with a distinct location along an X- transverse axis of the X, Y, Z coordinate system, the produced light being produced from an interaction in the probe region between the optical probe and a target traveling along the target axial path. The control apparatus is configured to analyze the detected light and determine position information relating to the target along the X-transverse axis of the X, Y, Z coordinate system.

[0020] Implementations can include one or more of the following features. For example, the one or more operational light beams can include a first amplified light beam configured to interact with the target to modify the shape and movement of the target to thereby form a modified target and a second amplified light beam configured to interact with the modified target to thereby convert the modified target to plasma that emits extreme ultraviolet light.

[0021] In other general aspects, a metrology system includes a light apparatus, a detection apparatus, and a control apparatus in communication with the detection apparatus. The light apparatus is configured to generate an optical probe propagating along a probe optical axis that intersects a target axial path at a probe region, the target axial path extending primarily along an X axis of an X,

Y, Z coordinate system. The detection apparatus is configured to detect produced light at a plurality of distinct wavelengths, each wavelength associated with a distinct location along an X-transverse axis of the X, Y, Z coordinate system, the produced light being produced from an interaction in the probe region between the optical probe and a target traveling along the target axial path. The control apparatus is configured to analyze the detected light and determine position information relating to the target along the X-transverse axis of the X, Y, Z coordinate system.

[0022] Implementations can include one or more of the following features. For example, the optical probe can be a broadband optical probe. The control apparatus can be configured to determine position information relating to the target along the X axis of the X, Y, Z coordinate system based on the analysis of the detected light.

DESCRIPTION OF DRAWINGS

[0023] Fig. 1 is a block diagram of a metrology system including a light apparatus producing an optical probe directed to a probe region through which a target passes, a detection apparatus detecting produced light from the probe region, and a control apparatus configured to determine position information of a target from the produced light;

[0024] Fig. 2 A is a block diagram of an implementation of the metrology system of Fig. 1, in which the a probe optical axis of the optical probe is parallel with a Y axis of an X, Y, Z coordinate system;

[0025] Fig. 2B is a schematic illustration showing the probe region of the metrology system of Fig. 2 A, in which the target travels along the -X direction and is not offset from Y=0, and the optical probe includes three probing light beams;

[0026] Fig. 2C is a schematic illustration showing the detection apparatus of the metrology system of Figs. 2 A and 2B;

[0027] Fig. 2D is a front view of an implementation of a sensor apparatus of the detection apparatus of Fig. 2C, the sensor apparatus including a plurality of detectors, with each detector being configured to detect produced light at one of the distinct wavelengths lΐ, l2, l3;

[0028] Fig. 2E is a set of graphs, with each graph corresponding to an output from a respective detector of the sensor apparatus of Figs. 2C and 2D for a target positioned as shown in Fig. 2B;

[0029] Fig. 2F is a schematic illustration showing the probe region of the metrology system of Fig. 2A, in which the target is offset from Y=0;

[0030] Fig. 2G is a set of graphs, with each graph corresponding to an output from a respective detector of the sensor apparatus of Figs. 2C and 2D for a target positioned as shown in Fig. 2F;

[0031] Fig. 3A is a block diagram of an implementation of the metrology system of Fig. 1, in which the a probe optical axis of the optical probe is parallel with the Z axis of the X, Y, Z coordinate system such that the probe optical axis intersects the target axial path;

[0032] Fig. 3B is a schematic illustration showing the probe region of the metrology system of Fig. 3 A, in which the target travels along the -X direction and is not offset from Y=0, and the optical probe has a transverse extent along the Y axis, and moreover, there is a chromatic variation along this transverse extent;

[0033] Fig. 3C is a schematic illustration showing a view of the probe region of the metrology system of Figs. 3A and 3B, including a block diagram of an implementation of the detection apparatus;

[0034] Figs. 4A-4C are schematic illustrations of the view of the probe region of the metrology system of Figs. 3A-3C, in which the target interacts with the optical probe at different locations along the Y axis, and the detection apparatus is configured to capture these differences in location along the Y axis;

[0035] Fig. 5 is a schematic illustration of an implementation of the metrology apparatus of Fig.

3 A, in which the optical probe (collectively, probing light beams) travels along a path that, in the probe region, is parallel with an operational axis, such operational axis being defined by a direction along which the one or more operational light beams travel in a target region;

[0036] Fig. 6 is a block diagram of an extreme ultraviolet (EUV) light source that incorporates an implementation of the metrology system of Fig. 1, the EUV light source, when in operation, supplies an EUV light beam to an output apparatus, which can be a lithography exposure apparatus; and [0037] Fig. 7 is a flow chart of a procedure performed by the metrology system of Figs. 1, 2A, or 3A for determining position information relating to a target along the X axis and also the X-transverse axis.

DESCRIPTION

[0038] Referring to Fig. 1, a metrology system 100 is configured to determine position information of a target 105 traveling along a target axial path 110 toward a target region 115. In the target region 115, the target 105 interacts with one or more operational light beams 120. The target axial path 110 generally extends along a -X direction of an X, Y, Z coordinate system, such coordinate system being defined by a chamber that encloses the target region 115 (an example of a chamber 673 is shown in Fig. 6) and the one or more operational light beams 120 generally extend along the Z axis of this X,

Y, Z coordinate system. Thus, the target 105 generally travels along the -X direction on its way to the target region 115. However, due to various disturbances within the chamber or due to the flow physics of the target 105, the target 105 can also include motion along one or more directions that are perpendicular to the X axis, and such motion lies in the YZ plane. The metrology system 100 is configured to determine position information of the target 105 along the X axis, and also along a direction perpendicular or transverse to the X axis (an X-transverse axis). And, in some implementations, the metrology system 100 is particularly useful for determining the position information of the target 105 along the Y axis, such Y axis being generally perpendicular to the Z axis, along which the one or more operational light beams travel (Figs. 2A and 3A). [0039] The metrology system 100 includes a light apparatus 125, a detection apparatus 135, and a control apparatus 150. The light apparatus 125 is configured to generate an optical probe 130 propagating along a probe optical axis 130OA that intersects the target axial path 110 at a probe region 131. The detection apparatus 135 is configured to detect produced light 136. The produced light 136 is produced from an interaction in the probe region 131 between the optical probe 130 and a target 105 (within the probe region 131) that is traveling along the target axial path 110. For example, the produced light 136 can be a portion of the optical probe 130 reflected off the target 105, such signal increasing as the target 105 first reaches the optical probe 130 until the signal reaches a maximum as the target 105 is fully contained within the thickness of the optical probe 103, and then the signal decreases as the target 105 exits the optical probe 130.

[0040] The produced light 136 can, at any one moment, have a particular wavelength selected from a plurality of distinct wavelengths. The detection apparatus 135 is configured so that it can detect light at any of these distinct wavelengths. Moreover, each wavelength is associated with a distinct location along the X-transverse axis of the X, Y, Z coordinate system, the X-transverse axis being either the Y or the Z axis of the X, Y, Z coordinate system. In some specific examples that follow, the X- trans verse axis is the Y axis.

[0041] The control apparatus 150 is in communication with the detection apparatus 135. The control apparatus 150 can also be in communication with the light apparatus 125. The control apparatus 150 is configured to analyze the detected produced light 136, and to determine position information relating to the target 105 along both the X axis and the X-transverse axis of the X, Y, Z coordinate system. Thus, in addition to determining the time at which the target 105 interacts with the optical probe 130, the control apparatus 150 is able to determine position information about the target 105 along the same direction at which the wavelength of the produced light 136 changes, that is, along the X-transverse axis. The control apparatus 150 can furthermore effect an adjustment 160 to one or more characteristics relating to one or more of the target 105 and the target axial path 110 based on the determined position information of the target 105 along the X axis and also the X-transverse axis (which is based on the analysis of the detected produced light 136). For example, the adjustment 160 can be to the one or more operational light beams 120 to change one or more aspects of the operational light beams 120 relative to the target 105. As another example, a pointing and/or timing of pulse of the operational light beams 120 can be adjusted. As a still further example, the adjustment 160 can be to a target supply apparatus (Figs. 2 and 3) that produces the targets 105 to thereby adjust aspects relating to how the targets 105 are produced. In this way, the control apparatus 150 controls the trajectory of the targets 105 and the timing with which they arrive at the target region 115, so that the pulses of the operational light beam 105 irradiate the target 105 at the target region 115.

[0042] The target 105 is a target mixture that includes a target material and optionally impurities such as non-target particles. The target 105 can be, for example, a droplet of liquid or molten metal, a portion of a liquid stream, solid particles or clusters, solid particles contained within liquid droplets, a foam of target material, or solid particles contained within a portion of a liquid stream. The target 105 can include, for example, water, tin, lithium, xenon, or any material that, when converted to a plasma state, has an emission line in the EUV range. For example, the target 105 can include the element tin, which can be used as pure tin (Sn); as a tin compound such as SnBr4, SnBr2, SnH4; as a tin alloy such as tin-gallium alloys, tin-indium alloys, tin-indium-gallium alloys, or any combination of these alloys. The targets 105 are formed as a stream of targets 105 that are directed to the target region 115, passing through the probe region 131. The rate at which the targets 105 are produced, and also the rate at which the targets 105 pass through the probe region 131 can be on the order of several or tens of kilohertz (kHz), such as, for example, at least 50 kHz and up to or exceeding 100 kHz. Details on how the targets 105 are produced are provided below with reference to Fig. 6.

[0043] The light apparatus 125 can be configured to generate the optical probe 130 that includes light that is simultaneously at the plurality of distinct wavelengths. Moreover, each of the components of the light within the optical probe 130 that has a distinct wavelength can interact with the target 105 at a distinct location along the X-transverse axis within the probe region 131. Thus, the optical probe 130 has a chromatic variation along the X-transverse axis. For example, the optical probe 130 can include a first wavelength produced at a first location along the X-transverse axis, a second wavelength produced at a second location along the X-transverse axis, and a third wavelength produced at a third location along the X-transverse axis. As another example, the optical probe 130 is produced as a light curtain or other beam shape that is a light beam crossing the target axial path 110 of the target 105. In some implementations, the optical probe 130 is a continuous wave light beam. It is possible in some implementations for the optical probe 130 to be a pulsed light beam, if it is pulsed at a high enough frequency (for example, higher than the rate at which the target 105 are produced).

In some implementations, the optical probe 130 is made up of one or more laser beams. While in other implementations, the optical probe 130 is made up of one or more light beams that may not be laser beams.

[0044] This X-transverse chromatic variation within the optical probe 130 enables the detection apparatus 135 and the control apparatus 150 to measure variability of the position of the target 105 along the X-transverse axis. This is because the detection apparatus 135 is configured to sense this change in the wavelength distribution along the X-transverse axis. Different implementations for the light apparatus 125 and the optical probe 130 are described with reference to Figs. 2A, 3A, and 5. [0045] The detection apparatus 135 can include one or more light sensors such as photodiodes operating at a high enough bandwidth to detect each target 105 in the stream (via the produced light 136). Thus, if the targets 105 are produced at a rate of 50 kHz, then the light sensors within the detection apparatus 135 are fast enough to detect and process the produced light 136 (without aliasing) at a rate of 50 kHz. The detection apparatus 135 is configured to sense the wavelength distribution of the produced light 136. This means that the detection apparatus 135 is able to distinguish light of different wavelengths within the produced light 136 due to the X-transverse chromatic variation within the optical probe 130. Details of the detection apparatus 135 are discussed below with reference to Figs. 2 A, 3 A, and 5.

[0046] The control apparatus 150 includes an electronic processor and an electronic storage. The processor can be any type of electronic processor and can be more than one electronic processor. The processor can include one or more processors suitable for execution of a computer program such as a general or special purpose microprocessor, and any one or more processors of any kind of digital computer. Generally, a processor receives instructions and data from a read-only memory or a random access memory or both. The electronic storage stores instructions, perhaps as a computer program, that, when executed, cause the processor to communicate with other components of the metrology system 100 such as the detection apparatus 135 and the components that affect the adjustment 160 to the one or more characteristics relating to one or more of the target 105 and the target axial path 110. The electronic storage can include volatile memory, such as RAM. The electronic storage can include both non-volatile and volatile portions or components. Moreover, the control apparatus 150 can include various separate modules, and each module can be dedicated to a particular task. Also, these modules can be physically separated from each other or integrated with other parts of the metrology system 100.

[0047] Referring to Figs. 2A and 2B, an implementation 200 of the metrology system 100 is shown. In the metrology system 200, the probe optical axis 230OA is parallel with the Y axis of the X, Y, Z coordinate system. Thus, an optical probe 230 travels along the Y axis of this metrology system 200. The metrology system 200 includes a light apparatus 225 that produces the optical probe 230. The optical probe 230 includes three probing light beams 230_1, 230_2, 230_3 (shown more clearly in Fig. 2B), each probing light beam 230_1, 230_2, 230_3 being at a distinct respective center wavelength lΐ, l2, l3. Each probing light beam 230_1, 230_2, 230_3 propagates along the probe optical axis 230OA (which is parallel with the Y axis) and intersects the target axial path 210. Moreover, each probing light beam 230_1, 230_2, 230_3 is focused at a distinct respective location Y_l, Y_2, Y_3 along the probe optical axis 230OA.

[0048] In some implementations, the probing light beams 230_1, 230_2, 230_3 are laser beams. The probing light beams 230_1, 230_2, 230_3 can be circular in intensity profile (that is, in the XZ plane), and they would therefore have a typical through focus laser waist profile. In these implementations, the probing light beams 230_1, 230_2, 230_3 have a transverse shape that is symmetrical about the Y axis. In some implementations, the probing light beams 230_1, 230_2,

230_3 can be non-circular beams, in which the longitudinal position of the beam waist can be different for different transverse directions. This shape can be generated by using cylindrical lenses. For the case of cylindrical focused beams (“curtain”), the transverse profile has a chisel-like shape and is elongated in the Z axis.

[0049] In some implementation, the light apparatus 225 includes one light source such as a laser, and optical components for converting a single light beam into the three probing light beams 230_1, 230_2, 230_3 at the distinct wavelengths lΐ, l2, l3 and also having distinct focuses at Y_l, Y_2,

Y_3. In other implementations, the light apparatus 225 includes three lasers, each laser producing a respective probing light beam 230_1, 230_2, 230_3 at the distinct wavelength lΐ, l2, l3. In still other implementations, the light apparatus 225 includes a single laser or a broadband light source that produces three probing light beams 230_1, 230_2, 230_3 at the distinct wavelengths lΐ, l2, l3. The probing light beams 230_1, 230_2, 230_3 can be coupled from the light source or light sources toward the probe region 231 with the use of one or more fiber optic devices. The light apparatus 225 can further include a focusing device in the path of each probing light beam 230_1, 230_2, 230_3, the focusing device configured to focus that particular probing light beam to its respective and distinct focal location Y_l, Y_2, Y_3 along the probe optical axis 230OA.

[0050] In some implementations, the wavelengths lΐ, l2, l3 can be in the visible and/or near infra red (NIR) range. The separation between each wavelength (for example, the separation between lΐ and l2 or between l2 and l3 depends on the type and design of the optics (such as filters) within the light apparatus 225. And, in some implementations, the wavelength separation can be on the order of tens of nanometers (nm), about 20 nm, about 30 nm, or about 40 nm.

[0051] While three probing light beams 230_1, 230_2, 230_3 are shown in the implementation of the metrology system 200, in other implementations, the optical probe 230 includes more than three probing light beams.

[0052] Referring also in Fig. 2C, the detection apparatus 235 is configured to receive the produced light 236. Moreover, the detector 235 is oriented such that it can detect the produced light 236 (which can be light reflected off of the target 205) regardless of the position of the target 205 in the probe region 231. The produced light 236 can correspond to that portion of the respective probing light beam 230_1, 230_2, 230_3 that is reflected from or scattered from the target 205. As shown, the produced light 236 can travel along a path that is distinct from the probe optical axis 2300 A, and also is distinct from the target axial path 210.

[0053] The detection apparatus 235 includes optical components 237 for processing and modifying the produced light 236 and a sensor apparatus 242 receiving the processed light 239 from the optical components 237. The optical components 237 include one or more collection optics 238 such as lenses for beam shaping of the produced light 236 and optionally include a spatial filter and or a slit aperture. The optical components 237 can also include folding optics such as mirrors and/or prisms. The optical components 237 include a chromatic separation device 240, which can be a passive set of optical devices for separating the produced light 236 into light portions 241_1 , 241_2, 241_3 each having the distinct respective wavelength lΐ, l2, l3. For example, the chromatic separation device 240 can include a set of dichroic beam splitters or mirrors. In this way, the detection apparatus 235 can distinguish the produced light 236 between each of the distinct wavelengths lΐ, l2, l3.

[0054] Referring also to Fig. 2D, the sensor apparatus 242 includes a plurality of detectors 242_1, 242_2, 242_3, each detector being configured to detect produced light 236 at one of the distinct wavelengths lΐ, l2, l3, such produced light 236 being produced from the interaction between the optical probe 230 and the target 205 in the probe region 231. Each detector 242_1, 242_2, 242_3 can be an area or region of a photodetector. For example, the detector 242_1 can correspond to a first set of pixels of a photodiode array, the detector 242_2 can correspond to a second set of pixels of the photodiode array, and the detector 242_3 can correspond to a third set of pixels of the photodiode array. In other implementations, each detector 242_1, 242_2, 242_3 can correspond to a separate and distinct photodiode or photodiode array.

[0055] An output 243_1, 243_2, 243_3 of the respective detector 242_1, 242_2, 242_3 is provided to the control apparatus 250 for analysis. If the detector is a photodetector, then the output 243_1, 243_2, 243_3 corresponds to an amplitude of a photocurrent that is generated from the light interacting with the active region of that detector over time. Such photocurrent is proportional to the absorbed (or incident) light intensity over a wide range of optical powers. Moreover, the use of photodetectors enables high speed detection, as fast as the targets 205 are being produced, and thus enables the control apparatus 250 to perform the analysis on each target 205 that interacts with the optical probe 230.

[0056] As shown in Fig. 2E, the respective output 243_1, 243_2, 243_3 of the detectors 242_1, 242_2, 242_3 is shown for the interaction of Fig. 2B. Specifically, and for example, in Fig. 2B, the target 205 is mostly aligned with the focus Y_2 of the probing light beam 230_2. Accordingly, the output 243_2 of the detector 242_2 has a higher amplitude than the output 243_1 of the detector 242_1 and the output 243_3 of the detector 242_3.

[0057] As another example, in Fig. 2F, the target 205 has strayed along the -Y direction and is now more closely aligned with the focus Y_1 of the probing light beam 230_1. The respective outputs 243_1, 243_2, 243_3 of the detectors 242_1, 242_2, 242_3 for the position of the target 205 in Fig. 2F are shown in Fig. 2G. As shown, the amplitude of the output 243_1 at the detector 242_1 is greatest. Additionally, because the target 205 is offset from Y=0, the output 243_3 at the detector 242_3 is smaller than the output 243_2 at the detector 242_2.

[0058] The control apparatus 250 can determine the location of the target 205 along the Y direction by analyzing ratios of these output signals to each other. For example, the control apparatus 250 can analyze a ratio R12 of the output 243_1 to the output 243_2; a ratio R32 of the output 243_3 to the output 243_2; or a ratio R13 of the output 243_1 to the output 243_3.

[0059] In the implementation of Fig. 2A, the one or more operational light beams 220 are produced by an operational light source 221. The one or more operational light beams 220 generally extend along a direction that is parallel with the Z axis such that the operational light beam 220 interacts with the target 205 in a target region 215 that is downstream of the probe region 231. In this implementation, the optical probe 230 and the probing light beams 230_1, 230_2, 230_3 propagates along a direction that is not parallel with the direction of the operational light beam 220. For example, the optical probe 230 (and the probing light beams 230_1, 230_2, 230_3) can be perpendicular with the direction of the operational light beam 220. Additionally, the targets 205 are produced by a target supply apparatus 206. One or more of the target supply apparatus 206 and the operational light source 221 receives an instruction for adjustment 260 from the control apparatus 250 based on the analysis that the control apparatus 250 on the output from the detection apparatus 235. Specifically, the control apparatus 250 determines position information (for example, a position) of the target 205 along the Y axis of the X, Y, Z coordinate system. And, the control apparatus 250 can determine whether and how to adjust the target supply apparatus 206 and/or the operational light source 221 to account for a drift of the target 205 along the Y axis to ensure that the target 205 enters the target region 215 at the appropriate moment and location to interact with the one or more operational light beams 220, and to thereby efficiently produce EUV light.

[0060] Referring to Fig. 3A, another implementation 300 of the metrology system 100 is shown. In the metrology system 300, the probe optical axis 330OA is parallel with the Z axis of the X, Y, Z coordinate system such that the probe optical axis 330OA intersects the target axial path 310. Thus, in the metrology system 300, an optical probe 330 travels along the Z axis, at least in the probe region 331.

[0061] The metrology system 300 includes a light apparatus 325 that produces the optical probe 330. The optical probe 330 is a beam with transverse chromatic variation. That is, the chromatic variation extends along a direction perpendicular to the direction along which the optical probe 330 travels. In this example, the chromatic variation extends along the Y axis. The transverse chromatic variation of the optical probe 330 enables the measurement of the variation of the position of the target 305 along the Y axis because the distribution of wavelength in the produced light 336 changes as the target 305 moves along the Y axis.

[0062] To this end, the metrology system 300 includes a detection apparatus 335 configured to receive the produced light 336, and a control apparatus 350 configured to receive the output from the detection apparatus 335, to analyze the output, and determine position information about the target 305 along the X and Y directions. The control apparatus 350 can furthermore affect an adjustment 360 to one or more characteristics relating to one or more of the target 305 and the target axial path 310 based on the determined position information of the target 305 along the X axis and the X-transverse axis (which is based on the analysis of the detected produced light 336). The adjustment 360 can be made to one or both of an operational light source 321 (to thereby change one or more aspects of operational light beams 320 relative to the target 305) and a target supply apparatus 306 that produces the targets 305 to thereby adjust aspects relating to how the targets 305 are produced. In this way, the control apparatus 350 controls the trajectory of the targets 305 and the timing with which they arrive at the target region 315, so that the pulses of the operational light beam 305 irradiate the target 305 at the target region 315 and effectively produce EUV light.

[0063] Referring to Figs. 3B and 3C, the optical probe 330 has a transverse extent along the Y axis, and moreover, there is a chromatic variation along this transverse extent. In this particular implementation, for simplicity, five distinct wavelengths lΐ, l2, l3, l4, l5 are represented in the chromatic variation of the optical probe 330 across respective portions 330_1, 330_2, 330_3, 330_4, 330_5 of the optical probe 330. However, it is possible for there to be fewer or more than five distinct wavelengths. And, it is possible for the chromatic variation to be at distinct center wavelengths (as shown in Fig. 3C); or alternatively for the chromatic variation to be a continuous variation of wavelength across the transverse extent.

[0064] The detection apparatus 335 includes a chromatic separation device 340, which can be a passive set of optical devices for separating the produced light 336 into light portions 341_1, 341_2,

341_3, 341_4, 341_5, each portion having the distinct respective wavelength lΐ, l2, l3, l4, l5. The chromatic separation device 340 converts the wavelength separations into spatial separation. For example, the chromatic separation device 340 can include a set of dichroic beam splitters or mirrors. As another example, the chromatic separation device 340 includes a dispersive element such as a grating, which can be transmissive or reflective, or a dispersive optical element such as a prism. In this way, the detection apparatus 335 can distinguish the produced light 336 between each of the distinct wavelengths lΐ, l2, l3, l4, l5.

[0065] The detection apparatus 335 also includes a sensor apparatus 342 receiving the processed light portions 341_1, 341_2, 341_3, 341_4, 341_5. The sensor apparatus 342 includes a plurality of detectors 342_1, 342_2, 342_3, 342_4, 342_5, each detector being configured to detect produced light 336 at one of the distinct wavelengths lΐ, l2, l3, l4, l5 such produced light 336 being produced from the interaction between the optical probe 330 and the target 305 in the probe region 331. The sensor apparatus 342 can further include a chromatic beam separation system such as a dispersive element (for example, a grating or prism), or a series of dichroic filters or beam splitters, or a monolithic filter construction.

[0066] Each detector 342_1, 342_2, 342_3, 342_4, 342_5 can be an area or region of a photodetector. For example, the detector 342_1 can correspond to a first set of pixels of a photodiode array, the detector 342_2 can correspond to a second set of pixels of the photodiode array, the detector 342_3 can correspond to a third set of pixels of the photodiode array, the detector 342_4 can correspond to a fourth set of pixels of the photodiode array, and the detector 342_5 can correspond to a fifth set of pixels of the photodiode array. In other implementations, each detector 342_1, 342_2, 342_3, 342_4, 342_5 can correspond to a separate and distinct photodiode or photodiode array.

[0067] In the example shown in Fig. 3C, the target 305 is interacting with the portion 330_3 of the optical probe 330. In this example, the target 305 is fairly well aligned with the X axis and has not strayed too far along the Y axis. The produced light 336 will therefore have a predominant wavelength l3 and the signal associated with the wavelength l3 will dominate the overall signal analyzed by the detection apparatus 335. Thus, the light portion 341_3 is much greater in amplitude and power than the other light portions and the signal at the detector 342_3 is much greater than the signal at the other detectors. [0068] Figs. 4A-4C show the produced light 336 for different positions of the target 305 along the Y axis. For example, in Fig. 4A, the target 305 is offset along the -Y direction so that the target 305 interacts with the portion 330_4, and the predominant wavelength l 4 is reflected as the produced light 336 to the detection apparatus 335. Thus, the detector 342_4 senses the greatest amplitude of light and the other detectors sense relatively less amplitude of light. In Fig. 4B, the target 305 is offset along the +Y direction so that the target 305 interacts with the portion 330_2, and the predominant wavelength l2 is reflected as the produced light 336 to the detection apparatus 335. Thus, the detector 342_2 senses the greatest amplitude of light and the other detectors sense relatively less amplitude of light.

In Fig. 4C, the target 305 is offset significantly along the -Y direction so that the target 305 interacts with the portion 330_5, and the predominant wavelength l5 is reflected as the produced light 336 to the detection apparatus 335. Thus, the detector 342_5 senses the greatest amplitude of light and the other detectors sense relatively less amplitude of light.

[0069] In some implementations, the optical probe 305 can be a broadband optical probe beam, which is a beam having a continuous optical spectrum across the Y axis. In this example, the light apparatus 325 can include a single broadband light source producing the optical probe 305. In other implementations, the optical probe 305 can be made up of a plurality of probing light beams, each probing light beam having a distinct center wavelength. In this example, the light apparatus 325 can include a plurality of physically distinct light sources, each producing a probing light beam of a distinct center wavelength. In other implementations, the light apparatus 325 can be a supercontinuum light source converts laser light to light with a very broad spectral bandwidth to produce a super-wide continuous optical spectrum. The light apparatus 325 can use prisms and/or gratings to achieve chromatic separation. Moreover, the design of the light apparatus 325 can include an assessment of physical distances (over which the optical probe 305 must travel to reach the probe region 331) and signal levels to determine parameters such as magnification and numerical aperture of the components that are used to produce the optical probe 305.

[0070] The detection apparatus 335 can be implemented in any suitable way, such as, for example, a linear sensor array with a grating to convert the wavelength of the produced light 336 into a spatial separation. The detection apparatus 335 can include camera pixel arrays with integrated color filters, or can include a plurality of photodiodes with dichroic coatings.

[0071] An implementation 500 of the metrology system 300 is shown in Fig. 5. Similar to the metrology system 300, in the metrology system 500, a probe optical axis 530OA is parallel with the Z axis of the X, Y, Z coordinate system such that the probe optical axis 530OA intersects the target axial path 510. Thus, in the metrology system 500, an optical probe 530 travels along the Z axis, at least in the probe region 531.

[0072] The metrology system 500 includes a light apparatus 525 that produces the optical probe 530. The optical probe 530 is a beam with transverse chromatic variation that is projected onto the target axial path 510. That is, the chromatic variation extends along a direction perpendicular to the direction along which the optical probe 530 travels. In this example, the chromatic variation extends along the Y axis (as shown in Figs. 3B and 3C). The transverse chromatic variation of the optical probe 530 enables the measurement of the variation of the position of the target 505 along the Y axis because the distribution of wavelength in the produced light 536 changes as the target 505 moves along the Y axis.

[0073] To this end, the metrology system 500 includes a detection apparatus 535 configured to receive the produced light 536, and a control apparatus 550 configured to receive the output from the detection apparatus 535, to analyze the output, and determine position information about the target 505 along the X and Y directions. The control apparatus 550 can furthermore affect an adjustment 560 to one or more characteristics relating to one or more of the target 505 and the target axial path 510 based on the determined position information of the target 505 along the X axis and the X-transverse axis (which is based on the analysis of the detected produced light 536). The adjustment 560 can be made to one or both of an operational light source 521 (to thereby change one or more aspects of operational light beams 520 relative to the target 505) and a target supply apparatus 506 that produces the targets 505 to thereby adjust aspects relating to how the targets 505 are produced. In this way, the control apparatus 550 controls the trajectory of the targets 505 and the timing with which they arrive at the target region 515, so that the pulses of the operational light beam 505 irradiate the target 305 at the target region 515 and effectively produce EUV light.

[0074] In this implementation, the light apparatus 525 includes a broadband light source 526 that produces a broadband light beam 526b having all of the wavelengths of interest, chromatic shaping optical elements 527, and an imaging optical element 528. The chromatic shaping optical elements 527 separate the broadband light beam 526b into the probing light beams 530_1, 530_2, 530_3,

530_4, 530_5, each at a distinct center wavelength lΐ, l2, l3, l4, l5. In some implementations, the imaging optical element 528 includes a cylindrical focusing optic (such as a cylindrical lens) in the path of the probing light beams 530_1, 530_2, 530_3, 530_4, 530_5, the cylindrical focusing optic configured to form a distinct focus as the optical curtain along the Y axis at the probe region 531. In other implementations, the imaging optical element 528 includes a collimating optic in the path of the probing light beams 530_1, 530_2, 530_3, 530_4, 530_5, the collimating optic configured to collimate the probing light beams 530_1, 530_2, 530_3, 530_4, 530_5 at the probe region 531. In other implementations, the imaging optical element 528 images the probing light beams 530_1,

530_2, 530_3, 530_4, 530_5 to the probe region 531. That is, the imaging optical element 528 causes an image of each probing light beam to be delivered to the probe region.

[0075] In this implementation, the optical probe 530 (collectively, the probing light beams 530_1, 530_2, 530_3, 530_4, 530_5) travels along a path that, in the probe region 531, is parallel with an operational axis, such operational axis being defined by a direction along which the one or more operational light beams 520 travel in the target region 515. Moreover, the optical probe 530 can interact with at least some of the optical elements 523 with which the operational light beams 520 interact (these optical elements 523 can be referred to as operational optical elements). For example, this can be enabled if the operational optical elements have an operating range that encompasses the center wavelengths lΐ, l2, l3, l4, l5 of the optical probe 530. The optical probe 530 also passes through an EUV light collector (such as a mirror) 524 along a parallel path with the operational light beams 520.

[0076] The produced light 536 can be that portion of the optical probe 530 that is reflected from the target 505. Moreover, the produced light 536 can be reflected back along the operational axis in the probe region 531. In this way, the produced light 536 interacts with at least some of the operational optical elements as well. The optical probe 530 is coupled into the operational optical path by way of a beam splitter 522 and the produced light 536 is coupled out of the operational optical path by way of the beam splitter 522. The beam splitter 522 can be a chromatic splitter, such that the produced light 536 is, for example, transmitted, and the optical probe 530 is reflected.

[0077] While the optical probe 530 and the produced light 536 interact with at least some of the operational optical elements 523 in the metrology system 500, it is possible for the optical probe 530 and/or the produced light 536 to follow an entirely distinct path from the operational optical elements 523.

[0078] As discussed above, the detection apparatus 535 includes a chromatic separation device 540, which can be a passive set of optical devices 540_1, 540_2, 540_3, 540_4, 540_5 configured to separate the produced light 536 into light portions 541 _ 1, 541_2, 541_3, 541_4, 541_5, each portion having the distinct respective wavelength lΐ, l2, l3, l4, l5. In this implementation, the optical devices 540_1, 540_2, 540_3, 540_4, 540_5 are dichroic beam splitters or mirrors. In this way, the detection apparatus 535 can distinguish the produced light 536 between each of the distinct wavelengths lΐ, l2, l3, l4, l5.

[0079] The detection apparatus 535 also includes a sensor apparatus 542 receiving the processed light portions 541_1 , 541_2, 541_3, 541_4, 541_5. In practice, the relative sizes of the light portions

541 _ 1, 541_2, 541_3, 541_4, 541_5 would indicate the location of the target 505 along the Y axis while the overall signal or amplitude of all of the light portions 541_1, 541_2, 541_3, 541_4, 541_5 would indicate the location of the target 505 along the X axis. The sensor apparatus 542 includes a plurality of detectors 542_1, 542_2, 542_3, 542_4, 542_5, each detector being configured to detect the portion of the produced light 536 at one of the distinct wavelengths lΐ, l2, l3, l4, l5 such produced light 536 being produced from the interaction between the optical probe 530 and the target 505 in the probe region 531. Each detector 542_1, 542_2, 542_3, 542_4, 542_5 can be an area or region of a photodetector. For example, the detector 542_1 can correspond to a first set of pixels of a photodiode array, the detector 542_2 can correspond to a second set of pixels of the photodiode array, the detector 542_3 can correspond to a third set of pixels of the photodiode array, the detector 542_4 can correspond to a fourth set of pixels of the photodiode array, and the detector 542_5 can correspond to a fifth set of pixels of the photodiode array. In other implementations, each detector 542_1, 542_2, 542_3, 542_4, 542_5 can correspond to a separate and distinct photodiode or photodiode array.

[0080] In other implementations, the produced light 536 can be separated from the optical probe 530 using polarization management instead of a beam splitter 522. For example, such polarization management can include a polarizing beam splitter system with a polarizer before and quarter-wave after to generate and separate rotationally polarized beams of different handedness.

[0081] Referring to Fig. 6, an implementation 600 of the metrology system 100 is incorporated into an EUV light source 670 that, when in operation, supplies an EUV light beam 671 to an output apparatus 672, which can be a lithography exposure apparatus. The EUV light source 670 includes a vacuum chamber 673 that defines a first target space at which each target 605 interacts with a first operational light beam 620A to form a modified target 605m and a second target space at which each modified target 605m interacts with a second operational light beam 620B. the first and second target space are in the target region 615.

[0082] The light apparatus 625 and the detection apparatus 635 are arranged to interact with the target 605 in the probe region 631 prior to the target entering the target region 615.

[0083] The EUV light source 670 includes an EUV light collector (such as a mirror) 624 arranged relative to the second target space. The EUV light collector 624 collects EUV light 674 emitted from a plasma 675 that is produced when the modified target 605m interacts with the second operational light beam 620B. The EUV light collector 624 redirects that collected EUV light 674 as the EUV light beam 671 toward the output apparatus 672. The EUV light collector 624 can be a reflective optical device such as a curved mirror that is able to reflect light having EUV wavelength (that is, the EUV light 674) to form the produced EUV light beam 671.

[0084] The EUV light source 670 includes a target supply apparatus 606 that forms a stream of the targets 605 directed to the first target space for interaction with the first operational light beam 620A. The targets 605 are formed from target material that produces the EUV light 674 when in a plasma state, such as after interaction with the second operational light beam 620B. The first target space is, for example, a location at which the targets 605 are converted to the plasma state. The target supply apparatus 606 includes a reservoir 607 defining a hollow interior that is configured to contain a fluid target material. The target supply apparatus 606 includes a nozzle structure 608 having an opening (or orifice) 609 in fluid communication with the interior of the reservoir 607 at one end. The target material, in a fluid state, being under the force of a pressure P (as well as other possible forces such as gravity), flows from the interior of the reservoir 607 and through the opening 609 to form the stream of targets 605. The trajectory (the target axial path 610) of the targets 605 that are ejected from the opening 609 generally extends along the -X direction, although, as discussed above, it is possible for the trajectory of the targets 605 to include components along the plane perpendicular to the -X direction (that is, Y and Z components). [0085] Each modified target 605m is converted at least partially or mostly to plasma through its interaction with the pulses in the second operational light beam 620B produced by the operational light source 621, such interaction occurring in the second target space. As discussed above, each target 605 is a target mixture that includes a target material and optionally impurities such as non target particles. The target 605 can be, for example, a droplet of liquid or molten metal, a portion of a liquid stream, solid particles or clusters, solid particles contained within liquid droplets, a foam of target material, or solid particles contained within a portion of a liquid stream. The target 605 can include, for example, water, tin, lithium, xenon, or any material that, when converted to a plasma state, has an emission line in the EUV range. For example, the target 605 can include the element tin, which can be used as pure tin (Sn); as a tin compound such as SnBr4, SnBr2, SnH4; as a tin alloy such as tin-gallium alloys, tin-indium alloys, tin-indium-gallium alloys, or any combination of these alloys.

[0086] The EUV light source 670 can include a dedicated controller 678 in communication with the control apparatus 650 as well as other components (such as the target supply apparatus 606) of the EUV light source 670. Alternatively, it is possible for the control apparatus 650 to be a part of the controller 678.

[0087] The X, Y, Z coordinate system of the EUV light source 670 can be fixed or determined based on an aspect of the vacuum chamber 673. For example, the chamber 673 can be defined by a set of walls, and three points on one or more walls of the chamber 673 or within the space of the chamber 673 can provide reference for the X, Y, Z coordinate system. It is possible to fix one or more of the components of the light apparatus 625 and the detection apparatus 635 to one or more walls of the chamber 673.

[0088] The EUV light source 670 can further include other metrology apparatuses not shown. For example, the EUV light source 670 can include a coarse target steering camera and a fine target steering camera positioned to view the targets 605 as they travel toward the first target space, such steering cameras being in communication with the controller 678. The controller 678 can analyze the data from these steering cameras to determine a position of the target 815 in one or more of the Y and Z directions. As another example, the EUV light source 670 can include a set of sensors arranged and configured to detect or sense the EUV light 674; such information about the EUV light 674 can be analyzed by the controller 678 for use in other aspects or control of the EUV light source 670.

[0089] Referring to Fig. 7, the metrology system 100 (which can be the metrology system 200,

300, or 500) can perform a procedure 780. The metrology system 100 generates the optical probe 130, as described above (781). The optical probe 130 is directed as a curtain to cross the target axial path 110 along an X-transverse direction (which can be in the YZ plane). As the target 105 crosses the curtain of the optical probe 130 (and interacts with the optical probe 130), light 136 is produced and then detected (782). In particular, the detection apparatus 135 detects the produced light 136 at a plurality of distinct wavelengths, with each wavelength being associated with a distinct location along the X-transverse direction of the X, Y, Z coordinate system. The control apparatus 150 analyzes this detected light and determines position information relating to the target along the X axis and also the X-transverse axis (783). The control apparatus 150 determines whether the target 105 is on the desired trajectory (or target axial path 110) to the target region 115 (784) based on the determined position information (783). If the target 105 is not on the desired trajectory (784), then the control apparatus 150 affects the adjustment 160 to the one or more characteristics relating to one or more of the target 105 and the target axial path 110 based on the determined position information of the target 105 along the X axis and also the X-transverse axis (785). The control apparatus 150 can additionally perform other analyses such as calculating a time at which the target 105 will reach the target region 115 (786) and also send a signal to the operational light source (such as 221, 331) instructing the operational light source 221, 331 to produce a pulse of the operational light beam 220 at such a time that the pulse reaches the target region 115 at the same time as the target 105 in question (787). The control apparatus 150 can additionally use the information obtained for diagnostics purposes, to make long term predictions about components of or stability of the EUV light source 670 over time.

[0090] The flowchart shown in Fig. 7 only shows the actions relating to a single target 105. In practice, the target supply apparatus 206, 306 is continuously generating targets 105 as described above. And, since there is a sequential series of targets 105, there will similarly be a sequential series of flashes of the produced light 136 that are detected at the detection apparatus 135, and a series of timing signals generated at the detection apparatus 135 and analyzed by the control apparatus 150. This causes the operational light source 221, 321 to fire a series of pulses and irradiate a series of targets 105 at the target region 115 to create the EUV light 674. Additionally, the control apparatus 150 operates to affect the adjustment 160 sequentially as well and for each target 105 in a feed forward manner (that is, before the target 105 reaches the target region 115). This enables the target 105 to be adjusted prior to it arriving at the target region 115 [0091] The embodiments can be further described using the following clauses:

1. A metrology system comprising: a light apparatus configured to generate an optical probe that includes light of a plurality of distinct wavelengths, the optical probe including the distinct wavelengths of the light propagating along a probe optical axis that intersects a target axial path at a probe region; a detection apparatus configured to detect produced light at the plurality of distinct wavelengths, the produced light being produced from an interaction in the probe region between the optical probe and a target traveling along the target axial path; and a control apparatus in communication with the detection apparatus, the control apparatus configured to analyze the detected light and adjust, based on the analysis, one or more characteristics relating to one or more of the target and the target axial path.

2. The metrology system of clause 1, wherein the light apparatus comprises: one or more optical sources configured to generate a plurality of probing light beams as the optical probe, each probing light beam propagating along the probe optical axis that intersects the target axial path and each probing light beam having a distinct center wavelength.

3. The metrology system of clause 2, wherein each probing light beam having a distinct center wavelength is focused at a distinct location along the probe optical axis and within the probe region.

4. The metrology system of clause 1, wherein the light apparatus comprises: one or more optical sources configured to generate a probing light beam as the optical probe, the probing light beam propagating along the probe optical axis that intersects the target axial path and the probing light beam defined by a continuous spectrum of center wavelengths.

5. The metrology system of clause 1, wherein the optical probe has a distinct focus along the probe optical axis and within the probe region.

6. The metrology system of clause 5, further comprising a cylindrical focusing optic in the path of the optical probe, the cylindrical focusing optic configured to form the distinct focus as an optical curtain of the optical probe along a direction perpendicular to the probe optical axis.

7. The metrology system of clause 1, wherein the optical probe is collimated along the probe optical axis or is imaged at the probe region.

8. The metrology system of clause 1, wherein the detection apparatus comprises: a plurality of detectors, each detector configured to detect produced light from the interaction between a respective probing light beam of the optical probe and the target.

9. The metrology system of clause 8, wherein each detector is configured to detect a portion of the respective probing light beam incident on the target.

10. The metrology system of clause 9, wherein each detector being configured to detect the portion of the respective probing light beam incident on the target comprises each detector being configured to detect a portion of the respective probing light beam reflected from or scattered from the target.

11. The metrology system of clause 8, wherein each detector is configured to detect produced light having a wavelength that is distinct from the wavelength of the produced light detected by the other detectors.

12. The metrology system of clause 1, wherein the detection apparatus is configured to distinguish produced light between each of the distinct wavelengths.

13. The metrology system of clause 1, wherein the produced light travels along a path that is distinct from the probe optical axis and also distinct from the target axial path.

14. The metrology system of clause 1, wherein the produced light travels along a path that is parallel with an operational axis, the operational axis defined by a direction along which one or more operational light beams travel, the one or more operational light beams interacting with the target in a target region that is downstream of the probe region.

15. The metrology system of clause 14, wherein the produced light is a portion of the probe light beam that is reflected from the target back along the operational axis. 16. The metrology system of clause 15, wherein the produced light interacts with at least some of the same optics with which the one or more operational light beams interact.

17. The metrology system of clause 1, wherein, along the target axial path, the probe region is upstream of a target region in which the target interacts with one or more operational light beams.

18. The metrology system of clause 17, wherein the target axial path extends at least along an X axis and the probe optical axis is not parallel with the X axis.

19. The metrology system of clause 18, wherein the control apparatus is configured to determine a position of the target along a Y direction that is perpendicular to the X axis.

20. The metrology system of clause 19, wherein the probe optical axis is parallel with a Y axis, and the operational light beams generally travel along a Z axis.

21. The metrology system of clause 20, wherein the light of the plurality of wavelengths has an extent such that the wavelength of the light changes along the Y axis.

22. The metrology system of clause 19, wherein the probe optical axis is perpendicular to the Y axis.

23. The metrology system of clause 22, wherein the light of the plurality of wavelengths extends such that the wavelength of the light changes along the Y axis.

24. The metrology system of clause 17, wherein the one or more operational light beams include a first amplified light beam configured to interact with the target to modify the shape and movement of the target to thereby form a modified target and a second amplified light beam configured to interact with the modified target to thereby convert the modified target to plasma that emits extreme ultraviolet light.

25. The metrology system of clause 1, wherein the control apparatus being configured to adjust one or more characteristics relating to one or more of the target and the target axial path comprises one or more of: the control apparatus being configured to instruct a target material supply to adjust one or more aspects relating to production of the target; and the control apparatus being configured to instruct an operational light source to adjust one or more aspects relating to production of one or more operational light beams that interact with the target in a target region downstream of the probe region.

26. The metrology system of clause 1, wherein the detection apparatus is configured to detect produced light at the plurality of distinct wavelengths at a rate that is as fast as or faster than the rate at which targets pass the probe region and the control apparatus is configured to affect the adjustment to the one or more characteristics relating to the target upon which the analysis for the target is based.

27. The metrology system of clause 26, wherein the control apparatus being configured to adjust one or more characteristics relating to the target include the control apparatus being configured to instruct an operational light source to adjust a pointing of one or more operational light beams that interact with the target in a target region downstream of the probe region, the adjustment of the pointing being relative to a Z axis of an X, Y, Z coordinate system, in which the target axial path extends mostly along an X axis, and the probe optical axis is either aligned with the Y axis or aligned with the Z axis.

28. An extreme ultraviolet (EUV) light system comprising: a target supply apparatus configured to form a stream of targets directed to a target region, each target traveling along a target axial path that extends primarily along an X axis of an X, Y, Z coordinate system; an operational optical source configured to produce one or more operational light beams directed to the target region, at least one operational light beam configured to interact with the target to form a modified target; and a metrology system comprising: a light apparatus configured to generate an optical probe propagating along a probe optical axis that intersects the target axial path at a probe region; a detection apparatus configured to detect produced light at the plurality of distinct wavelengths, each wavelength associated with a distinct location along an X-transverse axis of the X, Y, Z coordinate system, the produced light being produced from an interaction in the probe region between the optical probe and a target traveling along the target axial path; and a control apparatus in communication with the detection apparatus, the control apparatus configured to analyze the detected light and determine position information relating to the target along the X- transverse axis of the X, Y, Z coordinate system.

29. The EUV light system of clause 28, wherein the one or more operational light beams include a first amplified light beam configured to interact with the target to modify the shape and movement of the target to thereby form a modified target and a second amplified light beam configured to interact with the modified target to thereby convert the modified target to plasma that emits extreme ultraviolet light.

30. A metrology system comprising: a light apparatus configured to generate an optical probe propagating along a probe optical axis that intersects a target axial path at a probe region, the target axial path extending primarily along an X axis of an X, Y, Z coordinate system; a detection apparatus configured to detect produced light at a plurality of distinct wavelengths, each wavelength associated with a distinct location along an X-transverse axis of the X, Y, Z coordinate system, the produced light being produced from an interaction in the probe region between the optical probe and a target traveling along the target axial path; and a control apparatus in communication with the detection apparatus, the control apparatus configured to analyze the detected light and determine position information relating to the target along the X- transverse axis of the X, Y, Z coordinate system.

31. The metrology system of clause 30, wherein the optical probe is a broadband optical probe. 32. The metrology system of clause 30, wherein the control apparatus is configured to determine position information relating to the target along the X axis of the X, Y, Z coordinate system based on the analysis of the detected light. .

[0092] Other implementations are within the scope of the claims.