Pulse-assisted laser-sustained plasma in flowing high-pressure liquids

Abstract

A pulse-assisted LSP broadband light source within a flowing high-pressure liquid or supercritical fluid is disclosed. The light source includes a fluid confinement structure for confining the high-pressure liquid or supercritical fluid. The light source includes a primary laser pumping source and a high-repetition-rate pulse-assisted laser source, where the primary laser pumping source is configured to direct a primary pump beam into a plasma formation region of the fluid. The primary beam and the pulse-assisted beam are configured to sustain a plasma within the plasma formation region of the fluid within the fluid confinement structure. A light collecting element is configured to collect broadband light emitted from the plasma for use in downstream applications.

Description

[Technical Field]

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 410,636, filed September 28, 2022, which is hereby incorporated by reference in its entirety.

[0002] The present invention relates generally to plasma-based radiation sources, and more particularly to laser-sustained plasma (LSP) broadband light sources, including pulse-assisted plasmas formed in flowing high-pressure liquids or supercritical fluids. [Background technology]

[0003] With the continued increase in demand for integrated circuits with ever-smaller device features, the need for improved illumination sources for use in inspecting these ever-smaller devices also continues to grow. One such illumination source is the laser-sustained plasma (LSP) light source. LSP light sources are capable of producing high-power, broadband light. Typically, LSP light sources operate by focusing laser radiation into a volume of gas, such as argon or xenon, to excite the gas into a plasma state capable of emitting light. This effect is typically referred to as "pumping" the plasma. LSPs used in broadband plasma (BBP) light sources have limited brightness. Several methods have been suggested to increase such brightness. More specifically, fast-moving gas or liquid streams contained within cells or liquid jets have been proposed to increase brightness. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2019 / 0033204 [Patent Document 2] U.S. Patent Application Publication No. 2021 / 0120659 [Patent Document 3] U.S. Patent Application Publication No. 2016 / 0268120 Summary of the Invention [Problem to be solved by the invention]

[0005] These solutions suffer from the drawback that the plasma can be quenched by high velocity liquid and / or gas flows at relatively low flow velocities, such as above about 10 m / s. It would therefore be desirable to provide a system and method that remedies one or more of the deficiencies in the previous solutions noted above. [Means for solving the problem]

[0006] According to one or more embodiments of the present disclosure, a laser-sustained plasma (LSP) broadband light source is disclosed. In an exemplary embodiment, the LSP broadband light source includes a fluid confinement structure for confining a fluid. In an exemplary embodiment, the LSP broadband light source includes a primary laser pumping source configured to direct a primary pumping beam toward a plasma formation region of the fluid. In an exemplary embodiment, the LSP broadband light source includes a pulse-assisted laser source configured to direct a pulse-assisted beam toward the plasma formation region of the fluid, the primary beam and the pulse-assisted beam being configured to sustain a plasma within the plasma formation region of the fluid within the fluid confinement structure. In an exemplary embodiment, the LSP broadband light source includes a light collecting element configured to collect at least a portion of the broadband light emitted from the plasma. In an exemplary embodiment, the LSP broadband light source may be implemented within an optical system, such as, but not limited to, an inspection system, a metrology system, or a lithography system.

[0007] According to one or more additional and / or alternative embodiments of the present disclosure, an LSP broadband light source is disclosed. In an exemplary embodiment, the LSP broadband light source includes a fluid confinement structure. In an exemplary embodiment, the LSP broadband light source includes a plurality of jet nozzles configured to direct a plurality of fluid jets to impinge within the fluid confinement structure, the plurality of fluid jets including a first fluid jet and at least one second fluid jet. In an exemplary embodiment, the LSP broadband light source includes a primary laser pumping source configured to direct a primary pumping beam toward the impingement point of the plurality of fluid jets. In an exemplary embodiment, the LSP broadband light source includes a pulse-assisted laser source configured to direct a pulse-assisted beam toward the impingement point of the plurality of fluid jets, the primary beam and the pulse-assisted beam configured to sustain a plasma within a plasma formation region of the fluid confinement structure at the impingement point of the plurality of fluid jets. In an exemplary embodiment, the LSP broadband light source includes a light collecting element configured to collect at least a portion of the broadband light emitted from the plasma. In an exemplary embodiment, the LSP broadband light source may be implemented in an optical system, such as, but not limited to, an inspection system, a metrology system, or a lithography system.

[0008] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the present disclosure. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate the subject matter of the present disclosure. The description and drawings together serve to explain the principles of the present disclosure. [Brief explanation of the drawings]

[0009] Many advantages of the present disclosure may be better understood by those skilled in the art by reference to the following drawings.

[0010] [Figure 1A] FIG. 1 is a conceptual diagram illustrating a pulse-assisted LSP broadband light source within a flowing fluid in accordance with one or more embodiments of the present disclosure. [Figure 1B]FIG. 1 is a conceptual diagram illustrating a pulse-assisted LSP broadband light source within a flowing fluid in accordance with one or more embodiments of the present disclosure. [Figure 1C] FIG. 10 illustrates the laser intensity of a pulse-assisted laser output and the corresponding broadband emission of the generated plasma where overlap occurs between pulses of the broadband emission, in accordance with one or more embodiments of the present disclosure. [Figure 1D] FIG. 10 illustrates the laser intensity of a pulse-assisted laser output and the corresponding broadband emission of the generated plasma with no overlap between pulses of the broadband emission, in accordance with one or more embodiments of the present disclosure. [Figure 1E] FIG. 1 is a simplified schematic diagram illustrating a pulse-assisted LSP broadband source in which the optical path of the pump beam does not overlap with the optical path of the pulse-assisted beam, in accordance with one or more embodiments of the present disclosure. [Figure 1F] FIG. 1 is a simplified schematic diagram illustrating a pulse-assisted LSP broadband source in which the optical path of the pump beam overlaps with the optical path of the pulse-assisted beam through the use of a dichroic mirror, in accordance with one or more embodiments of the present disclosure. [Figure 1G] FIG. 1 is a simplified schematic diagram illustrating a pulse-assisted LSP broadband source in which a pulse-assisted beam is injected into a laser fiber of a primary pump source, in accordance with one or more embodiments of the present disclosure. [Figure 2A] FIG. 1 is a conceptual diagram illustrating an LSP broadband light source having a liquid jet for supplying plasma generating material, in accordance with one or more embodiments of the present disclosure. [Figure 2B] FIG. 1 is a conceptual diagram illustrating an LSP broadband light source having two colliding liquid jets for supplying plasma generating material, in accordance with one or more embodiments of the present disclosure. [Figure 3] FIG. 1 is a simplified schematic diagram illustrating an optical characterization system implementing a pulse-assisted LSP broadband light source in accordance with one or more embodiments of the present disclosure. [Figure 4] FIG. 1 is a flow diagram illustrating a method for generating broadband light in a flowing fluid with a primary pump beam and a pulsed-assist pump beam in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] Reference will now be made in detail to the subject matter disclosed herein, which is illustrated in the accompanying drawings. The present disclosure has been particularly shown and described with reference to certain embodiments and certain features thereof. The embodiments described herein are to be construed as illustrative and not limiting. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail can be made therein without departing from the spirit and scope of the present disclosure.

[0012] 1A-3, a broadband light source including a pulse-assisted laser-sustained plasma in a flowing high-pressure liquid is illustrated in accordance with one or more embodiments of the present disclosure.

[0013] Embodiments of the present disclosure relate to the operation of an LSP broadband source by augmenting pump laser power with a high-repetition-rate pulse-assisted laser beam to sustain LSPs within a flowing high-pressure liquid or supercritical fluid. More specifically, embodiments of the present disclosure can sustain a plasma within a flowing high-pressure liquid or supercritical fluid by using a laser source with sufficient intensity to form a self-sustaining liquid breakdown. The high laser intensity required for self-disruption is achieved by adding a second, high-repetition-rate, short-pulse-assisted laser. This allows the plasma to be sustained by a high-power primary pump laser, such as a continuous-wave (CW) laser. The liquid is maintained at high pressure within a fluid confinement structure (e.g., a cell, valve, or chamber), which also directs the fluid flow in the plasma region.

[0014] 1A and 1B illustrate a pulse-assisted broadband LSP light source 100 in accordance with one or more embodiments of the present disclosure. In an embodiment, pulse-assisted broadband LSP light source 100 includes a fluid confinement structure 107 for confining a fluid 109 (e.g., a high-pressure liquid or a supercritical fluid), a primary laser pumping source 102, a pulse-assisted laser source 104, and a light collecting element 110. In additional and / or alternative embodiments, broadband LSP light source 110 includes a recirculation loop 112.

[0015] As shown in FIG. 1B , in an embodiment, a fluid confinement structure 107 confines the fluid 109. For example, the fluid confinement structure 107 may be a transparent fluid confinement structure 107 configured to confine the fluid 109. The fluid confinement structure 107 may include a transparent cell, a transparent valve, or a chamber with one or more transparent windows. In an embodiment, the fluid confinement structure 107 may have a concave contour that constricts the fluid passing through a plasma formation region of the fluid confinement structure 107, increasing the velocity and pressure of the fluid. The fluid 109 may include, but is not limited to, a high-pressure gas or a supercritical fluid. In an embodiment, a recirculation loop 112 may flow the fluid 109 through the fluid confinement structure 107. In an embodiment, the recirculation loop 112 includes a recirculation pump 114 that recirculates the fluid through the recirculation loop 112. In this regard, the recirculation loop 112 may supply a cold fluid 113 to an input side of the fluid confinement structure 107 and remove a hot fluid 115 from an output side of the fluid confinement structure 107 .

[0016] In an embodiment, a primary laser pumping source 102 directs a primary pumping beam 103 toward a plasma formation region of the fluid 109, and an assist laser source 104 directs a pulsed assist beam 105 toward the plasma formation region of the fluid 109. In an embodiment, the primary beam 103 and the pulsed assist beam 105 maintain a plasma 106 within the plasma formation region of the fluid 109 within the fluid confinement structure 107. In an embodiment, the primary beam 103 and the pulsed assist beam 105 may provide instantaneous pumping power above the liquid-gas breakdown threshold of the fluid 109 and sufficient to form a gas cavity 111 within the fluid 109 in the fluid confinement structure 107 and maintain the plasma 106 within the gas cavity 111. Note that the recirculation pump 114 may move the fluid 109 (e.g., a high-pressure liquid or supercritical fluid) through the fluid confinement structure 107 at a flow rate sufficient to quench the CW-pumped plasma (without the assist pulsed laser 104).

[0017] The primary laser pumping source 102 may include any laser pumping source known in the art. In an embodiment, the primary laser pumping source 102 may include one or more continuous wave (CW) lasers. For example, the primary laser pumping source 102 may include, 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 CO lasers. The primary laser pumping source 102 may operate at high power, i.e., greater than 5 kW (e.g., greater than 10 kW).

[0018] The pulse-assisted laser source 104 may include any pulsed laser source known in the art. In embodiments, the pulse-assisted laser source 104 may include one or more picosecond or femtosecond pulsed laser sources. The pulse-assisted laser source 104 may include, but is not limited to, one or more pulsed fiber-based NIR lasers, one or more pulsed coherently combined fiber lasers, and / or one or more pulsed thin-disk lasers. The 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 one or more pulsed lasers may operate at a power greater than about 25 W (e.g., greater than 50 W), which increases the instantaneous power near the focal point to a value greater than the liquid-gas breakdown threshold of the plasma 106.

[0019] In an embodiment, the light source 100 includes one or more focusing optics for focusing / directing the primary pump beam 103 into the plasma 106. The light source 100 may also include one or more focusing optics for focusing / directing the pulsed assist beam 105 into the plasma 106. The one or more focusing optics may include any optical element known in the art for directing and / or focusing laser light, including, but not limited to, lenses, mirrors, prisms, polarizers, gratings, filters, or beam splitters. In additional and / or alternative embodiments, one or more focusing optics of the primary pump beam 103 and / or the pulsed assist beam 105 may be compensated. For example, one or more focusing optics (e.g., 214 or 216 in FIGS. 1E-1G ) may be compensated to correct for aberrations caused by an optically transmissive portion of the fluid confinement structure 107 (e.g., a cell, valve, or chamber window).

[0020] By way of non-limiting example, during operation, the instantaneous pumping power of the light source 100 may be maintained above the liquid-gas breakdown threshold of the fluid by increasing the primary pump laser power to about 100 kW with a focal spot of about 100 μm, or by adding a pulse-assisted laser source 104 with a sufficiently high instantaneous intensity to ensure liquid-gas breakdown. Typical instantaneous intensities required to achieve liquid-gas breakdown are about 10 11 From 10 13 W / cm 2In an embodiment, the repetition rate of the pulse-assisted laser source 104 may be sufficiently high so that the plasma does not completely quench between pulses. In an embodiment, the plasma quench time may be approximately 1 microsecond. In this example, the repetition rate may be selected to be greater than approximately 1 MHz. The pulse width of the pulse-assisted laser 104 may be selected from approximately 1 to 10 picoseconds for low repetition rates, but may be selected in the range of 100 femtoseconds for repetition rates of approximately 1 GHz. Such a configuration provides the required breakdown threshold power even at relatively modest pulse-assisted laser energies of approximately 50 to 100 W average power at a focal spot of approximately 100 μm. The resulting plasma 106 absorbs power from a primary pump laser, which provides the primary power source for the plasma 106. When the output of the primary pump laser 102 is greater than 10 W at the focal spot, the plasma 106 is quenched. 11 From 10 13 W / cm 2 If the plasma 106 is insufficient to achieve a breakdown strength of 100 m / s, it is quenched by a cold liquid / gas flow supplied to the fluid confinement structure 107. By using the pulse-assisted laser 104, the plasma discharge is maintained regardless of the fluid flow rate. In an embodiment, the pressure inside the fluid is maintained above about 100 bar (10 MPa) to ensure high brightness. This is achieved by pressurizing the fluid 109 within the fluid confinement structure 107. In an embodiment, the flow rate through the fluid confinement structure 107 may be about 10 m / s.

[0021] It should be noted that the various parameters of light source 100 described in the non-limiting examples should not be construed as limitations on the scope of the present disclosure. Instead, it should be understood that these examples are provided for illustrative purposes only, and that various laser powers, frequencies, pulse durations, fluid pressures, and fluid velocities may be used depending on the details of operation of light source 100.

[0022] Fluid 109 confined and circulated within fluid confinement structure 107 may include a liquid or a supercritical fluid. For example, fluid 109 may include, but is not limited to, water, ammonia, an organic solvent, etc. Fluid 109 may also include one or more cryogenic liquids, including, but not limited to, liquid Ne, liquid Ar, liquid Kr, liquid Xe, liquid N2, liquid O2, etc. In embodiments, fluid 109 may include a mixture of two or more fluids. For example, fluid 109 may include a mixture of two or more liquids or supercritical fluids mentioned herein.

[0023] In embodiments, the fluid 109 may be maintained at pressure and temperature conditions above the critical conditions such that the fluid 109 becomes a supercritical fluid. For example, the fluid 109 may include Ar at a temperature above about 151 K and / or a pressure above 49 bar (4.9 MPa). As another example, the fluid 109 may include Kr at a temperature above about 209 K and / or a pressure above 55 bar (5.5 MPa). Similarly, mixtures of gases above the critical conditions may be used. In the case of a liquid, a liquid-gas interface is formed between the plasma and the cold liquid. This interface may cause additional reflection losses and may also cause refraction of the pump laser light. The shape of the interface is influenced by processes occurring downstream of the plasma, such as, but not limited to, cavitation-collapse of gas bubbles. If the liquid is maintained at supercritical conditions, such an interface is not formed.

[0024] In embodiments, the fluid 109 may be maintained near its critical point. For example, the fluid 109 may be maintained under conditions such that the fluid 109 is a liquid upstream of the plasma 106, but becomes a supercritical fluid (liquid-gas) downstream of the plasma 106 where the heat released from the plasma region causes the fluid 109 to be at a higher temperature.

[0025] In an embodiment, light collecting element 110 is configured to collect broadband light 108 emitted from plasma 106. Light collecting element 110 may include any one or more optical elements known in the art configured to collect and / or focus broadband light 108, 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, etc. It should be appreciated that light collecting element 110 may be configured to collect and / or focus broadband light 108 generated by plasma 106 for use in one or more downstream processes, including, but not limited to, imaging processes, inspection processes, metrology processes, lithography processes, etc.

[0026] FIG. 1C is a diagram showing laser intensity 150 and plasma emission 160 as a function of time, illustrating plasma dynamics when a pulse-assisted laser source 104 assists a CW laser source by modulating the plasma emission, according to one or more embodiments of the present disclosure. In this embodiment, the primary CW pumping laser is below the liquid-gas breakdown threshold at the focal point. The intensity of the pumping-assisted laser source is above the liquid-gas breakdown threshold. In this embodiment, the plasma emission response is partially modulated between laser pulses of the pulse-assisted laser source, while the continuous absorption of power from the CW pumping laser provides a steady broadband output.

[0027] FIG. 1D is a diagram showing laser intensity 150 and plasma emission 170 as a function of time, illustrating plasma dynamics when a pulse-assisted laser source 104 assists a CW laser source without overlap between plasma emission pulses, according to one or more embodiments of the present disclosure. In this embodiment, the primary CW pumping laser is below the liquid-gas breakdown threshold at the focal point. The intensity of the pumping-assisted laser source is above the liquid-gas breakdown threshold. In this embodiment, the plasma emission is not continuous, and the plasma emission pulses do not overlap or are close to overlapping.

[0028] FIG. 1E is a simplified schematic diagram illustrating a broadband LSP light source 100 according to one or more embodiments of the present disclosure. Note that various embodiments described with respect to FIGS. 1A through 1D should be construed as extending to the embodiment of FIG. 1D as well. In this embodiment, the light collecting element 110 is a curved mirror 110. For example, the light collecting element 110 may include, but is not limited to, an elliptical mirror, a spherical mirror, or a parabolic mirror. In the embodiment, the primary pump beam 103 and the pump assist beam 105 do not share an optical path before entering the light collecting element 110. For example, the primary pump beam source 102 directs the pump beam 103 through a pumping module including one or more laser shaping optics 118. This causes the pump beam 103 to pass through a dichroic mirror 122 (e.g., a cold mirror) and be directed toward the fluid 109 within the fluid confinement structure 107. The pulsed assist source 104 may also be configured to direct the pulsed assist beam 105 through one or more side ports formed through a sidewall of the light collecting element 110 and toward the fluid 109 confined within the fluid confinement structure 107. As described above, the pump beam 103 and the pulsed assist beam 105 operate to sustain the plasma 106. The broadband light 108 emitted by the plasma 106 may then be collected by the light collecting element 110 and directed by a dichroic mirror 122 to one or more downstream optical elements. For example, the dichroic mirror 122 may direct the broadband illumination 108 to a homogenizer 124.

[0029] FIG. 1F is a simplified schematic diagram illustrating a broadband LSP light source 100 in accordance with one or more embodiments of the present disclosure. Note that various embodiments described with respect to FIGS. 1A through 1E should be construed as extending to the embodiment of FIG. 1F . In this embodiment, a primary pump beam 103 and a pump assist beam 105 share an optical path before entering a light collecting element 110 (e.g., an elliptical mirror, a spherical mirror, a parabolic mirror). For example, a primary pump source 102 directs the pump beam 103 through a pump module including one or more laser-shaping optics 118. This causes the primary pump beam 103 to pass through a dichroic mirror 122 (e.g., a cold mirror) and be directed toward a fluid 109 within a fluid confinement structure 107. Additionally, a pulse assist source 104 may be configured to direct the pulse assist beam 105 toward a first dichroic mirror 116. The first dichroic mirror 116 is configured to reflect the pulsed assist beam 105 towards the light collecting element 110 while transmitting the primary pump beam 103 to the light collecting element 110. After the first dichroic mirror 116, the primary pump beam 103 and the pulsed assist beam 105 share an optical path to the light collecting element 110. The primary pump beam 103 and the pulsed assist beam 105 may then pass through a second dichroic mirror 122 and be reflected by the light collecting element 110 towards the fluid confined within the fluid confinement structure 107. As described above, the pump beam 103 and the pulsed assist beam 105 operate to sustain the plasma 106. Broadband light 108 emitted by the plasma 106 may then be collected by the light collecting element 110 and directed by the dichroic mirror 122 to one or more downstream optical elements (e.g., a homogenizer 124).

[0030] FIG. 1G is a simplified schematic diagram illustrating a broadband LSP light source 100 in accordance with one or more embodiments of the present disclosure. It should be noted that the various embodiments described with respect to FIGS. 1A through 1F should also be interpreted as extending to the embodiment of FIG. 1G. In this embodiment, a pump assist beam 105 is injected into one or more laser fibers of a primary pump source 102 for a primary pump beam 103. As a result, the primary pump beam 103 and the pump assist beam 105 share an optical path as the beams 103 and 105 exit the beam-shaping optics 118. Upon exiting the beam-shaping optics 118, the primary pump beam 103 and the pulse assist beam 105 pass through a dichroic mirror 122 (e.g., a cold mirror) and are directed toward a light collecting element 110. The light collecting element 110 then directs the primary pump beam 103 and the pulse assist beam 105, which share an optical path, toward a fluid 109 within a fluid confinement structure 107. As described above, pump beam 103 and pulse-assisted laser 105 operate to sustain plasma 106. Broadband light 108 emitted by plasma 106 may then be collected by light collecting element 110 and directed by dichroic mirror 122 to one or more downstream optical elements (e.g., homogenizer 124).

[0031] While much of this disclosure has been described focusing on the operation of broadband light source 100 with high-pressure gas or supercritical fluid flowing through a transparent plasma cell or build, such configurations are not intended to limit the scope of this disclosure. It should be recognized that the use of pulse assist source 104 and the corresponding high-repetition pulse assist beam 105 can be implemented in the context of any high-pressure liquid or supercritical fluid.

[0032] 2A illustrates a broadband LSP light source 100 according to one or more additional and / or alternative embodiments. In this embodiment, one or more liquid jets are used to create a region of localized high pressure within a target liquid. In an embodiment, the light source 100 includes a target material source 202, a primary pumping source 102, a primary pumping focusing optic 214, a pulse-assisted laser source 104, a pulse-assisted focusing optic 216, and a set of collecting optics 110. In an embodiment, the LSP source 100 includes a debris collector 204.

[0033] In embodiments, a target material source 202 delivers one or more target materials into the chamber 201. For example, the target material source 202 may supply one or more target materials 206 into the chamber 201 in the form of a liquid jet, liquid droplets, cryojet, frozen droplets, or a combination of these target material forms. In embodiments, flow delivery parameters of the target material 206 from the target material source 202 are adjusted so that either all of the material delivered from the target material source 202 is vaporized in the plasma region or some of the material passes through the plasma and is collected by the debris collector 204. In embodiments, the debris collector 204 is located on the opposite side of the chamber from the target material source 202. The target material source 202 may deliver any type of target material known in the art for LSP broadband sources. For example, the target material may include, but is not limited to, liquid, supercritical, or solid Ar, Xe, Ne, He, Kr, N, O, HO, ammonia, organic solvents, etc. The target material may also include a mixture of two or more of the materials listed above.

[0034] In an embodiment, the pump laser focusing optics 214 focus the pump beam 103 into the chamber 201 through the pump laser window 210. In an embodiment, the pump laser focusing optics 214 focus the pump beam 103 onto one or more target materials 206, thereby generating and / or sustaining the plasma 106. Similarly, the pulse-assisted optics 216 focus the pulse-assisted beam 105 into the chamber 201 through the pulse-assisted laser window 212. In an embodiment, the pulse-assisted laser focusing optics 216 focus the pulse-assisted beam 105 onto the one or more target materials 206. In this regard, the pump beam and the pulse-assisted beam generate and / or sustain the plasma 106 in the manner described above, generating the broadband light 108. The broadband light 108 may be collected by the collection optics 110 and directed to one or more downstream applications 220 through one or more apertures 218. It should be noted that the pumping laser focusing optics 214 and the pulse-assisted laser optics 216 may include any optical element known in the art for directing and / or focusing radiation, including, but not limited to, lenses, mirrors, prisms, polarizers, gratings, filters, or beam splitters.

[0035] A general structure for implementing a broadband light source having one or more liquid jets and creating a localized region of high pressure is described in U.S. Patent No. 10,806,016, filed July 16, 2018, the entire contents of which are incorporated herein by reference.

[0036] FIG. 2B illustrates a broadband LSP light source 100 according to one or more additional and / or alternative embodiments. In this embodiment, two or more liquid jets are used to create a stable gas region of high density and low velocity at the point of impact of the jets. At the point of impact, a primary pumping beam 103 and a pulse-assisted beam 105 may be focused at this point to generate a plasma 106. The colliding jets create a stable gas region of high density and low velocity at their point of impact. The velocity at the point of impact approaches zero. Having a region of near-zero velocity helps ensure plasma sustainability at low pumping powers. In an embodiment, the light source 100 includes a pair of jet nozzles 202 a and 202 b, a primary pumping source 102, a primary pumping focusing optic 214, a pulse-assisted laser source 104, a pulse-assisted focusing optic 216, and a light collecting element 110. The set of injection nozzles may include a first injection nozzle 202 a and a second injection nozzle 202 b for delivering target material jets 206 a and 206 b, respectively, for collision within the gas confinement structure 206 (e.g., a chamber, lamp, or cell). In an embodiment, the pump laser focusing optics 214 focuses the pump beam 103 at the collision point between the first liquid jet 206 a and the second liquid jet 206 b, and the pulse-assisted laser focusing optics 216 focuses the pulse-assisted beam 105 at the collision point between the first liquid jet 206 a and the second liquid jet 206 b, thereby generating and / or sustaining the plasma 106. In this regard, the pump beam and the pulse-assisted beam generate and / or sustain the plasma 106 and generate the broadband light 108 in the manner described above. The materials in streams 206a and 206b may include, but are not limited to, liquid, supercritical, or solid Ar, Xe, Ne, He, Kr, N2, O2, HO, ammonia, organic solvents, etc. The materials may also include mixtures of two or more of the above listed materials. The broadband light 108 may be collected by collection optics 110 and directed through one or more apertures 218 to one or more downstream applications 220.It should be noted that the pumping laser focusing optics 214 and the pulse-assisted laser optics 216 may include any optical element known in the art for directing and / or focusing radiation, including, but not limited to, lenses, mirrors, prisms, polarizers, gratings, filters, or beam splitters.

[0037] A general structure implementing a broadband light source having two or more colliding liquid jets to create a localized region of high pressure and low velocity is described in U.S. Patent Application No. 18 / 132,162, filed April 7, 2023, the entire contents of which are incorporated herein by reference.

[0038] The generation of laser-sustained plasma is also generally described in U.S. Patent No. 7,435,982, issued October 14, 2008, which is incorporated herein by reference in its entirety. The generation of plasma is also generally described in U.S. Patent No. 7,786,455, issued August 31, 2010, which is incorporated herein by reference in its entirety. The generation of plasma is also generally described in U.S. Patent No. 7,989,786, issued August 2, 2011, which is incorporated herein by reference in its entirety. The generation of plasma is also generally described in U.S. Patent No. 8,182,127, issued May 22, 2012, which is incorporated herein by reference in its entirety. The generation of plasma is also generally described in U.S. Patent No. 8,309,943, issued November 13, 2012, which is incorporated herein by reference in its entirety. Plasma generation is also generally described in U.S. Patent No. 8,525,138, issued February 9, 2013, which is incorporated herein by reference in its entirety. Plasma generation is also generally described in U.S. Patent No. 8,921,814, issued December 30, 2014, which is incorporated herein by reference in its entirety. Plasma generation is also generally described in U.S. Patent No. 9,318,311, issued April 19, 2016, which is incorporated herein by reference in its entirety. Plasma generation is also generally described in U.S. Patent No. 9,390,902, issued July 12, 2016, which is incorporated herein by reference in its entirety. In a general sense, the various embodiments of the present disclosure should be construed as extending to any plasma-based light source known in the art.

[0039] 3 is a simplified schematic diagram illustrating an optical characterization system 300 implementing the LSP broadband light source 100, in accordance with one or more embodiments of the present disclosure. In one embodiment, the system 300 includes the LSP light source 100, an illumination arm 303, a collection arm 305, a detector assembly 314, and a controller 318 including one or more processors 320 and a memory 322.

[0040] It should be noted that system 300 may include any imaging, inspection, metrology, lithography, or other characterization system known in the art. In this regard, system 300 may be configured to perform inspection, optical metrology, lithography, and / or any form of imaging on sample 307. Sample 307 may include any sample known in the art, such as, but not limited to, a wafer, a reticle, an optical mask, etc. It should be noted that system 300 may incorporate one or more of the various embodiments of LSP light source 100 described throughout this disclosure.

[0041] In one embodiment, the sample 307 is placed on a stage assembly 312, which facilitates movement of the sample 307. The stage assembly 312 may include any stage assembly 312 known in the art, such as, but not limited to, an XY stage, an R-θ stage, etc. In other embodiments, the stage assembly 312 may adjust the height of the sample 307 during inspection or imaging to maintain focus on the sample 307.

[0042] In one embodiment, illumination arm 303 is configured to direct broadband light 118 from broadband LSP light source 100 toward sample 307. Illumination arm 303 may include any number and type of optical components known in the art. In one embodiment, illumination arm 303 includes one or more optical elements 302, a beam splitter 304, and an objective lens 306. In this regard, illumination arm 303 may be configured to focus broadband light 118 from broadband LSP light source 100 onto the surface of sample 307. One or more optical elements 302 may include any optical element or combination of optical elements known in the art, such as, 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. It should be noted that collection location 128 may include, but is not limited to, one or more of optical elements 302, beam splitter 304, or objective lens 306.

[0043] In one embodiment, system 300 includes a collection arm 305 configured to collect light reflected, scattered, diffracted, and / or emitted from sample 307. In other embodiments, collection arm 305 may direct and / or focus light from sample 307 to sensor 316 of detector assembly 314. Note that sensor 316 and detector assembly 314 may include any sensor and detector assembly known in the art. Sensor 316 may include, but is not limited to, a CCD sensor or a CCD-TDI sensor. Additionally, sensor 316 may include, but is not limited to, a line sensor or an electron impact line sensor.

[0044] In one embodiment, the detector assembly 314 may be communicatively coupled to a controller 318 that includes one or more processors 320 and a memory 322. For example, the one or more processors 320 may be communicatively coupled to the memory 322, where the one or more processors 320 are configured to execute a set of program instructions stored in the memory 322. In one embodiment, the one or more processors 320 are configured to analyze the output of the detector assembly 314. In one embodiment, the set of program instructions are configured to cause the one or more processors 320 to analyze one or more characteristics of the sample 307. In another embodiment, the set of program instructions are configured to cause the one or more processors 320 to modify one or more characteristics of the system 300 to maintain focus on the sample 307 and / or the sensor 316. For example, the one or more processors 320 may be configured to adjust the objective lens 306 or one or more optical elements 302 to focus the broadband light 118 from the broadband LSP light source 100 onto the surface of the sample 307. As another example, the one or more processors 320 may be configured to adjust the objective lens 306 and / or one or more optical elements 310 to collect illumination from the surface of the sample 307 and focus the collected illumination onto the sensor 316.

[0045] It should be noted that system 300 may be configured in any optical configuration known in the art, including, but not limited to, a dark-field configuration, a bright-field configuration, etc. System 300 may be configured as any type of metrology tool known in the art, including, but not limited to, a spectroscopic ellipsometer with one or more illumination angles, a spectroscopic ellipsometer for measuring Mueller matrix elements (e.g., using a rotational compensator), a single-wavelength ellipsometer, an angle-resolved ellipsometer (e.g., a beam profile ellipsometer), a spectroscopic reflectometer, a single-wavelength reflectometer, an angle-resolved reflectometer (e.g., a beam profile reflectometer), an imaging system, a pupil imaging system, a spectral imaging system, or a scatterometer.

[0046] Additional details of various embodiments of the optical characterization system 300 can be found in U.S. Pat. No. 7,957,066, issued July 7, 2011, entitled "Split Field Inspection System Using Small Catadioptric Objectives," U.S. Patent Application Publication No. 2007 / 0002465, published January 4, 2007, entitled "Beam Delivery System for Laser Dark-Field Illumination in a Catadioptric Optical System," U.S. Pat. No. 5,999,310, issued December 7, 1999, entitled "Ultra-broadband UV Microscope Imaging System with Wide Range Zoom Capability," and U.S. Pat. No. 7,525,649, issued April 28, 2009, entitled "Surface Inspection System Using Laser Line Illumination with Two-Dimensional Imaging." "Illumination with Two Dimensional Imaging," U.S. Patent Application Publication No. 2013 / 0114085, published May 9, 2013, by Wang et al., entitled "Dynamically Adjustable Semiconductor Metrology System," U.S. Patent No. 5,608,526, issued March 4, 1997, by Piwonka-Corle et al., entitled "Focused Beam Spectroscopic Ellisometry Method and System," by Rosencwaig et al.No. 6,297,880, entitled "Apparatus for Analyzing Multi-Layer Thin Film Stacks on Semiconductors," issued October 2, 2001, to Chris B., et al., which are incorporated herein by reference in their entireties.

[0047] The one or more processors 320 of the present disclosure may include any one or more processing elements known in the art. In this sense, the one or more processors 320 may include any microprocessor-type device configured to execute software algorithms and / or instructions. In one embodiment, the one or more processors 320 may comprise a desktop computer, mainframe computer system, workstation, image computer, parallel processor, or other computer system (e.g., network computer) configured to execute programs configured to operate the system 300 and / or broadband LSP light source 100 described throughout this disclosure. It should be appreciated that the steps described throughout this disclosure may be performed by a single computer system or, alternatively, by multiple computer systems. In general, the term “processor” may be broadly defined to include any device having one or more processing elements that execute program instructions from a non-transitory memory medium 322. Additionally, different subsystems of the various disclosed systems may include processors or logic elements suitable for performing at least some of the steps described throughout this disclosure. Accordingly, the above description should be construed as merely illustrative and not limiting of the present disclosure.

[0048] The memory medium 322 may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 320. For example, the memory medium 322 may include a non-transitory memory medium. For example, the memory medium 322 may include, but is not limited to, read-only memory, random access memory, magnetic or optical memory devices (e.g., disks), magnetic tape, solid-state drives, etc. In other embodiments, the memory 322 may be configured to store one or more results and / or output of the various steps described herein. Furthermore, it should be noted that the memory 322 may be stored in a common controller housing with one or more processors 320. In alternative embodiments, the memory 322 is located remotely from the physical location of the processors 320. For example, one or more processors 320 may access a remote memory (e.g., a server) accessible over a network (e.g., the Internet, an intranet, etc.). In other embodiments, the memory medium 322 holds program instructions that cause one or more processors 320 to perform the various steps described throughout this disclosure.

[0049] 4 is a flow diagram illustrating a method 400 for generating broadband light 118 in accordance with one or more embodiments of the present disclosure. It should be noted that all or some of the steps of method 400 may be implemented by broadband LSP light source 100. However, it should also be recognized that method 400 is not limited to broadband LSP light source 100 in that all or some of the steps of method 400 may be performed by additional or alternative system-level embodiments.

[0050] In step 402, method 400 includes generating a primary pump beam. In step 404, method 400 includes directing the primary pump beam toward a plasma formation region of a fluid, where the fluid comprises at least one of a high-pressure liquid or a supercritical fluid. In step 406, method 400 includes generating a pulsed assist beam. In step 408, method 400 includes directing the pulsed assist beam into the plasma formation region of the fluid, where the primary pump beam and the pulsed assist beam are configured to sustain a plasma within the plasma formation region of the fluid. In step 410, method 400 includes collecting at least a portion of the broadband light emitted from the plasma.

[0051] Those skilled in the art will recognize that the components, operations, devices, objects, and related discussions described in this disclosure are used as examples to clarify the concepts, and that various configuration modifications are contemplated. Thus, the specific examples and related discussions used in this disclosure are intended as representative of a more general class. In general, the use of a specific example is intended as representative of that class, and the absence of specific components (e.g., operations), devices, and objects should not be construed as limiting.

[0052] With respect to the use of substantially plural and / or singular terms in this disclosure, those skilled in the art will be able to convert the plural to the singular and / or the singular to the plural as appropriate in the context and / or application. For clarity, the various singular / plural permutations have not been explicitly set forth herein.

[0053] The subject matter described in this disclosure may depict different components contained within or associated with other components. It should be understood that such depicted structures are for illustrative purposes only, and that in fact, many other structures can be implemented to achieve the same functionality. In a conceptual sense, configurations of components that achieve the same functionality are substantially "associated" with each other in that the desired functionality is achieved. Thus, combining any two components of the present disclosure to achieve a particular function can be viewed as those components being "associated" with each other in that the desired functionality is achieved, regardless of structure or intermediate components. Similarly, any two associated components can be viewed as being "connected" or "coupled" to each other to achieve the desired functionality, and any two associated components can be viewed as being "couplable" to each other to achieve the desired functionality. Specific examples of "couplable" include, but are not limited to, physically matable and / or physically interacting components and / or wirelessly interacting and / or wirelessly interacting components and / or logically interacting and / or logically interacting components.

[0054] It should further be understood that the present invention is defined by the appended claims. Those skilled in the art will generally understand that the terms used in this disclosure, and particularly in the appended claims (e.g., the body of the appended claims), are generally intended as "open" terms (e.g., the term "comprises" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "including" should be interpreted as "including but not limited to," etc.). Furthermore, those skilled in the art will understand that if a specific number of elements to be included in a claim is intended, such intention will be explicitly recited in the claim; in the absence of such recitation, no such intention exists. For example, to aid in understanding, the following appended claims may use the introductory phrases "at least one" and "one or more" to introduce claim elements. However, the use of such phrases should not be construed as implying that the introduction of a claim element by the indefinite article "a" or "an" limits a particular claim including such introduced claim element to inventions containing only one such element, even if the same claim also contains the introductory phrase "one or more" or "at least one" and an indefinite article such as "a" or "an" (e.g., "a" and / or "an" should typically be interpreted to mean "at least one" or "one or more"). The same applies when a definite article is used to introduce a claim element. Also, even when an introduced claim element is explicitly recited by a specific number, those skilled in the art will recognize that such a recitation should typically be interpreted as at least the recited number (e.g., a recitation of "two elements" alone, without any other modifier, typically means at least two elements or more than two elements).Furthermore, where a convention similar to "at least one of A, B, and C, etc." is used, such a description is generally intended to be interpreted as one of ordinary skill in the art would understand this convention (e.g., "a system having at least one of A, B, and C" includes, but is not limited to, a system having only A, a system having only B, a system having only C, a system having both A and B, a system having both A and C, a system having both B and C, and / or a system having both A, B, and C). Where a convention similar to "at least one of A, B, or C, etc." is used, such a description is generally intended to be interpreted as one of ordinary skill in the art would understand this convention (e.g., "a system having at least one of A, B, or C" includes, but is not limited to, a system having only A, a system having only B, a system having only C, a system having both A and B, a system having both A and C, a system having both B and C, and / or a system having both A, B, and C). Furthermore, those skilled in the art will understand that nearly all disjunctive words and / or phrases presenting two or more alternative terms, whether in the specification, claims, or drawings, should be understood to contemplate the possibility of including one or both of those terms. For example, the phrase "A or B" is understood to include the possibility of "A," or the possibility of "B," or the possibility of "A and B."

[0055] The present disclosure and many of its attendant advantages will be understood from the foregoing description. It will also be apparent that various changes in form, construction, and arrangement of parts may be made without departing from the disclosed subject matter or sacrificing the advantages thereof. The described forms are exemplary only, and it is intended that the following claims cover such modifications. It will further be understood that the invention is defined by the appended claims.

Claims

1. 1. A broadband light source, comprising: a fluid confinement structure for confining a fluid; a primary laser pumping source configured to direct a primary pump beam into a plasma formation region of the fluid; a pulse-assisted laser source configured to direct a pulse-assisted beam into the plasma formation region of the fluid, the primary beam and the pulse-assisted beam configured to sustain a plasma in the plasma formation region of the fluid within the fluid confinement structure; a light collecting element configured to collect at least a portion of the broadband light emitted from the plasma; a broadband light source, including

2. 10. The broadband light source of claim 1, The pulse-assisted laser source is a broadband light source configured to increase instantaneous pumping power to a value above the liquid-gas breakdown threshold of the fluid.

3. 10. The broadband light source of claim 1, The pulse-assisted laser source is a broadband light source that includes a pulsed laser.

4. 10. The broadband light source of claim 1, The pulse-assisted laser source is configured to operate at a repetition rate sufficient to avoid complete extinction of the plasma between pulses of the pulse-assisted beam of the pulse-assisted laser source.

5. 10. The broadband light source of claim 1, The pulse-assisted laser source is a broadband light source configured to operate at a repetition rate greater than 0.5 MHz.

6. 10. The broadband light source of claim 1, The pulse-assisted laser source is a broadband light source configured to generate pulses shorter than 5 picoseconds.

7. 10. The broadband light source of claim 1, The pulse-assisted laser source is configured to operate at a power greater than 10 W.

8. 10. The broadband light source of claim 1, The laser pumping source is a broadband light source, including a continuous wave (CW) laser source.

9. 9. A broadband light source according to claim 8, The CW laser source is a broadband light source operating at a power greater than 5 kW.

10. 10. The broadband light source of claim 1, The broadband light source, wherein the fluid comprises at least one of a high pressure liquid or a supercritical fluid.

11. 10. The broadband light source of claim 1, The fluid comprises at least one of water, ammonia, or one or more organic solvents.

12. 10. The broadband light source of claim 1, The fluid comprises a cryogenic liquid.

13. 13. The broadband light source of claim 12, The fluids include liquid Ne, liquid Ar, liquid Kr, liquid Xe, and liquid N. ２ , or liquid O ２ A broadband light source comprising at least one of:

14. 10. The broadband light source of claim 1, The broadband light source further comprising a recirculation pump for circulating said fluid through said fluid confinement structure.

15. 10. The broadband light source of claim 1, The broadband light source further comprising a primary pumping focusing optic configured to focus the primary pumping beam within the plasma formation region of the fluid.

16. 10. The broadband light source of claim 1, The broadband light source further includes a pulse-assisted laser focusing optic configured to focus the pulse-assisted laser beam within the plasma formation region of the fluid.

17. 10. The broadband light source of claim 1, A broadband light source, wherein at least one of the primary pumping focusing optics or the pulse-assisted laser focusing optics is compensated to correct aberrations caused by said fluid confinement structure.

18. 1. A broadband light source, comprising: a fluid confinement structure; and a plurality of jet nozzles configured to direct a plurality of fluid jets for impact within the fluid confinement structure, the plurality of fluid jets comprising a first fluid jet and at least one second fluid jet; a primary laser pumping source configured to direct a primary pumping beam at an impact point of the plurality of fluid jets; a pulse-assisted laser source configured to direct a pulse-assisted beam at the impact points of the multiple fluid jets, wherein the primary beam and the pulse-assisted beam are configured to sustain a plasma within a plasma formation region of the fluid confinement structure at the impact points of the multiple fluid jets; a light collecting element configured to collect at least a portion of the broadband light emitted from the plasma; a broadband light source, including

19. 20. The broadband light source of claim 18, The pulse-assisted laser source is a broadband light source configured to increase the instantaneous power of the plasma to a value above a liquid-gas breakdown threshold.

20. 20. The broadband light source of claim 18, The pulse-assisted laser source is a broadband light source that includes a pulsed laser.

21. 20. The broadband light source of claim 18, The pulse-assisted laser source is configured to operate at a repetition rate sufficient to avoid complete extinction of the plasma between pulses of the pulse-assisted beam of the pulse-assisted laser source.

22. 20. The broadband light source of claim 18, The pulse-assisted laser source is a broadband light source configured to operate at a repetition rate greater than 0.5 MHz.

23. 20. The broadband light source of claim 18, The pulse-assisted laser source is a broadband light source configured to generate pulses shorter than 5 picoseconds.

24. 20. The broadband light source of claim 18, The pulse-assisted laser source is configured to operate at a power greater than 10 W.

25. 20. The broadband light source of claim 18, The laser pumping source is a broadband light source, including a continuous wave (CW) laser source.

26. 26. The broadband light source of claim 25, The CW laser source is a broadband light source operating at a power greater than 5 kW.

27. 20. The broadband light source of claim 18, A broadband light source, wherein one or more fluid jets of the plurality of fluid jets comprises at least one fluid jet of water, ammonia, or one or more organic solvents.

28. 20. The broadband light source of claim 18, A broadband light source, wherein one or more of the plurality of fluid jets comprises a fluid jet of a cryogenic liquid.

29. 29. The broadband light source of claim 28, The cryogenic liquid is liquid Ne, liquid Ar, liquid Kr, liquid Xe, liquid N ２ , or liquid O ２ A broadband light source comprising at least one of:

30. 20. The broadband light source of claim 18, The broadband light source further comprising a primary pumping focusing optic configured to focus the primary pumping beam within the plasma formation region of the fluid.

31. 20. The broadband light source of claim 18, The broadband light source further includes a pulse-assisted laser focusing optic configured to focus the assisting pulsed laser beam within the plasma formation region of the fluid.

32. 32. The broadband light source of claim 31, The broadband light source, wherein at least one of the primary pumping focusing optics or the pulse-assisted laser focusing optics comprises at least one of a lens or a mirror.

33. 33. The broadband light source of claim 32, A broadband light source, wherein at least one of the primary pumping focusing optic or the pulse-assisted laser focusing optic comprises one or more annular optical elements.

34. 20. The broadband light source of claim 18, The plurality of fluid ejection nozzles are fluidly coupled to one or more fluid sources.

35. 20. The broadband light source of claim 18, The broadband light source, wherein the fluid confinement structure comprises at least one of a plasma chamber, a plasma cell, or a plasma lamp.

36. 1. A system comprising:

1. A broadband source comprising: a fluid confinement structure for confining a fluid; a primary laser pumping source configured to direct a primary pump beam into a plasma formation region of the fluid; a pulse-assisted laser source configured to direct a pulse-assisted beam into the plasma formation region of the fluid, the primary beam and the pulse-assisted beam configured to sustain a plasma in the plasma formation region of the fluid within the fluid confinement structure; a light collecting element configured to collect at least a portion of the broadband light emitted from the plasma; a broadband source comprising: a set of illuminator optics configured to direct the broadband light from the light collecting element onto one or more samples; a detector assembly; a set of projection optics configured to receive illumination from a surface of the one or more samples and direct the illumination from the one or more samples to the detector assembly; Including, the system.

37. 1. A system comprising:

1. A broadband light source, comprising: a fluid confinement structure; and a plurality of jet nozzles configured to direct a plurality of fluid jets to impinge within the fluid confinement structure, the plurality of fluid jets; a plurality of jet nozzles including a first fluid jet and at least one second fluid jet; a primary laser pumping source configured to direct a primary pumping beam at an impact point of the plurality of fluid jets; a pulse-assisted laser source configured to direct a pulse-assisted beam at the impact points of the multiple fluid jets, wherein the primary beam and the pulse-assisted beam are configured to sustain a plasma within a plasma formation region of the fluid confinement structure at the impact points of the multiple fluid jets; a light collecting element configured to collect at least a portion of the broadband light emitted from the plasma; a broadband light source comprising: a set of illuminator optics configured to direct the broadband light from the light collecting element onto one or more samples; a detector assembly; a set of projection optics configured to receive illumination from a surface of the one or more samples and direct the illumination from the one or more samples to the detector assembly; Including, the system.

38. 1. A method comprising: generating and directing a primary pump beam into a plasma formation region of a fluid, the fluid comprising at least one of a high pressure liquid or a supercritical fluid; generating and directing a pulsed assist beam into the plasma formation region of the fluid, wherein the primary pump beam and the pulsed assist beam are configured to sustain a plasma within the plasma formation region of the fluid; collecting at least a portion of the broadband light emitted from the plasma; A method comprising:

Images