Laser sustained plasma generation in supersonic gas jets

Abstract

A LSP broadband light source is disclosed. The light source can include a gas containment structure. The light source can include a plurality of jet nozzles, where the jet nozzles are configured to generate supersonic gas jets and direct the supersonic gas jets to collide within the gas containment structure to form a local high pressure region at a collision point. The light source can include a primary laser pump source, where the primary laser pump source is configured to direct a primary pump beam to the local high pressure region formed at the collision point. The light source can include a pulsed auxiliary laser source, where the pulsed auxiliary laser source is configured to direct a pulsed auxiliary beam to the local high pressure region at the collision point. The light source can include a light collector element configured to collect broadband light emitted from a plasma.

Description

[0001] Cross-reference of related applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 524,866, filed July 4, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure generally relates to plasma-based radiation sources, and more specifically, to laser-supplied plasma (LSP) broadband sources containing plasma generated in localized high-pressure regions produced by one or more supersonic gas jets. Background Technology

[0004] As the demand for integrated circuits with increasingly smaller device features continues to grow, so too does the need for improved lighting sources for testing these miniaturized devices. One such lighting source comprises a laser-supplied plasma (LSP) source. LSP sources are capable of producing high-power broadband light. LSP sources typically operate by focusing laser radiation into a gas volume to excite the gas (e.g., argon or xenon) into a plasma state capable of emitting light. This effect is often referred to as “pumping” the plasma. LSPs used in broadband plasma (BBP) sources are limited in brightness. Several methods have been proposed to increase this brightness. LSP-based lighting solutions in stagnant lamps have been shown to have limited radiation due to the tendency of the plasma to grow in the direction of the pump laser that absorbs the laser. As the pump laser power increases, the plasma becomes larger and the absorption at the periphery of the plasma becomes so significant that the power reaching the plasma focus begins to decrease and the LSP becomes dimmer. Gas flow solutions with laminar subsonic gas flow require the recirculation of large volumes of high-pressure gas, which becomes technically challenging. Typical values ​​for such systems require the recirculation of a good portion of one kilogram of gas per second at pressures exceeding 100 bar. This arrangement also requires a transparent high-pressure container or a chamber with high-pressure windows for optical input-output, all of which increase structural complexity and operational safety. Liquid jet-based systems require cryogenic cooling to liquefy the internally high-pressure gas to generate a sufficiently fast liquid jet. At the desired velocity, the liquid jet tends to become unstable and break into a spray, and the LSP can become noisy. Therefore, it is desirable to provide an LSP source that overcomes the shortcomings associated with previous methods. Summary of the Invention

[0005] According to one or more embodiments of this disclosure, a laser-suppressed plasma (LSP) broadband light source is disclosed. In an illustrative embodiment, the light source includes a gas confinement structure. In an illustrative embodiment, the light source includes a plurality of jet nozzles configured to generate a plurality of supersonic gas jets and guide the plurality of supersonic gas jets to collide within the gas confinement structure to form a local high-pressure region at the collision point of the plurality of supersonic gas jets. In an illustrative embodiment, the light source includes a main laser pump source configured to guide a main pump beam to the local high-pressure region formed at the collision point of the plurality of supersonic gas jets. In an illustrative embodiment, the light source includes a pulse-assisted laser source configured to guide a pulse-assisted beam to the local high-pressure region at the collision point of the plurality of supersonic gas jets, wherein the main pump beam and the pulse-assisted beam are configured to sustain the plasma within the local high-pressure region. In an illustrative embodiment, the light source includes a light collector element configured to collect at least a portion of broadband light emitted from the plasma. In illustrative embodiments, the LSP broadband light source may be implemented within an optical system (e.g., but not limited to, an inspection system, a metrology system, or a lithography system).

[0006] According to one or more additional and / or alternative embodiments of this disclosure, a broadband LSP light source is disclosed. In an illustrative embodiment, the light source includes a gas confinement structure. In an illustrative embodiment, the light source includes one or more jet nozzles configured to generate one or more supersonic gas jets. In an illustrative embodiment, the light source includes a main laser pump source configured to direct a main pump beam into a local high-pressure region formed by the supersonic gas expansion of the one or more supersonic gas jets. In an illustrative embodiment, the light source includes a pulse-assisted laser source configured to direct a pulse-assisted beam into the local high-pressure region formed by the supersonic gas expansion of the one or more supersonic gas jets, wherein the main pump beam and the pulse-assisted beam are configured to maintain plasma within the local high-pressure region. In an illustrative embodiment, the light source includes a light collector element configured to collect at least a portion of broadband light emitted from the plasma.

[0007] It should be understood that the foregoing general description and the following detailed description are merely illustrative and explanatory and do not necessarily limit this disclosure. The accompanying drawings, incorporated in and forming a part of this specification, illustrate the subject matter of this disclosure. The description, together with the drawings, serves to explain the principles of this disclosure. Attached Figure Description

[0008] Those skilled in the art can better understand the many advantages of this disclosure by referring to the accompanying drawings.

[0009] Figures 1A to 1B A conceptual view illustrating a broadband LSP light source having multiple impacting supersonic jets for forming a local high-pressure gas region for plasma generation, according to one or more embodiments of the present disclosure.

[0010] Figure 2 This describes the gas velocity of the airflow within an LSP source according to one or more embodiments of the present disclosure.

[0011] Figure 3 This describes the pressure of the gas within a gas containment structure according to one or more embodiments of the present disclosure.

[0012] Figures 4A to 4B A conceptual view illustrating a single nozzle for generating a single supersonic jet according to one or more embodiments of the present disclosure.

[0013] Figure 5A A simplified schematic view illustrating an LSP broadband light source according to one or more embodiments of the present disclosure, wherein the optical path of the pump beam does not overlap with the optical path of the pulse-assisted beam.

[0014] Figure 5B The following is a simplified schematic view illustrating an LSP broadband light source according to one or more embodiments of the present disclosure, wherein the optical path of the pump beam overlaps with the optical path of the pulse-assisted beam by using a dichroic mirror.

[0015] Figure 5C A simplified schematic view illustrating an LSP broadband light source according to one or more embodiments of the present disclosure, wherein a pulsed auxiliary beam is injected into the laser fiber of the main pump source.

[0016] Figure 6 A simplified schematic view illustrating an optical characterization system for implementing a pulse-assisted LSP broadband light source according to one or more embodiments of the present disclosure.

[0017] Figure 7 A flowchart illustrating a method for generating broadband light according to one or more embodiments of the present disclosure is provided. Detailed Implementation

[0018] The disclosed subject matter will now be described in detail with reference to the accompanying drawings. Certain embodiments and specific features of this disclosure have been particularly shown and described. The embodiments set forth herein should be considered illustrative rather than restrictive. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail may be made without departing from the spirit and scope of this disclosure.

[0019] General reference Figures 1A to 4BThis describes a broadband light source comprising laser-supplied plasma according to one or more embodiments of the present disclosure.

[0020] Embodiments of this disclosure relate to forming a localized high-pressure gas region positioned near the laser focus of a main pump laser and / or a pulsed auxiliary laser to sustain plasma at that location. The high-pressure region may be formed at the Mach disk of one or more supersonic gas jets during supersonic gas expansion, or at the collision point of two or more supersonic gas jets. The one or more supersonic gas jets may be formed by having one or more nozzles (e.g., convergent nozzles, diffusing nozzles, or cylindrical nozzles). Due to the small size of the high-pressure region, the pump laser beam can propagate through the surrounding low-pressure / ambient gas region within the gas containment structure and to the high-pressure region without significant absorption. Due to the lack of absorption in the low-pressure region, the laser beam is efficiently delivered to the high-pressure region, where it is efficiently absorbed by the high-pressure plasma. Strong absorption regions are independent of laser power. Therefore, as laser power increases, the density of absorbed energy in the small high-pressure region also increases, which in turn produces a more radioactive (brighter) plasma.

[0021] The implementation of a localized high-pressure region allows for increased spectral radiation (brightness) compared to that achievable in a stagnant high-pressure source. The brightness of the LSP in a stagnant high-pressure source is limited by absorption at the plasma periphery. As pump power increases, the plasma periphery grows, and its absorption limits how much power can be delivered to the laser focus. In the proposed solution, a plasma periphery also grows; however, its absorption is lower because it is located in a low-pressure region of the environment. This allows all pumped laser radiation to be delivered to the high-pressure region formed by (several) supersonic jets.

[0022] Compared to high-pressure flow solutions, embodiments of this disclosure do not require a high-pressure plasma-containing gas container, the construction of which is a major challenge for high-power UV-VUV LSP sources. Embodiments of this disclosure require only a relatively low-pressure (e.g., up to about 10 bar) or even atmospheric enclosure. Unlike liquid jets used with CW pump sources, the supersonic gas jet solution of this disclosure eliminates the limitations associated with cryogenic jet operation, liquid jet instability, and liquid jet dissociation due to interaction with ambient gases and shock waves from gas outflows from the interaction region.

[0023] Unlike pulsed operation, this solution operates in CW mode, which is beneficial for optical metrology and inspection applications requiring high-brightness sources. CW operation significantly reduces optical damage in such systems.

[0024] Figures 1A to 1B This describes a broadband LSP light source 100 according to one or more embodiments of the present disclosure.

[0025] In one embodiment, the light source 100 includes a gas confinement structure 101, a main laser pump source 102, a pulsed laser source 104, two or more jet nozzles 107a, 107b, and a light collector element 111. In additional and / or alternative embodiments, such as Figure 1B As shown, the broadband LSP light source 100 includes a recirculation loop 112.

[0026] Two or more jet nozzles 107a, 107b may comprise a first jet nozzle 107a and a second jet nozzle 107b (or any number of nozzles). In an embodiment, the two or more jet nozzles 107a, 107b may comprise two or more high-pressure (e.g., above 50 bar) nozzles configured to generate two or more supersonic gas jets 106a, 106b. The two or more jet nozzles 107a, 107b may be configured to guide the two or more supersonic gas jets 106a, 106b to collide with each other within the gas containment structure 101 to form a local high-pressure region 109. The local high-pressure region 109 is a region where the ambient pressure 134 is measured and is greater than the ambient pressure. For example, the ambient pressure may be 1 bar, wherein the local high-pressure region 109 is at a pressure between 10 bar and 100 bar. It should be noted that the ambient pressure (e.g., about 1 bar) is less than the pressure of nozzles 107a and 107b and the temperature of nozzles 107a and 107b is sufficient to prevent the gas from liquefying when it is discharged from nozzles 107a and 107b.

[0027] It should be recognized that the light source 100 can be implemented using any number and type of gas components. In embodiments, the gas used to generate the supersonic jet(s) of this disclosure may comprise one or more inert gases. For example, one or more inert gases may include, but are not limited to, xenon, argon, neon, or helium. As another example, the gas may comprise one or more non-inert gases. In embodiments, the gas may comprise a mixture of two or more gases. For example, the gas may comprise a mixture of two or more inert gases (e.g., Ar / Xe). As another example, the gas may comprise a mixture of an inert gas and a non-inert gas, or a mixture of two or more non-inert gases.

[0028] In one embodiment, the main laser pump source 102 is configured to guide the main pump beam 103 to a local high-pressure region 109 formed at the collision point of two or more supersonic gas jets 106a, 106b. In another embodiment, the pulsed auxiliary laser source 104 is configured to guide the pulsed auxiliary beam 105 to the local high-pressure region 109 at the collision point of two or more supersonic gas jets 106a, 106b. In this regard, the main pump beam 103 and / or the pulsed auxiliary beam 105 are configured to generate and maintain plasma 110 within the local high-pressure region 109.

[0029] The main laser pump source 102 may comprise any laser pump source known in the art. In embodiments, the main laser pump source 102 may comprise one or more continuous wave (CW) lasers. For example, the main laser pump source 102 may comprise, but is not limited to, one or more fiber-based near-infrared (NIR) lasers, one or more direct photodiode lasers, and / or one or more CO2 lasers. It should be noted that the main laser pump source 102 is not limited to a single laser. For example, the main pump source 102 may comprise any number of additional laser sources. For example, the main pump source 102 may comprise a first main pump source emitting a first wavelength and at least a second main pump source emitting a second wavelength, etc.

[0030] The pulse-assisted laser source 104 may comprise any pulsed laser source known in the art. In embodiments, the pulse-assisted laser source 104 may comprise one or more picosecond or femtosecond pulsed laser sources. For example, one or more pulse-assisted laser sources 104 may operate at a repetition rate greater than about 50 kHz (e.g., greater than 100 kHz). For example, one or more pulse-assisted laser sources 104 may operate at a repetition rate greater than 1 MHz. The pulse-assisted laser source 104 may comprise, but is not limited to, one or more pulsed fiber-based NIR lasers, one or more pulsed coherently coupled fiber lasers, and / or one or more pulsed thin disk lasers. It should be noted that the main laser pump source 102 is not limited to a single laser. For example, the pulse-assisted laser source 104 may comprise any number of additional laser sources. For example, the pulse-assisted laser source 104 may comprise a first pulse-assisted laser source emitting a first wavelength and at least a second pulse-assisted laser source emitting a second wavelength, etc.

[0031] It should be noted that the scope of this disclosure is not limited to the use of both the main pump source 102 and the pulsed auxiliary source 104. In additional and / or alternative embodiments, source 100 may use only one or more main pump sources 102 to maintain plasma 110 at the local high-pressure region 109. In additional and / or alternative embodiments, source 100 may use only one or more pulsed auxiliary sources 104 to maintain plasma 110 at the local high-pressure region 109.

[0032] In an embodiment, the light source 100 includes one or more focusing optics 122 for focusing / guiding the main pump beam 103 to the plasma 110. Additionally, the light source 100 may include one or more focusing optics 124 for focusing / guiding the pulse-assisted beam 105 to the plasma 110. It should be noted that the pump laser focusing optics 122 and the pulse-assisted laser optics 124 may include any optical elements known in the art for guiding and / or focusing radiation, including, but not limited to, lenses, mirrors, prisms, polarizers, gratings, filters, or beam splitters. In an embodiment, the gas containment structure 101 may include one or more transparent portions. For example, the gas containment structure 101 may include, but is not limited to, input windows 126, 128 for receiving the main pump laser beam 103 and the pulse-assisted beam 105. Additionally, the gas containment structure 101 may include an exit window (not shown). However, it should be noted that since most of the gas within the containment structure can be maintained at a relatively low pressure (e.g., approximately 1 bar of ambient pressure), high-pressure windows are not required for operation.

[0033] U.S. Patent Application No. 18 / 372,590, filed September 25, 2023, describes an implementation of a pulse-assisted laser source combined with a main laser source, the entire contents of which are incorporated herein by reference.

[0034] In one embodiment, the recirculation pump 130 recirculates the gas through the gas containment structure 101. In this regard, the recirculation loop 112 can supply gas to nozzles 107a, 107b to form supersonic jets 106a, 106b to create a localized high-pressure region 109 for generating / maintaining plasma 109. Furthermore, the recirculation loop 112 removes hot gas from plasma 110 and cools the gas via one or more heat exchangers 132. The cooled gas can then be recirculated back through the system and driven into the collision region 109 via nozzles 107a, 107b. The recirculation loop 112 may include, but is not limited to, one or more pumps 130, one or more heat exchangers 132, and / or one or more filters for driving nozzles 107a, 107b.

[0035] In an embodiment, light collector element 111 is configured to collect broadband light 118 emitted from plasma 110. Light collector element 111 may include any one or more optical elements known in the art configured to collect and / or focus broadband light 118, including, but not limited to, one or more mirrors, one or more prisms, one or more lenses, one or more diffractive optical elements, one or more parabolic mirrors, one or more elliptical mirrors, one or more spherical mirrors, and the like. It should be appreciated that light collector element 111 may be configured to collect and / or focus broadband light 118 generated by plasma 110 for use in one or more downstream processes, including, but not limited to, imaging processes, inspection processes, metrology processes, photolithography processes, and the like. Broadband light 118 may be collected by light collector element 111 and guided through one or more apertures 119 to one or more downstream applications 121.

[0036] Figures 2 to 3 Simulated views 200, 300 illustrating the operation of a light source 100 according to one or more embodiments of the present disclosure. Figure 2 Describe the gas velocity of the airflow within the gas confinement structure 100 and Figure 3 The pressure within the gas containment structure 100 is depicted. Views 200 and 300, showing simulated gas velocities and pressures, indicate a high-pressure, low-velocity region 109 of several hundred micrometers formed by the collision of two supersonic gas jets 106a and 106b. The simulation is performed using convergent nozzles with elongated shapes and relatively shallow divergence angles. Moreover, the approximate local pressure-to-ambient-pressure ratio within the gas containment structure is sufficient for the operation of source 100. The diamond shock wave structure generated when the pressure ratio at the nozzle is much higher than the critical pressure can be managed by designing the nozzle shape, nozzle throat, length of the divergence section, and other parameters specific to the selected gas (e.g., an inert gas) and any other requirements of source 100.

[0037] In this example, it should be noted that if the CW-pumped laser intensity near the focal point is higher than approximately 10⁹ W / cm², 2 Up to approximately 1013 W / cm 2The gas dissociation threshold is reached. In this case, the gas flow cannot blow it away and the plasma self-initiates. To assist this process and ensure plasma stability, even in the presence of a fast gas flow, a series of picosecond / femtosecond pulses with a high repetition rate of about 1 MHz to about 1000 MHz can be used. This can be provided by a pulse-assisted laser 104 with a low average power that exceeds the dissociation threshold during each pulse, and the pulses are close enough that the plasma has no time to quench between pulses. For example, a 20 kW CW pump laser can be combined with a 2 kW 100 MHz 300 ps pulse-assisted laser. The pressure dependence of the dissociation threshold in laser-induced plasmas is discussed in "Pressure dependence of the laser-induced breakdown thresholds of gases and droplets" by Jon P. Davis et al., Vol. 29, No. 15, p. 2303, which is incorporated herein by reference in its entirety.

[0038] It should be noted that the various parameters of the light source 100 described in the non-limiting examples should not be interpreted as limiting the scope of this disclosure. These examples are provided for illustrative purposes only, and it should be understood that various laser powers, frequencies, pulse durations, gas pressures, and gas velocities may be utilized, given the details of the operating light source 100.

[0039] While much of this disclosure focuses on using two or more impact jets to generate localized high-pressure regions, this configuration should not be construed as limiting the scope of this disclosure. Rather, any number of gas / fluid flow arrangements can be implemented to generate localized high-pressure gas regions (relative to ambient pressure) suitable for plasma generation.

[0040] Figure 4A This illustration shows a conceptual view 400 of a single nozzle 107 for generating a single supersonic jet 106 according to one or more embodiments of the present disclosure. In this embodiment, a high-pressure region (e.g., relative to a lower-pressure ambient gas) is formed within the supersonic gas flow. For example, a Mach disk within the shock wave of the supersonic gas flow (e.g., a diamond shock wave). The localized high-pressure region 109 can be formed using one or more Mach disks 136 of the supersonic gas flow. Plasma 110 can be generated and maintained at the localized high-pressure region 109 associated with the one or more Mach disks 136. Figure 4BAs shown, a localized high-pressure region 109 can be formed at the exit of the supersonic jet nozzle 107. In this example, plasma 110 can be generated and maintained at the localized high-pressure region 109 formed at the exit of the supersonic jet nozzle 107.

[0041] Figure 5A A simplified schematic view illustrating a broadband LSP light source 100 according to one or more embodiments of the present disclosure is provided. It should be noted here that, regarding… Figures 1A to 4B The various embodiments described should be interpreted as extending to Figure 5A An embodiment is described below. In this embodiment, the light collector element 506 is a curved mirror. For example, the light collector element 506 may include, but is not limited to, an elliptical mirror, a spherical mirror, or a parabolic mirror. In this embodiment, the main pumping beam 103 and the pulsed auxiliary beam 105 do not share an optical path before entering the light collector element 506. For example, the main pumping source 102 may guide the main pumping beam 103 through the beam-forming optics 122 and the steering mirror 502. Also, the main pumping beam 103 passes through the dichroic mirror 504 (e.g., a cold mirror) and is guided toward the local high-voltage region 109. Additionally, the pulsed auxiliary source 104 may be arranged to guide the pulsed auxiliary beam 105 through one or more side ports 507 formed by penetrating the walls (e.g., sidewalls) of the light collector element 506 and into the local high-voltage region 109. In this example, nozzles 107a and 107b are arranged in a top / bottom configuration, wherein the point of impact and the local high-pressure region 109 coincide with the focal point of the light collector element 506 (e.g., the focal point of an elliptical reflector). As previously described herein, the main pump beam 103 and the pulsed auxiliary beam 105 are used to sustain the plasma 110. The broadband light 118 emitted by the plasma 110 can then be collected by the light collector element 506 and guided by the dichroic mirror 504 to one or more downstream optical elements 121.

[0042] Figure 5B A simplified schematic view illustrating a broadband LSP light source 100 according to one or more embodiments of the present disclosure is provided. It should be noted here that, regarding… Figures 1A to 5A The various embodiments described should be interpreted as extending to Figure 5BIn this embodiment, the main pump beam 103 and the pulsed auxiliary beam 105 share an optical path before entering the light collector element 506 (e.g., an elliptical mirror, a spherical mirror, or a parabolic mirror). For example, the main pump source 102 may guide the main pump beam 103 through a pump module containing one or more laser-forming optics 508. The main pump beam 103 also passes through a dichroic mirror 504 (e.g., a cold mirror) and is guided toward a local high-voltage region 109. Additionally, the pulsed auxiliary source 104 may be arranged to guide the pulsed auxiliary beam 105 to a first dichroic mirror 502. The first dichroic mirror 502 is configured to transmit the main pump beam 103 toward the light collector element 506 while simultaneously reflecting the pulsed auxiliary beam 105 toward the light collector element 506. After the first dichroic mirror 502, the main pump beam 103 and the pulsed auxiliary beam 105 share an optical path to the light collector element 506. Next, the main pump beam 103 and the pulsed auxiliary beam 105 can pass through the second dichroic mirror 504 and be reflected by the light collector element 506 into the local high-voltage region 109. As previously described herein, the main pump beam 103 and the pulsed auxiliary beam 105 are used to sustain the plasma 110. The broadband light 118 emitted by the plasma 110 can then be collected by the light collector element 506 and guided by the dichroic mirror 504 to one or more downstream optical elements 121.

[0043] Figure 5C A simplified schematic view illustrating a broadband LSP light source 100 according to one or more embodiments of the present disclosure is provided. It should be noted here that, regarding… Figures 1A to 5B The various embodiments described should be interpreted as extending to Figure 5C In this embodiment, the pulsed auxiliary beam 105 is injected into one or more laser fibers of the main pump source 102 of the main pump beam 103. Therefore, when beams 103 and 105 exit the beamforming optics 508, the main pump beam 103 and the pulsed auxiliary beam 105 share an optical path. After exiting the beamforming optics 508, the main pump beam 103 and the pulsed auxiliary beam 105 are guided through a dichroic mirror 504 (e.g., a cold mirror) toward a light collector element 506, which in turn guides the main pump beam 103 and the pulsed auxiliary beam 105, sharing the optical path, to a local high-voltage region 109. As previously described herein, the main pump beam 103 and the pulsed auxiliary beam 105 are used to sustain the plasma 110. The broadband light 118 emitted by the plasma 110 can then be collected by the light collector element 506 and guided by the dichroic mirror 504 to one or more downstream optical elements 121.

[0044] It should be noted that Figure 5A The nozzle arrangement depicted is not limited to a top / bottom arrangement or two nozzles. It is considered that two or more nozzles (e.g., 2, 3, 4, 5, 6, etc.) can be arranged in any alignment geometry (e.g., side-to-side, radial, etc.). Furthermore, in Figures 5A to 5CA single nozzle configuration can be implemented within the embodiments depicted herein.

[0045] U.S. Patent No. 7,435,982, issued October 14, 2008, also substantially describes the generation of plasma using lasers; the entire contents of that patent are incorporated herein by reference. U.S. Patent No. 7,786,455, issued August 31, 2010, also substantially describes the generation of plasma; the entire contents of that patent are incorporated herein by reference. U.S. Patent No. 7,989,786, issued August 2, 2011, also substantially describes the generation of plasma; the entire contents of that patent are incorporated herein by reference. U.S. Patent No. 8,182,127, issued May 22, 2012, also substantially describes the generation of plasma; the entire contents of that patent are incorporated herein by reference. U.S. Patent No. 8,309,943, issued November 13, 2012, also substantially describes the generation of plasma; the entire contents of that patent are incorporated herein by reference. The generation of plasma is generally described in U.S. Patent No. 8,525,138, issued February 9, 2013, the entire contents of which are incorporated herein by reference. The generation of plasma is also generally described in U.S. Patent No. 8,921,814, issued December 30, 2014, the entire contents of which are incorporated herein by reference. The generation of plasma is also generally described in U.S. Patent No. 9,318,311, issued April 19, 2016, the entire contents of which are incorporated herein by reference. The generation of plasma is also generally described in U.S. Patent No. 9,390,902, issued July 12, 2016, the entire contents of which are incorporated herein by reference. In a general sense, the various embodiments of this disclosure should be interpreted as extending to any plasma-based light source known in the art.

[0046] Figure 6 A simplified schematic view illustrates an optical characterization system 300 implementing an LSP broadband light source 100 according to one or more embodiments of the present disclosure. In an embodiment, the system 300 includes an LSP light source 100, an illumination branch 603, a collection branch 605, a detector assembly 614, and a controller 618 including one or more processors and memories.

[0047] It should be noted that system 600 may include any imaging, inspection, metrology, lithography, or other characterization system known in the art. In this respect, system 600 may be configured to perform inspection, optical metrology, lithography, and / or any form of imaging on sample 607. Sample 607 may comprise any sample known in the art, including, but not limited to, semiconductor wafers, photomasks, flat panel displays, and the like. It should be noted that system 600 may be incorporated into one or more of the various embodiments of the LSP light source 100 described throughout this disclosure.

[0048] In an embodiment, sample 607 is positioned on stage assembly 612 to facilitate movement of sample 607. Stage assembly 612 may include any stage assembly 612 known in the art, including but not limited to XY stages, R-θ stages, and the like. In an embodiment, stage assembly 612 is capable of adjusting the height of sample 607 during inspection or imaging to maintain focus on sample 607.

[0049] In an embodiment, illumination branch 603 is configured to direct broadband light 118 from broadband LSP source 100 to sample 607. Illumination branch 603 may include any number and type of optical components known in the art. In one embodiment, illumination branch 603 includes one or more optical elements 602, beam splitter 604, and objective lens 606. In this respect, illumination branch 603 may be configured to focus broadband light 118 from broadband LSP source 100 onto the surface of sample 607. The one or more optical elements 602 may include any optical element or combination of optical elements known in the art, including, but not limited to, one or more mirrors, one or more lenses, one or more polarizers, one or more gratings, one or more filters, one or more beam splitters, and the like.

[0050] In one embodiment, system 600 includes a collection branch 605 configured to collect light reflected, scattered, diffracted, and / or emitted from sample 607. In another embodiment, collection branch 605 may guide and / or focus light from sample 607 onto sensor 616 of detector assembly 614. It should be noted that sensor 616 and detector assembly 614 may include any sensor and detector assembly known in the art. Sensor 616 may include, but is not limited to, a CCD sensor or a CCD-TDI sensor. Furthermore, sensor 616 may include, but is not limited to, a line sensor or an electron-bombarded line sensor.

[0051] In one embodiment, detector assembly 614 is communicatively coupled to controller 618, which includes one or more processors and memory. For example, one or more processors may be communicatively coupled to memory, wherein one or more processors are configured to execute a set of program instructions stored in memory. In one embodiment, one or more processors are configured to analyze the output of detector assembly 614. In one embodiment, the set of program instructions is configured to cause one or more processors to analyze one or more characteristics of sample 607. In one embodiment, the set of program instructions is configured to cause one or more processors to modify one or more characteristics of system 600 to maintain focus on sample 607 and / or sensor 616. For example, one or more processors may be configured to adjust objective lens 606 or one or more optical elements 602 to focus broadband light 118 from broadband LSP source 100 onto the surface of sample 607. As another example, one or more processors may be configured to adjust objective lens 606 and / or one or more optical elements 610 to collect illumination from the surface of sample 607 and focus the collected illumination onto sensor 616.

[0052] It should be noted that System 600 can be configured with any optical configuration known in the art, including but not limited to dark-field configuration, bright-field orientation, and the like. System 600 can be configured with any type of metrological instrument known in the art, such as but not limited to a spectroradiometer with one or more illumination angles, a spectroradiometer for measuring Mueller matrix elements (e.g., using a rotation compensator), a single-wavelength ellipsometer, an angle-resolved ellipsometer (e.g., a beam profiler), a spectroreflectometer, a single-wavelength reflectometer, an angle-resolved reflectometer (e.g., a beam profiler), an imaging system, a pupil imaging system, a spectroscopic imaging system, or a scatterometer.

[0053] Additional details of various embodiments of the optical characterization system 300 are described in the following: U.S. Patent Publication 7,957,066B2, entitled "Split Field Inspection System Using Small Catadioptric Objectives," published June 7, 2011; U.S. Patent Publication 2007 / 0002465, entitled "Beam Delivery System for Laser Dark-Field Illumination in a Catadioptric Optical System," published January 4, 2007; U.S. Patent Publication 5,999,310, entitled "Ultra-broadband UV Microscope Imaging System with Wide Range Zoom Capability," published December 7, 1999; and U.S. Patent Publication 28, 2009, entitled "Surface Inspection System Using Laser Line Illumination with Two Dimensional..." U.S. Patent 7,525,649 entitled “Dynamically Adjustable Semiconductor Metrology System”, published by Wang et al. on May 9, 2013; U.S. Patent Publication 2013 / 0114085 entitled “Dynamically Adjustable Semiconductor Metrology System”, published by Piwonka-Corle et al. on March 4, 1997; and U.S. Patent 6,297,880 entitled “Apparatus for Analyzing Multi-Layer Thin Film Stacks on Semiconductors”, published by Rosencwaig et al. on October 2, 2001, are all incorporated herein by reference in their entirety.

[0054] Figure 7 The illustration depicts a flowchart of a method 700 for generating broadband light 118 according to one or more embodiments of the present disclosure. It should be noted that the steps of method 700 may be implemented entirely or partially by the broadband LSP light source 100. However, it should be further appreciated that method 700 is not limited to the broadband LSP light source 100, as all or part of the steps of method 700 may be implemented in additional or alternative system-level embodiments.

[0055] In step 702, method 700 includes generating one or more supersonic gas jets to form a local high-pressure region. In step 704, method 700 includes generating a main pump beam and directing the main pump beam into the local high-pressure region formed by the one or more supersonic gas jets. In step 706, method 700 includes generating a pulsed auxiliary beam and directing the pulsed auxiliary beam into the local high-pressure region formed by the one or more supersonic gas jets, wherein the main pump beam and the pulsed auxiliary beam maintain the plasma within the local high-pressure region. In step 708, method 700 includes collecting at least a portion of the broadband light emitted from the plasma.

[0056] Those skilled in the art will recognize that the components, operations, devices, objects, and accompanying discussions described herein are used as examples for conceptual clarity and are open to various configuration modifications. Therefore, as used herein, the specific examples and accompanying discussions are intended to represent their more general categories. In general, the use of any specific example is intended to represent its category, and the omission of specific components (e.g., operations), devices, and objects should not be considered limiting.

[0057] Regarding the use of virtually any plural and / or singular terms in this document, those skilled in the art may convert plural to singular and / or singular to plural as needed by the context and / or application. Various singular / plural arrangements are not explicitly described herein for clarity.

[0058] The topics described herein sometimes illustrate different components contained within or connected to other components. It should be understood that such depicted architectures are merely exemplary, and many other architectures can in fact be implemented to achieve the same functionality. Conceptually, any arrangement of components that achieve the same functionality is effectively “associated” to achieve the desired functionality. Therefore, any two components combined herein to achieve a particular functionality can be considered “associated” with each other to achieve the desired functionality, regardless of the architecture or intermediate components. Similarly, any two such associated components can also be considered “connected” or “coupled” to each other to achieve the desired functionality, and any two elements that can be such associated can also be considered “coupled” to each other to achieve the desired functionality. Specific examples of “coupleable” include, but are not limited to, physically mating and / or physically interacting components and / or wirelessly interacting and / or logically interacting components.

[0059] Furthermore, it should be understood that the invention is defined by the appended claims. Those skilled in the art will understand that, generally, the terms used herein and especially in the appended claims (e.g., the body of the appended claims) are intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “at least having,” the term “includes” should be interpreted as “including but not limited to,” and so on). Those skilled in the art will further understand that if a particular number of the introduced claim statements are intended, then this intention will be explicitly stated in the claims, and if such a statement is not present, then this intention does not exist. For example, to aid understanding, the following appended claims may contain the use of the introductory phrases “at least one” and “one or more” to introduce claim statements. However, the use of such phrases should not be construed as implying that the introduction of a claim statement by the indefinite article “a(a)” or “an” limits any particular claim containing such an introduction to an invention containing only one such statement, even if the same claim contains the introductory phrase “one or more” or “at least one” and indefinite articles such as “a(a)” or “an” (e.g., “a(a)” and / or “an” should generally be interpreted as “at least one” or “one or more”); the same applies to the use of definite articles used to introduce a claim statement. Furthermore, even if a specific number of introduced claim statements are explicitly stated, those skilled in the art will recognize that such a statement should generally be interpreted as indicating at least the number stated (e.g., a bare statement of “two statements” without other modifiers generally indicates at least two statements or two or more statements). Furthermore, in examples where conventions similar to "at least one of A, B, and C, and similar ones" are used, this construction generally implies that a person skilled in the art would understand the meaning of the convention (e.g., "a system having at least one of A, B, and C" would include, but is not limited to, systems having only A, only B, only C, both A and B, both A and C, both B and C, and / or both A, B, and C, and similar ones). In examples where conventions similar to "at least one of A, B, or C, and similar ones" are used, this construction generally implies that a person skilled in the art would understand the meaning of the convention (e.g., "a system having at least one of A, B, or C" would include, but is not limited to, systems having only A, only B, only C, both A and B, both A and C, both B and C, and / or both A, B, and C, and similar ones). Those skilled in the art will further understand that virtually any extractive word and / or phrase presenting two or more alternatives, whether in the detailed description, claims, or description of the drawings, should be understood to imply the possibility of including one, any, or both of the items.For example, the phrase “A or B” would be understood as containing the possibility of “A” or “B” or “A and B”.

[0060] It is believed that this disclosure and its many accompanying advantages will be understood from the foregoing description, and it will be apparent that various changes can be made to the form, construction, and arrangement of the components without departing from the disclosed subject matter or sacrificing all its significant advantages. The described forms are merely illustrative, and the following claims are intended to cover and encompass such changes. Furthermore, it should be understood that the invention is defined by the appended claims.

Claims

1. A broadband light source, comprising: Gas confinement structure; Multiple jet nozzles, wherein the multiple jet nozzles are configured to generate multiple supersonic gas jets and guide the multiple supersonic gas jets to collide within the gas containment structure to form a local high-pressure region at the collision point of the multiple supersonic gas jets. A main laser pump source, wherein the main laser pump source is configured to guide the main pump beam to a local high-pressure region formed at the collision point of the plurality of supersonic gas jets; A pulsed-assisted laser source, wherein the pulsed-assisted laser source is configured to guide a pulsed-assisted laser beam to the local high-pressure region at the collision point of the plurality of supersonic gas jets. The main pump beam and the pulsed auxiliary laser beam are configured to maintain plasma within the local high-pressure region; and A light collector element configured to collect at least a portion of broadband light emitted from the plasma.

2. The broadband light source according to claim 1, wherein one or more of the plurality of jet nozzles comprises: At least one of a divergent nozzle, a cylindrical nozzle, or a converging nozzle.

3. The broadband light source according to claim 1, wherein a shock wave is generated at the collision point of the plurality of supersonic gas jets.

4. The broadband light source according to claim 3, wherein the shock wave comprises a diamond shock wave.

5. The broadband light source according to claim 1, wherein the local high-pressure region has a pressure greater than the pressure of the environmental pressure region within the gas containment structure.

6. The broadband light source according to claim 1, wherein the light collector element comprises an elliptical reflector.

7. The broadband light source according to claim 6, wherein the pulse-assisted laser beam is guided through an aperture within the wall of the elliptical reflector to the collision point of the plurality of supersonic gas jets.

8. The broadband light source according to claim 1, wherein the main laser pump source comprises a continuous wave (CW) laser source.

9. The broadband light source according to claim 1, wherein the pulse-assisted laser source comprises a pulsed laser.

10. The broadband light source according to claim 1, wherein one or more of the plurality of supersonic gas jets comprises one or more gas jets of inert gases.

11. The broadband light source according to claim 10, wherein the one or more inert gases include at least one of xenon, argon, neon or helium.

12. The broadband light source of claim 1, wherein one or more of the plurality of supersonic gas jets comprises a gas jet containing a mixture of two or more gases.

13. The broadband light source of claim 1, further comprising a main pump focusing optics configured to focus the main pump beam into the local high-pressure region.

14. The broadband light source of claim 1, further comprising a pulse-assisted laser focusing optics configured to focus the pulse-assisted laser beam into the local high-pressure region.

15. The broadband light source according to claim 1, further comprising: A recirculation loop configured to circulate gas through the gas containment structure, wherein the recirculation loop supplies gas to the plurality of jet nozzles.

16. The broadband light source of claim 15, wherein the recirculation loop comprises one or more air pumps, one or more heat exchangers, or one or more filters.

17. A broadband light source, comprising: Gas confinement structure; One or more jet nozzles, wherein the one or more jet nozzles are configured to generate one or more supersonic gas jets; A main laser pumping source, wherein the main laser pumping source is configured to guide the main pumping beam to a local high-pressure region formed by the supersonic gas expansion of the one or more supersonic gas jets; A pulsed-assisted laser source, wherein the pulsed-assisted laser source is configured to guide a pulsed-assisted beam to the localized high-pressure region formed by the expansion of supersonic gas from the one or more supersonic gas jets. The main pump bundle and the pulsed auxiliary bundle are configured to maintain plasma within the local high-pressure region; and A light collector element configured to collect at least a portion of broadband light emitted from the plasma.

18. The broadband light source according to claim 17, wherein the local high-pressure region is formed at the Mach disk of the supersonic gas expansion.

19. A system comprising: Broadband light sources, including: Gas confinement structure; Multiple jet nozzles, wherein the multiple jet nozzles are configured to generate multiple supersonic gas jets and guide the multiple supersonic gas jets to collide within the gas containment structure to form a local high-pressure region at the collision point of the multiple supersonic gas jets. A main laser pump source, wherein the main laser pump source is configured to guide the main pump beam to a local high-pressure region formed at the collision point of the plurality of supersonic gas jets; A pulsed-assisted laser source, wherein the pulsed-assisted laser source is configured to guide a pulsed-assisted beam to the local high-pressure region at the collision point of the plurality of supersonic gas jets. The main pump beam and the pulsed auxiliary beam are configured to maintain plasma within the local high-pressure region; and A light collector element configured to collect at least a portion of broadband light emitted from the plasma; A set of illuminator optics configured to direct the broadband light from the light collector element to one or more samples; Detector assembly; and A set of projection optics configured to receive illumination from the surface of one or more samples and to direct the illumination from the one or more samples to the detector assembly.

20. A system comprising: Broadband light sources, including: Gas confinement structure; One or more jet nozzles, wherein the one or more jet nozzles are configured to generate one or more supersonic gas jets; A main laser pumping source, wherein the main laser pumping source is configured to guide the main pumping beam to a local high-pressure region formed by the supersonic gas expansion of the one or more supersonic gas jets; A pulsed-assisted laser source, wherein the pulsed-assisted laser source is configured to guide a pulsed-assisted beam to the localized high-pressure region formed by the expansion of supersonic gas from the one or more supersonic gas jets. The main pump beam and the pulsed auxiliary beam are configured to maintain plasma within the local high-pressure region; and A light collector element configured to collect at least a portion of broadband light emitted from the plasma; A set of illuminator optics configured to direct the broadband light from the light collector element to one or more samples; Detector assembly; and A set of projection optics configured to receive illumination from the surface of one or more samples and to direct the illumination from the one or more samples to the detector assembly.

21. A method comprising: One or more supersonic gas jets are generated to create local high-pressure areas; Generate a main pump bundle and direct the main pump bundle into the local high-pressure region formed by the one or more supersonic gas jets; A pulsed auxiliary beam is generated and directed into the local high-pressure region formed by the one or more supersonic gas jets, wherein the main pump beam and the pulsed auxiliary beam maintain plasma in the local high-pressure region; and At least a portion of the broadband light emitted from the plasma is collected.

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