阅读说明：本技术 确定极紫外光源中目标的运动特性 (Determining motion characteristics of an object in an extreme ultraviolet light source ) 是由 R·J·拉法克 于 2020-01-27 设计创作，主要内容包括：一种装置包括：诊断系统,被配置为在当前目标进入目标空间之前并且与沿着轨迹(TR)行进的当前目标(110c)诊断地交互；第一检测装置(120),被配置为检测第一光；第二检测装置(130),被配置为检测第二光；以及控制系统(150),与第一检测装置和第二检测装置通信。第一光包括：从当前目标与诊断系统之间的交互产生的光(140),以及从由先前目标产生的等离子体发射的光(142)。第二光包括：从由先前目标产生的等离子体发射的光(142)。控制系统(150)被配置为：基于从第一检测装置和第二检测装置的相应的输出产生的第一信号和第二信号,产生分析信号；以及基于产生的分析信号,估计当前目标的属性。(An apparatus comprising: 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) in communication with the first detection device and the second detection device. The first light includes: light (140) resulting from interaction between the current target and the diagnostic system, and light (142) emitted from a plasma generated by a previous target. The second light includes: light (142) emitted from a plasma generated by a previous target. The control system (150) is configured to: generating an analysis signal based on first and second signals generated from respective outputs of the first and second detection means; and estimating a property of the current target based on the generated analysis signal.)

1. A method, 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 comprises light emitted from the plasma generated by a previous target and light generated from the effected interaction between the current target and the diagnostic system;

detecting second light at a second detection region, wherein the second light comprises light emitted from a plasma of the previous target;

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

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: EUV light in an Extreme Ultraviolet (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 resulting 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: filtering the light resulting from the interaction between the current target and the diagnostic system based on one or more of: spectral, polarization, and/or spatial properties of the light resulting 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; and

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 different location and time than the first interaction between the current target and the first diagnostic probe.

7. The method of claim 1, wherein enabling the 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 the current target trajectory.

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 attribute of the current target comprises estimating one or more of:

a time of arrival of the current target at a particular location in space;

a speed, velocity, and/or acceleration of the current target; and

a time interval between an arrival of the current target at a particular location in space and an arrival of another target at the particular location in 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 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 preferential radiation pulse.

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

13. The method of claim 1, wherein the light resulting from the interaction between the current target and the diagnostic system comprises light from the diagnostic system that is reflected or scattered from the current target.

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 and second signals are digitized and a difference between each time-stamped sample of the first and second digitized signals is calculated.

16. The method of claim 1, wherein detecting second light at the second detection region comprises detecting an amount of the light resulting from the achieved interaction between the current target and the diagnostic system, wherein the detected amount of the light resulting from the achieved interaction between the current target and the diagnostic system at the second detection region is less than the amount of the light resulting from the achieved interaction between the current target and the diagnostic system that was detected at the first detection region.

17. An apparatus, comprising:

a diagnostic system configured to diagnostically interact with the current target traveling along the trajectory before the current target enters the target space;

a first detection device configured to detect a first light, the first light comprising:

light resulting from interaction between the current target and the diagnostic system, an

Light emitted from a plasma generated by a previous target;

a second detection device configured to detect a 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 analysis signal based on first and second signals generated from respective outputs of the first and second detection means; and is

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 comprises a component that Emits Ultraviolet (EUV) light when converted to plasma.

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

20. The apparatus of claim 17, wherein the diagnostic system comprises a diagnostic light beam, and the diagnostic light resulting 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 apparatus of claim 17, wherein the first detection device comprises a first light detector and the second detection device comprises a second light detector.

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

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

24. The apparatus of claim 21, wherein the second detection apparatus 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 configured to suppress the light resulting 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: spectral filters and polarization filters.

27. The apparatus of claim 21, wherein the first detection means comprises a blocking device having a band pass that overlaps with a wavelength of the light resulting 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 configured to diagnostically interact with the current target before the current target travels along the trajectory and enters the target space, each interaction between the current target and a 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; and

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

30. The device of claim 17, wherein a spectral bandwidth of the light resulting from the interaction between the current target and the diagnostic system is substantially narrower than a spectral bandwidth of the light emitted from the plasma resulting from the previous target.

31. The device 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 configured to electronically subtract the second signal from the first signal.

32. A method of estimating attributes 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 resulting from interaction between the current target and a diagnostic system and background light emitted from the plasma resulting from a previous target, the diagnostic light having a spectral bandwidth substantially narrower than a spectral bandwidth of the background light;

limiting the amount of the diagnostic light that passes through to a second detection region and allowing all of the background light to pass through to the second detection region;

detecting the background light at the second detection area;

generating an analytical signal based on:

a signal generated by the detected light at the first detection area, an

A background signal generated by the detected light at the second detection area; and estimating a property of the current target based on the generated analysis signal.

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

34. The method of claim 32, further comprising limiting an amount of background light passing through to the first detection region, wherein limiting the amount of background light passing through to the first detection region allows a portion of the background light to reach the first detection region, the allowed portion of background light being at the same scale in power as the diagnostic light reaching the first detection region.

Technical Field

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

Background

Extreme Ultraviolet (EUV) light, e.g., light having a wavelength of about 50nm or shorter electromagnetic radiation (sometimes also referred to as soft x-rays) and including a wavelength of about 13nm, may be used in a lithographic process to produce extremely small features in a substrate, e.g., a silicon wafer.

Methods of producing EUV light include, but are not necessarily limited to: a material with, for example, xenon, lithium or tin is converted into an emission line in the EUV range in the plasma state. In one such method, commonly referred to as laser produced plasma ("LPP"), the desired plasma may be produced by irradiating the target material (e.g., in the form of droplets, plates, ribbons, streams or clusters of material) with an amplified beam, which may be referred to as a drive laser. For this process, plasma is typically generated in a sealed container (e.g., a vacuum chamber) and monitored using various types of dosing equipment.

Disclosure of Invention

In some general aspects, a method includes 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. The method further comprises the following steps: the method includes detecting first light at a first detection area, detecting second light at a second detection area, 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 a current target based on the generated analysis signal. The first light includes light emitted from a plasma generated by a previous target and light generated from an effected interaction between a present target and the diagnostic system. The second light includes light emitted from a previous target plasma.

Implementations may include one or more of the following features. For example, the light emitted from the plasma generated by the target component may include: extreme Ultraviolet (EUV) light in the EUV wavelength range and non-EUV light outside the EUV wavelength range.

The second light at the second detection region may be detected by suppressing at least part of the light resulting from interaction between the current target and the diagnostic system. Light resulting from interaction between the current target and the diagnostic system may be suppressed by filtering light resulting from interaction between the current target and the diagnostic system based on one or more of: spectral, polarization, and/or spatial properties of light resulting from interaction between the current target and the diagnostic system.

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 different location and time than the first interaction between the current target and the first diagnostic probe.

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 a trajectory of the current target. The diagnostic system may be directed toward the current target by directing a diagnostic light beam toward the current target.

The attributes of the current target may be estimated by estimating one or more of: the time of arrival of the current target at a particular location in space; the speed, velocity, and/or acceleration of the current target; and a time interval between the arrival of the current target at a particular location in space and the arrival of another target at a particular location in space.

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

The first light and the second light may be detected by detecting the first light and the second light during or after a previous (e.g., immediately previous) target has interacted with the preferential radiation pulse.

The spectral bandwidth of light emitted from the plasma of the previous target may be significantly wider than the spectral bandwidth of light resulting from the interaction between the current target and the diagnostic system. The light resulting 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.

The analysis signal may be generated from the first signal and a 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 a difference between each time-stamped sample of the first digitized signal and the second digitized signal.

The second light at the second detection region may be detected by detecting an amount of light resulting from an effected interaction between the present target and the diagnostic system. The detected amount of light resulting from an effected interaction between the current target and the diagnostic system at the second detection region may be less than the amount of light resulting from an effected interaction between the current target and the diagnostic system detected at the first detection region.

In other general aspects, an apparatus includes: a diagnostic system configured to diagnostically interact with a current target traveling along a trajectory before the current target enters a target space; a first detection device configured to detect the first light; a second detection device configured to detect the second light; and a control system in communication with the first detection device and the second detection device. The first light includes: light resulting from 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: generating an analysis signal based on first and second signals generated from respective outputs of the first and second detection means; and estimating a property of the current target based on the generated analysis signal.

Implementations may include one or more of the following features. For example, the apparatus may further include an object delivery system configured to release the plurality of objects along a trajectory toward the target space. Each target includes components that Emit Ultraviolet (EUV) light when converted to plasma.

The apparatus may also include an optical source configured to generate pulses of radiation directed toward the target space. The plasma generated by the previous target is generated as a result of interaction between the previous target and the preferential radiation pulse.

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

The first detection means may comprise a first light detector and the second detection means may comprise a second light detector. Each of the first and second light detectors may include one or more of: 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. The first and second photodetectors may have approximately equal viewing and collection angles. The second detection arrangement may comprise a blocking device configured to restrict at least a majority of light resulting from interaction between the current target and the diagnostic system from reaching the second light detector. The blocking means may comprise a filter in the optical path between the target space and the second light detector, the filter being configured to suppress light resulting from interaction between the current target and the diagnostic system. The filter may include one or more of the following: spectral filters, polarization filters, and spatial filters. The first detection means may comprise a blocking device having a band pass that overlaps with the wavelength of light resulting from interaction between the current target and the diagnostic system.

The diagnostic system may include a first diagnostic probe and a second diagnostic probe, each configured to diagnostically interact with a 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.

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 pulse directed toward the target space if the estimated properties are outside acceptable specifications.

The spectral bandwidth of light resulting 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.

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

In other general aspects, a method of estimating a property 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, at a first detection region, diagnostic light resulting from interaction between a current target and a diagnostic system and background light emitted from a plasma generated by a previous target, the spectral bandwidth of the diagnostic light being substantially narrower than the spectral bandwidth of the background light. The method includes limiting an amount of diagnostic light that passes through to the second detection region and allowing all of the background light to pass through to the second detection region. The method further includes detecting background light at the second detection region 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 a property of the current target based on the generated analysis signal.

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

The method may further comprise limiting the amount of background light passing through to the first detection region. Limiting the amount of background light that passes through to reach the first detection region may allow a portion of the background light to reach the first detection region, the allowed portion of the background light being at the same scale in power as the diagnostic light reaching the first detection region.

Drawings

FIG. 1A is a schematic and block diagram of a metrology device including first and second detection devices for determining one or more properties of a target directed toward a target space;

FIG. 1B is a schematic diagram of an implementation of a diagnostic region where a diagnostic probe interacts with each target and target space;

FIG. 2 is a schematic and block diagram of an implementation of the metering device of FIG. 1A;

FIG. 3A is a schematic and block diagram of a first view of an implementation of the metrology device of FIG. 1A implemented in an Extreme Ultraviolet (EUV) light source;

FIG. 3B is a schematic and block diagram of a second view of an implementation of the metrology device of FIG. 1A implemented in the Extreme Ultraviolet (EUV) light source of FIG. 3A;

FIG. 4 is a block diagram of an implementation of a control device of the EUV light source of FIGS. 3A and 3B, the block diagram also including an implementation of a control system of the metrology device of FIG. 1A or 2;

FIG. 5 is a schematic and block diagram of an implementation of an optical source of the EUV light source of FIGS. 3A and 3B, and also shows radiation pulses from the optical source interacting with a target in a target space;

FIG. 6A is a schematic and block diagram of an implementation of a diagnostic system that produces a single diagnostic beam;

FIG. 6B is a schematic and block diagram of an implementation of a diagnostic system that produces two diagnostic light beams from a single light source;

FIG. 6C is a schematic and block diagram of an implementation of a diagnostic system that produces two diagnostic light beams from respective light sources;

FIG. 7 is a flow chart of a process performed by the metering device of FIG. 1A, FIG. 2, FIG. 3A or FIG. 3B;

FIG. 8 is a schematic illustration of an example of output signals from respective first and second detection devices of the metering device of FIG. 1A, FIG. 2, FIG. 3A or FIG. 3B, showing signal processing performed by the control system and an analysis signal resulting from the signal processing;

FIG. 9 is a schematic and block diagram of another implementation of the metering device of FIG. 1A;

FIG. 10 is a schematic and block diagram of another implementation of the metering device of FIG. 1A;

FIG. 11 is a schematic and block diagram of an implementation of an EUV light source including an implementation of the metrology device of FIG. 1A;

FIG. 12 is a block diagram of an implementation of an EUV light source that may include the apparatus of FIG. 1A; and is

Figure 13 is a block diagram showing more detail of the EUV light source of figure 12.

Detailed Description

Referring to fig. 1A, the metrology device 100 includes a diagnostic system 105, the diagnostic system 105 configured to generate one or more diagnostic probes 106, the diagnostic probes 106 diagnostically interacting with the in-plane target 110c traveling along the trajectory TR and before the in-plane target 110c enters the target space 115. The metrology device 110 may be implemented in an EUV light source (such as the EUV light source 360 shown in fig. 3A and 3B) that uses a target 110 that is at least partially converted to a plasma 114 by interacting the target 100 with a radiation pulse 364 (as shown in fig. 3A and 3B) in a target space 115.

Although the trajectory TR may partially overlap the Z-axis and/or the Y-axis, the trajectory TR generally extends along the-X-axis. The metrology device 100 comprises a first detection device 120, the first detection device 120 being configured to detect the first light. The first light includes light 140 resulting from interaction between the current target 110c and the diagnostic system 105 and light 142 emitted from plasma 144 generated by one or more previous targets 110p within the target space 115. The previous target 110p is any target that reaches the target space 115 before the current target 110c reaches 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 110 c. In fig. 1A, the previous target 110p has generated a 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 altered by being at least partially converted to a plasma 144. Thus, the previous target 110p is schematically depicted as being different from the current target 110c in fig. 1A (as well as fig. 2 and 3A). The schematic depictions of the target 110, the current target 110c, and the previous target 110p in fig. 1-3A are for illustration purposes only. The actual geometry, density and properties of these objects may be different from those shown in fig. 1-3A. For example, the current target 110c may be a shape other than a sphere, and the previous target 110p may assume a shape other than the shape shown or may be a dispersed collection of particles in space.

The metering device 100 also includes a control system 150, the control system 150 being in communication with the first sensing device 120. The control system 150 is configured to estimate one or more attributes of the current target 110c based on at least the output from the first detection device 120. The estimated attribute of the current target 110c may be an attribute related to the motion, 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 the following: the arrival time of the current target 110c at a particular location in space (such as the target space 115); the speed, velocity, or acceleration of the current target 110 c; or the time interval between the arrival of the current target 110c at a particular location in space and the arrival of another target at that particular location in space. Thus, the determined or estimated properties of the current target 110c may be used by the EUV light source 360 to adjust or control aspects of the subsequent radiation pulses directed to the target space 115 to ensure that when the current target 110 '(which current target 110' may be the current target 110c) reaches the target space 115 (see fig. 3A and 3B) the subsequent radiation pulses reach the target space 115 (or an optimal location within the target space 115).

A plurality 111 of targets (each generally designated 110) are directed along a trajectory TR toward a target space 115. Each target 110 includes components that Emit Ultraviolet (EUV) light, such as EUV light 361 shown in fig. 3A and 3B, when converted to plasma 144. These targets 110 travel (e.g., ballistically) from the generation area (such as from the target delivery system 155) toward the target space 115. Attributes (such as arrival or motion) of the present target 110' are estimated by probing the present target 110c as the present target 110c travels along the trajectory TR with the diagnostic probe(s) 106 generated by the diagnostic system 105 under control of the control system 150, detecting aspects of the interaction between the diagnostic probe(s) 106 and the current target 110c, and analyzing these detected aspects.

Unfortunately, there may be a significant 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 plasma 144 is generated by one or more previous targets 110p that entered target space 115 before current target 110c interacted with diagnostic probe(s) 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 broadband optical radiation 142 is much greater than the intensity of light 140. Thus, the broadband optical radiation 142 interferes with the signals resulting from the direct interaction between the diagnostic probe(s) 106 and the current target 110 c. Thus, the first detection device 120 detects (wanted signal) light 140 generated from the interaction between the current target 110c and the diagnostic probe(s) 106 and (unwanted signal) light 142 emitted from a plasma 144 generated by one or more previous targets 110 p.

The broadband optical radiation 142 is largely unpolarized. Furthermore, the broadband optical radiation 142 tends to include three different wavelength bands as follows. The broadband optical radiation 142 includes EUV light (such as EUV light 361 collected in an EUV light source 361 shown in fig. 3A and 3B). The EUV light has a wavelength range of about 50nm or less. Broadband optical radiation 142 also includes light having a wavelength range that overlaps with the wavelength of light 140 produced as a result of interaction of diagnostic probe(s) 106 and target 110. Finally, the broadband optical radiation 142 comprises light having a wavelength range comprising a range of wavelengths that can be detected by the first detection device 120.

The metrology device 100 is designed to effectively suppress the effects 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 properties of the current target 110c and thereby estimate characteristics of the present target 110'. The metrology device 100, and in particular the control system 150, is able to determine properties of the present target 110c by suppressing the influence of the broadband optical radiation 142 on the calculations by directly preventing or reducing the amount of light 140 resulting from interaction between the present target 110c and the diagnostic probe(s) 106 reaching the second detection device 130 arranged in the vicinity of 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 110 p. Thus, the second light has less (or none if the blockage is perfect) light 140 generated due to the interaction between the current target 110c and the diagnostic probe(s) 106. Thus, the second detection means 130 obtains a very good representation of the unwanted plasma flash leakage signal present in the signal detected at the first detection means 120, which contributes to noise.

In other words, the first detection apparatus 120 and the second detection apparatus 130 are configured or positioned to receive light 140 and broadband optical radiation 142 generated as a result of interaction between the present target 110c and the diagnostic probe(s) 106. Except that the first detection means 120 is more sensitive to light 140 and the second detection means 130 is more sensitive to broadband optical radiation 142.

The control system 150 communicates with the second sensing device 130 to receive the output from the second sensing device 130 at the same time the control system 150 receives the output from the first sensing device 120. As discussed in more detail with reference to fig. 7 and 8, 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 resulting from the interaction between the current target 110c and the diagnostic probe(s) 106. In this manner, the metrology device 100 is able to accurately and efficiently estimate the attributes of the current target 110c relative to a prioritized design that uses only the output from a single detection device.

Furthermore, 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 110 c. Furthermore, the metrology device 100 does not need to (or perform) an analysis that would require complete suppression of the signal from the broadband optical radiation 142 emitted by the plasma 144 previously generated by the target 110 p. 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 the removal of spectral components from the broadband optical radiation 142. In practice, 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 may still leak through any available bandwidth filter. The metrology device 100 does not require the broadband optical radiation 142 to be substantially blocked or removed.

In general, the spectral bandwidth of light 140 resulting from the interaction between the current target 110c and the diagnostic probe(s) 106 is significantly narrower than the spectral bandwidth of light 142 emitted from the plasma 144 generated by the previous target 110 p. Thus, the light 142 is referred to as broadband optical radiation. For example, the spectral bandwidth of light 140 may be several hundred times lower than the total spectral bandwidth of light 142.

References to the designation of "first light" and "second light" by the respective first detection device 120 and second detection device 130 do not imply a particular temporal order of arrival at the respective first detection device 120 and second detection device 130. The terms "first" and "second" are used only to distinguish two different devices 120, 130 and do not convey any information about the timing of the first and second lights. For example, the first light (detected by the first detection device 120) may be present at the first detection device 120 and detected at the first detection device 120 at the same time as the second light is detected by the second detection device 130. Alternatively, the first light may reach the first detection device 120 before the second light reaches the second detection device 130 or after the second light reaches the second detection device 130.

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

For example, in order to accurately adjust aspects of subsequent radiation pulses that will interact with a current target 110 '(the current target 110' may be a current target 110c) in the target space 115, the motion of the current target 110c needs to be estimated. To a first approximation, the location of the current target 110c is related to the starting location, the velocity of the current target 110c, and the acceleration of the current target 110 c. In order to make the first approximation 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 changes (in this example, it decelerates) after the previous plasma event (which occurred when the previous target 110p interacted with the preferential radiation pulse) because there is an impact deceleration of the current target 110c due to the force from the plasma 144. Thus, as shown in the implementation of fig. 1B, it may be beneficial to measure a property (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 preferential radiation pulse). After the interaction between the previous target 110p and the preferential radiation pulse, the current target 110c decelerates rapidly, and then as the deceleration drops substantially after a short period of time, the velocity of the current target 110c may be considered substantially constant. The current target 110c decelerates from the rate (prior to generating plasma from the previous target 110 p) to the current rate. Because the diagnostic probe 106 is close enough to the target space 115 (and the plasma 144 created by the interaction of the previous target 110p and the preferential radiation pulse), it can be safely assumed that no other forces act to alter the current target 110c and that the estimation of the properties of the current target 110c is more accurate. Thus, the metrology device 100 is even more useful in this implementation depicted in FIG. 1B, where the first detection device 120 detects not only diagnostic light (light 140) but also broadband optical radiation 142 having 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 practice, 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 with the diagnostic probe 106 closer to the target space 115 and thus closer to the plasma 144.

Referring to fig. 2, an implementation of a metering device 200 is shown. The metering device 200 includes a first sensing device 220 and a second sensing 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 and second light detectors 222, 232 may include one or more of a photodiode, a phototransistor, a photoresistor, and a photomultiplier tube. In other implementations, each of the first and second photodetectors 222, 232 includes one or more thermal detectors, such as pyroelectric detectors, bolometers, or calibrated Charge Coupled Devices (CCDs) or CMOSs.

The outputs of the first and second photodetectors 222, 232 are respective signals 223, 233 (such as voltage signals) related to the current generated from the light detected at the respective first and second photodetectors 222, 232. The first photodetector 222 and the second photodetector 232 have substantially equal viewing and collection angles. For example, the viewing and collection angles of the first and second photodetectors 222, 232 may be approximately equal in the XYZ coordinate system. It may be assumed that the first light detector 222 is a linear detector such that the signal output by the first light detector 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 light detector 232 is also a linear detector.

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 an analysis of the signals 223, 233 output from the detectors 222, 232, respectively.

The diagnostic system 205 generates a diagnostic beam 206 as the diagnostic probe 106. The diagnostic beam 206 is directed towards the trajectory TR such that light 140 is generated when the current target 110c passes through the diagnostic beam 206. In some implementations, the diagnostic light beam 206 has a center 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 110 c. The first detection means 220 comprises a blocking device 224, which blocking device 224 may be a spectral filter having a transmission range comprising the wavelength of the light 140 resulting from the interaction between the current target 110c and the diagnostic light beam 206. For example, as shown, the blocking device 224 may be a band pass filter having a band pass Δ λ centered at the wavelength of the diagnostic beam 206 of the diagnostic system 205. As described above, the blocking device 224 cannot suppress all of the broadband optical radiation 142, and thus at least a majority of the broadband optical radiation 142 leaks through the blocking device 224 and reaches the first photodetector 222.

The second detection means 230 also comprises a blocking device 234. The blocking device 234 is configured to limit at least a portion (or a majority) of the light 140 resulting 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 configured to suppress light 140 resulting from 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 Δ λ that is detuned from the center wavelength of the diagnostic beam 206 by an amount, such as approximately 20-50 nanometers (nm). Because the light 140 resulting from the interaction between the diagnostic light beam 206 and the current target 110c is weak and spectrally narrow (particularly with respect to the light 142), the light 140 may be blocked or greatly suppressed below an acceptable noise level with the blocking device 234. Furthermore, because the spectrum of the broadband optical radiation 142 (particularly with respect to the light 140) is very broad, 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 photodetector 232 is the same as the amount of optical power that leaks from the broadband optical radiation 142 to the first photodetector 222.

The signal sampled by the second detector 232 is in a different spectral band (or wavelength range) and also in a different spatial location than the signal sampled by the first detector 222. However, it may 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.

In some implementations, blocking device 224 is a separate structure from first light detector 222 and blocking device 224 operates independently of first light detector 222, and blocking device 234 is a separate structure from second light detector 232 and blocking device 234 operates independently of second light detector 232. This is shown in figure 2. It is alternatively possible that blocking device 224 and first light detector 222 are to be integrated into a single device or single device, and blocking device 234 and second light detector 232 are to be integrated into a single device or single device. For example, a single device may be a sensor that only senses light of a particular polarization or a particular wavelength range.

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

Referring to fig. 3A and 3B, the metrology device 100 (or 200) is implemented in an EUV light source 360 to measure one or more properties of the target 100. 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, which has been generated by interaction between the target 110 and a radiation pulse 364, to an output device 366. As described above, the metrology device 100 (or 200) measures and analyzes one or more movement attributes (such as velocity, and acceleration) of the current target 110c as the current target 110c travels along the trajectory TR toward the target space 115. 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 a target (or axial) direction that lies 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-direction and the Z-direction that are perpendicular to the-X-direction. Furthermore, 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 at the time of release of the target 110 and the environment within the chamber 368.

The EUV light source 360 generally includes an EUV light collector 370, an optical source 372, an actuation system 374 in communication with the optical source 372, and a control 351 in communication with the control system 150 and the target delivery system 155, the optical source 372, and the actuation system 374.

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

Optical source 372 generates pulsed beam of radiation 364 and directs pulsed beam of radiation 364 toward target space 115 generally along the Z-direction (although pulsed beam of radiation 364 may be angled with respect to the Z-direction). In the schematically represented fig. 3A, a pulsed beam of radiation 364 is shown directed in the-Y direction. The optical source 372 includes: a light source that generates radiation pulses 364, a beam delivery system that includes an optical steering assembly that changes the direction or angle of the radiation pulse beam 364, and a focusing assembly that focuses the radiation pulse beam 364 into the target space 115. Exemplary optical turning assemblies include optical elements (such as lenses and mirrors) that turn or direct pulsed beams of radiation 364 as desired by refraction or reflection. An actuation system 374 may be used to control or move various features of the optical components of the beam delivery system and focusing assembly, as well as to adjust aspects of the light source that generates the radiation pulses 364. An implementation of optical source 372 is discussed below with reference to FIG. 5.

An actuation system 374 is coupled to the components of optical source 372 and is also in communication with control device 351 and under the control of control device 351. The actuation system 374 can modify or control the relative positioning between the radiation pulse 364 and the target 110 in the target space 115. For example, the actuation system 374 is configured to adjust one or more of the timing of the release of the radiation pulse 364 and the direction in which the radiation pulse 364 travels.

The target delivery system 155 is configured to release the stream (or streams 111) of targets 110 at a particular rate. The metrology device 100 takes this rate into account when determining the total amount of time required to perform the measurement and analysis of the moving property (or properties) of the current target 110c and to effect changes to other aspects or components of the EUV light source 360 based on the measurement and analysis. For example, control system 150 may communicate the results of the measurements and analysis to control device 351, and control device 351 determines how to adjust one or more signals to actuation system 374 to adjust one or more characteristics of radiation pulses 364 directed to target space 115.

Adjustment of one or more characteristics of radiation pulses 364 can improve the relative alignment between current target 110' and radiation pulses 364 in target space 115. Target 110' is now the target that has entered target volume 115 when radiation pulse 364 (just adjusted) arrives in target volume 115. Such adjustment of one or more characteristics of the radiation pulse 364 improves the interaction between the present target 110' and the radiation pulse 364 and increases the amount of EUV light 361 produced by such interaction. As shown in FIG. 3A, the target 110p has previously interacted with a preferential radiation pulse (not shown) to produce a plasma 144 of emitted light 142.

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

In other implementations, the current goal 110' is another goal, i.e., a goal other than the current goal 110c, and follows the current goal 110c in time. In these implementations, the adjustment of one or more characteristics of the radiation pulse 364 occurs over a relatively long time frame such that it is not feasible to affect the interaction between the current target 110c (whose motion properties of the current target 110c have just been analyzed) and the radiation pulse 364. On the other hand, it is feasible to influence 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 after the analysis of the motion attribute of the current target 110c is completed to the time the current target 110c enters the target space 115. Depending on the relatively long time frame, another object may be adjacent to the current object 110 c. Alternatively, another target may be adjacent to an intermediate target, which is adjacent to the current target 110 c. In these other implementations, it is assumed that the other target (which is not the current target 110c) is traveling with a movement attribute that is sufficiently similar to the detected or estimated movement attribute of the current target 110 c.

Each of the targets 110 (including the previous target 110p and the current target 110c, as well as all other targets produced by the target delivery system 155) includes a material that emits EUV light when converted to plasma. Each target 110 is converted, at least in part or in large part, to plasma by interaction with a radiation pulse 364 generated by an optical source 372 within the target space 115. Each target 110 produced by the target delivery system 155 is a target mixture that includes a target material and optional impurities (such as non-target particles). The target material is a substance that can be converted into a plasma state, the emission line of which is in the EUV range. For example, the target 110 may be a drop of liquid or molten metal, a portion of a liquid stream, a solid particle or cluster, a solid particle contained within a drop, a foam of the target material, or a solid particle contained within a portion of a liquid stream. For example, the target material may 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 may be tin element, which may be pure tin (Sn); as tin compounds (such as SnBr4, SnBr2, SnH 4); as a tin alloy (such as a tin-gallium alloy, a tin-indium-gallium alloy, or any combination of these alloys). In the absence of impurities, each target 110 then includes only the target material. The discussion provided herein is an example where each target 110 is a droplet made of a molten metal (such as tin). However, each target 110 generated by the target delivery system 155 may take other forms.

The target 110 may be provided to the target space 115 by passing molten target material through a 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 present target 110 '(which present target 110' may be the present target 110c) interacting with the radiation pulses 364 may also have interacted with one or more preferential radiation pulses. Alternatively, the present target 110' interacting with the radiation pulse 364 may reach the target space 115 without interacting with any other radiation pulse.

The control device 351 is in communication with the control system 150 and is also in communication with other components of the EUV light source 360, such as an actuation system 374, a target delivery system 355, and an optical source 372. Referring to fig. 4, an implementation 451 of the control device 351 is shown and an implementation 450 of the control system 150 is shown. The control device 451 includes a control system 450, but the control system 450 may be physically separate from the control device 451 and still remain in communication. In addition, features or components of the control device 451 may be shared with the control system 450, including features not shown in fig. 4.

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 in communication with the diagnostic system 105. For example, the signal processing module 452 receives the signal 223 from the first photo-detector 222 and the signal 233 from the second photo-detector 232, where the signals 223, 233 are voltage signals related to currents generated from light detected at the respective first photo-detector 222 and second photo-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 may provide signals 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 diagnostic probe(s) 106.

The signal processing module 452 also determines whether adjustments to subsequent radiation pulses 364 output from the optical source 372 are needed based on the determination of the one or more movement properties of the current target 110 c. Also, if adjustments are needed, the signal processing module 452 sends appropriate signals to the optical source actuation module 454, and the optical source actuation module 454 interfaces with the optical source 372. The optical source actuation module 454 may be within the control device 451 (as shown in fig. 4) or may be integrated within the control system 450.

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 that is designed to be configured by a customer or designer after manufacture. The field programmable hardware circuit may be dedicated hardware that receives one or more values of the time stamp, performs calculations on the received values, and uses one or more look-up tables to estimate the time of arrival of the present target 110' at the target space 115. In particular, field programmable hardware circuitry may be used to quickly perform calculations to adjust one or more characteristics of the radiation pulses 364 within a relatively short time frame to achieve an adjustment of one or more characteristics of the radiation pulses 364 interacting with the current target 110c whose motion attributes have just been analyzed by the signal processing module 452.

The control device 451 also includes an optical source module 456, the optical source module 456 being configured to interface with components of an optical source 372, the optical source 372 including a beam delivery system and focusing components and any optical amplifiers. The control device 451 includes a target delivery module 457 configured to interface with the target delivery system 155. Furthermore, the control device 451 and the control system 450 may comprise other modules specifically configured to interface with other components of the EUV light source 100 not shown.

The control system 450 typically includes or has access to one or more of digital electronic circuitry, computer hardware firmware, and software. For example, the control system 450 may access the memory 458, and the memory 458 may 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 by way of example: semiconductor memory devices such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and a CD-ROM disk. 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).

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 processors. One or more programmable processors can each execute a program of instructions to perform a desired function by operating on input data and generating appropriate output. Generally, a processor will receive instructions and data from the memory 458. Any of the above may be supplemented by, or incorporated in, specially-designed ASICs (application-specific integrated circuits).

Furthermore, any one or more of the modules 452, 453, 454, 456, 457 may comprise their own digital electronic circuitry, computer hardware, firmware, and software, as well as dedicated memory, input and output devices, programmable processors, and computer program products. Also, any one or more of the modules 452, 453, 454, 456, 457 may access and use the memory 458, the input devices 459i, the output devices 459o, the programmable memory, and the computer program product.

Although the control system 450 is shown as a separate and complete unit, each of its components and modules may be separate units. The control means 451 may comprise other components, such as a dedicated memory, an input/output device, a processor and a computer program product, which are not shown in fig. 4.

In some implementations, the optical source 372 includes one or more light generators and one or more optical amplifier systems, where the optical amplifier systems receive output from the light generators to thereby generate the pulsed beam of radiation 364.

In some implementations, such as shown in fig. 5, optical source 372 is designed as optical source 572, and optical source 572 generates primary 564A and primary 564B pulsed beams of radiation 564B that are directed toward respective target locations within target space 115.

The optical source 572 includes a first optical amplifier system 573_1 and a second optical amplifier system 573_2, the first optical amplifier system 573_1 including a series of one or more optical amplifiers through which the primary pulsed radiation beam 564A passes, and the second optical amplifier system 573_2 including a series of one or more optical amplifiers through which the primary pulsed radiation 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.

Further, although not required, the optical source 572 can 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 can be used as light generators 576_1, 576_2 are Q-switch, Radio Frequency (RF) pumped, axial flow, carbon dioxide (CO) that can be operated at a repetition rate of, for example, 100kHz₂) An oscillator.

The optical amplifiers within the optical amplifier systems 573_1, 573_2 can each contain a gain medium in a respective beam path along which light beams 577_1, 577_2 from respective light generators 576_1, 576_2 propagate. When the gain medium of the optical amplifier is excited, the gain medium provides photons to the optical beam, amplifying optical beams 577_1, 577_2 to produce an amplified optical beam that forms primary pulsed radiation beam 564A or primary pulsed radiation beam 564B.

The wavelengths of light beams 577_1, 577_2 or radiation pulse beams 564A, 564B may be different from each other so that radiation pulse beams 564A, 564B may be separated from each other if they are combined at any point within optical source 572. If the radiation pulse beams 564A, 564B consist of CO₂Amplifier generated, primary pulsed beam of radiation 564A may have a wavelength of 10.26 microns (μm) or 10.207 μm, and primary pulsed beam of radiation 564B may have a wavelength of 10.59 μm. The wavelengths are selected to more easily achieve separation of 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), then different wavelengths may be used to adjust the relative gain between the two beams 564A, 564B even though they are passing through the same amplifier.

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

Optical source 572 may include a beam path combiner 578c whose beam of beam path combiner 578c covers the beam of primary radiation pulse 564A and the beam of main radiation pulse 564B and places beams 564A, 564B on the same optical path for at least some of the distances between optical source 572 and target space 115. Furthermore, optical source 572 may include a beam path splitter 578s that separates the beam of primary radiation pulses 564A from the beam of main radiation pulses 564B such that both beams 564A, 564B may be individually steered and focused within target space 115.

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

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 comprising CO₂And may 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 comprise pulsed laser devices, such as pulsed gas discharge CO₂An amplifier, the pulsed gas discharge CO₂The amplifier utilizes a relatively high power (e.g., 10kW or higher) and high pulse repetition rate (e.g., 50 k)Hz or higher) that produce radiation at about 9.3 μm or about 10.6 μm. An exemplary optical amplifier that may be used in each of the systems 573_1, 573_2 is an axial flow high power CO with abrasion free gas circulation and capacitive RF excitation₂A laser.

Further, 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 diffusion cooled CO₂A laser system.

The optical amplifier systems 573_1, 573_2 may comprise 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 a mirror), partially transmissive optics (such as a beam splitter), or partially transmissive mirrors, as well as dichroic beam splitters.

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

Although the optical amplifiers may be separate and dedicated systems, at least one of the amplifiers of the optical amplifier system 573_1 may be in the optical amplifier system 573_2 and at least one of the amplifiers of the optical amplifier system 573_2 may be in the optical amplifier system 573_ 1. In such systems 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 pulses 564A may cause a change in one or more characteristics of pulses 564B, and vice versa.

As shown, an example of the 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. Interaction between the initial radiation pulse 564A and the target 510 at the first target position 515_1 causes the target 510 to modify its shape so as to deform and geometrically expand as it moves through the target space 115 and become a modified target 510m as it reaches the second target position 515_ 2. Interaction between the main radiation pulse 564B and the modified target 510m at the second target position 515_2 converts at least part of the modified target 510 into the plasma 144 emitting EUV light 361. As some of the material of target 510 interacts with primary radiation pulse 564A, it may be converted into a plasma. However, the properties of the primary radiation pulse 564A are selected and controlled such that the primary radiation pulse 564A has a primary effect on the target 510, which is a deformation and modification of the geometric distribution of the target 510.

The interaction between the primary radiation pulse 510 and the target 510 ablates material from the surface of the target 510, and the ablation provides a force that deforms the target 510 such that the shape of the target 510 is different from the shape of the target 510 prior to the interaction with the primary radiation pulse 564A. For example, prior to interacting with primary radiation pulse 564A, target 510 may have a droplet-like shape upon exiting target delivery system 155, while after interacting with primary radiation pulse 564A, the shape of target 510 is deformed such that the shape of modified target 510m is closer to the shape of a disk (such as a pancake shape) upon reaching second target location 515_ 2. After interacting with the primary radiation pulse 564A, the target 510 may be a material that is not ionized (a material that is not a plasma) or a material that is minimally ionized. After interacting with the primary radiation pulse 564A, the target 510m may be, for example, a liquid or molten metal disk, a continuous segment of target material without voids or substantial gaps, a mist of particles or nanoparticles, or an atomic vapor cloud.

Furthermore, as shown in FIG. 5, the interaction between target 510 and primary radiation pulses 564A that causes ablation of material from the surface of target 510 may provide that some thrust or velocity may be achieved in the Z direction for target 510. The extension of the modified target 510m as it travels in the X-direction from the first target position 515_1 to the second target position 515_2 and the velocity obtained 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).

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

Referring to fig. 6A, in 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 light beam 606A from a light source 607A. The diagnostic light beam 606A is directed as a light curtain to traverse the trajectory TR at location x, such that each of the targets 110 traverses the light curtain on their way to the target space 115. The light source 607A generates a single light beam 611A, which light beam 611A is directed through one or more optical elements 608A (such as mirrors, lenses, apertures, and/or filters), which optical elements 608A modify the light beam 611A to form a single diagnostic light beam 606A.

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 1070nm and 50W power. In this example, when the current target 110c passes through the diagnostic light beam 606A at time t, at least some of the diagnostic light beam 606A is reflected or scattered from the current target 110c to form light 640A, which light 640A is detected by the metrology device 100 (by 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 time of arrival of the current target 110 'at the target space 115 and adjust the characteristics of the radiation pulse 364 accordingly to ensure interaction of the radiation pulse 364 with the present target 110' in the target space 115. The metrology device 100 may also rely on some assumptions about the path of the present target 110 'to perform calculations to estimate the arrival time of the present target 110' at the target space 115. For example, the metrology device 100 may assume a particular velocity of the present target 110' at a particular point along the trajectory TR.

The diagnostic beam 606A may be a gaussian beam such that its transverse profile of optical intensity may be described by a gaussian function. The focus or beam waist of diagnostic beam 606A may be configured to overlap at trajectory TR or in the-X direction. In addition, optical element 608A may include refractive optics that ensure that the focus (or beam waist) of diagnostic beam 606A overlaps trajectory TR.

Referring to fig. 6B, in some implementations, the diagnostic system 105 is designed as a diagnostic system 605B. The diagnostic system 605B generates two diagnostic beams 606B _1 and 606B _2 as one or more diagnostic probes 106. Diagnostic light beam 606B _1 is directed as a first light curtain to pass through trajectory TR at a first location (e.g., location X1 along the X axis) such that each of the targets 110 passes through the first light curtain on its way to the target space 115. The diagnostic light beam 606B _2 is directed as a second light curtain to traverse the trajectory TR at a second location (e.g., location X2 along the X axis) such that each of the targets 110 traverses the second light curtain en route to the target space 115 and after having traversed the first light curtain. The diagnostic beams 606B _1, 606B _2 are separated at the track TR by a distance Δ x, which is equal to x2-x 1. The double screen diagnostic system 605B may be used to determine not only the location and arrival information of the target 110, but also the velocity or velocity of the target 110.

In some implementations, the diagnostic system 605B includes a single light source 607B that produces a single light beam 611B and one or more optical elements 608B that receive the single light beam and split the light beam 611B into two diagnostic light beams 606B _1, 606B _ 2. Further, optical assembly 608B may include an assembly for directing diagnostic beams 606B _1, 606B _2 toward respective positions x1, x2 along trajectory TR.

In some implementations, the optical assembly 608B includes a beam splitter that splits the single light beam from the single light source 607B into two diagnostic light beams 606B _1, 606B _ 2. The beam splitter may be, for example, a dielectric mirror, a beam splitter cube, or a polarizing beam splitter. One or more of the optical components 608B may be reflective optics positioned to redirect either or both of the diagnostic beams 606B _1, 606B _2 such that the diagnostic beams 606B _1, 606B _2 are each directed toward the track TR.

In other implementations, the optical component 608B includes beam splitting optics (such as diffractive optics or binary phase diffraction gratings, birefringent crystals, intensity beamsplitters, polarizing beamsplitters, or dichroic beamsplitters) and refractive optics (such as focusing lenses). Light beam 611B is directed through beam splitting optics that split light beam 611B into two beams that travel in different directions and are directed through refractive optics to produce diagnostic light beams 606B _1, 606B _ 2. The beam splitting optics may split beam 611B such that diagnostic beams 606B _1, 606B _2 are separated by a set distance (e.g., 0.65mm along the X-direction) at trajectory TR. In this example, x2-x1 is 0.65 mm. Furthermore, the refractive optics may ensure that the focal point (or beam waist) of each of the diagnostic beams 606B _1, 606B _2 overlaps the trajectory TR.

As shown in this example, the diagnostic beams 606B _1, 606B _2 are directed such that they intersect the trajectory TR at different positions X1, X2, but typically intersect at substantially similar angles relative to the X axis. For example, the diagnostic beams 606B _1, 606B _2 are directed at about 90 relative to the X-axis. In other implementations, the angles at which the diagnostic beams 606B _1, 606B _2 are directed relative to the X-axis may be adjusted using splitting and refracting optics such that they fan out toward the trajectory TR and intersect the trajectory TR at different and distinct angles. For example, diagnostic beam 606B _1 can intersect track TR at approximately 90 relative to the-X direction, while diagnostic beam 606B _2 can intersect track TR at an angle less than 90 relative to the-X direction.

Each of the diagnostic beams 606B _1, 606B _2 can be a gaussian beam such that a transverse profile of the optical intensity of each diagnostic beam 606B _1, 606B _2 can be described using a gaussian function. The focal point or beam waist of each diagnostic beam 606B _1, 606B _2 can be configured to overlap at the track TR or-X direction.

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 1070nm and 50W power. In this example, the current target 110c passes through the first diagnostic light beam 606B _1 at time t1 (and position x1), and at least some of the diagnostic light beam 606B _1 is reflected or scattered from the current target 110c to form light 640B _1 (as light 140), which light 640B _1 is detected by the metrology device 100 (by the first detection device 120). Further, the current target 110c passes through the second diagnostic light beam 606B _2 at time t2 (and position x2), and at least some of the diagnostic light beam 606B _2 is reflected or scattered from the current target 110c to form light 640B _2 (such as light 140), which light 640B _2 is detected by the metrology device 100 (via the first detection device 120).

The separation Δ d between diagnostic beams 606B _1, 606B _2 at trajectory TR can be adjusted or customized depending on the rate at which target 110 is released from target delivery system 155 and the size and material of target 110. For example, the spacing Δ d may be less than the spacing between adjacent targets 110. As another example, the spacing Δ d may be determined or set based on the spacing between adjacent targets 110 to provide greater accuracy in measurements performed based on the interaction between the diagnostic beams 606B _1, 606B _2 and the current target 110 c. To some extent, generally speaking, the greater the interval Δ d, the higher the accuracy of the measurements performed. For example, the separation Δ d may be between about 250 μm and 800 μm.

The interaction between the diagnostic beams 606B _1, 606B _2 and the current target 110c enables the control system 150 to determine a movement attribute (such as the velocity V of the current target 110c along the-X direction). It is also possible to determine a trend in the velocity V or to change the velocity V over many targets. The change 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 if some assumptions are made about the movement of the current target 110 c.

The wavelength of the diagnostic probe 106 (such as diagnostic beam 206, diagnostic beam 606A, and diagnostic beams 606B _1, 606B _2) produced by the diagnostic system should be sufficiently different from the wavelength of the radiation pulse 364 produced 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 through. In some implementations, the wavelength of the diagnostic light beams 206, 606A, 606B _1, 606B _2 is 532nm or 1550 nm.

Referring to FIG. 7, a procedure 700 is performed by the metrology device 100 (or 200) to estimate one or more attributes of the current target 110 c. Initially, the metering device 100 enables interaction between the diagnostic system 105 and the current target 110c (705). This interaction may be between one or more diagnostic probes (such as, for example, probe 106, probe 206, diagnostic beam 606A, or diagnostic beams 606B _1, 606B _2) and the current target 110c as the current target 110c traverses 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 a diagnostic probe 106 that crosses the X-axis and is therefore in the path of the current target 110c when it is released towards the target space 115.

The metrology device 100 detects a first light at a first detection region (710). The first light comprises broadband optical radiation (light 142) emitted from a plasma 144 generated by the previous target 110 p. The first light includes light 140 resulting from interaction between the current target 110c and the diagnostic system 105. For example, the first detection device 220 may detect the first light. In this example, the first light is detected at the first light detector 222, and the first light detector 222 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 the control system 150, 250. The light 140 resulting from the interaction between the current target 110c and the diagnostic system 105 may include light from the diagnostic probe 106 reflected from the current target 110 c.

Referring to fig. 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, the blocking device 224 transmitting light having a center wavelength corresponding to the center wavelength of the light 140, and the blocking device 224 having a transmission bandwidth of about 10-20 nm. First signal 823 displays an intensity peak 823_1 and an intensity peak 823_2, intensity peak 823_1 being associated with light 140 resulting from interaction between current target 110c and diagnostic system 105, intensity peak 823_2 being associated with light 140 resulting from interaction between target 110 adjacent to current target 110c and diagnostic system 105. The first signal 823 also displays intensity peaks 823_3, 823_4 associated with the light 142. As is apparent from this example, the intensity or amplitude of peaks 823_3, 823_4 due to broadband optical radiation 142 is the same order of magnitude as the intensity or amplitude of peaks 823_1, 823_2 due to diagnostic light 140.

In general, the shape of the signal 223 output from the first light detector 222 may fluctuate and vary depending on various parameters in the first light detector 222 and the blocking device 224. The signal 823 shown in fig. 8 is only one example that provides what the signal 223 might look like. Other shapes for signal 223 are possible.

Referring again to fig. 7, the metrology device 100 detects 715 the second light at the second detection region. The second light comprises broadband optical radiation (light 142) emitted from the plasma 144 generated by the previous target 110 p. Most of the light 140 is prevented from reaching the second detection region. For example, the second detection device 230 may detect the second light. In this example, the second light is detected at the second light detector 232, and the second light detector 232 may be considered a 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 may be blocked with the blocking device 234 based on one or more of the spectral, polarization, and spatial properties of the diagnostic light 140.

Referring to fig. 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 photo-detector 232. In this example, the second light detector 232 is provided with a blocking device 234, the blocking device 234 transmitting light having a center wavelength that is offset from the center wavelength of the light 140 by 50nm, and the blocking device 234 having a transmission bandwidth of about 10-20 nm. The second signal 833 only shows the intensity peaks 823_3, 823_4 associated with the light 142 because the blocking device 234 has blocked a significant amount of the diagnostic light 140. It is not necessary that blocking device 234 block 100% of light 140; in contrast, blocking device 234 need only block enough light in light 140 to obtain a clear representation of the peak associated with light 142, so that second signal 833 can be used to remove the signal due to light 142 from first signal 823 in the following steps.

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 preferential radiation pulse 364. In general, the metrology device 100 detects a first light (710) and a second light (715) that are parallel to each other. That is, the signals 223, 233 (hereinafter referred to as S1(t) and S2(t), respectively) from the respective first and second detection devices 220, 230 are each continuously transmitted to the control system 250 and acquired at the same time t.

The metrology 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). For example, referring to fig. 8 and 4, the signal processing module 452 receives first and second signals 823 and 833 from the first and second optical detectors 222 and 232, respectively. The signal processing module 452 electronically subtracts the first signal 823 from the second signal 833 to obtain an analysis signal 880. The signal processing module 452 may perform electronic subtraction by digitizing each of the first 823 and second 833 signals and then compute the difference between each set of sample points (in the corresponding digitized signals). In other implementations, the signal processing module 452 performs electronic subtraction using analog electronics.

The signal processing module 452 may perform the subtraction based on an assumption about the second signal generated from the detected second light. In particular, it may be assumed that the multiplicative gain factor may be estimated and accessed by the signal processing module 452. For example, multiplicative gain factors may be estimated as input parameters and stored in the memory 458 for access by the signal processing module 452. As another example, the multiplicative gain factor may be estimated in a dynamic manner by an on-line measurement that appropriately scales the second signal produced from the detected second light so that when subtraction is performed, part of the signal from the light 142 is effectively cancelled or substantially reduced. The multiplicative gain factors are discussed in more detail below.

The signal sampled by the second detector 232 is in a different spectral band (or wavelength range) and also in a different spatial location than the signal sampled by the first detector 222. However, it may 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.

The analysis signal 880 contains a representation of the diagnostic light 140 without the need to acquire a time gate to isolate the diagnostic light 140 from the broadband optical radiation 142. Analysis signal 880 includes peaks 880_1, 880_2 that correspond to peaks 823_1, 823_2, respectively, of first signal 823.

One or more properties of the current target 110c are estimated based on the analysis signal (725). For example, the signal processing module 452 may process or analyze the analysis signals 880 to estimate a time of arrival of the current target 110c (or the present target 110') at a particular location in space (such as a region within the target space 115), to estimate a velocity, or acceleration of the current target 110c, or to estimate a time interval between the arrival of the current target 110c at a particular location in space and the arrival of another target at that particular location in space.

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

For example, the signal processing module 452 may include a time module that receives the analysis signal 880 and digitally time stamps 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 neighboring target interacts with the diagnostic probe 106. For example, the time stamps t _1 and t _2 are as shown in fig. 8.

The positions of the timestamps t _1 and t _2 may be selected by the signal processing module 452 to generally correspond to the center positions 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 a time derivative of the filtered signal, and use a 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 differ depending on the shape of the current target 110c (e.g., the targets 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 centroid but not to the shape of the transient peak signal 823.

These timestamps may then be used to determine the movement attributes of the current target 110 c. The signal processing module 452 may also access other data stored in the memory 458 related to the current target 110c or the diagnostic system 105. For example, the memory 458 may store information related to a prioritized rate associated with the current target 110 c. If the diagnostic system is designed as the dual beam diagnostic system 605B of fig. 6B, the memory 458 may store information related to the separation Δ d between the diagnostic beams 606B _1, 606B _2 or may store the location at which the diagnostic probe 108 interacts with each target.

The signal processing module 452 may use the timestamp output from the dual beam diagnostic system 605B of fig. 6B to determine the speed or velocity of the current target 110 c.

The signal processing module 452 may determine that the present target 110' (which may be the present target 110c) will be at a location within the target space 115. The signal processing module 452 can determine the predicted time of arrival of the present object 110' at the object location by using the estimated velocity and other information stored in the memory 458. In particular, the memory 458 may store the distance between the intersection of the diagnostic beam 606B _2 with the trajectory TR of the current target 110c and the target position along the X-direction in the target space 115. The signal processing module 452 may determine when the current target 110c traverses the path of the diagnostic light beam 606B _ 2. Thus, the signal processing module 452 may estimate or determine the target location at which the current target 110c arrived in the target space 115 as the stored distance divided by the estimated velocity.

One or more outputs from the signal processing module 452 may be considered control signals and directed to an optical source actuation module 454 that interfaces with an optical source 372. The control signal from signal processing module 452 provides instructions that cause actuation module 454 to adjust aspects of 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 radiation pulses 364 travel.

In some implementations, if blocking devices 224, 234 fail to sufficiently and physically distinguish between diagnostic light 140 and broadband optical radiation, signal processing module 452 may perform additional processing to distinguish between diagnostic light 140 and broadband optical radiation 142 in first signal 832. One reason this additional processing works is that there is a difference in the difference between the two signals 223, 233 on the first 222 and second 232 photo-detectors, 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). Furthermore, the time dependence of the signals 223, 233 is the same. As an example, if signal 223 is denoted as S1(t) and signal 233 is denoted as S2(t), then if S1(t) ═ a × f (t) + b and S2(t) ═ c × f (t) + d, the signals typically have the same time dependence f (t), 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 the same up to a constant multiplicative factor.

Specifically, signals S1(t) and S2(t) may be represented in terms of signals related to diagnostic light 140 and broadband optical radiation 142, as follows. If the signal from the diagnostic light 140 is denoted d (t) and the broadband optical radiation 142 is denoted p (t + t '), where t is the 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 the two signals as follows: s1(t) ═ e × d (t) + f × p (t + t'), where e and f are fixed constants determined by the spectra of blocking device 224, first photodetector 222, and diagnostic light 140 and broadband optical radiation 142. The signal S2(t) detected at the second optical detector 232 according to the sensitivity of the second optical detector 232 is a linear superposition of the 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 photodetector 232, and the spectra of the diagnostic light 140 and the broadband optical radiation 142.

The diagnostic light 140d (t) may be solved by solving a linear equation:

d(t)＝[S1(t)-S2(t)-(f-h)*p(t+t’)]/(e-g)

the signals S1 and S2 are the raw signals 223, 233 at the output of the respective light detectors 222, 232. Given the freedom to select a user variable multiplicative gain factor for at least one of the signals (such as S1), then:

d(t)＝[S1(t)-a*S2(t)-(f-a*h)*p(t+t’)]/(e-a*g)

if the user selects a ═ f/h, then:

d(t)＝[S1(t)-(f/h)*S2(t)]/(e-f*g/h),

which is insensitive to the signal p (t + t') from the broadband optical radiation 142.

In other implementations (such as that shown in fig. 6C), 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 produces light beams 611C _1, 611C _2, respectively. Each of the light beams 611C _1, 611C _2 passes through a respective one or more optical elements 608C _1, 608C _2, which optical elements 608C _1, 608C _2 can alter or adjust the characteristics of the light beams 611C _1, 611C _ 2. The output of each of the one or more optical elements is a respective diagnostic light beam 606C _1, 606C _ 2. The optical assemblies 608C _1, 608C _2 may include assemblies for directing the respective diagnostic beams 606C _1, 606C _2 toward respective positions x1, x2 along the trajectory TR. Examples of optical components 608C _1, 608C _2 are discussed above with reference to optical component 608B.

Each of the diagnostic beams 606C _1, 606C _2 can be a gaussian beam such that a transverse profile of the optical intensity of each diagnostic beam 606C _1, 606C _2 can be described using a gaussian function. The focal point or beam waist of each diagnostic beam 606C _1, 606C _2 can be configured to overlap at the track TR or-X direction.

Each light source 607C _1, 607C _2 may be a solid state laser. In one example, the solid-state laser is a YAG laser (such as neodymium-doped YAG (Nd: YAG)) operating in the 1010nm-1070nm range and at a power in the Watt-prone range. In another example, the solid state laser is an ytterbium-doped fiber laser operating in the range of 1010nm-1070nm (e.g., at 1020nm or 1070 nm), depending on other considerations. In this example, similar to the design of FIG. 6B, 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 beam 606C _1 is reflected or scattered from the current target 110C to form light 640C _1 (as light 140), which light 640C _1 is detected by the metrology device 100 (by the first detection device 120). Further, 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 beam 606C _2 is reflected or scattered from the current target 110C to form light 640C _2 (as light 140), which light 640C _2 is detected by the metrology device 100 (by the first detection device 120).

The separation Δ d between the diagnostic beams 606C _1, 606C _2 at the trajectory TR can be adjusted or customized depending on 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 Δ d may be less than the spacing between adjacent targets 110. As another example, the spacing Δ d may be determined or set based on the spacing between adjacent targets 110 to provide greater accuracy for measurements performed based on the interaction between the diagnostic beams 606C _1, 606C _2 and the current target 110C. To some extent and in general, the greater the interval Δ d, the higher the accuracy of the measurements performed. For example, the spacing Δ d may be between about 250 μm and 800 μm.

The interaction between the diagnostic beams 606C _1, 606C _2 and the current target 110C enables the control system 150 to determine a movement attribute (such as the velocity V of the current target 110 along the-X direction). It is also possible to determine a trend in the velocity V or a velocity V that changes over a number of objects. Changes in the movement properties of the current target 110C along the-X direction may also be determined using only the diagnostic light beams 606C _1, 606C _2 if some assumptions are made about the motion of the current target 110C.

The wavelengths of the diagnostic beams 606C _1, 606C _2 generated by the diagnostic system 605C should be sufficiently different from the wavelength of the radiation pulse 364 generated by the optical source 372 such that 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 pulse 364 when the broadband optical radiation 142 passage is achieved. In some implementations, the wavelength of the diagnostic light beams 606C _1, 606C _2 is 532nm or 1550 nm.

Referring also to fig. 9, in another implementation, the blocking devices 224 and 234 implemented in the metering device 200 shown in fig. 2 may be designed to bias the filters 924, 934 rather than spectral filters. In this manner, in the metrology device 900, polarization is used to distinguish between blocked light and light allowed to pass to the light detector. In this implementation, the diagnostic light 940 resulting from the interaction between the diagnostic light beam 906 and the current target 110c is polarized. Because the diagnostic light beam 906 has a particular polarization, the diagnostic light 940 can be polarized. Alternatively, the diagnostic beam 906 can be passed through a polarizer 941 to clean the polarization state of the diagnostic beam 906. In contrast, broadband optical radiation 142 is unpolarized due to its properties. In this example, blocking device 924 is a polarizing filter that is oriented parallel to the polarization of diagnostic light 940 and attenuates broadband optical radiation 142 by half (because broadband optical radiation 142 is unpolarized). The diagnostic light 140 may be attenuated by a variable amount depending on the angle between the polarizing filter 924 and the direction of the polarization vector of the diagnostic light 940. The diagnostic light 940 may not be perfectly polarized, particularly 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 and second detection devices 920, 930 with respect to the direction and trajectory of the diagnostic probe 906. On the other hand, the blocking device 934 is a polarizing filter oriented orthogonal to the polarization of the diagnostic light 940, such 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.

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

In other implementations of the metrology device 1000, as shown in fig. 10, the blocking devices 224 and 234 implemented in the metrology device 200 shown in fig. 2 may be designed to each include a spectral filter (such as the spectral filters 224, 234) and a polarizing filter (such as the polarizing filters 924, 934) arranged in series and used simultaneously. Such a design may increase the amount of diagnostic light 140 blocked by blocking device 234.

In other implementations, the blocking means 224, 234 implemented in the metering device 200 shown in fig. 2 may be designed as spatial filters instead of spectral filters. The two spatial positions that can be distinguished are at two slightly different angles to the normal vector of the pupil or entrance of the detection means 220, 230. Each blocking device 224, 234 comprises a lens placed at the position of the pupil and two slightly different angles are translated to a position near the focal point of the lens. Each blocking device 224, 234 comprises a mask (which defines an opening, such as a slit or aperture) placed between the lens and the respective light detector 222, 232, such that the diagnostic light 140 passes and the broadband optical radiation 142 is blocked (or vice versa).

Referring 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, which target delivery system 1155 directs a stream 1111 of the target 1110 towards a target space 1115 in a chamber 1168. The target space 1115 (under control of the actuation system 1174) receives a beam or series of amplified radiation pulses 1164 generated from an optical source 1172. As described above, each target 1110 includes a substance that emits EUV light 1161 when converted into a luminescent plasma 1144. Interaction between the species within the target 110 and the radiation pulse 1164 within the target space 1115 converts at least some of the species in the target 1110 to 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, the broadband optical radiation 1142 including EUV light 1161, since the luminescent plasma 1144 has elements with emission lines in the EUV wavelength range.

The luminescent plasma 1144 may be considered a highly ionized plasma with an electron temperature of tens of electron volts (eV). Higher energy EUV 1161 may be generated with 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 light-emitting plasma 1144, and at least a portion 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 a portion of the EUV light of the emitted EUV light 1161. A surface 1171 of the EUV light collector 1170 may be a reflective surface positioned to receive a portion of the EUV light 1161 emitted and direct the collected EUV light 1161 for use outside of the EUV light source 1160 through an output device 1166, which may be a lithographic apparatus. The reflective surface 1171 directs the collected EUV light 1161 to a secondary focal plane where the EUV light 1161 is subsequently captured for use by the output device 1166. An exemplary lithographic apparatus is discussed with reference to fig. 12 and 13.

The 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. The EUV light collector 1170 further comprises an aperture 1173, the aperture 1173 allowing the radiation pulse 1164 to pass through the EUV light collector 1170 towards the target space 1115.

The target delivery system 1155 may comprise a droplet generator arranged within the EUV chamber 1168, and the target delivery system 1155 is arranged to emit a high frequency stream 1111 of droplets (target 1110) towards the target space 1115. In operation, radiation pulses 1164 are delivered in synchronization with the operation of the drop generator to deliver radiation pulses 1164 to convert each drop (each target 1110) into a luminescent plasma 1144. The transmission frequency of the liquid may be a few kilohertz, for example 50 kHz.

In some implementations, as discussed above with reference to fig. 5, energy from the radiation pulse 1164 is instead delivered in at least two pulses: 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 target space 1115 to vaporize the fuel material into a small cloud that continues to follow a trajectory, and then a primary pulse of energy (such as 564B) is delivered to a cloud at a second target location 515_2 in target space 1115 to generate a luminescent plasma 1144. A trap (which may be a container, for example) may be provided on the opposite side of the EUV chamber 1168 to trap this fuel (i.e., target species or target 1110) for whatever reason is not turned into a plasma.

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. Droplets of 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).

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

Referring to fig. 12, in some implementations, the metrology device 100 (or 200, 1100) is implemented within an EUV light source 1260, which EUV light source 1260 provides EUV light 1262 to a lithography device 1266 (output 366). The lithographic 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 table) MT constructed 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 table (e.g. a wafer table) WT constructed 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 patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, 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 for example whether or not the patterning device is held 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 table, which may be fixed or movable as required. For example, the support structure MT may ensure that the patterning device is at a desired position with respect to the projection system PS.

The term "patterning device" should be broadly interpreted as referring to any device that can be used to impart a patterned radiation beam with a pattern in its cross-section, such as to create a pattern in a target portion of the substrate. The pattern imparted to the radiation beam may correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit. The patterning device may 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 employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix.

Similar to the illumination system IL, the projection system PS can include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic 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 vacuum for EUV radiation, as other gases may absorb too much radiation. Thus, a vacuum environment can be provided for the entire beam path by means of the vacuum wall and the vacuum pump.

As described herein, the apparatus is of a reflective type (e.g., employing a reflective mask).

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 "multiple stage" machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure.

Referring also to FIG. 13, the illuminator IL receives an EUV radiation beam (EUV light 1262) from an EUV light source 1260. Methods of generating EUV light include, but are not necessarily limited to, converting a material into a plasma state with at least one element (xenon, lithium, or tin) using one or more emission lines in the EUV range. In one such method, a desired plasma, commonly referred to as a laser produced plasma ("LPP"), may be produced by irradiating a fuel, such as a droplet, stream or cluster of material having the desired emission line elements, with a laser beam. The EUV light source 1260 may be designed similar to the 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 elements 370 or 1170).

As shown in fig. 12 and 13, the radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the 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 the projection system PS, which focuses the beam onto a target portion of the substrate W. From X_w、Y_w、Z_wGiven the coordinate system of the substrate, the substrate table WT can be moved accurately, e.g. so as to position different target portions in the path of the radiation beam B, using the second positioner PW and position sensor PS2 (e.g. an interferometric device, linear encoder or capacitor sensor). Similarly, the first positioner PM and another position sensor PS1 can be used to accurately position the patterning device (e.g. mask) MA with respect to the path of the radiation beam B. Patterning device (e.g. mask) MA and substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2.

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

1. in step mode, the support structure (e.g., mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion at one time (i.e., a single static exposure). Then, the substrate table WT is at X_wAnd/or Y_wAre directionally offset so that different target portions may be exposed.

2. In scan mode, the support structure (e.g. mask table) MT and the substrate table WT (e.g. along X)_wAnd/or Y_w) Synchronously scanned, and 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.

3. In another mode, the support structure (e.g., mask table) MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.

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

FIG. 13 shows an implementation of lithographic apparatus 1266 in more detail, including EUV light source 1260, illumination system IL, and projection system PS. The EUV light source 1260 is constructed as discussed above when describing EUV light sources 360 or 1160.

The systems IL and PS are also contained in their own vacuum environment. The Intermediate Focus (IF) of the EUV light source 1260 is arranged such that it is located at or near the aperture in the closed structure. The virtual source point IF is an image of the radiation emitting plasma (e.g., EUV light 362 or 1162).

From the aperture of intermediate focus IF, radiation beam 1262 passes through illumination system IL, which in this example comprises a facet field mirror device IL1 and a facet pupil mirror device IL 2. These devices form a so-called "fly's eye" illuminator that is arranged to provide a desired angular distribution of the radiation beam ILB at patterning device MA, and a desired uniformity of the radiation intensity at patterning device MA (as shown with reference to IL 3). The patterned light beam PSB is formed when the light beam ILB is reflected at the patterning device MA, which is held by the support structure (mask table) MT, and is imaged by the projection system PS via reflective elements PS1, PS2 onto a substrate W held by the substrate table WT. To expose a target portion on a substrate W, the substrate table WT and patterning device table MT are rotated while X is_w、Y_w、Z_wThe radiation pulses B are generated while performing a synchronized movement in the coordinate system to scan the pattern on the patterning device MA through the illumination slit.

Each system IL and PS is arranged within its own vacuum or near-vacuum environment defined by an enclosed structure similar to the EUV chamber 1168. There may generally be more elements in the illumination system IL and the projection system PS than shown. Furthermore, there may be from one to six additional reflective elements in the illumination system IL and/or the projection system PS in addition to those shown in FIG. 13.

Other aspects of the invention are set forth in the following numbered clauses.

1. A method, comprising:

enabling interaction between the 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 comprises light emitted from a plasma generated by a previous target and light generated from an effected interaction between a present target and a diagnostic system;

detecting second light at a second detection region, wherein the second light comprises light emitted from a plasma of a previous target;

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

based on the generated analysis signal, a property of the current target is estimated.

2. The method according to clause 1, wherein the light emitted from the plasma generated by the target assembly comprises: extreme Ultraviolet (EUV) light in the EUV wavelength range and non-EUV light outside the EUV wavelength range.

3. The method according to clause 1, wherein detecting the second light at the second detection region comprises suppressing at least part of the light resulting from interaction between the current target and the diagnostic system.

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

5. The method of clause 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; and

a second interaction between the current target and a second diagnostic probe of the diagnostic system.

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

7. The method according to clause 1, wherein effecting 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.

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

9. The method according to clause 1, wherein estimating the attributes of the current target comprises estimating one or more of:

the time of arrival of the current target at a particular 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 particular location in space and the arrival of another target at a particular location in space.

10. The method according to 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.

11. The method according to 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 preferential radiation pulse.

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

13. The method according to clause 1, wherein the light resulting from the interaction between the current target and the diagnostic system comprises light reflected or scattered from the current target from the diagnostic system.

14. The method according to clause 1, wherein generating the analytic signal from the first signal and the second signal comprises electronically subtracting the second signal from the first signal.

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

16. The method according to clause 1, wherein detecting the second light at the second detection region comprises detecting an amount of light resulting from an effected interaction between the current target and the diagnostic system, wherein the detected amount of light resulting from the effected interaction between the current target and the diagnostic system at the second detection region is less than the amount of light resulting from the effected interaction between the current target and the diagnostic system that was detected at the first detection region.

17. An apparatus, comprising:

a diagnostic system configured to diagnostically interact with a current target traveling along a trajectory before the current target enters a target space;

a first detection device configured to detect first light, the first light including:

light resulting from interaction between the current target and the diagnostic system, an

Light emitted from a plasma generated by a previous target;

a second detection device configured to detect second light, the second light including light emitted from plasma generated by a previous target; and

a control system in communication with the first detection device and the second detection device and configured to:

generating an analysis signal based on first and second signals generated from respective outputs of the first and second detection means; and is

Based on the generated analysis signal, a property of the current target is estimated.

18. The apparatus of clause 17, further comprising a target delivery system configured to release a plurality of targets along a trajectory toward the target space, wherein each target comprises a component that Emits Ultraviolet (EUV) light when converted to plasma.

19. The apparatus according to clause 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 the preferential radiation pulse.

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

21. The apparatus according to clause 17, wherein the first detection means comprises a first light detector and the second detection means comprises a second light detector.

22. The apparatus according to clause 21, wherein each of the first and second light detectors comprises one or more of: 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.

23. The apparatus according to clause 21, wherein the first light detector and the second light detector have substantially equal viewing and collection angles.

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

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

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

27. The apparatus according to clause 21, wherein the first detection means comprises a blocking device having a band pass that overlaps with a wavelength of light resulting from interaction between the current target and the diagnostic system.

28. The apparatus of clause 17, wherein the diagnostic system comprises a first diagnostic probe and a second diagnostic probe, each diagnostic probe configured to diagnostically interact with the current target before the current target travels along the trajectory and enters 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 clause 17, further comprising:

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 configured to adjust one or more properties of the radiation pulse directed toward the target space if the estimated properties are outside acceptable specifications.

30. The apparatus according to clause 17, wherein the spectral bandwidth of light resulting from the interaction between the current target and the diagnostic system is substantially narrower than the spectral bandwidth of light emitted from the plasma generated by the previous target.

31. The apparatus of 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 configured to electronically subtract the second signal from the first signal.

32. A method of estimating attributes of a moving object, 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 resulting from interaction between a current target and a diagnostic system and background light emitted from a plasma generated by a previous target, the spectral bandwidth of the diagnostic light being substantially narrower than the spectral bandwidth of the background light;

limiting the amount of diagnostic light that passes through to the second detection region and allowing all of the background light to pass through to the second detection region;

detecting background light at a second detection region;

generating an analytical signal based on:

a signal generated by the detected light at the first detection area, an

A background signal generated by the detected light at the second detection region; and is

An attribute of the current target is estimated based on the generated analysis signal.

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.

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