light emission monitoring

Abstract

A system is provided comprising a vacuum chamber having an internal region configured to receive a target and a light beam. The target material emits extreme ultraviolet (EUV) light when in a plasma state. The system also includes a detection system configured to image the internal region by detecting light emission from atoms, ions, or molecules within the internal region and by generating a representation of the spatial distribution of light emission within the internal region. A control system is connected to the detection system. The control system is configured to analyze the representation of the spatial distribution to determine the spatial distribution of light emission from atoms, ions, or molecules within the internal region and to determine whether to adjust the characteristics of the light beam and / or the characteristics of the vacuum chamber based on the spatial distribution of the light emission.

Description

Technology Field

[0001] Cross-reference regarding related applications

[0002] This application claims priority to U.S. Application No. 62 / 751,267, filed on October 26, 2018, with the title of the invention “MONITORING LIGHT EMISSIONS,” which is incorporated herein by reference in its entirety.

[0003] The present invention relates to monitoring light emission. The light emission may be the emission of light generated in a vacuum chamber of an extreme ultraviolet (EUV) light source. Background Technology

[0004] Extreme ultraviolet ("EUV") light, for example, electromagnetic radiation having a wavelength of 100 nanometers (nm) or less (sometimes referred to as soft X-rays) including light at wavelengths of, for example, 20 nm or less, 5 to 20 nm, or 13 to 14 nm, can be used in a photolithography process to initiate polymerization in a resist layer, thereby creating extremely small features on a substrate, for example, a silicon wafer.

[0005] Methods for generating EUV light involve, but are not limited to, converting a material containing elements such as xenon, lithium, or tin into EUV-range emission lines in a plasma state. In one such method, commonly referred to as a laser-generated plasma ("LPP"), the required plasma can be generated by irradiating a target material, for example in the form of a droplet, plate, tape, stream, or cluster of material, with amplified light, which may be referred to as a drive laser. For this process, the plasma is typically generated within a sealed vessel (e.g., a vacuum chamber) and monitored using various types of instrumentation. means of solving the problem

[0006] In one general embodiment, the system comprises a vacuum chamber comprising an inner region—the inner region is configured to receive a target and a light beam, the target comprises a target material, and the target material emits extreme ultraviolet (EUV) light when in a plasma state; a detection system configured to image the inner region, detect light emission from atoms, ions, or molecules within the inner region, and generate a representation of the spatial distribution of light emission in the inner region; and a control system connected to the detection system and configured to analyze the representation of the spatial distribution of light emission to determine the spatial distribution of light emission from atoms, ions, or molecules in the inner region; and to determine whether to adjust at least one characteristic of the light beam and / or at least one characteristic of the vacuum chamber based on the spatial distribution of light emission.

[0007] The implementation may include one or more of the following features. Photoluminescence may include fluorescence. Fluorescence may include laser-induced fluorescence. A control system configured to analyze the representation may further include a control system configured to compare the spatial distribution of fluorescence within the internal region at least two different times to estimate the velocity of ions within the internal region and to compare the estimated velocity with a velocity specification, and the control system may be configured to determine whether to adjust the gas pressure based on the comparison of the estimated velocity and the velocity specification.

[0008] The system may also further include one or more spectral filters configured to be positioned relative to the detection system, and the spectral filters are configured to allow only some wavelengths to reach the detection system. Each of the one or more spectral filters may be configured to transmit light having a wavelength within one of the emission lines of a plurality of emission lines of the target material. In some embodiments, at least one of the one or more spectral filters may be configured to transmit wavelengths within the visible light range. The vacuum chamber may be further configured to contain gas in an internal region, and the spectral filters may be configured to transmit light having a wavelength in the emission line of the gas.

[0009] The control system may be configured to accept multiple representations of an internal region, each of which may be associated with different times, and the control system may be configured to analyze the representations of the internal region, which may include the control system analyzing each of the multiple representations to determine the spatial distribution of light emission within the internal region at each different time. Light emission within the internal region may arise from an energy event within the internal region, and the different times are all times occurring after the energy event. The energy event may include an interaction between a light beam and a target, and the light emission may be emission from (a) a target material, (b) a plasma formed from the interaction between the light beam and the target material, and / or (c) a fragment formed from the interaction between the light beam and the target.

[0010] The control system may be configured to accept an extended exposure representation for the internal region, the extended exposure representation for the internal region comprising the average of the spatial distribution of emissions within the internal region over a given period. The vacuum chamber may be further configured to contain gas within the internal region, the energy event may be an interaction that adds energy to the gas, and the light emission may be an emission from the gas. The interaction that adds energy to the gas may include (a) an interaction between the light beam and the gas, (b) an interaction between the gas and the plasma formed from the interaction between the light beam and the target, and / or (c) an interaction between the gas and the ions.

[0011] A control system configured to analyze a representation to determine the spatial distribution of light emission in an internal region may include a control system configured to estimate the spatial distribution and / or shape of the intensity of light emission.

[0012] In some embodiments, the system also includes a first spectral filter configured to transmit light having a wavelength within a first wavelength band; and a second spectral filter configured to transmit light having a wavelength within a second wavelength band, wherein the control system configured to analyze the expression may include the control system estimating the amount of light emission in the first wavelength band and estimating the amount of light emission in the second wavelength band, and the control system may be further configured to estimate the ionization fraction of the target material based on comparing the estimated amount of light emission in the first wavelength band and the estimated amount of light emission in the second wavelength band. The control system may determine whether to adjust at least one characteristic of the light beam based on the estimated ionization fraction. The control system may determine whether to adjust the directional orientation of the light beam based on the estimated ionization fraction.

[0013] The light beam may include a main pulsed light beam having sufficient energy to convert at least a portion of the target material into a plasma emitting EUV light.

[0014] The light beam may include a pre-pulsed light beam.

[0015] Representations for spatial distributions may include 2-dimensional representations.

[0016] The light beam may include a pulsed light beam, and the control system configured to adjust at least one characteristic of the light beam may include the control system configured to adjust at least one characteristic of a pulse that occurs after the pulsed light beam.

[0017] In another general embodiment, an EUV light source comprises: a vacuum chamber configured to contain a gas in an internal region and to receive a light beam from a target—the target comprises a target material that emits extreme ultraviolet (EUV) light in a plasma state; a monitor comprising at least one sensor configured to detect emissions from the gas in the internal region and to generate an indication of the detected emissions; and a control system connected to the monitor, wherein the control system is configured to analyze the indication of the detected emissions and to determine whether to adjust at least one characteristic of the light beam and / or at least one characteristic of the vacuum chamber based on the analysis.

[0018] The implementation may include one or more of the following features. The monitor may include a detection system configured to image a portion of an internal region and to generate a representation of the spatial distribution of detected emissions within the portion. The control system may be configured to accept a plurality of representations over a predetermined period, each representation representing the spatial distribution of detected emissions within the portion at different times within the period, and the control system may be configured to determine whether to adjust at least one characteristic of the light beam and / or at least one characteristic of the vacuum chamber based on two or more of the plurality of representations.

[0019] The gas may contain hydrogen, and the detected emission may include H-alpha (H-α) and / or H-beta (H-β) emissions from hydrogen.

[0020] The EUV light source may further include a first spectral filter configured to transmit a first wavelength band; and a second spectral filter configured to transmit a second wavelength band, wherein, in operation, the first spectral filter and the second spectral filter may be located between a part and a detection system; and the control system configured to analyze the detected emission may include the control system configured to compare a representation of the emission transmitted by the first spectral filter with a representation of the emission transmitted by the second spectral filter; and the determination of whether to adjust at least one characteristic of the light beam and / or at least one characteristic of the vacuum chamber may be based on the comparison.

[0021] The EUV light source may also include a pressure controller connected to the inside of the vacuum chamber, the pressure controller is configured to change the pressure of the gas inside the vacuum chamber, and the control system may be connected to the pressure controller.

[0022] In another general embodiment, a method for controlling an EUV light source comprises: providing a target in a target area of ​​a vacuum chamber containing gas in an internal area; causing an interaction between a light beam and a target within the target area; detecting light emission from atoms, ions, and / or molecules within the internal area of ​​the vacuum chamber—the light emission is in response to an energy event within the vacuum chamber, the energy event includes an event that adds energy to the target and / or gas—analyzing the detected light emission to determine the spatial distribution of the light emission within the internal area; and determining whether to adjust the characteristics of the light beam and / or gas based on the analysis.

[0023] An implementation of any of the technologies described above may include an EUV light source, system, method, process, device, or apparatus. Details of one or more implementations are provided in the accompanying drawings and the description below. Other features will become apparent from the description and drawings, and from the claims. Brief explanation of the drawing

[0024] The present invention is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, in accordance with general convention, the various features of the drawings are not necessarily in a fixed proportion. On the contrary, the dimensions of the various features may be expanded or reduced at will for clarity. Identical numbers denote the same features throughout the specification and drawings. Figure 1a is a block diagram of an example of an extreme ultraviolet (EUV) light source. Figure 1b is an example of the temporal profile of an optical pulse. Figure 2 is a block diagram of another example of an extreme ultraviolet (EUV) light source. Figure 3 is a flowchart of an example process for controlling an EUV light source. Figures 4a to 4d are exemplary images of laser-induced fluorescence. Figure 5 is exemplary data related to the analysis of light emission from a gas. Figures 6a and 6b are block diagrams of examples of lithography devices. Figure 7 is a block diagram of an example of an EUV light source. Specific details for implementing the invention

[0025] A technique for controlling an extreme ultraviolet (EUV) lithography system and / or an EUV source based on the analysis of light emissions occurring within the vacuum chamber of an EUV source is disclosed.

[0026] Referring to FIG. 1a, a block diagram of an extreme ultraviolet (EUV) light source (100) is shown. The EUV light source (100) includes a sensor system (130) and a control system (150). The sensor system (130) monitors the emission of light occurring inside a vacuum chamber (109) and provides information regarding the emission to the control system (150). The emission is analyzed by the control system (150), and the control system is configured to adjust one or more components of the EUV light source (100) based on the analysis of the emission. The emission may be from plasma (196), gas (122), target material and / or debirs (195) within a target (121p). Monitoring emissions within the vacuum chamber (109) allows for the determination and control of various parameters of the EUV source (100) that affect the performance of the EUV source. For example, information from the sensor system (130) can be used to determine a portion or fraction of the target material (or fuel) ionized by a plasma generation event and / or to determine the amount of energy deposited on the gas (122) within the vacuum chamber (109). Knowledge of these parameters enables the control system (150) to improve the performance of the EUV light source (100).

[0027] The monitored emission is light emitted from one or more materials within the vacuum chamber (109). The materials include atoms, molecules, and / or ions. The emission may be any type of emission, including light emanating from the materials. For example, the emission may be optical emission resulting from atoms excited by a high-temperature source. In another example, the emission may be fluorescence from atoms, molecules, or ions. Fluorescence is the emission of light by a material that has absorbed light or other electromagnetic radiation.

[0028] Furthermore, the emission may be laser-induced fluorescence. Laser-induced fluorescence is a process in which atoms, ions, or molecules absorb laser light and electrons in the material are excited to a higher energy level. After excitement, the electrons decay to a lower energy level, and the atoms, ions, or molecules emit light. This emitted light is laser-induced fluorescence. Laser-induced fluorescence can be generated by irradiating the material with an optical beam (106) (which may be a laser) and / or by irradiating the material with a laser beam (115) generated by a probe laser (108). Any laser suitable for exciting the material in the manner of interest may be used as the probe laser (108). For example, the probe laser (108) may be a laser (such as an optical parametric oscillator or another type of tunable laser) that can be tuned to produce one of several different wavelengths.

[0029] The wavelength of a specific emission is determined by the properties of the material and the amount of energy used to excite the material. Furthermore, certain materials can generate emissions of more than one wavelength. For example, when a hydrogen electron transitions from the third lowest energy level to the second lowest energy level, hydrogen gas emits light at a wavelength of 658.28 nanometers (nm). This emission is called H-alpha (H-α) emission. However, hydrogen gas also emits light at other wavelengths. For example, hydrogen gas, when a hydrogen electron transitions from the fourth lowest energy level to the second lowest energy level, emits light at a wavelength of 486.14 nm. This emission is called H-beta (H-β) emission. Hydrogen also possesses other emission lines. The wavelength emitted by hydrogen gas depends on the amount of excitation energy, which determines the energy level at which the electron is excited from the ground state. Similarly, other materials that may be present in the vacuum chamber (109) emit light of a specific wavelength according to their respective physical properties and energy (the material is excited by this energy).

[0030] By analyzing these emissions, the control system (150) can monitor conditions within the vacuum chamber (109) and, accordingly, adjust the environment within the vacuum chamber (109). In particular, the control system (150) is configured to analyze and adjust one or more characteristics of a subsequent (subsequently occurring) pulse of the optical beam (106) and / or one or more characteristics of the vacuum chamber (109) based on the monitored emissions. The characteristics of the subsequent pulse of the optical beam (106) that can be adjusted may include, for example, size (e.g., beam waist at the plasma formation location (123)), average and / or maximum energy, temporal duration and / or position relative to the plasma formation location (123). The adjustable characteristics of the vacuum chamber (109) include, for example, the pressure of the gas (122), the temperature of the gas (122), the flow rate of the gas (122), the direction of flow of the gas (122), the size of the target (121p) and / or the spacing of the targets within the stream (121) of the target.

[0031] Before discussing the control system (150) in detail, the various components of the EUV source (100) are discussed.

[0032] The EUV source (100) also includes a target supply system (110) that releases a stream (121) of the target. The target supply system (110) includes a target forming device (117), which defines an orifice (119) fluidly connected to a reservoir (118). When in operation, the target material is in a flowable state (e.g., the target material is melted and at a temperature higher than its melting point) and the reservoir (118) is pressurized to a pressure (P). The pressure (P) is greater than the pressure inside the vacuum chamber (109). Thus, when in operation, the target material flows through the orifice (119) and into the vacuum chamber (109) to form a stream (121) of the target. In the example of FIG. 1a, the stream of targets (121) generally moves from the orifice (119) to the plasma formation location (123) in the x direction, and the target (121p) (one of the targets in the stream (121)) is at the plasma formation location (123) at the time shown in FIG. 1a.

[0033] The target within the stream of targets (121) may be a drop of target material. The target material may be any material that emits EUV light when in a plasma state. For example, the target material may include water, tin, lithium, and / or xenon. The target material may be a target mixture containing the target material and impurities such as non-target particles. The target material is a material that has emission lines in the EUV range when in a plasma state. The target material may be, for example, a drop of liquid or molten metal, a portion of a liquid stream, solid particles or clusters, solid particles contained within a liquid drop, a foam of the target material, or solid particles contained within a liquid stream. The target material may be, for example, water, tin, lithium, xenon, or any material that has emission lines in the EUV range when converted to a plasma state. For example, the target material may be elemental tin, which may be as pure tin (Sn); as tin compounds, for example, SnBr4, SnBn, SnH4; Tin alloys, for example, tin-gallium alloys, tin-indium alloys, tin-indium-gallium alloys, or any combination of these alloys may be used. Furthermore, in the absence of impurities, the target material comprises only the target material.

[0034] During the operation of the EUV source (100), plasma (196) is formed by interacting the optical beam (106) with the target (121p) at the plasma formation location (123). The plasma contains fine or small particles collectively referred to as plasma particles. Plasma particles may be, for example, vaporized, atomized, and / or ionized particles of fuel, and the monitored emission may include emission from any of these materials. The interaction of the optical beam with the target material (wherein the optical beam has sufficient energy to convert at least a portion of the target material into plasma) is referred to as a plasma generation event. Each plasma generation event also generally generates fragments (e.g., fragments or pieces of the target material that are not converted into plasma (196)), and the monitored emission may include emission from the fragments. Thus, during the operation of the EUV source (100), the plasma (196) and the fragments (195) exist within the chamber (109) after the plasma generation event.

[0035] The EUV source (100) also includes a light generation module (105), which generates an optical beam (106). The light generation module (105) may be, for example, a carbon dioxide (CO2) laser or a solid-state laser. The light generation module (105) may include various other components not shown in FIG. 1a, such as a preamplifier, a power amplifier, an optical element (such as a mirror) used to direct the light, and a beam combiner. In some implementations, the light generation module (105) may include one or more optical sources and one or more lasers, and may also include different types of lasers. FIG. 2 shows an example of a light generation module (205) that includes one or more optical sources.

[0036] The optical beam (106) may be a series of pulses, each of which is separated from the pulse closest in time. FIG. 1b shows an example of the temporal profile (optical power as a function of time) of a pulse (104) within the train. Pulse (104) is an example of one of the pulses that may be part of the optical beam (106). Pulse (104) has a peak power (103) and a finite temporal duration (102). In the example of FIG. 1b, the pulse duration (102) is the time during which the pulse (104) has non-zero power. The time during which the pulse (104) increases from zero to the peak power (103) is the rise time of the pulse. In other implementations, the pulse duration (102) and / or rise time may be based on other metrics. For example, the pulse duration (102) may be shorter than the time the pulse (104) has non-zero power, such as the full-width at half maximum (FWHM) of the pulse (104). Similarly, the rise time may be measured between two values ​​other than zero optical power and peak optical power (103).

[0037] In the illustrated example, the power of the pulse (104) increases monotonically from zero power to peak power (103) and decreases monotonically from peak power (103) to zero. Other temporal profiles are possible. For example, the power of the pulse may increase non-monotonically from zero to peak power. The pulse may have one or more peak energy points. Furthermore, pulses within a series of pulses constituting the optical beam (106) may have different temporal profiles.

[0038] An optical beam (106) is directed into a vacuum chamber (109) on an optical path (107) by a beam delivery system (111) comprising one or more optical components (112). The optical component (112) may include any component capable of interacting with the optical beam (106). The component (112) may also include a device capable of forming and / or shaping a pulse (104). For example, the optical component (112) may include a passive optical device such as a mirror, a lens and / or a prism, and any associated mechanical mounting device and / or electronic driver. This component may steer and / or focus the optical beam (106). Additionally, the optical component (112) may include a component that alters one or more characteristics of the optical beam (106). For example, the optical component (112) may include an active optical device, such as an acousto-optic modulator and / or an electro-optic modulator, capable of changing the temporal profile of an optical beam (106) to form a pulse (104).

[0039] The pulse (104) leaves the beam delivery system (111) and enters the vacuum chamber (109). The pulse (104) passes through the hole (113) of the optical element (114) and reaches the plasma formation location (123). The interaction between the pulse (104) and the target material within the target (121p) generates a plasma (196) that emits light (197). The light (197) contains light having a wavelength corresponding to the emission line of the target material within the target (121p).

[0040] The light (197) includes EUV light (198) and out-of-band light. Out-of-band light is light of a wavelength that is not within the range of EUV light. For example, the target material may include tin. In this implementation, the light (197) includes EUV light (198) and also includes out-of-band light such as deep ultraviolet (DUV) light, visible light, near-infrared (NIR) light, mid-wavelength infrared (MWIR) light and / or long-wavelength infrared (LWIR) light. The EUV light (198) may include light having a wavelength of, for example, 5 nanometers (nm), 5 nm to 20 nm, 10 nm to 120 nm, or less than 50 nm. DUV light may include light having a wavelength of about 120 nm to 300 nm, visible light may include light having a wavelength of about 390 nm to 750 nm, NIR light may include light having a wavelength of about 750 nm to 2500 nm, MWIR light may have a wavelength of about 3000 nm to 5000 nm, and LWIR light may have a wavelength of about 8000 nm to 12000 nm.

[0041] The optical element (114) has a reflective surface (116) positioned to receive at least a portion of the light (197). The reflective surface (116) has a coating portion that reflects the EUV light (198) but does not reflect the out-of-band component of the light (197), or reflects only a nominal amount of the out-of-band component of the light (197). In this way, the reflective surface (116) directs only the EUV light (198) toward the lithography device (199).

[0042] The EUV source (100) also includes a gas management system (140) that supplies gas (122) to a vacuum chamber (109). The gas (122) may be, for example, hydrogen or oxygen. The gas management system (140) may include pumps, valves, and other components used for managing the gas. The gas management system (140) is configured to control various characteristics of the gas (122) supplied to the vacuum chamber, such as, for example, temperature, pressure, and / or flow rate. For example, the gas management system (140) may supply the gas (122) at a flow rate sufficient to move debris (such as debris (195)) in a controlled manner and / or control the temperature and / or pressure of the gas (122) to affect aspects of plasma production.

[0043] The EUV light source (100) also includes a sensor system (130), and the sensor system provides a signal (157) containing data related to the monitored emission to the control system (150). As mentioned above, the monitored emission may include emission from the plasma (196), emission from the gas (122), and / or emission from the debris (195). The sensor system (130) includes a sensor module (134) that includes one or more sensors (135). The sensor (135) is any detector or sensor capable of detecting or sensing light having a wavelength of the emission of interest. Thus, in the example of FIG. 1a, the sensor (135) may be a sensor capable of detecting emission from the plasma (196), a sensor capable of detecting one or more wavelengths that may be emitted from the gas (122), and / or a sensor capable of sensing the wavelength of light emitted from the debris (195).

[0044] In some implementations, the sensor (135) may generate data containing spatial information regarding the emission. For example, the sensor (135) may be a two-dimensional array of sensors, each sensor configured to detect light emitted from a specific part of the vacuum chamber (109). Each sensor is fixed and has a known position relative to the part of the vacuum chamber (109) that the sensor monitors, so that the relative position of the detected emission can also be determined. In this implementation, the spatial information shows how the emission is distributed within the vacuum chamber (109). Data from the sensor (135) may be used to form a two-dimensional spatial representation (such as an image) of the vacuum chamber (109) (or a part of the vacuum chamber (109)) along with an image showing the relative position of the monitored emission within the vacuum chamber (109).

[0045] Furthermore, the sensor (135) can generate many two-dimensional spatial representations of the monitored emissions within the vacuum chamber (109) over a certain period. For example, the sensor (135) may be a video sensor that captures frames (images) collected at a frame rate determined by the video sensor. In this implementation, each frame is a representation of the emissions within the vacuum chamber (109) at different times. In another example, the sensor is a camera having an exposure mechanism that allows the sensor to detect emissions over a limited period. In this implementation, the data generated by the sensor (135) represents the time average of the emissions within the vacuum chamber (109). The sensor module (134) may include one or more sensors. In this implementation, the sensors (135) are positioned at different locations for a specific area of ​​the vacuum chamber (109) so that the data generated by the sensor (135) can be used to generate a three-dimensional spatial representation of the monitored emissions.

[0046] Furthermore, the sensor system (130) may also include a spectrum filter module (137). The spectrum filter module (137) includes one or more spectrum filters (136). The spectrum filter (136) allows for the control of specific wavelengths or wavelengths detected by the sensor (135). In this way, specific emissions can be separated from the total emissions within the vacuum chamber so that only the emissions of interest are monitored. When included in the sensor system (130), the spectrum filter (136) is positioned in an optical path between the sensor (135) and the monitored portion inside the vacuum chamber (109).

[0047] A spectrum filter (136) is any filter that can allow some wavelengths or only specific wavelengths to reach the sensor (135) while substantially preventing any other wavelengths from reaching the sensor (135). The spectrum filter (136) may be, for example, a spectrum filter that allows only visible light to reach the sensor (135) or a spectrum filter that allows only specific wavelengths within the visible spectrum to reach the sensor (135). The spectrum filter (136) may separate wavelengths based on transmission, reflection, and / or absorption. For example, the spectrum filter (136) may be a multilayer dielectric stack that transmits wavelengths within a wavelength band while reflecting or absorbing all other wavelengths. In another example, the spectrum filter (136) may be a dichroic mirror or grating that reflects different wavelengths in different directions.

[0048] The spectrum filter module (137) may include one or more spectrum filters (136). For example, in some implementations, the sensor module (134) includes one or more sensors (135), and the spectrum filter module (137) includes a spectrum filter (136) for each of the sensors.

[0049] The EUV light source (100) also includes a control system (150) that analyzes emissions within a vacuum chamber (109) using information from a sensor system (130). The control system (150) also provides a command signal (159) generated based on information regarding emissions within the vacuum chamber (109) to a light generation module (105), a target supply system (110), a gas management system (140), and / or a beam delivery system (111).

[0050] The control system (150) includes an analysis module (152). The analysis module (152) analyzes information from the sensor system (130) and determines whether to adjust the optical beam (106) and / or vacuum chamber (109) based on the analysis. The operation of the control system (150) and the analysis module (152) is further discussed with reference to FIG. 3. In the example of FIG. 1a, the analysis module (152) of the control system (150) is implemented using an electronic processor (154), an electronic storage unit (156), and an I / O interface (158). The electronic processor (154) includes one or more processors suitable for executing computer programs, such as general-purpose or special-purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, the electronic processor receives instructions and data from read-only memory, random access memory (RAM), or both. The electronic processor (154) may be any type of electronic processor. The electronic processor (154) executes commands that configure the analysis module (152).

[0051] The electronic storage unit (156) may be volatile memory, such as RAM, or non-volatile memory. In some implementations, the electronic storage unit (156) includes non-volatile and volatile parts or components. The electronic storage unit (156) may store data and information used in the operation of the control system (150). For example, the electronic storage unit (156) may store instructions (e.g., in the form of a computer program) that implement the analysis module (152). The analysis module (152) may receive information from the sensor system (130) and also receive information from the light generation module (105), the gas management system (140), the supply system (110), and / or the beam delivery system (111).

[0052] The electronic storage unit (156) may also store, possibly as a computer program, instructions that cause the electronic processor (154) to communicate with components within the light generation module (105), gas management system (140), beam delivery system (111), supply system (110), and / or sensor system (130) when executed. For example, the instructions may be instructions that cause the electronic processor (154) to provide a command signal (159) generated by the analysis module (152) to the light generation module (105), gas management system (140), supply system (110), and / or beam delivery system (111).

[0053] The command signal (159) is a signal that causes the components of the light generation module (105) and / or the beam delivery system (111) to act in a manner that adjusts the optical beam (106), or a signal that causes the gas management system (140) to adjust the characteristics of the gas (122). For example, the command signal (159) may be a signal containing sufficient information to cause the valve and / or pump of the gas management system (140) to start, stop, or otherwise continue to operate. In another example, the command signal (159) is a signal that can adjust the characteristics of the target supply system (110) to change the speed at which the target reaches the plasma formation location (123). In this example, the command signal (159) may be a signal containing sufficient information to cause the target forming device (117) to vibrate at different speeds so that the size and / or speed of the target reaching the plasma formation location (123) is changed. In another example, the command signal (159) is a signal that operates in the light generation module (105) and / or the beam delivery system (111) to change the characteristics of the beam (106). For example, the command signal (159) may be a signal sufficient to move a mirror within the beam delivery system (111) or a signal sufficient to adjust the operation of an electro-optical modulator within the beam delivery system (111).

[0054] The I / O interface (158) is any type of interface that allows the control system (150) to exchange data and signals with an automated process running on an operator, a light generation module (105), one or more components of the light generation module (105), a lithography device (199), and / or another electronic device. For example, in some implementations, the analysis module (152) may be programmed by the end user to include analysis specific to the end user. In this implementation, the analysis module may be programmed through the I / O interface (158). The I / O interface (158) may include one or more of communication interfaces such as a visual display, a keyboard, and a parallel port, a Universal Serial Bus (USB) connection, and / or any type of network interface such as Ethernet. The I / O interface (158) may also allow communication without physical contact, for example, through IEEE 802.11, Bluetooth, or Near Field Communication (NFC) connections.

[0055] Referring to FIG. 2, a block diagram of an EUV light source (200) is shown. The EUV light source (200) is another example of an implementation of an EUV light source. The EUV light source (200) is identical to the EUV light source (100) (Fig. 1a) except that the EUV light source (200) uses a light generating module (205) comprising a first optical source (208_1) that emits a first optical beam (206_1) and a second optical source (208_2) that emits a second optical beam (206_2). Pulse (204_1) is a pulse of the first optical beam (206_1), and pulse (204_2) is a pulse of the second optical beam (206_2). Pulse (204_2) may be referred to as a "pre-pulse" optical beam, and pulse (204_1) may be referred to as a "main pulse" optical beam.

[0056] The EUV light source (200) includes an optical element (114), but for simplification, only the hole (113) of the optical element (114) is shown in FIG. 2. The pulse (204_2) propagates along the beam path (207_2), passes through the hole (113) of the optical element (114), and is delivered to an initial target area (224) through a beam delivery system (211_2). The initial target area (224) receives an initial target (221p) from the supply system (110). The initial target area (224) is displaced in the -x direction relative to the plasma formation location (123).

[0057] The pulse (204_2) interacts with the target (221p) in the initial target region (224) to condition the target (221p) and form a deformed target (221m). Conditioning can enhance the ability of the target (221p) to absorb the pulse (204_1). For example, although EUV emitting plasma (196) is generally not generated in the initial target region (224), the interaction between the pulse (204_2) and the target (221p) can change the shape, volume, and / or size of the distribution of the target material within the initial target (221p) and / or reduce the density gradient of the target material along the propagation direction of the main pulse (204_1). Furthermore, the interaction between the pulse (204_2) and the initial target (221p) can generate a pre-plasma or plasma that does not necessarily emit EUV light. The deformed target (221m) may be, for example, a disc-shaped distribution of the target material having a larger range in the xy plane than the target (221p) and a smaller range along the z-axis than the target (221p). The deformed target (221m) drifts to a plasma formation location (123) and is irradiated by a pulse (204_1) to form a plasma (196).

[0058] In the implementation of FIG. 2, the control system (150) is connected to an optical source (208_2) and a beam delivery system (211_2) so that the control system (150) can be used to control the characteristics of the second optical beam (206_2) (or the optical pulse that occurs subsequently or after the optical beam (206_2)). For example, the control system (150) can adjust the pulse energy of the pulse that occurs after the optical beam (206_2), the position of the pulse that occurs after the optical beam (206_2) relative to the expected position of the target (221p), and / or the duration of the pulse that occurs after the optical beam (206_2). In this way, the control system (150) can be used to control parameters of the control of the initial target (221p). The control system (150) is also connected to the optical source (208_1) and the beam delivery system (211_1) and can also be used to control the characteristics of the optical beam (206_1) (or pulses of the optical beam (206_1)). Furthermore, the control system (150) is connected to the gas management system (140) and can adjust one or more characteristics of the gas (122).

[0059] The optical sources (208_1, 208_2) may be, for example, two lasers. For example, the optical sources (208_1, 208_2) may be two carbon dioxide (CO2) lasers. In other embodiments, the optical sources (208_1, 208_2) may be different types of lasers. For example, the optical source (208_2) may be a solid-state laser and the optical source (208_1) may be a CO2 laser. In the example of FIG. 2, the first and second optical beams (206_1, 206_2) are pulsed. The first and second optical beams (206_1, 206_2) may have different wavelengths. For example, in an implementation in which the optical source (208_1, 208_2) comprises two CO2 lasers, the wavelength of the first optical beam (206_1) may be about 10.26 micrometers (μm), and the wavelength of the second optical beam (206_2) may be between 10.18 μm and 10.26 μm. The wavelength of the second optical beam (206_2) may be about 10.59 μm. In this implementation, the optical beams (206_1, 206_2) are generated from different lines of CO2 lasers, and as a result, optical beams (206_1, 206_2) having different wavelengths are generated even though both beams are generated from the same type of source.

[0060] The pulses (204_1 and 204_2) may have different energies and different durations. For example, the pre-pulse (204_2) may have a duration of at least 1 ns, and for example, the pre-pulse may have a duration of 1 to 100 ns and a wavelength of 1 µm or 10 µm. In one example, the pre-pulse of radiation is a laser pulse having an energy of 15 to 60 mJ, a pulse duration of 20 to 70 nanoseconds (ns), and a wavelength of 1 to 10 micrometers (µm). In some examples, the pre-pulse may have a duration of less than 1 ns. For example, the pre-pulse may have a duration of 300 picoseconds (ps) or less, 100 ps or less, 100 to 300 ps, ​​or 10 to 100 ps.

[0061] Each of the beam delivery systems (211_1 and 211_2) is similar to the beam delivery system (111) (Fig. 1a). In the example of Fig. 2, the first optical beam (206_1) and the second optical beam (206_2) interact with separate beam delivery systems and travel along separate optical paths. However, in other implementations, the first optical beam (206_1) and the second optical beam (206_2) may share all or part of the same optical path and may also share the same beam delivery system.

[0062] Referring to FIG. 3, a flowchart of a process (300) is shown. The process (300) is an example of a process that can be performed by a control system (150).

[0063] Light emitted from a material within a vacuum chamber (109) is detected (310). The emitted light is detected by a sensor (135). The material may be atoms, ions, and / or molecules. The material may be part of a gas (122), plasma (196), and / or debris (195). The light emitted from the material may be fluorescence or laser-induced fluorescence. The emitted light is detected by a sensor (135). The sensor (135) generates data indicating the characteristics of the emitted light. For example, the data may indicate the intensity of the emitted light. In some implementations, the data indicates the relative position of the emitted light in the vacuum chamber (109). In such implementations, the data may be used to form a two-dimensional representation, such as an image. Furthermore, in some implementations, the sensor module (134) includes one or more sensors (135). One or more sensors (135) may be positioned relative to a specific part of the vacuum chamber (109). In this implementation, data from the sensor (135) can be used together to form a three-dimensional representation of the spatial distribution of light emission within the vacuum chamber (109).

[0064] In some implementations, the sensor (135) collects data over a relatively short period (e.g., less than 20 microseconds (µs), such as a 10 nanosecond (ns) period) so that the detected emission is associated with a single plasma generation event. This implementation allows one or more components of the EUV light source (100 or 200) to be changed on a pulse-to-pulse basis. Furthermore, monitoring over a relatively short period allows for the generation of fast time-resolved images, as shown in FIGS. 4a through 4d and FIG. 5. In other implementations, the sensor (135) collects data over a longer period so that the detected emission is associated with one or more plasma generation events.

[0065] An indication of the detected emission is analyzed (320). The indication is data received from the sensor system via a signal (157). The signal (157) contains information describing the emission, such as the intensity of the detected emission. In some implementations, the signal (157) contains location information regarding the detected emission. For example, the signal (157) may include readings from a two-dimensional array of sensors (135), and the intensity of the emission detected by each sensor in the array is included in the signal (157). Based on this information, the control system (150) determines the relative location of the detected emission.

[0066] As discussed above, in some implementations, the sensor system (130) includes a spectrum filter module (137) and one or more spectrum filters (136). In such implementations, the spectrum filter (136) determines which wavelengths reach the sensor or sensors (135). For example, the spectrum filter (136) may include a filter designed to allow only wavelengths associated with H-α emission to reach the sensor (150). In this implementation, the signal (157) may include data indicating that a specific signal (157) contains information associated with the detected H-α emission.

[0067] Additionally, the signal (157) may include data related to the conditions under which the emission was generated. For example, the signal (157) may include information regarding the sensor, such as an exposure signal. In another example, the signal (157) may include information regarding the environment within the vacuum chamber. Examples of such environmental information include the temperature, pressure and / or flow rate of the gas (122), and information regarding the optical beam (106), such as pulse duration, pulse energy and / or pulse wavelength.

[0068] The analysis module (152) of the control system (150) can perform various analyses on indications of detected emissions. Various analyses may be stored in the electronic storage unit (156) as computer programs executable by, for example, the electronic processor (154). Any type of analysis on the detected emissions may be performed. Specific examples of data and corresponding analyses of such data are discussed in relation to FIGS. 4a through 4d and FIG. 5. Analyses other than those discussed in these examples may be performed by the analysis module (152).

[0069] Referring to FIGS. 4a through 4d, an example is shown in which the emission is laser-induced fluorescence of neutral atomic tin. In this example, tin is used as the target material, and the neutral atomic tin may be tin fragments and / or tin that are not converted into plasma (196). In the example of FIGS. 4a through 4d, the sensor (135) is a camera that images the plasma formation location (123) and generates a two-dimensional image of the vacuum chamber (109).

[0070] In the examples of FIGS. 4a through 4d, the sensor (135) is an enhanced charge-coupled device (ICCD) having an exposure time of about 10 nanoseconds (ns), a spectral filter (136) is placed between the sensor (135) and the plasma formation site (123), and laser-induced fluorescence is formed by exciting neutral tin atoms with a laser beam (115) from a probe laser (108). In this example, the probe laser (108) is an adjustable laser, and the laser beam (115) is a pulsed light beam having pulses with a duration of several nanoseconds (e.g., 10 ns or less). Additionally, the probe laser (108) is tuned so that the laser beam (115) has a wavelength of 286.3 nm, which excites neutral tin atoms in the ground state. A fraction or percentage of neutral tin atoms decay through an electronic transition that emits light (laser-induced fluorescence) at 317.5 nm. The spectrum filter (136) in this example is a band-pass filter centered at 317.5 nm. Additionally, FIGS. 4a through 4d relate to a system using a pre-pulse and a main pulse. Accordingly, these figures are discussed with respect to FIG. 2.

[0071] FIG. 4a is an image (400A) of laser-induced fluorescence from neutral tin in the vacuum chamber (109) at 200 nanoseconds (ns) after the pre-pulse (pulse (204_2) of FIG. 2) interacts with the initial target (22lp) (Fig. 2). FIG. 4b is an image (400B) of laser-induced fluorescence from neutral tin in the vacuum chamber (109) at 1900 ns after the pre-pulse interacts with the initial target (221p). FIG. 4c is an image (400C) of laser-induced fluorescence from neutral tin in the vacuum chamber (109) at 300 ns after the main pulse (pulse (204_1) of FIG. 2) interacts with the modified target (220m) (Fig. 2). FIG. 4d is an image (400D) of laser-induced fluorescence from neutral tin in the vacuum chamber (109) at 900 ns after the main pulse interacts with the deformed target (220 m). Each pixel of each image (400A to 400D) represents the amount of laser-induced fluorescence within a specific area of ​​the vacuum chamber (109). The interaction between the main pulse and the deformed target (220 m) is a plasma generation event.

[0072] The analysis module (152) determines the amount of tin ionized by interaction by analyzing images (400A to 400D) to determine the intensity of specific spectral lines and the relative intensity of these lines. For example, the intensity of emission from neutral tin can be compared with the intensity of tin ionized individually or in pairs to determine the fraction of atoms of the target material that are ionized after a plasma generation event. In the examples of FIGS. 4a to 4d, the intensity of emission is proportional to the number of tin atoms and neutral tin atoms. Thus, if the intensity of emission from neutral tin atoms decreases while the intensity from ion species increases, then this is evidence that the ionization fraction is changing.

[0073] Other features of the images (400A to 400D) may be analyzed. For example, the spatial distribution of the intensity may be analyzed to estimate the distance traveled by the neutral tin atom and / or the velocity of the neutral tin atom. For example, as shown in FIG. 4d, the distance traveled from the origin (the location of the interaction between the main pulse and the deformed target (220 m)) and the elapsed time (900 ns after the interaction in this example) provide the velocity of this neutral tin atom.

[0074] Furthermore, the orientation angle of the fluorescence represents the angle or orientation of the deformed target (220m) with respect to the propagation direction of the main pulse, and the orientation angle of the fluorescence changes as the orientation of the deformed target (220m) changes. Accordingly, the orientation of the deformed target (220m) can also be determined from images such as images (400A to 400D).

[0075] The analysis module (152) also determines other information regarding emission from images (400A to 400D). For example, the analysis module (152) may apply a shape operator to identify a ring structure (401) in image (400C). After a plasma generation event, the ring structure (401) expands in space over time. The analysis module (152) also identifies the ring structure (401) within image (400D). The velocity of tin atoms can be estimated by comparing the spatial characteristics of the ring structure (401) within image (400C) with those of the ring structure (401) within image (400D). For example, the radius and / or diameter of the ring structure (401) within images (401C and 401D) can be compared with and used with the knowledge of the amount of time between images (400C and 400D) to estimate the velocity of tin atoms. Furthermore, in some implementations, the velocity of the tin atom is determined from a single image. For example, if the time from the interaction between the main pulse and the modified target (220m) is known for a single image, the velocity of the tin atom can be determined from a single image. When the velocity of the tin atom is determined from two or more images, the change in the velocity of the tin atom can also be determined.

[0076] Furthermore, a shape operator may be used to determine the orientation of the ring structure (401). The orientation of the ring structure provides an indication of the orientation of the deformed target (220m). For example, the major and minor axes of the ring structure (401) can be estimated after identifying the ring structure (401), and the orientation of the ring structure (401) can be estimated from the axes.

[0077] Images (400A to 400D) are provided as examples of data that the sensor system (130) can provide to the control system (150). Other types of laser-induced fluorescence may also be monitored. For example, images showing laser-induced fluorescence of ions of the target material formed during a plasma generation event may be generated and provided to the control system (150). In another example, emissions from the gas (122) are analyzed. The gas (122) may emit light, for example, due to heat within the vacuum chamber (109) from the pulse (104) (or pulse (204_1) and / or pulse (204_2) of FIG. 2) and / or ions moving within the gas (122), by the formation of plasma (196), or by direct excitation by the probe laser (108). FIG. 5 shows an example involving the analysis of emissions from the gas (122) to determine the amount of energy deposited on the gas (122) as a result of a plasma generation event.

[0078] In the example of FIG. 5, the gas (122) was hydrogen gas, and the sensor (135) was a camera that generated a two-dimensional image of the plasma formation location (123). A pulse of light converts at least a portion of the target material into a plasma emitting EUV light. In the example of FIG. 5, the pulse energy was 860 millijoules (mJ), the wavelength of the pulse was 10 µm, and the duration of the pulse was 10 ns. The target was a tin droplet with a radius of about 50 µm. In this implementation, the spectral filter (136) was a band-pass filter having a narrow spectral band centered on the H-α emission wavelength and was placed between the plasma formation location (123) and the sensor (135). Thus, H-α emission reached the sensor (135), but light of other wavelengths was substantially prevented from reaching the sensor (135).

[0079] Four two-dimensional images (500A to 500D) (among more images taken) are shown in FIG. 5. Each of the images (500A to 500D) was acquired at a different time. Thus, the images (500A to 500D) are images of the relative intensity or amount of H-α emission at the plasma formation location (123) at four different times.

[0080] The analysis module (152) is configured to analyze images such as 500A through 500D to determine the spatial characteristics of a shock wave or blast wave (504). The blast wave (504) is formed within the gas (122) by a plasma generation event. Spatial characteristics may include, for example, radius, diameter, orientation of the semi-major axis, orientation of the major axis, orientation of the minor axis, and / or circumference of the blast wave (504). The analysis module (152) detects the blast wave (504) within one or more images collected by the camera by applying shape operators and imaging processing techniques to the images. For example, the general shape of the blast wave (504) is known to be circular, and the analysis module (152) may apply a morphological filter that detects circular objects within the image to find the blast wave (504) within the image from the camera. In another example, the analysis module (152) may apply an edge detector that depends on the difference in intensity between the emission at the edge of the shock wave (504) and the background.

[0081] Once the spatial characteristics of the explosion wave (504) are estimated, the analysis module (152) applies the Taylor-Sedov equation to estimate the amount of energy (E) deposited in the gas (122). The Taylor-Sedov equation is as follows:

[0082]

[0083] Here, E is the energy deposited in the gas (122), r is the radius of the explosion wave, ρ0 is the density of the gas (122), and t-t0 is the time after plasma generation. The radius (r) at a specific time (t) is estimated from an image of the plasma formation location (123) captured at time (t). The analysis module (152) estimates the amount of energy deposited in the gas (122) using Equation 1 and the estimate of the radius of the explosion wave (504) at a specific time (t). The analysis module (152) can also determine other information from the images (500A to 500D). For example, FIG. 5 also includes a plot of the relative total H-α emission as a function of time since the plasma generation event. To generate the plot (501), the values ​​of each pixel of the image collected by the camera at a specific time are summed and normalized. The result is plotted as a function of time. Images (500A to 500D) correspond to four points included in the plot (501).

[0084] The data shown in FIGS. 4a through 4d is an example of the types of data that the sensor system (130) can provide to the control system (150) via the signal (157). However, the sensor system (130) may be configured to collect any other data regarding emissions within the vacuum chamber (109), and the analysis module (152) may also be configured to analyze such data. For example, in some implementations, the plasma formation location (123) is monitored by one or more sensors (135), each of which has a spectral filter (136) corresponding to a specific emission line of the target material or gas (122). In this implementation, each sensor (135) provides data specifying the spatial distribution of one of the emission lines of the material at the plasma generation location (123) under the same operating conditions. The emissions measured from each sensor are compared with emissions measured by other sensors to determine the characteristics of the environment within the vacuum chamber (109). For example, when comparing different possible emissions from the target material, such comparison leads to an estimation of the portion of the target material ionized to form the plasma (196).

[0085] Furthermore, the analysis module (152) may be configured to compare the spatial distribution of a specific type of emission at two different times after a plasma event. For example, in an implementation where tin is used as the target material, the sensor (135) may be used with a filter (136) that allows only the emission from ionized tin to reach the sensor (135). By comparing images of the emission of ionized tin taken at different times, the analysis module (152) may estimate the velocity and / or direction of movement of the tin ions.

[0086] Accordingly, the analysis module (152) analyzes information and data from the sensor system (130).

[0087] In addition to analyzing data provided from the sensor system (130), the control system (150) also determines whether to adjust the EUV light source (100 or 200) based on the analysis (330). Adjustment of the EUV light source (100 or 200) may be adjustment of any component of the EUV light source (100 or 200) and may include adjustment of one or more components of the EUV light source (100 or 200). Whether adjustment is made and (if so) the nature of the adjustment depends on the results of the analysis discussed in relation to 320.

[0088] The EUV light source (100 or 200) may be associated with various performance specifications, and an analysis of emissions may be used to determine whether the EUV light source (100 or 200) is operating within one or more performance specifications. Conversion efficiency (CE) is an example of a performance specification. Conversion efficiency is the ratio of energy supplied to the EUV light source (100 or 200) to the conversion of EUV light. CE depends on the ionization fraction (the portion of the target material converted into ions). As discussed above, an analysis of emissions may be used to estimate the ionization fraction. To increase the ionization fraction, the duration and / or energy of the pulses within the optical beam (106) may be increased. Thus, if the CE is below a specified CE, the control system (150) may issue a command signal (159) to the light generation module (105) to change the duration and / or intensity of the pulses within the optical beam (106).

[0089] In another example, the control system (150) may issue a command signal (159) to the light generation module (205) (Fig. 2) to change the characteristics of the pre-pulse (204_2). As described above, the pre-pulse (204_2) adjusts the target by changing the shape and / or density of the target so that the deformed target (221m) (Fig. 2) is more favorable for plasma generation. The light generation module (205) may be adjusted so that the intensity and / or duration of the pre-pulse (204_2) causes the deformed target (211m) produced later to have a lower density and / or a different shape. Furthermore, in some implementations, the control system (150) issues a command signal to the beam steering system (211_1) to change the position of the pre-pulse (204_2) relative to the initial target position (224). Furthermore, the size of the target in the stream (121) can be adjusted to reduce the ionization fraction. In this implementation, a command signal (159) is provided to the target supply system (110) to change the vibration frequency of the target forming device (117), for example, so that the size of the target in the stream (121) is reduced.

[0090] In another example, the analysis of the emission produces an estimated ion velocity greater than the desired ion velocity. In this example, the control system (150) issues a command signal (159) to the gas management system (140). The gas management system (140) increases the pressure of the gas (122) so that the ions generated in the subsequent plasma generation event have a lower velocity. In another example, the analysis of the emission shows a relatively large amount of tin atoms at once immediately after the plasma generation event. A relatively large amount of tin atoms immediately after the plasma generation event is an indication of excessive debris within the vacuum chamber (109). The control system (150) issues a command signal (159) to the gas management system (140) to increase the flow rate of the gas (122) and / or change the direction of the gas (122) flow to move the debris away from the optical element (114).

[0091] In another example, an analysis of the emission is used to generate an estimate of the amount of energy deposited on the gas (122). The estimated amount of energy is compared to a threshold and / or specification (e.g., an allowable energy amount range), and if the estimated amount of energy is greater than the threshold or does not meet the threshold, the control system (150) may command the photogenerating module (205) to reduce the power of the pre-pulse (204_2). Reducing the power or pre-pulse (204_2) generally reduces the amount of ions and / or pre-pulse plasma generated during the interaction between the pre-pulse (204_2) and the initial target (221p), thereby reducing the energy deposited on the gas (122).

[0092] In some implementations, the control system (150) issues a command signal (159) to one or more components or systems of the EUV light source (100 or 200). For example, to increase the ionization fraction, the control system (150) may issue a command signal (159) to a light generation module (105 or 205), a target supply system (110), and a gas management system (140). Furthermore, under some conditions, all performance specifications are met and / or the EUV light source (100) is operating acceptablely, and no adjustment is made.

[0093] After determining whether to adjust the EUV light source (100 or 200), the control system (150) determines whether to continue monitoring the vacuum chamber (109) (340). If monitoring continues, process 300 returns to step 310. If monitoring does not continue, process 300 terminates. Furthermore, in some implementations, the process (300) is run continuously during the operation of the EUV light source (100 or 200) so that the control system continuously monitors the EUV light source (100 or 200). In this implementation, the control system (150) does not determine whether to continue monitoring the vacuum chamber (109) but instead monitors the vacuum chamber (109) continuously and without interruption during the operation of the EUV light source (100 or 200).

[0094] FIG. 6a is a block diagram of a lithography device (600) including a source collector module (SO). The lithography device (600) is:

[0095] ● A lighting system (illuminator) (IL) configured to adjust a radiation beam (B) (e.g., EUV radiation);

[0096] ●A support structure (e.g., mask table) (MT) connected to a first positioner (PM) configured to support a patterning device (e.g., mask or reticle) (MA) and also configured to accurately position the patterning device;

[0097] ● A substrate table (e.g., wafer table) (WT) connected to a second positioner (PW) configured to hold a substrate (e.g., a resist-coated wafer) (W) and also configured to accurately position the substrate; and

[0098] ● It includes a projection system (e.g., a reflective projection lens system) (PS) configured to project a pattern applied to a radiation beam (B) by a patterning device (MA) onto a target portion (C) of a substrate (W) (e.g., including one or more dies).

[0099] A lighting system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical elements, or any combination thereof, to direct, shape, or control radiation.

[0100] 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 lithography device, and other conditions, such as whether the patterning device is maintained in a vacuum environment, for example. The support structure may utilize mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device. The support structure may be, for example, a frame or table that can be fixed or movable as needed. The support structure can ensure that the patterning device is in a desired position, for example, relative to a projection system.

[0101] The term "patterning device" should be broadly interpreted to refer to any device that can be used to impart a pattern to the cross-section of a radiation beam, such as creating a pattern on a target portion of a substrate. The pattern imparted to the radiation beam may correspond to a specific functional layer within the device created on the target portion, such as an integrated circuit.

[0102] The 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 various hybrid mask types as well as binary, alternating phase-shift, and attenuated phase-shift masks. An example of a programmable mirror array uses a matrix array of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart patterns to the radiation beam reflected by the mirror matrix.

[0103] Like the illumination system (IL), the projection system (PS) may include various types of optical elements, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical elements, or any combination thereof, suitable for the exposure radiation being utilized or for other factors such as the use of a vacuum. Since other gases can absorb too much radiation, it may be desirable to use a vacuum for EUV radiation. Therefore, a vacuum environment can be provided throughout the entire beam path with the help of vacuum walls and vacuum pumps.

[0104] In the examples of FIG. 6a and FIG. b, the device may be of the reflective type (e.g., using a reflective mask). The lithography device may be of the type having two or more (dual-stage) substrate tables (and / or two or more patterning device tables). In such a “multi-stage” machine, additional tables may be used simultaneously, or preparation steps may be performed on one or more tables while one or more other tables are being used for exposure.

[0105] Referring to FIG. 6a, the illuminator (IL) receives an extreme ultraviolet radiation beam from a source collector module (SO). Methods for generating EUV light include, but are not limited to, converting a material into a plasma state having at least one element, such as xenon, lithium, or tin, with one or more emission lines within the EUV range. In one such method, the required plasma, often called a laser-generated plasma (“LPP”), can be generated by irradiating a fuel, such as a droplet, stream, or cluster of material having the required line emission element, with a laser beam. The source collector module (SO) may be part of an EUV radiation system containing a laser, which is not visible in FIG. 6a, for providing a laser beam to excite the fuel. The resulting plasma outputs radiation, such as EUV radiation, which is collected using a radiation collector placed in the source collector module. The laser and the source collector module may be separate entities, for example, when a carbon dioxide (CO2) laser is used to provide the laser beam for fuel excitation.

[0106] In such cases, the laser is not considered to form part of the lithography system, and the radiation beam travels from the laser to the source-collector mirror with the help of a beam delivery system, for example, which includes a suitable directional mirror and / or beam expander. In other cases, for example, when the source is a discharge-generated plasma EUV generator commonly referred to as a DPP source, the source may be an essential part of the source-collector module.

[0107] The illuminator (IL) may include a regulator for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial range of the intensity distribution within the pupil plane of the illuminator (generally referred to as σ-outer and σ-inner, respectively) may be adjusted. Additionally, the illuminator (IL) may include various other components such as faceted fields and pupil mirror devices. The illuminator (IL) may be used to adjust the radiation beam to have a desired uniformity and intensity distribution across the cross-section of the radiation beam.

[0108] A radiation beam (B) is incident on a patterning device (e.g., mask) (MA) held on a support structure (e.g., mask table) (MT) and is patterned by the patterning device. After being reflected from the patterning device (e.g., mask) (MA), the radiation beam (B) passes through a projection system (PS), and the projection system focuses the beam onto a target portion (C) of a substrate (W). With the help of a second positioner (PW) and a position sensor (PS2) (e.g., an interferometer device, a linear encoder, or a capacitive sensor), the substrate table (WT) can be moved precisely to position different target portions (C), for example, in the path of the radiation beam (B). Similarly, a first positioner (PM) and another position sensor (PS1) can be used to accurately position the patterning device (e.g., mask) (MA) in the path of the radiation beam (B). A patterning device (e.g., a mask) (MA) and a substrate (W) can be aligned using patterning device alignment marks (M1, M2) and substrate alignment marks (P1, P2).

[0109] The described device may be used in at least one of the following modes:

[0110] 1. In step mode, the support structure (e.g., mask table) (MT) and the substrate table (WT) are basically kept in a fixed state, while the entire pattern applied to the radiation beam (B) is projected onto the target portion (C) at once (i.e., a single static exposure). Then, the substrate table (WT) is shifted in the X and / or Y directions so that different target portions (C) can be exposed.

[0111] 2. In scan mode, the support structure (e.g., mask table) (MT) and the substrate table (WT) are scanned simultaneously while the pattern applied to the radiation beam is projected onto the target portion (C) (i.e., single dynamic exposure). The speed and orientation of the substrate table (WT) relative to the support structure (e.g., mask table) (MT) can be determined by the magnification (reduction) and image inversion characteristics of the projection system (PS).

[0112] 3. In another mode, the support structure (e.g., mask table) (MT) is kept in a basically fixed state holding the programmable patterning device, and the substrate table (WT) is moved or scanned while the pattern imparted by the radiation beam is projected onto the target portion (C). In this mode, a pulsed radiation source is typically used, and the programmable patterning device is updated as needed after each movement of the substrate table (WT) or between successive radiation pulses during scanning. This mode of operation can be easily applied to maskless lithography using a programmable patterning device, such as a programmable mirror array of the type referred to above.

[0113] Combinations and / or variations of the usage modes described above or completely different usage modes may also be used.

[0114] FIG. 6b shows in more detail an implementation of a lithography device (600) comprising a source collector module (SO), an illumination system (IL), and a projection system (PS). The source collector module (SO) is configured and positioned so that a vacuum environment can be maintained within the enclosure structure (220) of the source collector module (SO). The systems (IL and PS) are likewise contained within their own vacuum environments. The EUV radiation-emitting plasma (2) can be formed by a laser-generated LPP plasma source. The function of the source collector module (SO) is to deliver the EUV radiation beam (20) from the plasma (210) so that the radiation beam is focused to a virtual source point. The virtual source point is commonly referred to as an intermediate focus (IF), and the source collector module is positioned so that the intermediate focus (IF) is located in or near the hole (221) of the enclosure structure (220). The virtual source point (IF) is an image of the radiation-emitting plasma (2).

[0115] From the hole (221) at the intermediate focus (IF), radiation crosses the illumination system (IL), which in this example includes a faceted field mirror device (22) and a faceted pupil mirror device (24). These devices form a so-called "fly's eye" illuminator, which is arranged to provide a desired angular distribution of the radiation beam (21) at the patterning device (MA) as well as a desired uniformity of radiation intensity at the patterning device (MA) (as shown by reference numeral 660). Upon reflection of the beam (21) at the patterning device (MA) held by a support structure (mask table) (MT), a patterned beam (26) is formed, and the patterned beam (26) is imaged onto a substrate (W) held by a substrate table (WT) via a reflection element (28, 30) by a projection system (PS). In order to expose a target portion (C) on a substrate (W), a pulse of radiation is generated while scanning a pattern on a patterning device (MA) through a slit of illumination by performing synchronized movement for the substrate table (WT) and the patterning device table (MT).

[0116] Each system (IL and PS) is arranged within its own vacuum or near-vacuum environment, defined by an enclosure structure similar to the enclosure structure (620). Generally, more elements may exist in the lighting system (IL) and projection system (PS) than are shown. Additionally, there may be more mirrors than are shown. For example, in addition to the reflective element shown in FIG. 6b, there may be one to six additional reflective elements in the lighting system (IL) and / or projection system (PS).

[0117] Considering the source collector module (SO) in more detail, a laser energy source containing a laser (623) is arranged to deposit laser energy (624) onto a fuel containing a target material. The target material may be any material that emits EUV radiation in a plasma state, such as xenon (Xe), tin (Sn), or lithium (Li). The plasma (2) is a highly ionized plasma having an electron temperature of tens of electron volts (eV). Higher energy EUV radiation may be generated from other fuel materials, such as terbium (Tb) and gadolidium (Gd). Energetic radiation generated during the deexcitation and recombination of these ions is emitted from the plasma, collected by a near-vertical incident collector mirror (3), and focused into an opening (621). The plasma (2) and the opening (621) are located at the first and second focal points of the collector (CO), respectively.

[0118] The collector (3) shown in FIG. 6b is a single curved mirror, but the collector may take other forms. For example, the collector may be a Schwarzschild collector having two radiation collecting surfaces. In an embodiment, the collector may be a grazing incident collector comprising a plurality of substantially cylindrical reflectors nested together.

[0119] For example, to deliver fuel, which is liquid tin, a droplet generator (626) is positioned within an enclosure structure (620) and is positioned to fire a high-frequency stream (628) of droplets toward a desired location in the plasma (2). The droplet generator (626) may be a target forming device (216) and / or may include an adhesive such as an adhesive (234). When operated, laser energy (624) is delivered simultaneously with the operation of the droplet generator (626) to deliver an impulse of radiation, thereby transforming each fuel droplet into plasma (2). The delivery frequency of the droplets may be several kilohertz, for example, 50 kHz. In practice, the laser energy (624) is delivered in at least two pulses: to vaporize into a small cloud, a pre-pulse with limited energy is delivered to the droplet before reaching the plasma location, and then the main pulse of the laser energy (624) is delivered to the cloud at the desired location to create plasma (2). A trap (630) is provided on the opposite side of the enclosure structure (620) to capture fuel that does not turn into plasma for any reason.

[0120] A droplet generator (626) comprises a reservoir (601) containing a fuel liquid (e.g., molten tin) and a filter (669) and a nozzle (602). The nozzle (602) is configured to eject droplets of the fuel liquid toward a plasma (2) formation location. Droplets of the fuel liquid may be ejected from the nozzle (602) by a combination of pressure within the reservoir (601) and vibrations applied to the nozzle by a piezoelectric actuator (not shown).

[0121] As will be known to a skilled reader of this specification, reference axes (X, Y, and Z) may be defined to measure and describe the geometry and behavior of the device, its various components, and the radiation beam (20, 21, 26). In each part of the device, local reference frames of the X, Y, and Z axes may be defined. In the example of FIG. 6b, the Z axis is approximately aligned with the direction of the optical axis (O) at a given point within the system, and is perpendicular to the plane of the patterning device (reticle) (MA) and perpendicular to the plane of the substrate (W). In the source collector module, the X axis is approximately aligned with the direction of the fuel stream (628), while the Y axis is orthogonal to the X axis and points out of the page as shown in FIG. 6b. Meanwhile, near the support structure (MT) holding the reticle (MA), the X axis crosses the scanning direction, which is aligned with the Y axis. For convenience, in this area of ​​the schematic drawing FIG. 6b, the X-axis points outside the drawing as indicated again. This designation is common in the art and will be adopted herein for convenience. In principle, any reference frame may be selected to describe the device and its behavior.

[0122] Additional components used as a whole for the operation of the source collector module and the lithography device (600) exist within the typical device but are not described herein. These include an array for reducing or mitigating the effects of contamination within a sealed vacuum, for example, to prevent deposits of fuel material from damaging or degrading the performance of the collector (3) and other optical systems. Other features that exist but are not described in detail are all sensors, controllers, and actuators involved in the control of the various components and subsystems of the lithography device (600).

[0123] Referring to FIG. 7, an implementation of an LPP EUV light source (700) is shown. The light source (700) can be used as a source collector module (SO) within a lithography device (600). Furthermore, the light generating module (105) of FIG. 1 may be part of a drive laser (715). The drive laser (715) may be used as a laser (625) (Fig. 6b).

[0124] An LPP EUV light source (700) is formed by irradiating the target mixture (714) at a plasma formation location (705) with an amplified light beam (710) traveling along a beam path toward the target mixture (714). The target material discussed in relation to FIGS. 1a, 2, and 3, and the target within the stream (121) of FIGS. 1a and 2, may be or include the target mixture (714). The plasma formation location (705) is located inside (707) of a vacuum chamber (730). When the amplified light beam (710) strikes the target mixture (714), the target material within the target mixture (714) is converted into a plasma state having elements with emission lines within the EUV range. The generated plasma has specific characteristics that depend 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 fragments emitted from the plasma.

[0125] The light source (700) also includes a supply system (725) for delivering, controlling, and directing a target mixture (714) in the form of a liquid droplet, a liquid stream, solid particles or clusters, solid particles contained within a liquid droplet, or solid particles contained within a liquid stream. The target mixture (714) includes a target material, such as, for example, water, tin, lithium, xenon, or any material having an emission line within the EUV range when converted to a plasma state. For example, the tin element may be used as pure tin (Sn); as a tin compound, for example, SnBr4, SnBr2, SnH4; as a tin alloy, for example, a tin-gallium alloy, a tin-indium alloy, a tin-indium-gallium alloy, or any combination of these alloys. The target mixture (714) may also contain impurities, such as non-target particles. Thus, in the absence of impurities, the target mixture (714) consists only of the target material. The target mixture (714) is delivered by the supply system (725) into the interior (707) of the chamber (730) and to the plasma formation location (705).

[0126] The light source (700) includes a drive laser system (715) that generates an amplified light beam (710) due to population inversion in the gain medium or media of the laser system (715). The light source (700) includes a beam transfer system between the laser system (715) and the plasma formation location (705), and the beam transfer system includes a beam transfer system (720) and a focusing assembly (722). The beam transfer system (720) receives the amplified light beam (710) from the laser system (715), controls and modifies the amplified light beam (710) as needed, and outputs the amplified light beam (710) to the focusing assembly (722). The focusing assembly (722) receives the amplified light beam (710) and focuses the beam (710) to the plasma formation location (705).

[0127] In some implementations, the laser system (715) may include one or more optical amplifiers, lasers, and / or lamps to provide one or more main pulses and, in some cases, one or more pre-pulses. Each optical amplifier includes a gain medium, an excitation source, and an internal optical system capable of optically amplifying a desired wavelength with high gain. The optical amplifier may or may not have a laser mirror or other feedback device forming a laser cavity. Thus, the laser system (715) generates an amplified light beam (710) due to population inversion in the gain medium of the laser amplifier even when there is no laser cavity. Furthermore, the laser system (715) may generate an amplified light beam (710) that is a coherent laser beam when there is a laser cavity to provide sufficient feedback to the laser system (715). The term “amplified light beam” includes one or more of light from a laser system (715) that is only amplified but not necessarily a coherent laser oscillation, and light from a laser system (715) that is amplified and also a coherent laser oscillation.

[0128] The optical amplifier of the laser system (715) may include a filling gas containing CO2 as a gain medium and may amplify light with a gain of more than 800 times at wavelengths of about 9,100 to about 11,000 nm, particularly at about 10,600 nm. An amplifier and laser suitable for use in the laser system (715) may include a pulsed laser device, for example, a pulsed gas-discharge CO2 laser device, which operates at a relatively high power of, for example, 10 kW or more and a high pulse repetition rate of, for example, 40 kHz or more, to generate radiation at about 9,300 nm or about 10,600 nm, for example, with DC or RF excitation. The pulse repetition rate is, for example, 50 kHz. The optical amplifier within the laser system (715) may also include a cooling system, such as water, which can be used when operating the laser system (715) at higher power.

[0129] The light source (700) includes a collector mirror (735) having a hole (740) to allow an amplified light beam (710) to pass through and reach a plasma formation location (705). The collector mirror (735) may be an elliptical mirror having a primary focus at the plasma formation location (705) and a secondary focus (also called an intermediate focus) at an intermediate location (745), for example, and EUV light may be output from the light source (700) at the intermediate location and input, for example, into an integrated circuit lithography tool (not visible). The light source (700) may also include an open hollow conical shroud (750) (e.g., a gas cone) tapered from the collector mirror (735) toward the plasma formation location (705) to allow the amplified light beam (710) to reach the plasma formation location (705) while reducing the amount of plasma-generating debris entering the focusing assembly (722) and / or beam transport system (720). For this purpose, a gas flow may be provided to the shroud toward the plasma formation location (705).

[0130] The light source (700) may also include a master 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 indicating the position of a droplet relative to a plasma formation location (705), for example, and provide this output to the droplet position detection feedback system (756), which can calculate, for example, the droplet position and trajectory and allow the droplet position error to be calculated from the droplet position and trajectory on a per-droplet basis or on an average basis. The droplet position detection feedback system (756) thus provides the droplet position error as an input to the master controller (755). Accordingly, the master controller (755) may provide, for example, laser position, direction, and timing correction signals to a laser control system (757) that may be used to control, for example, a laser timing circuit, and / or to a beam control system (758) that controls the position and shape of an amplified light beam of a beam transport system (720) to change the point and / or focal power of a beam focal spot within a chamber (730).

[0131] The supply system (725) includes a target material delivery control system (726) operable in response to a signal from a master controller (755) to change the emission point of a droplet when it is emitted by a target material supply device (727) to correct, for example, an error in the droplet reaching the required plasma formation location (705). The target material supply device (727) includes a target forming device using an adhesive such as an adhesive (234).

[0132] Additionally, the light source (700) may include one or more light source detectors (765 and 770) that measure 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, but are not limited thereto. The light source detector (765) generates a feedback signal for use by the master controller (755). The feedback signal may indicate an error in parameters, such as the timing and focus of the laser pulse, for example, to properly intercept the droplet at the correct place and time for effective and efficient EUV light generation.

[0133] The light source (700) may also include a guide laser (775) that can be used to help align various parts of the light source (700) or to adjust the amplified light beam (710) to a plasma formation location (705). In relation to the guide laser (775), the light source (700) includes a measurement system (724) placed within a focusing assembly (722) to sample a portion of the light from the guide laser (775) and the amplified light beam (710). In another embodiment, the measurement system (724) is placed within a beam transfer system (720). The measurement system (724) may include an optical element that samples or diverts a subset of light, and such optical element is made of any material capable of withstanding the power of the guide laser beam and the amplified light beam (710). The beam analysis system consists of a measurement system (724) and a master controller (755) because the master controller (755) analyzes the sampled light from the guide laser (775) and uses this information to adjust the components within the focus assembly (722) through the beam control system (758).

[0134] Accordingly, in summary, the light source (700) generates an amplified light beam (710) directed along a beam path to irradiate the target mixture (714) at the plasma formation location (705), thereby converting the target material within the mixture (714) into a plasma that emits light within the EUV range. The amplified light beam (710) operates at a specific wavelength (which is also referred to as the drive laser wavelength) determined based on the design and characteristics of the laser system (715). Additionally, if the target material provides sufficient feedback back to the laser system (715) to generate coherent laser light, or if the drive laser system (715) includes suitable optical feedback to form a laser cavity, additionally, the amplified light beam (710) may be a laser beam.

[0135] The foregoing description merely illustrates the principles of the embodiments of the present invention. Accordingly, it will be recognized that those skilled in the art may devise various arrangements that embody the principles of the present invention and fall within the spirit and scope of the present invention, even if not explicitly described or illustrated in this specification. Furthermore, all examples and conditional language cited in this specification are intended primarily for clearly educational purposes only and to help readers of this specification understand the principles of the present invention and the concepts to which the inventors have contributed to the development of the present technology; furthermore, such specifically cited examples and conditions should be interpreted as having no limitations. Moreover, all statements in this specification citing specific examples of the principles, aspects, and embodiments of the present invention, as well as their structural and functional equivalents, are intended to include both currently known equivalents and equivalents to be developed in the future, that is, any developed element that performs the same function regardless of structure.

[0136] The description of exemplary embodiments is intended to be read in conjunction with the drawings of the accompanying drawings, which are to be considered part of the entire written description. In the description, relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “top,” “bottom,” “upward,” “downward,” “topmost,” and “bottommost,” and their derivatives (e.g., “horizontally,” “downward,” “upward,” etc.), are to be interpreted to refer to an orientation such as that described at the time or shown in the drawings under discussion. These relative terms are for convenience of description and do not require the device to be configured or operated in a specific direction. Unless otherwise clearly stated, terms relating to attachment, connection, etc., such as “connected” and “interconnected,” refer to both movable and rigid attachments or relationships, as well as relationships in which structures are fixed or attached to one another directly or indirectly through interposed structures.

[0137] Although the present invention has been described in terms of exemplary embodiments, it is not limited thereto. Other embodiments are within the scope of the claims. The appended claims should be interpreted broadly to include other variations and embodiments of the present invention, which may be made by those skilled in the art without departing from the scope and range of the equivalents of the present invention.

[0138] Implementations of the present invention may be further described using the following sections:

[0139] 1. The system is,

[0140] A vacuum chamber comprising an inner region—the inner region is configured to receive a target and a light beam, the target includes a target material, and the target material emits extreme ultraviolet (EUV) light when in a plasma state;

[0141] A detection system configured to image an internal region, to detect light emission from atoms, ions, or molecules within the internal region, and to generate a representation of the spatial distribution of light emission in the internal region; and

[0142] It is connected to the detection system, and

[0143] To analyze the representation of the spatial distribution of light emission to determine the spatial distribution of light emission from atoms, ions, or molecules in the internal region; and

[0144] It includes a control system configured to determine whether to adjust at least one characteristic of the light beam and / or at least one characteristic of the vacuum chamber based on the spatial distribution of light emission.

[0145] 2. In the system of Section 1, light emission includes fluorescence.

[0146] 3. In the system of Section 2, fluorescence includes laser-induced fluorescence.

[0147] 4. The system of Section 1 further includes one or more spectral filters configured to be positioned relative to the detection system, and the spectral filters are configured to allow only some wavelengths to reach the detection system.

[0148] 5. In the system of Section 4, each of one or more spectral filters is configured to transmit light having a wavelength within one of the emission lines of a plurality of emission lines of the target material.

[0149] 6. In the system of Section 5, at least one of the one or more spectral filters is configured to transmit wavelengths within the visible light range.

[0150] 7. In the system of Section 4, the vacuum chamber is further configured to contain gas in an internal region, and the spectrum filter is configured to transmit light having a wavelength in the emission line of the gas.

[0151] 8. In the system of Section 1, the control system is configured to accept multiple representations of an internal region, each of which is associated with a different time, and the control system is configured to analyze the representations of the internal region, and the control system is configured to analyze each of the multiple representations to determine the spatial distribution of light emission within the internal region at each different time.

[0152] 9. In the system of Section 8, light emission within the inner region arises from an energy event within the inner region, and the different times are all times that occur after the energy event.

[0153] 10. In the system of Section 9, the energy event involves an interaction between a light beam and a target, and the light emission is an emission from (a) the target material, (b) the plasma formed from the interaction between the light beam and the target material, and / or (c) the fragment formed from the interaction between the light beam and the target.

[0154] 11. In the system of Section 1, the control system is configured to accept an extended exposure representation for an internal region, the extended exposure representation for an internal region includes the average of the spatial distribution of emissions within the internal region over a predetermined period.

[0155] 12. In the system of Section 9, the vacuum chamber is further configured to contain gas within an internal region, the energy event involves an interaction that adds energy to the gas, and the light emission is an emission from the gas.

[0156] 13. In the system of Section 12, interactions that add energy to the gas include (a) interactions between the light beam and the gas, (b) interactions between the gas and the plasma formed from the interaction between the light beam and the target, and / or (c) interactions between the ions and the gas.

[0157] 14. In the system of Section 1, the control system configured to analyze a representation to determine the spatial distribution of light emission in an internal region includes the control system configured to estimate the spatial distribution and / or shape of the intensity of light emission.

[0158] 15. The system of Section 1 is,

[0159] A first spectrum filter configured to transmit light having a wavelength within a first wavelength band; and

[0160] It further includes a second spectrum filter configured to transmit light having a wavelength within a second wavelength band,

[0161] The control system configured to analyze the representation includes the control system being configured to estimate the amount of light emission in a first wavelength band and the amount of light emission in a second wavelength band, and the control system is further configured to estimate the ionization fraction of the target material based on comparing the estimated amount of light emission in the first wavelength band and the estimated amount of light emission in the second wavelength band.

[0162] 16. In the system of Section 15, the control system determines whether to adjust at least one characteristic of the light beam based on the estimated ionization fraction.

[0163] 17. In the system of Section 16, the control system determines whether to adjust the orientation of the light beam based on the estimated ionization fraction.

[0164] 18. In the system of Section 1, the light beam includes a main pulsed light beam containing sufficient energy to convert at least a portion of the target material into a plasma emitting EUV light.

[0165] 19. In the system of Section 1, the light beam includes a pre-pulsed light beam.

[0166] 20. In the system of Section 4, the control system configured to analyze the representation further comprises the control system being configured to compare the spatial distribution of fluorescence within the internal region at least twice at different times to estimate the velocity of ions within the internal region and to compare the estimated velocity with the velocity specification, and the control system being configured to determine whether to adjust the gas pressure based on the comparison of the estimated velocity and the velocity specification.

[0167] 21. In the system of Section 1, the representation of the spatial distribution includes a 2-dimensional representation.

[0168] 22. In the system of Section 1, the light beam comprises a pulsed light beam, and the control system configured to adjust at least one characteristic of the light beam comprises the control system configured to adjust at least one characteristic of a pulse that occurs after the pulsed light beam.

[0169] 23. EUV light sources are:

[0170] A vacuum chamber configured to contain gas in an internal region and to receive a target—the target comprises a target material that emits extreme ultraviolet (EUV) light in a plasma state—and a light beam;

[0171] A monitor comprising at least one sensor configured to detect emissions from gas within an internal region and to generate an indication of the detected emissions; and

[0172] It connects to the monitor,

[0173] To analyze indications for detected emissions; and

[0174] It includes a control system configured to determine whether to adjust at least one characteristic of the light beam and / or at least one characteristic of the vacuum chamber based on analysis.

[0175] 24. In the EUV light source of Section 23, the monitor includes a detection system configured to image a portion of an internal region and to generate a representation of the spatial distribution of detected emissions within this portion.

[0176] 25. In the EUV light source of Section 24, the control system is configured to accept a plurality of representations over a predetermined period, each representation representing a spatial distribution of detected emissions within a portion at different times within the period, and the control system is configured to determine whether to adjust at least one characteristic of the light beam and / or at least one characteristic of the vacuum chamber based on two or more of the plurality of representations.

[0177] 26. In the EUV light source of Section 23, the gas contains hydrogen, and the detected emission includes H-alpha (H-α) and / or H-beta (H-β) emission from hydrogen.

[0178] 27. The EUV light source in Section 24

[0179] A first spectrum filter configured to transmit a first wavelength band; and

[0180] It further includes a second spectrum filter configured to transmit a second wavelength band,

[0181] When in operation, the first spectrum filter and the second spectrum filter are located between the part and the detection system; and

[0182] A control system configured to analyze detected emissions includes a control system configured to compare a representation of emissions transmitted by a first spectral filter with a representation of emissions transmitted by a second spectral filter; and a determination of whether to adjust at least one characteristic of the light beam and / or at least one characteristic of the vacuum chamber is based on the comparison.

[0183] 28. The EUV light source of Section 24 further includes a pressure controller connected to the inside of a vacuum chamber, the pressure controller is configured to change the pressure of the gas inside the vacuum chamber, and the control system is connected to the pressure controller.

[0184] 29. Methods for controlling an EUV light source are,

[0185] Providing a target to a target area of ​​a vacuum chamber containing gas in an internal area;

[0186] Causing interaction between the light beam and the target within the target area;

[0187] Detecting light emission from atoms, ions, and / or molecules within an internal region of a vacuum chamber—the light emission is in response to an energy event within the vacuum chamber, and the energy event includes an event that adds energy to a target and / or gas;

[0188] Analyzing detected light emission to determine the spatial distribution of light emission within an internal region; and

[0189] It includes determining whether to adjust the characteristics of the light beam and / or gas based on the analysis.

[0190] Other implementations are within the scope of the claims.

Claims

Claim 1 A vacuum chamber comprising an inner region—the inner region is configured to receive a target and a light beam, said target includes a target material, said target material emits extreme ultraviolet (EUV) light when in a plasma state—; a detection system configured to image said inner region, to detect light emission from atoms, ions, or molecules within said inner region and to generate a representation of the spatial distribution of light emission in said inner region; a control system connected to said detection system and configured to analyze the representation of said spatial distribution of light emission to determine the spatial distribution of light emission from atoms, ions, or molecules in said inner region; and to determine whether to adjust at least one characteristic of the light beam and / or at least one characteristic of said vacuum chamber based on said spatial distribution of light emission; and a system comprising one or more spectral filters configured to be positioned relative to said detection system, said spectral filters configured to allow only some wavelengths to reach said detection system. Claim 2 In claim 1, the light emission is a system including fluorescence. Claim 3 delete Claim 4 A system according to claim 1, wherein each of the one or more spectrum filters is configured to transmit light having a wavelength within one of the emission lines of the target material. Claim 5 A system according to claim 1, wherein the control system is configured to accept a plurality of representations for the internal region, each of the plurality of representations is associated with a different time, and the control system is configured to analyze the representations for the internal region, wherein the control system is configured to analyze each of the plurality of representations to determine the spatial distribution of light emission within the internal region at each of the different times. Claim 6 In claim 1, the control system is configured to accept an extended exposure representation for the internal region, wherein the extended exposure representation for the internal region comprises the average of the spatial distribution of the emission within the internal region over a predetermined period. Claim 7 A system according to claim 1 further comprising: a first spectrum filter configured to transmit light having a wavelength within a first wavelength band; and a second spectrum filter configured to transmit light having a wavelength within a second wavelength band, wherein the control system configured to analyze the expression comprises the control system estimating the amount of light emission in the first wavelength band and estimating the amount of light emission in the second wavelength band, and the control system further configured to estimate the ionization fraction of the target material based on comparing the estimated amount of light emission in the first wavelength band with the estimated amount of light emission in the second wavelength band. Claim 8 In claim 7, the control system is a system that determines whether to adjust at least one characteristic of the light beam based on the estimated ionization fraction. Claim 9 A system according to claim 1, wherein the light beam comprises a main pulsed light beam having sufficient energy to convert at least a portion of the target material into a plasma emitting EUV light. Claim 10 In claim 1, the control system configured to analyze the expression further comprises the control system being configured to compare the spatial distribution of fluorescence within the inner region at least twice at different times to estimate the velocity of ions within the inner region and to compare the estimated velocity with a velocity specification, and the control system being configured to determine whether to adjust the gas pressure based on the comparison of the estimated velocity and the velocity specification. Claim 11 A system according to claim 1, wherein the light beam comprises a pulsed light beam, and the control system is configured to adjust at least one characteristic of the light beam, and the control system is configured to adjust at least one characteristic of a pulse that occurs after the pulsed light beam. Claim 12 An EUV light source comprising: a vacuum chamber configured to contain a gas in an internal region and to receive a light beam from a target—the target comprising a target material that emits extreme ultraviolet (EUV) light in a plasma state; a monitor comprising at least one sensor configured to detect emissions from the gas in the internal region and to generate an indication of the detected emissions; and a control system connected to the monitor and configured to analyze the indication of the detected emissions and to determine whether to adjust at least one characteristic of the light beam and / or at least one characteristic of the vacuum chamber based on the analysis. Claim 13 In claim 12, the EUV light source comprising a detection system configured such that the monitor images a portion of the internal region and generates a representation of the spatial distribution of detected emissions within the portion. Claim 14 In paragraph 12, the above gas comprises hydrogen, and the detected emission comprises an EUV light source including H-alpha (H-α) or H-beta (H-β) emission from hydrogen. Claim 15 In claim 13, further comprising: a first spectrum filter configured to transmit a first wavelength band; and a second spectrum filter configured to transmit a second wavelength band, wherein, in operation, the first spectrum filter and the second spectrum filter are located between the part and the detection system; and wherein the control system is configured to analyze the detected emission, the control system is configured to compare a representation of the emission transmitted by the first spectrum filter with a representation of the emission transmitted by the second spectrum filter; and wherein the determination of whether to adjust at least one characteristic of the light beam and / or at least one characteristic of the vacuum chamber is based on the comparison. 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