Determining the motion characteristics of targets in extreme ultraviolet light sources

Abstract

An apparatus includes: a diagnostic system configured to diagnostically interact with a current target (110c) traveling along a trajectory (TR) before the current target enters a target space; a first detection device (120) configured to detect a first light; a second detection device (130) configured to detect a second light; and a control system (150) communicating with the first detection device and the second detection device. The first light includes: light (140) generated from an interaction between the current target and the diagnostic system, and light (142) emitted from plasma generated by a previous target. The second light includes: light (142) emitted from plasma generated by a previous target. The control system (150) is configured to: generate an analysis signal based on the first signal and the second signal generated from the respective outputs of the first detection device and the second detection device; and estimate a property of the current target based on the generated analysis signal.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Patent Application No. 62 / 798,725, filed on January 30, 2019, entitled “DETERMINING MOVING PROPERTIES OF A TARGET IN AN EXTREME ULTRAVIOLET LIGHT SOURCE,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The disclosed subject matter relates to systems and methods for measuring aspects of a target along its trajectory in a laser produced plasma extreme ultraviolet light source. Background Art

[0004] Extreme ultraviolet (EUV) light (e.g., electromagnetic radiation having a wavelength of approximately 50 nm or less (sometimes also called soft x-rays) and including wavelengths of approximately 13 nm) can be used in photolithography processes to create extremely small features in substrates (e.g., silicon wafers).

[0005] Methods of generating EUV light include, but are not necessarily limited to, converting a material having, for example, xenon, lithium, or tin, to emit lines in the EUV range in a plasma state. In one such method, often referred to as laser produced plasma ("LPP"), the desired plasma can be generated by irradiating a target material (e.g., in the form of droplets, slabs, ribbons, streams, or clusters of material) with an amplified beam of light, which may be referred to as a drive laser. For this process, the plasma is typically generated in a sealed container (e.g., a vacuum chamber) and monitored using various types of dosimetry equipment. Summary of the invention

[0006] In some general aspects, a method includes enabling an interaction between a diagnostic system and a current target traveling along a trajectory toward a target space, the current target including a component that emits light when converted to plasma. The method also includes: detecting first light at a first detection region, detecting second light at a second detection region, generating an analysis signal based on a first signal generated by the detected first light and a second signal generated by the detected second light, and estimating a property of the current target based on the generated analysis signal. The first light includes light emitted from plasma generated by a previous target and light generated from the enabled interaction between the current target and the diagnostic system. The second light includes light emitted from the previous target plasma.

[0007] Implementations can include one or more of the following features.For example, light emitted from a plasma produced by a target component can include extreme ultraviolet (EUV) light in the EUV wavelength range and non-EUV light outside the EUV wavelength range.

[0008] The second light at the second detection area can be detected by suppressing at least a portion of the light generated from the interaction between the current target and the diagnostic system. The light generated from the interaction between the current target and the diagnostic system can be suppressed by filtering the light generated from the interaction between the current target and the diagnostic system based on one or more of the following: spectral properties, polarization properties, and / or spatial properties of the light generated from the interaction between the current target and the diagnostic system.

[0009] The interaction between the current target and the diagnostic system may include: a first interaction between the current target and a first diagnostic probe of the diagnostic system; and a second interaction between the current target and a second diagnostic probe of the diagnostic system. The second interaction between the current target and the second diagnostic probe may occur at a location and time different from the location and time of the first interaction between the current target and the first diagnostic probe.

[0010] The interaction between the diagnostic system and the current target may be achieved by directing the diagnostic system towards the current target such that the diagnostic system and the current target interact at a region along the trajectory of the current target. The diagnostic system may be directed towards the current target by directing a diagnostic beam towards the current target.

[0011] The properties of the current target can be estimated by estimating one or more of the following: the arrival time of the current target at a specific location in space; the speed, velocity and / or acceleration of the current target; and the time interval between the arrival of the current target at a specific location in space and the arrival of another target at a specific location in space.

[0012] The method may include adjusting one or more properties of a radiation pulse directed toward the target space if the estimated target property is outside of acceptable specifications.

[0013] The first light and the second light may be detected by detecting the first light and the second light during or after a previous (eg, immediately previous) target has interacted with the prior radiation pulse.

[0014] The spectral bandwidth of light emitted from the plasma of the previous target may be significantly wider than the spectral bandwidth of light generated from the interaction between the current target and the diagnostic system.The light generated from the interaction between the current target and the diagnostic system may include light from the diagnostic system that is reflected or scattered from the current target.

[0015] The analysis signal may be generated from the first signal and the signal by electronically subtracting the second signal from the first signal. The analysis signal may be generated from the first signal and the second signal by digitizing the first signal and the second signal and calculating the difference between each time-stamped sample of the first digitized signal and the second digitized signal.

[0016] The second light at the second detection area can be detected by detecting the amount of light generated from the realized interaction between the current target and the diagnostic system. The detected amount of light generated from the realized interaction between the current target and the diagnostic system at the second detection area can be less than the amount of light generated from the realized interaction between the current target and the diagnostic system detected at the first detection area.

[0017] In other general aspects, the apparatus includes: a diagnostic system configured to diagnostically interact with a current target before the current target enters the target space and traveling along a trajectory; a first detection device configured to detect a first light; a second detection device configured to detect a second light; and a control system in communication with the first detection device and the second detection device. The first light includes: light generated from an interaction between the current target and the diagnostic system, and light emitted from a plasma generated by a previous target. The second light includes light emitted from a plasma generated by a previous target. The control system is configured to: generate an analysis signal based on the first signal and the second signal generated from the respective outputs of the first detection device and the second detection device; and estimate a property of the current target based on the generated analysis signal.

[0018] Implementations may include one or more of the following features. For example, the apparatus may also include a target delivery system configured to release multiple targets along a trajectory toward a target space. Each target includes a component that emits extreme ultraviolet (EUV) light when converted to plasma.

[0019] The apparatus may further include an optical source configured to generate a radiation pulse directed toward the target space.The plasma generated by the previous target is generated as a result of the interaction between the previous target and the prior radiation pulse.

[0020] The diagnostic system may include a diagnostic light beam, and the diagnostic light generated from the interaction between the current target and the diagnostic light beam may include the diagnostic light beam reflected or scattered from the current target.

[0021] The first detection device may include a first photodetector, and the second detection device may include a second photodetector. Each of the first photodetector and the second photodetector may include one or more of the following: a photodiode, the output of which is a voltage signal related to the current generated from the detected light; a phototransistor, a photoresistor, and a photomultiplier tube. The first photodetector and the second photodetector may have approximately equal viewing angles and collection angles. The second detection device may include a blocking device, which is configured to limit at least most of the light generated from the interaction between the current target and the diagnostic system from reaching the second photodetector. The blocking device may include a filter in the optical path between the target space and the second photodetector, which is configured to suppress the light generated from the interaction between the current target and the diagnostic system. The filter may include one or more of the following: a spectral filter, a polarization filter, and a spatial filter. The first detection device may include a blocking device having a bandpass that overlaps with the wavelength of the light generated from the interaction between the current target and the diagnostic system.

[0022] The diagnostic system may include a first diagnostic probe and a second diagnostic probe, each diagnostic probe configured to diagnostically interact with the current target as the current target travels along the trajectory and prior to entering the target space, each interaction between the current target and the diagnostic probe occurring at a different location and at a different time.

[0023] The apparatus may include an optical source configured to generate a plurality of radiation pulses directed toward a target space, and an actuation system in communication with the control system and the optical source. The actuation system may be configured to adjust one or more properties of the radiation pulses directed toward the target space if the estimated properties are outside of acceptable specifications.

[0024] The spectral bandwidth of light generated from the interaction between the current target and the diagnostic system may be significantly narrower than the spectral bandwidth of light emitted from the plasma generated by the previous target.

[0025] The control system may include an electronics module in communication with the first detection device and the second detection device, the electronics module being configured to electronically subtract the second signal from the first signal.

[0026] In other general aspects, a method for estimating properties of a moving target includes releasing a current target along a trajectory toward a target space, the current target including a component that emits light when converted to plasma. The method includes detecting diagnostic light generated from an interaction between the current target and a diagnostic system and background light emitted from a plasma generated by a previous target at a first detection area, the spectral bandwidth of the diagnostic light being significantly narrower than the spectral bandwidth of the background light. The method includes limiting the amount of diagnostic light that passes through to a second detection area, and allowing all of the background light to pass through to the second detection area. The method also includes detecting the background light at the second detection area and generating an analysis signal based on: a signal generated by the detected light at the first detection area, and a background signal generated by the detected light at the second detection area. The method includes estimating the properties of the current target based on the generated analysis signal.

[0027] Implementations may include one or more of the following features.For example, detecting diagnostic light and background light at a first detection region and detecting background light at a second detection region may include detecting background light at the first detection region and the second detection region.

[0028] The method may also include limiting the amount of background light that passes through to the first detection area. Limiting the amount of background light that passes through to the first detection area may allow a portion of the background light to reach the first detection area, the allowed portion of the background light being at the same scale in power as the diagnostic light reaching the first detection area. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1A is a schematic diagram and block diagram of a metrology device including a first detection device and a second detection device for determining one or more properties of a target directed toward a target space;

[0030] Figure 1B is a schematic diagram of the implementation of the diagnostic region where the diagnostic probe interacts with each target and the target space;

[0031] Figure 2 yes Figure 1A Schematic diagram and block diagram of the implementation of the metering device;

[0032] Figure 3A It is realized in extreme ultraviolet (EUV) light source Figure 1A A schematic diagram and a block diagram of a first view of an implementation of a metering device;

[0033] Figure 3B is Figure 3A The extreme ultraviolet (EUV) light source Figure 1A A schematic diagram and a block diagram of a second view of an implementation of a metering device;

[0034] Figure 4 yes Figure 3A and Figure 3B A block diagram of an implementation of a control device for an EUV light source, the block diagram also includes Figure 1A or Figure 2 Implementation of control systems for metering devices;

[0035] Figure 5 yes Figure 3A and Figure 3B A schematic diagram and block diagram of an implementation of an optical source of an EUV light source, and also illustrating radiation pulses from the optical source interacting with a target in a target space;

[0036] Fig. 6A is a schematic diagram and block diagram of an implementation of a diagnostic system that produces a single diagnostic beam;

[0037] Figure 6B is a schematic diagram and block diagram of an implementation of a diagnostic system that generates two diagnostic beams from a single light source;

[0038] Figure 6C is a schematic diagram and block diagram of an implementation of a diagnostic system that generates two diagnostic beams from respective light sources;

[0039] Figure 7 Is Figure 1A , Figure 2 , Figure 3A or Figure 3B A flowchart of the procedure performed by the metering device;

[0040] Figure 8 Is from Figure 1A , Figure 2 , Figure 3A or Figure 3B A schematic diagram of an example of output signals of the first detection device and the second detection device of the metering device, the schematic diagram showing the signal processing performed by the control system and the analysis signal generated by the signal processing;

[0041] Fig. 9 yes Figure 1A A schematic diagram and a block diagram of another implementation of a metering device;

[0042] Fig.10 yes Figure 1A A schematic diagram and a block diagram of another implementation of a metering device;

[0043] Fig.11 Yes Figure 1A A schematic diagram and block diagram of an EUV light source for implementing a metrology device;

[0044] Fig.12 Yes, it can include Figure 1A A block diagram of an implementation of an EUV light source of an apparatus; and

[0045] Fig.13 It is shown Fig.12 A block diagram of the EUV light source for more details. DETAILED DESCRIPTION

[0046] refer to Figure 1A The metrology device 100 includes a diagnostic system 105 configured to generate one or more diagnostic probes 106 that diagnostically interact with the current target 110c traveling along the trajectory TR and before the current target 110c enters the target space 115. The metrology device 110 can be operated at an EUV light source (such as, Figure 3A and Figure 3B The EUV light source 360 ​​shown in FIG. 1 is implemented by connecting the target 110 to the radiation pulse 364 in the target space 115 (eg, Figure 3A and Figure 3B ) interacts with a target 110 that is at least partially converted into plasma 114.

[0047] Although the trajectory TR may partially overlap with the Z axis and / or the Y axis, the trajectory TR generally extends along the -X axis. The metrology device 100 includes a first detection device 120, which is configured to detect a first light. The first light includes light 140 generated from an interaction between the current target 110c and the diagnostic system 105 and light 142 emitted from a plasma 144 generated by one or more previous targets 110p within the target space 115. The previous target 110p is any target that arrives at the target space 115 before the current target 110c arrives at the target space 115. The previous target 110p may be a target adjacent to the current target 110c, or there may be other targets between the previous target 110p and the current target 110c. Figure 1A , the previous target 110p has generated plasma 144 because it has interacted with the radiation pulse in the target space 115, and due to this interaction, the previous target 110p is modified by being at least partially converted into plasma 144. Therefore, the previous target 110p is schematically depicted as Figure 1A (as well as Figure 2 and Figure 3A ) is different from the current target 110c in FIG. Figure 3A The schematic depiction of target 110, current target 110c, and previous target 110p in FIG. 1 is for illustration purposes only. The actual geometry, density, and properties of these targets may be different from those in FIG. Figure 3A For example, current target 110c may be a shape other than a sphere, and previous target 110p may take on a shape other than that shown or may be a dispersed collection of particles in space.

[0048] The metrology device 100 also includes a control system 150 that communicates with the first detection device 120. The control system 150 is configured to estimate one or more properties of the current target 110c based at least on the output from the first detection device 120. The estimated properties of the current target 110c may be properties related to the movement, arrival, or location of the current target 110c relative to the target space 115. For example, the control system 150 may estimate one or more of: an arrival time of the current target 110c at a particular location in a space (such as the target space 115); a speed, velocity, or acceleration of the current target 110c; or a time interval between the arrival of the current target 110c at a particular location in the space and the arrival of another target at the particular location in the space. Thus, the determined or estimated properties of the current target 110 c may be used by the EUV light source 360 ​​to adjust or control aspects of subsequent radiation pulses directed to the target space 115 to ensure that when the current target 110 ′ (which may be the current target 110 c) reaches the target space 115 (see Figure 3A and Figure 3B )The subsequent radiation pulse arrives at the target space 115 (or the optimal positioning within the target space 115).

[0049] A plurality of targets 111 (each target generally designated 110) are directed along a trajectory TR toward a target space 115. Each target 110 includes a plasma 144 that emits extreme ultraviolet (EUV) light (such as, Figure 3A and Figure 3B 101 ). These targets 110 travel from a generation region (such as from a target delivery system 155) toward a target space 115 (e.g., ballistically). Properties (such as reach or motion) of the current target 110' are estimated by probing the current target 110c as it travels along a trajectory TR using the diagnostic probe(s) 106 generated by the diagnostic system 105 under the control of the control system 150, detecting aspects of the interaction between the diagnostic probe(s) 106 and the current target 110c, and analyzing aspects of these detections.

[0050] Unfortunately, there may be a large amount of broadband optical radiation (i.e., light 142) in the first light detected at the first detection device 120, and this light 142 may interfere with the calculations and analysis performed by the control system 150. This interference occurs because a plasma 144 is generated by one or more previous targets 110p that entered the target space 115 before the current target 110c interacted with the (multiple) diagnostic probes 106, and this plasma 144 emits broadband optical radiation 142. Therefore, this broadband optical radiation 142 is also referred to as a plasma flash leakage signal. The intensity of the broadband optical radiation 142 is much greater than the intensity of the light 140. Therefore, the broadband optical radiation 142 interferes with the signal generated from the direct interaction between the (multiple) diagnostic probes 106 and the current target 110c. Therefore, the first detection device 120 detects the (useful signal) light 140 generated from the interaction between the current target 110c and the (multiple) diagnostic probes 106 and the (unuseful signal) light 142 emitted from the plasma 144 generated by the one or more previous targets 110p.

[0051] The broadband optical radiation 142 is largely unpolarized. In addition, the broadband optical radiation 142 tends to include three different wavelength bands as follows. The broadband optical radiation 142 includes EUV light (such as Figure 3A and Figure 3B The broadband optical radiation 142 also includes light having a wavelength range that overlaps with the wavelength of the light 140 generated due to the interaction of the (multiple) diagnostic probes 106 and the target 110. Finally, the broadband optical radiation 142 includes light having a wavelength range that includes a range of wavelengths that can be detected by the first detection device 120.

[0052] The metrology device 100 is designed to effectively suppress the effect of broadband optical radiation 142 emitted from plasma 144 generated by one or more previous targets 110p on the calculations and analyses performed by the control system 150 to determine the properties of the current target 110c and thereby estimate the characteristics of the present target 110'. The metrology device 100, and in particular the control system 150, is capable of suppressing the effect of broadband optical radiation 142 on the calculations to determine the properties of the current target 110c by directly preventing or reducing the amount of light 140 generated from the interaction between the current target 110c and the (multiple) diagnostic probes 106 from reaching the second detection device 130 disposed adjacent to the first detection device 120. In this manner, the second detection device 130 is configured to detect the second light, which includes relatively more (or substantially only) broadband optical radiation 142 emitted from the plasma 144 generated by the previous target 110p. Therefore, the second light has less (or, if the blocking is perfect, no) light 140 generated due to the interaction between the current target 110c and the (multiple) diagnostic probes 106. Therefore, the second detection device 130 obtains a very good representation of the useless plasma flash leakage signal contributing to the noise present in the signal detected at the first detection device 120 .

[0053] In other words, the first detection device 120 and the second detection device 130 are configured or positioned to receive the light 140 and the broadband optical radiation 142 generated by the interaction between the current target 110c and the (multiple) diagnostic probes 106. The difference is that the first detection device 120 is more sensitive to the light 140, and the second detection device 130 is more sensitive to the broadband optical radiation 142.

[0054] The control system 150 communicates with the second detection device 130 to receive the output from the second detection device 130 at the same time as the control system 150 receives the output from the first detection device 120. Figure 7 and Figure 8 Discussed in more detail, the control system 150 subtracts or removes the signal output by the second detection device 130 (which is a good representation of noise) from the signal output by the first detection device 120 to obtain a substantially noise-free representation of the light 140 generated from the interaction between the current target 110 c and the diagnostic probe(s) 106. In this manner, the metrology device 100 is able to accurately and efficiently estimate properties of the current target 110 c relative to prior designs that use only the output from a single detection device.

[0055] In addition, the metrology device 100 effectively reduces or eliminates noise due to unwanted plasma flash leakage signals (broadband optical radiation 142) without imposing time gating or other geometric requirements that may require more careful alignment between the diagnostic probe(s) 106 and the current target 110c. In addition, the metrology device 100 does not require (or perform) analysis that would require complete suppression of signals from the broadband optical radiation 142 emitted from the plasma 144 generated by the previous target 110p. That is, the first detection device 120 and the second detection device 130 receive unwanted plasma flash leakage signals from the broadband optical radiation 142. The metrology device 100 does not require spectral components to be removed from the broadband optical radiation 142. In fact, it is quite difficult, if not impossible, to remove all spectral components of the broadband optical radiation 142, and some of the broadband optical radiation 142 will still leak through any bandwidth filter that may be used. The metrology device 100 does not require the broadband optical radiation 142 to be substantially blocked or removed.

[0056] In general, the spectral bandwidth of the light 140 generated from the interaction between the current target 110c and the (multiple) diagnostic probes 106 is significantly narrower than the spectral bandwidth of the light 142 emitted from the plasma 144 generated by the previous target 110p. Therefore, the light 142 is referred to as broadband optical radiation. For example, the spectral bandwidth of the light 140 can be hundreds of times lower than the total spectral bandwidth of the light 142.

[0057] The designation of "first light" and "second light" with reference to the respective first detection device 120 and the second detection device 130 does not imply a specific temporal order of arrival at the respective first detection device 120 and the second detection device 130. The terms "first" and "second" are used only to distinguish between two different devices 120, 130 and do not convey any information about the timing of the first light and the second light. For example, the first light (detected by the first detection device 120) may appear at the first detection device 120 and be detected at the first detection device 120 at the same time as the second detection device 130 detects the second light. Alternatively, the first light may arrive at the first detection device 120 before the second light arrives at the second detection device 130 or after the second light arrives at the second detection device 130.

[0058] The amount of broadband optical radiation 142 present in the first light (detected by the first detection device 120) increases as the distance dp between the diagnostic probe 106 and the target space 115 is reduced. The metrology device 100 enables detection of the current target 110c, where the distance dp is reduced. In addition, it is beneficial to ensure that the distance dp between one or more diagnostic probes 106 and the target space 115 is low enough to take into account the impact deceleration when the current target 110c approaches the target space 115. The impact deceleration of the current target 110c occurs due to the force from the plasma 144 generated by one or more previous targets 110p. In addition, the magnitude of these impact forces decreases as the distance from the target space 115 increases. Therefore, in some implementations, the diagnostic probe 106 is placed at a distance dp close enough to the target space 115 to measure or take into account the deceleration of the current target 110c.

[0059] For example, in order to accurately adjust aspects of a subsequent radiation pulse that will interact with a current target 110' (the current target 110' may be the current target 110c) in the target space 115, it is necessary to estimate the motion of the current target 110c. To a first approximation, the position of the current target 110c is related to the starting position, the velocity of the current target 110c, and the acceleration of the current target 110c. In order for the first approximation to be a good assumption, the velocity and acceleration should be substantially constant. In some cases, the acceleration may be assumed to be zero (0). The velocity of the current target 110c changed (in this example, it slowed down) after a previous plasma event (which occurred when the previous target 110p interacted with the prior radiation pulse) because there was an impact deceleration of the current target 110c due to the force from the plasma 144. Therefore, as Figure 1B As shown in the implementation of , it is beneficial to measure properties (such as velocity) of the current target 110c after the last impact event (i.e., after or during the previous target 110p (which may be the immediately previous target) has interacted with the priority radiation pulse). After the interaction between the previous target 110p and the priority radiation pulse, the current target 110c decelerates rapidly, and then as the deceleration drops significantly after a short period of time, the velocity of the current target 110c can be considered to be substantially constant. The current target 110c decelerates from the velocity (before plasma was generated from the previous target 110p) to the current velocity. Because the diagnostic probe 106 is sufficiently close to the target volume 115 (and the plasma 144 generated by the interaction of the previous target 110p and the priority radiation pulse), it can be safely assumed that no other forces are acting to modify the current target 110c, and the estimate of the properties of the current target 110c is more accurate. Therefore, the metrology device 100 is in Figure 1B144, where the first detection device 120 detects not only the diagnostic light (light 140) but also the broadband optical radiation 142 which has a relatively high intensity and thus significantly interferes with the light 140 due to the fact that the diagnostic probe 106 is so close to the plasma 144. In fact, it becomes more difficult to spatially filter the broadband optical radiation 142 from the light 140 because the intensity of the broadband optical radiation 142 is greater relative to the light 140 in the case where the diagnostic probe 106 is closer to the target space 115 and therefore closer to the plasma 144.

[0060] refer to Figure 2 , shows an implementation of a metering device 200. The metering device 200 includes a first detection device 220 and a second detection device 230 in communication with a control system 250. The first detection device 220 includes a first light detector 222, and the second detection device 230 includes a second light detector 232. Each of the first light detector 222 and the second light detector 232 may include one or more of a photodiode, a phototransistor, a photoresistor, and a photomultiplier tube. In other implementations, each of the first light detector 222 and the second light detector 232 includes one or more thermal detectors (such as, a pyroelectric detector), a bolometer, or a calibrated charged coupled device (CCD) or CMOS.

[0061] The outputs of the first photodetector 222 and the second photodetector 232 are respective signals 223, 233 (such as voltage signals) related to the current generated from the light detected at the respective first photodetector 222 and the second photodetector 232. The first photodetector 222 and the second photodetector 232 have approximately equal viewing angles and collection angles. For example, the viewing angles and collection angles of the first photodetector 222 and the second photodetector 232 may be approximately equal in an XYZ coordinate system. It may be assumed that the first photodetector 222 is a linear detector, such that the signal output by the first photodetector 222 is a linear superposition of the signal associated with the light 140 and the signal associated with the broadband optical radiation 142. Similarly, it may be assumed that the second photodetector 232 is also a linear detector.

[0062] In some implementations, the first light detector 222 and the second light detector 232 detect or sense light using the same mechanism. In other implementations, the first light detector 222 and the second light detector 232 detect or sense light using different mechanisms. The first light detector 222 and the second light detector 232 should both detect light based on the same correlation so that the control system 250 can perform analysis on the signals 223, 233 output from the detectors 222, 232, respectively.

[0063] The diagnostic system 205 generates a diagnostic beam 206 as the diagnostic probe 106. The diagnostic beam 206 is directed toward the trajectory TR so that light 140 is generated when the current target 110c passes through the diagnostic beam 206. In some implementations, the diagnostic beam 206 has a central wavelength in the near infrared region. For example, the light 140 may be a partial diagnostic beam of the diagnostic beam 206 that is reflected or scattered from the current target 110c. The first detection device 220 includes a blocking device 224, which may be a spectral filter having a transmission range including the wavelength of the light 140 generated from the interaction between the current target 110c and the diagnostic beam 206. For example, as shown, the blocking device 224 may be a bandpass filter having a bandpass Δλ centered at the wavelength of the diagnostic beam 206 of the diagnostic system 205. As described above, the blocking device 224 cannot suppress all broadband optical radiation 142, so at least most of the broadband optical radiation 142 leaks through the blocking device 224 and reaches the first light detector 222.

[0064] The second detection device 230 also includes a blocking device 234. The blocking device 234 is configured to limit at least a portion (or a majority) of the light 140 generated from the interaction between the current target 110c and the diagnostic light beam 206 from reaching the second light detector 232. For example, the blocking device 234 may include a spectral filter in the optical path between the target space 115 and the second light detector 232, the spectral filter being configured to suppress the light 140 generated from the interaction between the current target 110c and the diagnostic light beam 206. For example, the blocking device 234 may be a bandpass filter having a bandpass Δλ detuned from the central wavelength of the diagnostic light beam 206 by a certain amount, such as approximately 20-50 nanometers (nm). Because the light 140 generated from the interaction between the diagnostic light beam 206 and the current target 110c is relatively weak and spectrally narrow (especially relative to the light 142), the light 140 may be blocked or greatly suppressed to below an acceptable noise level using the blocking device 234. In addition, because the spectrum of the broadband optical radiation 142 is very broad (especially relative to the light 140) and also varies slowly in the near-infrared range, the amount of optical power that leaks from the broadband optical radiation 142 to the second optical detector 232 is the same as the amount of optical power that leaks from the broadband optical radiation 142 to the first optical detector 222.

[0065] The signal sampled by the second detector 232 is in a different spectral band (or wavelength range) and is also in a different spatial location than the signal sampled by the first detector 222. However, it can be assumed that the signal sampled by the second detector 232 has the same time dependence as the signal sampled by the first detector 222.

[0066] In some implementations, the blocking device 224 is a structure separate from the first light detector 222 and the blocking device 224 operates independently of the first light detector 222, and the blocking device 234 is a structure separate from the second light detector 232 and the blocking device 234 operates independently of the second light detector 232. Figure 2 As shown in . Alternatively, it is possible that the blocking device 224 and the first light detector 222 are to be integrated into a single device or a single device, and the blocking device 234 and the second light detector 232 are to be integrated into a single device or a single device. For example, the single device can be a sensor that only senses light of a specific polarization or a specific wavelength range.

[0067] Next, prior to a detailed discussion of the operation of the metrology apparatus 100 or 200 , a general description of the EUV light source 360 ​​in which the metrology apparatus 100 (or 200 ) is implemented is provided, followed by a discussion of other components of the metrology apparatus 100 or 200 .

[0068] refer to Figure 3A and Figure 3B , the metrology device 100 (or 200) is implemented in an EUV light source 360 ​​to measure one or more properties of a target 110. The EUV light source 360 ​​includes a target delivery system 155 that produces a plurality 111 of targets 110. The EUV light source 360 ​​provides EUV light 362 that has been generated by the interaction between the target 110 and the radiation pulse 364 to an output device 366. As described above, when the current target 110c travels along the trajectory TR toward the target space 115, the metrology device 100 (or 200) measures and analyzes one or more movement properties (such as speed, velocity, and acceleration) of the current target 110c. The target space 115 is defined within a chamber 368 of the EUV light source 360. The trajectory TR extends along a direction that can be considered as a target (or axial) direction, which is located in a three-dimensional X, Y, Z coordinate system defined by the chamber 368. As described above, the axial direction of the target 110 generally has a component parallel to the -X direction of the coordinate system of the chamber 368. However, the axial direction of the target 110 may also have components in one or more of the Y and Z directions that are perpendicular to the -X direction. In addition, each target 110 released by the target delivery system 155 may have a slightly different actual trajectory, and the trajectory depends on the physical properties of the target delivery system 155 when releasing the target 110 and the environment within the chamber 368.

[0069] EUV light source 360 ​​generally includes EUV light collector 370 , optical source 372 , an actuation system 374 in communication with optical source 372 , and control device 351 in communication with control system 150 and target delivery system 155 , optical source 372 , and actuation system 374 .

[0070] EUV light collector 370 collects as much EUV light 361 emitted from plasma 144 as possible and redirects the EUV light 361 as collected EUV light 362 toward output device 366. Light collector 370 may be a reflective optical device such as a curved mirror capable of reflecting light having an EUV wavelength (i.e., EUV light 361) to form generated EUV light 362.

[0071] The optical source 372 generates a radiation pulse beam 364 and directs the radiation pulse beam 364 toward the target space 115 generally in the Z direction (although the radiation pulse beam 364 can be angled relative to the Z direction). Figure 3A , the radiation pulse beam 364 is shown as being directed along the -Y direction. The optical source 372 includes: a light source that generates radiation pulses 364, a beam delivery system including an optical steering component that changes the direction or angle of the radiation pulse beam 364, and a focusing component that focuses the radiation pulse beam 364 onto the target space 115. An exemplary optical steering component includes optical elements (such as lenses and mirrors) that steer or guide the radiation pulse beam 364 by refraction or reflection as needed. The actuation system 374 can be used to control or move various features of the optical components of the beam delivery system and the focusing component, as well as to adjust aspects of the light source that generates the radiation pulses 364. Refer to the following Figure 5 The implementation of optical source 372 is discussed.

[0072] Actuation system 374 is coupled to components of optical source 372 and is also in communication with and under control of control device 351. Actuation system 374 is capable of modifying or controlling the relative positioning between radiation pulses 364 and target 110 in target space 115. For example, actuation system 374 is configured to adjust one or more of the timing of the release of radiation pulses 364 and the direction in which radiation pulses 364 travel.

[0073] The target delivery system 155 is configured to release the stream (or multiples 111) of targets 110 at a specific rate. The metrology device 100 takes this rate into account when determining the amount of time required to perform measurements and analysis of the current target 110c's movement property (or properties) and to affect changes to other aspects or components of the EUV light source 360 ​​based on the measurements and analysis. For example, the control system 150 can transmit the results of the measurements and analysis to the control device 351, which determines how to adjust one or more signals to the actuation system 374 to adjust one or more characteristics of the radiation pulse 364 directed to the target space 115.

[0074] Adjustment of one or more characteristics of radiation pulse 364 may improve the relative alignment between current target 110′ and radiation pulse 364 in target space 115. Current target 110′ is the target that has entered target space 115 when radiation pulse 364 (just adjusted) arrives in target space 115. Such adjustment of one or more characteristics of radiation pulse 364 improves the interaction between current target 110′ and radiation pulse 364 and increases the amount of EUV light 361 generated by such interaction. Figure 3A As shown, target 110 p has previously interacted with a prior radiation pulse (not shown) to produce plasma 144 that emits light 142 .

[0075] In some implementations, current target 110' is current target 110c. In these implementations, the adjustment of one or more characteristics of radiation pulse 364 occurs within a relatively short time frame. Relatively short time frame means that one or more characteristics of radiation pulse 364 are adjusted during the time after the analysis of the movement attributes of current target 110c is completed to the time when current target 110c enters target space 115. Because one or more characteristics of radiation pulse 364 can be adjusted within a relatively short time frame, there is enough time to affect the interaction between current target 110c (whose movement attributes have just been analyzed) and radiation pulse 364.

[0076] In other implementations, the current target 110 'is another target, i.e., a target other than the current target 110c, and follows the current target 110c in time. In these implementations, the adjustment of one or more characteristics of the radiation pulse 364 occurs within a relatively long time frame, so that it is not feasible to affect the interaction between the current target 110c (the motion attribute of the current target 110c has just been analyzed) and the radiation pulse 364. On the other hand, it is feasible to affect the interaction between another (or later) target and the radiation pulse 364. The relatively long time frame is a time frame greater than the time frame of the time when the current target 110c enters the target space 115 after the analysis of the motion attribute of the current target 110c is completed. Depending on the relatively long time frame, another target can be adjacent to the current target 110c. Or, another target can be adjacent to an intermediate target, and the intermediate target is adjacent to the current target 110c. In these other implementations, it is assumed that other targets (the other targets are not the current target 110c) are traveling with sufficiently similar mobile attributes to the detection or estimated mobile attributes of the current target 110c.

[0077] Each of the targets 110 (including the previous target 110p and the current target 110c, as well as all other targets generated by the target delivery system 155) includes a material that emits EUV light when converted to plasma. Each target 110 is at least partially or mostly converted to plasma by interaction with the radiation pulse 364 generated by the optical source 372 in the target space 115. Each target 110 generated by the target delivery system 155 is a target mixture including a target material and optional impurities (such as non-target particles). The target material is a substance that can be converted to a plasma state, and the emission line of the substance is in the EUV range. For example, the target 110 can be a drop of liquid or molten metal, a portion of a liquid stream, a solid particle or cluster, a solid particle contained in a droplet, a foam of the target material, or a solid particle contained in a portion of a liquid stream of a liquid stream. For example, the target material can include: water, tin, lithium, xenon, or any material that has an emission line in the EUV range when converted to a plasma state. For example, the target material can be a tin element, which can be pure tin (Sn); as a tin compound (such as SnBr4, SnBr2, SnH4); as a tin alloy (such as a tin-gallium alloy, a tin-indium alloy, a tin-indium-gallium alloy, or any combination of these alloys). In the absence of impurities, each target 110 includes only the target material. The discussion provided herein is an example in which each target 110 is a droplet made of a molten metal (such as tin). However, each target 110 produced by the target delivery system 155 can take other forms.

[0078] The target 110 may be provided to the target space 115 by passing the molten target material through the nozzle of the target delivery system 155 and allowing the target 110 to drift into the target space 115 along the trajectory TR. In some implementations, the target 110 may be directed to the target space 115 by a force. As discussed below, the current target 110' (which may be the current target 110c) interacting with the radiation pulse 364 may also have interacted with one or more prior radiation pulses. Alternatively, the current target 110' interacting with the radiation pulse 364 may arrive at the target space 115 without interacting with any other radiation pulses.

[0079] The control device 351 is in communication with the control system 150 and also in communication with other components of the EUV light source 360, such as the actuation system 374, the target delivery system 355, and the optical source 372. Figure 4, shows an implementation 451 of the control device 351 and shows an implementation 450 of the control system 150. The control device 451 includes the control system 450, but the control system 450 can be physically separated from the control device 451 and still maintain communication. In addition, features or components of the control device 451 can be shared with the control system 450, including Figure 4 Features not shown.

[0080] The control system 450 includes a signal processing module 452 configured to receive an output from the first detection device 120 and an output from the second detection device 130. The control system 450 includes a diagnostic control module 453 that communicates with the diagnostic system 105. For example, the signal processing module 452 receives a signal 223 from the first light detector 222 and a signal 233 from the second light detector 232, wherein the signals 223, 233 are voltage signals related to a current generated from light detected at the respective first light detector 222 and second light detector 232. In general, the signal processing module 452 analyzes the outputs from the first detection device 120 and the second detection device 130, and determines one or more movement attributes of the current target 110c based on the analysis. The diagnostic control module 453 controls the operation of the diagnostic system 105. For example, the diagnostic control module 453 can provide a signal to the diagnostic system 105 for adjusting one or more characteristics of the diagnostic system 105 and also for adjusting one or more characteristics of the (multiple) diagnostic probes 106.

[0081] The signal processing module 452 also determines whether a subsequent radiation pulse 364 output from the optical source 372 needs to be adjusted based on the determination of one or more movement attributes of the current target 110c. And, if adjustment is required, the signal processing module 452 sends an appropriate signal to the optical source actuator module 454, which interfaces with the optical source 372. The optical source actuator module 454 can be within the control device 451 (e.g., Figure 4 as shown) or can be integrated into the control system 450.

[0082] The signal processing module 452 may include one or more field programmable hardware circuits, such as a field programmable gate array (FPGA). An FPGA is an integrated circuit designed to be configured by a customer or designer after manufacturing. The field programmable hardware circuit may be dedicated hardware that receives one or more values ​​of a timestamp, performs calculations on the received values, and uses one or more lookup tables to estimate the time when the current target 110' arrives at the target space 115. In particular, the field programmable hardware circuit may be used to quickly perform calculations to adjust one or more characteristics of the radiation pulse 364 within a relatively short time frame to achieve the adjustment of one or more characteristics of the radiation pulse 364 interacting with the current target 110c, whose motion attributes have just been analyzed by the signal processing module 452.

[0083] The control device 451 also includes an optical source module 456 that is configured to interface with the components of the optical source 372, including the beam delivery system and focusing components and any optical amplifiers. The control device 451 includes a target delivery module 457 that is configured to interface with the target delivery system 155. In addition, the control device 451 and the control system 450 may include other modules that are specifically configured to interface with other components of the EUV light source 100 that are not shown.

[0084] The control system 450 typically includes or has access to one or more of digital electronic circuits, computer hardware firmware, and software. For example, the control system 450 can access a memory 458, which can be a read-only memory and / or a random access memory. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including, for example: semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks, such as internal hard disks and removable hard disks; magneto-optical disks; and CD-ROM disks. The control system 450 may also include or interface with one or more input devices 459i (such as a keyboard, touch screen, microphone, mouse, handheld input device, etc.) and one or more output devices 459o (such as a speaker and monitor).

[0085] The control system 450 may also include or have access to one or more programmable processors and one or more computer program products tangibly embodied in a machine-readable storage device for execution by the programmable processor. The one or more programmable processors can each execute a program of instructions to perform a desired function by operating input data and generating appropriate outputs. Typically, the processor receives instructions and data from the memory 458. Any of the above may be supplemented or incorporated by a specially designed ASIC (Application Specific Integrated Circuit).

[0086] In addition, any one or more of the modules 452, 453, 454, 456, 457 may include their own digital electronic circuits, computer hardware, firmware and software as well as dedicated memory, input and output devices, programmable processors, and computer program products. Likewise, any one or more of the modules 452, 453, 454, 456, 457 may access and use memory 458, input device 459i, output device 459o, programmable memory, and computer program products.

[0087] Although the control system 450 is shown as a single and complete unit, each of its components and modules can be a separate unit. The control device 451 may include other components, such as dedicated memory, input / output devices, processors, and computer program products. Figure 4 Not shown.

[0088] In some implementations, the optical source 372 includes one or more light generators and one or more optical amplifier systems, where the optical amplifier system receives output from the light generators to generate the radiation pulse beam 364 therefrom.

[0089] In some implementations, such as Figure 5 As shown, optical source 372 is designed as optical source 572 that generates primary radiation pulse beam 564A and main radiation pulse beam 564B that are directed toward corresponding target locations within target space 115 .

[0090] The optical source 572 includes a first optical amplifier system 573_1 including a series of one or more optical amplifiers through which the primary radiation pulse beam 564A passes, and a second optical amplifier system 573_2 including a series of one or more optical amplifiers through which the primary radiation pulse beam 564B passes. One or more amplifiers from the first system 573_1 can be in the second system 573_2; or one or more amplifiers in the second system 573_2 can be in the first system 573_1. Alternatively, it is possible that the first optical amplifier system 573_1 is completely separated from the second optical amplifier system 573_2.

[0091] In addition, although not required, the optical source 572 may include a first light generator 576_1 that generates a first pulsed light beam 577_1 and a second light generator 576_2 that generates a second pulsed light beam 577_2. For example, the light generators 576_1, 576_2 may each be a laser, a seed laser (such as a master oscillator), or a lamp. Exemplary light generators that may be used as the light generators 576_1, 576_2 are Q switches, radio frequency (RF) pumps, axial flow, carbon dioxide (CO2) oscillators that may be operated at a repetition rate of, for example, 100 kHz.

[0092] The optical amplifiers within the optical amplifier systems 573_1, 573_2 may each include a gain medium on a corresponding beam path along which a light beam 577_1, 577_2 from a corresponding light generator 576_1, 576_2 propagates. When the gain medium of the optical amplifier is excited, the gain medium provides photons to the light beam, amplifying the light beam 577_1, 577_2 to produce an amplified light beam that forms a primary radiation pulse beam 564A or a main radiation pulse beam 564B.

[0093] The wavelengths of the beams 577_1, 577_2 or radiation pulse beams 564A, 564B can be different from each other so that if they are combined at any point within the optical source 572, the radiation pulse beams 564A, 564B can be separated from each other. If the radiation pulse beams 564A, 564B are generated by a CO2 amplifier, the primary radiation pulse beam 564A can have a wavelength of 10.26 micrometers (μm) or 10.207 μm, and the main radiation pulse beam 564B can have a wavelength of 10.59 μm. The wavelengths are selected to more easily achieve separation of the beams 564A, 564B using dispersive optics or dichroic mirrors or beam splitter coatings. In the case where beams 564A, 564B propagate together in the same amplifier chain (e.g., where some of the amplifiers in optical amplifier system 573_1 are in optical amplifier system 573_2), different wavelengths can be used to adjust the relative gain between the two beams 564A, 564B, even though they are passing through the same amplifier.

[0094] For example, once separated, the beams 564A, 564B can be directed or focused to two separate locations (such as, respectively, the first target location 515_1 and the second target location 515_2) within the target space 115. In particular, the separation of the beams 564A, 564B also enables the target 510 to expand as the target 510 travels from the first target location 515_1 to the second target location 515_2 after interacting with the beam of the primary radiation pulse 564A.

[0095] The optical source 572 may include a beam path combiner 578c whose beam covers the beam of the primary radiation pulses 564A and the beam of the main radiation pulses 564B and places the beams 564A, 564B on the same optical path within at least some of the distances between the optical source 572 and the target space 115. In addition, the optical source 572 may include a beam path splitter 578s that separates the beam of the primary radiation pulses 564A from the beam of the main radiation pulses 564B so that the two beams 564A, 564B can be separately steered and focused within the target space 115.

[0096] Additionally, the beam of primary radiation pulses 564A may be configured to have a pulse energy that is less than the pulse energy of the beam of main radiation pulses 564B. This is because primary radiation pulses 564A are used to modify the geometry of target 510, while main radiation pulses 564B are used to convert the modified target into plasma 144. For example, the energy of primary radiation pulses 564A may be 5-100 times less than the energy of main radiation pulses 564B.

[0097] In some implementations, each optical amplifier system 573_1, 573_2 includes a set of three optical amplifiers, although as few as one amplifier or more than three amplifiers may be used. In some implementations, each of the optical amplifiers in each system 573_1, 573_2 includes a gain medium that includes CO2 and can amplify light having a wavelength between about 9.1 μm and about 11.0 μm, and in particular, at about 10.6 μm, at a gain greater than 1000. The optical amplifiers in each system 573_1, 573_2 may be operated similarly or at different wavelengths. Suitable amplifiers and lasers for use in the optical amplifier systems 573_1, 573_2 may include pulsed laser devices, such as pulsed gas discharge CO2 amplifiers that generate radiation at about 9.3 μm or about 10.6 μm using DC or RF excitation at relatively high power (e.g., 10 kW or more) and high pulse repetition rate (e.g., 50 kHz or more). An exemplary optical amplifier that may be used in each of systems 573_1 , 573_2 is an axial flow high power CO2 laser with wear-free gas circulation and capacitive RF excitation.

[0098] Additionally, although not required, one or more of the optical amplifier systems 573_1, 573_2 may include a first amplifier that functions as a preamplifier. The preamplifier, if present, may be a diffusion cooled CO2 laser system.

[0099] The optical amplifier systems 573_1, 573_2 may include optical elements for directing and shaping the respective light beams 577_1, 577_2. For example, the optical amplifier systems 573_1, 573_2 may include reflective optics such as mirrors, partially transmissive optics such as beam splitters, or partially transmissive mirrors and dichroic beam splitters.

[0100] The optical source 572 also includes an optical system 579, which may include one or more optical devices (such as reflective optical devices (such as mirrors), partially reflective and partially transmissive optical devices (such as beam splitters), refractive optical devices (such as prisms or lenses), passive optical devices, active optical devices, etc.) for guiding the light beams 577_1, 577_2 through the optical source 572.

[0101] Although the optical amplifiers may be separate and dedicated systems, at least one of the amplifiers of optical amplifier system 573_1 may be in optical amplifier system 573_2, and at least one of the amplifiers of optical amplifier system 573_2 may be in optical amplifier system 573_1. In such a system where at least some of the amplifiers and optics overlap between optical amplifier systems 573_1, 573_2, the beam of primary radiation pulses 564A and the beam of main radiation pulses 564B may be coupled together such that a change in one or more characteristics of pulse 564A may cause a change in one or more characteristics of pulse 564B, and vice versa.

[0102] As shown, an example of a target 510 interacts with two radiation pulses 564A, 564B within the target space 115. The radiation pulses 564A, 564B may be directed generally along the Z direction. The interaction between the initial radiation pulse 564A and the target 510 at the first target location 515_1 causes the target 510 to modify its shape so that it deforms and geometrically expands as it moves through the target space 115, and becomes a modified target 510m when it reaches the second target location 515_2. The interaction between the primary radiation pulse 564B and the modified target 510m at the second target location 515_2 converts at least a portion of the modified target 510 into a plasma 144 that emits EUV light 361. When some of the material of the target 510 interacts with the primary radiation pulse 564A, it may be converted into a plasma. However, the properties of the primary radiation pulse 564A are selected and controlled so that the primary effect of the primary radiation pulse 564A on the target 510 is the deformation and modification of the geometric distribution of the target 510.

[0103] The interaction between the primary radiation pulse 510 and the target 510 causes material to be ablated from the surface of the target 510, and the ablation provides a force that deforms the target 510 so that the shape of the target 510 is different from the shape of the target 510 before interacting with the primary radiation pulse 564A. For example, before interacting with the primary radiation pulse 564A, the target 510 may have a shape similar to a droplet when leaving the target delivery system 155, and after interacting with the primary radiation pulse 564A, the shape of the target 510 is deformed so that the shape of the modified target 510m is closer to the shape of a disk (such as a pancake shape) when arriving at the second target position 515_2. After interacting with the primary radiation pulse 564A, the target 510m may be a non-ionized material (a material that is not a plasma) or a minimally ionized material. After interacting with the primary radiation pulse 564A, for example, the target 510m may be a liquid disk or a molten metal disk, a continuous segment of the target material without voids or substantial gaps, a mist of microparticles or nanoparticles, or an atomic vapor cloud.

[0104] In addition, if Figure 5 As shown, the interaction between the target 510 and the primary radiation pulse 564A, which causes material to be ablated from the surface of the target 510, can provide some propulsion or velocity in the Z direction for the target 510. The expansion of the modified target 510m in the X direction as it travels from the first target position 515_1 to the second target position 515_2 and the velocity achieved in the Z direction depends on the energy of the primary radiation pulse 564A, and in particular, on the energy delivered to the target 510 (i.e., intercepted by the target 510).

[0105] As described above, EUV light source 360 ​​adjusts one or more characteristics of radiation pulses 364 directed to target space 115 based on an analysis of one or more movement properties determined for current target 110c. Thus, EUV light source 360 ​​may adjust one or more characteristics of primary radiation pulse 564A, one or more characteristics of main radiation pulse 564B, or one or more characteristics of both primary radiation pulse 564A and main radiation pulse 564B.

[0106] refer to Fig. 6AIn some implementations, the diagnostic system 105 is designed as a diagnostic system 605A. As one or more diagnostic probes 106, the diagnostic system 605A generates a single diagnostic beam 606A from a light source 607A. The diagnostic beam 606A is directed as a light curtain to traverse the trajectory TR at the location x, so that each of the targets 110 passes through the light curtain on their way to the target space 115. The light source 607A generates a single light beam 611A, which is directed through one or more optical elements 608A (such as, mirrors, lenses, apertures and / or filters), which modify the light beam 611A to form a single diagnostic beam 606A.

[0107] The light source 607A may be a solid-state laser (such as a YAG laser), which may be a neodymium-doped YAG (Nd:YAG) laser operating at 1070 nm and 50 W of power. In this example, when the current target 110 c passes through the diagnostic beam 606A at time t, at least some of the diagnostic beam 606A is reflected or scattered from the current target 110 c to form light 640A, which is detected by the metrology device 100 (via the first detection device 120). The metrology device 100 uses this information (in combination with information from the second detection device 130) to estimate the arrival time of the current target 110 ′ at the target space 115, and accordingly adjusts the characteristics of the radiation pulse 364 to ensure interaction of the radiation pulse 364 with the current target 110 ′ in the target space 115. The metrology device 100 may also perform calculations relying on some assumptions about the path of the current target 110 ′ to estimate the arrival time of the current target 110 ′ at the target space 115. For example, the metering device 100 may assume that the target 110 ′ is currently at a particular velocity at a particular point along the trajectory TR.

[0108] The diagnostic beam 606A can be a Gaussian beam, so that the transverse profile of its optical intensity can be described by a Gaussian function. The focus or beam waist of the diagnostic beam 606A can be configured to overlap at the track TR or in the -X direction. In addition, the optical element 608A can include a refractive optical device that ensures that the focus (or beam waist) of the diagnostic beam 606A overlaps the track TR.

[0109] refer to Figure 6BIn some implementations, the diagnostic system 105 is designed as a diagnostic system 605B. The diagnostic system 605B generates two diagnostic light beams 606B_1 and 606B_2 as one or more diagnostic probes 106. The diagnostic light beam 606B_1 is directed as a first light curtain to cross the track TR at a first position (e.g., position x1 along the X-axis), so that each of the targets 110 passes through the first light curtain on the way to the target space 115. The diagnostic light beam 606B_2 is directed as a second light curtain to cross the track TR at a second position (e.g., position x2 along the X-axis), so that each of the targets 110 passes through the second light curtain on the way to the target space 115 and after having passed through the first light curtain. The diagnostic light beams 606B_1, 606B_2 are separated by a distance Δx at the track TR, and the distance Δx is equal to x2-x1. The dual-curtain diagnostic system 605B can be used not only to determine the position and arrival information of the target 110, but also to determine the speed or velocity of the target 110.

[0110] In some implementations, the diagnostic system 605B includes a single light source 607B that generates a single light beam 611B and one or more optical components 608B that receive the single light beam and split the light beam 611B into two diagnostic light beams 606B_1, 606B_2. In addition, the optical component 608B may include components for directing the diagnostic light beams 606B_1, 606B_2 toward respective positions x1, x2 along the trajectory TR.

[0111] In some implementations, the optical assembly 608B includes a beam splitter that splits a single beam from a single light source 607B into two diagnostic beams 606B_1, 606B_2. For example, the beam splitter can be a dielectric mirror, a beam splitter cube, or a polarization beam splitter. One or more of the optical assemblies 608B can be reflective optical devices positioned to redirect either or both of the diagnostic beams 606B_1, 606B_2 such that both diagnostic beams 606B_1, 606B_2 are directed toward the trajectory TR.

[0112] In other implementations, the optical assembly 608B includes a beam splitting optical device (such as a diffractive optical device or a binary phase diffraction grating, a birefringent crystal, an intensity beam splitter, a polarization beam splitter, or a dichroic beam splitter) and a refractive optical device (such as a focusing lens). The light beam 611B is directed through the beam splitting optical device, which splits the light beam 611B into two beams that travel in different directions and are directed through the refractive optical device to produce diagnostic beams 606B_1, 606B_2. The beam splitting optical device can separate the light beam 611B so that the diagnostic beams 606B_1, 606B_2 are separated by a set distance (e.g., 0.65 mm along the X direction) at the track TR. In this example, x2-x1=0.65 mm. In addition, the refractive optical device can ensure that the focus (or beam waist) of each diagnostic beam in the diagnostic beams 606B_1, 606B_2 overlaps with the track TR.

[0113] As shown in this example, the diagnostic beams 606B_1, 606B_2 are directed so that they intersect the track TR at different positions x1, x2, but generally at substantially similar angles relative to the X-axis. For example, the diagnostic beams 606B_1, 606B_2 are directed at approximately 90° relative to the X-axis. In other implementations, separation optics and refractive optics can be used to adjust the angles at which the diagnostic beams 606B_1, 606B_2 are directed relative to the X-axis so that they fan out toward the track TR and intersect the track TR at different and distinct angles. For example, the diagnostic beam 606B_1 can intersect the track TR at approximately 90° relative to the -X direction, while the diagnostic beam 606B_2 can intersect the track TR at an angle less than 90° relative to the -X direction.

[0114] Each of the diagnostic beams 606B_1 , 606B_2 may be a Gaussian beam, such that the transverse profile of the optical intensity of each diagnostic beam 606B_1 , 606B_2 may be described by a Gaussian function. The focus or beam waist of each diagnostic beam 606B_1 , 606B_2 may be configured to overlap at the trajectory TR or -X direction.

[0115] The light source 607B may be a solid-state laser (such as a YAG laser), which may be a neodymium-doped YAG (Nd:YAG) laser operated at 1070 nm and a power of 50 W. In this example, the current target 110 c passes through the first diagnostic beam 606B_1 at time t1 (and position x1), and at least some of the diagnostic beam 606B_1 is reflected or scattered from the current target 110 c to form light 640B_1 (as light 140), which is detected by the metrology device 100 (via the first detection device 120). Furthermore, current target 110c passes through second diagnostic beam 606B_2 at time t2 (and position x2), and at least some of diagnostic beam 606B_2 is reflected or scattered from current target 110c to form light 640B_2 (such as light 140), which is detected by metrology device 100 (via first detection device 120).

[0116] The spacing Δd between the diagnostic beams 606B_1, 606B_2 at the trajectory TR can be adjusted or customized according to the rate at which the target 110 is released from the target delivery system 155 and the size and material of the target 110. For example, the spacing Δd can be less than the spacing between adjacent targets 110. As another example, the spacing Δd can be determined or set based on the spacing between adjacent targets 110 to provide a higher accuracy of the measurement performed based on the interaction between the diagnostic beams 606B_1, 606B_2 and the current target 110c. To a certain extent, in general, the larger the spacing Δd, the higher the accuracy of the measurement performed. For example, the spacing Δd can be between about 250μm and 800μm.

[0117] The interaction between the diagnostic beams 606B_1, 606B_2 and the current target 110c enables the control system 150 to determine a movement property such as the velocity V of the current target 110c along the -X direction. Trends in the velocity V or changes in the velocity V over many targets may also be determined. If some assumptions are made about the movement of the current target 110c, changes in the movement properties of the current target 110c along the -X direction may also be determined using only the diagnostic beams 606B_1, 606B_2.

[0118] The wavelength of the diagnostic probe 106 (such as the diagnostic beam 206, the diagnostic beam 606A, and the diagnostic beams 606B_1, 606B_2) generated by the diagnostic system should be sufficiently different from the wavelength of the radiation pulse 364 generated by the optical source 372 so that the blocking device 234 can block the light 140 reflected from the current target 110c and any stray light from the radiation pulse 364, while allowing the broadband optical radiation 142 to pass. In some implementations, the wavelength of the diagnostic beam 206, 606A, 606B_1, 606B_2 is 532nm or 1550nm.

[0119] refer to Figure 7 , the procedure 700 is executed by the metrology device 100 (or 200) to estimate one or more properties of the current target 110c. Initially, the metrology device 100 implements an interaction between the diagnostic system 105 and the current target 110c (705). The interaction may be between one or more diagnostic probes (such as, for example, probe 106, probe 206, diagnostic beam 606A, or diagnostic beam 606B_1, 606B_2) and the current target 110c when the current target 110c crosses the path of the diagnostic probe 106. For example, the control system 150 may be configured to send a signal to the diagnostic system 105 to generate the diagnostic probe 106 across the X axis and thus in the path of the current target 110c when it is released toward the target space 115.

[0120] The metrology device 100 detects first light at a first detection region (710). The first light includes broadband optical radiation (light 142) emitted from a plasma 144 generated by a previous target 110p. The first light includes light 140 generated from an interaction between a current target 110c and a diagnostic system 105. For example, a first detection device 220 may detect the first light. In this example, the first light is detected at a first light detector 222, which may be considered a first detection region. A first signal (such as signal 223) is generated from the detected first light and the first signal 223 is directed to a control system 150, 250. The light 140 generated from the interaction between the current target 110c and the diagnostic system 105 may include light from the diagnostic probe 106 that is reflected from the current target 110c.

[0121] refer to Figure 8, an example of a first signal 823 is shown. The first signal 823 is a voltage signal related to a time-varying current generated from light detected at the first light detector 222. In this example, the first light detector 222 is provided with a blocking device 224 that transmits light having a central wavelength corresponding to the central wavelength of the light 140, and the blocking device 224 has a transmission bandwidth of approximately 10-20 nm. The first signal 823 shows an intensity peak 823_1 associated with the light 140 generated from the interaction between the current target 110c and the diagnostic system 105, and an intensity peak 823_2 associated with the light 140 generated from the interaction between the target 110 adjacent to the current target 110c and the diagnostic system 105. The first signal 823 also shows intensity peaks 823_3, 823_4 associated with the light 142. As is apparent from this example, the intensity or amplitude of the peaks 823_3 , 823_4 due to the broadband optical radiation 142 is of the same order of magnitude as the intensity or amplitude of the peaks 823_1 , 823_2 due to the diagnostic light 140 .

[0122] In general, the shape of the signal 223 output from the first light detector 222 may fluctuate and change according to various parameters in the first light detector 222 and the blocking device 224 . Figure 8 The signal 823 shown in FIG. 8 merely provides one example of what the signal 223 may look like. Other shapes for the signal 223 are possible.

[0123] Reference again Figure 7 , the metrology device 100 detects second light at the second detection region (715). The second light includes broadband optical radiation (light 142) emitted from the plasma 144 generated by the previous target 110p. Most of the light in the light 140 is blocked from reaching the second detection region. For example, the second detection device 230 can detect the second light. In this example, the second light is detected at the second light detector 232, which can be considered as the second detection region. A second signal (such as, signal 233) is generated from the detected second light and the second signal 233 is directed to the control system 150, 250. As discussed in more detail below, the diagnostic light 140 can be blocked using the blocking device 234 based on one or more of the spectral properties, polarization properties, and spatial properties of the diagnostic light 140.

[0124] refer to Figure 8, an example of a second signal 833 is shown. The second signal 833 is a voltage signal related to a time-varying current generated from light detected at the second light detector 232. In this example, the second light detector 232 is provided with a blocking device 234 that transmits light having a central wavelength that is 50 nm offset from the central wavelength of the light 140, and the blocking device 234 has a transmission bandwidth of approximately 10-20 nm. The second signal 833 only shows intensity peaks 823_3, 823_4 associated with the light 142 because the blocking device 234 has blocked a large amount of diagnostic light in the diagnostic light 140. It is not necessary for the blocking device 234 to block 100% of the light 140; instead, the blocking device 234 only needs to block enough light in the light 140 to obtain a clear representation of the peak associated with the light 142, so that the second signal 833 can be used to remove the signal caused by the light 142 from the first signal 823 in the following steps.

[0125] In some implementations, the metrology device 100 detects the first light (710) and the second light (715) during or after a previous (e.g., immediately previous) target 110 has interacted with the priority radiation pulse 364. Typically, the metrology device 100 detects the first light (710) and the second light (715) parallel to each other. That is, the signals 223, 233 (hereinafter referred to as S1(t) and S2(t) respectively) from the respective first detection device 220 and second detection device 230 are both continuously sent to the control system 250 and acquired at the same time t.

[0126] The metering device 100 generates an analysis signal based on a first signal generated from the detected first light and a second signal generated from the detected second light (720). Figure 8 and Figure 4 , the signal processing module 452 receives the first signal 823 and the second signal 833 from the first light detector 222 and the second light detector 232, respectively. The signal processing module 452 electronically subtracts the first signal 823 from the second signal 833 to obtain the analysis signal 880. The signal processing module 452 can perform the electronic subtraction by digitizing each of the first signal 823 and the second signal 833, and then calculating the difference between each set of sampling points (in the corresponding digitized signals). In other implementations, the signal processing module 452 performs the electronic subtraction using analog electronics.

[0127] The signal processing module 452 can perform the subtraction based on assumptions related to the second signal generated from the detected second light. Specifically, it can be assumed that the multiplication gain factor can be estimated and accessed by the signal processing module 452. For example, the multiplication gain factor can be estimated as an input parameter and stored in the memory 458 for access by the signal processing module 452. As another example, the multiplication gain factor can be estimated in a dynamic manner by an online measurement that appropriately scales the second signal generated from the detected second light so that when the subtraction is performed, a portion of the signal from the light 142 is effectively canceled or significantly reduced. The multiplication gain factor is discussed in more detail below.

[0128] The signal sampled by the second detector 232 is in a different spectral band (or wavelength range) and is also in a different spatial location than the signal sampled by the first detector 222. However, it can be assumed that the signal sampled by the second detector 232 has the same time dependence as the signal sampled by the first detector 222.

[0129] The analysis signal 880 contains a representation of the diagnostic light 140 without acquiring a time gating to isolate the diagnostic light 140 from the broadband optical radiation 142. The analysis signal 880 includes peaks 880_1 , 880_2 corresponding to the peaks 823_1 , 823_2 of the first signal 823, respectively.

[0130] One or more properties of the current target 110 c are estimated based on the analysis signal (725). For example, the signal processing module 452 can process or analyze the analysis signal 880 to estimate the arrival time of the current target 110 c (or the current target 110 ′) at a specific location in space (such as an area within the target space 115), to estimate the speed, velocity, or acceleration of the current target 110 c, or to estimate the time interval between the arrival of the current target 110 c at a specific location in space and the arrival of another target at the specific location in space.

[0131] The shape of the analysis signal 880 is related to the amount or intensity of the light 140 impinging on the first light detector 222. For example, the signal processing module 452 can convert the analysis signal 880 into a set of values ​​corresponding to the maximum intensity of the detected light. Each maximum intensity value can be digitally time-stamped and then used to determine one or more movement attributes of the current target 110c.

[0132] For example, the signal processing module 452 may include a time module that receives the analysis signal 880 and digitally timestamps each individual voltage peak 880_1, 880_2. The voltage peak 880_1 corresponds to the time when the current target 110c interacts with the diagnostic probe 106, and the voltage peak 880_2 corresponds to the time when the adjacent target interacts with the diagnostic probe 106. For example, the timestamps t_1 and t_2 are as follows: Figure 8 shown.

[0133] The locations of timestamps t_1 and t_2 may be selected by the signal processing module 452 to generally correspond to the center locations of the respective peaks 880_1, 880_2. For example, in some implementations, the signal processing module 452 may be configured to low pass filter the transient peak signal 823 from the first light detector 222 (the first light detector 222 may be a photodiode), the signal processing module 452 may determine the time derivative of the filtered signal, and use the zero crossing of the derivative to estimate where the center of the peak 880_1 is and select that location as t_1. In other implementations, the signal processing module 452 may select the location of the midpoint of the half maximum crossing as the location of t_1. The shape of the transient peak signal 823_1 may be different depending on the shape of the current target 110c (e.g., the target 110 may experience shape oscillations as they travel along the target trajectory), so in some implementations, the signal processing module 452 may be sensitive to the center of mass but not to the shape of the transient peak signal 823.

[0134] These timestamps can then be used to determine the movement properties of the current target 110c. The signal processing module 452 can also access other data related to the current target 110c or the diagnostic system 105 stored in the memory 458. For example, the memory 458 can store information related to the preferred speed associated with the current target 110c. If the diagnostic system is designed to Figure 6B If the dual beam diagnostic system 605B is used, the memory 458 may store information related to the spacing Δd between the diagnostic beams 606B_1 and 606B_2, or may store the position where the diagnostic probe 108 interacts with each target.

[0135] The signal processing module 452 can use Figure 6B The time stamp of the dual beam diagnostic system 605B output is used to determine the current speed or velocity of the target 110c.

[0136] The signal processing module 452 can determine the location where the current target 110' (which can be the current target 110c) will be within the target space 115. The signal processing module 452 can determine the predicted time for the current target 110' to arrive at the target location by using the estimated velocity and other information stored in the memory 458. Specifically, the memory 458 can store the intersection of the diagnostic beam 606B_2 and the trajectory TR of the current target 110c and the distance between the target location along the X direction in the target space 115. The signal processing module 452 can determine the time for the current target 110c to cross the path of the diagnostic beam 606B_2. Therefore, the signal processing module 452 can estimate or determine the arrival of the current target 110c at the target location in the target space 115 as the stored distance divided by the estimated velocity.

[0137] One or more outputs from the signal processing module 452 may be considered control signals and are directed to an optical source actuation module 454 that interfaces with the optical source 372. The control signals from the signal processing module 452 provide instructions that cause the actuation module 454 to adjust aspects of the optical source 372 to thereby adjust one or more of the timing of the release of one or more radiation pulses 364 and the direction in which the radiation pulses 364 travel.

[0138] In some implementations, if the blocking devices 224, 234 fail to adequately and physically distinguish the diagnostic light 140 from the broadband optical radiation, the signal processing module 452 may perform additional processing to distinguish the diagnostic light 140 from the broadband optical radiation 142 in the first signal 832. One reason this additional processing works is that there is a difference in the distinction between the two signals 223, 233 on the first light detector 222 and the second light detector 232, respectively. That is, one of the detectors (such as the first light detector 222) senses or detects more broadband optical radiation 142 than the other detector (such as the second light detector 232). In addition, the time dependence of the signals 223, 233 is the same. As an example, if the signal 223 is represented as S1(t) and the signal 233 is represented as S2(t), the signals generally have the same time dependence f(t) if S1(t)=a*f(t)+b and S2(t)=c*f(t)+d, where a, b, c, d are constants. That is, all of the time derivatives of S1 and S2 that exist (dS1 / dt, dS2 / dt, etc.) are identical up to a constant multiplication factor.

[0139] Specifically, the signals S1(t) and S2(t) may be represented according to signals related to the diagnostic light 140 and the broadband optical radiation 142 as follows. If the signal from the diagnostic light 140 is represented as d(t) and the broadband optical radiation 142 is represented as p(t+t'), where t is time and t' is the delay between the generation of the diagnostic light 140 and the generation of the broadband optical radiation 142. The signal S1(t) detected at the first light detector 222 according to the sensitivity of the first light detector 222 is a linear superposition of these two signals as follows: S1(t)=e*d(t)+f*p(t+t'), where e and f are fixed constants determined by the blocking device 224, the first light detector 222, and the spectra of the diagnostic light 140 and the broadband optical radiation 142. According to the sensitivity of the second light detector 232, the signal S2(t) detected at the second light detector 232 is the linear superposition of these two signals as follows: S2(t)=g*d(t)+h*p(t+t'), where g and h are fixed constants determined by the blocking device 234, the second light detector 232, and the spectra of the diagnostic light 140 and the broadband optical radiation 142.

[0140] The user-variable multiplication gain factor is free, then:

[0141] d(t)=[S1(t)-a*S2(t)-(fa*h)*p(t+t')] / (ea*g)

[0142] If the user selects a=f / h, then:

[0143]

[0144] In (such as, Figure 6C In other implementations (shown), instead of having a single light source (such as light source 607B) in diagnostic system 605B, diagnostic system 605C includes a pair of light sources 607C_1, 607C_2 (such as two lasers), each of which generates a light beam 611C_1, 611C_2, respectively. Each of the light beams 611C_1, 611C_2 passes through a corresponding one or more optical elements 608C_1, 608C_2, which can change or adjust the characteristics of the light beam 611C_1, 611C_2. The output of each of the one or more optical elements is a corresponding diagnostic beam 606C_1, 606C_2. The optical components 608C_1, 608C_2 may include components for directing the corresponding diagnostic beam 606C_1, 606C_2 toward a corresponding position x1, x2 along the trajectory TR. Examples of optical assemblies 608C_1 , 608C_2 are discussed above with reference to optical assembly 608B.

[0145] Each of the diagnostic beams 606C_1 , 606C_2 may be a Gaussian beam such that the transverse profile of the optical intensity of each diagnostic beam 606C_1 , 606C_2 may be described by a Gaussian function. The focus or beam waist of each diagnostic beam 606C_1 , 606C_2 may be configured to overlap at the trajectory TR or -X direction.

[0146] Each light source 607C_1, 607C_2 can be a solid-state laser. In one example, the solid-state laser is a YAG laser (such as a neodymium-doped YAG (Nd:YAG)) operating in the range of 1010nm-1070nm and at a power in the watt-trend range. In another example, depending on other considerations, the solid-state laser is an ytterbium-doped fiber laser operating in the range of 1010nm-1070nm (e.g., at 1020nm or 1070nm). In this example, similar to Figure 6B According to the design of FIG. 1 , the current target 110c passes through the first diagnostic light beam 606C_1 at time t1 (and position x1), and at least some of the diagnostic light beams 606C_1 are reflected or scattered from the current target 110c to form light 640C_1 (as light 140), which is detected by the metrology device 100 (via the first detection device 120). In addition, the current target 110c passes through the second diagnostic light beam 606C_2 at time t2 (and position x2), and at least some of the diagnostic light beams 606C_2 are reflected or scattered from the current target 110c to form light 640C_2 (as light 140), which is detected by the metrology device 100 (via the first detection device 120).

[0147] The spacing Δd between the diagnostic beams 606C_1, 606C_2 at the trajectory TR can be adjusted or customized according to the rate at which the target 110 is released from the target delivery system 155 and the size and material of the target 110. For example, the spacing Δd can be less than the spacing between adjacent targets 110. As another example, the spacing Δd can be determined or set based on the spacing between adjacent targets 110 to provide a higher accuracy for the measurement performed based on the interaction between the diagnostic beams 606C_1, 606C_2 and the current target 110c. To a certain extent and generally, the larger the spacing Δd, the higher the accuracy of the measurement performed. For example, the spacing Δd can be between about 250 μm and 800 μm.

[0148] The interaction between the diagnostic beams 606C_1, 606C_2 and the current target 110c enables the control system 150 to determine a movement property such as a velocity V of the current target 110 along the -X direction. Trends in the velocity V or a changing velocity V over many targets may also be determined. If some assumptions are made about the motion of the current target 110c, changes in the movement property of the current target 110c along the -X direction may also be determined using only the diagnostic beams 606C_1, 606C_2.

[0149] The wavelength of the diagnostic light beams 606C_1, 606C_2 generated by the diagnostic system 605C should be sufficiently different from the wavelength of the radiation pulses 364 generated by the optical source 372 so that when the broadband optical radiation 142 is passed, the blocking device 234 can block the light 640C_1, 640C_2 reflected from the current target 110c and any stray light from the radiation pulses 364. In some implementations, the wavelength of the diagnostic light beams 606C_1, 606C_2 is 532nm or 1550nm.

[0150] Also refer to Fig. 9 , in another implementation, Figure 2 The blocking devices 224 and 234 implemented in the illustrated metrology device 200 may be designed as bias filters 924, 934, rather than spectral filters. In this manner, in the metrology device 900, polarization is used to distinguish between light that is blocked and light that is allowed to pass through to the light detector. In this implementation, the diagnostic light 940 generated from the interaction between the diagnostic beam 906 and the current target 110c is polarized. Because the diagnostic beam 906 has a specific polarization, the diagnostic light 940 may be polarized. Alternatively, the diagnostic beam 906 may be passed through a polarizer 941 to purify the polarization state of the diagnostic beam 906. In contrast, the broadband optical radiation 142 is not polarized by its nature. In this example, the blocking device 924 is a polarization filter that is oriented parallel to the polarization of the diagnostic light 940 and attenuates the broadband optical radiation 142 by half (because the broadband optical radiation 142 is non-polarized). Depending on the angle between the polarization filter 924 and the direction of the polarization vector of the diagnostic light 940, the diagnostic light 140 may be attenuated by a variable amount. The diagnostic light 940 may not be perfectly polarized, especially after the polarized light 940 is scattered from the target 110. The polarization of the diagnostic light 940 may depend on the viewing angle of the first detection device 920 and the second detection device 930 relative to the direction and trajectory of the diagnostic probe 906. On the other hand, the blocking device 934 is a polarization filter oriented orthogonally to the polarization of the diagnostic light 940, so that only the unpolarized broadband optical radiation 142 passes through the second detector 932, and further, the unpolarized broadband optical radiation 142 will be attenuated by half.

[0151] In this implementation, the signals 923, 933 output from the respective detection devices 920, 930 will be Figure 8 The corresponding signals 823 , 833 shown in are very similar, and the processing of signals 923 , 933 is performed in a similar manner as the signals 823 , 833 described with reference to signals 823 , 833 .

[0152] In other implementations of the metering device 1000, such as Fig.10 As shown, in Figure 2 The blocking devices 224 and 234 implemented in the metering device 200 shown in FIG. 2 can be designed to each include a spectral filter (such as spectral filters 224, 234) and a polarization filter (such as polarization filters 924, 934) arranged in series and used simultaneously. This design can increase the amount of diagnostic light 140 blocked by the blocking device 234.

[0153] In other implementations, Figure 2 The blocking devices 224, 234 implemented in the metrology device 200 shown in FIG. 2 can be designed as spatial filters rather than spectral filters. The two spatial locations that can be distinguished are at two slightly different angles to the normal vector of the pupil or entrance of the detection device 220, 230. Each blocking device 224, 234 includes a lens placed at the location of the pupil, and the two slightly different angles are converted to a location near the focus of the lens. Each blocking device 224, 234 includes a mask placed between the lens and the corresponding light detector 222, 232 (the mask defines an opening (such as a slit or aperture)) so that the diagnostic light 140 passes and the broadband optical radiation 142 is blocked (or vice versa).

[0154] refer to Fig.11, an implementation 1100 of the metrology device 100 is shown in an implementation of an EUV light source 1160. The EUV light source 1160 includes a target delivery system 1155 that directs a stream 1111 of targets 1110 toward a target space 1115 in a chamber 1168. The target space 1115 receives (under control of an actuation system 1174) a beam or train of amplified radiation pulses 1164 generated from an optical source 1172. As described above, each target 1110 includes matter that emits EUV light 1161 when converted to a luminescent plasma 1144. The interaction between the matter within the target 1110 and the radiation pulses 1164 within the target space 1115 converts at least some of the matter in the target 1110 into a luminescent plasma 1144, and the luminescent plasma 1144 emits EUV light 1161. As described above, the luminescent plasma 1144 emits broadband optical radiation 1142 that includes EUV light 1161 because the luminescent plasma 1144 has elements having emission lines in the EUV wavelength range.

[0155] The luminescent plasma 1144 can be considered as a highly ionized plasma with an electron temperature of tens of electron volts (eV). Higher energy EUV 1161 can be generated using fuel materials (target 1110) other than tin, such as terbium (Tb) and gadolinium (Gd). EUV light 1161 generated during de-excitation and recombination of ions is emitted from the luminescent plasma 1144, and at least part of the EUV light 1161 is collected by an optical element 1170 (EUV light collector). The EUV light collector 1170 includes a surface 1171 that interacts with at least part of the emitted EUV light 1161. The surface 1171 of the EUV light collector 1170 can be a reflective surface that is positioned to receive part of the emitted EUV light 1161 and direct the collected EUV light 1161 for use outside the EUV light source 1160 through an output device 1166 that can be a lithography device. Reflective surface 1171 directs collected EUV light 1161 to a secondary focal plane where it is then captured for use by output device 1166. Fig.12 and Fig.13 An exemplary lithographic apparatus is discussed.

[0156] Reflective surface 1171 is configured to reflect light within the EUV wavelength range and may absorb, diffuse, or block light outside the EUV wavelength range. EUV light collector 1170 also includes an aperture 1173 that allows radiation pulses 1164 to pass through EUV light collector 1170 toward target space 1115 .

[0157] The target delivery system 1155 may include a droplet generator disposed within the EUV chamber 1168, and the target delivery system 1155 is arranged to emit a high frequency stream 1111 of droplets (targets 1110) toward a target space 1115. In operation, a radiation pulse 1164 is delivered synchronously with the operation of the droplet generator to deliver a radiation pulse 1164 to convert each droplet (each target 1110) into a luminescent plasma 1144. The delivery frequency of the liquid may be several kilohertz, for example 50 kHz.

[0158] In some implementations, as described above with reference to Figure 5 As discussed, energy from the radiation pulse 1164 is delivered in at least two pulses instead: that is, a pre-pulse (such as 564A) with limited energy is initially delivered to a droplet at a first target location 515_1 in the target space 1115 to vaporize the fuel material into a small cloud that continues to travel along the trajectory, and then a main pulse of energy (such as 564B) is delivered to the cloud at a second target location 515_2 in the target space 1115 to generate a luminous plasma 1144. A trap (e.g., which may be a container) may be provided on the opposite side of the EUV chamber 1168 to capture the fuel (i.e., target material or target 1110) that is not turned into plasma for any reason.

[0159] The droplet generator in the target delivery system 1155 includes a reservoir containing a fuel liquid (e.g., molten tin) as well as a filter and a nozzle. The nozzle is configured to eject droplets of the fuel liquid toward the target space 1115. The droplets of the fuel liquid may be ejected from the nozzle by a combination of pressure within the reservoir and vibration applied to the nozzle by a piezoelectric actuator (not shown).

[0160] The metrology device 1100 includes a control system 1150 (such as the control system 150) in communication with the first and second detection devices 1120, 1130 and the diagnostic system 1105, which is placed at an appropriate location within the chamber 1168 to allow the diagnostic probe 1106 to interact with the target 1110. The EUV light source 1160 includes a control device 1151, which is also in communication with the control system 1150 and other components of the EUV light source 1160, including the optical source 1172, the actuation system 1174, and the target delivery system 1155. As described above, the metrology device 1100 is designed to distinguish between diagnostic light 1140, which is generated from the interaction between the diagnostic probe 1106 and the current target 1110c, and broadband optical radiation 1142, which is emitted from the luminescent plasma 1144.

[0161] refer to Fig.12In some implementations, the metrology device 100 (or 200, 1100) is implemented within an EUV light source 1260 that provides EUV light 1262 to a lithography device 1266 (output device 366). The lithography device 1266 includes: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., EUV light 1262); a support structure (e.g., a mask stage) MT configured to support a patterning device (e.g., a mask or reticle) MA and connected to a first positioner PM configured to accurately position the patterning device; a substrate stage (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; and a projection system (e.g., a reflective 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., including one or more dies) of the substrate W.

[0162] The illumination system IL may include various types of optical components, such as refractive components, reflective components, magnetic components, electromagnetic components, electrostatic components or other types of optical components, or any combination thereof, for guiding, shaping or controlling radiation. The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions (such as whether the patterning device is maintained in a vacuum environment). The support structure MT may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. For example, the support structure MT may be a frame or a stage that can be fixed or moved as needed. For example, the support structure MT can ensure that the patterning device is in a desired position relative to the projection system PS.

[0163] The term "patterning device" should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section (such as to create a pattern in a target portion of a substrate). The pattern imparted to the radiation beam can correspond to a specific functional layer in a device (such as an integrated circuit) created in the target portion. The patterning device can be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include mask types such as binary, alternating phase shift, and 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 so as to reflect an incident radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam reflected by the mirror matrix.

[0164] Similar to the illumination system IL, the projection system PS may include various types of optical components, such as refractive components, reflective components, magnetic components, electromagnetic components, electrostatic components or other types of optical components, or any combination thereof, depending on the exposure radiation used or other factors (such as the use of a vacuum). It may be desirable to use a vacuum for EUV radiation because other gases may absorb too much radiation. Therefore, a vacuum environment may be provided for the entire beam path with the aid of a vacuum wall and a vacuum pump.

[0165] As described herein, the apparatus is reflective (eg, employing a reflective mask).

[0166] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and / or two or more patterning device tables). In such a "multi-stage" machine, the additional tables may be used in parallel, or preparatory steps may be performed on one or more tables while one or more other tables are being used for exposure.

[0167] Also refer to Fig.13 , illuminator IL receives a beam of EUV radiation (EUV light 1262) from an EUV light source 1260. Methods of generating EUV light include, but are not necessarily limited to, utilizing one or more emission lines in the EUV range to convert a material into a plasma state having at least one element (xenon, lithium, or tin). In one such method, a desired plasma, generally referred to as laser produced plasma ("LPP"), may be generated by irradiating a fuel (such as a droplet, stream, or cluster of material having the desired emission line elements) with a laser beam. EUV light source 1260 may be designed similarly to EUV light source 360 ​​or 1160. As described above, the resulting plasma 144 or 1144 emits output radiation (e.g., EUV radiation 361 or 1161 collected using optical element 370 or 1170).

[0168] like Fig.12 and Fig.13 As shown, the radiation beam B is incident on a patterning device (e.g., mask) MA held on a support structure (e.g., mask table) MT and is patterned by the patterning device. After reflection from the patterning device (e.g., mask), the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion of a substrate W. w , Y w , Z wGiven a coordinate system of the substrate, with the aid of a second positioner PW and a position sensor PS2 (e.g. an interferometry device, a linear encoder or a capacitor sensor), the substrate table WT can be accurately moved, for example, to position different target portions in the path of the radiation beam B. Similarly, a first positioner PM and a further position sensor PS1 can be used to accurately position the patterning device (e.g. mask) MA relative to the path of the radiation beam B. The patterning device (e.g. mask) MA and the substrate W may be aligned using the patterning device alignment marks M1, M2 and substrate alignment marks P1, P2.

[0169] The described apparatus may be used in at least one of the following modes:

[0170] 1. In step mode, the support structure (e.g. mask table) MT and the substrate table WT remain substantially stationary while the entire pattern imparted to the radiation beam is projected onto the target portion at one time (i.e. a single static exposure). The substrate table WT is then moved in X w and / or Y w Directionally offset, so that different target parts can be exposed.

[0171] 2. In scanning mode, the support structure (e.g., mask table) MT and the substrate table WT (e.g., along X w and / or Y w ) are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (e.g. mask table) MT may be determined by the magnification and image reversal characteristics of the projection system PS.

[0172] 3. In another mode, the support structure (e.g., mask table) MT is held substantially stationary to hold the programmable patterning device, and the substrate table WT is moved or scanned while projecting a pattern imparted to the radiation beam onto a target portion. In this mode, a pulsed radiation source is typically employed and the programmable patterning device is updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography utilizing a programmable patterning device, such as a programmable mirror array of the type described above.

[0173] Combinations and / or variations of the above-described modes of use or entirely different modes of use may also be employed.

[0174] Fig.13 An implementation of a lithographic apparatus 1266 is shown in more detail, including an EUV light source 1260, an illumination system IL, and a projection system PS. The EUV light source 1260 is constructed as discussed above when describing the EUV light source 360 ​​or 1160.

[0175] Systems IL and PS are also contained in their own vacuum environments. The intermediate focus (IF) of EUV light source 1260 is arranged so that it is located at or near an aperture in the closed structure. The virtual source point IF is an image of the radiation emitting plasma (eg, EUV light 362 or 1162).

[0176] From the aperture of the intermediate focus IF, the radiation beam 1262 passes through an illumination system IL which, in this example, comprises a faceted field mirror arrangement IL1 and a faceted pupil mirror arrangement IL2. These arrangements form a so-called "fly's eye" illuminator which is arranged to provide a desired angular distribution of the radiation beam ILB at the patterning device MA, and a desired uniformity of radiation intensity at the patterning device MA (as shown with reference to IL3). When the beam ILB is reflected at the patterning device MA held by the support structure (mask table) MT, a patterned beam PSB is formed and the patterned beam PSB is imaged by the projection system PS via reflective elements PS1, PS2 onto a substrate W held by a substrate table WT. In order to expose a target portion on the substrate W, the substrate table WT and the patterning device table MT are positioned at an X-axis position. w , Y w , Z w The radiation pulses B are generated when a synchronized motion is performed in the coordinate system to scan the pattern on the patterning device MA through the illumination slit.

[0177] Each system IL and PS is arranged in its own vacuum environment or near-vacuum environment defined by a closed structure similar to EUV chamber 1168. There may typically be more elements in the illumination system IL and the projection system PS than shown. In addition, in addition to Fig.13 In addition to those reflective elements shown in FIG. 8 , there may be one to six additional reflective elements in the illumination system IL and / or the projection system PS.

[0178] Further aspects of the invention are set out in the following numbered clauses.

[0179] 1. A method comprising:

[0180] enabling interaction between a diagnostic system and a current target traveling along a trajectory toward a target space, the current target including a component that emits light when converted to plasma;

[0181] detecting first light at a first detection region, wherein the first light includes light emitted from a plasma generated by a previous target and light generated from an effected interaction between a current target and the diagnostic system;

[0182] detecting second light at a second detection region, wherein the second light includes light emitted from the plasma of the previous target;

[0183] generating an analytical signal based on a first signal generated by the detected first light and a second signal generated by the detected second light; and

[0184] Based on the generated analysis signal, the properties of the current target are estimated.

[0185] 2. The method of clause 1, wherein light emitted from the plasma generated by the target component comprises extreme ultraviolet (EUV) light in the EUV wavelength range and non-EUV light outside the EUV wavelength range.

[0186] 3. The method of clause 1, wherein detecting the second light at the second detection region comprises suppressing at least a portion of the light generated from an interaction between the current target and the diagnostic system.

[0187] 4. A method according to clause 3, wherein suppressing light generated from the interaction between the current target and the diagnostic system includes filtering the light generated from the interaction between the current target and the diagnostic system based on one or more of the following items: spectral properties, polarization properties and / or spatial properties of the light generated from the interaction between the current target and the diagnostic system.

[0188] 5. The method of clause 1, wherein the interaction between the current target and the diagnostic system comprises:

[0189] a first interaction between the current target and a first diagnostic probe of the diagnostic system; and

[0190] A second interaction between the current target and a second diagnostic probe of the diagnostic system.

[0191] 6. The method of clause 5, wherein the second interaction between the current target and the second diagnostic probe occurs at a location and time that is different from the location and time that the first interaction between the current target and the first diagnostic probe occurs.

[0192] 7. The method of clause 1, wherein enabling interaction between the diagnostic system and the current target comprises directing the diagnostic system toward the current target such that the diagnostic system and the current target interact at a region along a trajectory of the current target.

[0193] 8. The method of clause 7, wherein directing the diagnostic system toward the current target comprises directing diagnostic light toward the current target.

[0194] 9. The method of clause 1, wherein estimating the property of the current target comprises estimating one or more of the following:

[0195] The arrival time of the current target at a specific location in space;

[0196] The current target speed, velocity and / or acceleration; and

[0197] The time interval between the arrival of the current target at a specific location in space and the arrival of another target at a specific location in space.

[0198] 10. The method of clause 1, further comprising adjusting one or more properties of the radiation pulse directed toward the target space if the estimated target property is outside of acceptable specifications.

[0199] 11. The method of clause 1, wherein detecting the first light and the second light comprises detecting the first light and the second light during or after a previous target has interacted with the prior radiation pulse.

[0200] 12. The method of clause 1, wherein the spectral bandwidth of light emitted from the plasma of the previous target is significantly wider than the spectral bandwidth of light generated from the interaction between the current target and the diagnostic system.

[0201] 13. The method of clause 1, wherein the light generated from the interaction between the current object and the diagnostic system includes light from the diagnostic system that is reflected or scattered from the current object.

[0202] 14. The method of clause 1, wherein generating the analysis signal from the first signal and the second signal comprises electronically subtracting the second signal from the first signal.

[0203] 15. The method of clause 1, wherein generating the analysis signal from the first signal and the second signal comprises: digitizing the first signal and the second signal, and computing a difference between each time-stamped sample of the first digitized signal and the second digitized signal.

[0204] 16. A method according to claim 1, wherein detecting a second light at a second detection area includes detecting an amount of light generated from an implemented interaction between a current target and a diagnostic system, wherein the detected amount of light generated from an implemented interaction between the current target and the diagnostic system at the second detection area is less than the amount of light generated from an implemented interaction between the current target and the diagnostic system detected at the first detection area.

[0205] 17. An apparatus comprising:

[0206] a diagnostic system configured to diagnostically interact with the current target before the current target enters the target space and while traveling along the trajectory;

[0207] The first detection device is configured to detect a first light, wherein the first light comprises:

[0208] light generated from the interaction between the current target and the diagnostic system, and

[0209] light emitted from a plasma created by a previous target;

[0210] a second detection device configured to detect second light, the second light comprising light emitted from the plasma generated by the previous target; and

[0211] A control system in communication with the first detection device and the second detection device and configured to:

[0212] generating an analytical signal based on the first signal and the second signal generated from the respective outputs of the first detection device and the second detection device; and

[0213] Based on the generated analysis signal, the properties of the current target are estimated.

[0214] 18. The apparatus of clause 17, further comprising a target delivery system configured to release a plurality of targets along a trajectory toward a target space, wherein each target comprises a component that emits extreme ultraviolet (EUV) light when converted to plasma.

[0215] 19. The apparatus of clause 17, further comprising an optical source configured to generate a radiation pulse directed toward a target space, wherein the plasma generated by a previous target is generated as a result of an interaction between the previous target and the prior radiation pulse.

[0216] 20. The apparatus of clause 17, wherein the diagnostic system comprises a diagnostic light beam, and the diagnostic light generated from the interaction between the current target and the diagnostic light beam comprises the diagnostic light beam reflected or scattered from the current target.

[0217] 21. The device according to clause 17, wherein the first detection means comprises a first light detector and the second detection means comprises a second light detector.

[0218] 22. An apparatus according to clause 21, wherein each of the first photodetector and the second photodetector comprises one or more of the following: a photodiode whose output is a voltage signal related to a current generated from the detected light; a phototransistor, a photoresistor, and a photomultiplier tube.

[0219] 23. The device of clause 21, wherein the first light detector and the second light detector have substantially equal viewing angles and collection angles.

[0220] 24. The device according to clause 21, wherein the second detection device comprises a blocking device configured to restrict at least a majority of light generated from the interaction between the current target and the diagnostic system from reaching the second light detector.

[0221] 25. Apparatus according to clause 24, wherein the blocking means comprises a filter in an optical path between the target volume and the second light detector, the filter being configured to suppress light resulting from interaction between the current target and the diagnostic system.

[0222] 26. The device according to clause 25, wherein the filter comprises one or more of the following: a spectral filter and a polarization filter.

[0223] 27. The device according to clause 21, wherein the first detection device comprises a blocking device having a bandpass overlapping with the wavelength of light generated from the interaction between the current target and the diagnostic system.

[0224] 28. An apparatus according to clause 17, wherein the diagnostic system includes a first diagnostic probe and a second diagnostic probe, each diagnostic probe being configured to diagnostically interact with the current target as the current target travels along the trajectory and before entering the target space, each interaction between the current target and the diagnostic probe occurring at a different location and at a different time.

[0225] 29. The apparatus according to clause 17, further comprising:

[0226] an optical source configured to generate a plurality of radiation pulses directed toward a target space; and

[0227] An actuation system, in communication with the control system and the optical source, is configured to adjust one or more properties of a radiation pulse directed toward the target space if the estimated properties are outside of acceptable specifications.

[0228] 30. The apparatus of clause 17, wherein the spectral bandwidth of light generated from the interaction between the current target and the diagnostic system is significantly narrower than the spectral bandwidth of light emitted from the plasma generated by the previous target.

[0229] 31. The device according to clause 17, wherein the control system comprises an electronic module in communication with the first detection device and the second detection device, the electronic module being configured to electronically subtract the second signal from the first signal.

[0230] 32. A method for estimating an attribute of a moving target, the method comprising:

[0231] releasing a current target along a trajectory toward a target space, the current target including a component that emits light when converted to plasma;

[0232] detecting, at a first detection region, diagnostic light generated from an interaction between a current target and the diagnostic system and background light emitted from a plasma generated by a previous target, the spectral bandwidth of the diagnostic light being significantly narrower than the spectral bandwidth of the background light;

[0233] limiting the amount of diagnostic light that passes through to the second detection area and allowing all of the background light to pass through to the second detection area;

[0234] detecting background light at a second detection area;

[0235] Generates an analysis signal based on:

[0236] a signal generated by the detected light at the first detection region, and

[0237] a background signal generated by the detected light at the second detection region; and

[0238] The properties of the current target are estimated based on the generated analysis signal.

[0239] 33. The method of clause 32, wherein detecting at the first detection area and the second detection area comprises detecting background light at the first detection area and the second detection area.

[0240] 34. The method according to clause 32 also includes limiting the amount of background light that passes through to the first detection area, wherein limiting the amount of background light that passes through to the first detection area allows a portion of the background light to reach the first detection area, and the allowed portion of the background light is on the same scale in power as the diagnostic light that reaches the first detection area.

Claims

1. A method for measuring a target along a trajectory of the target, comprising: enabling interaction between a diagnostic system and a current target traveling along a trajectory toward a target space, the current target including a component that emits light when converted to plasma; detecting first light at a first detection region, wherein the first light includes light emitted from the plasma generated by a previous target and light generated from the interaction achieved between the current target and the diagnostic system; detecting second light at a second detection region, wherein the second light includes light emitted from a plasma of the previous target; generating an analytical signal based on a first signal generated by the detected first light and a second signal generated by the detected second light; as well as Based on the generated analysis signal, a property of the current target is estimated.

2. The method of claim 1 , wherein the light emitted from the plasma generated by the target component comprises: Extreme ultraviolet (EUV) light in the EUV wavelength range and non-EUV light outside the EUV wavelength range. 3 . The method of claim 1 , wherein detecting second light at the second detection region comprises suppressing at least a portion of the light generated from the interaction between the current target and the diagnostic system.

4. The method of claim 3, wherein suppressing light generated from the interaction between the current target and the diagnostic system comprises: The light generated from the interaction between the current target and the diagnostic system is filtered based on one or more of: spectral properties, polarization properties, and / or spatial properties of the light generated from the interaction between the current target and the diagnostic system.

5. The method of claim 1, wherein the interaction between the current target and the diagnostic system comprises: a first interaction between the current target and a first diagnostic probe of the diagnostic system; as well as A second interaction between the current target and a second diagnostic probe of the diagnostic system.

6. The method of claim 5, wherein the second interaction between the current target and the second diagnostic probe occurs at a location and time different from the location and time of the first interaction between the current target and the first diagnostic probe.

7. The method according to claim 1, wherein implementing the interaction between the diagnostic system and the current target comprises: The diagnostic system is directed toward the current target such that the diagnostic system and the current target interact at a region along a trajectory of the current target. 8 . The method of claim 7 , wherein directing the diagnostic system toward the current target comprises directing diagnostic light toward the current target.

9. The method of claim 1 , wherein estimating the property of the current target comprises estimating one or more of: The arrival time of the current target at a specific position in space; the speed, velocity and / or acceleration of the current target; and The time interval between the arrival of the current target at a specific position in the space and the arrival of another target at the specific position in the space.

10. The method of claim 1, further comprising adjusting one or more properties of a radiation pulse directed toward the target space if the estimated target property is outside of acceptable specifications.

11. The method of claim 1, wherein detecting the first light and the second light comprises detecting the first light and the second light during or after a previous target has interacted with a prior radiation pulse.

12. The method of claim 1, wherein a spectral bandwidth of the light emitted from the plasma of the previous target is significantly wider than a spectral bandwidth of the light generated from the interaction between the current target and the diagnostic system.

13. The method of claim 1, wherein the light generated from the interaction between the current object and the diagnostic system includes light from the diagnostic system that is reflected or scattered from the current object.

14. The method of claim 1, wherein generating the analysis signal from the first signal and the second signal comprises electronically subtracting the second signal from the first signal.

15. The method of claim 1, wherein generating the analysis signal from the first signal and the second signal comprises: The first signal and the second signal are digitized, and a difference between each time-stamped sample of the first digitized signal and the second digitized signal is calculated.

16. A method according to claim 1, wherein detecting a second light at the second detection area includes detecting an amount of the light generated from the interaction achieved between the current target and the diagnostic system, wherein the detected amount of the light generated from the interaction achieved between the current target and the diagnostic system at the second detection area is less than the amount of the light generated from the interaction achieved between the current target and the diagnostic system detected at the first detection area.

17. An apparatus for measuring an object along its trajectory, comprising: a diagnostic system configured to diagnostically interact with the current target before the current target enters the target space and as it travels along the trajectory; A first detection device is configured to detect a first light, wherein the first light comprises: light generated from interaction between the current target and the diagnostic system, and light emitted from a plasma created by a previous target; a second detection device configured to detect second light, the second light comprising the light emitted from the plasma generated by the previous target; and a control system in communication with the first detection device and the second detection device and configured to: generating an analytical signal based on first and second signals generated from respective outputs of the first and second detection devices; and Based on the generated analysis signal, a property of the current target is estimated.

18. The apparatus of claim 17, further comprising a target delivery system configured to release a plurality of targets along a trajectory toward the target space, wherein each target includes a component that emits extreme ultraviolet (EUV) light when converted to plasma.

19. The apparatus of claim 17, further comprising an optical source configured to generate a radiation pulse directed toward the target space, wherein the plasma generated by the previous target is generated as a result of an interaction between the previous target and a prior radiation pulse.

20. The apparatus of claim 17, wherein the diagnostic system comprises a diagnostic light beam, and the diagnostic light generated from the interaction between the current target and the diagnostic light beam comprises the diagnostic light beam reflected or scattered from the current target.

21. The device of claim 17, wherein the first detection device comprises a first light detector and the second detection device comprises a second light detector.

22. An apparatus according to claim 21, wherein each of the first light detector and the second light detector comprises one or more of the following items: a photodiode, the output of which is a voltage signal related to the current generated from the detected light; a phototransistor, a photoresistor, and a photomultiplier tube.

23. The device of claim 21, wherein the first light detector and the second light detector have approximately equal viewing angles and collection angles.

24. The apparatus of claim 21, wherein the second detection device comprises a blocking device configured to restrict at least a majority of the light generated from the interaction between the current target and the diagnostic system from reaching the second light detector.

25. The apparatus of claim 24, wherein the blocking device comprises a filter in an optical path between the target space and the second light detector, the filter being configured to suppress the light generated from the interaction between the current target and the diagnostic system.

26. The apparatus of claim 25, wherein the filter comprises one or more of: a spectral filter and a polarization filter.

27. The apparatus of claim 21, wherein the first detection device comprises a blocking device having a passband that overlaps with a wavelength of the light generated from the interaction between the current target and the diagnostic system.

28. The apparatus of claim 17, wherein the diagnostic system comprises a first diagnostic probe and a second diagnostic probe, each diagnostic probe being configured to diagnostically interact with the current target as the current target travels along the trajectory and before entering the target space, each interaction between the current target and the diagnostic probe occurring at a different location and at a different time.

29. The apparatus of claim 17, further comprising: an optical source configured to generate a plurality of radiation pulses directed toward the target space; as well as An actuation system is in communication with the control system and the optical source, the actuation system being configured to adjust one or more properties of a radiation pulse directed toward the target space if the estimated property is outside of acceptable specifications.

30. The apparatus of claim 17, wherein a spectral bandwidth of the light generated from the interaction between the current target and the diagnostic system is significantly narrower than a spectral bandwidth of the light emitted from the plasma generated by the previous target.

31. The apparatus of claim 17, wherein the control system comprises an electronics module in communication with the first detection device and the second detection device, the electronics module being configured to electronically subtract the second signal from the first signal.

32. A method for estimating an attribute of a moving target, the method comprising: releasing a current target along a trajectory toward a target space, the current target including a component that emits light when converted to plasma; detecting, at a first detection region, diagnostic light generated from an interaction between the current target and a diagnostic system and background light emitted from the plasma generated by a previous target, the spectral bandwidth of the diagnostic light being significantly narrower than the spectral bandwidth of the background light; limiting the amount of the diagnostic light that passes through to the second detection area and allowing all of the background light to pass through to the second detection area; detecting the background light at the second detection area; Generates an analysis signal based on: a signal generated by the detected light at the first detection region, and a background signal generated by the detected light at the second detection region; And based on the generated analysis signal, the property of the current target is estimated.

33. The method of claim 32, wherein detecting at the first detection zone and the second detection zone comprises detecting the background light at the first detection zone and the second detection zone.

34. The method of claim 32, further comprising limiting the amount of background light that passes through to reach the first detection area, wherein limiting the amount of background light that passes through to reach the first detection area allows a portion of the background light to reach the first detection area, the allowed portion of the background light being on the same scale in power as the diagnostic light that reaches the first detection area.

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