Laser-sustained plasma generation in ultrasonic gas jets
The use of supersonic gas jets to form localized high-pressure regions in LSP light sources addresses radiance and stability issues, enhancing brightness and simplifying operation by eliminating complex high-pressure vessels and cryogenic cooling.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- KLA CORP
- Filing Date
- 2024-07-01
- Publication Date
- 2026-07-10
Smart Images
Figure 2026523062000001_ABST
Abstract
Description
Technical Field
[0001] Reference to Related Applications This application claims priority to U.S. Provisional Application No. 63 / 524,866 (July 4, 2023), which is hereby incorporated by reference in its entirety.
[0002] The present disclosure generally relates to plasma-based radiation sources, and more particularly to laser-sustained plasma (LSP) broadband light sources that include plasmas generated within a locally high-pressure region produced by one or more supersonic gas jets.
Background Art
[0003] As the demand for integrated circuits with increasingly smaller device features continues to grow, the need for improved illumination sources used to inspect these increasingly shrinking devices continues to increase. One such illumination source involves laser-sustained plasma (LSP) light sources. LSP light sources can produce high-power broadband light. LSP light sources typically operate by focusing laser radiation into a gas volume to excite a gas such as argon or xenon into a plasma state, and the plasma state can emit light. This effect is typically called plasma "pumping". LSPs used in broadband plasma (BBP) light sources have limited radiance. Several methods have been proposed to increase such radiance. LSP-based light source solutions in stationary lamps have been shown to have limited radiance as a result of the plasma tending to grow in a direction in which the pump laser absorbs the laser light. As the pump laser power increases, the plasma grows larger, and absorption at the periphery of the plasma becomes more pronounced as the power reaching the plasma focus begins to decrease, and the LSP becomes dimmer. Gas flow through solutions with layered subsonic gas flow requires the recirculation of large amounts of high-pressure gas, which is technically difficult. Typical values for such systems require a good rate of recirculation of 1 kilogram of gas / second under pressures exceeding 100 bar. This configuration also requires a transparent high-pressure vessel or a chamber with a high-pressure window for optical input-output, all of which increase structural complexity and operational safety. Liquid jet-based systems require cryogenic cooling to liquefy the high-pressure gas internally in order to generate a sufficiently fast liquid jet. At the required speed, the liquid jet tends to become unstable and atomize, and the LSP can become noisy. [Prior art documents] [Patent Documents]
[0004] [Patent Document 1] U.S. Patent Application Publication No. 2021 / 0120659 [Overview of the project] [Problems that the invention aims to solve]
[0005] Therefore, there is a need to provide an LSP source that solves the shortcomings associated with conventional approaches. [Means for solving the problem]
[0006] A laser-sustained plasma (LSP) broadband light source is disclosed according to one or more embodiments of the present disclosure. In exemplary embodiments, the light source includes a gas containment structure. In exemplary embodiments, the light source includes a plurality of jet nozzles, which are configured to generate a plurality of supersonic gas jets and to direct the plurality of supersonic gas jets to collide within the gas containment structure, thereby forming localized high-pressure regions at the collision points of the plurality of supersonic gas jets. In exemplary embodiments, the light source includes a primary laser pump source, which is configured to direct a primary pump beam to the localized high-pressure regions formed at the collision points of the plurality of supersonic gas jets. In exemplary embodiments, the light source includes a pulse-assisted laser source, which is configured to direct a pulse-assisted beam to the localized high-pressure regions at the collision points of the plurality of ultrasonic gas jets, and the primary beam and pulse-assisted beam are configured to maintain the plasma within the localized high-pressure regions. In exemplary embodiments, the light source includes a focusing element configured to focus at least a portion of the broadband light emitted from the plasma. In exemplary embodiments, the LSP broadband light source may be implemented within an optical system such as an inspection system, measurement system, or lithography system, but is not limited to these.
[0007] LSP broadband light sources are disclosed according to one or more additional and / or alternative embodiments of this disclosure. In exemplary embodiments, the light source includes a gas containment structure. In exemplary embodiments, the light source includes one or more jet nozzles, each configured to generate one or more supersonic gas jets. In exemplary embodiments, the light source includes a primary laser pump source, which is configured to direct a primary pump beam to a local high-pressure region formed by the supersonic gas expansion of one or more supersonic gas jets. In exemplary embodiments, the light source includes a pulse-assisted laser source, which is configured to direct a pulse-assisted beam to a local high-pressure region formed by the supersonic gas expansion of one or more supersonic gas jets, and the primary beam and pulse-assisted beam are configured to maintain plasma within the local high-pressure region. In exemplary embodiments, the light source includes a focusing element configured to focus at least a portion of the broadband light emitted from the plasma.
[0008] It should be understood that both the above summary and the following detailed description are illustrative and descriptive, and do not necessarily limit the scope of this disclosure. The accompanying drawings incorporated herein and forming part of this disclosure illustrate the subject matter of this disclosure. Both the description and the drawings serve to illustrate the principles of this disclosure. [Brief explanation of the drawing]
[0009] Many of the advantages of this disclosure can be better understood by those skilled in the art by referring to the accompanying drawings. [Figure 1A] A conceptual diagram of a broadband LSP light source having multiple impact ultrasonic jets for forming a localized high-pressure gas region for plasma generation is shown, according to one or more embodiments of the present disclosure. [Figure 1B] A conceptual diagram of a broadband LSP light source having multiple impact ultrasonic jets for forming a localized high-pressure gas region for plasma generation is shown, according to one or more embodiments of the present disclosure. [Figure 2] The gas velocity of the gas flow in the LSP source according to one or more embodiments of this disclosure is shown. [Figure 3] The pressure of the gas within a gas containment structure according to one or more embodiments of the present disclosure is shown. [Figure 4A] A conceptual diagram of a single nozzle used to generate a single supersonic jet according to one or more embodiments of the present disclosure is illustrated. [Figure 4B] A conceptual diagram of a single nozzle used to generate a single supersonic jet according to one or more embodiments of the present disclosure is illustrated. [Figure 5A] A simplified schematic diagram of an LSP broadband light source in which the optical path of the pump beam does not overlap with the optical path of the pulse-assisted beam, according to one or more embodiments of the present disclosure, is shown. [Figure 5B] A simplified schematic diagram of an LSP broadband light source according to one or more embodiments of the present disclosure is shown, 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. [Figure 5C] A simplified schematic diagram of an LSP broadband light source according to one or more embodiments of the present disclosure is shown, in which a pulse-assisted beam is injected into a laser fiber of a primary pump source. [Figure 6] A simplified schematic diagram of an optical characterization system implementing a pulse-assisted LSP broadband light source according to one or more embodiments of the present disclosure is shown. [Figure 7] This flowchart shows a method for generating broadband light according to one or more embodiments of the present disclosure. [Modes for carrying out the invention]
[0010] Hereinafter, we refer in detail to the disclosed subject matter shown in the accompanying drawings. This disclosure is specifically shown and described with respect to particular embodiments and their particular features. The embodiments described herein are to be construed as illustrative rather than restrictive. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail can be made without departing from the spirit and scope of this disclosure.
[0011] Generally, referring to Figures 1A to 4B, one or more embodiments of the present disclosure describe a broadband light source including a laser-sustained plasma.
[0012] Embodiments of this disclosure relate to the formation of a localized high-pressure gas region located near the laser focal point of a primary pump laser and / or pulse-assisted laser, for maintaining a plasma at that location. The high-pressure region may be formed in a Mach disk in the supersonic gas expansion of one or more supersonic jets, or at the collision point of two or more supersonic gas jets. One or more supersonic gas jets may be formed by one or more nozzles (e.g., a converging-diverging nozzle, a converging nozzle, or a cylindrical nozzle). Because the high-pressure region is small, the pump laser beam can propagate to the high-pressure region through the surrounding low-pressure / peripheral gas region within the gas containment structure 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. The region of strong absorption is independent of the laser power. Therefore, as the laser power increases, the density of absorbed energy in the small high-pressure region also increases, which then generates a more radiant (brighter) plasma.
[0013] The implementation of a localized high-pressure region allows for an increase in spectral radiance (brightness) beyond what can be achieved in a stationary high-pressure source. LSP brightness in a stationary high-pressure source is limited by absorption in the plasma periphery. As pump power increases, the plasma periphery grows, and absorption in the periphery limits how much power can be delivered to the laser focus. However, in the proposed solution, the plasma periphery also grows, but because it is located in the surrounding low-pressure region, absorption in the periphery is low. This allows all pump laser radiation to be delivered to the high-pressure region formed in the supersonic jet.
[0014] Compared with high-pressure flow-through solutions, embodiments of the present disclosure do not require a high-pressure plasma-containing gas vessel, and its configuration is a major issue in high-power UV-VUV LSP sources. Embodiments of the present disclosure do not require relatively low pressures (e.g., up to about 10 bar) or even an atmospheric enclosure. Unlike the liquid jets used with CW pump sources, the supersonic gas jet solution of the present disclosure removes limitations associated with cryogenic jet operation, liquid jet instability, and liquid jet destruction due to interaction with the ambient gas, and shock waves from gas outflow in the interaction region.
[0015] Unlike pulsed operation, this solution operates in a CW regime that is beneficial for optical measurement and inspection applications that require a high-brightness source. CW operation significantly reduces optical damage in such systems.
[0016] Figures 1A - 1B show a broadband LSP light source 100 according to one or more embodiments of the present disclosure.
[0017] In an embodiment, the light source 100 includes a gas confinement structure 101, a primary laser pump source 102, a pulse assist laser source 104, two or more jet nozzles 107a, 107b, and a focusing element 111. In additional and / or alternative embodiments, as shown in FIG. 1B, the broadband LSP light source 100 includes a recirculation loop 112.
[0018] The two or more jet nozzles 107a, 107b may include a first jet nozzle 107a and a second jet nozzle 107b (or any number of nozzles). In embodiments, the two or more jet nozzles 107a, 107b may include two or more high-pressure (e.g., greater than 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 direct 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 measured relative to an ambient pressure region 134 and is greater than the ambient pressure. For example, the ambient pressure may be 1 bar, and the local high-pressure region 109 is a pressure of 10 to 100 bar. It should be noted that the ambient pressure (e.g., approximately 1 bar) is lower than the pressure at nozzles 107a and 107b, and the temperature of nozzles 107a and 107b is sufficient to avoid gas liquefaction during discharge from nozzles 107a and 107b.
[0019] It is recognized that the light source 100 can be implemented with any number and type of gas components. In embodiments, the gas used to generate the ultrasonic jet of the present disclosure may include one or more noble gases. For example, one or more noble gases may include, but are not limited to, xenon, argon, neon, or helium. As another example, the gas may include one or more non-noble gases. In embodiments, the gas may include a mixture of two or more gases. For example, the gas may include a mixture of two or more noble gases (e.g., Ar / Xe). As another example, the gas may include a mixture of a noble gas and a non-noble gas, or a mixture of two or more non-noble gases.
[0020] In the embodiment, the primary laser pump source 102 is configured to direct the primary pump beam 103 to a localized high-pressure region 109 formed at the collision point of two or more supersonic gas jets 106a, 106b. In the embodiment, the pulse-assisted laser source 104 is configured to direct the pulse-assisted beam 105 to the localized high-pressure region 109 at the collision point of two or more supersonic gas jets 106a, 106b. In this regard, the primary beam 103 and / or the pulse-assisted beam 105 are configured to generate and maintain plasma 110 within the localized high-pressure region 109.
[0021] The primary laser pump source 102 can include any laser pump source known in the art. In embodiments, the primary laser pump source 102 may include one or more continuous-wave (CW) lasers. For example, the primary laser pump 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 CO2 lasers. The primary laser excitation source 102 is not limited to a single laser. For example, the primary pump source 102 may include any number of additional laser sources. For example, the primary pump source 102 may include a first primary pump source emitting a first wavelength and at least a second primary pump source emitting a second wavelength, and so on.
[0022] The pulse-assisted laser source 104 may include any pulse-assisted laser source known in the art. In embodiments, the pulse-assisted laser source 104 may include one or more picosecond or femtosecond pulse-assisted 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 include, but is not limited to, one or more pulsed fiber-based NIR lasers, one or more pulse-coherent coupled fiber lasers, and / or one or more pulsed thin-film disk lasers. The primary laser excitation source 102 is not limited to a single laser. For example, the pulse-assisted laser source 104 may include any number of additional laser sources. For example, the pulse-assisted laser source 104 may include a first pulse-assisted laser source emitting a first wavelength and at least a second pulse-assisted laser source emitting a second wavelength, and so on.
[0023] It should be noted that the scope of this disclosure is not limited to the use of both the primary pump source 102 and the pulse support source 104. In additional and / or alternative embodiments, the source 100 may maintain the plasma 110 in the local high-pressure region 109 using only one or more primary pump sources 102. In additional and / or alternative embodiments, the source 100 may maintain the plasma 110 in the local high-pressure region 109 using only one or more pulse support sources 104.
[0024] In embodiments, the light source 100 includes one or more focusing optics 122 for focusing / directing the primary pump beam 103 to the plasma 110. Furthermore, the light source 100 may include one or more focusing optics 124 for focusing / directing the pulse-assisted beam 105 to the plasma 110. It should be noted herein that the pump laser focusing optics 122 and the pulse-assisted laser optics 124 may include, but are not limited to, any optical elements known in the art for guiding and / or focusing radiation, including lenses, mirrors, prisms, polarizers, gratings, filters, or beam splitters. In embodiments, 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 accommodating the primary pump laser beam 103 and the pulse-assisted beam 105. In addition, the gas containment structure 101 may include an exit window (not shown). However, it should be noted that a high-pressure window is not a requirement for operation, as much of the gas within the containment structure can be held at relatively low pressure (for example, ambient pressure is about 1 bar).
[0025] The implementation of a pulse-assisted laser source combined with a primary laser source is discussed in U.S. Patent Application No. 18 / 372,590 (September 25, 2023), which is incorporated herein by reference in its entirety.
[0026] In this embodiment, a recirculation pump 130 recirculates the gas through a gas containment structure 101. In this regard, a recirculation loop 112 can supply the gas to nozzles 107a, 107b to form ultrasonic jets 106a, 106b, creating a localized high-pressure region 109 for generating / maintaining a plasma 109. The recirculation loop 112 then carries away the hot gas from the plasma 110 and cools the gas through one or more heat exchangers 132. The cooled gas is then circulated through the system and may be driven into the impact region 109 through 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 the nozzles 107a, 107b.
[0027] In embodiments, the focusing element 111 is configured to focus broadband light 118 emitted from the plasma 110. The focusing element 111 may include one or more optical elements known in the art configured to focus and / or concentrate 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, etc. It should be noted herein that the focusing element 111 may be configured to collect and / or concentrate broadband light 118 generated by the plasma 110 for use in one or more downstream processes, including, but not limited to, imaging processes, inspection processes, measurement processes, lithography processes, etc. The broadband light 118 may be focused by the focusing element 111 and directed through one or more apertures 119 to one or more downstream applications 121.
[0028] Figures 2 and 3 show simulated figures 200 and 300 of the operation of the light source 100 according to one or more embodiments of the present disclosure. Figure 2 shows the gas velocity of the gas flow within the gas containment structure 100, and Figure 3 shows the pressure within the gas containment structure 100. Figures 200 and 300, showing the simulated gas velocity and pressure, show a high-pressure, low-speed region 109 of several hundred microns formed by the collision of two supersonic gas jets 106a and 106b. The simulation was performed using a convergent-divergent nozzle with an elongated, relatively shallow divergence angle. A local pressure-to-ambient pressure ratio of approximately 10 within the gas containment structure is also suitable for the operation of the source 100. The diamond shock wave structure that occurs when the pressure ratio on the nozzle is much higher than the critical pressure can be controlled by designing the nozzle geometry, nozzle throat, length of the divergence section, and other parameters specific to the selected gas (e.g., selected noble gas) and any other requirements of the source 100.
[0029] In this example, the CW pump laser intensity near the focal point is approximately 10⁹–10¹³ W / cm². 2Note that if the pressure is higher than the gas breakdown threshold, the gas flow cannot blow it away, and the plasma self-starts. To support this process and ensure plasma stability even in the presence of a high-speed gas flow, a series of picosecond / femtosecond pulses with a high repetition rate of approximately 1–1000 MHz may be used. This may be provided by a pulse-assisted laser 104 with a lower average power exceeding the breakdown threshold in each pulse, and the pulses are close together so that the plasma does not have 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 breakdown threshold in laser-induced plasmas is discussed in Jon P. Davis, et al., Pressure dependence of the laser-induced breakdown thresholds of gas and droplets, APPLIED OPTICS, Vol.29, No.15, p.2303, which is incorporated herein by reference in its entirety.
[0030] It should be noted that the various parameters of the light source 100 described in the non-limiting examples should not be construed as limitations on the scope of this disclosure. Rather, these examples are provided solely for illustrative purposes, and it should be understood that various laser powers, frequencies, pulse widths, gas pressures, and gas velocities may be available, taking into account the details of the light source 100 in operation.
[0031] Much of this disclosure focuses on the use of two or more impacting jets to generate localized high-pressure zones, but this configuration should not be interpreted as a limitation to the scope of this disclosure. Rather, it is intended that any number of gas / fluid flow configurations can be implemented to generate localized high-pressure gas regions (relative to ambient pressure) suitable for plasma generation.
[0032] Figure 4A illustrates a conceptual diagram 400 of a single nozzle 107 used to generate 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 low-pressure ambient gas) is formed within the supersonic gas flow. For example, a Mach disk in a shock wave of an ultrasonic gas flow (e.g., a diamond shock wave). The local high-pressure region 109 may be formed using one or more Mach disks 136 of the supersonic gas flow. Plasma 110 may be generated and maintained in the local high-pressure region 109 associated with one or more Mach disks 136. As shown in Figure 4B, the local high-pressure region 109 may be formed at the outlet of the supersonic jet nozzle 107. In this example, plasma 110 may be generated and maintained in the local high-pressure region 109 formed at the outlet of the ultrasonic jet nozzle 107.
[0033] Figure 5A shows a simplified schematic diagram of a broadband LSP light source 100 according to one or more embodiments of the present disclosure. Note that, in this specification, the various embodiments described with respect to Figures 1A to 4B should be interpreted as extending to the embodiment in Figure 5A. In this embodiment, the focusing element 506 is a curved mirror. For example, the focusing element 506 may include, but is not limited to, an elliptical, spherical, or parabolic mirror. In the embodiment, the primary pump beam 103 and the pump support beam 105 do not share an optical path before entering the focusing element 506. For example, the primary pump source 102 can direct the pump beam 103 through a beam shaping optical system 122 and a rotating mirror 502. The pump beam 103 then passes through a dichroic mirror 504 (e.g., a cold mirror) and is directed towards a local high-pressure region 109. In addition, the pulse support source 104 can be positioned to direct the pulse support beam 105 into the local high-pressure region 109 through one or more side ports 507 formed by penetrating the wall (e.g., side wall) of the focusing element 506. In this example, the nozzles 107a and 107b are positioned in a top / bottom configuration where the collision point and the local high-pressure region 109 coincide with the focal point of the focusing element 506 (e.g., the focal point of an elliptical reflector). As previously stated herein, the pump beam 103 and the pulse support beam 105 act to maintain the plasma 110. The broadband light 118 emitted by the plasma 110 can then be focused by the focusing element 506 and directed by the dichroic mirror 504 to one or more downstream optical elements 121.
[0034] Figure 5B shows a simplified schematic diagram of a broadband LSP light source 100 according to one or more embodiments of the present disclosure. It should be noted that the various embodiments described with respect to Figures 1A to 5A should be interpreted as extending to the embodiment in Figure 5B. In this embodiment, the primary pump beam 103 and the pump support beam 105 share an optical path before entering the focusing element 506 (e.g., an elliptical mirror, a spherical mirror, or a parabolic mirror). For example, the primary pump source 102 can direct the pump beam 103 through a pump module including one or more laser shaping optics 508. The primary pump beam 103 then passes through a dichroic mirror 504 (e.g., a cold mirror) and is directed to a local high-pressure region 109. Furthermore, the pulse support source 104 can be positioned to direct the pulse support beam 105 to a first dichroic mirror 502. The first dichroic mirror 502 is configured to transmit the primary pump beam 103 toward the focusing element 506 while reflecting the pulse support beam 105 toward the focusing element 506. Following the first dichroic mirror 502, the primary pump beam 103 and the pulse support beam 105 share an optical path to the focusing element 506. The primary pump beam 103 and the pulse support beam 105 then pass through the second dichroic mirror 504 and are reflected by the focusing element 506 into the local high-pressure region 109. As previously stated herein, the pump beam 103 and the pulse support beam 105 act to maintain the plasma 110. The broadband light 118 emitted by the plasma 110 is then focused by the focusing element 506 and directed by the dichroic mirror 504 to one or more downstream optical elements 121.
[0035] Figure 5C shows a simplified schematic diagram of a broadband LSP light source 100 according to one or more embodiments of the present disclosure. Note that the various embodiments described with respect to Figures 1A to 5B should be interpreted as extending to the embodiment in Figure 5C. In this embodiment, the pump-assisted beam 105 is injected into one or more laser fibers of the primary pump source 102 for the primary pump beam 103. As a result, the primary pump beam 103 and the pump-assisted beam 105 share an optical path as the beams 103 and 105 exit the beam shaping optical system 508. After exiting the beam shaping optical system 508, the primary pump beam 103 and the pulse-assisted beam 105 are directed through a dichroic mirror 504 (e.g., a cold mirror) to a focusing element 506, which then directs the primary bump beam 103 and the pulse-assisted beam 105, which share an optical path, to a local high-pressure region 109. As previously stated herein, the pump beam 103 and the pulse-assisted beam 105 act to maintain the plasma 110. Next, the broadband light 118 emitted by the plasma 110 can be focused by the light-gathering element 506 and directed by the dichroic mirror 504 to one or more downstream optical elements 121.
[0036] It should be noted that the nozzle configuration shown in Figure 5A is not limited to a top / bottom configuration or two nozzles. Two or more nozzles (e.g., 2, 3, 4, 5, 6, etc.) may be arranged in any alignment geometry (e.g., left-right, radial, etc.). In addition, single-jet configurations may be implemented within the embodiments depicted in Figures 5A to 5C.
[0037] The generation of laser-sustained plasma is also generally described in U.S. Patent No. 7,435,982 (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 (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 (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 (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 (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 (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 (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 (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 (July 12, 2016), which is incorporated herein by reference in its entirety. In a general sense, the various embodiments of this disclosure should be construed to extend to any plasma-based light source known in the art.
[0038] Figure 6 shows a simplified schematic diagram of an optical characterization system 300 implementing an LSP broadband light source 100 according to one or more embodiments of the present disclosure. In the embodiments, the system 300 includes the LSP light source 100, an illumination arm 603, a collection arm 605, a detector assembly 614, and a controller 618 including one or more processors and memory.
[0039] It should be noted that, as described herein, system 600 may include any imaging, inspection, measurement, lithography, or other characterization systems known in the art. In this regard, system 600 may be configured to perform inspection, optical measurement, lithography, and / or imaging of any form on sample 607. Sample 607 may include, but is not limited to, any sample known in the art, including semiconductor wafers, reticles, photomasks, flat panel displays, etc. It should be noted that system 600 may incorporate one or more of the various embodiments of the LSP light source 100 described throughout this disclosure.
[0040] In the embodiment, the sample 607 is placed on a stage assembly 612 to facilitate the movement of the sample 607. The stage assembly 612 may include any stage assembly known in the art, including, but not limited to, an XY stage, an R-θ stage, etc. In the embodiment, the stage assembly 612 can adjust the height of the sample 607 during inspection or imaging to maintain focus on the sample 607.
[0041] In one embodiment, the illumination arm 603 is configured to direct broadband light 118 from the broadband LSP light source 100 onto the sample 607. The illumination arm 603 may include any number and type of optical components known in the art. In one embodiment, the illumination arm 603 includes one or more optical elements 602, a beam splitter 604, and an objective lens 606. In this regard, the illumination arm 603 can be configured to focus broadband light 118 from the broadband LSP light source 100 onto the surface of the sample 607. The one or more optical elements 602 may include, but are 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, etc., any optical elements or combinations of optical elements known in the art.
[0042] In one embodiment, the system 600 includes a collection arm 605 configured to collect light reflected, scattered, diffracted, and / or emitted from the sample 607. In another embodiment, the collection arm 605 may direct and / or focus the light from the sample 607 to a sensor 616 of a detector assembly 614. It should be noted that the sensor 616 and detector assembly 614 may include any sensor and detector assembly known in the art. The sensor 616 may include, but is not limited to, a CCD sensor or a CCD-TDI sensor. Furthermore, the sensor 616 may include, but is not limited to, a line sensor or an electron shock line sensor.
[0043] In an embodiment, the detector assembly 614 is communicatively coupled to a controller 618 which includes one or more processors and memory. For example, one or more processors may be communicatively coupled to memory and configured to execute a set of program instructions stored in memory. In an embodiment, one or more processors are configured to analyze the output of the detector assembly 614. In an embodiment, the set of program instructions is configured to cause one or more processors to analyze one or more characteristics of the sample 607. In an embodiment, the set of program instructions is configured to cause one or more processors to modify one or more characteristics of the system 600 in order to maintain focus on the sample 607 and / or the sensor 616. For example, one or more processors may be configured to adjust the objective lens 606 or one or more optical elements 602 to focus broadband light 118 from the broadband LSP light source 100 onto the surface of the sample 607. As another example, one or more processors may be configured to adjust the objective lens 606 and / or one or more optical elements 610 to collect illumination from the surface of the sample 607 and focus the collected illumination onto the sensor 616.
[0044] It should be noted that System 600 may be composed of any optical configuration known in the art, including but not limited to dark-field configurations and bright-field orientations. System 600 may be composed of any type of measuring tool known in the art, such as, but not limited to, a spectroscopic ellipsometer having one or more illumination angles, a spectroscopic ellipsometer for measuring Müller matrix elements (e.g., using a rotational compensator), a single-wavelength ellipsometer, an angle-resolved ellipsometer (e.g., a beam profile ellipsometer), a spectroreflectometer, 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 scatometer.
[0045] Further details of various embodiments of the Optical Characterization System 300 can be found in U.S. Patent Application Publication No. 7,957,066B2, entitled "Split Field Inspection System Using Small Catadioptric Objectives," published on June 7, 2011; U.S. Patent Application Publication No. 2007 / 0002465 ("Beam Delivery System for Laser Dark-Field Illumination in a Catadioptric Optical System," published January 4, 2007); U.S. Patent No. 5,999,310 ("Ultra-broadband UV Microscope Imaging System with Wide Range Zoom Capability," December 7, 1999); U.S. Patent No. 7,525,649 ("Surface Inspection System Using Laser Line Illumination with Two Dimensional Imaging," April 28, 2009); and U.S. Patent Application Publication No. 2013 / 0114085 ("Dynamically Adjustable Semiconductor Metrology"). The following are described in U.S. Patent No. 5,608,526 ("Focused Beam Spectroscopic Ellipsometry Method and System, by Piwonka-Corle et al.", published May 9, 2013), U.S. Patent No. 6,297,880 ("Apparatus for Analyzing Multi-Layer Thin Film Stacks"), the entirety of which is incorporated herein by reference.
[0046] Figure 7 shows a flowchart illustrating a method 700 for generating broadband light 118 according to one or more embodiments of the present disclosure. It should be noted herein that the steps of method 700 may be implemented in whole or in part by a broadband LSP light source 100. However, it should be further recognized that method 700 is not limited to the broadband LSP light source 100 in that additional or alternative system-level embodiments may perform all or part of the steps of method 700.
[0047] In step 702, method 700 includes generating one or more supersonic gas jets to form a localized high-pressure region. In step 704, method 700 includes generating a primary pump beam and directing the primary pump beam to the localized high-pressure region formed by one or more supersonic gas jets. In step 706, method 700 includes generating a pulsed-supported beam and directing the pulsed-supported beam to the localized high-pressure region formed by one or more supersonic gas jets, wherein the primary pump beam and the pulsed-supported beam maintain the plasma within the localized high-pressure region. In step 708, method 700 includes focusing at least a portion of the broadband light emitted from the plasma.
[0048] Those skilled in the art will recognize that the components, actions, devices, objects, and accompanying discussions described herein are used as examples for conceptual clarity, and that various configuration modifications are considered. Therefore, as used herein, the specific examples and accompanying discussions described are intended to be representative of their more general class. In general, the use of any particular example is intended to represent its class, and the exclusion of specific components (e.g., actions), devices, and objects should not be interpreted as limitation.
[0049] With regard to the use of substantially any plural and / or singular terms herein, those skilled in the art can convert from plural to singular and / or singular to plural as appropriate to the context and / or use. Various singular / plural substitutions are not explicitly stated herein for the sake of clarity.
[0050] The subject matter described herein illustrates different components that, in some cases, are contained within or connected to other components. It should be understood that such depicted architectures are merely illustrative, and in practice, many other architectures can be implemented to achieve the same functionality. Conceptually, any arrangement of components to achieve the same function is effectively “associated” in such a way that the desired function is achieved. Thus, any two components in this specification combined to achieve a particular function, whether in architecture or as intermediate components, can be considered “associated” with each other in such a way that the desired function is achieved. Similarly, any two such associated components can also be considered “connected” or “joined” with each other in such a way that the desired functionality is achieved, and any two components that can be associated in such a way can also be considered “joinable” with each other in such a way that the desired functionality is achieved. Specific examples of joinable components include, but are not limited to, physically joinable and / or physically interacting components and / or wirelessly interactable and / or wirelessly interacting components and / or logically interacting and / or logically interactable components.
[0051] Furthermore, it should be understood that the present invention is defined by the appended claims. Generally, it will be understood by those skilled in the art that the terms used herein and in particular in the appended claims (e.g., the body of the appended claims) are generally intended to be “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,” and the term “includes” should be interpreted as “includes but not limited to,” etc.). It will further be understood by those skilled in the art that if a specific number of claims to be introduced is intended, such intention will be explicitly stated in that claim, and if such statement is not made, such intention does not exist. For example, for the sake of understanding, the following appended claims may include introducing the claims using the introductory phrases “at least one” and “one or more.” However, the use of such phrases should not be interpreted as meaning that the introduction of a claim description with the indefinite article "a" or "an" limits any particular claim containing such introduced description to an invention containing only one such description. The same applies to the use of clear articles used to introduce a claim description, even if the same claim contains an introductory phrase such as "one or more" or "at least one" and an indefinite article such as "a" or "an" (for example, "a" and / or "an" should typically be interpreted as meaning "at least one" or "one or more"). Furthermore, even if a specific number of claims being introduced is explicitly listed, it will be recognized that such descriptions should typically be interpreted as meaning at least the number listed (for example, a bare list of "two lists" without other modifying factors typically means at least two lists, or two or more lists).Furthermore, in instances where conventional expressions similar to "at least one of A, B, and C" are used, such configurations are generally intended to be understood by those skilled in the art as conventional expressions (for example, "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 conventional expressions similar to "at least one of A, B, or C" are used, such constructions are generally intended to be understood by those skilled in the art as conventional expressions (for example, "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). It will further be understood by those skilled in the art that virtually any disjunct words and / or phrases presenting two or more alternative terms, wherever they appear in the description, claims, or drawings, should be understood as intending to include the possibility of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibility of "A" or "B" or "A and B".
[0052] Many of the present disclosure and its associated advantages will be understood from the foregoing description, and it will become clear that various modifications can be made to the form, structure, and arrangement of the components without departing from the disclosed subject matter or sacrificing any of its material advantages. The described forms are for illustrative purposes only, and it is the intent of the following claims to encompass and include such modifications. Furthermore, it should be understood that the present invention is defined by the appended claims.
Claims
1. A broadband light source, Gas containment structure, Multiple jet nozzles are configured to generate multiple supersonic gas jets, to collide the multiple supersonic gas jets within the gas containment structure, and to direct them so as to form local high-pressure regions at the collision points of the multiple supersonic gas jets. A primary laser pump source is configured to direct the primary pump beam towards the localized high-pressure region formed at the collision point of the plurality of supersonic gas jets, A pulse-assisted laser source is configured to direct a pulse-assisted laser beam into the local high-pressure region at the collision points of the plurality of supersonic gas jets, and the primary pump beam and the pulse-assisted laser beam are configured to maintain plasma within the local high-pressure region. A light-gathering element configured to focus at least a portion of the broadband light emitted from the plasma, A broadband light source including
2. One or more of the aforementioned multiple jet nozzles are At least one of a convergence-divergence nozzle, a cylindrical nozzle, or a convergence nozzle, A broadband light source according to claim 1, comprising:
3. The shock wave is generated at the collision point of the multiple supersonic gas jets. The broadband light source according to claim 1.
4. The aforementioned shock wave includes a diamond shock wave. The broadband light source according to claim 3.
5. The aforementioned local high-pressure region has a pressure higher than the pressure in the surrounding pressure region within the gas containment structure. The broadband light source according to claim 1.
6. The light-gathering element includes an elliptical reflector, The broadband light source according to claim 1.
7. The pulse-assisted laser beam is directed through an opening in the wall of the elliptical reflector towards the collision point of the plurality of supersonic gas jets. The broadband light source according to claim 6.
8. The primary laser pump source includes a continuous wave (CW) laser source. The broadband light source according to claim 1.
9. The pulse-assisted laser source includes a pulsed laser, The broadband light source according to claim 1.
10. One or more of the aforementioned supersonic gas jets include one or more noble gas gas jets. The broadband light source according to claim 1.
11. The one or more noble gases include at least one of xenon, argon, neon, or helium. The broadband light source according to claim 10.
12. One or more of the aforementioned supersonic gas jets include a gas jet containing a mixture of two or more gases. The broadband light source according to claim 1.
13. A primary pump focusing optical system configured to focus the primary pump beam into the local high-pressure region, A broadband light source according to claim 1, further comprising:
14. A pulse-assisted laser focusing optical system configured to focus the pulse-assisted laser beam onto the local high-pressure region, A broadband light source according to claim 1, further comprising:
15. A recirculation loop is configured to circulate the gas through the gas containment structure and to supply the gas to the plurality of jet nozzles. A broadband light source according to claim 1, further comprising:
16. The recirculation loop comprises one or more gas pumps, one or more heat exchangers, or one or more filters. A broadband light source according to claim 15, including the following:
17. A broadband light source, Gas containment structure, One or more jet nozzles configured to generate one or more supersonic gas jets, A primary laser pump source is configured to direct a primary pump beam to a local high-pressure region formed by the supersonic gas expansion of one or more supersonic gas jets, A pulse-assisted laser source is configured to direct a pulse-assisted beam to the local high-pressure region formed by the supersonic gas expansion of one or more supersonic gas jets, and the primary pump beam and the pulse-assisted beam are configured to maintain plasma within the local high-pressure region. A light-gathering element configured to focus at least a portion of the broadband light emitted from the plasma, A broadband light source including
18. The aforementioned local high-pressure region is formed in the Mach disk of the supersonic gas expansion. The broadband light source according to claim 17.
19. It is a system, A broadband light source, Gas containment structure, Multiple jet nozzles are configured to generate multiple supersonic gas jets, to collide the multiple supersonic gas jets within the gas containment structure, and to direct them so as to form local high-pressure regions at the collision points of the multiple supersonic gas jets. A primary laser pump source is configured to direct the primary pump beam towards a localized high-pressure region formed at the collision point of the plurality of supersonic gas jets, A pulse-assisted laser source is configured to direct a pulse-assisted beam to the local high-pressure region at the collision points of the plurality of supersonic gas jets, and the primary pump beam and the pulse-assisted beam are configured to maintain plasma within the local high-pressure region. A light-gathering element configured to focus at least a portion of the broadband light emitted from the plasma, A broadband light source including, A set of illumination optical systems configured to guide broadband light from the light-collecting element to one or more samples, Detector assembly and A set of projection optical systems configured to receive illumination from the surface of one or more samples and direct the illumination from the one or more samples toward the detector assembly, A system that includes this.
20. It is a system, A broadband light source, Gas containment structure, One or more jet nozzles configured to generate one or more supersonic gas jets, A primary laser pump source is configured to direct a primary pump beam to a local high-pressure region formed by the supersonic gas expansion of one or more supersonic gas jets, A pulse-assisted laser source is configured to direct a pulse-assisted beam to the local high-pressure region formed by the supersonic gas expansion of one or more supersonic gas jets, and the primary pump beam and the pulse-assisted beam are configured to maintain plasma within the local high-pressure region. A light-gathering element configured to focus at least a portion of the broadband light emitted from the plasma, A broadband light source including, A set of illumination optical systems configured to guide broadband light from the light-collecting element to one or more samples, Detector assembly and A set of projection optical systems configured to receive illumination from the surface of one or more samples and direct the illumination from the one or more samples toward the detector assembly, A system that includes this.
21. It is a method, A step of generating one or more supersonic gas jets to form a local high-pressure region, The steps include generating a primary pump beam and directing the primary pump beam towards a localized high-pressure region formed by one or more supersonic gas jets, A step of generating a pulse-assisted beam and directing the pulse-assisted beam to the local high-pressure region formed by one or more supersonic gas jets, wherein the primary pump beam and the pulse-assisted beam maintain plasma within the local high-pressure region. The steps include: focusing at least a portion of the broadband light emitted from the plasma; A method that includes this.