Alignment of an extreme ultraviolet light source

Abstract

An apparatus includes a vessel comprising an interior space; a material supply system configured to provide targets comprising a target material along a path in the interior space; a detection system configured to detect scattered light resulting from an interaction between one of the targets and a metrology beam and to generate information based on the interaction; and a control system configured to adjust the path based on the information generated by the detection system. The target material produces extreme ultraviolet (EUV) light in a plasma state. The metrology beam does not convert the target material into the plasma state.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Application No. 63 / 031,265, filed May 28, 2020, entitled “ALIGNMENT OF EXTREME ULTRAVIOLETLIGHT SOURCE,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a technique for aligning extreme ultraviolet (EUV) light sources. Background Technology

[0004] EUV light can be, for example, electromagnetic radiation (sometimes referred to as soft X-rays) with wavelengths of 100 nanometers (nm) or smaller, and includes light with wavelengths of, for example, 20 nm or smaller, between 5 and 20 nm, or between 13 and 14 nm. This EUV light can be used in photolithography processes to create extremely small features in a substrate, such as a silicon wafer, by initiating polymerization in a resist layer. Methods for generating EUV light include, but are not limited to, converting materials into a plasma state, including elements such as xenon, lithium, or tin with emission lines in the EUV range. In one such method, commonly referred to as laser-generated plasma (LPP), the desired plasma can be generated by irradiating a target material (e.g., in the form of droplets, plates, strips, streams, or clusters) with an amplified beam called a driving laser. For this process, the plasma is typically generated in a sealed container (e.g., a vacuum chamber) and monitored using various types of metrological equipment. Summary of the Invention

[0005] In one aspect, an apparatus includes: a container including an internal space; a material supply system configured to supply a target comprising target material along a path in the internal space; a detection system configured to detect scattered light generated by an interaction between one of the targets and a measurement beam, and to generate information based on the interaction; and a control system configured to adjust the path based on the information generated by the detection system. The target material generates extreme ultraviolet (EUV) light in a plasma state. The measurement beam does not convert the target material into a plasma state.

[0006] The implementation may include one or more of the following features.

[0007] The device may also include reflective optics within an internal space. The reflective optics may include a principal focal point and an intermediate focal point. A control system may be configured to adjust a path such that the path intersects the principal focal point of the reflective optics. The control system may also be configured to adjust a guiding element that directs light along its propagation direction within the container such that the propagation direction intersects the principal focal point. A detection system may be configured to detect scattered light after it has been reflected by the reflective optics. The detection system may include an imaging sensor and may be configured to image the scattered light after it has been reflected from the reflective optics. The detection system may include a component at the intermediate focal point or at a location between the intermediate focal point and a scanner that receives light from the device. The component may include a mask, and the detection system may also include a detector configured to detect light transmitted through the mask. The component may include a detector configured to be placed at or removed from the intermediate focal point. The component may include an imaging plane. The imaging plane may include a material that allows the imaging system to sense the scattered light. The imaging plane may include frosted glass. The imaging plane may include a film or a coating. The imaging plane may substantially block debris from the target material.

[0008] Each point along the path can be a position in a three-dimensional coordinate system, and the control system can be configured to adjust the position of at least one point on the path in at least two of the three dimensions. The control system can be configured to adjust the position of the path by controlling a material supply system.

[0009] The device may also include a measurement light source. The measurement light source may be a laser configured to generate visible light or a laser configured to generate infrared light. The measurement light source may be a pulsed light source, and the measurement beam may include multiple light pulses. The measurement light source may be a continuous wave light source, and the measurement beam may include a continuous wave beam.

[0010] In another aspect, an extreme ultraviolet (EUV) light source includes: a container; a target material supply system configured to supply a target to the interior of the container; and a device. The target comprises target material that emits EUV light when in a plasma state, and the target travels along a path inside the container. The device is configured to align the path of the target with the focal point of an optical element inside the container. The device includes: a detection system configured to detect scattered light generated by the interaction between one of the targets and a measurement beam, and to generate information based on the interaction; and a control system configured to adjust the path of the target based on the information generated by the detection system. The measurement beam does not convert the target material into a plasma state, and one of the targets is configured to act as a point source when irradiated by the measurement beam.

[0011] The implementation may include one or more of the following features.

[0012] EUV light sources may also include steering elements configured to receive an amplified beam with energy sufficient to convert at least some of the target material into a plasma state.

[0013] EUV light sources may also include a final steering element, which may include a steering mirror configured to adjust the direction of the incident beam. The final steering mirror may be located outside the container.

[0014] The optical element can be a reflective optical element, which may include a principal focal point and an intermediate focal point, and the device can be configured to align the path of the target with the principal focal point of the reflective optical element. The detection system may include a first sensor and a second sensor, the first sensor being configured to detect an image of one of the targets at the intermediate focal point. The reflective optical element may be located between the second sensor and the first sensor.

[0015] In another approach, one method includes: guiding a target along a path inside a container; providing a measurement beam into the container to generate scattered light; detecting the scattered light at a detection system; and adjusting the path based on information about the scattered light from the detection system. Each target comprises target material that emits EUV light in a plasma state. The scattered light is generated by the interaction between the measurement beam and one of the targets.

[0016] In another aspect, an apparatus for an optical system includes: a detection system comprising components configured to receive scattered measurement light; and a control system. The scattered measurement light includes light scattered from a target. Each target travels along a path, each target includes target material that reflects the measurement light, and each target is configured to act as a point source when illuminated by the measurement light. The control system is configured to adjust the path of each target to intersect with the principal focal point of the optical system.

[0017] The implementation may include one or more of the following features.

[0018] The target may include target material that emits EUV light when in a plasma state, and the target may be a target in a moving target stream. The target may be substantially spherical.

[0019] In another aspect, a method for inspecting optical elements in a container of an extreme ultraviolet (EUV) light source includes: illuminating a target with a measurement beam to scatter the measurement beam from the target; imaging an optical element in the container that receives the scattered measurement beam; and inspecting the optical element based on the imaged optical element. The target comprises a target material that emits EUV light when in a plasma state, and the measurement beam does not convert the target material into a plasma state.

[0020] In another approach, one method includes: providing a measurement beam into the interior of a container; imaging scattered light generated by the interaction between the measurement beam and a target material droplet to determine information about the path, the scattered light being reflected from optical elements associated with a primary focus and secondary focuses; adjusting the path based on the information such that the path intersects with the primary focus of the optical elements; and adjusting a steering element to guide the light along the propagation direction intersecting with the primary focus. The interaction between the measurement beam and the target material droplet does not produce plasma emitting EUV light.

[0021] The implementation may include one or more of the following features.

[0022] The method may further include: after adjusting the path and after adjusting the steering element, providing an amplified beam to the adjusted steering element such that the amplified beam is directed to the main focus. The amplified beam may have sufficient energy to convert at least some of the target material in the target material droplet into plasma that emits EUV light. The steering element may include a reflective optical element that receives some of the scattered light, and adjusting the steering element may include: moving the steering element and imaging the scattered light to align it with the reflective optical element such that the propagation direction intersects the main focus of the optical element. The scattered light may be imaged at a secondary focus of the optical element and at a location between the amplified beam source and the optical element.

[0023] Implementations of any of the above-described technologies may include EUV light sources, systems, methods, processes, equipment, or apparatus. Details of one or more embodiments are set forth in the accompanying drawings and the following description. Other features will be apparent from the description, the drawings, and the claims. Attached Figure Description

[0024] Figure 1 This is a block diagram of the device.

[0025] Figure 2A and Figure 2B This is a block diagram of another device.

[0026] Figure 2C yes Figure 2A and Figure 2B A perspective view of the optical elements of the device.

[0027] Figures 3A-3E yes Figure 2A and Figure 2B Block diagrams of various example implementations of the first sensor of the device.

[0028] Figure 4 This is a flowchart illustrating an example of the process for aligning a light source.

[0029] Figure 5 This is a flowchart illustrating an example of a process for inspecting optical components.

[0030] Figure 6A It is an image of a reflective surface.

[0031] Figure 6B This is another image of the reflective surface.

[0032] Figure 7 This is a block diagram of an EUV light source. Detailed Implementation

[0033] Figure 1 This is a block diagram of device 100. Device 100 is an EUV source that emits extreme ultraviolet (EUV) light 197. EUV light 197 is generated by producing plasma 196 that emits EUV light 197. Plasma 196 is formed by radiating a target 122 with an amplified beam 106. As described below, device 100 includes a detection system 130. Detection system 130 allows device 100 to be aligned without generating plasma 196 using reflected or scattered light 198. The reflected or scattered light 198 is generated by the interaction between one of the targets 122 and the measurement beam 108. The interaction between the target 122 and the measurement beam 108 does not interfere with the target 122 and does not generate plasma 196. Aligning device 100 without generating plasma 196 allows device 100 to be aligned more easily and efficiently. For example, device 100 can be aligned by the manufacturer before it is installed and used by the end user. This results in reduced installation time and a more productive experience for the end user. Furthermore, since plasma 196 also emits debris that could damage components, systems, and devices in device 100, the lifespan and overall performance of device 100 are increased by aligning device 100 with light 198 and not generating plasma 196.

[0034] The apparatus 100 includes a container 110 having an internal space 112. The internal space 112 is a vacuum space maintained under vacuum. The apparatus 100 also includes a material supply system 120 that launches a target 122 through a nozzle 113. For simplicity, in Figure 1 Only one target 122 is marked. However, the material supply system 120 can launch more than one target 122. The target 122 travels along path 121 within the interior 112. Figure 1 In the example, path 121 is typically along the X direction.

[0035] Material supply system 120 delivers, controls, and guides target 122 along path 121. Target 122 is made of a target mixture in the form of, for example, droplets, droplets comprising solid particles or clusters, solid particles contained within droplets, or solid particles contained within a liquid stream. Target 122 may be substantially spherical and may have a diameter, for example, from about 15 μm to 40 μm. Target mixture includes target material. Target material is any material that has an emission line in the EUV range when converted to a plasma state. Target material may be, for example, water, tin, lithium, and / or xenon, or substances comprising such materials. For example, elemental tin may be used as pure tin (Sn); as tin compounds, such as SnBr4, SnBr2, SnH4; as tin alloys, such as tin-gallium alloys, tin-indium alloys, tin-indium-gallium alloys, or any combination of these alloys. Target mixture may also include impurities such as non-target particles. Thus, in the absence of impurities, target mixture consists only of target material.

[0036] The interaction between the magnifying beam 106 and one of the targets 122 generates plasma 196. The magnifying beam 106 is any type of beam with energy sufficient to convert at least some of the target material in the target 122 into plasma 196. The magnifying beam 106 can be generated by, for example... Figure 2A and Figure 2B The light source 205 generates a pulsed laser beam. A measurement beam 108 also propagates within the interior 112. The measurement beam 108 interacts with the target 122 and generates light 198, which is reflected and / or scattered light, but this interaction does not alter the properties of the target 122 (such as, for example, size, shape, and / or density) or convert the target material into plasma 196. In other words, the measurement beam 108 generates light 198 by interacting with the target 122 without interfering with the optical probe of the target 122.

[0037] The detection system 130 detects light 198 and provides information related to light 198 to the control system 150. The control system 150 acts on one or more components of the device 100 to align the device 100 using information from the detection system 130. For example, the control system 150 may control the material supply system 120 to adjust the path 121 such that the path 121 (and the target 122) aligns with optical elements (such as...) in the interior 112. Figure 2A-2C The main focal points of the reflecting optical element 240 intersect. In another example, the control system 150 adjusts the optical element (such as optical element 263) based on information about the light 198, which causes the magnified beam 106 to be redirected.

[0038] refer to Figure 2A and Figure 2B A block diagram of device 200 is shown. Device 200 is a derivative of device 100. Figure 1The implementation method of ). Figure 2A The apparatus 200 is shown when the measuring beam 108 interacts with one of the targets 122 and produces light 198. Figure 2B The apparatus 200 is shown at a later time when the magnified beam 106 interacts with another target 122 and generates plasma 196.

[0039] The apparatus 200 includes a container 210 and a supply system 120 that supplies a target 122 to the interior 212 of the container 210. The target 122 travels along a path 221. The apparatus 200 also includes a measurement light source 209 and a main light source 205. The measurement light source 209 generates a measurement beam 108. The main light source 205 generates a magnified beam 106.

[0040] The device 200 also includes an optical element 240 in the interior 212. Figure 2A and Figure 2B A side cross-sectional view of the optical element 240 is shown. Figure 2C A perspective view of optical element 240 is shown. Optical element 240 is an elliptical parabolic mirror having a reflective surface 241 and a through-hole 245. The reflective surface 241 is curved. The through-hole 245 is located approximately at the center of the reflective surface 241 and extends through the optical element 240. The through-hole 245 provides a channel for the magnified light beam 106. A point light source at the principal focal point 242 is focused by the reflective surface 241 to the intermediate focal point 243. The principal focal point 242 is located between the reflective surface 241 and the intermediate focal point 243. The reflective surface 241 is made of a material that reflects EUV light 197 and incident light 198. Therefore, the reflective surface 241 reflects the incident EUV light 197 and incident light 198 to the intermediate focal point 243 and towards the scanner device 299.

[0041] To optimize the amount of EUV light 197 collected by optical element 240 and provided to scanner device 299, the propagation paths of path 221 and amplified beam 106 are aligned with the master focus 242. In other words, path 221 and beam 106 are guided through master focus 242. Conventionally, EUV light 197 is used to align path 221 and amplified beam 106 with master focus 242. For example, some existing systems repeatedly generate plasma 196 and measure the amount of EUV light 197 generated while adjusting the propagation direction of path 221 and / or amplified beam 106. When the maximum amount of EUV light 197 is generated, it is assumed that amplified beam 106 and path 221 are aligned or nearly aligned with master focus 242. This method requires generating plasma 196, which can damage other objects in surface 241 or interior 212. Furthermore, because each system has its own misalignment with master focus 242, conventional methods do not position master focus 242 relative to all systems that should be aligned with master focus 242. Furthermore, the conventional method needs to be repeated whenever a component aligned with the main focus 242 is replaced or moved for maintenance.

[0042] On the other hand, the device 200 uses light 198, which does not require the generation of plasma 196, to align path 221 and magnified beam 106 with the master focus 242. By using light 198 instead of EUV light 197, the device 200 avoids the contamination and damage that can occur with conventional methods. Furthermore, because EUV light 197 is not used for alignment, the device 200 can be aligned without generating any plasma 196. Therefore, the device 200 can be aligned by the manufacturer before installation and use by the end user. In addition, the use of light 198 allows multiple systems (supply system 120, master light source 205, and measurement light source 209) to be aligned to a common point (master focus 242). In other words, the light scattered from target 122 is used to identify the position of master focus 242 relative to multiple systems and components, thereby allowing supply system 120, measurement light source 209, and master light source 205 to be aligned with master focus 242 without generating plasma 196.

[0043] Before discussing an example of using lamp 198 to align device 200, the configuration of device 200 will be discussed in more detail.

[0044] Refer again Figure 2AA measurement light source 209 is coupled to an external region 211 of the container 210 at a viewing port 207. The viewing port 207 is sealed at the external region 211, allowing a vacuum to be maintained within the interior 212. The viewing port 207 includes a window or other element that is transparent to the wavelengths in the measurement beam 108. The measurement light source 209 generates the measurement beam 108, and the beam 108 passes through the transparent portion of the viewing port 207 and propagates within the interior 212. The measurement light source 209 may be, for example, a laser. The measurement beam 108 may be a continuous beam or a pulsed beam. The measurement beam 108 may include wavelengths in the visible light region (approximately 380 nanometers to 740 nanometers (nm)) and / or the near-infrared (NIR) region (approximately 0.7 μm to 5 μm). For example, the measurement light source 209 may be a laser that generates light with the following center wavelengths: 523nm, 808nm, 820nm, 908nm, 980nm, 1064nm, 1070nm, or 1550nm.

[0045] refer to Figure 2B The main light source 205 emits an amplified beam 106. The main light source 205 can be any type of light source capable of emitting the amplified beam 106. For example, the main light source 205 can be a carbon dioxide (CO2) laser. The center wavelength of the amplified beam 106 can be, for example, 10.6 μm or another wavelength between 9 μm and 11 μm. The amplified beam 106 can be a pulsed beam.

[0046] The light beam 106 travels through optical path 265 into the interior space 212. Optical path 265 is defined by optical elements 263 and 264. In the example shown, optical elements 263 and 264 are reflective optical elements such as mirrors. However, any type of optical element that guides the light can be used as elements 263 and 264. Figure 2A and Figure 2B The example shown has two optical elements. However, fewer or more optical elements can define path 265. Figure 2A and Figure 2B In one example, optical elements 263 and 264 are located outside the container 210. However, in other embodiments, optical element 264 is located inside the interior 212. In some embodiments, both optical elements 264 and 263 are located inside the interior 212.

[0047] Optical element 263 is coupled to actuator 262, while optical element 264 is coupled to actuator 267. Each actuator 262 and 267 is any type of device controllable to move optical elements 263 and 264, respectively. For example, each actuator 262 and 267 may include a motor, hinge, translation stage, or a combination of these elements. Each actuator 262 and 267 can be manually adjusted, or each actuator 262 and 267 may be coupled to a control system 250 for electronic control. The propagation direction of the amplified beam 106 within the interior 212 is adjusted by controlling one or more of the actuators 262 and 267.

[0048] The device 200 also includes a detection system 230 that receives information about the light 198 from one or more sensors. Figure 2A and Figure 2B In the example, the detection system 230 includes a first sensor 231 and a second sensor 238. The first sensor 231 includes an active element 232 configured to sense light 198 at or near the intermediate focal point 243. The active element 232 can be any type of active element that is sensitive to light 198. The active element 232 can be a single element that generates a certain amount of sensing light at a specific location, or the active element 232 can be a two-dimensional sensor array that generates two-dimensional image data. Figures 3A-3E Various example implementations relating to the first sensor 231.

[0049] Figure 3A and Figure 3B An embodiment of the first sensor 231 is shown as a movable sensor 331A, which includes an active sensing element 232. The movable sensor 331A is mechanically mounted to a mobility system 334 that enables the movable sensor 331A to move. For example, the mounting system 334 may be an arm or a track. The mounting system 334 may be manually controllable or may be coupled to a control system 250. When activated, the mounting system 334 moves the first sensor 331A from a first position (…). Figure 3A Move to the second position. Figure 3BWhen sensor 331A is in the first position, sensor 331A is displaced in the X direction relative to the intermediate focal point 243. When sensor 331A is in the second position, active sensing element 232 is located at the intermediate focal point 243. Therefore, when sensor 331A is in the second position, active element 232 is positioned to capture light reflected from reflective surface 241. When sensor 331A is in the first position, active element 232 is not positioned to capture light reflected from reflective surface 241, and sensor 331A does not block light reflected from surface 241. As described above, during the operation of device 200, EUV light 197 passes through intermediate focal point 243 and enters scanner device 299. Therefore, when sensor 331A is in the first position, it does not prevent EUV light 197 from reaching scanner device 299. In other words, when device 200 is being used to generate EUV light 197, sensor 331A is positioned in the first position (…). Figure 3A At the second position, when the device 200 is aligned, the sensor 331A is positioned at the second position. Figure 3B ) place.

[0050] Figure 3C This is a block diagram of sensor 331C and component 337. Sensor 331C is a component of sensor 231 ( Figure 2A and Figure 2B In another embodiment, sensor 331C includes an active sensing element 232. Sensor 331C is positioned away from the central focal point 243, and component 337 is used to scatter light 198 onto the active sensing element 232. Component 337 is any object that scatters light 198. For example, component 337 can be frosted glass, an imaging screen, a film, or a membrane. Component 337 can be positioned at the central focal point 243 or at a location shifted relative to the central focal point 243 in the Z or -Z direction. Figure 3C In the example shown, the component is displaced in the Z direction relative to the central focus 243.

[0051] Component 337 may be a movable component positioned at or near the intermediate focal point 243 only when light 198 is measured, and removed when EUV light 197 is generated. In some embodiments, component 337 scatters wavelengths in light 198 but transmits EUV light 197. In these embodiments, component 337 does not interfere with the delivery of EUV light 197 to scanner device 299 and remains in place while device 200 is being used to generate EUV light 197. Furthermore, this type of component 337 may also prevent or inhibit debris from plasma 196 from reaching scanner 299.

[0052] Figure 3D This is a perspective view of reflective surface 241, movable sensor 331D, and component 337D. Component 337D is a mask. Figure 3E This is a block diagram of mask 337D in the XY plane. Mask 337D includes a transparent portion 346 and an opaque portion 348. The transparent portion 346 is made of a material that is transparent or transmits light at the wavelength of light 198. For example, the transparent portion 346 can be made of quartz or plastic. The opaque portion 348 is made of a material that blocks or does not transmit wavelengths of light 198.

[0053] The center 347 of the transparent portion 346 of mask 337D is located at the intermediate focal point 243. The center 347 is aligned with the center of optical element 240 in the X and Y directions. The transparent portion 346 has the same shape as the focused image of reflective surface 241. When the point light source at the principal focal point 242 illuminates reflective surface 241, a focused image of reflective surface 241 is formed at the intermediate focal point 243. When illuminated by measurement beam 109, target 122 acts as a point light source. Therefore, when target 122 is at principal focal point 242, the image of reflective surface 241 is focused at intermediate focal point 243. When target 122 is at principal focal point 242, the amount of light transmitted by transparent portion 346 is maximum.

[0054] The movable sensor 331D is movable along the X and -X directions and / or the Y and -Y directions. When the movable sensor 331D is positioned to measure light passing through the transparent portion 346, the movable sensor 331D is aligned with the center 347 of the transparent portion 346 in the XY plane and displaced in the Z direction relative to the center of the transparent portion 346. When the device 200 is not aligned, the mask 337D and the sensor 331D can be moved along the X or -X and / or Y and -Y directions such that they no longer interact with light reflected from the reflective surface 241.

[0055] Back Figure 2A and Figure 2B The detection system 230 also includes a second sensor 238. The second sensor 238 includes an active element 239 sensitive to the wavelength of the light 198. The active element 239 may be, for example, an imaging sensor that captures two-dimensional data. The second sensor 238 is positioned along the optical path 265. A portion of the light 198 propagates in the -Z direction and along the optical path 265 through a via 245. This portion of the light 198 is referred to as return light 198 or reverse light 198. The second sensor 238 is used to detect the return light 198. For example, the active element 239 may be positioned to receive reflections of the return light 198 from the reflective optics 263.

[0056] Device 200 is coupled to control system 250. Control system 250 includes electronic processing module 251, electronic memory 252, and I / O interface 253. Electronic processing module 251 includes one or more processors adapted to execute computer programs, such as general-purpose or special-purpose microprocessors, and any one or more processors of any type of digital computer. Typically, the electronic processor receives instructions and data from read-only memory, random access memory (RAM), or both. Electronic processing module 251 may include any type of electronic processor. One or more electronic processors of electronic processing module 251 execute instructions and access data stored in electronic memory 252. One or more electronic processors are also capable of writing data to electronic memory 252.

[0057] Electronic memory 252 can be any type of computer-readable or machine-readable medium. For example, electronic memory 252 can be volatile or non-volatile memory such as RAM. In some embodiments, electronic memory 252 includes both non-volatile and volatile portions or components. Electronic memory 252 can store data and information used in the operation of control system 250. Electronic memory 252 can also store instructions (e.g., in the form of computer programs) that cause control system 250 to interact with components and subsystems in device 200 and / or scanner device 299. For example, instructions could be instructions that cause electronic processing module 251 to provide command signals to material supply 120 to change the direction of path 221, and / or to provide command signals to actuators 262 and 267 to change the propagation direction of amplified beam 106. Electronic memory 252 can also store information received from device 200 and / or scanner device 299. Electronic memory 252 also stores implementations regarding... Figure 4 and 5 Instructions for the process under discussion.

[0058] I / O interface 253 is any type of interface that allows control system 250 to exchange data and signals with an operator, other devices, and / or automated processes running on another electronic device. For example, in embodiments where rules or instructions stored on electronic memory 252 can be edited, this editing can be done via I / O interface 253. I / O interface 253 may include one or more visual displays, a keyboard, and communication interfaces such as parallel ports, Universal Serial Bus (USB) connections, and / or any type of network interface such as, for example, Ethernet. I / O interface 253 may also allow communication without physical contact via, for example, IEEE 802.11, Bluetooth, or Near Field Communication (NFC) connections.

[0059] The control system 250 is coupled to the various components of the device 200 via data connection 254. Data connection 254 is... Figure 2Aand Figure 2B It is shown in dashed lines. Figure 2A and Figure 2B In this diagram, the material supply system 120, detection system 230, and actuator 262 are shown coupled to the control system 250. However, other components of the device 200 may also be coupled to the control system 250. For example, actuator 267 may be coupled to the control system 250. Furthermore, scanner device 299 and / or main light source 205 may be coupled to the control system 250.

[0060] Data connection 254 is any type of connection that allows the transmission of data, signals, and / or information. For example, data connection 254 can be a physical cable or other physical data conduit (such as a cable that supports data transmission based on IEEE 802.3), a wireless data connection (such as a data connection that provides data via IEEE 802.11 or Bluetooth), or a combination of wired and wireless data connections.

[0061] The device 200 is provided as an example, and other implementations are possible. For example, the device 200 may be packaged separately from the control system 250, and the device 200 need not include the control system 250. The control system 250 is shown as a single control system. However, the control system 250 may be implemented as multiple control systems. For example, the control system 250 may be implemented as multiple local control systems, each associated with a specific component or subsystem of the device 200, wherein each local control system communicates with a host controller.

[0062] Similarly, the device 200 can be packaged separately from the scanner device 299 and the main light source 205, and the device 200 need not include the scanner device 299 or the main light source 205. In some embodiments, the device 200 includes an additional light source that provides a pre-pulsed beam that interacts with the target 122 before the amplified beam 106 interacts with the target 122. The pre-pulsed beam is used to modify one or more properties of the target 122 (such as size, shape, and / or density). Furthermore, the device 200 may include additional metrological light sources besides the metrological light source 209. Other metrological light sources may be mounted in the container 210.

[0063] Figure 4 This is a flowchart of process 400. Process 400 is an example of a process for aligning a light source. Regarding device 200 ( Figure 2A-2CThe discussion then moves to process 400. Process 400 can be executed by control system 250. For example, process 400 can be executed by one or more electronic processors in processing module 251. Process 400 can be executed before device 200 is shipped to the end user or before device 200 is installed at the end user's site. However, process 400 can also be executed during the life of device 200. For example, process 400 can be executed by the end user after device 200 has been installed at the end user's site.

[0064] Process 400 uses light 198 to align device 200 and is independent of the generation of plasma 196. When target 122 is illuminated by measurement beam 209, target 122 acts as a point source, and the light 198 generated by the interaction is used for alignment device 200.

[0065] A first sensor (410) is provided. The first sensor measures light 198 at or near the intermediate focal point 243. For example, the first sensor 331A can be moved such that the active element 232 is positioned at the intermediate focal point 243, as... Figure 3B As shown. In another example, component 337 is mounted at or near the intermediate focal point 243, such that light 198 received at the intermediate focal point 243 is directed to the active element 232. In yet another example, the first sensor 331D is positioned in the Z direction relative to the mask 337D, as shown. Figure 3D As shown.

[0066] A measurement beam is provided to the interior 212 (420). The measurement beam is any beam that acts as an optical probe and generates light 198 without interfering with the target 122. The measurement beam can be, for example, beam 108. The measurement beam 108 interacts with the target 122 to generate light 198. When the target 122 is at the principal focus 242, the measurement beam 108 is provided to the interior 212 at a time synchronized with the target 122.

[0067] As described above, light 198 is reflected and / or scattered light generated when beam 108 is incident on target 122. Target 122 is substantially spherical and acts as a point light source by reflecting the measurement beam 108. At least some of the light 198 is incident on reflective surface 241 and reflected toward intermediate focal point 243. The light 198 reaching intermediate focal point 243 is detected by active sensing element 232 of first sensor 231. Sensor 231 generates information or data based on the detected light 198 and provides this information to control system 250. This information may be, for example, two-dimensional image data representing an image of reflective optical surface 241 at intermediate focal point 243. In another example, the information about light 198 is the intensity of light 198 at or near intermediate focal point 243.

[0068] Information from the first sensor 231 is analyzed (430). As described above, when the target 122 is at the principal focus 242, the image of the reflective surface 241 is focused at the intermediate focus 243. The target 122 travels along path 221. Therefore, when the target 122 is at the principal focus 242, path 221 also intersects with the principal focus 242. By analyzing the information from the first sensor 231, process 400 determines whether path 221 intersects with the principal focus 242. In embodiments where the information from the first sensor 231 is two-dimensional image data, the image collected by sensor 231 is analyzed to determine the time when the reflective surface 241 is focused. For example, the reflective surface 241 can be considered focused when the imaging edge of the reflective surface 241 has a shape that most closely approximates the actual shape of the edge of the reflective surface 241. In another example, when using mask 337D, the reflective surface 241 is considered focused when the amount of light detected by the active element 232 is maximum. In the embodiment using mask 337D, when the maximum amount of light is transmitted through transparent portion 346, target 122 is located at main focal point 242.

[0069] Based on this analysis, it is determined whether path 221 intersects with the main focus 242 (440). If path 221 does not intersect with the main focus 242, path 221 is adjusted (450). For example, if information from the first sensor 231 indicates that light is reflected only from a small central portion of the reflective surface 241, or if light overfills the reflective surface 241, or if the distribution of reflected light is not centered on the center of the reflective surface 241, path 221 can be adjusted in the direction and extent to which the target material droplet 122 is better aligned with the main focus 242 as desired. Path 221 is adjusted in the Y and Z directions by adjusting the target supply system 120. For example, control system 150 can issue a command to move nozzle 113 to adjust path 221 in the Y and / or Z directions. Nozzle 113 can be moved, for example, by driving an actuator (not shown) mechanically mounted on nozzle 113. Process 400 is executed (420)-(450) until path 221 is aligned with the main focus 242 in the Y and Z directions.

[0070] Additionally, information from the first sensor 231 is used to align path 221 with the principal focus 242 in the X direction. The X coordinate of the principal focus 242 is found by scanning (moving) the measurement beam 108 along the X and / or -X directions until the principal focus 242 is located.

[0071] Light 198 can also be used to align the second sensor 238 with the main focus 242. By aligning the second sensor 238 with the main focus 242, the propagation direction of the magnified beam 106 is also aligned with the main focus 242. In order to align the second sensor 238 with the main focus 242, the return light 198 (which is the portion of light 198 that passes through the through-hole 245 and reaches the path 265) is imaged by the second sensor 238. The second sensor 238 generates information about the detected return light 198. The information from the second sensor 238 is analyzed (460). When the target material droplet 122 is at the main focus 242, the target 122 should appear as a point in the image of the target 122 generated by the second sensor 238. Because the path 221 is aligned with the main focus 242 using (420)-(450) as described above, if the image of the target 122 generated by the second sensor 238 does not show the target 122 as a point, then the optical element 263 is not aligned with the main focus 242. When optical element 263 is not aligned with the main focus 242, optical element 263 will not guide the forward-entering beam (such as magnifying beam 106) to the main focus 242.

[0072] Analysis of the information from the second sensor 238 is used to determine whether the target 122 appears as a point in the image, and to determine whether the second sensor 238 is aligned with the main focus 242 (470). Analyzing the information from the second sensor 238 may include applying a shape filter or other spatial filter to the image data from the second sensor 238. When the target 122 appears as a point source in the image data, the shape filter or mask has the shape of the image of the target 122. Alternatively or additionally, light 198 may be compared with a reference mark on the second sensor 238 to determine whether the second sensor 238 is aligned with the main focus 242.

[0073] If target 122 appears as a point in the image from second sensor 238, then optical element 263 is aligned relative to principal focus 242 and is not adjusted. Process 400 ends. If target 122 does not appear as a point in the image from second sensor, then optical element 263 is adjusted (480). Control system 250 issues a command to actuator 262 to move optical element 263. Another target 122 is irradiated with measurement beam 108, and the information from second sensor 238 is analyzed again (460). Control system 250 continues to command actuator 262 to adjust optical element 263 until target 122 appears as a point in the image generated by second sensor 238.

[0074] When the device 200 is used to generate EUV light 197, the optical element 263 delivers the amplified beam 106 to the interior 212. As discussed with respect to (460)-(480), the optical element 263 is also aligned with the main focus 242 by aligning the second sensor 238 with the main focus 242. Therefore, the optical element 263 also delivers the forward-entering beam (such as the amplified beam 106) to the main focus 242. In this way, the amplified beam 106 is aligned with the main focus 242 without actually delivering the amplified beam 106 to the interior 212 and without generating the plasma 196 that emits EUV light 197. Furthermore, although in Figure 2A and 2B The device 200 shows a main light source 205, but the main light source 205 is not required to align the magnified beam 106 with the main focus 242.

[0075] In embodiments where beam 106 and other beams (such as a pre-pulse beam) guided by optical element 263 into interior 212 are pulsed beams, the generation of plasma 196 is optimized when the pulse arrives at the main focus 242 simultaneously with one of the targets 122. Measurement beam 108 can also be used to determine the timing of the optical pulse. Specifically, measurement beam 108 can be used to determine the time at which the pulse of beam 106 (or the pulse of the pre-pulse beam) should arrive at the main focus 242 such that the optical pulse and the target 122 are simultaneously at the main focus 242.

[0076] After aligning the target path 221 and the measurement beam 108 to the main focus 242 in process 400, the pulses of the measurement beam 108 are directed to the main focus 242. Light 198 (which is the reflection and / or scattering of the pulses of the measurement beam 108 leaving one of the targets 122) is temporally resolved by detecting the light 198 at a second sensor 238 (or another detector, such as a photodiode) that receives light from path 265. The reflected pulse (light 198) precisely determines the time it takes for one of the irradiated targets 122 to pass through the main focus 242. There is a delay between the time of the pulse forming beam 106 (or other forward-entry light pulses propagating along path 265) and the time it takes for the forward-entry light pulses to reach the main focus 242. This delay is called the pulse delay time and is equal to the speed of light in the medium multiplied by the path length between the pulse source and the main focus 242. The time taken for target 122 to pass through main focus 242 minus the pulse delay time provides the time at which a forward-entry pulse source (such as main source 205) should be activated, excited, or aroused to generate a pulse. Control system 250 can determine the pulse delay time and the activation time of the forward-entry pulse source. Furthermore, target 122 can be emitted from material supply system 120 at regular intervals. Light 198 can also be used to confirm or measure the emission rate of the target, and knowledge of the rate can be used to set the timing of light pulse generation.

[0077] Figure 5 This is a flowchart of process 500. Process 500 is an example of a process for inspecting optical element 240. Process 500 is discussed in relation to apparatus 200. Process 500 can be executed by control system 250. For example, process 500 can be executed by one or more electronic processors in processing module 251. Process 500 can be executed after path 221 has been aligned with main focus 242 and after apparatus 200 has been used to generate plasma 196.

[0078] A measurement beam 108 is applied to one of the targets 122 (510). The measurement beam 108 is scattered and / or reflected from the target 122 to generate light 198. The light 198 is reflected off the reflective surface 241 and imaged at the first sensor 231 (520). The first sensor 231 generates image data of the reflective surface 241. The reflective surface 241 is examined based on the generated image data (530).

[0079] As described above, target 122 acts as a point light source, and when target 122 is illuminated at the principal focal point 242, light 198 reflected from reflective surface 241 produces a focused image of reflective surface 241 at intermediate focal point 243. This focused image can be used to inspect reflective surface 241. For example, the focused image can show damage and debris that has formed on reflective surface 241 due to the formation of plasma 196.

[0080] Moreover, the image produced by light 198 is a clearer image of the reflective surface 241 than the image of the reflective surface 241 formed by EUV light 197. Figure 6A and Figure 6B Examples of corresponding images 687A and 687B of reflective surface 241. Figure 6A Image 687A of the reflective surface 241 formed using EUV light 197. Figure 6B Image 687B shows the reflective surface 241 formed by light 198 in an embodiment where the measurement beam 108 has a wavelength of 1070 nm. Image 687A ( Figure 6A The horizontal bar in the middle region of the image is the EUV detector. The image of the reflective surface 241 formed by light 198 is clearer and more suitable for inspecting the reflective surface 241. For example, a defect 689 is present in images 687A and 687B. However, defect 689 is clearer in image 687B. Image 687B (which is an image of the reflective surface 241 obtained based on light 198) allows for a more efficient inspection of the reflective surface 241 and can allow for such inspection either automatically (e.g., by a computer program implemented on control system 250) or manually by examining the image without removing the optical element 240 from container 210.

[0081] refer to Figure 7This illustrates an embodiment of the LPP EUV light source 700. The LPP EUV light source 700 is an EUV light source 100 ( Figure 1 The implementation of the method is as follows. By providing a measurement beam (such as measurement beam 108) into the interior 707 of the vacuum cavity 730 of the light source 700, processes 400 and 500 can be performed with the EUV light source 700.

[0082] The EUV light source 700 includes a target supply system 727. The EUV light source 700 may include a measurement source for generating a measurement beam, such as a measurement beam 108. Figure 2A The measurement light source 209 of the EUV light source 700 may also include a detection system, such as the detection system 130. Figure 1 ) or detection system 230 ( Figure 2A and Figure 2B It detects the scattered light generated by the interaction between the measurement beam and the target provided from the target supply system 727.

[0083] An LPP EUV source 700 is formed by irradiating the target mixture 714 at the plasma formation region 705 with an amplified beam 710 traveling along a beam path toward the target mixture 714. (About...) Figure 1 The target material in the target 122 under discussion may be or includes a target mixture 714. The plasma formation region 705 is located within the interior 707 of the vacuum cavity 730. When the magnifying beam 710 strikes the target mixture 714, the target material within the target mixture 714 is converted into a plasma state with an emission line in the EUV range. The resulting plasma possesses certain characteristics depending on the composition of the target material within the target mixture 714. These characteristics may include the wavelength of the EUV light generated by the plasma and the type and amount of debris released from the plasma.

[0084] The light source 700 includes a driving laser system 715 that generates an amplified beam 710 due to population inversion within one or more gain media of the laser system 715. The light source 700 includes a beam delivery system between the laser system 715 and a plasma formation region 705. The beam delivery system includes a beam transport system 720 and a focusing assembly 722. The beam transport system 720 receives the amplified beam 710 from the laser system 715, redirects and modifies the amplified beam 710 as needed, and outputs the amplified beam 710 to the focusing assembly 722. The focusing assembly 722 receives the amplified beam 710 and focuses the beam 710 onto the plasma formation region 705.

[0085] In some embodiments, the laser system 715 may include one or more optical amplifiers, lasers, and / or lamps for providing one or more master pulses and, in some cases, one or more pre-pulses. Each optical amplifier includes a gain medium capable of optically amplifying a desired wavelength at high gain, an excitation source, and internal optics. The optical amplifier may or may not have a laser mirror or other feedback device forming a laser cavity. Thus, even without a laser cavity, the laser system 715 generates an amplified beam 710 due to population inversion in the gain medium of the laser amplifier. Furthermore, if a laser cavity is present to provide sufficient feedback to the laser system 715, the laser system 715 can generate an amplified beam 710 as a coherent laser beam. The term "amplified beam" includes one or more of the following: light from the laser system 715 that is only amplified but not necessarily a coherent laser oscillation; and light from the laser system 715 that is amplified and is also a coherent laser oscillation.

[0086] The optical amplifier in laser system 715 may include a filling gas, including CO2, as a gain medium, and may amplify light with wavelengths between approximately 9100 nm and approximately 11000 nm, particularly with wavelengths around 10600 nm, at a gain of greater than or equal to 900 times. Suitable amplifiers and lasers for laser system 715 may include pulsed laser devices, such as pulsed gas discharge CO2 laser devices that generate radiation of approximately 9300 nm or approximately 10600 nm, for example, which utilize DC or RF excitation operating at relatively high power (e.g., 10 kW or higher) and high pulse repetition rate (e.g., 40 kHz or higher) to generate the aforementioned radiation. The pulse repetition rate may be, for example, 50 kHz. The optical amplifier in laser system 715 may also include a cooling system, such as water, which may be used when laser system 715 is operated at higher power.

[0087] The light source 700 includes a collector mirror 735 having an aperture 740 to allow the amplified beam 710 to pass through and reach the plasma formation region 705. The collector mirror 735 may be, for example, an ellipsoidal mirror having a primary focal point at the plasma formation region 705 and a secondary focal point (also referred to as an intermediate focal point) at an intermediate position 745, from which EUV light can be output from the light source 700 and input to, for example, an integrated circuit lithography tool (not shown). The light source 700 may also include a hollow conical shroud 750 (e.g., a gas cone) with open ends, which tapers gradually from the collector mirror 735 toward the plasma formation region 705 to reduce the amount of plasma-generated debris entering the focusing assembly 722 and / or the beam delivery system 720, while allowing the amplified beam 710 to reach the plasma formation region 705. For this purpose, an airflow directed to the plasma formation region 705 may be provided within the shroud.

[0088] The light source 700 may also include a main controller 755 connected to a droplet position detection feedback system 756, a laser control system 757, and a beam control system 758. The light source 700 may include one or more target or droplet imagers 760 that provide an output representing, for example, the position of a droplet relative to a plasma formation region 705, and provide this output to the droplet position detection feedback system 756, which can, for example, calculate the droplet position and trajectory, and calculate the droplet position error droplet-by-drop or on average based on the droplet position and trajectory. Therefore, the droplet position detection feedback system 756 provides the droplet position error as input to the main controller 755. Thus, the main controller 755 can provide laser position, direction, and timing correction signals to, for example, the laser control system 757, which may be used to control, for example, a laser timing circuit, and / or to the beam control system 758, which controls the position and shape of the amplified beam of the beam delivery system 720 to change the position and / or focal length of the beam within the cavity 730.

[0089] The supply system 725 includes a target material delivery control system 726, which is operable in response to a signal from the main controller 755, for example, to modify the release point of the droplets released by the target supply system 727 to correct errors in the droplets reaching the desired plasma formation region 705.

[0090] Additionally, the light source 700 may include light source detectors 765 and 770 for measuring one or more EUV light parameters, including but not limited to pulse energy, energy distribution as a function of wavelength, energy within a specific wavelength band, energy outside a specific wavelength band, and angular distribution of EUV intensity and / or average power. The light source detector 765 generates a feedback signal used by the main controller 755. The feedback signal may be, for example, an error in parameters such as the timing and focal length of a laser pulse, to properly intercept the droplet at the correct position and time for effective and efficient EUV light generation.

[0091] The light source 700 may also include a guide laser 775, which can be used to align various portions of the light source 700 or to help direct the amplified beam 710 toward the plasma formation region 705. In conjunction with the guide laser 775, the light source 700 includes a measurement system 724 disposed within a focusing assembly 722 to sample a portion of the light from the guide laser 775 and the amplified beam 710. In other embodiments, the measurement system 724 is disposed within a beam delivery system 720. The measurement system 724 may include optical elements for sampling or redirecting a subset of the light, such optical elements being made of any material capable of withstanding the power of the guide laser beam and the amplified beam 710. A beam analysis system is formed by the measurement system 724 and a master controller 755, as the master controller 755 analyzes the sampled light from the guide laser 775 and uses this information to adjust components within the focusing assembly 722 via a beam control system 758.

[0092] Therefore, in summary, the light source 700 generates an amplified beam 710, which is guided along a beam path to radiate the target mixture 714 at the plasma formation region 705, thereby converting the target material within the mixture 714 into a plasma that emits light in the EUV range. The amplified beam 710 operates at a specific wavelength (also known as the driving laser wavelength) determined based on the design and characteristics of the laser system 715. Additionally, the amplified beam 710 can be a laser beam when the target material provides sufficient feedback back to the laser system 715 to generate coherent laser light, or if the driving laser system 715 includes suitable optical feedback to form a laser cavity.

[0093] Other aspects of the invention are set forth in the following numbered clauses.

[0094] 1. An apparatus comprising:

[0095] A container, including its internal space;

[0096] A material supply system is configured to provide a target comprising target material along a path in the internal space, wherein the target material generates extreme ultraviolet (EUV) light when in a plasma state.

[0097] A detection system is configured to detect scattered light generated by the interaction between one of the targets and a measurement beam, and to generate information based on the interaction, wherein the measurement beam does not convert the target material into the plasma state; and

[0098] The control system is configured to adjust the path based on the information generated by the detection system.

[0099] 2. The apparatus according to Clause 1 further includes:

[0100] The reflective optical element in the internal space includes a principal focal point and an intermediate focal point, and wherein...

[0101] The control system is configured to adjust the path such that the path intersects with the principal focal point of the reflective optical element.

[0102] 3. The apparatus according to Clause 2, wherein the control system is further configured to adjust a steering element that guides the light along the propagation direction in the container such that the propagation direction intersects the main focal point.

[0103] 4. The apparatus according to Clause 2, wherein the detection system is configured to detect the scattered light after the scattered light has been reflected from the reflective optical element.

[0104] 5. The apparatus according to Clause 2, wherein the detection system includes an imaging sensor and the detection system is configured to image the scattered light after the scattered light has been reflected from the reflective optical element.

[0105] 6. The apparatus according to Clause 2, wherein the detection system includes a component at the intermediate focal point or at a location between the intermediate focal point and a scanner device receiving light from the apparatus.

[0106] 7. The apparatus according to Clause 6, wherein the component includes a mask, and the detection system further includes a detector configured to detect light transmitted through the mask.

[0107] 8. The apparatus according to Clause 6, wherein the component includes a detector configured to be placed at or removed from the intermediate focus.

[0108] 9. The apparatus according to Clause 6, wherein the component includes an imaging plane comprising a material that allows the scattered light to be sensed by the imaging system.

[0109] 10. The apparatus according to Clause 9, wherein the imaging plane comprises frosted glass.

[0110] 11. The apparatus according to Clause 9, wherein the imaging plane comprises a film or a surface film.

[0111] 12. The apparatus according to Clause 9, wherein the imaging plane substantially blocks fragments of target material.

[0112] 13. The apparatus according to Clause 1, wherein each point along the path is a position in a three-dimensional coordinate system, and the control system is configured to adjust the position of at least one of the points of the path in at least two of the three dimensions.

[0113] 14. The apparatus according to Clause 13, wherein the control system is configured to adjust the position of the path by controlling the material supply system.

[0114] 15. The apparatus according to Clause 1 further includes a measuring light source.

[0115] 16. The apparatus according to Clause 15, wherein the measurement light source is a laser configured to generate visible light or a laser configured to generate infrared light.

[0116] 17. The apparatus according to Clause 15, wherein the measurement light source is a pulsed light source and the measurement beam comprises a plurality of light pulses.

[0117] 18. The apparatus according to Clause 15, wherein the measurement light source is a continuous wave light source and the measurement beam comprises a continuous wave beam.

[0118] 19. An extreme ultraviolet (EUV) light source, comprising:

[0119] container;

[0120] A target material supply system configured to supply a target to the interior of the container, wherein the target comprises target material that emits EUV light when in a plasma state, and the target travels along a path within the interior of the container; and

[0121] An apparatus configured to align the path of the target with the focal point of an optical element within the interior of the container, the apparatus comprising:

[0122] A detection system is configured to detect scattered light generated by the interaction between one of the targets and a measurement beam, and to generate information based on the interaction, wherein the measurement beam does not convert the target material into the plasma state, and the one of the targets is configured to act as a point source when irradiated by the measurement beam; and

[0123] The control system is configured to adjust the path of the target based on the information generated by the detection system.

[0124] 20. The EUV light source according to Clause 19 further includes a steering element configured to receive an amplified beam having energy sufficient to convert at least some of the target material into the plasma state.

[0125] 21. The EUV light source according to Clause 19 further includes a final steering element, the final steering element comprising a steering mirror configured to adjust the direction of the incident beam.

[0126] 22. The EUV light source as described in Clause 21, wherein the final steering mirror is outside the container.

[0127] 23. An EUV light source according to Clause 19, wherein the optical element is a reflective optical element comprising a principal focus and an intermediate focus, and the device is configured to align the path of the target with the principal focus of the reflective optical element.

[0128] 24. The EUV light source according to Clause 23, wherein the detection system includes a first sensor and a second sensor, the first sensor being configured to detect an image of the target at the intermediate focal point, and the reflective optical element being located between the second sensor and the first sensor.

[0129] 25. A method comprising:

[0130] The targets are guided along a path inside the container, each target comprising target material that emits EUV light when in a plasma state;

[0131] A measurement beam is provided to the interior of the container to generate scattered light, the scattered light being generated by the interaction between one of the targets and the measurement beam;

[0132] The scattered light is detected at the detection system; and

[0133] The path is adjusted based on information about the scattered light from the detection system.

[0134] 26. An apparatus for an optical system, the apparatus comprising:

[0135] The detection system includes a component configured to receive scattering measurement light, the scattering measurement light comprising light scattered from a target, wherein...

[0136] Each target travels along the path, each target includes target material that reflects the measurement light, and each target is configured to act as a point light source when illuminated by the measurement light; and

[0137] The device also includes a control system configured to adjust the path of each target to intersect with the main focus of the optical system.

[0138] 27. The apparatus according to Clause 26, wherein the target comprises target material that emits EUV light when in a plasma state, and the target is a target in a moving target stream.

[0139] 28. The apparatus according to Clause 27, wherein the target is substantially spherical.

[0140] 29. A method for inspecting optical elements in a container of an extreme ultraviolet (EUV) light source, the method comprising:

[0141] A measurement beam is used to illuminate a target to scatter the measurement beam from the target, wherein the target comprises a target material that emits EUV light when in a plasma state, and the measurement beam does not convert the target material into the plasma state;

[0142] Imaging the optical element in the container that receives the scattered measurement beam; and

[0143] The optical element is examined based on the imaged optical element.

[0144] 30. A method comprising:

[0145] Provide a measurement beam to the interior of the container;

[0146] The scattered light generated by the interaction between the measurement beam and the target material droplet is imaged to determine information about the path, wherein the scattered light is reflected from optical elements associated with the primary and secondary focal points;

[0147] Based on the information, the path is adjusted such that it intersects with the principal focal point of the optical element; and

[0148] The steering element is adjusted to guide the light along the propagation direction intersecting the main focal point, wherein...

[0149] The interaction between the measurement beam and the target material droplet does not produce plasma that emits EUV light.

[0150] 31. The method described under clause 30 further includes:

[0151] After adjusting the path and after adjusting the steering element, a magnified beam is provided to the adjusted steering element such that the magnified beam is provided to the main focal point, and wherein...

[0152] The amplified beam has sufficient energy to convert at least some of the target material in the droplet into plasma that emits EUV light.

[0153] 32. The method according to Clause 31, wherein the steering element comprises a reflective optical element that receives some of the scattered light, and adjusting the steering element comprises: moving the steering element and imaging the scattered light to align it with the reflective optical element such that the propagation direction intersects with the principal focal point of the optical element.

[0154] 33. The method according to clause 32, wherein the scattered light is imaged at the secondary focal point of the optical element and at a location between the source of the amplified beam and the optical element.

[0155] The above-described embodiments and other embodiments are within the scope of the claims.

Claims

1. An apparatus for aligning extreme ultraviolet (EUV) light, comprising: A container, including its internal space; A material supply system is configured to provide a target comprising target material along a path in the internal space, wherein the target material generates extreme ultraviolet (EUV) light when in a plasma state. A detection system is configured to detect scattered light generated by the interaction between one of the targets and a measurement beam, and to generate information based on the interaction, wherein the measurement beam does not convert the target material into the plasma state. as well as The control system is configured to adjust the path based on the information generated by the detection system.

2. The apparatus according to claim 1, further comprising: The reflective optical element in the internal space includes a principal focal point and an intermediate focal point, and wherein... The control system is configured to adjust the path such that the path intersects with the principal focal point of the reflective optical element.

3. The apparatus of claim 2, wherein the control system is further configured to adjust a guiding element that directs light along a propagation direction in the container such that the propagation direction intersects the main focal point.

4. The apparatus of claim 2, wherein the detection system is configured to detect the scattered light after the scattered light has been reflected from the reflective optical element.

5. The apparatus of claim 2, wherein the detection system includes an imaging sensor, and the detection system is configured to image the scattered light after the scattered light has been reflected from the reflective optical element.

6. The apparatus of claim 2, wherein the detection system includes a component at the intermediate focal point or at a location between the intermediate focal point and a scanner device receiving light from the apparatus.

7. The apparatus of claim 6, wherein the component includes a mask, and the detection system further includes a detector configured to detect light transmitted through the mask.

8. The apparatus of claim 6, wherein the component includes a detector configured to be placed at or removed from the intermediate focus.

9. The apparatus of claim 6, wherein the component includes an imaging plane comprising a material that allows the scattered light to be sensed by the imaging system.

10. The apparatus of claim 9, wherein the imaging plane comprises frosted glass.

11. The apparatus of claim 9, wherein the imaging plane comprises a film or a surface film.

12. The apparatus of claim 9, wherein the imaging plane substantially blocks target material fragments.

13. The apparatus of claim 1, wherein each point along the path is a position in a three-dimensional coordinate system, and the control system is configured to adjust the position of at least one of the points along the path in at least two of the three dimensions.

14. The apparatus of claim 13, wherein the control system is configured to adjust the position of the path by controlling the material supply system.

15. The apparatus of claim 1, further comprising a measuring light source.

16. The apparatus of claim 15, wherein the measurement light source is a laser configured to generate visible light or a laser configured to generate infrared light.

17. The apparatus of claim 15, wherein the measurement light source is a pulsed light source, and the measurement beam comprises a plurality of light pulses.

18. The apparatus of claim 15, wherein the measurement light source is a continuous wave light source, and the measurement beam comprises a continuous wave beam.

19. An extreme ultraviolet (EUV) light source, comprising: container; A target material supply system is configured to supply a target to the interior of the container, wherein the target comprises target material that emits EUV light when in a plasma state, and the target travels along a path within the interior of the container; as well as An apparatus configured to align the path of the target with the focal point of an optical element within the interior of the container, the apparatus comprising: A detection system is configured to detect scattered light generated by the interaction between one of the targets and a measurement beam, and to generate information based on the interaction, wherein the measurement beam does not convert the target material into the plasma state, and the one of the targets is configured to act as a point source when irradiated by the measurement beam; and The control system is configured to adjust the path of the target based on the information generated by the detection system.

20. The extreme ultraviolet light source of claim 19 further includes a deflecting element configured to receive an amplified beam having energy sufficient to convert at least some of the target material into the plasma state.

21. The extreme ultraviolet light source of claim 19, further comprising a final steering element, the final steering element comprising a steering mirror configured to adjust the direction of the incident beam.

22. The extreme ultraviolet light source of claim 21, wherein the final steering element is outside the container.

23. The extreme ultraviolet light source of claim 19, wherein the optical element is a reflective optical element comprising a principal focus and an intermediate focus, and the device is configured to align the path of the target with the principal focus of the reflective optical element.

24. The extreme ultraviolet light source of claim 23, wherein the detection system comprises a first sensor and a second sensor, the first sensor being configured to detect an image of the target at the intermediate focal point, and the reflective optical element being located between the second sensor and the first sensor.

25. A method for aligning extreme ultraviolet (EUV) light, comprising: The targets are guided along a path inside the container, each target comprising target material that emits EUV light when in a plasma state; A measurement beam is provided to the interior of the container to generate scattered light, the scattered light being generated by the interaction between one of the targets and the measurement beam; The scattered light is detected at the detection system; as well as The path is adjusted based on information about the scattered light from the detection system.

26. An apparatus for an optical system, the apparatus comprising: The detection system includes a component configured to receive scattering measurement light, the scattering measurement light comprising light scattered from a target, wherein... Each target travels along the path, each target includes target material that reflects the measurement light, and each target is configured to act as a point light source when illuminated by the measurement light; and The apparatus also includes a control system configured to adjust the path of each target to intersect with the main focal point of the optical system.

27. The apparatus of claim 26, wherein the target comprises a target material that emits EUV light when in a plasma state, and the target is a target in a moving target stream.

28. The apparatus of claim 27, wherein the target is spherical.

29. A method for inspecting optical elements in a container of an extreme ultraviolet (EUV) light source, the method comprising: A measurement beam is used to illuminate a target to scatter the measurement beam from the target, wherein the target comprises a target material that emits EUV light when in a plasma state, and the measurement beam does not convert the target material into the plasma state; Imaging the optical element in the container that receives the scattered measurement beam; and The optical element is inspected based on the imaging of the optical element.

30. A method for aligning extreme ultraviolet (EUV) light, comprising: Provide a measurement beam to the interior of the container; The scattered light generated by the interaction between the measurement beam and the target material droplet is imaged to determine information about the path, wherein the scattered light is reflected from optical elements associated with the primary and secondary focal points; The path is adjusted based on the information so that it intersects with the principal focal point of the optical element; as well as Adjust the steering element used to guide the light along the propagation direction intersecting the main focal point. The interaction between the measurement beam and the target material droplet does not generate plasma that emits EUV light.

31. The method of claim 30, further comprising: After adjusting the path and after adjusting the steering element, a magnified beam is provided to the adjusted steering element such that the magnified beam is provided to the main focal point, and wherein... The amplified beam has sufficient energy to convert at least some of the target material in the droplet into plasma that emits EUV light.

32. The method of claim 31, wherein the steering element comprises a reflective optical element that receives a portion of the scattered light, and adjusting the steering element comprises: The steering element is moved and the scattered light is imaged to align with the reflective optical element such that the propagation direction intersects with the principal focal point of the optical element.

33. The method of claim 32, wherein the scattered light is imaged at the secondary focal point of the optical element and at a location between the source of the amplified beam and the optical element.

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